Cold

[ecoli]

what would it look like? would it BECOME light?

 

light has a finite amount of energy... lucky for us.

[reyam200]

so would it be a EM radiation. i assume a infinitly high fequiency(lol)but theres probably limits on that as well.

but if the laws of physics were broken then it wouldn't have a limit. would it?

 

im confuesd

[nathan322]

The problem with zero Kelvin is that if you could ever reach it and tried to measure it, the surrounding energy would fill it before you could measure it.

[swansont]

what would it look like? would it BECOME light?

 

No (you aren't the first person to ask that, and I wonder what would induce that thought). It would require an increasing amount of energy to speed something up as v approached c. The E vs v graph is asymptotic at v = c.

[starbug1]

As mentioned above, 0K would be the absence of energy - so what would we be achieving this 0K for?

 

Despite having no energy at 0 K, there still would (theoretically) be reactions taking place. So I think there is a purpose.

[Nashyboyo]

i think you've answered the question now guys, lets not reiterate. How about a cup of tea ?

[BigMoosie]

i think you've answered the question now guys, lets not reiterate. How about a cup of tea ?

 

Go away

 

Despite having no energy at 0 K, there still would (theoretically) be reactions taking place. So I think there is a purpose.

 

Surely the only reactions taking place would be exothermic so it would no longer be absolute zero?

[starbug1]

Surely the only reactions taking place would be exothermic so it would no longer be absolute zero?

 

Many theories have been proposed on this whole absolute zero problem. Chances are slim for us ever doing it, which is an open path for more speculation. I've heard of reactions taking place that would seem straight out of a sf story. Magnetic reactions, crazy side affects of relativity, anything that breaks the laws of physics, dynamics, whatever, is probable to happen during absolute zero. This is why it can't happen, theoretically, but I think it can be reached. Not on earth, not by humans, but it can be done.

[Klaynos]

One problem I see with achive 0K is that how do we know we've achived it unless we apply some outside energy to the system to check thefore moving away from the 0K point? Although I suspect people are working on this if it hasn't already been solved :|

[Morbid Steve]

One problem I see with achive 0K is that how do we know we've achived it unless we apply some outside energy to the system to check thefore moving away from the 0K point? Although I suspect people are working on this if it hasn't already been solved :|

 

That is correct, and is the only problem we have achieving it. It is impossible to achieve / and know that we have, for just the reason you have stated!

[Edtharan]

The reason you can never achieve absolute Zero temperature dose not need QM or the falability of our models of the laws of physics (our models can be broken at extremes but the reality out models are simulating can't) to prevent it.

 

To cool something you must move heat away from it. This heat has to have some where to go (Heat is a for of energy and energy can't be created or destroyed). So you must have something of a lower temperature so that the heat can move there. This means that to achieve a temerature of 0 kelvin then you must have something at a temperature lower than 0 kelvin.

 

If you think about this then you will reliase that as 0 kelvin is the theoretical lower limit for temperature then nothing can be below this and so no temperature can be lowered to 0 kelvin.

[swansont]

To cool something you must move heat away from it. This heat has to have some where to go (Heat is a for of energy and energy can't be created or destroyed). So you must have something of a lower temperature so that the heat can move there. This means that to achieve a temerature of 0 kelvin then you must have something at a temperature lower than 0 kelvin.

 

 

Not quite — you can put atomic ensembles into a state with a negative temperature (a population inversion), but these are non-equilibrium states, and don't give you a way of reaching zero.

[J.C.MacSwell]

Not quite — you can put atomic ensembles into a state with a negative temperature (a population inversion), but these are non-equilibrium states, and don't give you a way of reaching zero.

 

Can you elaborate? Negative temperature makes me think negative kinetic energy. Would you not need imaginary (square root of negative) velocities?

[jdurg]

One problem I see with achive 0K is that how do we know we've achived it unless we apply some outside energy to the system to check thefore moving away from the 0K point? Although I suspect people are working on this if it hasn't already been solved :|

 

You'd probably have to do an indirect measurement, but as to how that could be done stumps me. Something like a series of objects A=>B=>C where C is a 'heat pump' and is able to constantly take heat energy away from the object to its left. B is a similar thing. If C is no longer absorbing anymore energy from B then B must have absorbed all the energy from A so A must be at absolute zero. Something to that effect.

[sunspot]

Temperature is often equated with the vibrations of matter and the energy that is given off. Room temperature is at the range of chemical vibrations. At absolute zero there would be no vibration or energy release since there is no temperature. This means that even the subparticles of matter could no longer give off vibrational energy levels. As far as I know, this would cause these particles to disappear, since their movement is essential to the integrity of matter. The bottom line is that matter and energy would both disappear at absolute zero.

 

If we look at the other extreme, matter vibrations would become highly energetic and the energy output the same. In a finite universe, energy and temperature would have an upper limit, when matter and energy both becomes two equated singularities. Any further vibrations of matter could not give off energy beyond this temp because there would not be enough mass/energy within the universe. If we go one step further, this would bring up to the same place as absolute zero, where matter and energy can not exist.

 

Here is an interesting graph. If we plot temperature, it would become sort of a circle where zero and limiting temperature overlap to close the circle. The decrease from the highest temp is reflected by space increasing from absolute zero, will movement from absolute zero is reflected by potential for extreme temperature.

[swansont]

Can you elaborate? Negative temperature makes me think negative kinetic energy. Would you not need imaginary (square root of negative) velocities?

 

I'm referring to the distribution of atomic states. If you have a two-stste system, with states 1 (ground state) and 2 (excited state):

 

 

[math] N_2/N_1 = e^{-(E_2-E_1)/kT} [/math]

 

which means that at some temperature, you expect some small fraction of atoms to be in an excited state. If you create a population inversion, the solution requires T<0, but as I said, that's a prepared state and not something you find naturally.

[Edtharan]

Not quite — you can put atomic ensembles into a state with a negative temperature (a population inversion), but these are non-equilibrium states, and don't give you a way of reaching zero.

I thought this was done by knocking off atoms or molecules that have a higher energy (temperature) than the other. It was not so much cooling as removing "hot" atoms and thereby lowering the average temperature of the group.

[swansont]

I thought this was done by knocking off atoms or molecules that have a higher energy (temperature) than the other. It was not so much cooling as removing "hot" atoms and thereby lowering the average temperature of the group.

 

You're probably thinking of evaporative cooling, which does involve this process, and leaves you with an equilibrium state.

[aguy2]

I found my car this morning blanketed by frost. After cleaning it, I started driving and thought if heat is a source of energy, what is “COLD”? is it negative enerty?

 

Normally 'cold' is not concidered a 'thing', while something like 'heat' is concidered a 'thing'. If cold where to be temporarily thought of as a thing, we might see cold as a thing that tends to 'attract' heat. Carrying this analogy further we might see 'stillness' as being attractive to 'movement', 'dark' as being attractive to 'light', 'vacuum' as being attractive to 'air', ect.

 

Is this something like the line of reasoning you experienced?

 

aguy2

[TimbaLanD]

Ok, let’s say we fire a bullet into space from a space shuttle in orbit. Let’s assume when the bullet leaves the gun its temperature is 200Deg C. What will happen to the temperature as it travels the vacuum of space?

[swansont]

Ok, let’s say we fire a bullet into space from a space shuttle in orbit. Let’s assume when the bullet leaves the gun its temperature is 200Deg C. What will happen to the temperature as it travels the vacuum of space?

 

It will radiate and the temperature will drop until it reaches an equilibrium with the microwave background.

[TimbaLanD]

so, when the heat radiates from the bullet and goes where?

[swansont]

so, when the heat radiates from the bullet and goes where?

 

 

Pretty much everywhere, isotropically.

[Edtharan]

so, when the heat radiates from the bullet and goes where?

Into the background radiation (not just microwave radiation). The bullet will be absorbing radiation from all around it in space (ther is the microwave radiation, light and heat from the sun, light and heat from other stars, etc). But all this other energy would be less than the bullet at 200DegC, so the bullet would be radiating more energy than it recieved. The bullet will loose this heat energy as radiation and cool down. Eventuall this will drop it to a temerature where the energy radiated from the bullet is equal to the radiation of the energy that is hitting it (from the rest of the universe), at this point it wont loose any more energy as all the energy it looses will be replaced. It is now at an equilbrium.

 

This is also why you can't reduce an object to 0DegK, because there will alwase be radiation (your cooling device will also radiate a small amount of heat) that will add to the energy that your object has.

[TimbaLanD]

Good explanation! So, basically the heat will radiate from the bullet into space but where does it finally settle in? I think I am looking at radiation as particles escaping from the bullet. If this is the case, where do these particles go? They must go and settle somewhere, surely?