Short answer: position and velocity are relative, acceleration isn’t. The laws of physic are the same in two inertial frames of reference, they are NOT the same if one frame is accelerating, hence the discrepency.
Only humans commit inhuman acts.
The laws of physics are the same, even if one frame is not inertial. That’s general relativity.
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rocks</font>
Yeah, I think it all boils down to your point of reference. If your reference point is B, then A is accelerating. If your reference point is A, then B is decelerating.
In the end, its all relative to the observer.
I think.
Special Relativity is weird, but easy. But it posits a world in which nothing ever accelerates; everything keeps moving in straight lines (whatever that means) forever.
Special Relativity doesn’t even need light. You can prove with basic algebra that there’s a magic speed that you can’t go faster than. Before Einstein, everyone thought (as it were) that the magic speed was infinity. (They took it so much for granted that they didn’t even know the magic speed was there, but the math can be done in theory, if you just don’t assume that relative velocities simply add, which, of course, everybody did.)
General Relativity works with acceleration, but is not only weird, but incredibly difficult. It involves doing calculus on tensors (super-matrices where subscripts have subscripts). We’re not even sure that Einstein got it right (although he’s clearly close).
Bottom line: if you want the real answer, it’s much too difficult to give here. But if you want the quick and dirty answer, the one who accelerates (and he can feel that he’s accelerating, because it produces a false [in a certain sense of the word "false] “gravity” field in the opposite direction to his acceleration) will find, on his return, that his clock has been running slower.
Heavy gravity fields also slow clocks, since it is a basic principle of General Relativity that you can’t tell the difference between “false” and “true” gravity.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
This is misleading. Non-accelerating frames of reference have a special place, but things can certainly accelerate in a special-relativistic universe. You can even describe things from an accelerating frame of reference if you like, but it gets more complicated.
It is too clear, and so it is hard to see.
Six Easy Pieces consists of six lectures from the Lectures on Physics, I1, I2, I3, I4, I7, and I37. It’s seems that Six Not-so-easy Pieces also consists of six of those lectures. Does anybody have the names of the chapters/lectures?
I’d think these would be possibilities:
I9 Newton’s Laws of Dynamics
I15 Special Theory of Relativity
I16 Relativistic Energy and Momentum
I17 Space-Time
II42 Curved Space
What’s the other(s)?
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rocks</font>
Hold onto your seat. There’s a certain sect (cult? I hesitate to use the word school) of “Christian Creationist” astronomers who assert that this is exactly the explanation for the observed effect.
That’s right, folks. The entire Universe rotates around the Earth each day. As does the Sun “actually”.
Check out Phil Plait’s Bad Astronomy Homepage. There’s usually one of the geeks hanging around the message board, posting just the sort of messages you’d expect.
As a frame of reference, that’s allowed. The laws of physics still “work.” The problem with such creation scientists is that they insist that that is the only interpretation, and quote relativists as being on their side.
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rocks</font>
I think we’re at cross-purposes here. It is certainly not possible to assert that there are no privileged frames of reference if one A) allows Special Relativity only, B) allows accelerated frames of reference, and C) references the real world.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
I think ZenBeam was referring to your comment that special relativity “posits a world in which nothing ever accelerates.” ZenBeam calls that misleading, I think it’s false. I don’t think the theory of special relativity restricts things to non-accelerated behavior anymore than Newton’s theory.
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rocks</font>
That’s really spooky. I believe the bible but I think it’s reasonable that God may have not meant for all of Genesis to be a blueprint for the universe. Maybe some of it is meant to be allegorical but I’ll probably roast in hell for suggesting such blasphemy. (At least I’ll have company from some SDMB folks) What puzzles me is how that theory is in any way “creationist” as opposed to merely being crackpot science.
The earth as the unmoving center of the universe theory is interesting though. Will it take a Mitchelson Morley interferometer experiment performed on the moon to disprove it?
On this topic though I think the OP asked something that can’t be succinctly answered. This is the kind of thing that I didn’t get to until the end of a year college physics course.
That’s really spooky. I believe the bible but I think it’s reasonable that God may have not meant for all of Genesis to be a blueprint for the universe. Maybe some of it is meant to be allegorical but I’ll probably roast in hell for suggesting such blasphemy. (At least I’ll have company from some SDMB folks) What puzzles me is how that theory is in any way “creationist” as opposed to merely being crackpot science.
The earth as the unmoving center of the universe theory is interesting though. Will it take a Mitchelson Morley interferometer experiment performed on the moon to disprove it?
On this topic though I think the OP asked something that can’t be succinctly answered. This is the kind of thing that I didn’t get to until the end of a year college physics course.
RM Mentock:
Sorry, haven’t checked back. Your right I did lose a piece! The Six Not So Easy Pieces are:
- vectots
- Symmetry in Physical Laws
- The special theory of relativity
- Relativistic Energy and Momentum
- Space Time
- Curved Space
Ooops.
Actually I don’t think Feynman discussed “Vectots” in that book. (Though the study of vectots is grossly neglected in today’s sciences"
The actual chapter was “Vectors.”
For anyone who’s interested, the corresponding chapters in Lectures On Physics are
I11. vectots
I52. Symmetry in Physical Laws
I15. The special theory of relativity
I16. Relativistic Energy and Momentum
I17. Space Time
II42. Curved Space
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rocks</font>
S.R. supposes that acceleration doesn’t happen in the same sense that classical optics assumes that light is made of waves. Yes, acceleration does happen; but you can’t use Special Relativity to analyze it and keep the assumption that there are no privileged frames of reference.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
You’ve completely lost me with the optics analogy.
I don’t think anyone has said that non-accelerating frames of reference aren’t priveledged in SR, as compared with arbitrarily accelerating frames of reference.
It is too clear, and so it is hard to see.
But that’s my point. The whole idea of SR and GR, the reason for the very word “relativity”, is that there shouldn’t be privileged frames of reference. But when you have SR and no more, non-accelerating frames are privileged.
The reference to optics is simply that most theories have simpler (usually older) forms that cover only some cases. You don’t need quantum analysis to make eyeglasses.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
I don’t see any a priori reason for non-accelerating frames of reference not to be priveleged. You can’t make a measurement to tell your absolute position or absolute velocity, but you can tell if you are accelerating or not. If you didn’t have gravity due to mass, there wouldn’t be a need for GR in an SR universe; without gravity, GR is an ad-hoc mathematical addition.
It is too clear, and so it is hard to see.
The whole idea of SR is that there shouldn’t be preferred frames of reference? That’s not true, but you may not have meant that. Anyway, the original objection was to your saying that special relativity “posits a world in which nothing ever accelerates,” which is also not true.
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