Does acceleration of charged particles always produce radiation?

If acceleration of charged particles produces radiation, how about:
electrons around the nucleus?
random walk of electrons in an electrically conducting material?
if you just fire hydrogen atoms, do the accelerations of the protons and electrons produce radiation, or do they cancel out because the atom is neutral?

At the very least, shouldn’t radiation be produced during cathodic emission, like the opposite of how bremsstrahlung radiation is produced?

Electrons round a nucleus are not in orbit - they occupy a wave function defined by the Schroedinger equation. They do not accelerate in the sense that a newtonian object in orbit does, so do not emit radiation.

The solar-system model of an atom falls into the category that The Science Of Diskworld calls Lies-To-Children - it paints a picture that illustrates the truth, but is wrong in many aspects.

As for electrons moving in a metal, again, acceleration is not the correct way to think of how the electrons move.

For neutral atoms, it is hard to accelerate them without charge unless you have a gravity well ( hole), then collisions produce heat that makes a plasma, and you get radiation that way.


It may be that ALL quantum physics can be explained, in reasonably plain lay English, ONLY as “lies to children”, short of actually working out the gory mathematics of it.

Can anybody point to any description of quantum anything, in lay terms for the general (non-technical) audience, that is any more accurate than that?

Hmm I thought so about atoms. So electrons in a potential well (atoms, metals) behave like waves and are “smeared out” and aren’t considered accelerating?

For neutral atoms, how about if you blast them with a laser, say, in fusion experiments?

It is all lies-for-children, but quantum physicists tell better lies that give a better reflection of reality than “oh, it’s a bit like a solar system with electrons orbiting a nucleus”. String theory physicists tell outrageous lies, but we still have not yet worked out if those lies give valid and useful answers, or whether the lies curl up on themselves in a tiny loop too small to detect.

And there are better guides to quantum physics for lay-people. I can’t give any names, because I haven’t read any, but I did lots of physics at University (not a major, but a supporting subject for Analytical Chemistry, which involves quantum) so I try to keep up. Others may make suggestions. However, The Science Of Diskworld is an engaging read, and addresses (in an overarching way) how lies-to-children improve and shed light on how the universe really works. However, it does show it’s age a bit, as some of the lies we tell have changed even since 2000, when it was written.


Again, the laser pulse strips the electrons from the nucleus - you don’t want electrons shielding the nucleus, because they (via Pauli Exclusion) will not allow the nuclei to get close enough for fusion. So the laser pulse creates a plasma and the subsequent pressure allows fusion of the nuclei to occur. This is why it is easier to fusion hydrogen and helium - getting the electron-free nuclei is pretty easy. It is much harder (ie it needs to be hotter) to strip heavier atoms of all their electrons.


This deserves some sort of prize. :smiley:

Radiation, remember, is just electric and magnetic fields that have the ability to propagate arbitrarily far. The fields produced by a positive charge moving in a given way would exactly cancel those produced by a negative charge moving in the same way, whether the two charges are moving or not. So yes, on a classical level the radiation of two superimposed charges would cancel out to zero.

It should, but the accelerations involved in bremsstrahlung are much much higher than those involved in accelerations involved in cathode emission. The amount of power radiated is proportional to the square of the acceleration, and increases rapidly with the particle’s velocity as well; so a particle accelerating slowly from rest will radiate a minuscule amount of power compared to a particle moving at high speed and decelerating quickly.

How about QED by Feynman?

Jim Al-Khalili’s Quantum: A Guide for the Perplexed is a great layman’s introduction to quantum mechanics that doesn’t dumb down or horrifically simplify the tenets of quantum mechanics, and has some beautiful illustrations to boot. Al-Khalili does a particularly good job of dispensing with the mysticism and supposed contradictions.

Understanding quantum mechanics–insofar as we do understand it–really isn’t that difficult or requiring of esoteric mathematics to grasp the fundamentals. It is just that the principles of quantum mechanics run contrary to our everyday experience, particularly the non-locality and observer interaction which causes the seemingly magical effects in the dual slit experiment, or the wigginess that is quantum tunnelling. The really important thing to understand is that at the quantum level, there are no particles; there are only fields (defined as probability waveforms) that interact with other fields in a way that makes them appear to be particles at that particular moment. And cause-and-effect as we understand it in the macroscopic level does not apply at the level of fundamental particles.


For me, the best way to understand quantum mechanics is to follow the historical trail of experiments. The OP is a good illustration of one step in that trail: Experiments led to a picture of the atom as a mini-solar system, but that apparently contradicted earlier accepted principles on electro-dynamics (accelerated charges produce electromagnetic radiation, which would cause the revolving electron to lose energy, which would cause the orbit to decay and the electron to eventually fall into the nucleus). So the model had to be modified by Bohr’s orbital theory–which was better but still inconsistent with other experiments.

With a “macro” level theory like Newton’s laws, their truth (or at least the value in assuming they’re correct) can be verified more or less directly or intuitively. So it’s possible to understand their ramifications in a deductive sense, i.e. you can “start” with the laws and deduce or explain experiments afterwards. The weird and non-intuitive aspects of quantum mechanics make a similar approach problematic for understanding–sure some folks can “start” with Schrodinger’s equation and work it all out from there, but it’s not nearly as easy to grasp. IMO the best route to understanding QM is to follow the logical path taken by the physicists who developed it over the first few decades of the 20th century, false steps and all.

Oh, you’re right. The electrons are accelerating throughout their entire flight towards the anode. I thought they stayed at the same speed once they left the cathode.

But if the charges cancel out, how close do they have to be to cancel out?

Try this. I am a physics major, but I have only read the preliminaries of that sequence. However, I greatly enjoy Lesswrong and so far the writers seem to know what they’re doing.

To exactly cancel, I think they do have to be exactly on top of each other. If the two charges were separated by a small distance, then you’d effectively have an accelerating dipole instead. I don’t have my copies of Griffiths or Jackson handy, but I’m pretty sure this would radiate a small amount, though the fields would still mostly cancel out. My intuition is that the resulting radiation pattern would be more like a quadrupole pattern rather than a dipole pattern, but don’t quote me on that.

Easy: “The protons and neutrons are contained with a small volume, with the electrons in a larger volume around the protons and neutrons”. There, that has just as much informational content as the “miniature solar system” model, but without the lies.