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Could Dark Energy be Dark Matter cooling?

by Reverend2010
Tags: dark energy, dark matter
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nikkkom
#37
Sep10-12, 04:35 PM
P: 611
Gosh. It's really not *that* complicated.

We already know one "dark matter" particle: it's neutrino. It has mass, but does not interact electromagnetically. If a narrow beam of one solar mass of neutrinos would fly through Solar System, we wouldn't see it, but sure as hell we will feel its attraction. (Thankfully, neutrinos never travel in such humongous massive tight beams)

So dark matter not merely CAN exist, we know it DOES EXIST, at least a part of it, and we are pretty confident what it is. It is not mysterious.

But since we also are pretty sure that (known) neutrinos alone can't explain what we see, it's not too difficult to postulate that there exist other similar particles: ones which have mass, but do not interact electromagnetically. To match observations, we postulate that these particles are more massive than (known) neutrinos.

So why are you guys so freaked out by "mysterious" dark matter? Are you feeling the same about neutrinos? I think not...
twofish-quant
#38
Sep10-12, 10:46 PM
P: 6,863
Quote Quote by nikkkom View Post
But since we also are pretty sure that (known) neutrinos alone can't explain what we see, it's not too difficult to postulate that there exist other similar particles: ones which have mass, but do not interact electromagnetically. To match observations, we postulate that these particles are more massive than (known) neutrinos.
It is in fact *very* difficult to postulate that there are other similar particles.

Basically you start off with one equation that describes how particles behave. It's very, very difficult to add a new particle without causing the equation to either predict things that we don't see or be inconsistent theoretically.

One particular problem with massive particles is that massive particles will decay into less massive particles unless there is something that prevents that from happening. For example, there is something called baryon number. Because the proton is the lightest particle with a non-zero baryon number, it can't decay to something lighter. However heavier particles can and do decay into the proton.

So if you invent a "heavy particle" you are going to have to mathematically describe how that particle interacts with other particles, and this is rather difficult to do without tripping of something that we already know

So why are you guys so freaked out by "mysterious" dark matter? Are you feeling the same about neutrinos? I think not...
Everything is easy until you know why it's hard. The bottom line is that you just can't randomly add a particle. Adding a particle is like adding an element in the periodic table. If you want to add something at the end, no problem. If you want to add something between carbon and nitrogen, big problem.

You can graph the known particles and the form a nice chart. There is no obvious place to put another particle. You can assume that there is a heavier neutrino, but that means you need a heavy quark and all of that violates experiments that say that you have only three families of particles.
nikkkom
#39
Sep11-12, 12:57 AM
P: 611
Quote Quote by twofish-quant View Post
It is in fact *very* difficult to postulate that there are other similar particles.

Basically you start off with one equation that describes how particles behave. It's very, very difficult to add a new particle without causing the equation to either predict things that we don't see or be inconsistent theoretically.
You did not understand me.

I am not saying that to add a particle to the Standard Model is very easy. I am somewhat familiar with the math involved, I know that it's not trivial.

I am saying that some people seem to think that postulated dark matter is a very unusual kind of matter we never saw before, and thus they find it hard to believe it may be a viable theory. But dark matter is not something unlike we ever saw before - neutrinos are similar to it, and we know about neutrinos for what, 80 years already.
nikkkom
#40
Sep11-12, 12:59 AM
P: 611
Quote Quote by twofish-quant View Post
You can graph the known particles and the form a nice chart. There is no obvious place to put another particle. You can assume that there is a heavier neutrino, but that means you need a heavy quark and all of that violates experiments that say that you have only three families of particles.
Well, how about right-handed, so-called "sterile neutrinos"? Seesaw mechanism which gives them large mass? People are working on such models right now...
twofish-quant
#41
Sep11-12, 03:16 AM
P: 6,863
Quote Quote by nikkkom View Post
I am saying that some people seem to think that postulated dark matter is a very unusual kind of matter we never saw before, and thus they find it hard to believe it may be a viable theory.
Dark matter passes the principle of "least weirdness". It's weird but everything else is even weirder.

But dark matter is not something unlike we ever saw before - neutrinos are similar to it, and we know about neutrinos for what, 80 years already.
We know that ordinary neutrinos are *not* similar to dark matter. You can invent something about weird neutrinos. One other thing is that even if you restrict yourself to baryonic matter, most of that material is dark.

Well, how about right-handed, so-called "sterile neutrinos"? Seesaw mechanism which gives them large mass? People are working on such models right now...
Yes, exactly....

http://arxiv.org/pdf/1102.4774.pdf

http://arxiv.org/abs/1204.3902

But the point here is that you just can't invoke a new particle. Every time you invoke a new particle you have to do a ton of work to justify that new particle.
nikkkom
#42
Sep11-12, 03:24 AM
P: 611
Quote Quote by twofish-quant View Post
We know that ordinary neutrinos are *not* similar to dark matter.
Are you argumentative a-hole or something?

I am not going to argue what level of similarity is required to qualify for word "similar".

If you think neutrinos are sufficiently different from hypothetical dark matter particles (they have different mass! wooo hooo) so that word "similar" can't be applied, feel free to think that way. I don't care.

One other thing is that even if you restrict yourself to baryonic matter, most of that material is dark.
"Dark matter" is a misnomer. It is not in fact dark, it seems to be transparent. Baryonic matter is not. Even as a dilute gas, it is detectable by observations in EM.
Chronos
#43
Sep11-12, 05:11 AM
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Neutrinos are very 'hot' compared to dark matter. The only DM models that appear to work require non-relativistic velocities.
twofish-quant
#44
Sep11-12, 09:34 PM
P: 6,863
Calm down.

Quote Quote by nikkkom View Post
If you think neutrinos are sufficiently different from hypothetical dark matter particles (they have different mass! wooo hooo) so that word "similar" can't be applied, feel free to think that way. I don't care.
This is the problem with these sorts of arguments. You see two things and they are "similar". I see the same two things and they aren't.

Now there are reasons why neutrinos don't look the same as other particles to me is that I did a lot of research on neutrino radiation hydrodynamics. To me saying that the dark matter particle and neutrinos are similar because they both interact with the weak force only is like saying that a bowling ball and an orange are similar because they are both round. This doesn't make much sense to a professional bowler or an orange grower.

Now I'm not going to get annoyed if someone says that things look similar. Just don't get too annoyed at me if I tell you that they don't look similar to me, because they don't.

Remember ***you*** are the one that asked:

So why are you guys so freaked out by "mysterious" dark matter? Are you feeling the same about neutrinos? I think not..
Now I answer the question by saying, WIMP's may look like neutrinos to you, but to someone that has researched neutrinos for a decade, they look very different to me. Now if they look the same to you, that's fine, but you asked the question.

"Dark matter" is a misnomer. It is not in fact dark, it seems to be transparent. Baryonic matter is not. Even as a dilute gas, it is detectable by observations in EM.
If it's not ionized or not in compact bodies. Ionized hydrogen is quite difficult to detect. One interesting thing is that if you add up all of the baryonic matter that we can account for, it's still much, much less than the amount that we infer is out there from cosmology.
ibysaiyan
#45
Sep16-12, 10:05 AM
P: 442
Quote Quote by JcX View Post
The idea of dark matter comes from mathematical model of gravitational force.
Scientist suggests that there must be matter that we don't see in our universe, maybe between galaxies that exert the gravitational effects that we feel.
The content/percentage of dark matter is chosen to fit and balance all the gravitational effects that has been observed in the universe (expansion of universe, perturbation of orbits, etc).
We predicted the existence of them, but we can't be really sure of what dark matter is.

Some theories such one those who suggest multi-dimensional universe says that dark matter is actually some matters in other universe. String Theory says that only gravitons are able to escape from the membrane of the dimension, hence only gravitational forces are able to penetrate between dimensions. Living in this dimension, we can feel the gravitational effects from other dimension, but we don't see them, that's why we called them Dark Matter.
That's one of the explanation that I liked a lot... although...... it's hard to imagine.
Is it ?
I was led to believe that it was more of an observational find rather than resolving a mathematical discrepancy.

We are trying to answer the accountability of mass surrounding the center of galaxies. Basically , Astronomers assumed that mass density (hence radial speed) would decrease as the distance from the galactic radius increases , however, to their surprise it did not and stayed fairly constant.

There are various contenders of DM: Mainly the WIMPs , MACHOS however recent studies highlight towards WIMPs.


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