Dark Matter.....

[ToraToraTora]

OK, it's generally accepted that 27% of the universe is dark matter, we know it has gravity, and we know it must be there to make the universe work, or at least explain the observations and measurements. Matter as we know it makes approx 5% of the universe. Many questions have been asked what it is and when asked the same I always say, beyond its gravity we simply have no clue thus we make up the name to make our equations work. So as it's Friday 3 points to discuss:
1) Do you think there is life in the Dark matter universe?
2) Do you think they would notice our 5% missing in the same way we have noticed their 27%?
3) Speculate as to the nature of dark matter.

[jim360]

1) No.
2) Also no.
3) I come here to take a break from my day job... :P

[RATTER15]

Does it matter?

[jim360]

(I'll put up a more interesting answer later today, couldn't resist the short one first though :P)

[mikey4444]

Ruddy hell TTT....not asking for much are you !

[Old_Geezer]

No
N/A
It's the same stuff as comes in the Guinness bottle.

[ToraToraTora]

jim I knew you would not leave it as at your first go. You are perhaps the only person on here that initially springs to mind when this sort of question comes up. I eagerly await your more comprehensive answer though If I do not get back until tomorrow it's because it's Friday and from 5pm I will be experimenting with the falling Down Water.

[douglas9401]

I had all of this figured out one warm Sunday in 1973.
It's all gone now, sadly, apart from the odd flashback when staring vacantly at patterned wallpaper for any period of time.

The methodical scientific approach, keeping accurate records etc. is probably, on reflection, a better way to go.

[Zacs-Master]

Douglas, I had some wallpaper like that once. All fractals and Mandelbrot thingys.

Tora, nice to see you're continued posting of questions which you haven't a hope of understanding the answer to. Crack on lad.

[ToraToraTora]

that's incredibly insulting ZM, no need for that. Aside from Jim I'd say there is no regular on here that is remotely close to my knowledge of physics and astronomy. If that's meant to get a rise it did well done give yourself a gold star. The fact that I consider you one of the more intelligent people on here means that you are able to get this response, I'd ignore most of the other morons, I am saddened and surprised, this is science not chatterbank.

[jim360]

"Aside from Jim I'd say there is no regular on here that is remotely close to my knowledge of physics and astronomy."

Well it's nice to know that I'm "close to" your knowledge of physics, eh? :P

[ToraToraTora]

jim you are way ahead of me, perhaps I did not put that too well, I hope you know what I meant.

[douglas9401]

Careful Tora, it might be discovered that dark matter is actually composed almost entirely of shed moron skin and you're dismissing one of the great secrets of the universe.

Then you'd look silly.

[jim360]

It's difficult to say something like "I knew what you meant" without also sounding like an arrogant little so-and-so... But I'd be careful before asserting that I know more about any given topic than a stranger on the internet, with the obvious exception of my very specific (and very narrow) field of research.

I don't see any point in not asking questions. If you understand the answer, great; if you don't, then ask another one until you do, and work your way back up from there. Problem solved.

[Zacs-Master]

I had no idea that you had an extensive knowledge of physics and astronomy Tora almost on a par with Jim's. I'd guess that his knowledge (and more importantly, understanding) and yours are some interstellar distance apart.

I cant really see the point in speculating whether dark matter holds life forms when we can't even conceive how to detect it.

Now......where to pin that gold star.

[jim360]

I mean, realistically, my answer to part (1) is still "no", because I don't think that's how Dark matter works. I suppose one can't rule it out altogether, maybe "life" is an even weirder concept than anyone gives it credit for. But "life" requires complexity, requires interactions between many particles, requires some reasonable way of transferring energy, probably requires some sort of chemical rather than merely physical interactions also -- I just don't see it as reasonable for Dark Matter to be capable of that.

Maybe if "Dark Matter" turned out actually to be something closer to a literally overlapping Universe, far closer to the sci-fi understanding of "parallel"... but that's not really how we understand it today, as a generic placeholder for the 27% missing mass that isn't Dark Energy)

That rather makes (2) moot, but in the highly unlikely event that "Dark Matter life" were a thing, and in the highly unlikely event that such life were complex enough to notice, then it certainly would be aware of it -- the only point here being that there's a certain symmetry at play. Dark Matter barely interacts with "normal" matter; so vice versa you'd see the same thing, if that were possible.

As to (3): well, I could throw out a bunch of exotic physics names here. In rough order of plausibility (as I see it right now): Axions, Supersymmetric particles, Right-handed Neutrinos, or accidentally beggaring up General Relativity at large scales. I don't really know which -- although if you favour a particle explanation then it's apparently such a weakly-interacting particle that we might never be able to see it without blowing up a star or something :/

[Old_Geezer]

Yay ! We're blowing up a star, blowing up a star, ee aye addio we're blowing up a star. :-D

(Try not to make it our nearest one please.)

[ToraToraTora]

thanks jim, I just started to think that as dark matter to us is basically a name we give to stuff so our equations fit the observations that the "stuff" would be so completely different to what we know as matter that all our understanding of the chemistry of life etc would be similarly different. Perhaps any beings living in the dark matter would see our 5% as their "dark matter" and each of us would be none the wiser. If they could see only what we know as dark matter their sky would look a lot more crowded and our 5% may not even be noticed and could merely be written off as an arithmetical error. Just a thought experiment really.

[Zacs-Master]

Could it (DM) be put down to the interaction of parallel universes. Some sort of effect of the two adjacent time frames meshing together?

[jim360]

Tell me what you mean by parallel universe and I'll tell you if DM can be put down to that. But so far as I understand it, observationally Dark Matter tends to congregate nearish to Normal Matter (eg one of the reasons we predict its existence is to explain observations associated with other galaxies), so I think that makes it almost certainly a phenomenon associated with *our* universe, as opposed to an overlapping one.

[jim360]

// ... the "stuff" would be so completely different to what we know as matter that all our understanding of the chemistry of life etc would be similarly different.//

For sure -- *if* Dark Matter were capable of sustaining "life", whatever "life" means would be something very different for them as opposed to us. So I don't want to rule it out entirely because it's simply impossible to say anything meaningful about something you don't have any handle on other than knowing that it's there -- but the most sensible guess is that Dark Matter is too exotic (or too boring) to lead to anything we could meaningfully call "life".

I think 5% in these calculations is enough that, if you were capable of making the observation at all, you'd probably notice that something was missing. But again it's weird to assume that there's anything out there capable of "noticing", so it's hard to say.