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Name: Judy
Status: student
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Question:
The nucleus of an atom is surrounded by one or more electron wave packet levels. When an atom is accelerated to a significant percentage of the speed of light, do the electrons find it more difficult to keep up with the nucleus and to continue to orbit around the nucleus? In other words, when the atom accelerates do the electrons exist as particles or wave clouds and do their orbits take longer to complete because they are trying to outrun the nucleus (in order to complete a revolution)? Do we even know the answer to this question?



Replies:
Hi Judy,

This is a classic example of how subatomic particles are not like "little moons orbiting a little planet". Electrons don't actually revolve around or orbit nuclei. To think of electrons as 'trying to catch up' to an 'orbit' doesn't make sense given how electrons actually behave.

Rather than thinking of electrons as discrete particles orbiting around the nucleus, it may be useful to think of them as being a 'smear' that's distributed all around the nucleus all at once. By 'smear', I don't just mean 'so fast you can't see it clearly', I mean actually everywhere at once. If the 'smear' of the electron is all around the nucleus all the time, then thinking of an electron as 'catching up' no longer makes sense. The electron is already everywhere it could be (and always was everywhere it could be). At very small scale, things can be counter-intuitive and just plain weird!

Also, electrons don't change from wave-like to particle-like. They are both at the same time. In some experiments they appear to act more like particles, while in other experiments, they appear to act more like waves (still weird and confusing). But that doesn't mean they alternate between one state and the other, it just means that one description fits that particular behavior better than the other description.

There is one more layer of complexity. You mention the speed of light, which is important in general relativity. General relativity is very successful in describing large-scale phenomena like gravity. In contrast, quantum theory is very successful at explaining the behavior of very small things (like subatomic particles). So in a way, your question is probing how these two theories come together. Answering that question, unifying the two theories, is something that is still being actively pursued by scientists.

In closing, you might appreciate a legal analogy: for small scales, quantum theory has 'jurisdiction', and for large scales general relativity has 'jurisdiction'. Where they meet, how to unify them, or if an entirely new set of 'laws' is needed, still requires more research to determine.

I hope this has helped a little,

Burr


In general, the electrons in an atom or molecule "move much faster" than the nuclei. This principle, called the Born-Oppenheimer approximation. This allows one to separate the variables of motion of the nucleii from the variables of motion of the electrons. Because the electron mass is only about 1/000 that of the nucleii, it is the nucleii that are sluggish compared to the speed of motion of the electrons. Nonetheless, a good question.

Vince Calder


If the atom is moving at a constant velocity, no matter how close to the speed of light that velocity might be, the electrons and nucleus will have no difficulty staying together. As far as they are concerned, it will be just like standing still. Their physics will seem completely normal in their constant-velocity reference frame. From our reference frame, it will appear that the electrons are moving unusually slowly, and the energies of electronic transitions will appear to be unusually low (if the atom is moving away from us) or unusually high (if the atom is moving toward us). These effects arise from the difference in velocity between the observer (us) and the observed (atom), not from any actual change in the behavior of the atom.

Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming


Hi Judy,

This is a classic example of how subatomic particles are not like "little moons orbiting a little planet". Electrons do not actually revolve around or orbit nuclei. To think of electrons as 'trying to catch up' to an 'orbit' doesn't make sense given how electrons actually behave.

Rather than thinking of electrons as discrete particles orbiting around the nucleus, it may be useful to think of them as being a 'smear' that's distributed all around the nucleus all at once. By 'smear', I do not just mean 'so fast you cannot see it clearly', I mean actually everywhere at once. If the 'smear' of the electron is all around the nucleus all the time, then thinking of an electron as 'catching up' no longer makes sense. The electron is already everywhere it could be (and always was everywhere it could be). At very small scale, things can be counter-intuitive and just plain weird!

Also, electrons do not change from wave-like to particle-like. They are both at the same time. In some experiments they appear to act more like particles, while in other experiments, they appear to act more like waves (still weird and confusing). But that does not mean they alternate between one state and the other, it just means that one description fits that particular behavior better than the other description.

There is one more layer of complexity. You mention the speed of light, which is important in general relativity. General relativity is very successful in describing large-scale phenomena like gravity. In contrast, quantum theory is very successful at explaining the behavior of very small things (like subatomic particles). So in a way, your question is probing how these two theories come together. Answering that question, unifying the two theories, is something that is still being actively pursued by scientists.

In closing, you might appreciate a legal analogy: for small scales, quantum theory has 'jurisdiction', and for large scales general relativity has 'jurisdiction'. Where they meet, how to unify them, or if an entirely new set of 'laws' is needed, still requires more research to determine.

I hope this has helped a little,

Burr Zimmerman



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