CrypticFish

I should clarify I am just a layman by the way, so sorry if anything I say seems silly. The 0.7c thing mainly comes from the various sources I have seen recently which attribute some velocity to an electron, but you are right to say it probably doesn't have velocity in the traditional sense, I think the 0.7c thing comes from people attributing a traditional orbit to an electron on further reading. Can you clarify on why the sum of momenta is zero in the local frame of a system? I interpret that as the total value of momentum equalling zero because momentum in any one direction is negated by momentum in the opposite direction thus it essentially averages out to zero. Or is it due to the components having equal relative velocity? So am I being misguided in focusing too much on the relative velocity between quarks/gluons and electrons due to the lack of defined position or motion for an electron?

To clarify, what I am getting at is that I am a bit confused on how an atom or larger body can be said to have a momentum of 0 and thus be in its own reference frame when it's components do not have a momentum of zero. Obviously, functionally, a larger mass can be considered as being in its own reference frame that can be compared to other reference frames. Just confused on how it works out on the tiniest level. Just used perception for simplifications sake. Ultimately I'm trying to get at a comparison of the frame of a fundamental particle and the frame of a larger mass, i.e the timing of events, their relative position and the difference in these traits between frames (and ultimately if I am correct in saying the components of a larger mass exist in a significantly different frame to a larger mass).

I'll try to keep this concise: Elementary particles have very different relative velocities, with quarks and gluons moving at or near C, and electrons being much slower (eg sometimes ~0.7% C). With this in mind, an atom or larger mass is typically considered to be in its own reference frame, despite its components being at very different relative velocities. Why is this? For example, a human does not perceive any time dilation or length contraction between the particles of their own body. Is this because the experience of a larger mass is more or less the average of its component particles? Would it be true that if a quark or electron could perceive the world, there would be a high degree of difference to how it perceives the world compared to a human that can be attributed to relativity, in essence, experiencing a significantly different degree of length contraction, time dilation, and events that seem simultaneous to us may not be simultaneous to the particle, etc?