Why do people think dark matter is at absolute zero?

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Evan Martin

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Evan Martin  asked the Naked Scientists:
   Hello from Arizona in the US! I have been listening to your podcast "Naked Astronomy" for about a year now and it's inspired me to study astronomy in the hopes of being an astrophysicist. I'm currently taking an astronomy class and reading the chapter in radiation. My question is as follows.

If an object at absolute zero emits no thermal radiation, why don't scientists believe that the extra mass in galaxies (that we call dark matter, because we can't see it, but can detect through optical lensing, and mathematical models) is matter at absolute zero?
What do you think?
« Last Edit: 08/09/2011 22:30:02 by _system »


Offline Soul Surfer

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Why do people think dark matter is at absolute zero?
« Reply #1 on: 11/09/2011 20:45:15 »
In general dark matter is not considered to be at absolute zero.  When people refer to cold dark matter it is just cold in comparison to a star or most other material in the galaxy various temperatures have been considered and as there may be several types several temperatures or a range of temperatures may be considered.  There are also theories which involve warm dark matter.
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Why do people think dark matter is at absolute zero?
« Reply #2 on: 11/09/2011 23:04:59 »
Absolute zero is a classical (macroscopic you might say) definition of a state without motion. Motion is a result of distances measurable in time and as we scale down to QM we find that those definition lose their meaning. According to HUP we meet uncertainty as we scale down, making it impossible to define all variables of a thought up 'point' or object. That uncertainty is also what makes it possible for particles, virtually or not, to tunnel and have a infinite 'energy'.

So as we scale down, motion disappear, interchanged by probability as defined from our statistical experience of what happens when treating those occasions over a longer period of macroscopic time.

But macroscopically we have 'motion' and so, as a macroscopic symmetry, we find 'no motion' too.
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