Unified Theory

[fuhrerkeebs]

Ahh nice...gonna have to check into it (I love theories of q-gravity)

[noz92]

if we have no proof, or even testing on string theory, then why do we rely so much on in the feild of quantum physics?

[fuhrerkeebs]

Because you can apply quantum field theory to point particles and strings...and the point particle approach has given us consistently accurate experimental verification, even though we know that point particles are inconsistent with General relativity because have mass concentrated at an infinitesimal point creates black holes (albeit small ones, depending on the mass)

[noz92]

string theory seems to explain the 4 forces, so it seems almost as though string theory is TOE, what does string theory lack?

[fuhrerkeebs]

It doesn't make any predictions that we can test...therefore it is just a conjecture. And, although it unifies the 4 forces, we still don't know how gravity in string theory actually works...we just know it's there.

[noz92]

but TOE means theory of everything, and a scientific theory usually can't be proven, especially in something as complicated as quantum physics

[fuhrerkeebs]

You are right...a scientific theory usually can't be proven--in fact, according to Kant, a scientific theory can never actually be considered a "truth". But when people use the term theory of everything, they don't usually mean a theory of everything. They are usually referring to a theory of quantum gravity, which is what string theory is.

[Severian]

I get the impression that people on this site have an over-inflated notion of what string theory has achieved. While string theory is a great idea and hopefully will yeild great dividends in the future, it is nowhere near the level of development of our other lower energy theories.

 

Our low(er) energy theory - The Standard Model - is also based on quantum field theory and explains all the forces except gravity (though not in a unified way). It is now the best tested theory ever. Despite almost 30 years of testing in big colliders, there has been no deviation from the Standard Model observed (unless you count nuetrino masses, but that was really just an ansatz). This is a remarkable acheivement.

 

As fuhrerbeebs has pointed out, string theory has made no testable predictions. In order to test string theory directly we need to investigate energy regimes approximately 10,000,000,000,000,000 times those we currently probe at colliders. And until we do that, we cannot test string theory at all. (Martin recently pointed out to me some new ideas for testing some aspect of (admitedly 'non-standard') string theories, but in my opinion these are a long-shot.)

 

In principle we should be able to test string theory indirectly by working out what happpens at low energies. First of all, there is a factorisation of energy scales present in the Standard Model, so that the tests of the Standard model are independent of the physics at the string scale (this property is called 'renomalisability') so the low energy tests are not testing string theory at all. One can on the other hand ask if string theory reproduces the Standard Model at low energies (an indirect test) and indeed one finds that some string theories can (although the rigour of the maths leaves a little to be desired), but this is really just a consistancy test.

[jordan]

How far along is string theory now in terms of describing everything (not proof)? If we didn't have to worry about proving it, would science be done tomorrow and everything you could want would be in string theory? Or is string theory just say there are strings and we don't know how they solve all our questions? Or somewhere in between?

[fuhrerkeebs]

String theory still can't get gravity to work. Haha. Physics wouldn't be done even if string theory describes everything...you could spend years upoun years deriving things from a theory of everything. But string theory is still background dependent, so there is a long way to go.

[jordan]

Gravity still wont work, huh? Doesn't sound like a theory of everything to me. Oh well, I'll just wait and see what happens. Until I can actual understand all the math and stuff that goes on, I have no choice but to take people's word.

[noz92]

let's assume that we do -some day- discover a unified theory, would that be the end of all physics.

[noz92]

but then there's man's special (yet annoying way) of finding answers and thinking up ways to proove them wrong. could that mean that we never really find a unified theory.

[jordan]

let's assume that we do -some day- discover a unified theory, would that be the end of all physics.

Read post 35.

[noz92]

sorry, didn't see that post

[fuhrerkeebs]

And if we do find a unified field theory, how do we know it's correct? How can we distinguish between a very good approximation and an exact answer? Before Einstein, everybody thought the end of physics was in sight. The point: There's still hope for physics after the attack of a full fledged TOE.

[noz92]

we don't have to have it exactly correct, for instants, general relativity, thats probably mostly correct, but theres probably a few parts that arn't right, but so much of it probably is right, that we can safely rely on general relativity for most situations in physics. TOE may be something like this.

[jordan]

Interesting: Would you rather know the TOE in your lifetime or continue searching for it? I personaly find the search more interesting than the answer.

[noz92]

I don't know, the answer would seem more interesting because we could - in a way - know everything in the universe (about physics, math and other science), but you're right, the search is prety interesting.

[TheProphet]

Im with you on this one Jordan! I'd rather search than to find out that someone has found a TOE..

[fuhrerkeebs]

we don't have to have it exactly correct, for instants, general relativity, thats probably mostly correct, but theres probably a few parts that arn't right, but so much of it probably is right, that we can safely rely on general relativity for most situations in physics. TOE may be something like this.

 

How do you know something about GR is wrong? What do you consider wrong with it? I agree with you...I just want to hear your justification for it.

 

And I personally enjoy the search for the TOE more than actually finding a TOE...

[noz92]

i don't know if something is wrong with it or not. I just think the chances of 100% of it being correct are very slim. if i'm wrong, fine, but i'm just using that as an example.

 

and the search for TOE is getting more and more interesting with it's suspense, and the discoveries that we find in our search. I do agree with everyone on that, I just think that TOE will be much more interesting than it's search.

[fuhrerkeebs]

I'll tell you what I think is wrong with it...dark matter/energy

[noz92]

yes. how exactly did we come upon discovering that?

[fuhrerkeebs]

Dark matter/energy came about because what we observe is different from what GR tells us we should be observing.