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Are There More than Three Dimensions?

from Through the Wormhole; Up, down, backward, forward, side to side. If you want to get anywhere on Earth, these three dimensions are the only ways you can go. They describe any place in our reality. Or do they? Many scientists now believe our world is not three-dimensional. That somehow there are other ways to move. Discovering those hidden dimensions is the biggest prize in physics and would forever change the way we see the Universe. Susan Barry knows all too well the limits of human perception. She was born with her eyes severely crossed. She could only see two dimensions. But in her late 40s, Susan began a rigorous vision retraining program to try to teach her eyes to lock onto the same target and give her brain the chance to discover an extra dimension of space. One day, after her 48th birthday, something incredible happened. I went out to my car and I sat down in the driver's seat, and I went to look at the steering wheel, and it had popped out. It was popped out in space with this palpable pocket of space between the steering wheel and the dashboard. And I had never seen anything like that. And all that day, my stereo vision would emerge like intermittently, unexpectedly, and it would be amazing. The sudden appearance of this extra dimension was a revelation to Susan Barry. But the idea that another dimension beyond the three we know might be hiding from all of us is now at the center of the world's most important scientific investigations. Harvard professor of physics Lisa Randall is at the forefront of this hunt. She sees the world differently from you and me. It was just one day I was walking to work, and I realized I really did think that extra dimensions could be out there. The main reason for her conviction that there must be more than three dimensions? We're trying to understand what can explain why gravity is so much weaker than the other elementary forces. And one of the possibilities that we start to think about quite seriously in the last decade or two is that there could actually be additional dimensions of space. If that's true, it could be that gravity's weak because it's actually concentrated somewhere else in another dimension. The idea that extra dimensions might be a hidden part of our reality is as old as Plato. He imagined the world we live in to be like the wall of a cave lit by firelight. Shadows dance across our two-dimensional world cast by objects in the body of the cave in a third dimension that's hidden from us. A three-dimensional geometrical shape like the tetrahedron, which has four equal sides, could cast a distorted shadow on the wall so that one side looks much shorter than the others. Just as an extra dimension can hide the true length of one of the sides, so, too, it might be hiding the true strength of gravity. And Lisa Randall's efforts to learn about extra dimensions begins, like Plato's, with studying shadows. But this scientist thinks he's discovered a new way to detect them and that dimensions we can't see control the way everything in the Universe moves. What would it look like if we were to travel into a fourth dimension of space? It's not easy to imagine. But here's one way to get an idea. Think of the palm of my hand as a world of only two dimensions. If a three-dimensional ball were to pass through it, what would the inhabitants of my palm see? A circle that grew and then shrunk down to a dot before disappearing. So, if I could move into the fourth dimension, my three-dimensional projection would distort, shrink, and finally flicker out of this world, becoming totally dark. U.C. Irvine physicist Tim Tait thinks most of the matter in the Universe may have moved into the fourth dimension and gone dark. If Tim's right, dark matter is actually made of light, massless particles that appear to have mass because they are racing around a tiny fourth-dimensional loop that's too small for us to see. But how and when did these photons leave our three-dimensional world and enter the fourth dimension? One way you can try to understand this is if you think about a round-about in a playground. It's spinning around really fast. Actually get onto the round-about, a child is gonna have to run around it at the same speed that it's spinning. But if it's spinning faster than the child can actually run, then there's no way to get onto it safely. Most particles we have today just don't have that much energy. But when the Universe was very young, it was very small and it was very hot. And at that time, particles had a lot more energy, and they were able to actually get into the extra dimension. Right after the Big Bang, super high-energy particles of light may have blasted their way into the fourth dimension. In 2008, NASA launched the Fermi Space Telescope, a probe designed to pick up the intense radiation, gamma rays, created by cosmic cataclysms like exploding stars. But it should also detect gamma rays from dark-matter photons as they annihilate one another. So, as it collects data, we understand the gamma-ray sky, and we start to look for where the dark matter might be. Fermi has already discovered a sea of gamma rays emanating from the center of our galaxy. But much more work is needed to prove this signal is coming from the fourth dimension. So obviously, I hope that tomorrow we declare victory and explore the extra dimension. On the other hand, I don't know exactly when we're gonna discover it. I think, though, the prospects today are much better than they have been in the past. The Fermi telescope will continue gathering evidence from the depths of space until around 2015. But proof that there are more than three dimensions may not come from so far away. Right now the biggest experiment mankind has ever built is trying to find them under the Swiss Alps. The goal of science is to reveal to us the deepest workings of nature. And nothing in science attempts to go deeper than string theory. String theory says that every single particle of matter and energy in the Universe is actually a tiny, vibrating string... A string that vibrates not in three dimensions, but in nine. If string theory is right, at every point in space, there are six extra dimensions curled up incredibly tight. These hidden dimensions could solve all the mysteries of physics. But there's a problem. Since string theory was first proposed over 40 years ago, there's not a single shred of evidence to support it. Thousands of scientists are on the hunt for that evidence. Under the foothills of the Alps in Geneva lies the Large Hadron Collider, the LHC. It's a 17-mile-long circular racetrack designed to smash subatomic particles together at phenomenal energies. CalTech physics professor Maria Spiropulu has been working at the atom smashers in Geneva since she was an undergraduate. She has seen trillions of particles fly like subatomic shrapnel through the detectors. The LHC, I think, is the most ambitious and technologically complex scientific project that humanity has ever attempted. And the smaller an object is, the more energy it takes to see it. The energy of the subatomic particles racing around the LHC is staggeringly large. But there may be a way to prove that string theory and the six extra dimensions of space that come with it is correct, a way that does not require seeing tiny strings directly. Joe Polchinski is one of the world's leading string theorists. Like many physicists, he draws inspiration from being close to nature. In 1995, after many years of work, Joe made his way through the torturous math and discovered the source of strings. He called these objects d-branes. So we're out here on this nice hike out here in nature, and we've got this beautiful spider web, which is a nice model for some of these ideas. So d-branes are these higher-dimensional objects. They can be two-dimensional, three-dimensional, or even more. In 1609, Galileo peered through his telescope and spied the moons of Jupiter. His discovery of those four tiny points of light, invisible to the naked eye, changed our understanding of our world. Extra dimensions of space will be much harder to see than Galileo's moons, but if we discover them, it will change our understanding of the entire Universe. This piece of delicately balanced equipment could be the device that discovers the fourth dimension. It sits in a basement at the University of Washington and belongs to this man. Eric Adelberger, along with a small team, has spent the last decade watching this torsion balance twist back and forth, hoping it reveals evidence that there are more than three dimensions. Gravity is really an amazing story. It was the first of the fundamental forces that the physicists learned about. The more dimensions there are, the faster the force of gravity changes with distance. On the other side of the planet, at the Large Hadron Collider, particle physicist Maria Spiropulu is also looking for unexpected changes in the force of gravity. But if her experiment is successful, she'll create something never before seen on Earth a black hole. Harvard professor Lisa Randall has a radical new idea about extra dimensions, one that will change the way we see our entire Universe. She began with string theory, the idea that all the fundamental particles are just vibrations of tiny nine-dimensional strings.


we can explore a hypercube by looking at its three-dimensional shadows
we can explore a hypercube by looking at its three-dimensional shadows


The more dimensions there are, the faster the force of gravity changes with distance
The more dimensions there are, the faster the force of gravity changes with distance


Subatomic shrapnel through the detectors
Subatomic shrapnel through the detectors


Large Hadron Collider in Geneva
Large Hadron Collider in Geneva
  Then she added in Joe Polchinski's ideas that strings making up all the stuff in our Universe had to be stuck to a giant three-dimensional object called a brane. But there is one more twist to this epic hunt for warped or curled-up extra dimensions. One scientist thinks our search is doomed to failure. She does not believe there are more than three dimensions. She thinks there's only one. How do you build a universe? Do you need three dimensions? Or do you need four? Nine? Or more? These are the most fundamental questions scientists can ask about our reality. But the simplest questions are often the hardest to answer. Swarms of scientists at the Large Hadron Collider and labs around the world are hunting for evidence of extra dimensions, be they warped or curled up in tiny loops. They hope to make a major breakthrough within the next few years. But Renate Loll, a physicist at the University of Utrecht, isn't holding her breath. So one experiment that you can actually do to find out what the dimension is to let an ink drop fall in it and then see what happens, see how the ink spreads in the space. In water, ink spreads into three dimensions. On a piece of blotting paper, it spreads into two. But when Renate tested how things spread out inside her computer-simulated universes, the results looked something like this. Watch what happens now. It filled out much less ones than we expected on small scales, and that's a true indication that the dimension's actually smaller than what we expected. It's smaller than three. Renate's simulations looked like they had three dimensions, but at root, they only had one.     If her theories of gravity are right, it suggests that solid space is not solid at all. Down at the smallest scales, it might be built from a mesh of one-dimensional lines. Is this the fundamental truth about how space is formed? Is one dimension all there really is? So the order is, one would think of the dimension of a space as fixed, just God-given. It's just there. But what happens on very, very small scales? And there's the story we find is totally different. The space appears to have a smaller and smaller dimension as you explore it on smaller and smaller scales. Other scientists are not convinced Renate's one-dimensional universe is correct. Their bets are hedged on a universe with many extra dimensions. The truth is still elusive. But it's not out of reach. It's a problem we really want to solve. We really think there has to be an answer really tells us that something has to be there, and it could tell us that there's some really ex otic, underlying matter or physics or forces that we haven't thought about yet. In the end, there is, you know, some theory. There's some simple, elegant theory out there that accounts for all of nature, for everything we see, and we feel like we could be very, very close to it. So when you have shocking questions, it takes sometimes shocking ideas and answers to try to put your arms around this. Are there nine dimensions or only one? Is this hidden space warped or curled up in tiny loops? We don't know yet. But we can be evermore sure of one thing. The three-dimensional world we thought we lived in is only what we see. Reality is almost certainly a lot stranger.
List with pictures of the scientists, in order of their appearance in Through the Wormhole Are There More than Three Dimensions? documentary, who share us their knowledges:
Lisa Randall
Lisa Randall (professor of physics, Harvard)
  Tim Tait
Tim Tait (U.C. Irvine physicist)
  Maria Spiropulu
Maria Spiropulu (CalTech physics professor)
  Joe Polchinski
Joe Polchinski (physicist, leading string theorists)
  Eric Adelberger
Eric Adelberger (physicist, University of Washington)
  Renate Loll
Renate Loll (physicist, University of Utrecht)