The Case for Complex Dark Matter

King Neptune said:

"wrong-headed"!!! Does that mean that I attacked a religious truth of yours, or what?

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No, it means you don't appear to know what you're talking about. For starters, you've confused dark matter and dark energy. Religion didn't ever come into this discussion; you have science facts wrong, therefore I called your arguments "wrong-headed".

King Neptune said:

Did you notice the paragraph from an article in The Economist about this matter?

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I like to get my science from scientific papers published in peer-reviewed science journals by scientists, not from journalists who report on the economy.

If you make a claim, the burden of proof is on you. Right now, you're claiming that the analysis of data done by trained, appropriately-educated experts is wrong because you don't aesthetically like their conclusions. You need more than that, and more than a link to an article from The Economist (that you appear to have misunderstood), to convince anyone you aren't simply incorrect.

Why is this thread getting as bad as the politics board? Let's just agree to disagree. If you don't believe dark matter exists, then this thread should be of no interest to you, because the original topic was whether the nature of dark matter is this or that.

King Neptune said:

Ever since dark matter was introduced I have wondered why people are looking for it to be anything other than cold, ordinary matter. It is dark simply because it does not emit light, so it can't be seen; it can only be detected through its gravitational effects on other matter that can be seen. .

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Ah, but "dark matter" isn't really dark. It's invisible. Light passes through it, because it does not interact with electromagnetic energy. There's all kinds of cold dark ordinary matter in the universe, but it blocks light. Not the same thing.

As just one famous example:

http://www.atlasoftheuniverse.com/darknebs.html

caw

Probably a stupid question, but here goes. Imagine a wall made of dark matter. Could I bump into it and hurt my head?

morngnstar said:

Why is this thread getting as bad as the politics board? Let's just agree to disagree. If you don't believe dark matter exists, then this thread should be of no interest to you, because the original topic was whether the nature of dark matter is this or that.

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Apparently some people don't understand the difference between hypothesis and fact. There are a number of hypotheses about the nature of "dark matter", and some take their hypotheses very personally.

Personally, I suspect that eventually it will be found to be something completely different, but we will have to wait to see.

Teinz said:

Probably a stupid question, but here goes. Imagine a wall made of dark matter. Could I bump into it and hurt my head?

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No one knows for sure.

Introversion said:

The physicist James Bullock explains how a complicated “dark sector” of interacting particles may illuminate some puzzling observations of the centers of galaxies.



Sometimes the popular press likes to suggest that all the Big Problems in physics & cosmology have been All But Solved, but it certainly seems that the more we know, the more we realize that we don't know?

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Oh no, there are tons of unanswered questions including those that the media and the scientists like to treat as solved.....dark energy, dark matter, quantum gravity, string theory, black holes, the holographic universe, even gravity itself is yet to be explained....

Lee Smolin has written a lot on the problems of physics and I've written a couple of pieces on my blog as well.

Here's a piece in Discover Mag about the unanswered questions in Physics:

http://discovermagazine.com/2002/feb/cover

King Neptune said:

It is talking about both; although the emphasis is on dark energy, because there is more of it, apparently.

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And the two are very different things according to their current descriptions.

There is speculation, then there is hypothesis, then there is theory, then there is fact. A scientist will sit down and speculate about possible explanations for something. If one of them sounds like it makes more sense than "fairies and gremlins", he'll form an hypothesis, and suggest possible tests. If the hypothesis seems to pass some tests, it becomes a theory. The more tests it passes, the more "generally accepted" the theory is.
Generally speaking, theories don't become "facts." The Theory of Gravity is still just a theory, even though gravity is a fact. The statement that something is out there that's affecting galaxies is a fact, and we label that fact "Dark Matter." There are several theories about what "dark matter" might be, but the phrase "dark matter" is just a placeholder for whatever it is.
However, having said that, CDM has failed the falsification tests. If someone wants to posit CDM as an explanation, they're going to have to come up with a new (and complicated) explanation for why it's CDM, but fails the tests that have been done. In the end, that hypothesis will probably be more complicated and less elegant than the WIMP theory.
Personally, I like to think that it's normal matter, separated from our universe in some additional dimension, so that we can interact gravitationally but not otherwise. But that's just a personal preference and I'm certainly not going to try to defend it.

Angry Guy said:

However, having said that, CDM has failed the falsification tests. If someone wants to posit CDM as an explanation, they're going to have to come up with a new (and complicated) explanation for why it's CDM, but fails the tests that have been done.

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What tests? Unless there is something I haven't heard, Lambda-CDM is still the prevailing cosmological theory. That's still not saying much. CDM is still just a placeholder. It just says that it's cold (not very energetic) and dark (doesn't interact electromagnetically).

morngnstar said:

What tests? Unless there is something I haven't heard, Lambda-CDM is still the prevailing cosmological theory. That's still not saying much. CDM is still just a placeholder. It just says that it's cold (not very energetic) and dark (doesn't interact electromagnetically).

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Maybe it's a misunderstanding on my part, but I've always thought of CDM as normal baryonic matter, as opposed to the WIMPy stuff. Just cold, and therefore dark.

Angry Guy said:

Maybe it's a misunderstanding on my part, but I've always thought of CDM as normal baryonic matter, as opposed to the WIMPy stuff. Just cold, and therefore dark.

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That is my understanding also, but it is just one hypothesis. Until it will be a settled matter, I will remain open-minded about it; although I have a theory that I prefer.
https://en.wikipedia.org/wiki/Cold_dark_matter

King Neptune said:

That is my understanding also, but it is just one hypothesis. Until it will be a settled matter, I will remain open-minded about it; although I have a theory that I prefer.
https://en.wikipedia.org/wiki/Cold_dark_matter

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Um. I see that I bungled that explanation. What I meant was that when I say "CDM", I'm referring to normal matter of the cold, dark variety. Of which there is plenty, and which is very easy to detect. I don't believe that "Dark Matter" is normal baryonic matter that we haven't detected, simply because we HAVE detected normal baryonic matter, including the really really thin, really really cold stuff between galaxies. Which means that in order for Dark Matter to be normal baryonic matter that we haven't detected, it would have to be even thinner than the stuff that we HAVE detected, yet at the same time consist of thousands of times the mass of the stuff that we've already detected. In order to make that work, you'd have to posit some special state of matter that's undetectable despite being otherwise eminently detectable. Once you start invoking special states, how's that better than Dark Matter?

King Neptune said:

No one knows for sure.

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You know, nobody knows for sure that I don't have an invisible unicorn sitting on my head, but that doesn't mean there is one. The fact that no one knows for sure isn't evidence of anything; it's empty words.

The balance of evidence is that dark matter is not cold baryonic matter. If you don't want to change your mind, that's fine, but you're not changing anyone else's mind with an opinion. And so, I will stop arguing with something you take on faith.

On that Wikipedia page, it says that WIMPs are one possible candidate for CDM. The only candidate mentioned that is made of normal matter is MACHOs, which have been ruled out by gravitational lensing surveys.

Angry Guy said:

Um. I see that I bungled that explanation. What I meant was that when I say "CDM", I'm referring to normal matter of the cold, dark variety. Of which there is plenty, and which is very easy to detect. I don't believe that "Dark Matter" is normal baryonic matter that we haven't detected, simply because we HAVE detected normal baryonic matter, including the really really thin, really really cold stuff between galaxies. Which means that in order for Dark Matter to be normal baryonic matter that we haven't detected, it would have to be even thinner than the stuff that we HAVE detected, yet at the same time consist of thousands of times the mass of the stuff that we've already detected. In order to make that work, you'd have to posit some special state of matter that's undetectable despite being otherwise eminently detectable. Once you start invoking special states, how's that better than Dark Matter?

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That's what I thought you meant.