What is the temperature of a photon?

[ParanoiA]

Ok, so my co-worker asked what the temperature of a photon was. Obviously, I have no earthly idea and had never pondered that before.

 

Do photons have a temperature? And does it change with the wave-length?

[BhavinB]

I don't believe such a concept exists.

[Sisyphus]

They have energy, which is proportional to frequency, but not temperature. Temperature is derived from an average kinetic energy of atoms, so it doesn't really apply to a single particle.

[BhavinB]

They have energy, which is proportional to frequency, but not temperature. Temperature is derived from an average kinetic energy of atoms, so it doesn't really apply to a single particle.

 

even an ensemble of photons don't have the property of 'temperature'

[ParanoiA]

Well damn Sisyphus, you're just solving all of my problems. From wood stoves to particle physics, you're apparently the go-to guy.

 

Thanks.

[Riogho]

Isn't photons what you measure to check temperature?

 

Don't we check temperature by radiation of... photons?

 

So I guess it's like saying does elephant have elephant?

[YT2095]

I don't believe such a concept exists.

actually it does, and is used quite frequently in Photography, color temp is measured in Kelvin.

here`s a few references: http://en.wikipedia.org/wiki/Color_temperature

http://www.3drender.com/glossary/colortemp.htm

[BhavinB]

actually it does, and is used quite frequently in Photography, color temp is measured in Kelvin.

here`s a few references: http://en.wikipedia.org/wiki/Color_temperature

http://www.3drender.com/glossary/colortemp.htm

 

This is not an answer to the question asked.

The only reason colors are sometimes measured in temperature is because of the peak light emission of a blackbody.

This relates back to particles of mass and not photons. Photons themselves have no temperature.

[Royston]

Temperature is merely the direction of heat, and so can't be applied to the properties of an individual particle, such as a photon.

[insane_alien]

temperature is a scalar quantity, it does not have direction.

 

temperature is a measure of the average kinetic energy of molecules in the substance.

 

it is analogous to voltage in an electrical system. voltage does not have direction but current(heat) does.

[Royston]

temperature is a scalar quantity, it does not have direction.

 

True, but only in a system in equilibrium (i.e it has no direction...though it's not a vector like you said), with two bodies where heat flows between them, temperature determines a direction of heat...I should of been more specific.

[Klaynos]

actually it does, and is used quite frequently in Photography, color temp is measured in Kelvin.

here`s a few references: http://en.wikipedia.org/wiki/Color_temperature

http://www.3drender.com/glossary/colortemp.htm

 

This is fundamentally different from the temperature of an ensemble (or singular) photon.

 

Temperature is scalar.

 

Temperature gradients (and therefore heat transfers) are not.

[Flashman]

Temperature is a bulk property of matter, the end

 

 

Or maybe we can figure what photons smell like too, I'd figure something like pinesol.

[Baby Astronaut]

temperature is a scalar quantity, it does not have direction.

 

temperature is a measure of the average kinetic energy of molecules in the substance.

 

it is analogous to voltage in an electrical system. voltage does not have direction but current(heat) does.

Is there a micro and macro version of kinetics? Such as, "micro" would be atoms moving crazily away from each other and bouncing all over, and macro would be anything moving at same velocity if no forces would act upon it.

 

Otherwise, a lonely pebble cruising through space at 100,000 km per second would have high kinetic energy, and thus should measure blazing hot but in fact be stone cold.*

 

 

*(pun absolutely intended)

[Sisyphus]

Is there a micro and macro version of kinetics? Such as, "micro" would be atoms moving crazily away from each other and bouncing all over, and macro would be anything moving at same velocity if no forces would act upon it.

 

Otherwise, a lonely pebble cruising through space at 100,000 km per second would have high kinetic energy, and thus should measure blazing hot but in fact be stone cold.*

 

 

*(pun absolutely intended)

 

Yes and no. Kinetic energy is always relative. Temperature is the average kinetic energy of the atoms in a system relative to one another. So in that sense the overall velocity of the system doesn't count. But more importantly, it doesn't mean anything. A pebble cruising at 100,000 km per second relative to what?

[Flashman]

A pebble cruising at 100,000 km per second relative to what?

 

Relative to the platinum-iridium international standard point of reference kept in a cryo-stabilized vault at the National Physics Laboratory.

[swansont]

You can have an ensemble of photons that have the distribution of a blackbody. One can talk of their temperature, which is really the temperature of the object emitting/absorbing them, in thermal equilibrium. We speak of the 2.7 K temperature of space, which is determined by the distribution of photon energies.

[Baby Astronaut]

Yes and no. Kinetic energy is always relative. Temperature is the average kinetic energy of the atoms in a system relative to one another.[/i]

So are you saying that if a cloud of atoms were to zip 'round at near light speed relative to one another in the Large Hadron Collider, their kinetic energy would measure as temperature?

[npts2020]

So are you saying that if a cloud of atoms were to zip 'round at near light speed relative to one another in the Large Hadron Collider, their kinetic energy would measure as temperature?

 

No. When you throw a rock its temperature doesnt increase (except maybe some infintessimal amount from air friction). Temperature is only a measure of average internal kinetic energy of a system relative to itself. External kinetic energy is from one systems movement as a whole being measured relative to another system as a whole.

[DrP]

Yea - the fast moving rock is still cold. The atoms/molecules in that rock will be moving/vibrating slowly relative to each other because space is cold. The rock as a system may move fast - but it's internal energy is low as npts2020 said.

[Baby Astronaut]

Ahh.

 

So the reason a hot object is painful, is that an angry stream of its atoms collide into your skin atoms, which in turn slam into other cells' atoms. It's not really "heat" as we sense it but actually tiny little crashes, and if you get a moderate amount of those, like in a system of air molecules knocking into you at 85 Fahrenheit, you experience a warm and fuzzy sensation.

 

But maybe not. Strong winds hit you fast but don't warm you up. Or perhaps the internal kinetic motion of warmed air molecules/atoms is vastly faster than wind can ever be?

Edited November 14, 2008 by Baby Astronaut

[swansont]

Ahh.

 

So the reason a hot object is painful, is that an angry stream of its atoms collide into your skin atoms, which in turn slam into other cells' atoms. It's not really "heat" as we sense it but actually tiny little crashes, and if you get a moderate amount of those, like in a system of air molecules knocking into you at 85 Fahrenheit, you experience a warm and fuzzy sensation.

 

But maybe not. Strong winds hit you fast but don't warm you up. Or perhaps the internal kinetic motion of warmed air molecules/atoms is vastly faster than wind can ever be?

 

The reason hot things are painful to touch is that you are damaging cells, and pain is your body's way of telling you to stop doing whatever you're doing.

 

An atom with room-temperature thermal energy will be moving at a speed of order 100 m/s, which is significantly faster than a strong wind.

[Baby Astronaut]

The reason hot things are painful to touch is that you are damaging cells, and pain is your body's way of telling you to stop doing whatever you're doing.

Are you agreeing with me then?

 

I see it this way. You know how it stings when sand is being whipped at your face by high winds? I propose that a similar thing is happening at the atomic level when a person feels something hot.

 

If the heated item's atomic particles are really moving fast, then it's reasonable to suppose those particles will slam into into other atoms (of a hand in this case), by the thousands or even millions depending on its temperature. The hotter, the faster the particle's speeds relative to yours.

 

Maybe.

[swansont]

Are you agreeing with me then?

 

I see it this way. You know how it stings when sand is being whipped at your face by high winds? I propose that a similar thing is happening at the atomic level when a person feels something hot.

 

If the heated item's atomic particles are really moving fast, then it's reasonable to suppose those particles will slam into into other atoms (of a hand in this case), by the thousands or even millions depending on its temperature. The hotter, the faster the particle's speeds relative to yours.

 

Maybe.

 

No, that wasn't agreement. If one considers the average speed of a molecule at room temperature, which is comfortable, with the average speed of a molecule at water's boiling point, which is painful, the speed increase is only 13%. I don't think the picture of an angry stream of atoms slamming onto you jibes with that. You aren't feeling the impact, per se.

[heaventian]

In fact,the temperature is used to depict the coldness and hotness of a subject and it stand for the average velocity of molecules in the mass. so it has no meaning for a single molecule or photon.