Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum The multiverse and extra dimensions.

If I promise to avoid "infinity", and to keep the "Schröding-cat" in its box, perhaps I could toss a thought into the mix.


If we take “M” theory as perhaps being the most promising variety of string theory, and David Deutsch’s version of the multiverse (The Fabric of Reality, Penguin Books, 1998) as being perhaps the best explained multiverse theory, the nature of my question will emerge clearly.

String theory requires both extra dimensions and multiple universes. M theory involves 11 dimensions. We are told that 7 of these need to be rolled up so tightly that we cannot detect them. This is why we cannot observe them.

On the other hand trillions of universes occupy the same space with such precision of positioning that individual photons, in different universes, can interfere with one another, yet we cannot observe these universes and they are not rolled up. Why, then do the extra dimensions need to be rolled up to avoid detection?

Bill

The way you word it: "Why, then do the extra dimensions need to be rolled up to avoid detection?"

- indicates that you consider those proposed extra 7 dimensions to have been rolled up with the intention of avoiding detection, as opposed to them being rolled up solely due to the nature of the universe/multiverse.

Correct? And am I right in thinking that you therefore subscribe to the view that the aforesaid nature of the universe/multiverse has its origins in an intelligence?

If one takes that view then there's no way (short of prayer perhaps) to answer your "Why" question. On the other hand, if one doesn't then the question is null and void.

I didn't mean to bring infinity into the discussion, but I'm going to blame you for this. If the cosmos (I use that to cover universe or multiverse)contains intelligence, which obviously it does,and if it is infinite, it must be intelligent, and must always have been. Whether or not one refers to an intelligent cosmos as an intelligent designer, or even "God" seems to be a matter for personal belief rather than scientific enquiry.

As far as the rolling up of the extra dimensions is concerned, P S books do tend to give the impression that the rolling up is the reason we cannot see them. Obviously this is not the same as saying that they are rolled in order to hide them, but the question still remains, albeit worded differently:- Is there any reason why the extra dimensions could not be present, but undetectable, if they were not rolled up? If the answer to this is "yes", then why is it assumed that they are rolled up? I am reluctant to believe that this is just a matter of personal belief, or, surely, it would not be so widely accepted.

My understanding is that M-Theorists don't simply assume that those dimensions are 'rolled up' (whatever that means); rather, the mathematics requires that they are. It's all about rigorous mathematical self-consistency, as far as I know. The theory is either right or wrong. Nothing whatever to do with belief.

Which brings us back to the question of whether or not mathematical self-consistency equates to reality.

Thanks for your comments; a different perspective is always a good thing.

(We are told that...)

The maths of M-Theory equates exactly to known features of reality, despite the fact that it describes more than can be shown to be true (or falsified). The reality of M-Theory may or may not be the reality of our universe.

Michio Kaku (Hyperspace. Oxford University Press) in explaining the exigencies of heterotic strings says: “The heterotic string consists of a closed string that has two types of vibrations, clockwise and counterclockwise, which are treated differently. The clockwise vibrations live in a ten-dimensional space. The counter-clockwise live in a 26-dimensoinal space, of which 16 dimensions have been compactified.”

Is there a difference between "compactified" dimensions and "rolled up" dimensions?

Not sure, Bill. Your M.Kaku quote says that only 16 of 26 are compactified. But looking elsewhere it seems that 'rolled up' means the same thing...

"...it is assumed the extra dimensions are "wrapped" up on themselves, or "curled" up on Calabi-Yau spaces" - Compactification in string theory, Wikipedia

How about this? -

"According to string theory then, we live in a universe where our three familiar dimensions of space are “flat”, but there are additional dimensions which are curled-up very tightly so that they have an extremely small radius: 10-30 cm or less."
http://d0server1.fnal.gov/users/gll/public/edpublic.htm

How on Earth can there be a dimension with an infinitesimal radius that occupies the whole universe?

Sorry, Bill, I'm completely lost!

You beat me to it! Seems we are both lost. Let's hope someone else has the answer.

Wouldn't we be able to observe them through these interferences?

I know, it's a semantic kinda thing, but in this case it kinda means sumpin.

I don't think you could count this as seeing the other universes. You can interpret the interference as inferring that there are other universes present, but Deutsch's admission that the multiverse is not the majority view implies that other scientists believe there are other possible interpretations.

I've been thinking about this, and as well as the problem contained in your question there is another worrying thought. Some authors suggest that these extra dimensions may be so tightly rolled as to be infinitely small. How can you distinguish between something that is infinitely small, and something that does not exist? Surely, if it exists physically, it has a finite size.

Surely, indeed. So, I guess it doesn't 'exist physically', as we understand the term. If singularities exist, then it would seem that they exist in something other than the spacetime that we know, and that their only link with this universe is gravity. Perhaps the same can be said of 'compactified' dimensions.

“It’s life, Jim, but not as we know it” For “life” read “physical existence”.

If gravity is the link, it raises another question. Logically, gravity in our Universe comes from the energy of the Big Bang, which will have imparted enough "oomph" into all the matter and energy to bring it back to a single point. If gravity is weaker than one would expect, because it is leaking into other dimensions, does that mean that there will not be enough to bring everything back together? No big crunch? No bouncing universe?

I couldn't say what's logical regarding Big Crunch v Big Freeze. It seems we don't know nearly enough, but...


Quite possibly, it seems.

Leaking Gravity May Explain Cosmic Puzzle: http://www.freerepublic.com/focus/news/1353071/posts

"[New York University physiscist Georgi Dvali] borrows from string theory, which states that there are extra, hidden dimensions beyond the four we are familiar with: three directions and time. String theory suggests that gravitons -- hypothetical elementary particles transmitting gravitational forces -- can escape to other dimensions. Dvali says this would cause "leaks" in gravity over cosmic proportions, reducing gravitational pull at larger distances more than expected"

Actually this is something on the LHC agenda - to look for gravitons, and see if they can be witnessed sneaking off into other dimensions - which would be taken as support for String Theory.

But the question I'd like to ask Dr. Dvali is: what's to stop gravitons from dimension X re-entering our 4D spacetime?

Perhaps one should not suggest that the lack of gravitons leaking back has more to do with maintaining the theory than with the possible behaviour of gravitons.

Would I be right in thinking that gravity has become a force again, as it seems to when the occasion demands?

I suppose a description is applied according to the phenomena being observed, as in 'when is a particle not a particle?' - but in this case 'when is a force not a force?'. It seems that, in General Relativity, there are times when gravity can't be modeled as a force. Short answer is, I don't know. Hope LHC finds the graviton and Higgs Boson or whatever the culprit may be.

Edit...Just found this:
Relativity Still Holds Up: 5 Recent Tests That Prove Einstein Right (13 Oct 2010)
http://www.popularmechanics.com/science/space/deep/5-recent-tests-that-prove-einstein-right?src=rss

Redewenur, thanks for the link; interesting read.

One thing puzzled me in the comment on gravitational time dilation (jtankers): “Remaining the same distance from a strong gravitational field is the same as accelerating away from the strong gravitational field.”

I thought that remaining the same distance from a strong gravitational field was the same as accelerating in the absence of a gravitational field.

Is there something wrong with my reasoning?

Nothing wrong with your reasoning, Bill. The quoted sentence actually says exactly the same as yours, because "accelerating away from the strong gravitational field" isn't intended to imply an increase in distance from the field.

Is "Remaining the same distance from a strong gravitational field"
not the same as being stationary in a strong gravitational field?
That is, assuming one has to be in the G F in order to feel it.
If acceleration away from the G F is then added, does this not increase the apparent G F experienced by the subject?