Light takes 4 years to travel from the nearby star Alpha Centauri to the Earth; consequently, what we see today on Earth happened 4 years ago on the stars of Alpha Centauri.
A closed timelike curve (CTC) is a conjectured path to the past.
The Higgs singlet is a hypothetical byproduct of the Higgs boson; the Higgs singlet only feels the single force of gravity.
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A closed timelike curve (CTC) is a conjectured path to the past.
The Higgs singlet is a hypothetical byproduct of the Higgs boson; the Higgs singlet only feels the single force of gravity.
Thanks for watching. Follow for more videos.
#cosmosspacescience
#throughthewormhole
#season6
#episode2
#cosmology
#astronomy
#spacetime
#spacescience
#space
#nasa
#spacedocumentry
#morganfreeman
#timetravel
Category
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LearningTranscript
00:00We're all marching relentlessly forward through time.
00:10We accept that there's no way to get off this ride or to change our destiny.
00:17But what if that's not really true?
00:19What if we can send messages back in time?
00:25Copy that.
00:27And change events that have already happened.
00:30Can the future reach back and rewrite the present?
00:34Can time go backwards?
00:43Space.
00:45Time.
00:47Life itself.
00:50The secrets of the cosmos lie through the wormhole.
00:55We think of the past as being set in stone and the future as a blank slate where anything can happen.
01:16But Einstein's laws of relativity blur our concept of time.
01:23As the great man said, the distinction between the past, present, and future is only a stubbornly persistent illusion.
01:34If all of time is already out there, can we make the sands of time flow the other way?
01:45Craig Callender, at the University of California, San Diego, is a philosopher who studies physics and cognitive science.
01:57He wonders why we don't experience time the way it really is.
02:01We ordinarily think of our brains as just receiving this stream of information and giving it to us in a passive way.
02:09But in fact, we never really look underneath the hood and then see what really is going on.
02:14When you look at a smoothly moving clock hand, your brain can make time appear to stop and start whenever your mental focus changes.
02:23If you look at an analog clock and you're looking at the second hand as it's going around, just as you grab it with your attention, the second hand seems to pause momentarily.
02:32You also experience a pause in time whenever you look in the mirror.
02:37Shift your gaze from one eye to the other, and you will never see either in motion.
02:43The brain is pulling all these tricks on us all the time.
02:46Our brains distort time to help us take snapshots of the world and remember important events.
02:54If our concept of time is distorted, what's the reality?
02:59Albert Einstein's theory of relativity attempts to explain how time truly works.
03:05In his view, time is a dimension just like the three dimensions of space.
03:11And because of this, he believed that there is no such thing as a single universal now.
03:19Space has no single universal here, so why should time?
03:24So here we're in San Diego, there are other places, Boston, London, Moscow, there are all those other places.
03:31We can't see them, but we know they exist.
03:33Similarly, things are laid out in time that way, too.
03:37All of time already exists alongside the other three dimensions.
03:42In Einstein's description of time, Craig's actions of getting into the water, paddling over it and getting out, all happen alongside one another.
03:53This is called this view of reality, where all of time and space already exists, the block universe.
04:02And it looks like this cake.
04:05So let this end of the block be the Big Bang, this end of the block be the end of the universe.
04:11All the events are there, laid out.
04:13So some of these events might be your birth, some of them might be right now, some of them might be your death.
04:18They're all there.
04:20Of course, we don't see the block universe all at once.
04:24We each experience the universe as our own slice of now.
04:28Everything behind the slice becomes our past, and everything in front represents our future.
04:35So each observer will have a different slice, covering up into past, present, and future.
04:41That knife will be their present.
04:45But just as everyone can't have the same here, not everyone can agree on what now is.
04:52Or to put it another way, everyone has their own uniquely angled now slice.
04:58Consider your own slice of now here on Earth.
05:02Your now includes light in the night sky from the nearby star Alpha Centauri.
05:07But that light has taken over four years to reach you.
05:11So your present slice is actually angled to include past events on Alpha Centauri.
05:18For someone on Alpha Centauri looking toward Earth,
05:22their now slice includes events from four years in the past on our planet.
05:28And Einstein is saying that there's no distinguished cutting up of the cake.
05:32They're all equally legitimate ways of cutting up everything.
05:36And those slices will grab different events in the space-time manifold.
05:41Light zips around our planet in a small fraction of a second.
05:46So our brains trick us into agreeing on a single shared noun.
05:51And our brains also fool us into believing that time is moving,
05:56even though the past, present, and future exist together.
06:00Craig thinks this is because our brains are stringing together individual slices of noun,
06:07like frames of a movie.
06:09What's really going on, I think, is that you have memories only in one direction.
06:13You just can't get memories of the future.
06:15So there's baby you, dealt you, et cetera.
06:18You have this thread of identity running through space-time.
06:22That's why it feels like I'm flowing,
06:24because I'm building up this story of the self.
06:27There's nothing really moving through the block.
06:30Our sensations of time appear to be distorted, even fabricated.
06:35So can we learn to see time differently?
06:40Time never stops.
06:44But our brains can only register one moment in time,
06:48the moment we call the present.
06:52If all of time does exist at once,
06:56couldn't we change our viewpoint of time and maybe see our own future?
07:03Jim Hartle is a physicist at the University of California at Santa Barbara.
07:13He spent decades trying to wrap his head around Einstein's theory of time.
07:17There isn't a notion of past, present, and future in special relativity.
07:22So our impression of past, present, and future has to come from the way that we're constructed.
07:29Our brains constantly process information.
07:32And whatever is most recent becomes now.
07:36Our brains then move that information into our memory to make room for a new now.
07:42The present is the most recent information.
07:45The past, right, is what you've got in memory.
07:48We take the two and we try to predict, right, what we're going to see in the future.
07:53But what if we perceive time differently?
07:58Jim imagines brains constructed to interpret sequences of events in new ways.
08:04Take the fast-moving game of roller hockey.
08:08The players are all making decisions based on what's happening in their present.
08:12What would happen to a player if his experience of the present
08:16was what everyone else sees as the past?
08:19Let's say the goggles Jim hands to this player change his perspective on time.
08:25Let's say that those goggles contain a program that filters the events in our present
08:31and delays them by ten seconds.
08:34After the face-off, both teams scatter toward goal.
08:38The goggled player remains at center-rights.
08:41What happened ten seconds ago for everyone else feels like the present to him.
08:47When the goggled player finally precedes the puck moving toward the goal,
08:51the rest of the players have already skated to a corner of the rink.
08:56That player would never catch up with the puck.
08:59In hockey, a player seeing the past as his now would be perpetually late to the action
09:06and would be a useless player.
09:09In the natural world, the repercussions are more severe.
09:14If a hunter believed his prey to be in a time and place that it had already left,
09:19he'd never catch a meal.
09:21And his days would be numbered.
09:24Natural selection has guided the development of our brains to compute in that way.
09:29That's the most efficient survival mechanism, and alternatives to it get weeded out.
09:35Jim then wondered whether a brain artificially could construct it to experience more than one now
09:41might gain some advantage.
09:43It is possible to imagine brains that would have a conscious focus on all parts of its memory in the present,
09:52but it would waste valuable computational resources considering options that are useless.
09:58Imagine the hockey player having to make decisions where all moments are equally accessible.
10:04Everything in his experience feels like now.
10:07Jim suspects a brain like this would freeze into inaction, overwhelmed by a universe of choices.
10:14Our past, present, and future way of organizing the flow of time has evolved as best for our biological survival.
10:22Our brains have created a narrative of time that best suits our environment.
10:27But could other perceptions of what now is work better in other environments?
10:32It's a very intriguing question whether beings on other planets, for example,
10:39would have the same method of organizing time that we do, past, present, and future.
10:44Perhaps on other worlds, alien minds have devised ways to augment their own experience of time.
10:51They may be able to thrive with knowledge of the past, present, and future all at once.
10:58Could we ourselves learn how to manage multiple nows?
11:04It could be more likely than you think.
11:07One scientist thinks he's seen the future and detected its shadow, cast backward in time.
11:17You can get to where you want to go without taking the first step.
11:22Seems simple enough.
11:25But new research is hinting that the opposite could also be true.
11:30Where you end up might influence the path you're taking now.
11:35Sandhu Popescu is a professor of physics at the University of Bristol in England.
11:44He's made an unsettling discovery.
11:47The future might be reaching back and meddling with the past.
11:54The ideas dawned on Sandhu while he and his colleagues were exploring a fundamental mathematical concept called the pigeonhole principle.
12:03If I have three pigeons and I want to put them into two pigeonholes, then I necessarily end up with two pigeons in one hole.
12:15It's common sense.
12:17Three pigeons won't fit into two pigeonholes without two of them having to share.
12:22But if the pigeons were shrunk down to the size of atoms, then they would follow the strange rules of quantum mechanics.
12:30And then three pigeons could fit into two spaces and never share the same space.
12:36I can arrange a situation in which I can guarantee that no two particles will be found in the same box.
12:46This bizarre effect is possible because many skilled quantum objects don't have definite fixed locations.
12:54Quantum particles in general behave very differently from everyday objects that we know.
13:03For example, an atom can be in two or even more places at the same time.
13:09But when Sandhu began thinking about exactly how particles avoid sharing a space with one another,
13:15he found it had a radical consequence.
13:18Information about the future can travel backwards through time.
13:24The fact that when dealing with microscopic particles, the result of an experiment is not determined from the beginning,
13:34opens the possibility that the future will influence the past.
13:40Sandhu has set up an experiment to explore this curious situation.
13:47He fires batches of three electrons into a diamond-shaped apparatus.
13:54It has two tracks.
13:56One goes to the left, the other goes to the right, before merging again at a second fork.
14:02These two tracks are the two pigeonholes.
14:09To understand how Sandhu studies what the three electrons are doing, think of them as three hat-wearing toy pigeons.
14:18We have three pigeons and two pigeonholes.
14:21The road to the left and the road to the right.
14:25At least two of them should be in the same place.
14:28Now, the road is pretty narrow.
14:32So, even two pigeons being together, it's a crowd.
14:37Being a crowd, they collide.
14:40They collide with each other.
14:42Because these pigeons represent quantum particles, Sandhu can't actually watch them as they travel through the two tracks.
14:49If he did, he would disrupt their movement and ruin the experiment.
14:55We want to make sure that we do not disturb the particles.
15:01So, what we have to do is to perform the experiment in the dark.
15:06However, Sandhu does have a way of checking whether the pigeons have shared a track without disturbing their movement.
15:13He can wait for them to exit and see whether any of their hats have fallen off.
15:19A sure sign of a collision.
15:21As with everything in the quantum world, the results of the experiment are different every time it is run.
15:28I throw the three particles exactly in the same way.
15:34Sometimes I see hats.
15:36Sometimes I do not.
15:38But one aspect of the experiment seemed to fly in the face of those quantum mechanical rules of randomness.
15:45Whenever the pigeons exit together on one side, Sandhu finds they are always wearing hats.
15:52Two pigeons must have gone down the same track and, as if by magic, they did not collide.
16:01However, if instead Sandhu checks on the pigeons right before the fork, he sees something different.
16:10Sometimes he finds all three of them wearing their hats and sometimes two of them have lost their hats.
16:17If I check them before the fork, there were two possibilities of events that happened earlier.
16:25Namely, hats were lost or hats were not lost.
16:29If, on the other hand, I check the pigeons only later, I see that one of these possibilities disappeared.
16:37The question is, how can my decision of either checking here or checking there make one earlier possibility disappear?
16:47Sandhu believes the most natural explanation for what's happening is that information from the future travels backward through time.
16:56While the pigeons are still inside the tracks, they appear to already know that Sandhu is going to wait,
17:03and check on them only after they have exited.
17:07And so, they don't collide.
17:11We need to conclude that no matter how strange this may be, no matter how unusual,
17:18most probably what happens is that the future does influence the past.
17:24You've heard the expression, life is like a box of chocolates.
17:32There are so many possibilities, you never know what you're going to get.
17:37But the possibilities may not be as great as we think.
17:41The future could be reaching back and stealing some.
17:47In fact, the future of the entire universe could be controlling our lives right now.
17:56What has yet to happen affects what is happening now.
18:02At least, that's what we see in the subatomic world.
18:06But we're all made of atoms.
18:10The entire universe is.
18:13So, could the ultimate destiny of the cosmos affect what's possible in the here and now?
18:25Professor Paul Davies is a cosmologist at Arizona State University.
18:31He believes what happens in the future reaches back through time and affects what's happening in the present.
18:37And what's happening now is eliminating choices we thought we could have made in the past.
18:43For example, once his students stepped foot into his classroom, an earlier choice to ditch class is ruled out.
18:51Paul's students believe they could have skipped today's lecture if they wanted to.
18:56But he thinks that they never actually had that choice.
19:00What happens in the future and what happens in the past can be linked.
19:06So, somehow, the present knows what's going to happen in the future.
19:10And also, what happens now affects what could have happened in the past.
19:15Experiments with subatomic particles have already shown that the future position of an object limits where it can be in the present.
19:23Paul thinks the same thing might be happening at the level of our everyday reality.
19:28For example, at the end of the day, Paul enjoys an anniversary dinner with his wife.
19:34That means that certain events earlier in the day can't happen.
19:40So, supposing somebody walks in and offers me some tickets for a concert.
19:44Hey, Paul, I got this extra ticket for this concert tonight in Vegas.
19:48But we have to leave, like, right now.
19:50Do you want to come?
19:52Could Paul say yes to the concert invitation?
19:54If he does, his wife will be left alone.
19:58Hang on, let me just check my calendar.
20:02He may feel, right at the moment he checks his calendar, that he has a choice about what to do.
20:08Am I going to have to make a decision between the concert and the dinner?
20:12What am I going to do?
20:13But his calendar is irrelevant, even though he doesn't realize it in the present.
20:19Not going to that dinner is simply not an option.
20:22Miss it, and Paul's life, as he knows it, is over.
20:27Oh, no, there's something I really can't get out of.
20:30Sorry, I'll have to give it to somebody else.
20:33It's not that his wife will be mad.
20:36Paul does attend the dinner in the future.
20:39And that makes it impossible for Paul to do anything that would prevent it.
20:43I've got to do this, and I've got to do that, and how do I choose one or the other?
20:46And it turns out that all of these different possible pathways into the future
20:51constrain our freedom of action now.
20:54And Paul believes this same backward time effect is at play on a cosmic scale,
20:59from the distant future to the beginning of everything.
21:05To help make sense of this, imagine our universe is a chocolate factory.
21:11The Big Bang is the beginning of the production line,
21:15and the end of the universe is where the finished chocolates come out.
21:20Our present is somewhere in between.
21:24We may think what happens now changes their final state.
21:28But actually, what's inside the finished chocolates determines the ingredients that can be put in.
21:36There may be certain chocolate ingredients that are simply inconsistent with this final state.
21:43In the middle of the production line, it may appear the machines can add a cream filling or a raspberry filling.
21:50But since the finished chocolates contain raspberry, only the pink filling can possibly enter the line.
21:58The end limits what is possible now.
22:02And Paul thinks there's a similar limiting effect radiating back to our present from the ultimate future of the universe.
22:09If we imagine the final state of the universe being fixed by nature in some way,
22:17then that would have implications for the production line that we're seeing now.
22:21And the big difference with the chocolates is that whatever happens, there will be a final state of the chocolates.
22:29That is determined in advance by the internal machinery.
22:33But in the real universe, nobody, not even nature, knows what that final state will be.
22:39Although no one can say for sure, most scientists think the far future of the cosmos will be cold, dark, and completely empty of all particles.
22:51Paul thinks we might be able to detect the effects of this future on certain experiments we perform here and now.
23:00One idea is to fire a laser into deep space.
23:04As long as Paul's laser beam eventually runs into something, like a planet, then the laser will fire as normal.
23:11However, if Paul directs his laser into a completely empty patch of space, where nothing would ever block it,
23:18and it could, in theory, travel forever, the laser might not work.
23:23So you could point a laser at the dark parts of the sky, and you could notice that there wasn't any light on the air.
23:29There's not much light.
23:31Light wouldn't come out because no light is allowed in the far future of the universe.
23:38If the end state of the universe is indeed dark and empty, nothing from the present, like photons from the laser beam,
23:45can be allowed to reach it.
23:49Finding evidence that the future influences the present creates an intriguing possibility.
23:58Can we, right now, reach back and affect our own past?
24:07Quantum mechanics suggest the future can control the past.
24:14Maybe someday we'll turn theory into practice.
24:19But what are the limits?
24:21Could someone go back in time and change history?
24:26Stop Hitler before he starts a war?
24:31Or save JFK from an assassin's bullet?
24:40Todd Brunn likes to imagine what it would be like to live in the past.
24:46And as a professor of physics and electrical engineering at the University of Southern California,
24:51he's actually trying to work out whether traveling back in time is possible.
24:56The direction of time itself is something of a, of a mystery.
25:01In the equations of physics, it seems like you could run them either forwards or backwards.
25:06But everything we observe in the world around us points to time having only one possible direction, forwards.
25:14Everything grows older, everything decays.
25:19When we write on a chalkboard, the marks that we leave are chalk dust that crumbles off of the end of our stick of chalk and sticks to the board.
25:28If I move my stick of chalk over a chalkboard, the dust that crumbled off the end doesn't once again adhere to my stick of chalk and make it a longer stick of chalk.
25:38That's the arrow of time at work.
25:40However, if time is really a dimension, as Einstein says, time that's past still exists.
25:48It's simply located somewhere else in the four-dimensional universe.
25:52Space-time is the entire four-dimensional background for everything that happens and ever has happened and ever will happen in the universe.
26:03Events in our past may not be gone from the universe, but they are out of reach.
26:10If you travel faster than the speed of light, Einstein's equations of relativity say your time ticks backwards.
26:18The trouble is, it takes an infinite amount of energy to reach the speed of light.
26:24So, you could forget that.
26:26But there may be ways to get to the past.
26:29They're called closed time-light curves, strange distortions of the fabric of space-time that could give you a shortcut to a different moment in time.
26:42Some very exotic arrangements of matter in space-time can cause these paths to actually curve so much they curve all the way around back upon themselves.
26:52Time-traveling Todd wouldn't have to travel faster than light.
26:57As he moves forward, the fold in space-time would carry him backward to the same point in space, but at an earlier time.
27:05This is not the situation that we normally observe in the universe, but people can solve Einstein's equations and find these solutions that contain these closed time-light curves.
27:17The laws of physics say we can visit a point in the past.
27:21There's nothing stopping Todd visiting one of his ancestors and explaining how he managed to jump back in time.
27:29You might find this interesting.
27:33However, Todd thinks it's impossible to alter the past.
27:37Todd's ancestor must always have received a visitor from the future.
27:43The history of a single universe can only contain one set of actions.
27:49Things that are incompatible, things that are actual inconsistencies, should not be allowed.
27:55Anything the time traveler does must fit in with what's already happened.
28:03For example, let's say Todd is a time traveler who hopes to alter some past event.
28:09And imagine that event is a dance Todd wants to stop.
28:15The past has to be consistent.
28:17So, if I go into the middle of the dance and I try to disrupt it by pulling a dancer out of the flow of the dance, then it will have to be that that dancer left the dance at that very moment.
28:31No matter what Todd does, he will only fulfill the events and sequences that have already taken place.
28:38If I try to go and jump into the middle of the dance that's already happening, then it has to have been that in the past, if I mysteriously appeared at that point and joined the set, either the dance was always disrupted and I'm just fulfilling what already happened, or if the dance took place, then my attempts to disrupt it will be futile.
29:02It's as if the universe has a built-in safeguard to keep its history consistent.
29:08You simply can't kill your own grandfather.
29:15But there is one paradox that time travel may create.
29:18When time traveling Todd turns over those time machine plans to his ancestor,
29:23You might find this interesting.
29:25That ancestor could then pass down those plans back to time traveling Todd.
29:31Who uses the plans to build the time machine.
29:36Neither of them actually created the plans.
29:40The question is, where did the plans come from?
29:44The plans seemingly appeared out of nowhere.
29:46This is the kind of paradox that critics cite to quash the idea of time travel.
29:52And yet, Todd's calculations show that time travel can actually cause information to appear from nothing.
30:01In some of the mathematical models that we've developed for closed time-like curves, you can force the universe to cough up information without ever having calculated it.
30:12Todd sees a universe where moving backward in time is possible, but changing the course of history is not.
30:21However, no one has yet come close to building a working time machine.
30:25But maybe to reach the past, we won't need one.
30:32Traveling into the past, or meeting our prior selves, remains in the realm of science fiction.
30:40But modern technology may already be building a link between our present and our past selves.
30:56Hello?
30:58Tom Weiler is a physics professor at Vanderbilt University.
31:08He's hunting for a tiny time traveler.
31:12If he tracks it down, Tom may be able to send messages into the past.
31:21You have one new voice message.
31:24Hey, it's me.
31:25You left your wallet on the table.
31:27Don't forget to pick it up.
31:29And receive communication from the future.
31:33Tom's target is an as-yet undiscovered subatomic particle called the Higgs singlet.
31:40When our most powerful particle accelerator creates the Higgs boson, also known as the guard particle, it may not be created alone.
31:50The Higgs singlet may be part of the subatomic shrapnel.
31:55However, finding it will be a difficult task.
31:59The Higgs singlet may quickly escape our reality and move into another dimension of space.
32:07There's some mathematical arguments for why there should be more than three space dimensions.
32:12Because all of the particles we have measured up to now, the so-called standard model particles, cannot leave our three-dimensional space and travel in extra dimensions.
32:21So the Higgs singlet becomes a very special particle.
32:25To understand the special abilities of the Higgs singlet more clearly, imagine that this toy racetrack represents the dimensions of space.
32:35The flat straightaway symbolizes our three familiar dimensions.
32:39And the loop-de-loop stands in for an extra dimension.
32:44All particles we've discovered so far fill the pool of one or more of three fundamental forces.
32:50The electromagnetism, the strong force, and the weak force.
32:55Which force or forces a particle feels depends on its charge.
32:59It may have an electric charge, a weak charge, or a charge that makes it feel the strong force.
33:06We've not yet found a particle that has no charge.
33:11So when we look at a normal particle, because the particle carries some kind of charge, that charge sticks it to the three dimensions.
33:20And that's the example that's given by this green car.
33:26Because normal particles remain tied to our three dimensions, they can travel only one way through time.
33:33But Tom believes a Higgs singlet is different.
33:36It has no charge whatsoever.
33:39It's called a singlet because it only feels a single force, gravity.
33:45And that means it's free to stray from the usual path.
33:49Tom suspects a Higgs singlet may travel to an extra dimension of space that curls back on itself.
33:56He calls it the U-dimension.
33:59So the U-dimension is very, very small.
34:01The Higgs singlet perceives the extra dimension, which in this toy model is the loop that we see.
34:07As the Higgs singlet enters the loop, it's momentarily moving against the normal one-way flow of time.
34:15If I look at time, which Einstein told us is just another coordinate, there's nothing fundamental to his theory that says you can't have time growing negative.
34:24The Higgs particle will travel through positive time, then in this direction it will travel through negative time, then it will travel through positive time again.
34:32It looks like it has to go an extra distance and therefore take an extra time to get to the end point.
34:38But in fact, if in the extra dimension time runs backwards, then it's gaining time each time it goes around this loop.
34:46And that gives a clue for how to find it.
34:50The world's most powerful particle accelerator, the Large Hadron Collider in Switzerland, fires protons at one another at almost the speed of light.
35:02Their collisions create showers of subatomic debris, particles that live just a fraction of a second before popping out of existence.
35:10Tom suspects that one of these particles could be his mysterious time traveler.
35:16But to find the backwards and time traveling Higgs singlet, we'll have to look at what happens before the collision that created it.
35:24We're scattering the particle before, according to the time on our clocks, before it was produced.
35:31Currently, the LHC isn't set up to look at collisions before they happen.
35:38One of the standard protocols is that decay or re-collisions don't happen before the particle is produced.
35:46Unwittingly, we may be creating Higgs singlets.
35:52And Tom believes his mysterious particle could eventually lead us backward in time.
35:59Well, if you could control this thing, you could, at a minimum, send the particles as Morse code.
36:07You could send a signal to the past.
36:09You could even use it to send your younger self a message.
36:13Hey, this is me.
36:15You left your wallet on the table. Don't forget to pick it up.
36:18Communication links into the past may already exist.
36:23And this theoretical physicist thinks he's figured out what it takes to make one.
36:29Can we, in fact, build a time machine?
36:34I would love to have a time machine to be able to relive treasured moments.
36:44Or maybe to have a chance to do some things over.
36:48Time travel could be possible with the help of a wormhole.
36:55A cosmic shortcut through space and time.
37:03No one has ever seen a wormhole.
37:05So, maybe we'll just have to build one.
37:14Luke Butcher is a theoretical physicist with the University of Edinburgh in Scotland.
37:19He studies distortions of space-time.
37:23How energy warps the fabric of the universe.
37:27Einstein's equations are a relation between the energy and matter of the universe
37:33and the curvature that that matter causes.
37:35You go from a flat thing, you put some energy in,
37:38and Einstein says that the space will curve.
37:41And the more energy you put in, the more curved it gets.
37:43Wormholes are extreme distortions in space-time.
37:48They can, theoretically, link two different points in space
37:52and two different points in time.
37:55So, wormholes have not been observed,
37:58but we can study them mathematically.
38:00You write down the shape that you think space-time might be,
38:03then you can put them into Einstein's equations,
38:05and what those equations will spit out
38:07is the sorts of energy you need for that space-time to exist
38:11and to be stable.
38:12Luke started calculating what it would take to warp a patch of space-time
38:20into a wormhole someone could travel through.
38:23It needs a particular form of energy called negative energy.
38:27So, the best way of thinking about what negative energy is,
38:33is to think about what zero energy is.
38:36Zero energy is the vacuum.
38:38But the vacuum is not truly empty.
38:41It's filled with quantum particles popping in and out of existence.
38:46If we can get rid of some of those quantum fluctuations,
38:49we'll end up with negative energy.
38:54Scientists have been able to create small doses of negative energy in the lab.
38:59They place two conducting plates very close together
39:02to constrain the quantum fluctuations in the gap between them.
39:07Because the fluctuations inside are weaker than the ones outside,
39:12the gap has negative energy.
39:14If we could scale up this process,
39:17it's possible that we could manufacture enough negative energy
39:21to create a wormhole
39:23and use it to open a window to the past.
39:26But there's a problem.
39:28The mathematics say that wormholes are incredibly unstable.
39:32Once you try to enter them,
39:35they close right up.
39:37So, if you're trying to use this as a time machine
39:39or a shortcut from A to B,
39:41there's going to be no hope, right?
39:43Because this thing's going to collapse
39:44before you get from one side to the other.
39:46But as Luke dug deeper,
39:48he realized there might be a way
39:50to extend the lifespan of a wormhole
39:53by slimming it down.
39:55The interesting thing about a wormhole
39:57is that there's two different sorts of curvature going on.
40:00There's this long, longitudinal curvature,
40:04curvature through the wormhole like this.
40:06And there's also curvature going around the wormhole.
40:10A longer, thinner wormhole wouldn't need as much negative energy
40:14to stay open.
40:15And its narrowness would even create some of its own,
40:19making it far more stable.
40:21Essentially, this longitudinal curvature here
40:25needs to be balanced by something that holds it in.
40:29And so, very roughly speaking,
40:32the wicker pattern weaved around this side
40:35is analogous to the role that negative energy plays
40:38in keeping the wormhole stable.
40:40The tight circles of space-time
40:43around the throat of the wormhole
40:45create their own negative energy
40:47and keep the portal propped open.
40:50So, this wormhole, as you can see,
40:54is quite a lot longer and thinner
40:56than this wormhole that we started with,
40:58the typical wormhole.
40:59This wormhole, on the other hand,
41:01is very gently curved from top to bottom
41:04and has a very tight circumference.
41:06It requires less negative energy
41:08and generates more negative energy,
41:09so it should be more stable.
41:11Luke may have figured out
41:12how to create a more stable wormhole,
41:14but the question remains,
41:17could it work as a time machine?
41:20It's on the edge of our knowledge, really,
41:22but it's tantalizing
41:24because it's not definitively no
41:26and it's not definitively yes.
41:28In terms of the calculations I've done,
41:30you could send an object through
41:32moving very close to the speed of light
41:33and it would be able to squeeze through.
41:35Luke's wormhole is, by design,
41:38far too narrow for a person to squeeze through.
41:42But a light beam could probably make it,
41:45and that's all we would need
41:47to send a message back in time.
41:49Maybe in the future,
41:51someone will discover a new twist
41:53that allows a wormhole
41:54to usher through something bigger,
41:56like a person.
42:02It may seem that time relentlessly carries us
42:05from the past toward the future,
42:08but that's not the way the universe really works.
42:11What takes place in our past
42:14does not simply recede into history.
42:18It becomes imprinted into the fabric of the cosmos.
42:22One day, we may learn to weave the threads
42:27of the past and the future together,
42:30and truly play with the boundless possibilities of time.
42:35One day, we'll see you next time.
42:36One day, we'll see you next time.
42:38One day, we'll see you next time.
42:40Somewhere
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