It’s true that QED includes a non-zero amplitude for light traveling at superluminal (and subluminal) velocity over really really short eentsy-weentsy distances. I don’t know if anyone has ever devised an experiment to prove the existence of such a phenomenon.
jrf
Aren’t GPS satellites in geosynchronous orbit? If so then the system of you and the GPS satellite are not moving toward or away from each other and thus can be treated as a non accelerating frame, correct?
Nope.
It is too clear, and so it is hard to see.
No, GPS are not in geosynchronous orbit. And motion in a circle or ellipse is accelerating.
Regarding GPS, has anyone done the math to determine how off things would be by SR? Obviously the coarse adjustments were made prior to launch as described in the American Spectator article previously linked to by emarkp:
From this I gather that the GR correction is about 7 times more significant than the SR correction in the specific case of GPS. Begin hand wave of someone who dropped out of GR class: Since the acceleration is due to gravity and the orbit is nearly circular, the GR correction is constant (end hand wave - someone please correct me.)
The article goes on to describe the problem with SR and GPS:
So, I guess my question is has someone done the math to determine what the corrections should be? My off the top of my head guess is that the variations in orbital speed will cancel out over the long term, i.e. they will not build up. We’ve already accounted for 7000 ns retardation per second, so if the speed of the satellite varies the retardation from 6900 to 7100 ns over time, but still averages 7000 ns retardation due to SR, you won’t see a long-term affect. Or if you do, it will be very small. Is there something about the orbits that would make this argument unsound?
Until I read an article on the above SR calculations, I’m not worried about the long-term affect. Now, what about short-term? It seems to me that you can only see a portion of the satellites in orbit, those directly above you. Those satellites will not be far off of the average velocity, so while you are in contact with them the clocks won’t vary by more than a few ns - your GPS receiver will probably not be able to resolve this finely.
Anyone have a reference to SR & GPS calculations?
I took a look at the TAS article. It set off my bullshit detector several times, especially toward the end, where it falls back on sheer hand-waving and ignorance.
Since it doesn’t present any actual math, of course, it can’t actually be refuted as it stands. On the other hand, when physics is the name of the game, if you don’t do the math, you haven’t done anything.
Here’s one example of bullshit, though. Journals called “letters” will print anything that’s reasonably grammatical and on-topic; that’s what they’re for. Any loony can send something to a “letters”-type journal in any field, get it printed, and then claim that his theory was printed “in a journal”. It’s about as meaningful as saying that something is “on the Internet”.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
Douglips had a quote with
For 3 km/s, I get 4.32E-6 seconds per day = 4320 nanosecond/day. 7000 / 4320 = 1.62 = miles/km. I suspect someone dropped a conversion factor somewhere.
It is too clear, and so it is hard to see.
Physics Letters A in its
Guide for Authors that “All contributions will be refereed.” On the other hand, they say that Physics Letters A is an “outlet for novel and frontier physics.”
<font color=#DCDCDC>----------------
rocks </font><font color=#FCFCFC>Sure would be nice to have a preview feature</font>
Two points:
The TAS article was an overview. The article it was based on has the math. Try checking that URL.
So nothing useful is on the Internet? Or just because you didn’t read the actual article with the math means that it must be dismissed because it was in a “Letters” Journal?
I hear my ad hominem and strawman alarms going off.
emarkp, I’ve provided a link to extensive discussions over this with real professors of physics. Please read. Von Flandern (sp?) does not understand General Relativity. He does not realize that General Relativity perfectly predicts the orbits of the planets, for example, and does not need the speed of gravity to exceed c. Instead, he only shows Newtonian physics has to have instaneous gravity, which is correct. However, that theory is old and outdated, and GR predicts things much better without having that assumption. He also does not undestand that GPS’s take into account relativistic effects.
My link in my post above easily shows that this guy does not know what he’s talking about. Before posting again, I advise you to read it. Failing that, at least do a search on deja.com to read the debate first-hand.
GPS was specifically designed to take into account the effects predicted by relativity. No matter what hocus pocus you do to argue with the reality, if relativity were wrong GPS wouldn’t work. The fudge factor introduced would have randomly skewed the calculations.
So at best you can argue is that there is another explantion that creates effects exactly as predicted by special relativity. But if so, it’s your job to give that explanation.
My thanks to Avumede for posting some good links to discussions that happened in sci.physics and sci.physics.relativity. I’m pretty convinced now that Tom Van Flandern is wrong. He makes some arguments that seem to make sense intuitively, but he doesn’t appear to understand the GR model of gravity. I’ve discarded his article as part of my accepted information.
Now, as for quoting GPS as the ultimate proof RealityChuck, I have stated why I don’t buy it. You have ignored that. Believe it or not, simply asserting something over and over again does not make it true.
Until I see the calculations of the SR & GR effects on the GPS satellites and understand the issues of why it should/should not cause irreducible complexity in the computations, I can’t really say one way or the other whether GPS works because of SR, or in spite of SR.
My gut reaction is I would have heard more if SR predicted total failure and GPS worked anyway, so my guess would be that it works because of SR. However, I’d still be open to the calculations showing how SR would cause huge problems with GPS.
<sigh!>
Does ad hominem mean anything at all any more, or is it just a completely meaningless insult?
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
John W. Kennedy:
Sure, here’s how m-w.com defines ad hominem:
Main Entry: 1ad ho·mi·nem
Pronunciation: (’)ad-'hä-m&-"nem, -n&m
Function: adjective
Etymology: New Latin, literally, to the person
Date: 1598
1 : appealing to feelings or prejudices rather than intellect
2 : marked by an attack on an opponent’s character rather than by an answer to the contentions made
And here’s the quote of yours I was referring to:
Looks like ad hominem to me. You certainly didn’t address the issue.
There might have been a bit of misstatement that draws away from the discussion. It would be more accurate to say that GPS would not work correctly if relativistic time dilation was not accounted for and corrected.
Right. What I’m referring to is one of the articles linked to above says that according to SR, the corrections are continuously varying and therefore GPS cannot work. The article said that the ‘simple’ corrections for GR and average velocity SR were used and work fine, but (according to the article) the continuously variable speed of the satellites would introduce intractable complexity in the calculations.
My point is, without seeing the math behind the ‘SR says you get intractable complexity’ I am willing to buy the argument that ‘SR says you do NOT get intractable complexity’, because I was able to reason it out in my head on the previous page.
Then maybe you’d better try thinking harder. Or you could just get a textbook on elementary logic…
The statement, “This argument makes a deceptive appeal to authority by citing a statement made in an open forum as though it were ipso-facto blessed by the community,” is no more an ad-hominem argument than, “2 and 2 is 22,” is a statement in arithmetic.
And, seeing that it is impossible to refute a statement that has not been coherently made, about all I can say in answer to the vague and unspecific TAS article is that it bears the characteristic attributes of bad science.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
Ah, I think I see the problem. I thought you were dismissing the actual article that was posted in Physics Letters simply because a “Letters” mag is suspect (hence my charge of ad hominem). Now it appears to me that what you were saying is that the article in TAS made a claim of veracity based simply on the fact that the article was published. Is that in fact what you’ve been arguing?
My apologies if I misunderstood your argument. However, please look at the actual article that TAS was referring to (I posted the link in my first message). It actually makes data-based claims which should be able to be analyzed directly. Specifically, please read the issues with SR calculations wrt GPS.
From the Van Flandern article:
I guess what he’s saying is that if you were on a satellite, SR would dictate that you would see earth clocks moving slower than your clock, but that van Flandern says you would not.
After some searching, I’ve been unable to find a decent article outlining what the calculations are vs. the observations.
It sounds like van Flandern doesn’t believe the two-way street of SR, and believes that if you were on the satellite you’d see earth clocks moving faster than your clock.
This doesn’t seem that difficult to verify. If the correction for SR is 4320 ns/day, as calculated by ZenBeam, then if something were in orbit for 2000 days the difference would be about 8 milliseconds, easily measurable. So, after six years or so, either the satellites would report “Hey, your clocks are 8 milliseconds slower than mine” or “Hey, your clocks are still synchronized with mine.”
I guess the argument is that since we jacked their clock around so it looks to run at the same rate as ours, they (the satellites) must see our clock running slow, and eventually get out of sync. I think I understand the argument now, but I’m not sure what the appropriate response is in terms of doing calculations to determine what is right and wrong.
I’ll need to get a bit more curious before I pull out my SR text and try to figure this out, though, as I still have a job.