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Offline DrQuincy

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What is the coldest temperature in the Universe?
« on: 08/05/2008 08:29:08 »
Tim Bennett asked the Naked Scientists:
What is the coldest temperature in the universe? I know radiated heat can travel through space (i.e. a vacuum) but does this heat reach every part of the universe?

Is there a minimum temperature any given point in the universe will be?


What do you think?


 

Offline syhprum

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What is the coldest temperature in the Universe?
« Reply #1 on: 08/05/2008 09:46:30 »
The lowest naturally occurring temperature in the universe is that of the CMBR i.e 2.73K but in the laboratory temperatures in the order of micro Kelvins can be produced.
 

Offline na na

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What is the coldest temperature in the Universe?
« Reply #2 on: 08/05/2008 12:40:00 »
I would have to assume that if there is no "maximum" temp, there is no "minimum" temp.
 

Offline techmind

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What is the coldest temperature in the Universe?
« Reply #3 on: 08/05/2008 13:45:40 »
I would have to assume that if there is no "maximum" temp, there is no "minimum" temp.

No, the minimum possible temperature anywhere in our universe is "absolute zero", 0 Kelvin (-273.15 Celcius).

This can be inferred from many physical measurements, not least Charles' Law http://en.wikipedia.org/wiki/Charles%27s_law
which relates the volume of a fixed quantity of gas to its temperature. From measurements at easily-available temperatures (eg 0C and 100C) the graph can be extrapolated backwards, and reaches zero volume at -273 Celcius.
 

Offline Pumblechook

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lyner

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What is the coldest temperature in the Universe?
« Reply #5 on: 08/05/2008 15:11:44 »
You can have unlimited energy in a box (subject only to practicalities) but you can't have less than none. Temperature is the average energy per molecule - so 0K is the minimum. Don't be misled by the scale, which has equal steps for equal steps in energy but doesn't represent equal steps in difficulty of attaining that temperature.
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #6 on: 08/05/2008 15:57:53 »
The coldest temperatures in the universe are to be found in super-massive black holes - the temperature drops in proportion to the mass of the BH. 
 

lyner

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What is the coldest temperature in the Universe?
« Reply #7 on: 08/05/2008 16:19:50 »
That's interesting. This is an idea which must be very  theoretical. It would imply that the average KE of the particles is nearly zero. The density, being so high, would mean that the total KE inside would also be very high.
This sounds a bit like the fact that the highest temperature in the regions surrounding sun is actually the corona and not the surface. It's a matter of how temperature is defined, I think.
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #8 on: 08/05/2008 16:53:31 »
It is theoretical insofar as we haven't actually seen it, but it's implied by the  observation that a BH acts like a black-body radiator.

In the sun's corona, the temperature is a measure of the kinetic energy of the individual atoms, and in fact, a similar state exists within our own atmosphere.  While the kinetic energy of the individual atoms in the corona is higher than those on the suface of the sun, there are a lot less of them and subjectively, it would feel colder (were it not for the fact that you'd be right beside the sun).  The same thing occurs on the Earth where the temperature of the upper atmosphere is higher than it is at the surface, but because the upper atmosphere is so rarified it is subjectively colder.

With a BH though, it's temperature isn't a measure of the kinetic energy of the individual particles within it, because it is effectively just one single particle, but of how it radiates energy.  So yup, how you define temperature is relevent.

 

Offline Bored chemist

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What is the coldest temperature in the Universe?
« Reply #9 on: 08/05/2008 19:21:44 »
With the "right" deffinition of temperature the 2 energy levels of a laser during a population inversion represent a negative thermodynamic temperature. When the laser "fires" it returns to normal temperatures by going infinitely negative then falling back from an infinitely positive temperature.
This sort of result is only useful for annoying people trying to teach physics, as in 
"Please Sir, If the Boltzman distribution can be used to calculate temperature, surely the temperature in a laser can go negative and you just said temperatures can't do that.".
 

lyner

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What is the coldest temperature in the Universe?
« Reply #10 on: 08/05/2008 23:37:01 »
You've met that smartarse, too!
 

Offline Supercryptid

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What is the coldest temperature in the Universe?
« Reply #11 on: 08/05/2008 23:45:15 »
There is a theoretical upper limit to temperature called the Planck Temperature, whose value is ≈ 1.417 x 1032 Kelvins. Above this temperature, the particles that make up this superhot substance would collapse into black holes.

http://en.wikipedia.org/wiki/Planck_temperature
http://www.straightdope.com/classics/a3_347.html
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #12 on: 09/05/2008 00:56:04 »
I've got to confess that I've been more pre-occupied with looking at the apparent lower limits of resolution in the universe but the planck temp implies an upper limit too.  Hmm...

Even so, I'm not sure that 'collapse' is the right term to use here - perhaps it's better to think in terms of energy density.

...or perhaps not.  Dunno.

I find it very interesting that while BH's appear to have vanishingly small temperatures, as far as their black-body radiation is concerned, high enough temps can lead to a similar state, in terms of energy density.

So what would happen if you were able to heat a BH to the plank temp?  The attempt should just make it more massive, and therefore cooler.  Heh:) - Negative Energy becomes a requirement, looks at it's watch and decides that, once again, it's time to raise it's incomprehensible head above the parapet to check that nobody has spotted it yet:)
 

Offline science_guy

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What is the coldest temperature in the Universe?
« Reply #13 on: 09/05/2008 02:51:02 »
Quote
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.

0 kelvin, would usually mean NO energy, infinite energy is as far away as you can get from that goal.
 

Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #14 on: 09/05/2008 08:15:39 »
Just a little observation from someone who knows nothing about anything.

If nothing can escape from a blackhole then surely heat can't either. Doesn't that imply that the measurable temperature be absolute zero?

And as a supplementary - can absolute zero ever be measured? Wouldn't using something to make the measurements cause an increase in temperature?
« Last Edit: 09/05/2008 08:17:55 by DoctorBeaver »
 

Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #15 on: 09/05/2008 08:18:50 »
Negative Energy becomes a requirement, looks at it's watch and decides that, once again, it's time to raise it's incomprehensible head above the parapet to check that nobody has spotted it yet:)


 :D
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #16 on: 09/05/2008 16:22:19 »
I think that the temperature really only applies to the event horizon.

What I am curious about is that if gravitons are to exist, how do they escape a BH?
 

lyner

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What is the coldest temperature in the Universe?
« Reply #17 on: 09/05/2008 21:00:04 »
Quote
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.

0 kelvin, would usually mean NO energy, infinite energy is as far away as you can get from that goal.
What I meant is that, to get a refrigerator to cool a region to 0K, you would need infinite energy - nearer and nearer but never there. Very much like c.
 

Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #18 on: 09/05/2008 21:37:27 »

What I am curious about is that if gravitons are to exist, how do they escape a BH?


They jump the fence on a motorbike a la Steve McQueen!

 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #19 on: 09/05/2008 21:39:46 »
Heh - funny sometimes how the most obvious answers can elude you:)

 

Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #20 on: 09/05/2008 22:56:18 »
If I've got this right, gravitons are not theorised as particles that attract matter. What they do is warp spacetime. As such, they would not need to escape from the BH. Spacetime would be warped from within the BH and its warping would extend beyond the event horizon.

An analogy would be water going down a plughole. Nothing comes from the plughole into the water, but the water for quite a large area around is affected by the the hole "sucking" water into itself1.

1 I know that's not really what happens, but give me a break!
 

Offline shmengie

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What is the coldest temperature in the Universe?
« Reply #21 on: 10/05/2008 04:02:34 »
The condensate is cool! no, really, I mean it!

newbielink:http://www.google.com/search?q=bose+einstein+condensate&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a [nonactive]
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #22 on: 10/05/2008 19:03:43 »
I think the important thing about BHs is that whatever is inside the BH, that causes the distortion in spacetime, manages to exert it's influence outside the BH, which is something that nothing else that we are aware of is able to do.

The graviton only really makes sense to me if it distorts spacetime around itself, locally.  That way you can imagine gravitons being emitted by matter, propagating over time and following an inverse square law, falling off in intensity with distance.  But then we're back to how do they escape a BH?

Alternatively, a graviton could exist in a different number or set of dimensions, one or more of which could intersect the set of dimensions that make up our spacetime.  For example, a two-dimensional plane can intersect a three dimensional volume and fully occupy two of the dimensions but none of the third.

As such, you could speculate that a hypothetical two or fewer dimensional object may not be subject to laws that govern the behaviour of three-dimensional objects, or may only be subject to a subset of those laws.

Depending on how you mess with different dimensions, you could come up with different models for gravitons, from a stream of discrete particles, which when taken together produce a field, to the field being the expression of the entire life time of a single particle, with it's time-line dimension being mapped to our spatial dimensions.
 

Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #23 on: 10/05/2008 19:15:03 »
Yeah - that BEC is fascinating stuff, but not quite as cold as the temps theorised for supermassive BHs.  There's an interesting experiment described in the 'Unusual characteristics' section in the wikipedia article:)

http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate
 

Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #24 on: 11/05/2008 00:17:22 »
LeeE - have you come across the Randall-Sundrum warped extra dimensional theories of gravity? Or localisation?

Either of those could possibly explain how gravity "escapes" from a BH.
 

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What is the coldest temperature in the Universe?
« Reply #24 on: 11/05/2008 00:17:22 »

 

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