# The Naked Scientists Forum

### Author Topic: temperatur and vacuum  (Read 2909 times)

#### nordenskioeld

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##### temperatur and vacuum
« on: 26/01/2006 14:37:38 »
there are things about temperatur i don't understand:

1. temperatur in fact is motion of particles, what particles? atoms?

2. absolut zero means no motion at all, so there is no colder state possible, because there is not less motion than no motion, correct?

3. imagine some object in a vacuum, hold only by two tiny needles (in order to avoid motion coming from outside). so this object placed in a vacuum, what temperature will it have after a while? does it get colder because there are no particles hitting it?

thank you for helping me clearing my mind up on this & greetings from cold switzerland[:I]

#### DoctorBeaver

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##### Re: temperatur and vacuum
« Reply #1 on: 26/01/2006 17:49:14 »
The energy of the object would gradually radiate away as heat... I think

#### Soul Surfer

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##### Re: temperatur and vacuum
« Reply #2 on: 27/01/2006 00:10:22 »
Temperature is the motion of atoms and molecules.  This can be free motion as in gas molecules flying around and bumping into each other or constrained motion as in the vibrations and rotations of atoms in crystals.

Absolute zero is the coldest state possible but it does not mean that the atoms and molecules are still.  This is because many atoms and molcules are fermions ie they have half integer spins.  Now fermionic atoms and molecules cannot ocupy exactly the same energy level if they are in reasonable proximity to each other.  this means that higher energy quantum states have to exist even at absolute zero so there is always some moton.

If an object is thermally isolated and placed in a perfect vacuum.  the temperature that it finally adopts is dependant on the temperature of anything that surrounds the vacuum.  In a laboratory this would be the temperature of the vessel that contains the vacuum.  If it is in space it could be quite hot if the sun is shining on it but if it was deep space far away from anything else it woould cool down to a couple of degrees ot so above absolute zero because that's the temperature of the cosmic microwave background radiation.

The reason for this is of course thart all objects above absolute zero radiate electromagnetic radiation and although there are no particles in the vacuum there are plenty of photons.  Of course! how else would you expect your object to cool down or change temperature.

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#### sharkeyandgeorge

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##### Re: temperatur and vacuum
« Reply #3 on: 27/01/2006 11:18:01 »
i was going to argue but just read soulsurfers bio dosent seem much point now

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#### nordenskioeld

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##### Re: temperatur and vacuum
« Reply #4 on: 30/01/2006 08:51:01 »
thank you for your replies, it's more complicated than i thought, as usual, the same is true for my girlfriend

#### The Naked Scientists Forum

##### Re: temperatur and vacuum
« Reply #4 on: 30/01/2006 08:51:01 »