# a Relativity question **URL:** \ **Category:** Factual Questions\ **Created:** [January 31, 2000, 9:13pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948 "2000-01-31T21:13:00Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Momotaro](https://avatars.discourse-cdn.com/v4/letter/m/2bfe46/32.png) [@Momotaro](https://boards.straightdope.com/u/Momotaro)\ **Post date:** [February 2, 2000, 12:47pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/21 "2000-02-02T12:47:00Z")
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. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 2, 2000, 4:06pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/22 "2000-02-02T16:06:00Z")
The laws of physics _are_ the same, even if one frame is not inertial. That’s general relativity. \ rocks\ ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [February 2, 2000, 5:04pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/23 "2000-02-02T17:04:00Z")
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. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [February 2, 2000, 8:21pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/24 "2000-02-02T20:21:00Z")
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 ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [February 3, 2000, 5:22pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/25 "2000-02-03T17:22:00Z")
> [@](#): > > 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. 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._ ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 3, 2000, 5:34pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/26 "2000-02-03T17:34:00Z")
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)? \ rocks\ ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [February 4, 2000, 6:06am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/27 "2000-02-04T06:06:00Z")
> [@](#): > > Originally posted by Padeye: > One possible explanation is that the earth is in fact fixed in the universe and everything moves around it. Call it a hunch but I don’t think so. 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](http://www.badastronomy.com). There’s usually one of the geeks hanging around the message board, posting just the sort of messages you’d expect. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 3, 2000, 7:36pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/28 "2000-02-03T19:36:00Z")
> [@](#): > > Originally posted by **\George Papoon\** : > **That’s right, folks. The _entire Universe_ rotates around the Earth each day. As does the Sun “actually”.** 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. \one of the geeks rocks\ ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [February 5, 2000, 6:15am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/29 "2000-02-05T06:15:00Z")
> [@](#): > > 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. 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 ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 4, 2000, 7:21pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/30 "2000-02-04T19:21:00Z")
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. \------------------ rocks\ ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [February 4, 2000, 10:01pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/31 "2000-02-04T22:01:00Z")
> [@](#): > > Originally posted by George Papoon: > \*\* 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 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. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [February 4, 2000, 10:08pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/32 "2000-02-04T22:08:00Z")
> [@](#): > > Originally posted by George Papoon: > \*\* 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 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. ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [February 5, 2000, 12:23am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/33 "2000-02-05T00:23:00Z")
RM Mentock: Sorry, haven’t checked back. Your right I did lose a piece! The Six Not So Easy Pieces are: 1. vectots 2. Symmetry in Physical Laws 3. The special theory of relativity 4. Relativistic Energy and Momentum 5. Space Time 6. Curved Space ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [February 5, 2000, 12:26am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/34 "2000-02-05T00:26:00Z")
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.” ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 5, 2000, 2:46am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/35 "2000-02-05T02:46:00Z")
> [@](#): > > Originally posted by **\Scylla\** : > **The Six Not So Easy Pieces are:** 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 \------------------ rocks\ ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [February 8, 2000, 12:32am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/36 "2000-02-08T00:32:00Z")
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 ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [February 9, 2000, 6:36am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/37 "2000-02-09T06:36:00Z")
> [@](#): > > Originally posted by John W. Kennedy: > 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. 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._ ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [February 8, 2000, 7:31pm UTC](https://boards.straightdope.com/t/a-relativity-question/6948/38 "2000-02-08T19:31:00Z")
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 ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [February 9, 2000, 3:31am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/39 "2000-02-09T03:31:00Z")
> [@](#): > > 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. ## 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._ ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 9, 2000, 9:49am UTC](https://boards.straightdope.com/t/a-relativity-question/6948/40 "2000-02-09T09:49:00Z")
> [@](#): > > Originally posted by **\John W. Kennedy\** : > **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 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. \---------------- rocks\ [Previous page](https://boards.straightdope.com/t/a-relativity-question/6948.md?page=1) [Next page](https://boards.straightdope.com/t/a-relativity-question/6948.md?page=3)