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Author Topic: What is string theory?  (Read 4721 times)

Offline tangoblue

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What is string theory?
« on: 30/07/2010 22:01:24 »
can anyone please explain to me in laymans terms what string theory is because ive read about it and i still dont have a clue what it is.


 

Offline grizelda

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What is string theory?
« Reply #1 on: 04/08/2010 08:39:00 »
At this point in scientific exploration of the cosmos, most avenues of investigation have been exploited for the largest part of the information they can shed on the "Theory of everything": so without finding an easy answer, the areas left to explore are extremely specialized and expensive. String theory tries to do an end run around these limitations by reverse-engineering the universe, i.e. by finding a model which can output the universe we experience and measure, rather than take the measurements we have and extrapolate them into an explanation of our experience. So we end up with elements which we have not measured (strings, extra dimensions, etc.) but which can be shown to have the qualities which, when manipulated together, produce a model which is hopefully identical to our universe. Maybe, maybe not. Magicians do the same thing with hats.   
 

Offline LeeE

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What is string theory?
« Reply #2 on: 04/08/2010 17:13:20 »
First of all, I must make it clear that I'm not an expert on string theory.

I found grizelda's post very interesting though.  I keep a fairly distant and relaxed eye on developments in string theory and while much of it makes good sense to me there are some areas where I find it a bit inadequate.  What I've never read or had explained to me, or has never even just occurred to me though, is the philosophy behind the string theory 'project', for 'project' might be a better word for it.

Most of what we've learned in physics has been the result of analysis.  The technique of analysis is based upon a top-down approach to investigating something: our understanding of something starts with out first awareness of it - our first 'sight' - and then we analyse it, burrowing down through its hierarchy of sub-components towards a fundamental 'something' that cannot be further 'split'.

The inevitable result of a top-down analysis must always be abstract though, precisely because it cannot be described by anything other than itself or by other fundamental abstracts, if they incorporate equivalence.

Now the most interesting thing, to me, about grizelda's post is that it describes a bottom-up approach.  Instead of starting with the 'real' and ending with an abstract, the string theory seems to be all about starting with a hypothetical abstract and seeing how it might logically display the same behaviour as the observed 'reality'.  String theory then, isn't really a theory to describe an analysed reality but an exercise in logically developing a theoretical model for it.  Heh  :) which probably explains why some parts of it make a lot of sense to me.

Perhaps the reason that some people have problems with string theory is the idea that you can't get a valid result if you're starting with something you've imagined, for you could imagine anything.  However, with top-down analysis, the only result you can get, being abstract, is something that can only be imagined. 

Considering that the most fundamental answer, with either approach, will be abstract then either approach seems equally valid, with models produced by either technique liable to be eventually found wanting and replaced by newer models.

When both types of model converge precisely, then I think we might be in a position to say that we really do know how the universe works.
 

Offline tangoblue

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What is string theory?
« Reply #3 on: 08/08/2010 12:41:32 »
I think i get it a little bit, but somebody stop me if i ever want to be a physical theorist :). thanks for the detailed replies.
 

Offline golgeli

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What is string theory?
« Reply #4 on: 21/08/2010 16:21:45 »
 :D :-\
 

Offline chrisdsn

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What is string theory?
« Reply #5 on: 25/08/2010 05:21:48 »
A definition of string theory is hard, as what counts as string theory evolves quite quickly with time. Basically, we have two well tested physical theories: General Relativity, which describes gravity on a large scale, and Quantum Field Theory, which describes the interactions of particles due to the rest of the forces at the small scale. The predictions of both these theories agree very well with experiment; there is no experimental evidence to suggest they are wrong, and lot's to confirm their predictions.

The problem is that it's hard to come up with a Quantum Field Theory that includes Gravity which is not logically inconsistent, so based on our current understanding of Quantum Field Theory and General Relativity, both can't be correct. As such, a search should be made for a theory which looks like (but isn't) Quantum Field Theory at short distances, and looks like (but isn't) General Relativity at large distances, and is logically self consistent.

String Theory is an effort to find such a theory. Quantum Field theory works with particle (which exist at a specific point in space and time). String theory started by saying "what if, when you probe deeper, that point is actually two points connected by a line/string". This turned out to give a massive win: General Relativity can be work in this case, but only as long as you work in 24 dimensions (rather than the 4 -- 3 space, 1 time --  we experience). This solves one problem (combining GR and QFT), but adds one massive one: how you explain our four dimensional experiences in terms of those 24 dimensions. String theorists have striven to solve that problem for 20 years, but -- to be honest -- have yet to make significant progress.








       
 

Offline LeeE

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What is string theory?
« Reply #6 on: 25/08/2010 11:48:56 »
It's not really true to say that Relativity, or the various Quantum models, are incorrect but rather that neither are 'Theories of Everything' and as such it is more accurate to describe them as being incomplete.

Within their respective scopes i.e. within the areas that they do cover, both seem to be very clearly correct.
 

Offline Variola

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What is string theory?
« Reply #7 on: 27/08/2010 15:53:58 »



 ;D
 

Offline LeeE

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What is string theory?
« Reply #8 on: 27/08/2010 18:32:31 »
Nice one  :D
 

Offline tangoblue

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What is string theory?
« Reply #9 on: 12/10/2010 18:37:20 »
So in short its trying to link general relativity and quantum physics so that they agree with each other so to speak.
 

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What is string theory?
« Reply #9 on: 12/10/2010 18:37:20 »

 

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