Recent content by crastinus

To help myself understand the difficulty here, since I'm the OP, I think the question discussed in the last coupled of posts is this: "Is spacetime itself a map or is it the thing that gets mapped by us in some way?" Is that the question you guys are discussing? Or something else? What is the...

I can honestly say that I'm still trying to decipher what you said. I summoned up Feynman's ghost to interpret for me. He says this: "The guy is basically saying: Spacetime is the sheet of rubber and the EM field is the static on the sheet. Things move sometimes because the sheet is curved...

Assumptions are so much fun, though! :)

What is the relationship between the electromagnetic field and space-time? I am basically assuming that space-time is one big gravitational field. Is there a relationship between space-time and the field (I presume) created by the strong force (however negligible it may be at any significant...

I was taught that kinematics is the study of local motion without references to its causes (like forces, fields, etc.). That seems useful to say but perhaps it is not really that helpful. What are the kinds of kinematics? I can think of three kinds: classical kinematics (from mean speed to...

But even in the case of the ball being momentarily stationary with respect to me, it is still moving with respect to lots of other things, e.g. the sun, etc., right? As to the expansion of the universe from the beginning to now, of course, it’s not just expansion in the ordinary sense, since...

Maybe OP is also trying to get at a question like this: Is everything always moving relative to something else? I would think the answer is “yes”, if nothing else just based on the evidence of the history of the cosmos. There was a massive expansion to start it off, so it makes sense that...

Side question: Is it ever possible for one clock to read that some time has passed (a vanishingly small moment, presumably) and the other clock to read that no time has passed? Assuming both are functioning well. Just curious.

Thanks. But, wait: I'm little confused. If there is a tacit assumption of absolute time in what I said (and I see that there is!), then isn't there also an assumption of relative time in what you all said? Presumably so. But, of course, what you are saying is derived from the larger and...

Thanks! So, the problem here is that, by saying "they must run at different speeds" and "one must run slower than the other", I am making a tacit assumption that time is absolute in some reference frame. Is that right? (I'm trying to put it in my own words so I can actually understand it.)

If we have two clocks, A and B, that are identical, and if one is moving with respect to the other one, we know that they must run at different speeds. (Right?) One must run slower than the other. But we cannot tell which of the two clocks is the "moving" clock. So, how do we determine which...

Thanks for the responses! I just keep thinking about it. This is a sort simple "state space" with just position and distance. I wonder if there is any significance to it.

Imagine we draw a two dimensional finite plane with coordinate axes; for simplicity, let's make it a square. Now, suppose we add a third dimension that represents the possible distances between any two points on the square. Now we have a three dimensional space. What shape will that space have...

To add one perhaps final point of literature (recently pointed out to me): Mario Bunge argued in American Journal of Physics that we should not interpret Lagrangian formulations in a physical way. There is a response to his piece in the letters to the editor. Below are the references if you're...

I didn't know about that site, thanks.