String Theorist Ed Witten first discovered m-Theory in 1995. He was able to mathematically demonstrate that the five string theories, thought to be totally different, were actually the same. They were all different ways of looking at the same thing. All that needed to be adjusted were string coupling constants (this is not important to our discussion so I will not explain it here.) Ed Witten, in showing that the five theories were actually different ways of looking at the same thing, showed that, when another component called 11-D Supergravity (11-D signifying 11 dimensions) was added, the natural result was a unified theory of everything called M-Theory. A natural question is: what does M-Theory mean? The answer you will hear most often is no one knows. Reading Michio Kakus recent book Parallel Worlds, he seems to be sure it means Membrane, but other String Theorists are not so sure. Answers will vary mother, matrix, master, some even say its an upside-down W, for Witten. Most think that when M-Theory is finally verified, the M will be given a meaning.
What would a Theory of Everything do for us?
Right now, in physics, there is a great gap, currently unbridgeable, though the foundations are being laid for one. That is the gap between General Relativity and Quantum mechanics. General Relativity gives physicists a picture of the universe on its largest of scales, and how spacetime warps when there are massive bodies present in the universe. You can think of spacetime as a trampoline or a rubber sheet when discussing General Relativity. When you place a bowling ball, or other massive object on the sheet/trampoline, the sheet/trampoline bends, causing a curvature in the fabric of the sheet (spacetime). Spacetime according to General Relativity is smooth. Quantum mechanics however, gives us a radically different picture that not even Einstein would fully accept (ironically, he helped discover it.) Quantum mechanics discusses the universe on its smallest of scales, on distances where the universe obeys a totally foreign set of rules. Particles dont have to be in one spot, they can be in two, or three, or infinitely many. Despite the fact that Quantum mechanics isnt very understandable, even to those who study it for a living, it has been verified by countless experiments. So, why is there a gap? Well, in most parts of the universe, the two theories never run into one another. General Relativity leaves Quantum mechanics well enough alone, and vice versa. However, there are times, like at the Big Bang, as well as at the centers of Black Holes, where the input of both theories are necessary, but usually they give answers like infinity, which are a way of saying something is wrong.
What is needed is a quantum theory of gravity. The reason for a quantum theory of gravity is that gravity is the only force that cannot be described via quantum interaction, which means by particles or quanta. You see light because it is carried by photons, which are quanta of the Electromagnetic Force. The predicted quantum particle of gravity is called the graviton. Once we have this theory, we can get sensible answers of what went on during, or even before the Big Bang, as well as what goes on at the center of a black hole. Fortunately, M-Theory looks like a likely candidate as that theory of everything. Already it is giving us a new picture of space, time, and the nature of the universe. It has even provided us with an answer to an age-old question of where the universe came from. Though M-Theory is not currently testable, equipment is being produced that will be up and running within this decade that might be able to test some of the predictions made by M-Theory. As soon as 2020, physicists might even be able to detect the parallel universes posited by the theory.
False Vacuums and Ground States
To understand M-Theorys idea in regards to the origin of the universe, we must understand a false vacuum and ground states. A false vacuum has some characteristics of a real vacuum, which is a ground state. A ground state is what every object will return to, given the chance. Imagine Homer Simpson with a really tight belt on. His stomach is in the state of a false vacuum, because if that belt were not there, his stomach would go to its ground state, which would be a real vacuum. Physicists think the same thing happened with our universe. Because of the extreme temperatures and densities predicted by todays theories, the universe would be in a state of false vacuum. This false vacuum is what fueled the rapid expansion of space known today as Inflation. In Inflation the universe expanded rapidly, many times faster than the speed of light (this doesnt violate Einsteins theory because no information is transferred.) Inflation answered many problems that cosmologists ran into with the Big Bang Theory but it didnt tell us where the universe came from.
Spacetime Foam, Virtual Particles, Wormholes and Bubble Universes
Another vital part to understanding M-Theorys idea regarding the origin of the universe is that of spacetime foam. We learned before that General Relativity predicts the universe is smooth. However, there is a scale known as the Planck Length at which spacetime is no longer smooth. Instead, it is foamy. I always bring to mind an image of boiling water. In this spacetime foam, particles can come in and out of existence due to the uncertainty in the energy in this chaotic state. These particles are called virtual particles. Virtual particles always come in pairs, a particle and an anti-particle. During a tiny fraction of a second they are created, and then annihilate one another in a burst of energy. The presence of virtual particles has been verified by experiment, most notably the Casimir Effect. The Casimir Effect involves placing two metal plates very close to one another. Basically, because the virtual particles around them outnumber the ones in between, the plates get closer together by a very small amount, which increases the closer the plates get together. What is perhaps a more important result, at least when discussing M-Theory, is the idea of a wormhole.
When most people think of wormholes, they think of an object in space connecting two places in the same universe. However, a natural extension of this is a wormhole connecting one universe with another. The type of wormhole that would allow this, and could possibly be used, is known as a Lorentzian wormhole. Several things are conjectured about Lorentzian wormholes, but most importantly they require a strange substance called exotic matter. Unfortunately, due to M-Theorys current lack of predictive power in this area, no one is sure whether or not exotic matter exists or not. Due to the chaotic nature of the spacetime foam, it is possible that space itself rips, forming a wormhole, which would then close itself. Blowing bubbles with that liquid soap, like most people did when they were a kid, would be a good way to visualize it. You blew on the soap, and a bubble totally separate from the liquid formed. The chaos caused on the soap when you blew on it is similar to the spacetime foam, and the resulting action of soap to bubble would be the wormhole. What is the bubble? Another universe. In fact, the Bubble Universe Theory is a natural extension of the Inflationary theory we discussed earlier. After the wormhole collapsed that created the bubble universe, the universe would be in a state of a false vacuum, due to its size (which would be practically none, because the wormhole that made it was quantum in the first place.) This would lead to the tendency towards the ground state of a real vacuum, resulting in the expansion of the universe. This universe would, more than likely, be radically different than ours. However, the notion that universes can and are forever spawning out of the multiverse is a key idea to the origin of our universe. Our universe could very well have been a 13.7 billion year old bubble in the spacetime foam of the multiverse.
What is the nature of the Multiverse?
The multiverse is thought to be composed of eleven spacetime dimensions. This means the universe you and I live in has more than the normal three space dimensions we experience. How can this be possible? The answer lies in the size of the spatial dimensions. The three space dimensions we know and love are huge, comprising the entire visible universe. The seven other foreigners however, are not so big, in fact, they are so small not even atoms can fit in them. However, objects called strings (which are really supposed to be particles, if you had an even more precise method to look at them) can vibrate in them. Take a ring that normally fits around your index finger and try to shove your fist inside of it. Wont work? Thats like human beings as a whole trying to squeeze into the microscopic dimensions. However, your index finger can fit inside of it, much like the vibrations of strings can fit in the dimensions. The dimensions themselves are shaped like a circle, meaning anything within them simply goes around in circles. This means that when you and I walk around, we are essentially going through these microscopic dimensions trillions of times, but we never notice it because of their small size, and because they lead us right back where we came from. There is an overall shape to the extra spatial dimensions. Scientists and mathematicians call it a Calabi-Yau shape. I dont understand the mathematics behind it, so I cant really tell you how that exact shape was chosen.
(cont'd)
What would a Theory of Everything do for us?
Right now, in physics, there is a great gap, currently unbridgeable, though the foundations are being laid for one. That is the gap between General Relativity and Quantum mechanics. General Relativity gives physicists a picture of the universe on its largest of scales, and how spacetime warps when there are massive bodies present in the universe. You can think of spacetime as a trampoline or a rubber sheet when discussing General Relativity. When you place a bowling ball, or other massive object on the sheet/trampoline, the sheet/trampoline bends, causing a curvature in the fabric of the sheet (spacetime). Spacetime according to General Relativity is smooth. Quantum mechanics however, gives us a radically different picture that not even Einstein would fully accept (ironically, he helped discover it.) Quantum mechanics discusses the universe on its smallest of scales, on distances where the universe obeys a totally foreign set of rules. Particles dont have to be in one spot, they can be in two, or three, or infinitely many. Despite the fact that Quantum mechanics isnt very understandable, even to those who study it for a living, it has been verified by countless experiments. So, why is there a gap? Well, in most parts of the universe, the two theories never run into one another. General Relativity leaves Quantum mechanics well enough alone, and vice versa. However, there are times, like at the Big Bang, as well as at the centers of Black Holes, where the input of both theories are necessary, but usually they give answers like infinity, which are a way of saying something is wrong.
What is needed is a quantum theory of gravity. The reason for a quantum theory of gravity is that gravity is the only force that cannot be described via quantum interaction, which means by particles or quanta. You see light because it is carried by photons, which are quanta of the Electromagnetic Force. The predicted quantum particle of gravity is called the graviton. Once we have this theory, we can get sensible answers of what went on during, or even before the Big Bang, as well as what goes on at the center of a black hole. Fortunately, M-Theory looks like a likely candidate as that theory of everything. Already it is giving us a new picture of space, time, and the nature of the universe. It has even provided us with an answer to an age-old question of where the universe came from. Though M-Theory is not currently testable, equipment is being produced that will be up and running within this decade that might be able to test some of the predictions made by M-Theory. As soon as 2020, physicists might even be able to detect the parallel universes posited by the theory.
False Vacuums and Ground States
To understand M-Theorys idea in regards to the origin of the universe, we must understand a false vacuum and ground states. A false vacuum has some characteristics of a real vacuum, which is a ground state. A ground state is what every object will return to, given the chance. Imagine Homer Simpson with a really tight belt on. His stomach is in the state of a false vacuum, because if that belt were not there, his stomach would go to its ground state, which would be a real vacuum. Physicists think the same thing happened with our universe. Because of the extreme temperatures and densities predicted by todays theories, the universe would be in a state of false vacuum. This false vacuum is what fueled the rapid expansion of space known today as Inflation. In Inflation the universe expanded rapidly, many times faster than the speed of light (this doesnt violate Einsteins theory because no information is transferred.) Inflation answered many problems that cosmologists ran into with the Big Bang Theory but it didnt tell us where the universe came from.
Spacetime Foam, Virtual Particles, Wormholes and Bubble Universes
Another vital part to understanding M-Theorys idea regarding the origin of the universe is that of spacetime foam. We learned before that General Relativity predicts the universe is smooth. However, there is a scale known as the Planck Length at which spacetime is no longer smooth. Instead, it is foamy. I always bring to mind an image of boiling water. In this spacetime foam, particles can come in and out of existence due to the uncertainty in the energy in this chaotic state. These particles are called virtual particles. Virtual particles always come in pairs, a particle and an anti-particle. During a tiny fraction of a second they are created, and then annihilate one another in a burst of energy. The presence of virtual particles has been verified by experiment, most notably the Casimir Effect. The Casimir Effect involves placing two metal plates very close to one another. Basically, because the virtual particles around them outnumber the ones in between, the plates get closer together by a very small amount, which increases the closer the plates get together. What is perhaps a more important result, at least when discussing M-Theory, is the idea of a wormhole.
When most people think of wormholes, they think of an object in space connecting two places in the same universe. However, a natural extension of this is a wormhole connecting one universe with another. The type of wormhole that would allow this, and could possibly be used, is known as a Lorentzian wormhole. Several things are conjectured about Lorentzian wormholes, but most importantly they require a strange substance called exotic matter. Unfortunately, due to M-Theorys current lack of predictive power in this area, no one is sure whether or not exotic matter exists or not. Due to the chaotic nature of the spacetime foam, it is possible that space itself rips, forming a wormhole, which would then close itself. Blowing bubbles with that liquid soap, like most people did when they were a kid, would be a good way to visualize it. You blew on the soap, and a bubble totally separate from the liquid formed. The chaos caused on the soap when you blew on it is similar to the spacetime foam, and the resulting action of soap to bubble would be the wormhole. What is the bubble? Another universe. In fact, the Bubble Universe Theory is a natural extension of the Inflationary theory we discussed earlier. After the wormhole collapsed that created the bubble universe, the universe would be in a state of a false vacuum, due to its size (which would be practically none, because the wormhole that made it was quantum in the first place.) This would lead to the tendency towards the ground state of a real vacuum, resulting in the expansion of the universe. This universe would, more than likely, be radically different than ours. However, the notion that universes can and are forever spawning out of the multiverse is a key idea to the origin of our universe. Our universe could very well have been a 13.7 billion year old bubble in the spacetime foam of the multiverse.
What is the nature of the Multiverse?
The multiverse is thought to be composed of eleven spacetime dimensions. This means the universe you and I live in has more than the normal three space dimensions we experience. How can this be possible? The answer lies in the size of the spatial dimensions. The three space dimensions we know and love are huge, comprising the entire visible universe. The seven other foreigners however, are not so big, in fact, they are so small not even atoms can fit in them. However, objects called strings (which are really supposed to be particles, if you had an even more precise method to look at them) can vibrate in them. Take a ring that normally fits around your index finger and try to shove your fist inside of it. Wont work? Thats like human beings as a whole trying to squeeze into the microscopic dimensions. However, your index finger can fit inside of it, much like the vibrations of strings can fit in the dimensions. The dimensions themselves are shaped like a circle, meaning anything within them simply goes around in circles. This means that when you and I walk around, we are essentially going through these microscopic dimensions trillions of times, but we never notice it because of their small size, and because they lead us right back where we came from. There is an overall shape to the extra spatial dimensions. Scientists and mathematicians call it a Calabi-Yau shape. I dont understand the mathematics behind it, so I cant really tell you how that exact shape was chosen.
(cont'd)
