Dark Matter

[gfish]

I'm not a astrophysicist or anything, but am I the only one who finds the whole dark matter thing rather dubious? It just smells of hand-waving kludge to me. Our observations don't match our calculations, so 95% of the universe must be made of invisible matter that only interacts with the rest of us through gravity? The universe is certainly a very odd place, but I just can't get over the feeling that this is the luminiferous aether all over again.

Comments

[sistawendy.livejournal.com]

It does make the needle twitch on one's bogometer, doesn't it?

[jeffreycornish.livejournal.com]

Well, the problem is that you need dark matter to hold the whole thing (galaxies, clusters of galaxies) together, and to explain the flat rotation curve of most galaxies (the starts orbiting on the out fringes orbit just as fast as the stars near the core).

I consider it a wonderful mystery.

Now, quantum mechanics, that's spooky

[gfish.livejournal.com]

Oh, there's certainly something weird going on. I'm just not convinced by this explanation.

[gement.livejournal.com]

I've always thought of it as a conscious handwave, but perhaps I have misunderstood. But I thought it was "this makes the numbers add up, even though it doesn't make any sense. So we'll just leave that as a placeholder until someone comes up with something smarter."

[randomdreams.livejournal.com]

Einstein certainly seemed to feel it was conscious hand-waving, from what I've read. It smells like string 'theory': while it could explain some things we see, I'm really hoping for a cleaner explanation.

[stellar-dust.livejournal.com]

Apparently you can solve it by introducing infinite time dimensions (http://www.stanford.edu/~afmayer/)? Or something? Someday I will have time to go through his lectures, and/or read his (apparently upcoming) book.

[gfish.livejournal.com]

Yeah, that was one of the things that started me thinking about it recently (also this BBC article (http://news.bbc.co.uk/2/hi/science/nature/4679220.stm)). I was able to stumble through the lectures somewhat, and it certainly looks like a nice and elegant solution to a lot of little problems. But my relativity-fu is pretty weak, so I can't say much about the validity.

[ivy]

Big disclaimers about mapping intuition to physics, but... it never particularly made sense to me that we should have multiple space dimensions and one time dimension. I think the difference is most likely a matter of our perception. Even in the more recent takes on superstring theory, it's usually phrased as "nine space dimensions and one time", or, with supergravity, "ten space dimensions and one time". Holding on to one time dimension seems more likely to be an artifact of our measuring process.

Of course, this is based in no scientific data whatsoever, and I could be totally wrong.

[stellar-dust.livejournal.com]

I've had similar thoughts myself, which is one reason why this theory makes intuitive sense to me, too. ... But I haven't given it nearly the attention it deserves yet.

[tfabris.livejournal.com]

I see where you're coming from, and I agree it sounds like a kludge. But in the science of astrophysics, there's a lot that we still don't understand and we're still at the theorizing stage for so much of it. It's a young science.

Dark Matter is a theory. I agree that it sounds like we need a better one. But that's the beauty of science: You come up with a better theory and try to test it. So there could very well be a better competing theory comin' 'round the bend any day now.

I find that I don't get hung up too much on theories related to astrophysics, because I know that those theories are at a different level of solidity than ones found in, say, biology, or regular physics.

[rigel-p.livejournal.com]

>I find that I don't get hung up too much on theories related to astrophysics, because I know that those theories >are at a different level of solidity than ones found in, say, biology, or regular physics.

Gotta take some exception to that one. Admittedly, astrophysics is a lot harder because it is strictly observational- you can't actually crash two galaxies together to see what happens, you have to wait 'till it happens in nature, you only get one viewing angle, and you only get to view about 0.00001% of the total run of the "experiment". HOWEVER, I don't think that sends scientific rigor out the window. Biology has some well-established, demonstrable tenets. So does Astrophysics. Astrophysics has some rough new ideas that haven't been polished out to reliability yet. So does biology.

Try this: Take a bouquet of red and white pea blossoms (sweet pea will do in a pinch) to your favorite biologist, and ask them this: My mother has blue eyes, my father has blue eyes, my siblings and I, biological children of both, have brown eyes. Why?

[ash-blackwell.livejournal.com]

There is dark matter out there (planets count), but yeah, it's mostly a placeholder thing.

[peteralway.livejournal.com]

I feel a whole lot better about dark matter than I do about dark energy.

And while dark matter is a pretty vague concept, at least the name suggest that it's more of a question than an answer. A reasonable shorthand for "we don't know what's there but as far as we can tell there must be something." I think if it had a fancy latin or greek name or an acronym, I'd feel more that it was a deceptive answer. If someone called it "Umbratonium," it would sound a whole lot more like someone was hiding their ignorance.

[ivy]

[laughs at "umbratonium"] Not to mention that that sounds like a really heavy atom, which could lead to all kinds of unfortunate assumptions.

[peteralway.livejournal.com]

Well other candidates are Necronium, Occultonium, and Cryptonium--I thought Umbratonium was the least loaded of the shadowy names I could come up with.

$0.01

[rigel-p.livejournal.com]

I'll second that.

"Dark matter" as I understand it is a slang term for the as yet unknown answer to the question "Why does everything really big move as if it were a lot more massive than we observe it to be?"

Planets and non-glowy stuff was a first suggestion, but doesn't account for nearly enough mass- you run in to problems where as the proposed density of cold stuff increases to fit the required mass into the required space, you start to get absorbtion and re-emission effects. (eg, the view of the (bright) center of our galaxy is visible-light dim from here due to dust in the way, but you get a big radio signal)

http://astron.berkeley.edu/~mwhite/darkmatter/dm.html has much better clue than I.

Theories as to what it actually is range from the complicated to the truly wacky, but that's normal for a new question. It takes a while to figure out what question you're asking, let alone test the answers that people come up with.

[mathochist.livejournal.com]

I'm totally with you.
The matter we can see doesn't act according to what our equations say.
Conclusion: there must be a whole bunch of matter we can't see.
Huh???
Makes a hella lot more sense to me -- a lowly physics B.A., math B.S., and math M.S. -- to conclude that our equations are wrong.

[tfabris.livejournal.com]

Or...

Conclusion: Our equations might be wrong, or might make assumptions about the nature of matter and gravity that are incorrect...

[book-addict.livejournal.com]

See, I was going to say something here, but all the points I would have made have been covered already.
So it's left to me to point out just how very little one is expected to question these sorts of entities in the course of an astrophysics B.Sc. "There's this dark matter, because it explains the observations, and it's not your place to ask what it actually is..." or something like is that pretty much sums up my undergraduate third year.

In this case, it could be a particularly nonluminiferous aether.

[olafthunderfoot.livejournal.com]

~sits back with a beer~ yup!

[tfabris.livejournal.com]

I haven't read into all the sub-threads here, so this might have been mentioned already. Forgive me if this is a repeat:

http://www.pparc.ac.uk/Nw/EinsteinTheory.asp