Physicist Brian Greene explains superstring theory, the idea that minuscule strands of energy vibrating in 11 dimensions create every particle and force in the universe. 

View full lesson: http://ed.ted.com/lessons/brian-greene-on-string-theory

Talk by Brian Greene.

a virtually unknown German mathematician named Theodor Kaluza suggested a very bold and in some ways very bizarre idea.

He proposed that our universe might actually have more than the 3 dimensions that we are all aware of.

That is, in addition to left, right, back, forth, and up, down, Klutza proposed that there might be additional dimensions of space that for some reason we don't yet see.

Now, when someone makes a bold and bizarre idea, sometimes that's all it is.

Bold, bizarre, but it has nothing to do with the world around us.

This particular idea, however, although we don't yet know whether it's right or wrong, and at the end I'll discuss experiments which in the next few years may tell us whether it's right or wrong, this idea has had a major impact on physics in the last century and continues to inform a lot of cutting-edge research, so I'd like to tell you something about the story of these extra dimensions.

To begin, we need a little bit of backstory.

This is a year when Einstein is basking in the glow of having discovered the special theory of relativity and decides to take on a new project to try to understand fully the grand pervasive force of gravity.

And in that moment, there were many people around who thought that that project had already been resolved.

Newton had given the world a theory of gravity in the late 1600s that works well, describes the motion of planets, the motion of the moon and so forth, the motion of apocryphal apples falling from trees, hitting people in the head, all of that could be described using Newton's work.

But Einstein realized that Newton had left something out of the story because even Newton had written that although he understood how to calculate the effect of gravity, he had been unable to figure out how it really works How is it that the Sun 93 million miles away somehow it affects the motion of the earth?

How does the Sun reach out across empty inert space and exert?

Influence And that is a task to which Einstein set himself to figure out how gravity works.

And let me show you what it is that he found.

So Einstein found that the medium that transmits gravity is space itself.

Imagine space as a substrate of all there is.

Einstein said space is nice and flat if there's no matter present But if there is matter in the environment such as the Sun it causes the fabric of space to warp to curve And that communicates the force of gravity even the earth warps space around it now Look at the moon The moon is kept in orbit according to these ideas because it rolls along a valley in the curved environment that the Sun and the Moon and the Earth can all create by virtue of their presence.

If we go to a full frame view of this, the Earth itself is kept in orbit because it rolls along a valley in the environment that's curved because of the Sun's presence.

That is this new idea about how gravity actually works.

Now this idea was tested in 1919 through astronomical observations.

And this gained Einstein prominence around the world.

And that is what got Kaluza thinking he like Einstein was in search of what we call a unified theory That's 1 theory that might be able to describe all of nature's forces from 1 set of ideas 1 set of principles 1 Master equation if you will so kaluza said to himself Einstein has been able to describe gravity in terms of warps and curves in space, in fact, space and time, to be more precise.

Maybe I can play the same game with the other known force, which was at that time known as the electromagnetic force.

We know of others today, but at that time that was the only other 1 people were thinking about.

You know, the force responsible for electricity and magnetic attraction and so forth.

So Kaluza says, maybe I can play the same game and describe electromagnetic force in terms of warps and curves.

Einstein had already used up space and time.

Warps and curves to describe gravity didn't seem to be anything else to warp or curve So klutz has said well Maybe there are more dimensions of space.

He said if I want to describe 1 more force, maybe I need 1 more dimension So he imagined that the world had 4 dimensions of space, not 3.

And imagined that electromagnetism was warps and curves in that fourth dimension.

When he wrote down the equations describing warps and curves in a universe with 4 space dimensions, not 3, He found the old equations that Einstein had already derived in 3 dimensions Those were for gravity, but he found 1 more equation because of the 1 more dimension And when he looked at that equation, it was none other than the equation that scientists had long known to describe the electromagnetic force Amazing it just popped out He was so excited by this realization that he ran around his house screaming victory that he had found the unified theory.

Now clearly, Kalutz was a man who took theory very seriously.

In fact, there's a story that when he wanted to learn how to swim, he read a book, a treatise on swimming, then dove into the ocean.

This is a man who would risk his life on theory.

Now but for those of us who are a little bit more practically minded, 2 questions immediately arise from his observation.

Number 1, if there are more dimensions in space, where are they?

And number 2, does this theory really work in detail when you try to apply it to the world around us?

Now, the first question was answered in 1926 by a fellow named Oscar Klein.

He suggested that dimensions might come in 2 varieties.

There might be big, easy to see dimensions, but there might also be tiny, curled up dimensions, curled up so small, even though they're all around us, that we don't see them.

So, imagine you're looking at something like a cable supporting a traffic light.

But the cable looks one-dimensional from a distant viewpoint.

But you and I all know that it does have some thickness.

It's very hard to see it, though, from far away.

But if we zoom in and take the perspective of say a little ant walking around, little ants are so small that they can access all of the dimensions.

The long dimension but also this clockwise, counterclockwise direction.

And I hope you appreciate this, It took so long to get these ants to do this.

But this illustrates the fact that dimensions can be of 2 sorts, big and small, and the idea is that maybe the big dimensions around us are the ones that we can easily see, but there might be additional dimensions Curled up sort of like the circular part of that cable so small that they have so far remained invisible Let me show you what that would look like.

So if we take a look say at space itself I Can only show of course 2 dimensions on a screen some of you guys will fix that 1 day, but anything that's not flat on the screen as a new dimension goes smaller, smaller, smaller, and way down in the microscopic depths of space itself, this is the idea.

You could have additional curled up dimensions, here is a little shape of a circle, so small that we don't see them.

But if you were a little ultra-microscopic ant walking around, you could walk in the big dimensions that we all know about.

But you could also access the tiny curled up dimension that's so small that we can't see it with the naked eye or even with any of our most refined equipment, but deeply tucked into the fabric of space itself, the idea is there could be more dimensions, as we see there.

Now, that's an explanation about how the universe could have more dimensions than the ones that we see, but what about the second question that I asked?

Does the theory actually work when you try to apply it to the real world?

Well, it turns out that Einstein and Clutza and many others worked on trying to refine this framework and apply it to the physics of the universe as was understood at the time and In detail it didn't work in detail for instance They couldn't get the mass of the electron to work out correctly in this theory so many people worked on it but by the 40s certainly by the 50s this strange But very compelling idea of how to unify the laws of physics had gone away Until something wonderful happened in our age in our era a new approach to unify the laws of physics is being pursued by physicists such as myself, many others around the world.

It's called super string theory, as you were indicating.

And the wonderful thing is that super string theory has nothing to do at first sight with this idea of extra dimensions, but when we study super string theory, we find that it resurrects the idea in a sparkling new form.

Well, it's a theory that tries to answer the question, what are the basic, fundamental, indivisible, uncuttable constituents making up everything in the world around us?

So imagine we look at a familiar object, just a candle and a holder, and imagine that we want to figure out what it is made of.

So we go on a journey deep inside the object and examine the constituents.

So deep inside, we all know you go sufficiently far down, you have atoms.

We also all know that atoms are not the end of the story.

They have little electrons that swarm around a central nucleus with neutrons and protons.

Even the neutrons and protons have smaller particles inside of them known as quarks.

Deep inside any of these particles, there is something else.

The something else is this dancing filament of energy.

That's where the idea of string theory comes from.

And just like The vibrating strings that you just saw on a cello can vibrate in different patterns.

These can also vibrate in different patterns.

They don't produce different musical notes.

Rather they produce the different particles making up the world around us.

This is what the ultramicroscopic landscape of the universe looks like.

It's built up of a huge number of these little tiny filaments of vibrating energy, vibrating in different frequencies.

The different frequencies produce the different particles.

The different particles are responsible for all the richness in the world around us.

And there you see unification, because matter particles, electrons and quarks, radiation particles, photons, gravitons, are all built up from 1 entity.

So matter and the forces of nature all are put together under the rubric of vibrating strings and that's what we mean by a unified theory.

When you study the mathematics of string theory you find that it doesn't work in a universe that just has 3 dimensions of space.

It doesn't work in a universe with 4 dimensions of space, nor 5, nor 6.

Finally, you can study the equations and show that it works only in a universe that has 10 dimensions of space and 1 dimension of time.

It leads us right back to this idea of Kaluza and Klein that our world, when appropriately described, has more dimensions than the ones that we see.

Now you might think about that and say, well, okay, you know, if you have extra dimensions and they're really tightly curled up, yeah, perhaps, perhaps we won't see them if they're small enough, but, you know, if there's a little tiny civilization of green people walking around down there, you make them small enough and we won't see them either.

That is true, 1 of the other predictions of string theory.

No, that's not 1 of the other predictions of string theory.

But it raises the question, are we just trying to hide away these extra dimensions Or do they tell us something about the world?

And the remaining time I'd like to tell you 2 features of them.

First is, many of us believe that these extra dimensions hold the answer to what perhaps is the deepest question in theoretical physics, theoretical science.

When we look around the world, as Scientists have done for the last hundred years there appear to be about 20 numbers that really describe our universe These are numbers like the mass of the particles like electrons and quarks the strength of gravity the strength of the electromagnetic force a list of about 20 numbers that have been measured with incredible precision, but nobody has an explanation for why the numbers have the particular values that they do.

Not yet, but we believe the answer for why those numbers have the values they do may rely on the form of the extra dimensions.

And the wonderful thing is if those numbers had any other values than the known ones, The universe as we know it wouldn't exist.

Why are those numbers so finely tuned to allow stars to shine and planets to form when we recognize that if you fiddle with those numbers, if I had 20 dials up here and I let you come up and fiddle with those numbers, almost any fiddling makes the universe disappear.

And string theory suggests that those 20 numbers have to do with the extra dimensions.

So when we talk about the extra dimensions in string theory, it's not 1 extra dimension as in the older ideas of Kaluza and Klein.

This is what string theory says about the extra dimensions.

They have a very rich intertwined geometry.

This is an example of something known as a clubby out shape name isn't all that important but as you can see the extra dimensions fold in on themselves and intertwine in a very interesting shape interesting structure and the idea is that if this is what the extra dimensions look like then the microscopic landscape of our universe all around us would look like this on the tiniest of scales when you swing your hand you'd be moving around these extra dimensions over and over again but they're so small that we wouldn't know it.

So what is the physical implication though relevant to those 20 numbers?

If you look at the instrument, a French horn, notice that the vibrations of the air streams are affected by the shape of the instrument.

Now in string theory, all the numbers are reflections of the way strings can vibrate.

So just as those air streams are affected by the twists and turns in the instrument, strings themselves will be affected by the vibrational patterns and the geometry within which they are moving.

So let me bring some strings into the story and if you watch these little fellas vibrating around They'll be here in a second right there notice that the way they vibrate is affected by the geometry of the extra dimensions So if we knew exactly what the extra dimensions look like we don't yet But if we did we should be able to calculate the allowed notes the allowed Vibrational patterns and if we could calculate the allowed vibrational patterns,

we should be able to calculate the allowed notes, the allowed

vibrational patterns, and if we could calculate the allowed vibrational patterns, we should be able to calculate those 20 numbers.

And if the answer that we get from our calculations Agrees with the values of those numbers that have been determined through detailed and precise experimentation this in many ways would be the first fundamental explanation for why the Structure of the universe is the way it is Now the second issue that I want to finish up with is, how might we test for these extra dimensions more directly?

Is this just an interesting mathematical structure that might be able to explain some previously unexplained features of the world, or can we actually test for these extra dimensions?

And we think, this is I think very exciting, that in the next 5 years or so, we may be able to test for the existence of these extra dimensions.

In CERN, Geneva, Switzerland, a machine is being built called the Large Hadron Collider.

It's a machine that will send particles around a tunnel opposite directions, near the speed of light.

Every so often those particles will be aimed at each other so there's a head-on collision.

The hope is that if the collision has enough energy, it may eject some of the debris from the collision from our dimensions, forcing it to enter into the other dimensions.

Well, we'll measure the amount of energy after the collision, compare it to the amount of energy before, and if there's less energy after the collision than before, this will be evidence that the energy has drifted away and if it drifts away in the right pattern that we can calculate This will be evidence that the extra dimensions are there.

Let me show you that idea visually So imagine we have a certain kind of particles called a graviton.

That's the kind of debris We expect to be ejected out if the extra dimensions are real, but here's how the experiment will go You take these particles you slam them together you slam them together And if we are right some of the energy of that collision will go into debris that flies off into these extra dimensions So this is the kind of experiment that we'll be looking at in the next 5, 7 to 10 years or so.

And if this experiment bears fruit, if we see that kind of particle ejected by noticing that there's less energy in our dimensions than when we began, this will show that the extra dimensions are real.

And to me, this is a really remarkable story and a remarkable opportunity.

Going back to Newton with absolute space, didn't provide anything but an arena, a stage in which the events of the universe take place.

Einstein comes along and says, well, space and time can warp and curve.

And now, string theory comes along and says, yes, gravity, quantum mechanics, electromagnetism, all together in 1 package, but only if the universe has more dimensions than the ones that we see.

And this is an experiment that may test for them in our lifetime.


Speaker 0: Translators note

Speaker 1: In the year

Speaker 0: 1919

Speaker 1: a virtually unknown German mathematician named Theodor Kaluza suggested a very bold and in some ways very bizarre idea. He proposed that our universe might actually have more than the 3 dimensions that we are all aware of. That is, in addition to left, right, back, forth, and up, down, Klutza proposed that there might be additional dimensions of space that for some reason we don't yet see. Now, when someone makes a bold and bizarre idea, sometimes that's all it is. Bold, bizarre, but it has nothing to do with the world around us.

This particular idea, however, although we don't yet know whether it's right or wrong, and at the end I'll discuss experiments which in the next few years may tell us whether it's right or wrong, this idea has had a major impact on physics in the last century and continues to inform a lot of cutting-edge research, so I'd like to tell you something about the story of these extra dimensions. So where do we go? To begin, we need a little bit of backstory. Go to 1907. This is a year when Einstein is basking in the glow of having discovered the special theory of relativity and decides to take on a new project to try to understand fully the grand pervasive force of gravity.

And in that moment, there were many people around who thought that that project had already been resolved. Newton had given the world a theory of gravity in the late 1600s that works well, describes the motion of planets, the motion of the moon and so forth, the motion of apocryphal apples falling from trees, hitting people in the head, all of that could be described using Newton's work. But Einstein realized that Newton had left something out of the story because even Newton had written that although he understood how to calculate the effect of gravity, he had been unable to figure out how it really works How is it that the Sun 93 million miles away somehow it affects the motion of the earth? How does the Sun reach out across empty inert space and exert? Influence And that is a task to which Einstein set himself to figure out how gravity works.

And let me show you what it is that he found. So Einstein found that the medium that transmits gravity is space itself. The idea goes like this. Imagine space as a substrate of all there is. Einstein said space is nice and flat if there's no matter present But if there is matter in the environment such as the Sun it causes the fabric of space to warp to curve And that communicates the force of gravity even the earth warps space around it now Look at the moon The moon is kept in orbit according to these ideas because it rolls along a valley in the curved environment that the Sun and the Moon and the Earth can all create by virtue of their presence.

If we go to a full frame view of this, the Earth itself is kept in orbit because it rolls along a valley in the environment that's curved because of the Sun's presence. That is this new idea about how gravity actually works. Now this idea was tested in 1919 through astronomical observations. It really works. It describes the data.

And this gained Einstein prominence around the world. And that is what got Kaluza thinking he like Einstein was in search of what we call a unified theory That's 1 theory that might be able to describe all of nature's forces from 1 set of ideas 1 set of principles 1 Master equation if you will so kaluza said to himself Einstein has been able to describe gravity in terms of warps and curves in space, in fact, space and time, to be more precise. Maybe I can play the same game with the other known force, which was at that time known as the electromagnetic force. We know of others today, but at that time that was the only other 1 people were thinking about. You know, the force responsible for electricity and magnetic attraction and so forth.

So Kaluza says, maybe I can play the same game and describe electromagnetic force in terms of warps and curves. That raised a question. Warps and curves in what? Einstein had already used up space and time. Warps and curves to describe gravity didn't seem to be anything else to warp or curve So klutz has said well Maybe there are more dimensions of space.

He said if I want to describe 1 more force, maybe I need 1 more dimension So he imagined that the world had 4 dimensions of space, not 3. And imagined that electromagnetism was warps and curves in that fourth dimension. Now here's the thing. When he wrote down the equations describing warps and curves in a universe with 4 space dimensions, not 3, He found the old equations that Einstein had already derived in 3 dimensions Those were for gravity, but he found 1 more equation because of the 1 more dimension And when he looked at that equation, it was none other than the equation that scientists had long known to describe the electromagnetic force Amazing it just popped out He was so excited by this realization that he ran around his house screaming victory that he had found the unified theory. Now clearly, Kalutz was a man who took theory very seriously.

In fact, there's a story that when he wanted to learn how to swim, he read a book, a treatise on swimming, then dove into the ocean. This is a man who would risk his life on theory. Now but for those of us who are a little bit more practically minded, 2 questions immediately arise from his observation. Number 1, if there are more dimensions in space, where are they?

Speaker 0: We don't seem to see them.

Speaker 1: And number 2, does this theory really work in detail when you try to apply it to the world around us? Now, the first question was answered in 1926 by a fellow named Oscar Klein. He suggested that dimensions might come in 2 varieties. There might be big, easy to see dimensions, but there might also be tiny, curled up dimensions, curled up so small, even though they're all around us, that we don't see them. Let me show you that 1 visually.

So, imagine you're looking at something like a cable supporting a traffic light. This is in Manhattan, New Central Park. It's kind of irrelevant. But the cable looks one-dimensional from a distant viewpoint. But you and I all know that it does have some thickness.

It's very hard to see it, though, from far away. But if we zoom in and take the perspective of say a little ant walking around, little ants are so small that they can access all of the dimensions. The long dimension but also this clockwise, counterclockwise direction. And I hope you appreciate this, It took so long to get these ants to do this. But this illustrates the fact that dimensions can be of 2 sorts, big and small, and the idea is that maybe the big dimensions around us are the ones that we can easily see, but there might be additional dimensions Curled up sort of like the circular part of that cable so small that they have so far remained invisible Let me show you what that would look like.

So if we take a look say at space itself I Can only show of course 2 dimensions on a screen some of you guys will fix that 1 day, but anything that's not flat on the screen as a new dimension goes smaller, smaller, smaller, and way down in the microscopic depths of space itself, this is the idea. You could have additional curled up dimensions, here is a little shape of a circle, so small that we don't see them. But if you were a little ultra-microscopic ant walking around, you could walk in the big dimensions that we all know about. That's like the grid part. But you could also access the tiny curled up dimension that's so small that we can't see it with the naked eye or even with any of our most refined equipment, but deeply tucked into the fabric of space itself, the idea is there could be more dimensions, as we see there.

Now, that's an explanation about how the universe could have more dimensions than the ones that we see, but what about the second question that I asked? Does the theory actually work when you try to apply it to the real world? Well, it turns out that Einstein and Clutza and many others worked on trying to refine this framework and apply it to the physics of the universe as was understood at the time and In detail it didn't work in detail for instance They couldn't get the mass of the electron to work out correctly in this theory so many people worked on it but by the 40s certainly by the 50s this strange But very compelling idea of how to unify the laws of physics had gone away Until something wonderful happened in our age in our era a new approach to unify the laws of physics is being pursued by physicists such as myself, many others around the world. It's called super string theory, as you were indicating. And the wonderful thing is that super string theory has nothing to do at first sight with this idea of extra dimensions, but when we study super string theory, we find that it resurrects the idea in a sparkling new form.

So let me just tell you how that goes. Super string theory, what is it? Well, it's a theory that tries to answer the question, what are the basic, fundamental, indivisible, uncuttable constituents making up everything in the world around us? The idea is like this. So imagine we look at a familiar object, just a candle and a holder, and imagine that we want to figure out what it is made of.

So we go on a journey deep inside the object and examine the constituents. So deep inside, we all know you go sufficiently far down, you have atoms. We also all know that atoms are not the end of the story. They have little electrons that swarm around a central nucleus with neutrons and protons. Even the neutrons and protons have smaller particles inside of them known as quarks.

That is where conventional ideas stop. Here is the new idea of string theory. Deep inside any of these particles, there is something else. The something else is this dancing filament of energy. It looks like a vibrating string.

That's where the idea of string theory comes from. And just like The vibrating strings that you just saw on a cello can vibrate in different patterns. These can also vibrate in different patterns. They don't produce different musical notes. Rather they produce the different particles making up the world around us.

So these ideas are correct. This is what the ultramicroscopic landscape of the universe looks like. It's built up of a huge number of these little tiny filaments of vibrating energy, vibrating in different frequencies. The different frequencies produce the different particles. The different particles are responsible for all the richness in the world around us.

And there you see unification, because matter particles, electrons and quarks, radiation particles, photons, gravitons, are all built up from 1 entity. So matter and the forces of nature all are put together under the rubric of vibrating strings and that's what we mean by a unified theory. And here is the catch. When you study the mathematics of string theory you find that it doesn't work in a universe that just has 3 dimensions of space. It doesn't work in a universe with 4 dimensions of space, nor 5, nor 6.

Finally, you can study the equations and show that it works only in a universe that has 10 dimensions of space and 1 dimension of time. It leads us right back to this idea of Kaluza and Klein that our world, when appropriately described, has more dimensions than the ones that we see. Now you might think about that and say, well, okay, you know, if you have extra dimensions and they're really tightly curled up, yeah, perhaps, perhaps we won't see them if they're small enough, but, you know, if there's a little tiny civilization of green people walking around down there, you make them small enough and we won't see them either. That is true, 1 of the other predictions of string theory. No, that's not 1 of the other predictions of string theory.

But it raises the question, are we just trying to hide away these extra dimensions Or do they tell us something about the world? And the remaining time I'd like to tell you 2 features of them. First is, many of us believe that these extra dimensions hold the answer to what perhaps is the deepest question in theoretical physics, theoretical science. And that question is this. When we look around the world, as Scientists have done for the last hundred years there appear to be about 20 numbers that really describe our universe These are numbers like the mass of the particles like electrons and quarks the strength of gravity the strength of the electromagnetic force a list of about 20 numbers that have been measured with incredible precision, but nobody has an explanation for why the numbers have the particular values that they do.

Now, does string theory often answer? Not yet, but we believe the answer for why those numbers have the values they do may rely on the form of the extra dimensions. And the wonderful thing is if those numbers had any other values than the known ones, The universe as we know it wouldn't exist. This is a deep question. Why are those numbers so finely tuned to allow stars to shine and planets to form when we recognize that if you fiddle with those numbers, if I had 20 dials up here and I let you come up and fiddle with those numbers, almost any fiddling makes the universe disappear.

So can we explain those 20 numbers? And string theory suggests that those 20 numbers have to do with the extra dimensions. Let me show you how. So when we talk about the extra dimensions in string theory, it's not 1 extra dimension as in the older ideas of Kaluza and Klein. This is what string theory says about the extra dimensions.

They have a very rich intertwined geometry. This is an example of something known as a clubby out shape name isn't all that important but as you can see the extra dimensions fold in on themselves and intertwine in a very interesting shape interesting structure and the idea is that if this is what the extra dimensions look like then the microscopic landscape of our universe all around us would look like this on the tiniest of scales when you swing your hand you'd be moving around these extra dimensions over and over again but they're so small that we wouldn't know it. So what is the physical implication though relevant to those 20 numbers? Consider this. If you look at the instrument, a French horn, notice that the vibrations of the air streams are affected by the shape of the instrument.

Now in string theory, all the numbers are reflections of the way strings can vibrate. So just as those air streams are affected by the twists and turns in the instrument, strings themselves will be affected by the vibrational patterns and the geometry within which they are moving. So let me bring some strings into the story and if you watch these little fellas vibrating around They'll be here in a second right there notice that the way they vibrate is affected by the geometry of the extra dimensions So if we knew exactly what the extra dimensions look like we don't yet But if we did we should be able to calculate the allowed notes the allowed Vibrational patterns and if we could calculate the allowed vibrational patterns,

Speaker 0: we should be able to calculate the allowed notes, the allowed

Speaker 1: vibrational patterns, and if we could calculate the allowed vibrational patterns, we should be able to calculate those 20 numbers. And if the answer that we get from our calculations Agrees with the values of those numbers that have been determined through detailed and precise experimentation this in many ways would be the first fundamental explanation for why the Structure of the universe is the way it is Now the second issue that I want to finish up with is, how might we test for these extra dimensions more directly? Is this just an interesting mathematical structure that might be able to explain some previously unexplained features of the world, or can we actually test for these extra dimensions? And we think, this is I think very exciting, that in the next 5 years or so, we may be able to test for the existence of these extra dimensions. Here's how it goes.

In CERN, Geneva, Switzerland, a machine is being built called the Large Hadron Collider. It's a machine that will send particles around a tunnel opposite directions, near the speed of light. Every so often those particles will be aimed at each other so there's a head-on collision. The hope is that if the collision has enough energy, it may eject some of the debris from the collision from our dimensions, forcing it to enter into the other dimensions. How would we know it?

Well, we'll measure the amount of energy after the collision, compare it to the amount of energy before, and if there's less energy after the collision than before, this will be evidence that the energy has drifted away and if it drifts away in the right pattern that we can calculate This will be evidence that the extra dimensions are there. Let me show you that idea visually So imagine we have a certain kind of particles called a graviton. That's the kind of debris We expect to be ejected out if the extra dimensions are real, but here's how the experiment will go You take these particles you slam them together you slam them together And if we are right some of the energy of that collision will go into debris that flies off into these extra dimensions So this is the kind of experiment that we'll be looking at in the next 5, 7 to 10 years or so. And if this experiment bears fruit, if we see that kind of particle ejected by noticing that there's less energy in our dimensions than when we began, this will show that the extra dimensions are real. And to me, this is a really remarkable story and a remarkable opportunity.

Going back to Newton with absolute space, didn't provide anything but an arena, a stage in which the events of the universe take place. Einstein comes along and says, well, space and time can warp and curve. That's what gravity is. And now, string theory comes along and says, yes, gravity, quantum mechanics, electromagnetism, all together in 1 package, but only if the universe has more dimensions than the ones that we see. And this is an experiment that may test for them in our lifetime.

Amazing possibility. Thank you very much. Thank you. Thank you.

Speaker 0: Thank you. Thank you. Thank you. Thank you. Thank you.

Thank you. Thank you. Thank you. Thank you. That was absolutely fantastic.

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String theory - Brian Greene