00:00If you saw a wormhole in reality, it would appear round, spherical, a bit like a black hole.
00:08Light from the other side passes through and gives you a window to a faraway place.
00:13Once crossed, the other side comes fully into view, with your old home now receding into that shimmering spherical window.
00:21But are wormholes real, or are they just magic disguised as physics and maths?
00:27If they are real, how do they work, and where can we find them?
00:32For most of human history, we thought space was pretty simple.
00:35A big, flat stage where the events of the universe unfold.
00:39Even if you take down the set of planets and stars, there's still something left.
00:44That empty stage is space, and it exists. Unchanging and eternal.
00:50Einstein's theory of relativity changed that.
00:54It says that space and time make up that stage together, and they aren't the same everywhere.
01:01The things on the stage can affect the stage itself, stretching and warping it.
01:06If the old stage was like unmoving hardwood, Einstein's stage is more like a waterbed.
01:13This kind of elastic space can be bent and maybe even torn and patched together, which could make wormholes possible.
01:21Let's see what that would look like in 2D.
01:24Our universe is like a big, flat sheet.
01:27Bent in just the right way, wormholes could connect two very, very distant spots
01:32with a short bridge that you could cross almost instantaneously,
01:36enabling you to travel the universe even faster than the speed of light.
01:40So, where can we find a wormhole?
01:43Presently, only on paper.
01:46General relativity says they might be possible, but that doesn't mean they have to exist.
01:51General relativity is a mathematical theory.
01:54It's a set of equations that have many possible answers, but not all maths describes reality.
02:00But they are theoretically possible, and there are different kinds.
02:08The first kind of wormholes to be theorized were Einstein-Rosen bridges.
02:12They describe every black hole as a sort of portal to an infinite parallel universe.
02:17Let's try to picture them in 2D again.
02:19Empty space-time is flat, but curved by objects on it.
02:23If we compress that object, space-time gets more curved around it.
02:28Eventually, space-time becomes so warped that it has no choice but to collapse into a black hole.
02:35A one-way barrier forms, the event horizon, which anything can enter, but nothing can escape.
02:41Trapped forever at the singularity at its core.
02:45But maybe there is no singularity here.
02:48One possibility is that the other side of the event horizon looks a bit like our universe again,
02:53but mirrored upside down, where time runs backwards.
02:58In our universe, things fall into the black hole.
03:01In the parallel universe, with backwards time, the mirror black hole is spewing things out, a bit like a big bang.
03:08This is called a white hole.
03:10Unfortunately, Einstein-Rosen bridges can't actually be crossed.
03:14It takes an infinite amount of time to cross over to the opposite universe, and they crimp shut in the middle.
03:20If you go into a black hole, you won't become the stuff coming out of the white hole.
03:24You'll only become dead.
03:27So, to travel the cosmos in the blink of an eye, humans need a different kind of wormhole, a traversable wormhole.
03:35There we go.
03:38If string theory, or one of its variations, is the correct description of our universe,
03:43then we could be lucky, and our universe might even have a tangled web of countless wormholes already.
03:49Shortly after the big bang, quantum fluctuations in the universe at the smallest scales, far, far smaller than an atom,
03:56may have created many, many traversable wormholes.
04:00Threaded through them are strings, called cosmic strings.
04:04In the first billionth of a trillionth of a second after the big bang,
04:08the ends of these tiny, tiny wormholes were pulled light-years apart, scattering them through the universe.
04:15If wormholes were made in the early universe, whether with cosmic strings or some other way,
04:20they could be all over, just waiting to be discovered.
04:24One might even be closer than we realize.
04:27From the outside, black holes and wormholes can look very similar,
04:31leading some physicists to suggest the supermassive black holes in the center of galaxies are actually wormholes.
04:37It will be very hard to go all the way to the center of the Milky Way to find out, though, but that's okay.
04:43There might be an equally extremely hard way to get our hands on a wormhole. We could try to make one.
04:50To be traversable and useful, there are a few properties we want a wormhole to have.
04:56First, it must obviously connect two distant parts of space-time,
05:01like your bedroom and the bathroom, or Earth and Jupiter.
05:07Second, it should not contain any event horizons, which would block two-way travel.
05:14Third, it should be sufficiently sized so that the gravitational forces don't kill human travelers.
05:20The biggest problem we have to solve is keeping our wormholes open.
05:24No matter how we make wormholes, gravity tries to close them.
05:28Gravity wants to pinch it closed and cut the bridge, leaving only black holes at the ends.
05:34Whether it's a traversable wormhole with both ends and hours, or a wormhole to another universe,
05:40it will try to close unless we have something propping it open.
05:44For very old string theory wormholes, that's the cosmic strings job.
05:48For man-made wormholes, we need a new ingredient.
05:52Exotic matter.
05:54This isn't anything like we find on Earth, or even antimatter.
05:58It's something totally new and different and exciting, with crazy properties like nothing that's ever been seen before.
06:05Exotic matter is stuff that has negative mass.
06:08Positive mass, like people and planets and everything else in the universe, is attractive because of gravity.
06:14But negative mass would be repulsive. It would push you away.
06:18This makes a kind of anti-gravity that props open our wormholes.
06:23And exotic matter must exert enormous pressure to push spacetime open,
06:27greater even than the pressure at the centers of neutron stars.
06:31With exotic matter, we could weave spacetime however we see fit.
06:37We may even have a candidate for this exotic matter, the vacuum of space itself.
06:43Quantum fluctuations in empty space are constantly creating pairs of particles and antiparticles,
06:49only for them to be annihilated an instant later.
06:52The vacuum of space is boiling with them,
06:55and we can already manipulate them to produce an effect similar to the negative mass we're looking for.
07:01We could use this to stabilize our wormholes.
07:05Once we're keeping it open, the ends would start together,
07:09so we'd have to move them around to interesting places.
07:12We could start by wiring the solar system, leaving one end of each wormhole in orbit around the Earth.
07:18We could fling others into deep space.
07:21The Earth could be a wormhole hub for a vast interstellar human civilization,
07:26spread over light years, but only a wormhole away.
07:30However, wormholes have a dark side.
07:33Even opening a single wormhole kind of breaks the universe in fundamental ways,
07:38potentially creating time travel paradoxes and violating the causal structure of the universe.
07:44Many scientists think that this not only means they should be impossible to make,
07:49but that it's impossible for them to exist at all.
07:52So, for now, we only know that wormholes exist in our hearts and on paper in the form of equations.
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