B Basic Question: What are energy levels, of photons, for example?

[lazarericus]

TL;DR Summary

How do particles change energy levels?

I often read of photons manifesting different levels of energy. I know that energy increases as wavelength decreases and frequency increases. Are there other ways particles gain or lose energy? As water boils heat energy is transferred to the water causing water molecules to move faster and to bump into each other with greater momentum, but that energy isn't inherent. Is it frequency alone that transfers energy to particles, or frequency drops that cause them to lose energy?

 

[.Scott]

In the case of photons, yes, as energy increases wavelength decreases and frequency increases. But those are not usually described as "energy levels". There are ways of changing a photon's energy. First by red or blue shift - as when a photon rises or falls through a gravitational field or when the observer is moving towards or away from the transmitter. Photons can also be split with with a "spontaneous parametric down-converter", yielding two photons each with half the energy.

But the term "energy level" is most often used with electrons in orbitals. Such an electron can absorb or (sometimes) emit a photon causing it to jump from one orbital to another with a different energy level.

 

[lazarericus]

Thanks for this. Your answer is extremely helpful. I can see that I was actually asking two different questions. Regarding photons, I have never been clear on references to "high energy photons". Would that be a direct reference to frequency, e.g., gamma rays?
And subsumed within my question, I have not understood what causes electrons to jump between energy levels. Is that it, a photon added or lost, or are there also commonly other causes to gains or losses in electron energy levels?

 

[PeterDonis]

I often read of photons manifesting different levels of energy.

This is very vague and general. Can you give a specific example? Or, even better, a specific reference?

 

[PeterDonis]

I know that energy increases as wavelength decreases and frequency increases. Are there other ways particles gain or lose energy?

Wavelength decreasing and frequency increasing are not a way that particles gain energy. They are consequences of particles gaining energy.

 

[PeterDonis]

I have not understood what causes electrons to jump between energy levels. Is that it, a photon added or lost, or are there also commonly other causes to gains or losses in electron energy levels?

Same issue here. Photons being emitted are not causes of electrons going from a higher to a lower energy level. They are consequences of it.

A photon being absorbed is a cause of an electron going from a lower to a higher energy level in an atom; it is the only possible such cause. But once the electron is at the higher energy level, it dropping back to a lower energy level and emitting a photon as it does so is a random quantum event and does not have any particular cause other than the fact that it is possible--a lower energy level is available so there is some probability that the electron will drop back to it.

 

[lazarericus]

Thanks, Peter. I appreciate these clarifications. It is points like this that helps a person who knows very little about physics follow the extraordinary discoveries and theories of quantum mechanics and cosmology we are inheritors of today, and to be present day observers of discoveries like the Higgs and gravitational waves, both the result of machines we have only now developed the technology to build.

 

[vanhees71]

A photon being absorbed is a cause of an electron going from a lower to a higher energy level in an atom; it is the only possible such cause. But once the electron is at the higher energy level, it dropping back to a lower energy level and emitting a photon as it does so is a random quantum event and does not have any particular cause other than the fact that it is possible--a lower energy level is available so there is some probability that the electron will drop back to it.

The cause of spontaneous emission is that the excited state of the atom is only approximately an energy eigenstate. It was calculated neglecting the coupling to the quantized electromagnetic field, taking into account only the electromagnetic field of the nucleus within which the electrons move. The coupling to the radiation field is treated as a perturbation, usually in the dipole approximation, and this leads to a transition where the electron state changes to a lower (approximate) energy eigenstate and the emission of a photon.

 

[bhobba]

The cause of spontaneous emission is that the excited state of the atom is only approximately an energy eigenstate. It was calculated neglecting the coupling to the quantized electromagnetic field, taking into account only the electromagnetic field of the nucleus within which the electrons move. The coupling to the radiation field is treated as a perturbation, usually in the dipole approximation, and this leads to a transition where the electron state changes to a lower (approximate) energy eigenstate and the emission of a photon.

I know I post it a lot, but for further detail see:
http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

It's really the start of Quantum Field Theory (QFT) and historically why it is necessary. There are even some people that believe QFT in and of itself is the real 'interpretation' of QM:
https://www.amazon.com/dp/9812381767/?tag=pfamazon01-20

I will not give my opinion except it is an interesting take. I have a copy. But as to achieving its goal - you need to make up your own mind.

Thanks
Bill