M theory

[redcannon]

perhaps i should have just PMed ComradeRed about this, but perhaps someone else has an answer to this.

What the fuck is M theory? How is it different then other string theories?

[hajduk]

Originally posted by [email protected] 15, 2007 02:12 am
perhaps i should have just PMed ComradeRed about this, but perhaps someone else has an answer to this.

What the fuck is M theory? How is it different then other string theories?
M for MARX
MARX THEORY

[Joby]

It's hard for me to explain.

M theory ties all of string theory together via the 11th dimension. It opens the door to a lot, a lot, of different possibilities, including parrallell universes.

It's quite fascinating, really.

[Bat]

but also sounds meaningless

[ComradeRed]

Originally posted by [email protected] 14, 2007 06:12 pm
perhaps i should have just PMed ComradeRed about this, but perhaps someone else has an answer to this.

What the fuck is M theory? How is it different then other string theories?
I didn't get a PM from you recently... :huh:

Anyways, M theory is a sort of unification of the various String theories.

You see, there are a variety of String theories. They all have the basic idea of having a 1 dimensional object (a string rather than a point), but they differ in details...e.g. the number of dimensions in super symmetric string theory is 11 whereas in "non-super symmetric" string theory (the free bosonic string model) has 26 dimensions (well, 3 or 26 dimensions; but since we know there are 4 dimensions string theorists argue that there must thus be 26 dimensions).

M theory basically says all these theories derive from the same basic theory. This basic theory is M theory, to be more precise.

Short Answer: String theory is actually a collection of similar theories...there is no "single" string theory. A unification of these different string theories is M theory.

[redcannon]

Originally posted by [email protected] 15, 2007 07:13 pm
(well, 3 or 26 dimensions; but since we know there are 4 dimensions string theorists argue that there must thus be 26 dimensions).

what's the logic behind that? CR you should start a study group for physics, if one hasn't been created already. I'd join.

[hajduk]

UPS :rolleyes:

[ComradeRed]

Originally posted by redcannon+August 15, 2007 08:02 pm--> (redcannon @ August 15, 2007 08:02 pm)
[email protected] 15, 2007 07:13 pm
(well, 3 or 26 dimensions; but since we know there are 4 dimensions string theorists argue that there must thus be 26 dimensions).

what's the logic behind that? CR you should start a study group for physics, if one hasn't been created already. I'd join. [/b]
There is a term which breaks Lorentz invariance ("the speed of light being constant") in the free Bosonic String equation when Dirac quantizing it.

That is, quantizing it so the eigenvalue equations resemble familiar equations from classical or relativistic quantum mechanics.

If there are 26 dimensions, the term goes to zero and Lorentz invariance is preserved...something you care about as a particle physicist. But if you look, the universe is accelerating so broken Lorentz invariance isn't too bad...it's supported with empirical observations.

But then you have to explain why at the particle level Lorentz invariance is preserved, and it's easier to just say "There are 26 dimensions, end of discussion!"

As for an introduction to quantum gravity (this entire field), Here's a collection of some dude's notes (http://angryphysicist.wordpress.com/tag/carlips-class/) on the course. It's not complete of course, but it should be impressive.

[mikelepore]

There was a time when the scientific method involved people wondering about the reasons for the thing we see in the world, making hypotheses about the answers, and testing the hypotheses.

But now some physicists seem to think it's "science" to begin with desired results that no one ever sees at all, except in the movies, like asking what it might require for there to be time travel or parallel universes, then deriving mathematical models that would be consistent with such things, and adding parenthetically that there is no way, even in principle, to test such ideas.

I think someone should make up a new name for that hobby, instead of calling it science or physics. It's just not the same activity as what Maxwell, Planck, etc. did.

[redcannon]

Originally posted by [email protected] 18, 2007 04:37 am
There was a time when the scientific method involved people wondering about the reasons for the thing we see in the world, making hypotheses about the answers, and testing the hypotheses.

But now some physicists seem to think it's "science" to begin with desired results that no one ever sees at all, except in the movies, like asking what it might require for there to be time travel or parallel universes, then deriving mathematical models that would be consistent with such things, and adding parenthetically that there is no way, even in principle, to test such ideas.

I think someone should make up a new name for that hobby, instead of calling it science or physics. It's just not the same activity as what Maxwell, Planck, etc. did.
I'd have to disagree with you there. If our views of science were still limited to figuring out what we see on earth, we would have no hope of moving forward. We could be content with Newtonian physics, but progression would be nice. And what's wrong with asking what might be required to time travel or parallel universes? There's nothing wrong with thinking outside the conventional realm. Besides, Plank was all about the theoretical physics that you appear to despise.

or it could be that i didn't quite understand what you were saying.

[mikelepore]

But modern physics is based on what we observe. Stars that were known to be directly in back of the sun were found to be visible -- light was bending. The measured speed of light was found to be independent of the frame of reference. Facts like this required Einstein The kinetic energy of electrons in the photoelectric effect was found to depend on the frequency of the light instead of its brightness. Blackbody radiators didn't behave as expected. An electron hit by light was found to recoil in the way recognized as an elastic collision. Planck had to explain why. These are cases of observations being explained by a new model. It's all about applying the explanatory powers of the theory to observations.

But some cosmologists don't want to wait for any actual problem at all. They want to find a set of calculations that, while they don't demonstrate that there are more than one orthogonal universe, would be consistent with such a thing. Why? Obviously, to not be self-contradictory doesn't make anything true. To not be self-contradictory only leaves us with "not yet proven false." And what is it, after all, that is not yet proven false, not self-contradictory? Something that has no pragmatic implications for us -- a parallel universe that we would never be able to detect.

We can see the similarity with the debates about religion. The theist postulates the existence of something that is by definition undetectable either through reason or the senses, and then thinks it somehow profound that other people can't prove its nonexistence. Then the atheist points out that in principle neither can we disprove the existence of an invisible flying unicorn, and so the discussion goes around and around.