M Theory

[Deepwater6]

Does "M Theory" allow for travel between parallel universes? With the theory of two membranes colliding to create the big bang and the thought that it may have happend many times in the past would we be able to detect when two other branes collide?. if another collision in our own universe were to happen now with the current size of our universes expansion would it look like a big bang to scientists eons from now or would it have a different form/look?

 

thx

Deepwater

[CraigD]

Does "M Theory" allow for travel between parallel universes?

In the sense of baryonic matter, photons, or other matter or energy described in the Standard Model, I don’t think so, but I have only a shallow (pun intended ;)) understanding of brane theory.

 

What most brane theories I’ve read predict is that it might be possible for different brane universes to interact with, and so potentially communicate with, one another, via gravity, because unlike the other interactions, gravity is not confined to the branes’ 3+1 space+time dimensions.

 

The many universes predicted by brane theory aren’t the same kind as those in the Many Worlds interpretation or other usual “parallel universe” theories or interpretations (eg: no nearby universe where Adolph Hitler became a golden age SF writer rather than a notorious war criminal). Except possibly for sharing Big Bang-like creation events, they don’t branch from common past states, and the only guarantee of there being a very large number of them is if some of the non-compact (“bulk”) dimensions are predicted to be very long or infinite, and the total energy of the bulk is very great or infinite.

 

With the theory of two membranes colliding to create the big bang and the thought that it may have happend many times in the past would we be able to detect when two other branes collide?.

Maybe, in the same way we might detect any nearby brane universe with mass-energy in it: by gravitational anomalies.

 

if another collision in our own universe were to happen now with the current size of our universes expansion would it look like a big bang to scientists eons from now or would it have a different form/look?

The family of brane theories I know that predict many big bangs in our universe – the Stienhardt-Turock model predict that these cycles resemble a classical big bang-big crunch cyclic universe, except that energy is introduced to avoid the classical thermodynamic problem of the such a system “running down”. Why this is, rather than some more bizarre prediction, is beyond my understanding of brane theory.

[Deepwater6]

Very very interesting. Since these branes are so flexible would it be possible for one to fold up on itself? Colliding it's ends so to speak in the shape of a doughnut? From your response I got the feeling you are not in the brane theory camp. What theory do you feel is the most likely and why? thx

[Cyberia]

No evidence of branes. No evidence of other universes. No evidence of strings. No evidence of extra dimensions.

 

Not so much "M Theory" as "M Idea".

[lawcat]

No evidence of branes. . . . No evidence of strings. No evidence of extra dimensions.

 

Not so much "M Theory" as "M Idea".

 

I must side with Dr. D here. This is strictly tautology.

[Cyberia]

lawcat. Too many unproven ideas.

 

If there was a deeply religious planet of beings somewhere that had decided that the force that stops everything floating off into space (which we call gravity) was down to gods or demons and produced workings based on the effects, while the workings may be true in that they can be reproduced elsewhere and even used to calculate other effects and workings, the basic idea that there are gods or demons as a cause would still be wrong.

[CraigD]

No evidence of branes. No evidence of other universes. No evidence of strings. No evidence of extra dimensions.

 

Not so much "M Theory" as "M Idea".

I wouldn’t say there’s no evidence for “branes”, because in M theory, our universe is one. I agree there’s no evidence for other universes/branes.

 

I wouldn’t say there’s no evidence for strings or the higher-dimensional “bulk space” of string and M theory, but rather that the evidence doesn’t strongly suggest any one explanation of family of explanations. The problem with string and [m][brane] theories are that they’re a nearly infinite collection of theories that attempt to explain particle physics and gravity with fewer formal entities than the Standard Model’s ad-hoc “particle zoo” (which is itself a much-smaller zoo than the one it explained away, but lacking any explanation for gravity). The best, IMHO, that can be said for them is that they’re offered explanations, which are arguably better than the lack of any explanation at all (and also arguably not).

 

A couple of themes in criticism and support of “fewer entities in more dimensions” physics theories are apparent to me. The main criticism, is that, as Sexton notes, is that they’re not yet, in a strict, Popperian sense, theories at all, as they’ve yet to make any testable predictions, so can’t be experimentally supported or refuted. The main answer to this criticism is that some sting/brane theory (brane theory can be considered a kind of sting theory) could, but we’re just not smart enough to select one and use it to make precise, testable predictions.

 

In short, this argument is that some string theory is right, but no string theorists is smart enough to show it is. As mathematicians and physicists are suckers for being challenged with a problem someone claims they're not smart enough to solve, by many accounts, this argument has a lot to do with the popularity of string theory.

 

As best I’ve been able to discern (in most part from reading Lee Smolin’s The Trouble with Physics: the Rise of String Theory, the Fall of a Science, and What Comes Next), the main virtue of string theories is that they all predict the existence of gravity, while the SM doesn’t.

 

My big problem with string theory is that it’s so mathematically complicated I can’t, with my rusty BS background in math and mathematical physics, follow it. I have a hard time either criticizing or supporting it, because I don’t believe I fundamentally understand it, and as a rule, I don’t like dismissing ideas I don’t understand.

[lawcat]

lawcat. Too many unproven ideas.

 

If there was a deeply religious planet of beings somewhere that had decided that the force that stops everything floating off into space (which we call gravity) was down to gods or demons and produced workings based on the effects, while the workings may be true in that they can be reproduced elsewhere and even used to calculate other effects and workings, the basic idea that there are gods or demons as a cause would still be wrong.

 

 

Yup, nothing but math, in other words tautology.

[Cyberia]

Several years ago there was a mass exodus of learned people from "string theory" because they saw no future in the field (which I suppose means they could never prove what they believed). Of course, people still working in the field still churn out papers on strings.

[Moontanman]

Info possibly relevant to this discussion.

 

http://www.scientificamerican.com/article.cfm?id=multiverse-the-case-for-parallel-universe&WT.mc_id=SA_CAT_SPC_20110721

[Cyberia]

I had a quick look through the article and it does seem to take a lot for granted. The way I see it is that we would essentially have to look for something strange, that "does not belong in this universe" as evidence of a multiverse. Yet since there are many things we still do not know, if we did see something strange, we could not know if it has come from "elsewhere" or is just some part of this universe that we presently know nothing about.

[maddog]

CraigD,

 

An excellent expose' on the material surrounding M-theory. Like you my Abstract Algebra suffers. I did finally understand the problem with

the number of dimensions of why Supergravity doesn't work for instance.

 

Also, I did hear where Ed Witten had recently considered using Penrose's Twistor theory added to M-theory, though I didn't hear of the

outcome.

 

On a recent show that Morgan Freeman had on the Science channel where a physicist (I forget name) proposed adding a dimension to time

(basically a loop -- making a tube over a line). I found this to be equivalent of making time a complex number in polar coordinates which I prefer.

 

Your main point though I agree, progress won't be made until whatever theory can make prediction that corroborate the Standard Model and can

explain current anomalies.

 

maddog

[G Anthony Kent]

Collision between branes is called the ekpyrotic theory. Only if one adds in the supposition that these branes are not exactly flat can one reproduce observations. It's another ad hoc add-on that makes these kinds of speculations suspicious.

 

Now, if branes can bounce too, it is another ad hoc. If one surmises that they bounce repeatedly, one gets a periodic universe. Another ad hoc.

 

Then, it is highly questionable that any these are falsifiable hypotheses. See my recent post on the scientific method and quintessence (2dc11). It is safe to say that no experiment can disprove that any of these phenomena exist. This is mainly what "falsifiability" means.

 

The scientific method prohibits consideration of unfalsifiable hypotheses. Plain and simple.