# Q & A: relativity, quantum, etc.

Q:
Hello! I have two questions relating to 1) STR, 2) Observer effect1) Is it true that from photon's perspective moving away from the Sun, the Sun is moving away from it at the speed of light. If the answer is yes, would not this contradict the Special Theory of relativity (as the Sun's mass would be infinite). If the answer is no, what is the speed of the Sun from the photon's coordinate's system? The same question applies to far-away galaxies speeding away from us at ever-increasing speeds exceeding speed of light at the edges of the observed Universe. Isn't it also true that we are moving away from them at the speed exceeding the speed of light and this contradicts STR?2) Please clarify the Observer effect in quantum physics for me. Is it true that the results of the double-slit experiment with detection of particles at one of the slits collapsing the wave-function depend on whether an observer is in the room or not. If the observer is not in the room and the results of the detector are not recorded somehow the wave function is preserved despite detection of particles at the slits by a non-conscious detector. If it is the case, have experiments been conducted to identify whether the observer has to be somehow qualified to understand the contents of the experiment to result in the collapse of the wave function? Is there a lab open to the public where this mechanism can be observed? Thank you! Max
- Max (age 14)
Russia
A:

1) Relativity doesn't include any rest frame in which the photon is at rest, so it can't say anything about the photon's point of view.

As for the distant galaxies, special relativity doesn't limit the nominal change of distance coordinates as a function of time. SR is a theory describing flat local patches of spacetime. It's speed limit applies to the apparent speed of anything near the observer, not far away.

2) Quantum questions have less cut-and-dried answers. So far as we know, the conscious observer has nothing to do with the loss of interference. It's simpler to think that interactions with any large-scale object, leaving some sort of irreversible evidence, destroy any interference between different paths. We can't disprove the claims of those who are philosophically inclined to assign a big role to the observer, however, since by definition there cannot be evidence of which we are aware that has not registered in the mind of a conscious observer.

Mike W.

(published on 05/12/2017)