Magical Realist
Valued Senior Member
How do photons carry heat thru space? What is the property of photons that enables them to do this? Do photons always carry heat?
How does light carry heat?
- Thread starter Magical Realist
- Start date
Halc
Registered Senior Member
A photon is a quantum concept, and heat is a classical concept. You can't mix them like this.
The topic title is better since it references the classical concept of light, not photons.
Light has no temperature and does not carry heat. It has frame dependent energy and that energy, if absorbed by some material, might heat the material, as evidenced by Earth warming up during daylight hours.
Magical Realist
Valued Senior Member
Does not heat travel in infrared waves? What are these waves made of?
Halc
Registered Senior Member
Light is simply energy. A hot object can give off light at all sorts of frequencies (it is IR in some reference frames and not others), cooling the emitting object. That light can warm an object that absorbs the light, so in effect transferring heat even though it isn't heat enroute.
An example is a microwave oven that effectively shines a light that is designed to be absorbed by food and not by other stuff. It transfers energy (which isn't particularly thermal energy) to light which then transfers the energy to the food which manifests as heat. This isn't IR light, at least not in the frame of the oven.
In this case, light.
DaveC426913
Valued Senior Member
As Halc says, light is a quantized form of electromagnetic energy. (An electric field coupled with a magnetic field, whose cycles are 90 degrees out of phase.* They propagate together through space.) It has momentum.
When it hits something that can absorb the energy at that quantized frequency**, it absorbs that packet of energy, which is converted into a number of other types of energy.
A very common conversion is into the bonds of molecules (like little springs, molecular bonds wobble to-and-fro, up-and-down, side-to-side). This wobbling of molecular bonds is commonly detected as a warming of the material.*** . However, there are myriad other forms of energy it might be converted to. eg. It might kick electrons into higher orbitals (excitation, which is the source for fluorescence).
TLDR: light or photons do not "carry" heat; they carry momentum, which is simply a form of energy. And one form of energy can be converted to another - such as heat.
*
** not all frequencies of energy are absorbed by all materials, e.g. visible light passes through glass. That's the "quantized" part of light. There are no molecular bonds in glass that can be absorbed by the wavelengths of visible light. But ultraviolet light is, which is why glass can protect you from sun burn.
*** It may be helpful to note that atoms and molecules do not have temperatures. Temperature is a property of the average kinetic energy of a bulk material.
When it hits something that can absorb the energy at that quantized frequency**, it absorbs that packet of energy, which is converted into a number of other types of energy.
A very common conversion is into the bonds of molecules (like little springs, molecular bonds wobble to-and-fro, up-and-down, side-to-side). This wobbling of molecular bonds is commonly detected as a warming of the material.*** . However, there are myriad other forms of energy it might be converted to. eg. It might kick electrons into higher orbitals (excitation, which is the source for fluorescence).
TLDR: light or photons do not "carry" heat; they carry momentum, which is simply a form of energy. And one form of energy can be converted to another - such as heat.
*
** not all frequencies of energy are absorbed by all materials, e.g. visible light passes through glass. That's the "quantized" part of light. There are no molecular bonds in glass that can be absorbed by the wavelengths of visible light. But ultraviolet light is, which is why glass can protect you from sun burn.
*** It may be helpful to note that atoms and molecules do not have temperatures. Temperature is a property of the average kinetic energy of a bulk material.
Last edited:
"Heat" is technically defined to be a transfer of energy between two objects or systems due to a temperature difference between them.
Photons can transfer energy from one place to another. Absorbed energy can cause an object to heat up.
Infrared light can be described as electromagnetic waves or as bundles of photons. Classical electromagnetic waves can transfer energy from one place to another, and so can photons, so either way they can cause heating when they are absorbed by something (and cooling when they are emitted from something).
In the classical picture, oscillating electric and magnetic fields. In the quantum picture, photons are excitations of the electromagnetic field.
Light is photons. Photons are an electromagnetic wave and are a packet of energy. Heat is a description of how energy is transfered from hotter to colder. One of the methods of heat transfer is by radiation, radiation can be photonic, also called light.
But it gets worse. Hot items transfer heat outward and radiate energy in all directions. If that energy hits a hotter item, it can be absorbed, heat going from colder to hotter. The hotter item is radiating more heat out so the cooler-hot item receives more heat than it radiates. So heat, a macro feature, looks like it is only going from hot to cold.
A photon is a manifestation of energy. A short burst of undulating electric and magnetic fields. I don't think it's length has ever been measured? It might not be possible to measure it's length? It might only have a relativistic length?
The energy contained in a photon is measured by its frequency/wavelength (<<< Pun noted.). I guess it would be colloquially okay to say it carries it's energy in its wavelength? Depending on the wavelength and material it hits, it can be reflected, absorbed, or pass through. It is only heat and propulsion, for those materials that absorb it. It would be propulsion for those materials it bounces off. Right?
Sorry for the pondering.
But it gets worse. Hot items transfer heat outward and radiate energy in all directions. If that energy hits a hotter item, it can be absorbed, heat going from colder to hotter. The hotter item is radiating more heat out so the cooler-hot item receives more heat than it radiates. So heat, a macro feature, looks like it is only going from hot to cold.
A photon is a manifestation of energy. A short burst of undulating electric and magnetic fields. I don't think it's length has ever been measured? It might not be possible to measure it's length? It might only have a relativistic length?
The energy contained in a photon is measured by its frequency/wavelength (<<< Pun noted.). I guess it would be colloquially okay to say it carries it's energy in its wavelength? Depending on the wavelength and material it hits, it can be reflected, absorbed, or pass through. It is only heat and propulsion, for those materials that absorb it. It would be propulsion for those materials it bounces off. Right?
Sorry for the pondering.
Gawdzilla Sama
Valued Senior Member
I love these split level threads.