archived as http://www.stealthskater.com/Documents/Strings_07.doc [pdf]
more related articles at http://www.stealthskater.com/Science.htm#Strings
note: because important websites are frequently "here today but gone tomorrow", the following was archived from http://www.pbs.org/wgbh/nova/elegant/viewpoints.html on Jan 27, 2006. This is NOT an attempt to divert readers from the aforementioned website. Indeed, the reader should only read this back-up copy if the updated original cannot be found at the original author's site.
The Elegant Universe
Viewpoints on String Theory
PBS/NOVA October, 2003
[StealthSkater note: the following is an addendum companion article to the 3-part PBS/NOVA series on "The Elegant Universe" and superstring theory which is archived at doc pdf URL-doc URL-pdf ]
String theory has its supporters and its gainsayers among theoretical physicists. Even advocates admit that the theory could be entirely wrong (though naturally they don't think it is). In the following interviews, read what 7 physicists -- some string theorists and some not -- have to say about the theory and some of its more mind-bending components such as extra dimensions and supersymmetry.
1. Sylvester James Gates, University of Maryland
"Gravity is the odd man out for deep philosophical reasons."
2. Sheldon Glashow, Boston University
"The string theorists have a theory that appears to be consistent and very beautiful … and I don't understand it."
3. David Gross, University of California, Santa Barbara
"This revolution will likely change the way we think about space and time -- maybe even eliminate them completely as a basis for our description of reality."
4. Joe Lykken, Fermi National Accelerator Laboratory
"You really are looking for those few golden, rare events where something miraculous happens."
5. Amanda Peet, University of Toronto
"You can never prove that a theory of Nature is correct. All you can prove is that it is the best theory that you have."
6. Steven Weinberg, University of Texas at Austin
"If string unifies gravity with the other forces, then I think we will be within our rights to ring a bell and say, 'This is it!'"
7. Edward Witten, (Princeton) Institute for Advanced Study
"I would conclude that extra dimensions really exist. They are part of Nature."
Sylvester James Gates, Jr. has a number of "firsts" to his name. His doctoral dissertation at M.I.T. was the first ever at that university on supersymmetry. In 1994, he became the first recipient of the American Physical Society's Edward A. Bouchet Award, given to a minority physicist who has made significant contributions to his field. And when in 1998 he was named the first John S. Toll Professor of Physics at the University of Maryland, he became the first African-American to hold an endowed chair in physics at a major U.S. research university. Here, Gates talks about firsts that he hopes to see in string theory, including the first signs of supersymmetry and perhaps of that most elusive beast -- a unification of the 4 forces of Nature.
[NOVA]: Where does your fascination with physics comes from?
[Gates]: When I was 8 years old, my father bought a set of Encyclopedia Britannica. I was bored one day so I started opening the books. I came across Schroedinger's equation, which is one of the foundations of modern physics. It was like walking on a beach and finding a marvelous shell and being fascinated by it. I thought to myself, "Gee, one day I wonder if I could ever understand that."
Earlier, I had found out that stars were not just things you could look at but places you could go. I had the sense that science and technology were the ways that you got there, so there was this resonance with science and technology and mathematics. When I was in high school, my physics teacher wrote an equation on the blackboard and then performed a very simple experiment -- rolling a ball down an inclined plane. He showed that what I saw there in front of my eyes was described by the mathematical equation that he had written on the blackboard.
[NOVA]:: Were you surprised by that?
[Gates]: I was utterly shocked. It's not obvious from our everyday experience that mathematics has anything to do with Nature. For me, this was astounding because mathematics is something we do in our heads. It's like a game of "Dungeons and Dragons". It's a fantasy. But because mathematics must also adhere to logical precepts, it restricts our imagination. Why it is that mathematics is the only language that our species has found to describe Nature is a mystery that will probably never be solved. But it is the way that we have found our deepest understanding of Nature. For the theoretical physicist, mathematics is like an extra-sensory-perception organ that we use to see the Universe.
[NOVA]: What exactly are "strings"?
[Gates]: Strings create everything including space and time and even us. The way that this is done is unfortunately extremely mathematical and detailed. But I can use an analogy. If I took a little piece of spaghetti and plucked it, it would vibrate back-and-forth. As it vibrates, it makes a note. The note that you get depends on how you pluck it. Roughly speaking, the idea of strings is that when you pluck it a certain way, you might be looking at an electron. When you pluck it a different way, you might see a particle of light. If you pluck it a third way, you might be looking at a quark. All the particles are in fact different vibratory modes of this single object.
[NOVA]: Why are physicists so excited about strings? How do they advance our understanding of the Universe?
[Gates]: For about 2,000 years, essentially all of our physics has been based on billiard balls. The technical name is "geometrical point particle". But the idea at the end of the day was that if you can figure out how billiard balls work, then you can actually figure out everything. It got us to the Moon; it got us computers; it got us all sorts of marvelous technologies that we now take for granted.
But these billiard balls also ran us into a conflict between General Relativity and Quantum Mechanics. String theory seems to get us out of this. I think Einstein would be extremely happy with the way things developed because he called for a unified field theory long before anyone else imagined that such a thing was possible. And string theory very definitely is a unified field theory.
[NOVA]: Backtrack for us a bit. What do you mean by a "unified field theory"?
[Gates]: We have observed 4 forces in action in Nature. There's the force of gravity. There's the electromagnetic force -- we use that in computers, we use that in our modern information technology. There is the strong nuclear force -- the force from which the Sun derives its energy. We found the weak nuclear force when substances that were naturally radioactive -- such as radium -- were found to glow in the dark.
Could there be more forces? The answer is yes. There could be more, but we have not seen them in laboratory experiments. And physics is always about what we see in the laboratory. A unified field theory has to explain all of this and include gravity.
In the 1930s some physicists tried to study Einstein's equations of gravitation and combine those with the new laws of Quantum Theory (the physics of very small objects). When you try to put those two pieces of mathematics together, they do not coexist peacefully. In fact, you get nonsense out of those calculations. And so until string theory came along, there was this schism in which we had some laws that we knew worked very well but only for small things. We had other laws that worked very well for large things in gravitation. But when you tried to combine the laws, they broke down. It was only with string theory that we found a way to successfully marry these 2 very different sets of mathematical equations.
[NOVA]: Why has gravity resisted being incorporated with the other forces?
[Gates]: Gravity is the odd man out for deep philosophical reasons. When Newton wrote down his mathematical description of gravity, there was an assumption lurking in the equations -- they didn't depend on time. His equations say that something in one location can have an affect at another location far removed at the instant that it occurs. So the instant something happens here, it's automatically and instantaneously known at the second location. This idea of action at distance -- which is an almost magical kind of idea -- sits conceptually under Newton's description of gravity. Newton was aware of this and in his famous Principia spoke about the philosophical unpleasantness of including such an idea.
As soon as Einstein wrote down his equations, we understood that action at a distance can not apply in our Universe. Einstein's equations say that when an event occurs in one location, it takes some amount of time before it is known in another location. The fastest that the communication between these 2 separated points can occur is at the speed-of-light. The notion that there's a time separation between cause and effect leads us to the notion that something actually carries the information back-and-forth.
For the electromagnetic forces and by extension all the other forces, those carriers are things like the photon. When you look at Einstein's equations, since they are so very radically different from Maxwell's equations, the object that carries the information about the disturbance is something drastically different. This carrier is called the graviton. Part of the reason the descriptions could not be coalesced is that the equations of gravity are just so radically different from the equations of all the other forces.
[StealthSkater note: Actually, some quantum events (called "quantum entanglement") can and do occur instantaneously. This was known even in Einstein's day (he used the phrase "spooky action at a distance"). This gets into the physics of the Zero-Point Energy field -- the substrate of space-time. Engineering of this may one day lead to teleportation.]
[NOVA]: What is the nature of those gravitons?
[Gates]: Einstein's equations describe how space and time are curved. The analogy is that the Universe is like a sheet of rubber. When you put a piece of mass some place, it dents the rubber and causes things to fall in. And that's analogous to how gravity works.
Now if you were to take that mass that you dropped on a sheet of rubber and jiggle it back-and-forth, what would happen to the sheet of rubber? Very quickly you would build up ripples on the sheet of rubber as you take the mass point and jiggle it back-and-forth. Those ripples are in fact the graviton. So it's the waves of gravitational energy in space-time that are responsible for communicating the gravitational force.
[NOVA]: It's become a cliché that Einstein was a genius . What was it about the way he approached problems that made him such a genius?
[Gates]: Einstein made the statement once that imagination is more important than knowledge. For a long time, I was very puzzled by this statement. How could it be that imagination -- which I associated with play fantasies and hobbits and such matters -- could possibly be that that was more important than knowledge? Now, having worked as a physicist for over 2 decades, I think he was saying that when you try to create new knowledge, the only tool we have as humans is our imagination. The creation of new rational paradigms is itself an irrational process.
The genius of Einstein was such that when he wrote down his marvelously complicated equations of General Relativity, he gave a picture for what the equations meant and why they had to be. Suppose you were in an elevator standing on the surface of the Earth and had a ball in your hand. You let go of the ball and it falls. You wouldn't think very much about that because that's how gravity always acts. But suppose that I take you in this elevator with no windows so you can't see out. I put a rocket motor under it and I put you out in space. Then I turn the rocket motor 'on' so that it causes the acceleration to occur within the elevator. You're moving faster and faster. You're standing on the floor of the elevator. And you have this same ball in your hand … and you let go.
What happens to the ball? It appears from your point-of-view to fall to the floor. So for this man in the elevator, he cannot tell whether he is standing on the surface of the Earth, a gravitating body, or whether he is out in free space with a rocket that's driving the elevator to greater-and-greater speeds. When you translate that story to mathematics, it turns out you get Einstein's equations.
And that's what we're missing for string theory. We're still looking for that man in the elevator. [For more on Einstein and his genius, see the NOVA website Einstein Revealed.]
[NOVA]: How was this theory received at the time? Did people accept it or was it too radical an idea?
[Gates]: A prediction of this bending and flexing of the space-time grid is that light from stars can be bent. At the end of the First World War, an expedition returned from South America and said that we've seen the bending of starlight precisely as the theory of General Relativity predicts. At that point, the second great crowning of Einstein occurred. He was already a world-famous scientist. This one broke out into popular media. Einstein was like a rock star in his day.