Behavior of systems near absolute zero

[lemur]

Hmm, unless its being accelerated, I don't think so. But I guess, there may be some very small effect from the cosmic background radiation and larger effects from cosmic rays. But if nothing about the iron changes as its speed or energy level or the electron configuration, there's no reason to emit light as far as I know.

How can at atom or multiple atoms have energy > 0 and not emit ANY radiation? Doesn't energy ALWAYS express itself one way or the other. Maybe the question is what continues longer, particle vibration/momentum-tranfer or EM emission. Transfer makes more sense because every particle is always in motion to something else, so it could be completely cold and still eventually collide with something else and raise its energy-level as a result.

[Cap'n Refsmmat]

Anything with heat will emit some amount of thermal radiation, though it may be incredibly small.

 

http://en.wikipedia.org/wiki/Thermal_radiation

[steevey]

Anything with heat will emit some amount of thermal radiation, though it may be incredibly small.

 

http://en.wikipedia....ermal_radiation

 

But since energy is quantized, wouldn't iron with nothing about it changing in a vacuum of space so that it gets to the lowest possible energy state in space, wouldn't it eventually get to a point where it doesn't emit any form of heat?

 

Also, wouldn't matter with the presence of no radiation emit all its energy under that circumstance?

[steevey]

Anything with heat will emit some amount of thermal radiation, though it may be incredibly small.

 

http://en.wikipedia....ermal_radiation

 

But since energy is quantized, wouldn't iron with nothing about it changing in a vacuum of space so that it gets to the lowest possible energy state in space, wouldn't it eventually get to a point where it doesn't emit any form of heat? If the electrons aren't changing states, when would they even emit light?

 

Also, wouldn't matter with the presence of no radiation emit all its energy under that circumstance?

Edited February 10, 2011 by steevey

[Cap'n Refsmmat]

The lowest possible energy state is 0K, which is not obtainable. If there's heat in it, an electron will change energy states at some point. It may take a while, but it'll happen.

[lemur]

The lowest possible energy state is 0K, which is not obtainable. If there's heat in it, an electron will change energy states at some point. It may take a while, but it'll happen.

But do ALL the atoms in a lump of intergalactic iron maintain an energy level above 0k, or do some drop to absolute zero while waiting for the energy from others to circulate around to them? I.e. can that entire lump of iron never reach absolute zero? I suppose there's always light hitting it from surrounding galaxies, but can't that amount of energy at least be so little that SOME of the atoms become completely energy-less?

 

edit: darnit, I have been trying not to go too far off topic and I'm afraid I've done it again. Should this thread be split to one about energetic behavior near absolute zero?

Edited February 10, 2011 by lemur

[Cap'n Refsmmat]

Absolute zero can't be reached thermodynamically, so none of the atoms will hit 0K. You can, however, get arbitrarily close to 0, at which point there will be practically zero emissions.

[lemur]

Absolute zero can't be reached thermodynamically, so none of the atoms will hit 0K. You can, however, get arbitrarily close to 0, at which point there will be practically zero emissions.

How can atom can get arbitrarily close to absolute zero if energy is quantized? Isn't there some point where an atom emits its last photon and is done? If not, why would the "last drop" not get emitted at some point?

[Cap'n Refsmmat]

A single atom at absolute 0 would imply that it has zero kinetic energy, not that all its electrons are at ground state.

[lemur]

A single atom at absolute 0 would imply that it has zero kinetic energy, not that all its electrons are at ground state.

How can anything have zero kinetic energy when everything travels along geodesics that are stationary in themselves and have a velocity relative to anything they are framed together with? Still, in the period while they are waiting to collide with something else, they could be relatively motionless within their own inertial frame, or not?

Edited February 10, 2011 by lemur

[steevey]

A single atom at absolute 0 would imply that it has zero kinetic energy, not that all its electrons are at ground state.

 

So your saying even if there was 0 thermal energy or heat, there would still be the potential energy of other things like magnetic fields and forces and other properties? But then again, if the electrons have no energy, what possible shape of a cloud they could take? Cause here's what an equation would look like:

 

0s^1

 

which would be 0. The electron's shape would have 0 volume wouldn't it? You can't really do an Cartesian angle measurements to make a cloud shape from 0 can you?

Edited February 10, 2011 by steevey

[Cap'n Refsmmat]

The ground state of electrons still has energy. You can't have them with zero energy at all.

 

http://en.wikipedia.org/wiki/Zero_point_energy

[swansont]

But do ALL the atoms in a lump of intergalactic iron maintain an energy level above 0k, or do some drop to absolute zero while waiting for the energy from others to circulate around to them? I.e. can that entire lump of iron never reach absolute zero? I suppose there's always light hitting it from surrounding galaxies, but can't that amount of energy at least be so little that SOME of the atoms become completely energy-less?

 

Temperature is a property of a system, so it doesn't make sense to talk about some atoms within a system being at a different temperature. Electrons within the lump are colliding, and nuclei/atoms vibrating, which releases radiation.

 

A single atom at absolute 0 would imply that it has zero kinetic energy, not that all its electrons are at ground state.

 

Actually it sort of does. A single atom at rest does not have to be in the ground state. But you can't talk about a single atom being at 0K, you have to have a collection of atoms to have temperature make sense, so by quoting temperature one implies a group of atoms. The fraction of atoms in a thermal distribution with excited states depends on temperature. So a bunch of atoms at absolute zero would necessarily be in the ground state.

[alpha2cen]

The ground state of electrons still has energy. You can't have them with zero energy at all.

 

http://en.wikipedia....ro_point_energy

How do we know whether it is 0K or not?

I mean experimentally.

Are there any experimental standard?

We do not know whether we are at the North pole or not.

Edited February 10, 2011 by alpha2cen

[lemur]

Temperature is a property of a system, so it doesn't make sense to talk about some atoms within a system being at a different temperature. Electrons within the lump are colliding, and nuclei/atoms vibrating, which releases radiation.

 

Actually it sort of does. A single atom at rest does not have to be in the ground state. But you can't talk about a single atom being at 0K, you have to have a collection of atoms to have temperature make sense, so by quoting temperature one implies a group of atoms. The fraction of atoms in a thermal distribution with excited states depends on temperature. So a bunch of atoms at absolute zero would necessarily be in the ground state.

So temperature is a frame-dependent concept, thus absolute zero could only be absolute relative to the frame being considered. So two atoms at ground-state traveling parallel to each other in the same geodesic path could have a temperature of absolute zero relative to each other within the time-frame prior to any collisions with other particles in their path? I guess that is an abstract situation, though, which distracts from your valid point that temperature would measure the average kinetic energy of a system of interacting particles, not the behavior of any single or subset of those particles. Although, would it be possible to say that a certain percentage of an object, e.g. a meteoroid, could be at absolute zero as its heat migrates around its atoms? I.e. is there any validity in talking about patterns of heat-transfer within an object in terms of temperature differentials? I.e. can temperature refer to various parts of an object/system or must the system be unified by some natural logic?

[swansont]

So temperature is a frame-dependent concept, thus absolute zero could only be absolute relative to the frame being considered. So two atoms at ground-state traveling parallel to each other in the same geodesic path could have a temperature of absolute zero relative to each other within the time-frame prior to any collisions with other particles in their path? I guess that is an abstract situation, though, which distracts from your valid point that temperature would measure the average kinetic energy of a system of interacting particles, not the behavior of any single or subset of those particles. Although, would it be possible to say that a certain percentage of an object, e.g. a meteoroid, could be at absolute zero as its heat migrates around its atoms? I.e. is there any validity in talking about patterns of heat-transfer within an object in terms of temperature differentials? I.e. can temperature refer to various parts of an object/system or must the system be unified by some natural logic?

 

Temperature is frame dependent, but absolute zero would be the exception if it could be achieved, since it would look like uniform motion; if all of the atoms could be at rest, they would all move at some velocity in any other frame, and that would be indistinguishable from center-of-mass motion.

 

You can talks about temperature gradients in a material, but it still has to be a macroscopic effect. A metal bar with one end in ice water and the other end being heated by a flame will reach a steady-state condition, and you could talk about the temperature as a function of position along the bar. But not for individual atoms. Heat flow is from high temperature to low, but it is possible for a slow moving atom to give energy to a fast moving atom of the same mass. It just isn't likely, so the average effect (for a large collection) is in the other direction.

[lemur]

Temperature is frame dependent, but absolute zero would be the exception if it could be achieved, since it would look like uniform motion; if all of the atoms could be at rest, they would all move at some velocity in any other frame, and that would be indistinguishable from center-of-mass motion.

 

You can talks about temperature gradients in a material, but it still has to be a macroscopic effect. A metal bar with one end in ice water and the other end being heated by a flame will reach a steady-state condition, and you could talk about the temperature as a function of position along the bar. But not for individual atoms. Heat flow is from high temperature to low, but it is possible for a slow moving atom to give energy to a fast moving atom of the same mass. It just isn't likely, so the average effect (for a large collection) is in the other direction.

So what does this mean for an iron meteoroid traveling for a long period through intergalactic space (assuming this can/would happen). The meteoroid would radiate until it reached thermal equilibrium with the radiation it was receiving from distant galaxies. Then would parts of it be at absolute zero relative to the parts that were absorbing and conducting energy from the distant starlight? Then would you measure its temperature as a gradation from its surface to absolute zero, or assign it a mean temperature and claim absolute zero can never truly be reached?

 

Actually, I wonder if the gravity and other forces that hold the atoms of the meteoroid together would also result in energy that would also result in some degree of heat. So maybe absolute zero isn't achievable because there is no situation in which particles are completely devoid of interactive force?

 

 

[swansont]

Something in interstellar space would reach equilibrium at about 2.7K because that's the microwave background. If it were large enough for appreciable gravity, then compression would increase the internal temperature and you would have a gradient from the center to the edge. But this energy would conduct to the surface and radiate away eventually.

[lemur]

Something in interstellar space would reach equilibrium at about 2.7K because that's the microwave background. If it were large enough for appreciable gravity, then compression would increase the internal temperature and you would have a gradient from the center to the edge. But this energy would conduct to the surface and radiate away eventually.

What do you mean by "appreciable gravity?" Wouldn't any amount of gravity generate SOME amount of heat, no matter how small? Also, how much energy would be imparted to a meteoroid of say, 1 cubic meter with a perfectly smooth surface (to simplify things). Let's say it is a cube actually, so 6m^2. Is the background radiation you speak of enough to keep this cubic meter of iron at 2.7K? If so, what about something denser, like gold? Or would it radiate exactly as much energy out as it receives, simply as a matter of entropy to equilibrium?

[steevey]

The ground state of electrons still has energy. You can't have them with zero energy at all.

 

http://en.wikipedia....ro_point_energy

 

The ground state of an electric still has energy, but is it actually thermal energy if nothing about it and the atom is changing? Basically, heat is caused by infra-red photons with energy being carried across substances from electron to electron. So if an atom is at the lowest energy state (not 0K, but near it), and with matter being quantized, an electron shouldn't ever jump any energy level which means no photons if its undisturbed.

 

Also if all the particles in the system got to the same 0 energy state, wouldn't that violate impenetrability? Maybe that's a more accurate reason why 0K doesn't occur. There would always be forces resisting the particles from occupying the same space of 0 energy.

Edited February 11, 2011 by steevey

[Cap'n Refsmmat]

You forget quantum effects, which allow for some uncertainty in energy states. Particles without enough energy to escape some attractive force can still escape by uncertainty.

[alpha2cen]

Small particle objects have high surface energy. How big objects have no surface energy at 0K?

small particle + small particle--------------> big particle

At this time surface energy is released.

[steevey]

You forget quantum effects, which allow for some uncertainty in energy states. Particles without enough energy to escape some attractive force can still escape by uncertainty.

 

But where does uncertainty get the energy from in an undetermined particle? The energy is more precisely determined, so the position is that much less determined, but still, where does the electron all of a sudden get the energy to suddenly appear at the next energy level?

Edited February 11, 2011 by steevey

[Cap'n Refsmmat]

It doesn't "get" the energy from anywhere. It's just that the energy of the particle cannot be precisely determined, so it might just have enough energy to get out. And occasionally it does.

[swansont]

What do you mean by "appreciable gravity?" Wouldn't any amount of gravity generate SOME amount of heat, no matter how small? Also, how much energy would be imparted to a meteoroid of say, 1 cubic meter with a perfectly smooth surface (to simplify things). Let's say it is a cube actually, so 6m^2. Is the background radiation you speak of enough to keep this cubic meter of iron at 2.7K? If so, what about something denser, like gold? Or would it radiate exactly as much energy out as it receives, simply as a matter of entropy to equilibrium?

 

Enough gravity that there will be compression such that the dissipation of the energy takes time and heats up the object. A 1 kg chunk of material will not reshape itself under the influence of gravity.

 

If it's in thermal equilibrium (same temperature), it emits the same amount of energy as it receives.

 

The ground state of an electric still has energy, but is it actually thermal energy if nothing about it and the atom is changing? Basically, heat is caused by infra-red photons with energy being carried across substances from electron to electron. So if an atom is at the lowest energy state (not 0K, but near it), and with matter being quantized, an electron shouldn't ever jump any energy level which means no photons if its undisturbed.

 

Also if all the particles in the system got to the same 0 energy state, wouldn't that violate impenetrability? Maybe that's a more accurate reason why 0K doesn't occur. There would always be forces resisting the particles from occupying the same space of 0 energy.

 

The blackbody spectrum is a continuum — it does not rely on electrons making jumps between energy levels. Electrons in a material with high emissivity (such as a conductor) are free to move around; they collide and you get radiation from the accelerations.

 

Heat is not caused by infrared photons. Heat flow is caused by a temperature difference. Radiation from radiative heat transfer is often strong in the IR part of the spectrum, but that's temperature dependent.