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Jun
17
comment How does “warp drive” not violate Special Relativity causality constraints?
Let's say that Earth sends a radio signal (in all directions) when the ship leaves, and Alpha Centauri sends a signal when the ship arrives there. If the ship is FTL in proper time, are there not inertial frames (far from the ship) that would see the arrival as occurring before the ship's departure, clearly violating global causality?
Jun
17
comment How does “warp drive” not violate Special Relativity causality constraints?
So have I misunderstood all along? You're saying that it's not FTL from the point of view of Earth?
Jun
17
comment How does “warp drive” not violate Special Relativity causality constraints?
Let's say that Earth sends a radio signal (in all directions) when the ship leaves, and Alpha Centauri sends a signal when the ship arrives there. As I understand SR, observers in different inertial frames may disagree on the time difference between those two signals, but that the departure will always precede the arrival for all observers. There are all sorts of observers, not on the spacecraft or anywhere near it, who would see the events as violating causality if the craft were FTL. No?
Jun
16
comment How does “warp drive” not violate Special Relativity causality constraints?
@PhotonicBoom : Yes, but what of an observer in an inertial frame that is far enough away from the spacecraft that the observer is in essentially flat spacetime. Will they not see the events as being non-causal? Is that not a fairly fatal problem? What aspect of GR explicitly allows violations of causality? (I'm not a GR expert.)
Mar
5
comment Does a mirror help a near-sighted persion see at a distance clearer?
No, for a flat mirror, the apparent distance in this case is the total optical path length -- that is, the distance from eyes to the mirror plus the distance from the mirror to the object. Nothing dictates that it will be precisely twice the distance from the viewer to the object.
Mar
27
comment Does the sun rotate?
It would be an incredibly unlikely occurrence for the protostellar cloud to have so little net angular momentum that, after collapsing (think of the figure skater) it would not have a noticeable rotation. Possible, but ridiculously improbable.
Feb
20
comment Are there still 'everyday' phenomena unexplained by Physics?
Just because we don't understand what circumstances lead to the formation of ball lightning doesn't mean our current physical laws can't account for it. Do you have any reason to suspect that it's not governed by the usual electronmagnetic force, plasma physics, and so on, that govern regular lightning?
Dec
5
comment Is two cars colliding at 50mph the same as one car colliding into a wall at 100 mph?
Two cars moving toward each other, each at 50 mph, should be equivalent to one car at 100 mph colliding with a (previously) stationary car (assuming both are in neutral gear, the moving ones are just rolling). But that situation is not equivalent to hitting a wall.
Feb
27
comment How much detail can telescopes actually provide?
I'm not sure the analogy holds. When a ground-based telescope looks up, the thickest and most turbulent part of the atmosphere is close to the telescope, where small angular deviations are more important than angular deviations close to the target and far from the detector. A space-based telescope looking down is in the opposite (i.e., more favorable) configuration. So the diffraction limits of the optics may be a better metric of how good an earth-based scope can do.
Feb
8
comment Is time fundamentally different from space?
Isn't it a circular definition to simply say that "time" is the dimension along which spacetime events aren't "simultaneous?" Also, "x" is family of sets of spacetime events whose x coordinates are not the same. That still doesn't really say anything about what makes t different from x.
Jan
16
comment How exactly does time slow down near a black hole?
Actually, they are not in low earth orbit, either. LEO is about a 90 minute orbit, geosynchronous is a full day. GPS satellites orbit in 11h58m.
Sep
21
comment Are there planets that do not rotate on their axis?
You mean with a sidereal reference frame? Of course. What I was really trying to clarify is whether the original poster was considering a tidally-locked body to be rotating, or not. (I do.)
Sep
19
comment What is the average distance between objects in our asteroid belt?
Why was this downvoted?
Sep
12
comment On what planar regions are the Earth, Moon.. for that matter, all astronomical bodies, placed in the Universe?
It is worth noting that the moon is not always "up". Sometimes it's "up", sometimes it's "down," depending on the time of day and month. But when it's "down", you can't see it because the Earth (i.e., the ground) is blocking your view.