is time travel possible in a black hole

Could humans use black holes to time travel?

Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be visiting dinosaurs any time soon.

An artist's illustration of a black hole. The center of black holes are examples of singularities.

What are black holes?

Stretching space, stretching time, loops in time.

Black holes form natural time machines that allow travel to both the past and the future. But don’t expect to be heading back to visit the dinosaurs any time soon.

At present, we don’t have spacecraft that could get us anywhere near a black hole . But, even leaving that small detail aside, attempting to travel into the past using a black hole might be the last thing you ever do.

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth's gravitational field makes it extremely difficult to get to space. That’s why we build rockets: we have to travel very fast to break out of Earth's gravity .

Read more: How gravitational waves can 'see inside' black holes

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The gravitational field of a black hole is so strong that even light can't escape it. That's impressive, since light is the fastest thing known to science!

Incidentally, that’s why black holes are black: we can't bounce light off a black hole the way we might bounce a flashlight's beam off a tree in the dark.

Albert Einstein's general theory of relativity tells us matter and energy have a curious effect on the universe. Matter and energy bend and stretch space. The more massive an object is, the more space is stretched and bent around it.

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

3D illustration of the Earth and Sun on distorted spacetime. This shows the gravity and general theory of relativity concept.

That's why, when you get close enough to any massive object, including a black hole, you fall towards it. It's also why light can't escape a black hole: the sides of the valley are so steep that light isn't going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can't escape is called the event horizon.

Event horizons aren't just interesting for would-be time travellers: they're also interesting for philosophers, because they have implications for how we understand the nature of time.

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the centre of the black hole, your clock will tick slower, but you should still be able to escape so long as you don't cross the event horizon.

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That's what a black hole seems to do to time.

This creates a natural time machine. If you could somehow get onto the loop, which physicists call a closed timelike curve, you would find yourself on a trajectory through space that starts in the future and ends in the past.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!

So, you've found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

There are three problems. First, you can only travel into the black hole's past. That means that if the black hole was created after the dinosaurs died out, then you won’t be able to go back far enough.

Second, you'd probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you'd need to exit the event horizon. That means travelling faster than light, which we're pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo " spaghettification ." Sounds delicious, right?

Sadly, it's not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you'd probably be stretched so thin that you'd just be a string of atoms spiralling into the void.

So, while it's fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

This article is republished from The Conversation under a Creative Commons license. Read the original article .

Sam Baron is an associate professor at the Australian Catholic University whose areas of expertise include metaphysics, philosophy of science, philosophy of mathematics, philosophy of time and metaphilosophy. Sam completed his PhD in philosophy 2012 at the University of Sydney. Since then, he has published widely on topics in metaphysics and philosophy of science, in a range of philosophy journals.

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bolide2 The typical illustration of the idea of gravity as curvature of spacetime--a massive object shown on a distorted grid of "space," as illustrated in the article--is inadequate. It still requires us to imagine a force of gravity operating to move the object. Otherwise, why should the mere fact of being in curved space cause it to move? If gravity is actually just a curvature of spacetime-- Place two massive objects in empty space, near to each other but motionless relative to each other. Their mutual gravitational attraction (as Newton would say) will cause them to move toward each other. But how would Einstein explain that? What causes these objects, initially relatively at rest, to begin to be in relative motion? Reply
skynr13 Why wouldn't just mutual gravitational attraction be the answer? Basically, there attraction from this effect would make them want to just clunk into each other, to there possible destruction. But depending on there makeup the gravity they produce differs linearly, then they could begin orbiting each other for a time. Also, you are correct about the grid being inadequate. The curve or gravity well is not a dimple under the mass. It is within the mass, like two cones that emerge from the poles, where gravity is strongest. So, this gravity is also what attracts the two objects making the two objects appear to try to leapfrog over one another as they approach. It is also what causes them to go into orbit and develop a spin rotation in a kind of haphazard way. Reply
phrixus You're right that the 2D representation doesn't work very well. The thing is, the 3D picture you have in your head also doesn't work very well; in order to make it work, you need four dimensions. Remember that general relativity is about "spacetime", not just space. Nothing is ever actually stationary; everything is always traveling at C. If it's stationary in space, it's traveling at C in the time direction. As it moves in space, it diverts some fraction of its motion in time into space. Now, given that picture, we can reduce it back to two dimensions to make it possible to visualize. Imagine an infinite plane with two dots moving on parallel tracks at identical speeds. Overlay a grid over the plane to make the warping easier to see. Now, rather than distorting the plane in a third dimension like the typical rubber-sheet analogy, just "pinch" the grid lines inward towards each of the objects. If there's only one object, the effect is totally symmetrical and doesn't affect its trajectory at all. If there are two objects, though, each one starts to run into slightly skewed grid lines caused by the other one. In an attempt to follow a straight-line path, they end up curving towards each other, and the effect gets stronger the closer they are to each other (because the grid lines get more and more bent). Eventually, they collide and electromagnetic forces overwhelm the gravitational forces that are trying to make them occupy the same space. To say that again, it's hard to imagine with stationary objects, but there's no such thing as a stationary object in spacetime. With moving objects, you can imagine how they'd warp towards each other; if all their initial motion is in the time dimension, that warpage basically rotates part of their motion into the spatial dimensions. That's also why gravitational fields cause time dilation, because they rotate the "stationary" direction away from the time axis. Reply
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Are black holes time machines? Yes, but there’s a catch

Black holes form natural time machines that allow travel to both the past and the future. But don’t expect to be heading back to visit the dinosaurs any time soon.

At present, we don’t have spacecraft that could get us anywhere near a black hole. But, even leaving that small detail aside, attempting to travel into the past using a black hole might be the last thing you ever do.

What are black holes?

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth’s gravitational field makes it extremely difficult to get to space. That’s why we build rockets: we have to travel very fast to break out of Earth’s gravity.

The gravitational field of a black hole is so strong that even light can’t escape it. That’s impressive, since light is the fastest thing known to science!

Incidentally, that’s why black holes are black: we can’t bounce light off a black hole the way we might bounce a torch light off a tree in the dark.

Stretching space

Albert Einstein’s general theory of relativity tells us matter and energy have a curious effect on the universe. Matter and energy bend and stretch space. The more massive an object is, the more space is stretched and bent around it.

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

That’s why, when you get close enough to any massive object, including a black hole, you fall towards it. It’s also why light can’t escape a black hole: the sides of the valley are so steep that light isn’t going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can’t escape is called the event horizon.

Event horizons aren’t just interesting for would-be time travellers: they’re also interesting for philosophers, because they have implications for how we understand the nature of time .

Stretching time

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the centre of the black hole, your clock will tick slower, but you should still be able to escape so long as you don’t cross the event horizon.

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!

So, you’ve found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

There are three problems. First, you can only travel into the black hole’s past. That means that if the black hole was created after the dinosaurs died out, then you won’t be able to go back far enough.

Second, you’d probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you’d need to exit the event horizon. That means travelling faster than light, which we’re pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo “ spaghettification ”. Sounds delicious, right?

Sadly, it’s not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you’d probably be stretched so thin that you’d just be a string of atoms spiralling into the void.

So, while it’s fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

Sam Baron , Associate Professor, Philosophy of Science, Australian Catholic University

This article is republished from The Conversation under a Creative Commons license. Read the original article .

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Supernova 1987A, imaged by the Hubble and JWST. The faint blue source in the centre is the emission detected with the JWST/NIRSpec instrument. The bright stars to the left and right of the inner ring are unrelated to the supernova. Credit: Hubble Space Telescope WFPC-3/James Webb Space Telescope NIRSpec/J. Larsson

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Could We Ever Take Advantage of a Time-Warping Black Hole?

Entering a black hole comes with certain safety concerns. but could we take advantage of its time-warping capabilities from a distance.

Imagine a future in which humans have built advanced spacecraft, capable of traveling at a significant percentage of the speed of light. Scientists have also become aware of a large black hole in our galactic neighborhood — now well within our reach.

When a team of researchers assemble to travel to the black hole, one curious question might rise above all others: “What would happen if we flew straight into it?”

For now, this hypothetical scenario is still a long way off. Yet for as long as we have been aware of black holes, scientists have wondered what mysteries lie beyond the event horizon — the edge of a black hole, representing the “point of no return,” where even light is unable to escape the bizarre object’s gravitational pull.

Read More: Will Humans Ever Go Faster Than Light?

Black Hole Time Machine

Conventional wisdom, namely Einstein’s theory of general relativity (the best theory of gravity in town), predicts the presence of a singularity at the center of a black hole. It’s a point of infinite density that lies outside the bounds of our normal spacetime.

However, this prediction of a singularity does not necessarily mean it exists. Singularities tend to pop up at the very boundaries of our understanding — like inside black holes and at the Big Bang — and at the intersection of general relativity and quantum mechanics.

On the other hand, theorists working on a way to marry quantum mechanics with general relativity have suggested that something else might be going on at the center of black holes: Instead of forming a singularity, matter and energy may be sucked in and then spat out at some time in the distant future.

Yes, that's right, a time machine. Sort of.

All About Perspective: Loop Quantum Gravity

In their 2018 paper , researchers from Pennsylvania State University and Louisiana State University deploy the theory of loop quantum gravity. This theory posits that spacetime is quantized , meaning there is a smallest possible unit beyond which it cannot be divided further.

The researchers suggest that the strong curvature of spacetime near the center of a black hole extends into the future, which is structured like a white hole , or a blackhole in reverse. “Singularities are naturally resolved by the quantum geometry effects of loop quantum gravity,” write the authors.

From our perspective outside the black hole, matter and energy are continuously falling into it — because the spacetime around it is extremely distorted. But from the perspective of someone inside the black hole, matter and energy come in and bounce back out.

Keep in mind, however, that in terms of time relative to other events in the Universe, this bounce event may take billions or even trillions of years to occur.

Read More: This Is What a Black Hole Sounds Like

Inside a Black Hole

Whether a manned spacecraft could survive this bounce is a tough question. Any craft — and people onboard — would likely undergo a process known as spaghettification . Whilst crossing over the event horizon of the black hole, matter would be stretched flat like a long piece of spaghetti, possibly even to the point where it is just a long string of atoms.

It’s extremely unlikely that a spaceship (or human for that matter) would survive such an ordeal. And it's possible that the same thing would happen again on your way out — but in reverse.

For future scientists interested in the time-warping features of black holes, therefore, their best bet will be to stay in a relatively close orbit of a blackhole, taking advantage of its time-dilating properties from the outside.

Traveling Slower Through Time

One prediction of Einstein's general theory of relativity is that time will move slower the closer you are to an object of large mass. A strange consequence of this means that time moves slower if you are at sea level compared to on top of a mountain, as you are closer to Earth’s massive core at sea level.

Of course, in this example, the difference in the passing of time is negligible. But if you were instead on a spacecraft orbiting a large black hole, then the time-dilating effects would be significant indeed.

It’s possible that for every year you spent orbiting the black hole, for example, ten whole years may pass on Earth. Just be careful not to get too close to the event horizon.

Read More: What Is the Grandfather Paradox of Time Travel?

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Black Holes, Relativity And Time Travel

May 19, 2013 James Miller Black Holes , Time Travel 0

Stories in which people have traveled through time and experienced the effects of time dilation have been around for centuries, with one of the earliest found in the ancient Indian epic the Mahabharata, in which King Revaita travels to another world only to find on his return entire ages have passed.

But is time travel really possible ? Certainly, as we all travel forward in time by one hour per hour, but can we actually go faster or slower than that rate? Scientists now realize we can after Albert Einstein shook the foundations of physics by demonstrating the flexible and relative nature of time .

An atomic clock placed on top of a mountain, for instance, will experience a weaker gravitational force and so go faster than one placed in a valley, in accordance with Einstein’s theory of General Relativity. Also, as predicted by Special Relativity, an atomic clock on an airplane would run slower than a stationary one back on Earth as time slows down as speed increases.

Time Travel and Special Relativity

Consider the equation: Speed = Distance ÷ Time .

Einstein’s theory of special relativity suggests nothing can travel faster than the speed of light, so as the speed of an object approaches the maximum limit set by the speed of light (c), the other variables in the equation start to change with distances becoming shortened relative to time which becomes lengthened.

It actually works out that for a person traveling at 99% the speed of light, time is stretched and slows down by a factor of roughly 7, such that a return journey to a star system 7 light-years away would take the astronaut 2 years to complete, while to an observer on Earth over 14 years would have passed. If, however, our astronaut was able to reach a speed equal to 99.999% the speed of light, then 1 year on board his craft would pass for every 223 years back on Earth.

Time Travel and General Relativity

In addition to speed affecting time, Einstein discovered that gravity, too, causes time to slow down, with the effect more pronounced near a massive object. Therefore, a black hole with its intense gravitational field could potentially provide a fantastic means to travel through time by getting close enough to its Event Horizon without being swallowed up. In principle, by maintaining this “safe” distance you could travel centuries into the future relative to outside observers, although for you just a few hours or days would seem to have elapsed.

Time Travel to The Past

All the scenarios discussed so far involve traveling to the future, but is time travel to the past possible? Yes, in theory at least, as general relativity does allow for a tunnel through space-time linking two distant points in time, which then form a circular time loop called a wormhole or Einstein-Rosen bridge . Similar to a black hole, a wormhole would have a massive gravitational field capable of bending space-time , but in contrast to a black hole’s single point singularity which collapses matter, a wormhole may have a central spinning singularity-shaped ring, known as a Kerr black hole . It may then be possible to pass through its “empty” middle to a white hole on the other side, from which matter is subsequently expelled.

That said, many scientists question the theory of stable, traversable wormholes which are able to be crossed in both directions. Further concerns about time travel to the past are thrown up by temporal paradoxes , such as the Grandfather Paradox , which seem to imply their own negation. Nevertheless, the principles involved in using closed timelike curves to travel and return to one’s own spacetime may be perplexing but still remain theoretically possible.

Black Holes Could Work as Time Machines — If You Want to Die

Don’t expect to be heading back to visit the dinosaurs any time soon.

Nebula of paint and light on subject of art, design and creativity.

Black holes form natural time machines that allow travel to both the past and the future. But don’t expect to be heading back to visit the dinosaurs any time soon.

At present, we don’t have spacecraft that could get us anywhere near a black hole. But, even leaving that small detail aside, attempting to travel into the past using a black hole might be the last thing you ever do.

What are black holes?

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth’s gravitational field makes it extremely difficult to get to space. That’s why we build rockets: we have to travel very fast to break out of Earth’s gravity.

The gravitational field of a black hole is so strong that even light can’t escape it. That’s impressive since light is the fastest thing known to science!

Incidentally, that’s why black holes are black: we can’t bounce light off a black hole the way we might bounce a torch light off a tree in the dark.

IN SPACE - APRIL 10: In this handout photo provided by the National Science Foundation, the Event Ho...

M87, the first black hole event horizon ever imaged by telescopes.

Stretching space

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

That’s why, when you get close enough to any massive object, including a black hole, you fall toward it. It’s also why light can’t escape a black hole: the sides of the valley are so steep that light isn’t going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can’t escape is called the event horizon.

Event horizons aren’t just interesting for would-be time travelers: they’re also interesting for philosophers because they have implications for how we understand the nature of time .

Stretching time

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the center of the black hole, your clock will tick slower, but you should still be able to escape so long as you don’t cross the event horizon.

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn causes things to happen in the past!

Kino. Zurueck In Die Zukunft, Back To The Future, Zurueck In Die Zukunft, Back To The Future, Christ...

Not as easy as hopping in a DeLorean ...

So, you’ve found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

Second, you’d probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you’d need to exit the event horizon. That means traveling faster than light, which we’re pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo “ spaghettification ”. Sounds delicious, right?

Sadly, it’s not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you’d probably be stretched so thin that you’d just be a string of atoms spiraling into the void.

So, while it’s fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

This article was originally published on The Conversation by Sam Baron at Australian Catholic University. Read the original article here .

Space Science

Can you time travel through a black hole? - explainer

Here's what you need to know about black holes and whether it could allow someone to travel through time..

Black hole swallowing galaxy (photo credit: INGIMAGE)

What is a black hole?

But how does this relate to time travel, but that's just time travel into the future, what about going back.

December 1, 2015

12 min read

Can Time Travelers Reach the Past via Wormholes?

Astronauts already skip ahead in time, but the laws of physics seem to forbid going backward—or do they?

By Tim Folger

The famous writer H. G. Wells published his first novel, The Time Machine , in 1895, just a few years before Queen Victoria's six-decade reign over the U.K. ended. An even more durable dynasty was also drawing to a close: the 200-year-old Newtonian era of physics. In 1905 Albert Einstein published his special theory of relativity, which upset Isaac Newton's applecart and, presumably to Wells's delight, allowed something that had been impossible under Newton's laws: time travel into the future. In Newton's universe, time was steady everywhere and everywhen. It never sped up. It never slowed down. But for Einstein, time was relative.

Time travel is not merely possible—it has already happened, though not exactly as Wells imagined. The biggest journey through time so far, according to J. Richard Gott, an astrophysicist at Princeton University, was taken by Sergei K. Krikalev. Over the course of his long career, which began in 1985, the Russian cosmonaut spent 803 days in space. As Einstein proved, time passes more slowly for objects in motion than for those at rest, so as Krikalev hurtled along at 17,885 miles an hour onboard the Mir space station, time did not flow at the same rate for him as it did on Earth. While in orbit, Krikalev aged 1/48 of a second less than his fellow earthlings. Put another way, he traveled 1/48 of a second into the future.

The time-travel effect becomes easier to see as distances stretch longer and speeds creep higher. If Krikalev left Earth in 2015 and made a round-trip to Betelgeuse—a star that is about 650 light-years from Earth—at 99.995 percent the speed of light, then by the time he returned to Earth he would be only 10 years older. Sadly, everyone he knew would be long dead because 1,000 years would have passed on Earth; it would be the year 3015. “Time travel to the future, we know we can do,” Gott says. “It's just a matter of money and engineering!”

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Jumping a few nanoseconds—or even a few centuries—into the future is relatively straightforward, practical challenges aside. But going backward in time is harder. Einstein's special theory of relativity forbade it. After another decade of work, Einstein unveiled his general theory of relativity, which finally lifted that restriction. How someone would actually travel back in time, however, is a vexing problem because the equations of general relativity have many solutions. Different solutions assign different qualities to the universe—and only some of the solutions create conditions that permit time travel into the past.

Whether any of those solutions describes our own universe is an open question, which raises even more profound puzzles: Just how much tweaking of fundamental physics would it take to allow backward time travel? Does the universe itself somehow prevent such journeys even if Einstein's equations do not rule them out? Physicists continue to speculate, not because they imagine time travel to the past will ever be practical but because thinking about the possibility has led to some surprising insights about the nature of the universe we live in—including, perhaps, how it came to be in the first place.

A new way of looking at time With his special theory of relativity, Einstein made time malleable in a way that must have pleased Wells, who presciently believed that we inhabit a universe in which three-dimensional space and time are knit together into a four-dimensional whole. Einstein arrived at his revolutionary results by exploring the implications of two fundamental ideas. First, he argued that even though all motion is relative, the laws of physics must look the same for everyone anywhere in the universe. Second, he realized that the speed of light must be similarly unchanging from all perspectives: if everyone sees the same laws of physics operating, they must also arrive at the same result when measuring the speed of light.

To make light a universal speed limit, Einstein had to jettison two commonsense notions: that all observers would agree on the measurement of a given length and that they would also agree on the duration of time's passage. He showed that a clock in motion, whizzing past someone at rest, would tick more slowly than a stationary clock at the person's side. And the length of a ruler moving swiftly by would shorten. Yet for anyone who was traveling at the same speed as the clock and ruler, the passage of time and the length of the ruler would appear normal.

At ordinary speeds, the time-and-space-distorting effects of special relativity are negligible. But for anything moving at a hefty fraction of the speed of light (relative to the observer), they are very real. For example, many experiments have confirmed that the decay rate of unstable particles called muons slows by an order of magnitude when they are traveling at close to the speed of light. The speeding muons, in effect, are minuscule time travelers—subatomic Krikalevs—hopping a few nanoseconds into the future.

Gödel's strange universe Those speedy clocks and rulers and muons are all racing forward in time. Can they be thrown into reverse? The first person to use general relativity to describe a universe that permits time travel into the past was Kurt Gödel, the famed creator of the incompleteness theorems, which set limits on the scope of what mathematics can and cannot prove. He was one of the towering mathematicians of the 20th century—and one of the oddest. His many foibles included a diet of baby food and laxatives.

Gödel presented this model universe as a gift to Einstein on his 70th birthday. The universe Gödel described to his skeptical friend had two unique properties. It rotated, which provided centrifugal force that prevented gravity from crunching together all the matter in the cosmos, and thus created the stability Einstein demanded of any cosmic model. But it also allowed for time travel into the past, which made Einstein deeply uneasy. In Gödel's cosmos, space travelers could set out and eventually reach a point in their own past, as if the travelers had completed a circuit around the surface of a giant cylinder. Physicists call these trajectories in spacetime “closed timelike curves.”

A closed timelike curve is any path through spacetime that loops back on itself. In Gödel's rotating cosmos, such a curve would circle around the entire universe, like a latitude line on Earth's surface. Physicists have concocted a number of different types of closed timelike curves, all of which allow travel to the past, at least in theory. A journey along any of them would be disappointingly ordinary, however. Through the portholes of your spaceship, you would see stars and planets—all the usual sights of deep space. More important, time—as measured by your own clocks—would tick forward in the usual way; the hands of a clock would not start spinning backward even though you would be traveling to a location in spacetime that existed in your past.

“Einstein was already aware of the possibility of closed timelike curves back in 1914,” says Julian Barbour, an independent theoretical physicist who lives near Oxford, England. As Barbour recalls, Einstein said, “My intuition strives most vehemently against this.” The curves' existence would create all kinds of problems with causality—how can the past be changed if it has already happened? And then there is the hoary grandfather paradox: What happens to a time traveler who kills Granddad before Granddad meets Grandma? Would the demented, now parentless traveler ever be born?

Fortunately for fans of causality, astronomers have found no evidence that the universe is rotating. Gödel himself apparently pored over catalogs of galaxies, looking for clues that his theory might be true. Gödel might not have devised a realistic model of the universe, but he did prove that closed timelike curves are completely consistent with the equations of general relativity. The laws of physics do not rule out traveling to the past.

An annoying possibility Over the past few decades cosmologists have used Einstein's equations to construct a variety of closed timelike curves. Gödel conjured an entire universe that allowed them, but more recent enthusiasts have warped spacetime only within parts of our universe.

In general relativity, planets, stars, galaxies and other massive bodies warp spacetime. Warped spacetime, in turn, guides the motions of those massive bodies. As the late physicist John Wheeler put it, “Spacetime tells matter how to move; matter tells spacetime how to curve.” In extreme cases, spacetime might bend enough to create a path from the present back to the past.

Physicists have proposed some exotic mechanisms to create such paths. In a 1991 paper, Gott showed how cosmic strings—infinitely long structures thinner than an atom that may have formed in the early universe—would allow closed timelike curves where two strings intersected. In 1983 Kip S. Thorne, a physicist at the California Institute of Technology, began to explore the possibility that a type of closed timelike curve called a wormhole—a kind of tunnel joining two different locations in spacetime—might allow for time travel into the past. “In general relativity, if you connect two different regions of space, you're also connecting two different regions of time,” says Sean M. Carroll, a colleague of Thorne's at Caltech.

The entrance into a wormhole would be spherical—a three-dimensional entrance into a four-dimensional tunnel in spacetime. As is the case with all closed timelike curves, a trip through a wormhole would be “like any other journey,” Carroll says. “It's not that you disappear and are reassembled at some other moment of time. There is no respectable theory where that kind of science-fiction time travel is possible.” For all travelers, he adds, “no matter what they do, time flows forward at one second per second. It's just that your local version of ‘forward’ might be globally out of sync with the rest of the universe.”

Although physicists can write equations that describe wormholes and other closed timelike curves, all the models have serious problems. “Just to get a wormhole in the first place, you need negative energy,” Carroll says. Negative energy is when the energy in a volume of space spontaneously fluctuates to less than zero. Without negative energy, a wormhole's spherical entrance and four-dimensional tunnel would instantaneously implode. But a wormhole held open by negative energy “seems to be hard, probably impossible,” Carroll says. “Negative energies seem to be a bad thing in physics.”

Even if negative energy kept a wormhole open, just when you would be on the verge of turning that into a time machine, “particles would be moving through the wormhole, and every particle would loop back around an infinite number of times,” Carroll says. “That leads to an infinite amount of energy.” Because energy deforms spacetime, the entire thing would collapse into a black hole—an infinitely dense point in spacetime. “We're not 100 percent sure that that happens,” Carroll says. “But it seems to be a reasonable possibility that the universe is actually preventing you from making a time machine by making a black hole instead.”

Unlike black holes, which are a natural consequence of general relativity, wormholes and closed timelike curves in general are completely artificial constructs—a way of testing the bounds of the theory. “Black holes are hard to avoid,” Carroll says. “Closed timelike curves are very hard to make.”

Even if wormholes are physically implausible, it is significant that they fit in with the general theory of relativity. “It's very curious that we can come so close to ruling out the possibility of time travel, yet we just can't do it. I also think that it's annoying,” Carroll says, exasperated that Einstein's beautiful theory might allow for something so seemingly implausible. But by contemplating that annoying possibility, physicists may gain a better understanding of the kind of universe we live in. And it may be that if the universe did not permit backward time travel, it never would have come into existence.

Did the universe create itself? General relativity describes the universe on the largest scales. But quantum mechanics provides the operating manual for the atomic scale, and it offers another possible venue for closed timelike curves—one that gets at the origin of the universe.

“On a very small scale (10−30 centimeter) you might expect the topology of spacetime to fluctuate, and random fluctuations might give you closed timelike curves if nothing fundamental prevents them,” says John Friedman, a physicist at the University of Wisconsin–Milwaukee. Could those quantum fluctuations somehow be magnified and harnessed as time machines? “There's certainly no formal proof that you can't have macroscopic closed timelike curves,” Friedman says. “But the community of people who have looked at these general questions would bet pretty heavily against it.”

There is no doubt that the creation of a loop in spacetime on either a quantum scale or a cosmic one would require some very extreme physics. And the most likely place to expect extreme physics, Gott says, is at the very beginning of the universe.

In 1998 Gott and Li-Xin Li, an astrophysicist now at Peking University in China, published a paper in which they argued that closed timelike curves were not merely possible but essential to explain the origin of the universe. “We investigated the possibility of whether the universe could be its own mother—whether a time loop at the beginning of the universe would allow the universe to create itself,” Gott says.

Just as in standard big bang cosmology, Gott and Li's universe “starts” with a bout of inflation, where an all-pervasive energy field drove the universe's initial expansion. Many cosmologists now believe that inflation gave rise to countless other universes besides our own. “Inflation is very hard to stop once it gets started,” Gott says. “It makes an infinitely branching tree. We're one of the branches. But you have to ask yourself, Where did the trunk come from? Li-Xin Li and I said it could be that one of the branches just loops around and grows up to be the trunk.”

A simple two-dimensional sketch of Gott and Li's self-starting universe looks like the number “6,” with the spacetime loop at the bottom and our present-era universe as the top stem. A burst of inflation, Gott and Li theorized, allowed the universe to escape from the time loop and expand into the cosmos we inhabit today.

It is difficult to contemplate the model, but its main appeal, Gott says, is that it eliminates the need for creating a universe out of nothing. Yet Alexander Vilenkin of Tufts University, Stephen Hawking of the University of Cambridge and James Hartle of the University of California, Santa Barbara, have proposed models in which the universe does indeed arise out of nothing. According to the laws of quantum mechanics, empty space is not really empty but is filled with “virtual” particles that spontaneously pop into and out of existence. Hawking and his colleagues theorized that the universe burst into being from the same quantum-vacuum stew. But in Gott's view, the universe is not made out of nothing; it is made out of something—itself.

A cosmic chess game For now, there is no way to test whether any of those theories might actually explain the origin of the universe. The famed physicist Richard Feynman compared the universe to a great chess game being played by the gods. Scientists, he said, are trying to understand the game without knowing the rules. We watch as the gods move a pawn one space forward, and we learn a rule: pawns always move one space forward. But what if we never saw the opening of a game, when a pawn can move two spaces forward? We might also assume, mistakenly, that pawns always remain pawns—that they never change their identity—until we see a pawn transformed into a queen.

“You would say that's against the rules,” Gott says. “You can't change your pawn into a queen. Well, yes, you can! You just never saw a game that extreme before. Time-travel research is like that. We're testing the laws of physics by looking at extreme conditions. There's nothing logically impossible about time travel to the past; it's just not the universe we're used to.” Turning a pawn into a queen could be part of the rules of relativity.

Such wildly speculative ideas may be closer to philosophy than to physics. But for now, quantum mechanics and general relativity—powerful, counterintuitive theories—are all we have to figure out the universe. “As soon as people start trying to bring quantum theory and general relativity into this, the first thing to say is that they really have no idea what they're doing,” says Tim Maudlin, a philosopher of science at New York University. “It's not really rigorous mathematics. It's one piece of mathematics that sort of looks like general relativity and another little piece of mathematics that sort of looks like quantum theory, mixed together in some not entirely coherent way. But this is what people have to do because they honestly don't know how to go forward in a way that makes sense.”

Will some future theory eliminate the possibility of time travel into the past? Or will the universe again turn out to be far stranger than we imagine? Physics has advanced tremendously since Einstein redefined our understanding of time. Time travel, which existed only in the realm of fiction for Wells, is now a proved reality, at least in one direction. Is it too hard to believe that some kind of symmetry exists in the universe, allowing us to travel backward in time? When I put the question to Gott, he replies with an anecdote:

“There's a story where Einstein was talking to a guy. The guy pulled a notebook out and scribbled something down. Einstein says, ‘What's that?’ The guy says, ‘A notebook. Whenever I have a good idea, I write it down.’ Einstein says, ‘I've never had any need for a notebook; I've only had three good ideas.’”

Gott concludes: “I think we're waiting for a new good idea.”

Tim Folger is a freelance journalist who writes for National Geographic , Discover , and other national publications.

10 Questions You Might Have About Black Holes

spherical black hole surrounded by swirling disc of material

A black hole is an extremely dense object in space from which no light can escape. While black holes are mysterious and exotic, they are also a key consequence of how gravity works: When a lot of mass gets compressed into a small enough space, the resulting object rips the very fabric of space and time, becoming what is called a singularity. A black hole's gravity is so powerful that it will be able to pull in nearby material and "eat" it.

Want to visit a black hole? We don't recommend it. Find out why these gravitational mysteries are better studied from afar. › More

Here are 10 things you might want to know about black holes:

1. How can we learn about black holes if they trap light, and can't actually be seen?

No light of any kind, including X-rays, can escape from inside the event horizon of a black hole, the region beyond which there is no return. NASA's telescopes that study black holes are looking at the surrounding environments of the black holes, where there is material very close to the event horizon. Matter is heated to millions of degrees as it is pulled toward the black hole, so it glows in X-rays. The immense gravity of black holes also distorts space itself, so it is possible to see the influence of an invisible gravitational pull on stars and other objects.

2. How long does it take to make a black hole?

A stellar-mass black hole, with a mass of tens of times the mass of the Sun, can likely form in seconds, after the collapse of a massive star. These relatively small black holes can also be made through the merger of two dense stellar remnants called neutron stars. A neutron star can also merge with a black hole to make a bigger black hole, or two black holes can collide. Mergers like these also make black holes quickly, and produce ripples in space-time called gravitational waves.

More mysterious are the giant black holes found at the centers of galaxies — the "supermassive" black holes, which can weigh millions or billions of times the mass of the Sun. It can take less than a billion years for one to reach a very large size, but it is unknown how long it takes them to form, generally.

3. How do scientists calculate the mass of a supermassive black hole?

The research involves looking at the motions of stars in the centers of galaxies. These motions imply a dark, massive body whose mass can be computed from the speeds of the stars. The matter that falls into a black hole adds to the mass of the black hole. Its gravity doesn't disappear from the universe.

4. Is it possible for a black hole to "eat" an entire galaxy?

No. There is no way a black hole would eat an entire galaxy. The gravitational reach of supermassive black holes contained in the middle of galaxies is large, but not nearly large enough for eating the whole galaxy.

5. What would happen if you fell into a black hole?

It certainly wouldn't be good! But what we know about the interior of black holes comes from Albert Einstein's General Theory of Relativity.

For black holes, distant observers will only see regions outside the event horizon, but individual observers falling into the black hole would experience quite another "reality." If you got into the event horizon, your perception of space and time would entirely change. At the same time, the immense gravity of the black hole would compress you horizontally and stretch you vertically like a noodle, which is why scientists call this phenomenon (no joke) "spaghettification."

Fortunately, this has never happened to anyone — black holes are too far away to pull in any matter from our solar system. But scientists have observed black holes ripping stars apart , a process that releases a tremendous amount of energy.

6. What if the Sun turned into a black hole?

The Sun will never turn into a black hole because it is not massive enough to explode. Instead, the Sun will become a dense stellar remnant called a white dwarf.

But if, hypothetically, the Sun suddenly became a black hole with the same mass as it has today, this would not affect the orbits of the planets, because its gravitational influence on the solar system would be the same. So, Earth would continue to revolve around the Sun without getting pulled in — although the lack of sunlight would be disastrous for life on Earth.

7. Have black holes had any influence on our planet?

Stellar-mass black holes are left behind when a massive star explodes. These explosions distribute elements such as carbon, nitrogen and oxygen that are necessary for life into space. Mergers between two neutron stars, two black holes, or a neutron star and black hole, similarly spread heavy elements around that may someday become part of new planets. The shock waves from stellar explosions may also trigger the formation of new stars and new solar systems. So, in some sense, we owe our existence on Earth to long-ago explosions and collision events that formed black holes. On a larger scale, most galaxies seem to have supermassive black holes at their centers. The connection between the formation of these supermassive black holes and the formation of galaxies is still not understood. It is possible that a black hole could have played a role in the formation of our Milky Way galaxy. But this chicken-and-egg problem — that is, which came first, the galaxy or the black hole? — is one of the great puzzles of our universe.

8. What is the most distant black hole ever seen?

The most distant black hole ever detected is located in a galaxy about 13.1 billion light-years from Earth. (The age of the universe is currently estimated to be about 13.8 billion years, so this means this black hole existed about 690 million years after the Big Bang.)

This supermassive black hole is what astronomers call a “quasar,” where large quantities of gas are pouring into the black hole so rapidly that the energy output is a thousand times greater than that of the galaxy itself. Its extreme brightness is how astronomers can detect it at such great distances.

9. If nothing can escape from a black hole, then won't the whole universe eventually be swallowed up?

The universe is a big place. In particular, the size of a region where a particular black hole has significant gravitational influence is quite limited compared to the size of a galaxy. This applies even to supermassive black holes like the one found in the middle of the Milky Way. This black hole has probably already "eaten" most or all of the stars that formed nearby, and stars further out are mostly safe from being pulled in. Since this black hole already weighs a few million times the mass of the Sun, there will only be small increases in its mass if it swallows a few more Sun-like stars. There is no danger of the Earth (located 26,000 light years away from the Milky Way's black hole) being pulled in. Future galaxy collisions will cause black holes to grow in size, for example by merging of two black holes. But collisions won't happen indefinitely because the universe is big and because it's expanding, and so it's very unlikely that any sort of black hole runaway effect will occur.

10. Can black holes get smaller?

Yes. The late physicist Stephen Hawking proposed that while black holes get bigger by eating material, they also slowly shrink because they are losing tiny amounts of energy called "Hawking radiation."

Hawking radiation occurs because empty space, or the vacuum, is not really empty. It is actually a sea of particles continually popping into and out of existence. Hawking showed that if a pair of such particles is created near a black hole, there is a chance that one of them will be pulled into the black hole before it is destroyed. In this event, its partner will escape into space. The energy for this comes from the black hole, so the black hole slowly loses energy, and mass, by this process.

Eventually, in theory, black holes will evaporate through Hawking radiation. But it would take much longer than the entire age of the universe for most black holes we know about to significantly evaporate. Black holes, even the ones around a few times the mass of the Sun, will be around for a really, really long time!

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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

Image of galaxies, taken by the Hubble Space Telescope.

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

Illustration of GPS satellites orbiting around Earth

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

Illustration of a hand holding a phone with a maps application active.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

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The Missing Piece: Are Wormholes the Key to Time Travel?

Time travel -- it's a concept we're all too familiar with. From Hollywood Movies (shout out to Back to the Future) to theoretical physics, many theories have circulated regarding the bewildering topic of time travel. However, recently students at the California Institute of Technology1 have shed new light on a relatively dated theory: that wormholes may be the missing piece in the seemingly unsolvable puzzle behind time travel. So, step aside Doc Brown, because we're going to explore how a unique and mysterious part of our universe- the wormhole- connects to traveling through time!

Just like many principles in Physics, this concept finds its base in Einstein's Theory of General Relativity (for some background on this topic, view our previous blog post, "What happens to Matter inside a Black Hole?"). Basically, the theory attributes the characteristics of a wormhole to its incredibly high velocity. Similar to a black hole, a wormhole would compress an entering object to the size of a singularity and accelerate it to immeasurable speeds through the "throat" of the wormhole to the other side of the funnel. So, for now, think of a wormhole as a black hole that has a start and end point.2

Now, this is where the physics becomes complex. We know that a wormhole can basically "teleport" compressed objects at super speeds from one end to another, but how does that explain the time travel aspect? Well, the concept of time dilation can explain that. Time dilation is the relative difference in the passage of time between two entities due to a stark difference in either gravity or relative velocity. In the case of the wormhole, both are in play, which only compounds the effects. For a tangible example to grasp, let's look to the astronauts aboard the International Space Station. After 6 months aboard the ISS (where there is less gravity, but greater velocity of movement), these astronauts have actually aged .007 seconds less than the crew stationed on Earth.3 While this seems insignificant, we have to remember that because the velocity is increased but the gravity is decreased, each is actually mitigating the effects of the other. However, in a wormhole, where the effects of both gravity and velocity are exponentially amplified AND working in tandem, their relativistic effects are enormous.4

This graphic portrays an accurate depiction of velocities' effect on time dilation: http://upload.wikimedia.org/wikipedia/commons/7/72/Nonsymmetric_velocity_time_dilation.gif

Now that we have an understanding of time dilation, we want to leave you with this example. Imagine two test subjects at each side of a wormhole in the year 1995. One mouth of the wormhole has been accelerated to a point where relativistic effects (i.e. time dilation) apply significantly and the other mouth is stationary. When the two subjects pass through their respective mouths, they end up at where their counterpart stood... but at different times! The accelerated mouth would land its test subject in, let's say, 2000. However, the stationary mouth would place its test subject in a later year - we'll call it 2005- since the accelerated mouth exists in a different time caused by time dilation. The time travel becomes evident when we consider the following: what if the test subject who landed in 2005 stepped back into the mouth? They would end up in the year 2000, or 5 years in the past! A bit of manipulation, therefore, could technically transport this subject to any point in time between 2000 and 2005.5

Unfortunately, scientists have been unable to totally grasp how we could adapt the power of a wormhole into time machine-esq technology. We have yet to even theorize how we could accelerate a wormhole to relativistic speeds. Given that this is another theoretical aspect of our known universe, testing is extremely limited and all postulates have very little opportunity for tangible proof. What is certain, though, is that the advances we've made thus far in the field have brought us several pieces closer to solving the time traveler's puzzle!

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Black Holes Are Even Weirder Than You Imagined

By Rivka Galchen

An artistic rendering of two supermassive black holes.

Black holes are, of course, awesome. But, for scientists, they are more awesome. If a rainbow is marvellous, then understanding how all the colors of the rainbow are present, unified, in ordinary white light—that’s more marvellous. (Though, famously, in his poem “Lamia,” John Keats disagreed, blaming “cold philosophy” for unweaving the rainbow.) In recent years, the amount of data that scientists have discovered about black holes has grown exponentially. In January, astronomers announced that the James Webb Space Telescope had observed the oldest black hole yet—one present when the universe was a mere four hundred million years old. (It’s estimated that it’s now 13.8 billion years old.) Recently, two supermassive black holes, with a combined mass of twenty-eight billion suns, were measured and shown to have been rotating tightly around each other, but not colliding, for the past three billion years. And those are just the examples that are easiest for the public to make some sense of. To me, a supermassive black hole sounds sublime; to a scientist, it can also be a test of wild hypotheses. “Astrophysics is an exercise in incredible experiments not runnable on Earth,” Avery Broderick, a theoretical physicist at the University of Waterloo and at the Perimeter Institute, told me. “And black holes are an ideal laboratory.”

Broderick says that he studies black holes because they are very simple, theoretically and mathematically. As he explained it, a black hole has a mass, an electrical charge, and an angular momentum (meaning that it can spin). “And that’s pretty much it,” he said. “Their behavior is extreme, but the apparatus is something we think we understand.” Another “simple” way to think of a black hole is as an extraordinary amount of mass in a relatively small space. It exerts a gravitational pull so strong that not even light can escape it. Imagine the mass of Earth condensed to the volume of a marble; imagine a million suns condensed to the volume of a single sun—that’ll give you an idea of a black hole. Some black holes are formed by stars that have collapsed in on themselves. Other black holes are thought to have been formed by the inward collapse of enormous clouds of gas. (There are other theories, too.) To look “into” a black hole—from which no photon or wave or ray ever returns—requires considerable creativity. The interior of a black hole can only be deduced from changes exterior to it. Active black holes are encircled by intense brightness and billion-degree heat, given off by matter falling toward them—think of the fire of an incoming asteroid—while the black hole itself is unthinkably cold, a tiny fraction of a degree above absolute zero.

It’s in these simple, outlandish objects, Broderick explained, “that twentieth-century physics breaks down.” But what is the twentieth-century physics that is said to break down? Basically, there’s Albert Einstein’s theory of general relativity (which made a tiny but far-reaching correction to Isaac Newton’s concept of gravity), and there’s quantum mechanics. “General relativity is thought of as the theory of the very large and massive, and quantum mechanics is the theory of the very small or very cold,” Broderick said. Black holes are massive(general relativity), and cold (quantum mechanics). But, when scientists attempt to use these theories to describe what happens in the interior of a black hole, the implications are, as another astrophysicist put it, “a disaster.” Or, as Broderick put it, the theories “give very different answers.”

Some scientific terms have more charisma than others. Schrödinger’s cat, dark matter, the “plum pudding” model of the atom—these are more evocative than “eigenstates,” “neutron stars,” or “ribosomes.” “I had been searching for just the right term for months, mulling it over in bed, in the bathtub, in my car, wherever I had quiet moments,” the late physicist John Wheeler once said, about trying to find better language for what was then called a “gravitationally completely collapsed object.” Wheeler, who also read poetry, loved dreaming up vivid language for new concepts in physics. It is to Wheeler that we owe “wormholes,” the “participatory universe,” and “quantum foam”—names that carry something of the spirit of what they describe.

In 1967, Wheeler attended a discussion of the astrophysicist Jocelyn Bell ’s recent discovery of pulsars—celestial objects that flash out radiation. The discussion centered on what caused this curious phenomenon. A “completely collapsed object” was one explanation. When Wheeler spoke, he used that cumbersome term several times before finding himself simply saying “black hole.” The name stuck. (That, anyhow, is one of the origin stories—the term had been used in articles a few years earlier, and it is also said to have been shouted out as a suggestion to Wheeler by a conference attendee.)

For most people, the name evokes what the Nobel Prize-winning astrophysicist Saul Perlmutter termed “the Darth Vader aspect” of black holes: the objects are “deadly, silent, all-powerful, and looming.” The popular understanding of black holes, though not precise, has the accuracy that we associate with the poetry that Wheeler loved to read. “Not only does it swallow anything that comes too near it but no one lives to tell the tale . . . there are footprints leading in, and no footprints leading out,” Perlmutter said, describing how nonspecialists might think of them. “If black holes weren’t real, I think the science-fiction writers would have wanted to invent them.”

A hundred years ago, almost no one believed that black holes were real, not even Einstein, who wrote the equations that predicted them. He said that they were impossible, a quirk of mathematics. In 1935, at a meeting of the Royal Astronomical Society, the young astrophysicist Subrahmanyan Chandrasekhar presented his work, which suggested, instead, that what was impossible was essentially that black holes didn’t exist. Sir Arthur Eddington, one of the most respected elders of astronomy, had arranged Chandrasekhar’s talk and knew what he was going to speak about—and he scheduled himself to speak directly afterward. Eddington, who was polite, open-minded, and encouraging to younger scientists, dismissed Chandrasekhar’s idea as ludicrous, saying, “There should be a law of nature to prevent a star from behaving in this absurd way!” Eddington’s viewpoint won; talking about stellar collapse became a great way not to be taken seriously.

Decades passed. Then a few weird things were noticed. Astronomers began seeing something at the center of galaxies so bright that it outshone all the other stars in the galaxy put together. (This was the energy from things falling into a black hole.) Elsewhere, cosmic rays were detected from a part of the sky termed Cygnus X-1, in a pattern that seemed inexplicable. Ultimately, the concept of black holes came to account for and unify these baffling and seemingly disparate observations. Denying the existence of black holes became more awkward than accepting it. In the nineteen-seventies, Stephen Hawking had made a bet with Kip Thorne, a fellow-physicist, about whether the cosmic X rays coming from Cygnus X-1 could really be the result of a black hole. Hawking bet No, though he made the wager to counterbalance the outcome that he wanted to be true; he had spent years studying black holes. Only in 1990 had enough evidence accumulated to settle the bet in Thorne’s favor. (The payout was a subscription to Penthouse ; if Hawking had won, he would have received the satirical magazine Private Eye .)

From there, knowledge accelerated. Not only were black holes real but a giant one was at the center of our galaxy—actually, at the center of every galaxy—actually, not only at the center of galaxies but all over them, with our Milky Way alone housing many millions. And not only are there unthinkable numbers of black holes but sometimes they collide, sending tiny ripples of gravitational waves across the universe. In 2015, scientists at LIGO , an observatory whose construction had taken decades of dreaming and designing and revising, ran an experiment that within days detected those gravitational waves. The researchers described what they observed, evocatively, as ripples in the fabric of space-time.

The gravitational waves sent out by colliding black holes make a sound—or translate into a sound—something like a bell being rung. “You can tell if I’m pounding on this desk, or if I’m pounding on the floor,” Will Farr, an astrophysicist, said to me in his bright office at the Flatiron Institute, in Manhattan. “If I had musical instruments, it would sound prettier, but also you could tell if it was a trumpet or a trombone or drums or a clarinet—even when they’re making the same note.”

The sound made when you strike an object—or pull a bow across it, or blow air into a reed connected to it—carries information about the object’s shape, material makeup, and temperature. “You can identify an instrument by listening to what we call the spectrum—the different frequencies of the modes that are excited when you hit it,” Farr said. Black holes have modes, too, though they radiate in gravitational waves, not sound waves. So if you, say, pounded on a black hole, in theory, you could tell quite a bit about it. Two black holes colliding in effect do that pounding which scientists cannot themselves do—an experiment out in the cosmos.

Farr described the moment of collision between two holes as forming a shape like a “black peanut,” which eventually settles into a single, merged black hole. “Ringdown” is the term used to describe both that final merging and the “sound”—the waves—emitted by it. The ripples from a ringdown, if recorded precisely enough, could tell the story of a black hole: its spin, its mass, and its charge, and possibly information about the million-degree hot-gas ring external to it. “Basically, there’s currently no other way to probe this region of space-time except with gravitational waves,” Farr said. Light waves, radio waves, X rays—none of these ways of reading the universe let scientists see as far down toward the horizon of a black hole. “That’s one reason why it’s been revolutionary to have this tool.”

Ringdown may be used by researchers to test if general relativity accurately describes black holes. If it does, then the ringdown tones will come out one way; if not, then they won’t. “By examining the deviations in detail, tone by tone, you can try to understand where the deviation from general relativity is coming,” Farr said.

It will be a while before the public has a “feel” for gravitational waves, or for how black holes do or don’t unify quantum mechanics and general relativity. But those ideas still filter into the public imagination, however fuzzily. In 2020, the astrophysicist Andrea Ghez, of the University of California, Los Angeles, and a colleague received a Nobel for having tracked the path of objects near the center of our galaxy in sufficient detail to indicate that there must be a supermassive black hole there. In 2014, through an ingenious and sparsely funded passion project conducted by hundreds of scientists, the Event Horizon Telescope (E.H.T.) was assembled, with the goal of “photographing” a black hole. The E.H.T. is not one telescope but a network of initially eight and now eleven, spread across the planet. Together, the telescopes function as if they were one telescope with a lens the size of Earth. The E.H.T. gathered data on a distant black hole and then on a nearer one at the heart of the Milky Way. Images came through of the two black holes—or, rather, of the ring of stuff falling into the black holes.

To share the work with the general public, the scientists translated the data into astonishing images that were published all around the world. Because what the telescopes “saw” is at wavelengths outside the spectrum visible to the human eye, E.H.T. scientists made decisions about, for example, what color to use to depict the extreme heat of the plasma around the event horizon. (Even though blue flames are hotter than orange-red ones, they chose an orange-red color.) A number of scientists I spoke with about the images were gently indifferent, saying that they didn’t add to their fundamental understanding of black holes. Most were more impressed with the creative means of collecting the data than with the images themselves. (In contrast, for a certain crowd, the waveform that appeared when LIGO detected gravitational waves is a popular tattoo.) For other earthlings, that darkness, surrounded by its burning ring of fire, had the intimate quality of a Polaroid—but one of the alien that we call our universe.

Broderick, who was one of the first theoretical physicists to join the E.H.T., told me that, for scientists, the adage “seeing is believing” doesn’t always hold true; scientists often have to decide if they can trust what they see. He framed the E.H.T. as contributing both societal impact and scientific impact. It was “pleasingly novel to work on something I can tell my in-laws and mother about,” he said. He pointed out that it was estimated that half the world’s population had seen the first black-hole image: “I’m actually kind of curious; when was the last time so many newspapers had the same thing on their front page? We all shared this experience together, and there are precious few such things, and most of them are negative.” He saw the E.H.T. as a chance to make part of the story of physics real and visible.

As a kid, Broderick watched “Star Trek,” “Doctor Who,” and “anything adventurous,” he said, with his father, whom he would visit in the summer and on holidays. “He would record these movies and shows in anticipation of me coming, so we would binge-watch before it was a thing,” he said. His father was quadriplegic, and enjoyed photography and movies. Broderick told me that his viewing of “Star Trek” is not unrelated to his work as a theoretical physicist. In every episode, he said, the Starfleet travelled to incredible new places, and saw something different, and that was the adventure. “A part of what drew me to astrophysics was that Starfleet doesn’t exist. But I get to travel the universe with telescopes, large computers, blackboards, whiteboards, chalk—with whatever.” ♦

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Why are some supermassive black hole jets so short? Astronomers may have cracked the case

"These objects are a distinct species all of their own that live and die out in thousands of years rather than the millions of years that are common in galaxies with bigger jets."

artist's illustration of a black hole devouring a star, generating a pinkish swirl of gas and dust in deep space

A new investigation into a rare and short-lived type of galaxy has revealed that such objects harbor slumbering supermassive black holes that briefly awaken to rip apart a massive star and devour its remains as a giant cosmic breakfast.

"Compact Symmetric Objects," or CSOs, are active galaxies that have two jets blasting out from them at nearly the speed of light. These jets are common to active galactic nuclei (AGN) , which have supermassive black holes feeding on surrounding gas and dust at their hearts — but the jets of CSOs are different.

While jets from AGNs can extend for 230,000 light-years in both directions, CSO jets are stunted, stretching for just 1,500 light-years or so.

Scientists had previously theorized that CSO jets are short because they are newly formed or young. Now, a team led by California Institute of Technology (Caltech) scientists has determined that these jets simply have short lifetimes.

Related: New view of the supermassive black hole at the heart of the Milky Way hints at an exciting hidden feature (image)

"These CSOs are not young. You wouldn't call a 12-year-old dog young even though it has lived a shorter life than an adult human," study team leader Anthony Readhead, an emeritus professor of astronomy at Caltech, said in a statement . "These objects are a distinct species all of their own that live and die out in thousands of years, rather than the millions of years that are common in galaxies with bigger jets."

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Snacking black holes give galaxies a dog's life

To solve the mystery of CSOs and uncover their true nature, Readhead and colleagues spent two years scouring through 3,000 CSO candidates in past literature and astronomical data from the Very Long Baseline Array (VLBA) and other high-resolution radio telescopes.

"The VLBA observations are the most detailed in astronomy, providing images with details equivalent to measuring the width of a human hair at a distance of 100 miles [160 kilometers]," Readhead said.

The team confirmed 64 of these candidates as CSOs and also spotted an additional 15 of these rare galaxies . Analyzing these CSOs, the team concluded that these rare galaxy types expel jets for just 5,000 years or less and then fade away.

"The CSO jets are very energetic jets, but they seem to shut off," said team member Vikram Ravi, an assistant professor at Caltech. "The jets stop flowing from the source."

The team has identified a suspect in the emission of these jets: They theorize that at the heart of CSOs are supermassive black holes ripping apart stars that get too close to them in so-called " tidal disruption events ," or TDEs.

illustration showing an orange column of dust and gas in deep space

When stars venture too close to a black hole, the latter's immense gravity generates powerful tidal forces within the stellar body. These tidal forces stretch the star vertically while squashing it horizontally, a process called " spaghettification. "

This stellar noodle wraps around, forming a disk of matter that is gradually eaten by the supermassive black hole. But black holes are messy eaters , and some of this stellar matter is channeled to the poles of these cosmic monsters. From there, some of the material is blasted away as jets. This TDE process is accompanied by incredibly bright emissions of light that announce these feeding supermassive black holes to astronomers.

radar telescope image showing galaxies, represented as colorful clumps, against the blackness of deep space

"We think that a single star gets ripped apart, and then all that energy is channeled into jets along the axis the black hole is spinning around," Readhead explained. "The giant black hole starts out invisible to us, and then when it consumes a star, boom! The black hole has fuel, and we can see it."

However, it is not just any star that can be the messy cosmic meal that wakes up a black hole as a CSO. The team thinks it is only when a truly massive star gets ripped up by a supermassive black hole in a TDE that a CSO is created.

"The TDEs we've previously seen only lasted for a few years," Ravi explained. "We think that the remarkable TDEs powering CSOs last far longer because the disrupted stars are very large in size, very massive, or both."

radio telescope image showing orange flame-like objects erupting from a bright pinpoint of light in deep space

Readhead and colleagues were also able to construct a "cosmic family album" showing how CSOs and their jets evolve over time . Younger CSOs have shorter jets that are closer to the central supermassive black hole, while older CSOs have longer jets that stretch farther away from the site of the TDE.

The team determined that while the vast majority of CSOs will die out, 1% of them will go on to have long-lived events with extended jets like those seen in Cygnus A , a distant supermassive black hole whose jets are aimed at Earth, a class of object called a blazar .

In those 1-in-100 long-lived events, the researchers suggest that the central black hole is being fed by extra gas and dust being provided by the merger of its host galaxy with another.

— Supermassive black hole’s mysterious 'hiccups' likely caused by neighboring black hole's 'punches'

— Brightest quasar ever seen is powered by black hole that eats a 'sun a day'

— Scientists find black hole spaghettifying star remarkably close to Earth

For Readhead, these findings vindicate a theory he first posited in the 1990s, when only three CSOs had been discovered. This idea went mostly unrecognized by the wider scientific community when first suggested but should gain traction with this new evidence.

"The hypothesis was all but forgotten because years went by before observational evidence began to mount for TDEs," Readhead said. "These objects are indeed a distinct population with their own distinct origin, and it is up to us now to learn more about them and how they came to be.

"Being able to study these objects on timescales of years to decades rather than millions of years has opened the door to a whole new laboratory for studying supermassive black holes and the many unexpected and unpredictable surprises they hold."

The team's research was published last month across three studies in the The Astrophysical Journal .

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

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Time Travel Equation Solved By Astrophysicist

Posted: March 25, 2024 | Last updated: March 25, 2024

After a lifetime of pursuing the idea, Physics Professor Ronald Mallett at the University of Connecticut has potentially figured out the theoretical aspects of time travel. Professor Mallett believes that black holes, rotating light, and gravitational pulls may hold the key to exploring time, but it’s all theoretical for now. There are still a lot of hurdles and limitations to handle before time travel can have real, practical applications.

<p>If this method of warp drive is achieved, there are still other limitations to consider. </p><p>If data is sent via FTL communication channels, sensors must be developed to interpret the data. In other words, step one is figuring out how to manipulate warp bubbles and send coded messages through time and space, and step two is figuring out how to make the information useful to its recipient. </p>

A Life Spent Thinking About Time Travel

Love and loss pushed Professor Mallett into an obsession with time and space. When he was 10 years old, his father passed away from a heart attack. It was his father who nourished his love of science, but H.G. Wells’ book The Time Machine pushed him towards a focus on time travel.

He was hooked from the very first paragraph of the book, “Scientific people know very well that Time is only a kind of Space. And why cannot we move in Time as we move about in the other dimensions of Space?”

That paragraph never left him, and the professor let that time travel question guide him through school and into the Professor Emeritus of Physics position at the University of Connecticut.

Artist’s rendering of a supermassive black hole

Einstein And Black Holes

As he grew up, Professor Mallett spent much of his time on Albert Einstein’s theories about black holes. While his interest in time travel only continued to grow, a potential solution never showed itself. At least, not until the professor ended up in a hospital with a heart condition.

There, lying in the hospital bed, inspiration hit him. Black holes and the gravitational fields they created were the answer to time travel. These gravitational fields had the potential to lead to time loops, which then theoretically could allow people and objects to travel back in time.

<p>As weird as it sounds, black holes spin just like planets. Much like Earth, a black hole rotates at a speed determined by its surface gravity. For every object that turns, there is a maximum rate at which it can do so, and according to Science Alert, researchers have discovered the black hole in the middle of the Milky Way is now spinning at that rate.</p>

Black Holes Manipulating Gravity

While this idea offered an ability to manipulate time, the other problem was how to use these time loops for time travel.

Professor Mallett found this time travel solution much easier than the first problem. Strong and continuous beams of light, like a ring of lasers, with a particular rotation could be used to manipulate gravity and mimic the distorting effects of a black hole.

<p>Though the details are rather complicated, the big time travel picture is a lot simpler to grasp. The professor offers a comparison to help people understand. “Let’s say you have a cup of coffee in front of you. Start stirring the coffee with the spoon. It started to spin, right? That’s what a spinning black hole does. In Einstein’s theory, space and time are related to each other. That’s why it’s called space-time. So when the black hole spins, it will actually cause time to shift.”</p>

Though the details are rather complicated, the big time travel picture is a lot simpler to grasp. The professor offers a comparison to help people understand. “Let’s say you have a cup of coffee in front of you. Start stirring the coffee with the spoon. It started to spin, right? That’s what a spinning black hole does. In Einstein’s theory, space and time are related to each other. That’s why it’s called space-time. So when the black hole spins, it will actually cause time to shift.”

<p>Professor Mallett may now have a theory on time travel and a machine to use to make it possible, but that doesn’t mean it will be here in the next few decades. </p><p>There’s still a lot to figure out to make such travel practical, such as where the insane amount of energy such a machine would require could come from, and how big the machine would need to be. </p><p>There’s also a major constraint on the machine. According to his theories, time travel would only be possible to the very beginning of when the machine was first built. In this way, it’s more like a one-way message service. You can potentially go forward quite a distance, but going back in time is limited by the machine’s creation. </p>

Much To Figure Out

Professor Mallett may now have a theory on time travel and a machine to use to make it possible, but that doesn’t mean it will be here in the next few decades.

There’s still a lot to figure out to make such travel practical, such as where the insane amount of energy such a machine would require could come from, and how big the machine would need to be.

There’s also a major constraint on the machine. According to his theories, time travel would only be possible to the very beginning of when the machine was first built. In this way, it’s more like a one-way message service. You can potentially go forward quite a distance, but going back in time is limited by the machine’s creation.

Theoretical Aspects Of Time Travel

The professor has made a huge leap in figuring out the theoretical aspects of time travel, but there’s a lot more to discover and quite a few hurdles and paradoxes to figure out before scientists practically start messing around in time.

Still, the theory is a step in the right direction and does suggest that people can push past what science currently considers possible.

Source: Earth.com

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Is time travel even possible? An astrophysicist explains the science behind the science fiction

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Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York

Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time.

But is this just a fun idea for movies, or could it really happen?

The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the laws of thermodynamics , it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time.

It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.

Time is relative

However, physicist Albert Einstein’s theory of special relativity suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the speed of light – 671 million miles per hour! – will experience time slower than a person on Earth.

People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is 6 minutes and 5 milliseconds younger .

Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes , or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past.

However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be incredibly challenging to send humans through a wormhole space tunnel.

Paradoxes and failed dinner parties

There are also paradoxes associated with time travel. The famous “ grandfather paradox ” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.

Famously, physicist Stephen Hawking tested the possibility of time travel by throwing a dinner party where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up.

As he pointed out : “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

Telescopes are time machines

Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago.

NASA’s newest space telescope, the James Webb Space Telescope , is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.

While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.

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New image reveals Milky Way's black hole is surrounded by powerful "twisted" magnetic fields, astronomers say

Updated on: March 28, 2024 / 7:43 AM EDT / CBS/AFP

Astronomers have discovered powerful "twisted" magnetic fields spiraling around the black hole that sits at the center of the Milky Way, the European Southern Observatory said Wednesday .

A new image from the Event Horizon Telescope (EHT) for the first time showed in polarized light a ring of magnetic fields surrounding the Sagittarius A* black hole .

The fields are similar to those observed around the M87* black hole at the heart of the M87 Galaxy , which the ESO says suggests that strong magnetic fields may be common to all black holes.

A new view of the massive object at the centre of our Galaxy

"What we're seeing now is that there are strong, twisted, and organized magnetic fields near the black hole at the center of the Milky Way galaxy," said Sara Issaoun, from Harvard's Center for Astrophysics, and co-lead of the project.

Polarized light images allow the astronomers to isolate the magnetic field lines.

Supermassive black holes, which sit at the center of galaxies, have masses millions and even billions greater than the sun. They are believed to have emerged very early in the universe but their creation remains a mystery.

Nothing can escape their gravitational pull, not even light, making them impossible to observe directly.

But with M87* in 2019 and Sagittarius A* in 2022 , the EHT captured the halo of light that is produced by the flow of matter and gas that black holes suck in and eject.

"By imaging polarized light from hot glowing gas near black holes, we are directly inferring the structure and strength of the magnetic fields that thread the flow of gas and matter that the black hole feeds on," said Angelo Ricarte, member of the Harvard Black Hole Initiative and a co-lead of the project.

The ESO also released a video of the new findings, which were published Wednesday in The Astrophysical Journal Letters.

Mariafelicia De Laurentis, deputy scientist at the EHT and professor at the University of Naples Federico II in Italy, said that "since both (black holes) are pointing us toward strong magnetic fields, it suggests that this may be a universal and perhaps fundamental feature of these kinds of systems."

News of the magnetic fields comes just weeks after researchers studying a galaxy through NASA's James Webb Space Telescope announced multiple discoveries, including spotting the most distant active supermassive black hole ever found.

In November, scientists discovered the oldest black hole yet, estimated to have formed 470 million years after the Big Bang -- and 10 times bigger than the black hole in our own Milky Way.

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COMMENTS

Could humans use black holes to time travel?
Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be heading back to visit the dinosaurs any time soon. At present, we don't have ...
Are black holes time machines? Yes, but there's a catch
Yes, but there's a catch. Black holes could take us to the future, and maybe even the past. The hard part would be surviving the trip. Black holes form natural time machines that allow travel to ...
Can we time travel? A theoretical physicist provides some answers
The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of ...
Could We Ever Take Advantage of a Time-Warping Black Hole?
And it's possible that the same thing would happen again on your way out — but in reverse. For future scientists interested in the time-warping features of black holes, therefore, their best bet will be to stay in a relatively close orbit of a blackhole, taking advantage of its time-dilating properties from the outside.
Black Holes, Relativity And Time Travel
Time Travel and General Relativity. In addition to speed affecting time, Einstein discovered that gravity, too, causes time to slow down, with the effect more pronounced near a massive object. Therefore, a black hole with its intense gravitational field could potentially provide a fantastic means to travel through time by getting close enough ...
Black Holes Could Work as Time Machines
Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be heading back to visit the dinosaurs any time soon. But don't expect to be ...
Can you time travel through a black hole?
This is step one for black hole time travel: Just fly near one for a bit and then come back. ... Now, theoretical debates aside, does this mean that time travel is possible? Well, technically, it ...
Is Time Travel Possible?
Time traveling to the near future is easy: you're doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein's special theory of ...
Can Time Travelers Reach the Past via Wormholes?
Time travel is not merely possible—it has already happened, though not exactly as Wells imagined. ... Because energy deforms spacetime, the entire thing would collapse into a black hole—an ...
Time travel is possible
If we could travel close to the speed of light, or in the proximity of a black hole, time would slow down enabling us to travel arbitrarily far into the future. The really interesting question is ...
Physicists Just Figured Out How Wormholes Could Enable Time Travel
Physicists Just Figured Out How Wormholes Could Enable Time Travel. Theoretical physicists have a lot in common with lawyers. Both spend a lot of time looking for loopholes and inconsistencies in the rules that might be exploited somehow. Valeri P. Frolov and Andrei Zelnikov from the University of Alberta in Canada and Pavel Krtouš from ...
How is Time Changed Inside a Black Hole?
From your perspective, Sally appears to slow down as she approaches the black hole, and the time interval between her flashes of light gradually increases. Additionally, the light she sends back to you gradually gets dimmer and redder. According to your perspective, Sally never actually descends into the black hole; she will travel more and ...
Time travel
And, as physicist Stephen Hawking pointed out in his book " Black Holes and Baby Universes" (Bantam, 1994), "The best evidence we have that time travel is not possible, and never will be, is that ...
10 Questions You Might Have About Black Holes
A black hole is an extremely dense object in space from which no light can escape. While black holes are mysterious and exotic, they are also a key consequence of how gravity works: When a lot of mass gets compressed into a small enough space, the resulting object rips the very fabric of space and time, becoming what is called a singularity.
Is Time Travel Possible?
In Summary: Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.
The Missing Piece: Are Wormholes the Key to Time Travel?
Similar to a black hole, a wormhole would compress an entering object to the size of a singularity and accelerate it to immeasurable speeds through the "throat" of the wormhole to the other side ...
What Do Black Holes Have to do with Time Travel?
What Do Black Holes Have to do with Time Travel? Gornekk, Thailand, Physics, Finalist, Space Exploration Popular Vote Top Scorer: 2021 BJC. Created by Khan Academy.
What are wormholes? An astrophysicist explains these shortcuts through
A wormhole is like a tunnel between two distant points in our universe that cuts the travel time from one point to the other. ... It's possible that the Big Bang created ... black holes, which ...
Black Holes Are Even Weirder Than You Imagined
Black holes have modes, too, though they radiate in gravitational waves, not sound waves. So if you, say, pounded on a black hole, in theory, you could tell quite a bit about it.
Why are some supermassive black hole jets so short? Astronomers may
"The giant black hole starts out invisible to us, and then when it consumes a star, boom! The black hole has fuel, and we can see it." However, it is not just any star that can be the messy cosmic ...
Time Travel Equation Solved By Astrophysicist
Black holes and the gravitational fields they created were the answer to time travel. These gravitational fields had the potential to lead to time loops, which then theoretically could allow ...
Is time travel even possible? An astrophysicist explains the science
Scientists are trying to figure out if time travel is even theoretically possible. If it is, it looks like it would take a whole lot more knowledge and resources than humans have now to do it.
New image reveals Milky Way's black hole is surrounded by powerful
A new image from the Event Horizon Telescope (EHT) for the first time showed in polarized light a ring of magnetic fields surrounding the Sagittarius A* black hole.
Experts Capture Spiral Around A Black Hole What Caused It
For the first time ever, a collection of telescopes captured an image displaying the spiral of magnetic fields surrounding a supermassive black hole. - Videos from The Weather Channel | weather.com
6 presumed dead in Maryland bridge collapse; Dali cargo ship lost ...
The US Coast Guard says it is suspending its search and rescue efforts for the six individuals still missing after the collapse of the Francis Scott Key Bridge in Baltimore.

Could humans use black holes to time travel?

What are black holes?

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Are black holes time machines? Yes, but there’s a catch

What are black holes?

Stretching space

Stretching time

Loops in time

Astronomers map 1.3 million supermassive black holes

The Milky Way’s central black hole could have a hidden jet

The rumblings that led to the ‘alien spheres’ probably came from a truck

These supermassive black holes, equal to 28 billion Suns, are the heaviest ever measured

The oddities known as Centaurs may sprout their tails after jumping to new orbits

How does a black hole get to the center of a galaxy, and does the galaxy revolve around it?

JWST’s new look at Supernova 1987A reveals a neutron star

Could you travel through a black hole? This Week in Astronomy with Dave Eicher

Could We Ever Take Advantage of a Time-Warping Black Hole?

Black Hole Time Machine

All About Perspective: Loop Quantum Gravity

Inside a Black Hole

Traveling Slower Through Time

Black Holes, Relativity And Time Travel

Time Travel and Special Relativity

Time Travel and General Relativity

Time Travel to The Past

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Stretching space

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Loops in time

Can you time travel through a black hole? - explainer

What is a black hole?

Can Time Travelers Reach the Past via Wormholes?

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10 Questions You Might Have About Black Holes

1. How can we learn about black holes if they trap light, and can't actually be seen?

2. How long does it take to make a black hole?

3. How do scientists calculate the mass of a supermassive black hole?

4. Is it possible for a black hole to "eat" an entire galaxy?

5. What would happen if you fell into a black hole?

6. What if the Sun turned into a black hole?

7. Have black holes had any influence on our planet?

8. What is the most distant black hole ever seen?

9. If nothing can escape from a black hole, then won't the whole universe eventually be swallowed up?

10. Can black holes get smaller?

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Can we use time travel in everyday life?

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