Can Colder Bodies Send Photons to Hotter Ones?

• Alan Tomalty
The light from the flashlight is ultimately absorbed by the fire, but some of the light is still visible.

Alan Tomalty

Assuming no conduction and no convection will a colder body be able to send photons to a hotter body while the hotter body is sending photons to t. We all know that an equilibrium will result with a temperature somewhere between the two bodies but do the photons emitted by the cooler body ever end up in the hotter body?

Alan Tomalty said:
Assuming no conduction and no convection will a colder body be able to send photons to a hotter body while the hotter body is sending photons to t. We all know that an equilibrium will result with a temperature somewhere between the two bodies but do the photons emitted by the cooler body ever end up in the hotter body?
Yes, ALL bodies above absolute zero radiate. Warmer bodies just radiate more, so the NET for the colder body is that it absorbs more radiation than it sends out but that doesn't mean that it doesn't send any out.

Alan Tomalty said:
We all know that an equilibrium will result with a temperature somewhere between the two bodies but do the photons emitted by the cooler body ever end up in the hotter body?
The short answer is "yes". Some of the thermal radiation from the cool body will be absorbed by the hot body.

This scenario appears to assume that there is an ideal perfectly reflective box surrounding the pair of bodies. Otherwise, the equilibrium temperature would be that of the environment. All of the thermal radiation from either body will end up being reabsorbed. Some by the one body and some by the other.

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Alan Tomalty said:
Assuming no conduction and no convection will a colder body be able to send photons to a hotter body while the hotter body is sending photons to t. We all know that an equilibrium will result with a temperature somewhere between the two bodies but do the photons emitted by the cooler body ever end up in the hotter body?

To make this very clear, electromagnetic radiation can travel through vacuum (i.e. when conduction and convection are not possible). Infrared radiation is "heat", and it is a form of electromagnetic radiation. This is how heat from the sun reaches us.

The rest of your question has been addressed by the previous responses.

Zz.

How does the cool body know when to stop sending photons to the hot body? At equilbrium are each of them still continually sending photons to each other? Is each photon from the cool body at a lesser energy level than each one from the hot body? I don;t understand exactly how the 2 bodies end up with the same energy.

Alan Tomalty said:
How does the cool body know when to stop sending photons to the hot body?
It doesn't, because...
At equilbrium are each of them still continually sending photons to each other? Is each photon from the cool body at a lesser energy level than each one from the hot body?
At equilibrium the amount of energy flowing in each direction is the same. If there were any imbalance, then the object receiving more energy would warm up slightly, increasing the rate at which it radiated energy and reducing the imbalance. (As an aside, thinking in terms of photons instead of the intensity of the electromagnetic radiation just complicates the problem - photons aren't what you think they are)
I don't understand how the 2 bodies end up with the same energy
They don't. They end up with the same temperature.

phinds
Alan Tomalty said:
Assuming no conduction and no convection will a colder body be able to send photons to a hotter body while the hotter body is sending photons to t. We all know that an equilibrium will result with a temperature somewhere between the two bodies but do the photons emitted by the cooler body ever end up in the hotter body?

Yes. It's just like shining a flashlight into a fire.

1. Can colder objects really send photons to hotter ones?

Yes, this phenomenon is known as thermal radiation. All objects with a temperature above absolute zero (0 Kelvin) emit thermal radiation, regardless of their temperature relative to other objects.

2. How is it possible for colder bodies to send photons to hotter ones?

This occurs because of the nature of thermal radiation. Photons are constantly being emitted and absorbed by all objects, and the rate of emission is dependent on the temperature of the object. Colder objects emit photons at a lower rate than hotter objects, but they still emit them.

3. Does this violate the laws of thermodynamics?

No, it does not. While it may seem counterintuitive, the second law of thermodynamics only applies to closed systems. In an open system, such as our universe, energy can be exchanged between objects, and colder objects can transfer energy to hotter ones through thermal radiation.

4. How is this concept used in practical applications?

Thermal radiation is used in a variety of practical applications, such as thermography (thermal imaging), industrial processes, and even cooking. In thermography, colder objects appear as darker areas because they emit fewer photons, while hotter objects appear as brighter areas. In industrial processes, thermal radiation can be used to heat or cool objects, and in cooking, thermal radiation is responsible for browning and cooking food.

5. Can colder bodies actually make hotter ones even hotter through thermal radiation?

Yes, this is possible. When colder objects transfer energy to hotter objects through thermal radiation, the hotter objects can absorb this energy and become even hotter. However, the amount of energy transferred is dependent on the temperature difference between the two objects, so the colder object cannot make the hotter object infinitely hotter.