Has this idea been explored? Dark matter as matter in parallel universes...

Misericorde

I'd agree with that; it's hard not to become enamored with these ideas, but it's also hard not to fall out of love with them given time and reading. It's one of the joys of science that you get these amazing concepts to bat around, but the other side is the need for rigor. Without any hope of falsification or validation, someday yah just gotta move on I guess. I don't feel that physics has given us a handle on the nature of existence, just what it's meant to do: help us understand how the slice of reality we deal with operates, by what rules, and what constants exist. The how and why of it all seems to be an eternal question that is always, "just around the corner," and never is.

DavidMcC

I am not an "eternal inflationist" either, but I 've posted a lot in various threads about "what the point of all this is". In a nutshell, laws of physics that don't seem quite right - that look as if they're the product of interaction within a multiverse that can only be detected through gravity, but not light (expalining also why a lot of people discount the idea - you know, the "if you can't see it with light, it isn't there" attitude).

Misericorde

The laws of physics seem just fine, but our understanding of them leaves something to be desired. Why is that surprising, and why do you think the solution is anything other than the natural evolution of existing theories and development of new ones? Where does metaphysics enter the picture except to make people feel comfy or entertained while the real work of progress in the understanding of nature moves forward?

DavidMcC

They may seem "fine" to you, misericode, but I have noticed that some of them lack the simplicity and symmetry that one might expect of a universe made in the conventional way. Eg, there shouldn't have been an excess of matter over anti-matter, etc (as I've listed before). One example of "fine" is E=Mc^2, but most other physics looks dodgy, and that includes GR+ (ie, GR with the CC). Various aspects of cosmology, including dark matter, inflation, the existence of life, etc (I've listed them before), suggest that, even though we don't see other big bangs with light, they must have occurred in any case, and set up a situation in which we observe their interactions with each other, then struggle to fit them into a theory that denies their existence. Thus, I think understanding nature will only move forward when we stop denying that a big bang, as a natural process, must have happened randomly many times, and not in a neat serial row.
EDIT: In other words, I think it is absurd to dismiss the Smolin's LQG as meer metaphysics. Rather it is the "head in the sand" attitude to the multiple challenges to "one universe" that is the problem, generating all kinds of bizarre "explanations".

Misericorde

Uh huh, yet they predict and let us develop technology for all that it lacks the elegance you seem to want.

DavidMcC

LQC also makes predictions (and could have done so before if it hadn't been prematurely abandoned). Eg, it predicts that neither WIMPS nor MACHOS, etc will be found, and that dark energy will ultimately go to zero (when there is nothing more to feed on in the parent universe), although the time-scale for this is unclear.
It is not that I "want elegance", it's just that I see inelegance elsewhere in physics, in which it is caused by external effects. Eg, if you didn't know that the Earth was slowly rotating, you would just have to accept that Newton's law of motion, F=ma, was a mess, needing to have some strange extra terms (the Coriolis force, etc) to make it correct.
As foir technology, comparing any theories should produce that, it's nothing to do with which is better.

Chalnoth

Er, what? Where does it make these predictions? And if so, how the hell does it explain our observations of dark matter?

Misericorde

Ditto.

David Elm

The parallel universe part of your idea doesn't seem to hold water. If gravity was acting in more than 3 dimensions, then it would spread out faster than it currently does (1/r^2). I think this has been well measured and precluded.

On the other hand, I've seen some papers in the ArXive (xxx.lanl.gov) that indication that idea of self-interacting dark matter has some merit.

There is also a non-mainstream theory (developed by serious physicists, not fringe guys, but still not generally accepted) called "mirror matter" that proposes that there are two mutually invisible types of matter living in the same space. I don't know if I follow the argument that well, but it has to do with having two types of matter that violate CP conservation in opposite ways.

Other than the "mirror matter" development, I haven't seen much in the way of a theory of what that self interacting dark matter might be. One paper proposed an analogy to electrodynamics within dark matter, but they didn't go so far as to propose a different type of equivalent matter that was somehow different.

Perhaps these researchers are being deliberately cautious until they come across a good enough theory to hang their collective hats on.