Recent content by Afterthought

1) There's no way of telling some things in quantum mechanics (eg. uncertainty principle), but people still argue about what reality is like. Or did you mean something else by that? 2) Does GR really say that there's no way of telling? So if someone claims that they found a way to distinguish a...

I've heard that unlike Special Relativity, General Relativity claims that you can' say any reference frame is better than another frame, including frames in which Newton's Laws don't hold. I've seen debates about this specifically in the context of geo/helio-centrism. From what I understand...

Note: This is more of a math question than a physics question, but I'm posting it here since it's in the context of physics. I've been thinking about the classic example of a ball attached to a string and moving at constant speed in a circle. The acceleration is v^2/r and always facing in the...

Bumping this thread in case people didn't see it (I posted in the wrong forums initially).

I'm a senior undergrad majoring in physics. I've decided recently that I want to get a Masters to improve my chances in the job market (I'm still undecided if I want to get a PhD after that). So I've done my research, but am a bit confused, since information about Masters and PhD's are lumped...

I didn't mean that there was a need for a human, I only said human because that was the example I gave. But anyways, you answered the question so thank you.

Thanks, that made it a little clearer. One thing I still don't get is why the string attached to the ball doesn't count as an an extended object held together by electrostatic forces (and therefore could generate centripetal forces without aid of a human). Is it because of the "structurally...

Suppose you have a ball on a string, and you make the ball to move around in a circle. The force on the ball is caused by the tension of the string, and is called the centripetal force F = mv^2/r. If you were to let go at any moment, the ball would stop rotating and move with linear velocity...

Thank you for the links, checking them out right now. The derivation of the Doppler relations also seem helpful, I will try seeing (pun intended) if I can apply them to a simple problem.

My impression always was that when you describe a problem in special relativity, you are already implicitly taking into account the light that would need to travel for some person to theoretically "see" a special relativistic phenomenon. I was confronted recently in another thread that this...

Thank you again! I'd consider my question to be answered now that I know that.

This is what I meant by "materializing". Anyways, thank you, I think I'm slowly starting to get it. Let's say the rod is a light source whose frequency increases by time but not by distance in the frame of O'. When you see the rod in the frame of O at any instance, would you see a spectrum of...

Ah, so the balls aren't events. But if the rod magically appeared and disappeared an infinitesimally small moment later in frame O', wouldn't the balls qualify as events then, leading you to seeing a materializing rod in frame O? Can you clarify what you mean by "at any moment both balls are...

Suppose that frame O' moves at speed v = 0.6c relative to frame O. A rod with two balls is attached to its ends is 10 meters long in its rest frame, O'. Length contraction will tell you that in frame O, the rod is 8 meters long. But aren't the two balls at the ends "events"? They are clearly...

Hmm, that escaped me but that does seem to be correct. I would still consider my question to be open for further explanations.