Thread: Dark matter?

I have been watching videos and reading quite often about the universe and its galaxys.Does any know or have any theorys on what exactly this Dark matter is?

I can say that no one knows what it is. That's why it's still called dark matter. And, no, I have no serious theories about what it might be.

As far as I know, from what I have read, we don't really know what dark matter is. We have calculated it's existence from formulas, and "seen" it via gravitational lensing that it provides. So we know it exists, but in what form we don't really know.

There is at least one group of scientists in, I think it is Montana, that have a lab deep underground in an old mine, that are hoping to detect a dark matter particle as it passes through the earth and their lab equipment. But they have yet to detect anything. Could be other groups doing the same thing elsewhere in the world.

I am not sure what the mystery is here.

When we look to the heavens we can ONLY see objects which
radiate EM energy; either in the optical region or other portions
of the EM spectrum. Since we know all, or at least most, luminous objects
in the sky have cooler objects nearby [like the planets around our sun]
we should expect that there are countless objects out there which do not radiate
and as a concequece we can not see. That is Dark matter.

If the amount of this Dark Matter is high enough, then eventually the cosmos
will begin a contraction back to a singualrity and another Big Bang.
Right now this seems unlikely given the recent observations that the
expansion is accelerating and thus not decelerating.

Sorry, but that's not dark matter. That's already accounted for in the measure of normal matter. Plus, all the matter in orbit around stars make up only a fraction of the mass of the stars themselves. In addition to the stars and the stuff around them, the interstellar dust and other such known sources of matter are accounted for when counting up normal matter versus dark matter. After everything we know of is taken in to account, we only come up with about 1/5 or 1/6 of the mass required to make galaxies spin the way we see them spinning (in addition to other confirming observations).

perhaps in and around black holes then? They seem like a prime suspect for dark matter wells, no? Do we already know enough about their mass from the stars and objects around them, or is that a bit skeptical too?

Originally Posted by mysticmager1

I have been watching videos and reading quite often about the universe and its galaxys.Does any know or have any theorys on what exactly this Dark matter is?

Circa 1930 Zwicky,a Swiss Astronomer,reported seeing outer stars in an elliptical galaxy moving at 400 times the expected velocity for stars located at the rim. Zwicky concluded as there was insufficient force of gravityto moderate the excessive speeds there must be another source of gravity force, i.e. mass, that was accountable for the anomolous velocity spectrum.

Since then, there have been other observations confirming the estimated value (gravitational lensing).

Anyway, black holes are well enough understood to count them into the known matter. Plus, while they don't emit light at all, they're not exactly hidden. Their strong gravity makes them fairly obvious once you know what you're looking for.

No one has been able to come up with a testable theory yet on dark matter. It's a bit skeptical, but a few friends and I have been working on a theory in our class with our teacher on a certain theory pertaining to dark matter. In general, we are trying to find evidence or mathematical proof that dark matter is the matter in a parallel or alternate universe.

We are trying to prove that mathematically (since we know mathematically and theoretically alternate/parallel universes are possible) that their matter would be able to be detected by our technology. Our theory states that was we perceive to be as an unseen matter, is really the visible matter in that other universe. It is a working theory, so please give us your suggestions or comments.

Up to now, "Dark Matter" is a pure hypothesis derived from the apparent lack of normal matter causing gravitational forces. There are even a number of groups trying to figure out a possibility to explain the observed phenomena without the need of additional matter. So, in the end it may be that there is no "Dark Matter" after all, but the gravitational laws have to be modified instead. As far as I know, there is a lot of discussion going on about whether or not these alternative gravitational theories can account for the observed phenomena so far. But promising approaches exist that seem to be able to explain galactic rotation curves, gravitational lensing and the structure of the cosmic microwave background without the need for any "Dark Matter".

I can't say either way, of course, but if the ideas behind string theory make sense, then dark matter being matter in other branes would make sense. After all, string theory got started when they tried to explain the weakness of gravity by spreading it across extra dimensions. Pure speculation at this point though, and probably less testable than other ideas.

DM comes down to redshift. If stars in our galaxy are not rotating as fast as is believed (ie: a component of their redshifts is down to gravity between us and them) then DM is not needed.

Then again one second of arc on Earth is just 102 feet and at that scale, the Earth is flat. One second of arc of our journey around the galaxy is 855,211,333,477 miles which takes us 181 years to complete, so the Earth is travelling in virtually a perfect straight line. Residual circulation of the galaxy would just mean that over time the galaxy is very slowly getting ever larger rather than the wrong idea that things would just head off in a straight line (which does not happen).

Look at any picture of a spiral galaxy and it is shaped as though there is only light matter. No strange holes, bulges, etc which cannot be accounted for. If DM is in the halo, at maybe six times the mass of light matter, we would expect such galaxies to be ring doughnut shapes.

Some links:


http://www.cosmosmagazine.com/node/2289/full


http://www.sciencedaily.com/releases...1022154644.htm


.

Originally Posted by MagiMaster

I can't say either way, of course, but if the ideas behind string theory make sense, then dark matter being matter in other branes would make sense. After all, string theory got started when they tried to explain the weakness of gravity by spreading it across extra dimensions. Pure speculation at this point though, and probably less testable than other ideas.

The problem with strings is that they are just too small. Basically go down to the smallest thing we can see now. Then go down that far again, and that far yet again. It is difficult to believe anything that small could affect even a proton. It would be like a proton affecting something a tenth of a light year across.

As of yet, we have no evidence for more than three physical dimensions. A lot of people left string theory several years back, complaining it was a scientific dead end. But people still work in the field and still produce papers.

Who is to say that Dark matter is not a problematic estimation of behavior built around a complete misunderstnading of the fabric space itself.

Originally Posted by Cyberia

Originally Posted by MagiMaster

I can't say either way, of course, but if the ideas behind string theory make sense, then dark matter being matter in other branes would make sense. After all, string theory got started when they tried to explain the weakness of gravity by spreading it across extra dimensions. Pure speculation at this point though, and probably less testable than other ideas.

The problem with strings is that they are just too small. Basically go down to the smallest thing we can see now. Then go down that far again, and that far yet again. It is difficult to believe anything that small could affect even a proton. It would be like a proton affecting something a tenth of a light year across.

As of yet, we have no evidence for more than three physical dimensions. A lot of people left string theory several years back, complaining it was a scientific dead end. But people still work in the field and still produce papers.

First, I didn't say I believed this to be true. There's no evidence for it either way as far as I can tell. Strings are, as you say, much much smaller than we can detect.

Second, on some levels, I agree that it's hard to imagine something the size of a proton affecting something that size, except that the solar system is made of protons, neutrons and electrons, so I can kind of imagine the possibility there's something else.

I think I had a third point, but I forgot what it was...