N Scale Math Help Needed

[GaryHinshaw]

Where do they get the 11 from?  Why not 10, or 12?   Maybe the guy was counting with his hands in his pockets...?   

Ed

Well, I won't pretend to know the detailed answer to this question, but allow me to use an analogy that might give you the flavor of the answer.  String theory posits that the fundamental constituents of matter are 1-d sring-like objects, rather than 0-d point-like particles.  What we perceive as particles (protons, electrons, etc.) are actually quantized vibrational modes of these strings. 

For an analogy, think about musical instruments.  When you play a note on the violin, a 1-d string vibrates in 3-d space and generates a certain spectrum of harmonics, or overtones which makes it sound like a violin.  The pattern of overtones can be compared to the types of elementary particles a string theory can produce.  Now consider a cymbal, which is fundamentally a 2-d object living in 3-d: when you strike it, the pattern of overtones is much different, quite dissonant in fact.  That is because the overtones (modes) on this 2-d cymbal have frequencies that are not regularly spaced, so they tend to clash.  But this spectrum of overtones may be just the ticket to explain the spectrum of particles (excitations) we observe in nature.

It turns out that in order for string theory to produce excitations that have a hope of matching the particle zoo we observe (and to be otherwise mathematically self-consistent) the 1-d strings need to live in 10 dimensions.  Further, there is an elegant generalization of string theory, called M-theory, that lives in 10+1 dimensions, from which many different versions of string theory may be derived.  (My 11-d reference above actually refers to M-theory.)

As of today, this whole framework is just elegant mathematics, because string theorists are only able to predict how nature should behave on very small scales, or at very high energies.  Sadly, we do not have a hope of probing these regimes with current or even planned experiments.  It would require a machine far more capable than the Large Hadron Collider (LHC) to do so.  Putting string theory and M-theory to the test in our lifetimes will require the theorists to develop techniques for calculating "low-energy" phenomena that the LHC can potentially reach.

-gfh

[Kisatchie]

String Theory is a scientific fraud.


Hmm... you tell 'em,
Kiz...

[C855B]

String Theory is a scientific fraud.

Ah, but it's elegant mathematics. You have to keep the mathematicians happy, creative and focused, lest they get bored again and impose yet more miseries on our society such as commodities derivatives and credit default swaps.

[GaryHinshaw]

String Theory is a scientific fraud.

There are many scientists who feel they same way.  No so much fraud, just not science, because it can't be tested (yet).

Ah, but it's elegant mathematics. You have to keep the mathematicians happy, creative and focused, lest they get bored again and impose yet more miseries on our society such as commodities derivatives and credit default swaps.

Sad but true.  Many quants on Wall St were string theorists in grad school.

[DKS]

What bothers me about string theory is that it's called string theory. That's a terrible misuse of the term. Theories are well-understood, observable and measurable phenomena, whereas string theory is anything but.

[Dave V]

Actually there were 5 competing string theories in 4 spacetime dimensions until someone discovered that if you increased the number of spatial dimensions to 10 (with time being 11), you could unite all 5 theories.

Technically the 11-dimensional string theory is known as M-theory for Membrane.  The 7 unobserved spatial dimensions are posited to be really small and folded up into Calabi-Yau manifolds.

FWIW, string theory can potentially explain why gravity is so much weaker than the other three fundamental forces if one considers that we live on a 3-brane and gravitons are closed strings in those dimensions.

However I agree with the idea that string theory is perhaps more philosophy than rigorous science no matter how elegant the math may be.

EDIT:  Am I the only one who keeps thinking this says "meth help needed?"  It must be almost time for another season of Breaking Bad.

[GaryHinshaw]

Actually there were 5 competing string theories in 4 spacetime dimensions until someone discovered that if you increased the number of spatial dimensions to 10 (with time being 11), you could unite all 5 theories.

Minor quibble: the 5 competing string theories lived in 10 dimensions.  As I understand it () these 5 theories are all related to M-theory in 10+1 dimensions by a duality transformation. 

EDIT:  Am I the only one who keeps thinking this says "meth help needed?"

Yes.   

[eja]

I thought string theory had to do with the violins, violas, cellos and basses of an orchestra.  Either that, or something to do with cats and a ball of string ! 


eja

[Dave V]

Gary, you are correct; my apologies.  My memory was flawed on the subject.  A quick review also recalls that bosonic string theory requires a whopping 26 spacetime dimensions.

[GimpLizard]

Bartender? I'll have another, please. 

[GaryHinshaw]

Gary, you are correct; my apologies.  My memory was flawed on the subject.  A quick review also recalls that bosonic string theory requires a whopping 26 spacetime dimensions.

Your summary was impressive nonetheless!

[basementcalling]

I'm going for a beer. 

Would that be an N scale sized beer? If so, how many can you have before you reach the legal BAC limit?

[Dave V]

Ahhh...  Railwire thread drift.  All is right with the world. 

[C855B]

Yes, but it's Railwire thread drift. What other forums drift from the relative size of boxcars into a discussion of spacetime dimensions and string theory?

[eja]

What other forums drift from the relative size of boxcars into a discussion of spacetime dimensions and string theory?

Hopefully none