Author Topic: Einstein's lightning/train  (Read 19686 times)

Offline philately

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Re: Einstein's lightning/train
« Reply #30 on: August 06, 2013, 11:14:24 PM »
Ahh,    apparently, the clocks have to be accurate to within nanoseconds for any sort of useful GPS triangulation. It's more fun to ask the questions than to google the answers.
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Offline bobmath

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Re: Einstein's lightning/train
« Reply #31 on: August 07, 2013, 07:23:43 AM »
It's actually not JUST the satellite's speed that makes it have to factor in the time difference, but it being much farther from Earth's center of gravity than we are.
This is true.

If the GPS satellite is traveling at 18,000 mph, that's 0.0000268409 c.
By my calculation, orbital velocity is 8,000 mph at the altitude GPS satellites use. It takes more energy to get to a higher orbit, but perhaps unexpectedly you're going slower when you get there.

Quote
It would seem far more practical to simply send a sync signal up to the satellites, once a month or whatever. Perhaps they do both?
I'd guess they have a gradual way of adjusting the clocks, so they don't disrupt GPS service.

Offline philately

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Re: Einstein's lightning/train
« Reply #32 on: August 07, 2013, 11:23:19 PM »
Is it  theoretically possible to make a clock that is not affected (very much) by relativity? For example,  if the speed of light is constant,  the clock could measure the time it takes for light to travel between an emitter and a receiver and use that as one clock cycle? Perhaps this would be pointless...

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Offline bobmath

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Re: Einstein's lightning/train
« Reply #33 on: August 08, 2013, 06:01:52 AM »
Watch out for length contraction of the distance between the emitter and receiver.

Any device you try to build is ultimately going to depend on quantum mechanics, and that's "an area of active research." Meaning that we don't entirely know how to get relativity and quantum mechanics to play nice together.

Offline philately

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Re: Einstein's lightning/train
« Reply #34 on: August 08, 2013, 11:17:19 PM »
Are all clock designs equally affected by relativity (assuming the same reference frames)? For example,  an atomic clock,  a digital clock, a  pocket watch all on board a GPS satellite... perhaps there are a combination of relativistic effects and gravity,  acceleration,  etc?  I can't remember - does relativity affect the speed of electricity through circuits?
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Offline bobmath

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Re: Einstein's lightning/train
« Reply #35 on: August 09, 2013, 08:06:18 AM »
The idea is that time and space themselves are twisted, so it doesn't matter what type of clock you use. If you want to know the precise effect of the twisting on a particular clock mechanism, you rapidly get into questions that are hard to answer (and I'm already past my limit).

But most familiar phenomena are the result of electromagnetic forces. Mechanical clocks, digital clocks, atomic clocks, these are all based on electrons exchanging photons when you get down to it, so in a way they're not really all that different.

Gravity is the big exception, of course. That's the subject of general relativity, which is consistent with special relativity. So you're not going to be able to build a device that "defeats" relativity by using gravity.

Weak interactions (like pion decay) have been observed to follow relativity. I think.
« Last Edit: August 09, 2013, 08:27:40 AM by bobmath »

Offline philately

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Re: Einstein's lightning/train
« Reply #36 on: August 09, 2013, 10:54:15 AM »
Is it actually experimentally proven that many differing clock designs are affected equally? Would a clock that is unaffected by relativity disprove spacetime/SR?

Is length contraction limited to 1 axis at a given instant? I.e. parallel to the direction of motion? And didn't you say earlier that length contraction only affects external reference frames? So the distance between the emitter and receiver in a light clock would not change in its own reference frame and would not change in other reference frames, if oriented 90 to the direction of motion?

The rest of the clock depends on whether the speed of electricity is affected by SR. I can't remember...
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Offline bobmath

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Re: Einstein's lightning/train
« Reply #37 on: August 09, 2013, 12:39:28 PM »
What does it mean to "prove" something? In science, we can't really say more than "this theory is consistent with all observations." Maybe tomorrow we'll see something new and the theory will need to be revised. That happens from time to time. But our theories are pretty good, and it's hard to find exceptions to them.

Substitute "gravity" for "relativity." What if you found an object that was "unaffected by gravity"? (It just floated in the air instead of falling to the ground, I guess?) Would that "disprove gravity"? Well, it would be pretty interesting, anyway.

Yes, length contraction is parallel to the direction of motion. Yes, the orientation of your light clock matters, depending on what effect you're looking for.

Offline philately

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Re: Einstein's lightning/train
« Reply #38 on: August 18, 2013, 08:58:05 PM »
I don't really like the idea of space and time being twisted into spacetime and that's why I want a clock that is not affected by gravity or velocity. Perhaps the clock must be very small, lol.
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