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location Vancouver, Canada
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Jun
20
awarded  Popular Question
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
17
awarded  Nice Question
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.)
Jun
16
awarded  Student
Jun
16
asked How does “warp drive” not violate Special Relativity causality constraints?
Mar
5
awarded  Commentator
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.
Jan
22
awarded  Critic
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.
Nov
3
awarded  Yearling
Sep
19
answered Why is Light invisible?
Sep
5
answered Why do rainbows have distinct colors?
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.