Questions on Dark Matter?

Question

Is dark matter normal matter or a special type of matter?

is it dark because it does not reflect any light.(obsorbing all, or letting it pass through) or is it dark because there is no light to reflect? (i.e. no sun to brighten it)

Since it has gravity, has it condensed into lump's, planets and 'dark' suns?

and why is there so much of it when comparing the percentage to the amount 'bright' matter in our galaxy?

if its not made of neutros protons and electrons? why is it considered matter? simply because it has mass?

Answer 1

To answer your questions in order:

1. Dark matter is "special" in the sense that it is not made of protons, electrons, neutrons, or any other known particle. But since there's more of it than protons, electrons, etc., we should be calling ourselves the "special type of matter."

2. It is dark because it does not interact with the electromagnetic force in any way. Dark matter does not absorb or emit light at all. It is completely transparent.

3. It has condensed into lumps; we call them "galaxies." It is too hot to condense into objects smaller than galaxies.

4. Science doesn't answer "why" questions, only "what" and "how" questions.

5. Yes, we call it matter because it has mass. If it were made of protons, neutrons, or electrons, or indeed any electrically charged or magnetically polarized particles, then it would emit and absorb light.

6. Unlike the Ether, there are many multiple, completely independent lines of evidence to support the existence of dark matter. It's not just galaxy rotation, although that is one of the lines of evidence.

Answer 2

You are right on your question. But to understand why, you need to know why and how it has been proposed first.

When astronomers calculated the mass of the entire universe, of course in great approximation and only measuring certain part of it, they saw that the total gravitational power which keeps objects together, which is also approximately calculated, does not match with the amount of mass they have calculated.

Then some said, oh then probably we do not see all the matter of the universe. Then some hypothesized that there could be a form of matter which does not interact with light (or any type of EM) therefore invisible. There the word dark matter was born. So it's a hypothetical substance. Not quite like our ordinary matter. They cannot know the content or what it looks like. They only assume if its real, it creates a missing mass that generates visible gravitational effect within the universe.

Light or EM is abundant in universe. They calculate approx. 200 trillion photon per cubic meter empty space in darkest part of the universe, so it is certainly not lack of light, but this hypotetical mass does not interract with light.

Nobody really knows if DM is real or how much it is, it's just assumption and approximate calculation based on limited observations. It is possible that they could find a way to interact with it in future, or another clever man could find oops there is an observation error or calculation error somewhere... All possible. This is fun of science.
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P.S. It's a long lost wisdom that some still believes science does not answer "why" but "how"... It's theoretically true, but practically wrong. Without "why" in the mind nobody would try to find answer to "how". So actually the "why" question is the starting point of science. But at the end you cannot answer to "why" but you describe "how" in possible ways. Because you know "why!" but as long as it's a theory of how, you pretend not answering to "why".
Think about dark-matter. The very first question comes to mind is not how dark matter creates missing mass. The first question is why there is discrepency between mass and gravitational effects? You can't even rephrase the question to ask something like how in the hell mass does not match the grav? So the questions always start with why. But ends with explaining "how" for being MODEST.

Answer 3

Thinking about your last question about 'why', I can only tell you what scientists think is going on. Effectively, when you look at a rotating object (any!), you can model various things about it using various angular momentum formulae.

So when you look at the earth going round the sun. You can imagine that it is like a ball on the end of a rope being swung round. Various equations must hold for any body in angular rotation.

The reason dark matter comes about is because the formulas fail when we look at how galaxies rotate. It all comes down to the fact that galaxies simply do not contain enough mass for them to rotate the way they do.

Hence, it's is postulated that there is 'dark matter'. Matter that has mass but we can't see it for some reason. This additional matter means that the equations hold.

There is a lot of research done on this, but one should never discount the fact that maybe current scientific thinking is completely wrong. After all, it was only a hundred years ago that scientists were convinced that the universe was filled with a substance called 'ether' which provided a frame of reference for movement. Mr Einstein disagreed. 100 years later, ether is just a historical footnote.

Answer 4

Dark matter is found in the brains and models and theories of cosmologists. It is invented because without it their models of Big Bang more than13 billions of years ago would not fit the observable universe. Dark matter can not be seen and was not found yet. And even if there is dark matter somewhere it is not enough to explain why the spiral arms of rotating galaxies have such a shape after so many billions of years. So the term "dark energy" was invented to help to keep alive the theory of Big Bang. Something has to hold the galaxies together. They don't know what. But to speak about dark matter and dark energy sounds a bit more "scientific" than to admit that that Hubble Space Telescope has brought more new questions to the preconceived theory than answered the open questions.

Answer 5

I wish to reply to some of the not fully correct statements made and hopefully with a clarification.

Dark matter is considered matter because it interacts via the gravitational force, it has mass. For those who say that it doesn't interact with light in the same way normal matter does sounds quite foolish. Normal matter is a subset of massive particles, quarks, leptons, etc. Some of these particles directly interact with light, and some only interact, at the low energies that we live, in the manifestation of the weak or strong forces. One example would be the neutrino, this is a "normal" matter particle that doesn't interact via the electromagnetic force. So the are some "normal" matter particles that behave in this sort of manor.

Also those that say that dark matter doesn't interact with light in any way are again making a "foolish" statement. In fact some of the most compelling evidence for dark mater is in its interaction with light, via the gravitational force. This is know as gravitational lensing. When the dark matter passes between us and a galaxy for example, the galaxy become brighter. I just wanted to show another bit of evidence as to the postulation on the existence of dark matter.

Dark matter was not "invented to save cosmology" as one poster mentioned. It is a theory to explain the observational evidence like that mentioned above.

Cheers,
Jason

Answer 6

Hello dear!

Well, since ancient times, Greeks have mentioned Aether. AETH has to do with dark! Since people South of Egypt were not white, the Greeks called it AETHIOPIA!

Further, Black matter and energy compose more than 90% of the Universe and it is very "solid", thus, certain wavelengths are transported "instantly", compared to the matter we know!

Answer 7

Its actually a bit of a misnomer. It should really be called "unknown matter". We know its there because of the effects of its gravity on things like stars that we can see. We know it is not normal matter because it does not interact with light in the way normal matter does. Bu we do not know what it is, except that there is a lot of it.

Answer 8

It has mass, but you probably can't touch or see it. Or smell, hear or taste it, for that matter, because it interacts so weakly with matter. It has gravity, though, so its presence is inferred using methods more sophisticated than the five senses directly - by it's gravitational interaction with regular matter that we can see.

Answer 9

You can read more on this here; its a quite interesting topic Dark matter and the even more strange 'Dark Energy'.

http://en.wikipedia.org/wiki/Dark_matter

Answer 10

does it matter? hehe