Whenever I read physics books, I always hear about the eagerly anticipated Grand Unified Field Theory.

Just how long do most scientists think it will take before we get one?

five years? ten years? fifty or a hundred years? what’s the big hold-up?

Whenever I read physics books, I always hear about the eagerly anticipated Grand Unified Field Theory.

Just how long do most scientists think it will take before we get one?

five years? ten years? fifty or a hundred years? what’s the big hold-up?

Thus far, superstring and more recently, M-theory, seem to go a long way towards being the One Theory Of Everything. Unfortunately, at the moment we can only solve approximations of the equations, and there isn’t yet any experimental evidence to support it fully. But it’s looking good. Many physicists are confident that we’re close to having a unified theory of everything.

Incidentally, for more information on superstring and M-theory, read *The Elegant Universe* by Brian Greene. It’s a great read and I highly recommend it.

Yes, I’ve read books about M-theory in the past,

but what I want to know is specifics:

When are supercomputers predicted to be able to compute superstring theory calculations without resorting to approximations?

What experiments are currently planned to test the ultimate veracity of M-theory? And when will these series of experiments be completed to a sufficient degree to make M-Theory a practically accepted part of modern physics, and not just an appealing hypothesis?

I probably should have restated my question…

I already know what the current candidates are,

what I actually want to know is when will we be reasonably certain that and which one of these hypothetical theories is THE correct theory?

Asm I understand it, Grand Unified Theory is NOT a theory of everything…that is, gravity/general relativity is not included.

It is an attempt to completely unify The Strong Nuclear Force (Quantum Chromodynamics) with the Electro-Weak Force (Quantum Electrodynamics).

There are a number of solutions on paper, but the unification has yet to be observed. The cancled Superconducting Supercolider in Texas was to create energies high enough to probe that deep into the quantum world.

Before we can truly test M-theory, we have to actually know what it is; the theory is still being worked out. Even when it is developed, we’re a long way from being able to do calculations with resorting to approximations; we can’t even do that for QCD.

GUT is indeed a unified theory of strong, weak, and electromagnetic forces, and as far as I know **Enola Straight** is right on the money with his comments regarding it. A TOE would add gravity, but I’m a tad skeptical that we’ll find, test, and accept one within my lifetime; the theoretical challenges are enormous, and the experimental challenges are likewise, essentially because the regimes we’d need to look at are so exotic.

Yes a grand unified theory is one that unifies the standard model, a unified field theory is one that explains, electroweak, stong and gravtaional interactions.

M-theory is the best candidate and is essientially a theory that unifies the five different superstring theories, AFAIK most other attempts are not that active. there are sevral theories of quantum gravity which aren’t necesarily incompatible with string theory (if one of these quantum gravity theories prved to be correct a unified field theory would have the boundary conditon that it must approximate to quantum gravity in low-enrrgy situations).

The book people I have heard recommended quite alot which covers this general area is Lee smolin’s *Three Roads to Quantum Gravity*

It seems a bit odd to ask when a scientific theory will be discovered/achieved/proved. We don’t know the future, GUT or not.

I can answer the question of when we will be sure that we have a complete theory of everything: **never!**

Imagine you could predict anything you like using superstring theory, or your TOE of choice. You can test only a limited number of your predictions, due to technological problems (e.g. building an accelerator the size of the Solar System). There will always be realms that are inaccessible to you: too high energy, too far away in space or time, etc. So you can never be sure that your theory works for **all** of the situtuations for which you can make predictions.

This is going to sound wishy-washy, but that’s just tough. Some advancements can be anticipated: I can estimate, for example, when the first ten gigahertz computer chips will reach the mass market. These are generally refinements of existing ideas. Some advancements, however, cannot be anticipated. Generally, this happens when you need to come up with entirely new ideas. The Grand Unified Theory (if it even exists) or quantum gravity would require a whole slew of new ideas. It’s conceivable that the next Einstein is currently working on his Phd thesis that’ll make everything clear, but it’s also conceivable that that next Einstein won’t show up for another millenium.

Be gentle with us lowly peons with very little brain: Can anyone give a basic description of M-theory?

No.

I think I can.

It was discovered by adding a fifth dimension to 4D General Relativity, one can get Gravity AND Electromagnetism.

Add enough extra dimensions and you can descrive all the forces of physics: Gravity, Electromagnetism, Weake Nuclear Force, and Strong Nuclear Force. This theory was called Supergravity.

A similar theory was called Supersymmetry because at high enough energies the four forces are symmetric…that is display similar strengths over similar distances over similar intervals.

It was later discovered that the “particles” thought to transmit the forces displayed similar properties to the harmonic resonances of strings. One particle predicted by this “Superstring” theory, apparently was the elusive Graviton…indeed, when a field of gravitons were calculated into our macroscopic world, general relativity resulted.

Unfortunately, fully FIVE different superstring theories were presented, and they were uncompatible to each other.

Then one physisist (sorry, can’t remember the name) merely claimed that instead of five theories, there are five different ways of describing one reality. Simply adding one more dimension made all the pieces fit.

This is what we call M-theory…the Mother of all theories.

There is one problem with this theory…it can’t really be tested.

The strings which are believed to descrive ALL THINGS in the universe are operating on the order of the Planck Scale, the ultimate extreme of small. In order to probe the distances and intervals one would need near infinite energy…a cyclotron the size of the universe.

It was, I believe, Ed Whitten, whose name I’ve probably spelled wrong at this advanced hour.

I would add that a second problem is that not only can’t it really be tested due to technological limitations with experiment, but to the best of my (somewhat outdated) knowledge it hasn’t been used to make any predictions which are testable, correct, and unambigious. In my mind, that makes assigning the term “theory” to it a bit premature, but what do I know?

It’s actually *six* different superstring theories: Type I, Type IIA, Type IIB, Heterotic SO(32) and heterotic E[sub]8[/sub]XE[sub]8[/sub] and 11-dimensional supergravity. M-theory shows us how these seemingly distinct theories are, in fact, different faces of the same theory.

Slight hijack:

Is it just me, or does heteroic SO(32) make you think of a personal’s ad: Hetero / erotic significant other (age 32) ?