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Accelerated Atoms and Electron Structure
Name: Judy
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
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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Update: June 2012
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