Electron orbiting speed and time dilation

How fast does an electron (on average) orbit the nucleus of its atom? I’m not looking for an exact answer, but am wondering what the passage of time is like from the perspective of the electron. From its perspective, do the movements of the nucleus appear to be sped up and the electron’s own movements (from the electron’s perspective) seemed slowed down?

In a similar question, for a photon traveling at 1 c since the beginning of the universe (or a close approximation thereto), how much subjective time has passed for the photon since the big bang?

Electrons don’t orbit, in the sense you are thinking. They actually changed the name to “orbital” for that reason. But you can find some discussion of relativistic effects upon electrons in certain circumstances here.

If you attempt to ignore quantum mechanics and calculate a classical “speed” for the electron in a hydrogen atom, you’ll find that it’s exactly the fine structure constant times the speed of light. Relativistic effects at this scale are small, but measurable with sensitive enough equipment, and in fact relativistic effects are observed for electrons in atoms (though it takes a theory much more sophisticated than ignoring quantum effects to correctly say what they are). This is the domain of quantum field theory, or more specifically, quantum electrodynamics.

None at all. Photons are eternal; all times are the same time to a photon.

That is what I had hoped.

There is no need for fancy equipment to measure this. Relativistic effects have considerable effect on the third row transition metal chemistry. Third row elements tend to make much more stable bonds than there second row counterparts. In homogeneous catalysis, palladium is used very frequently. It switches up its bonding fast enough that it makes a very useful catalyst, on the other hand platinum tends to form stable complexes that palladium will never form.

I want to be clear though. I’m not a physicist, I’ve just read that this is a result relativistic effects, and I believe it because these differences in reactivity are pretty hard to reconcile. It is this way with all third row to second row metals. The second row is fast acting, the third row is slow.

Then how can a photon be emitted where none was there before? (if indeed that’s what “emit” means.) How can one photon (I’m guessing) be at one point in space at one time (from our perspective) and another point in space at another time?

Well, the point here is that from the perspective of the photon, no time passes (in a sense, time is dilated to a stop), even though to us outside observers, time flows normally; it’s what you get if you take the limit of v -> c for a particle’s movement.

However, the ‘point of view’ of a photon is a bit of a problematic concept, since there pretty much just isn’t such a thing; usually, the point of view of something is the frame of reference in which it is at rest, which, since photons travel at c in all frames of reference according to the postulates of special relativity, doesn’t exist for a photon. So it’s IMHO a bit difficult to decide if it’s meaningful at all to say that photons don’t experience time passing, or even whether or not the question can be asked sensibly.

What if light isn’t travelling at c?
(I know I’m grabbing questions completely out of my rear end here, but still curious.)

There is no law that says light has to travel at c. C was a solution to Maxwell’s equations, which turned out to be the speed at which light travels. If scientists discovered tomorrow that photons actually have a tiny mass and therefore light does not travel at c, c would still be c and would not change to accommodate the “new” speed of light.

For an interesting answer see the movie Mindwalk.


Yeah, but I was referring to this (bolded parts):

It is an assumption (though one based on experiments) that the photon is massless. If it is massless, then it must travel at c, and have no rest frame. For a photon to have a rest frame, then either it must have a (very small, but nonzero) mass (which is plausible, though considered unlikely), or Special Relativity must be wrong (don’t count on it; it’s the most thoroughly-proven theory in all of science).

Things get a bit complicated when dealing with light propagation in matter, and you’d need quantum electrodynamics to appreciate the full complexity; however, as an analogy, I don’t think it’s too wrong to picture light getting absorbed and re-emitted as it transitions the medium, which introduces an overall delay and thus an apparent macroscopic ‘slowing’ of the light – however, the individual photons, ‘in between absorptions’, still travel at c.