# Some relativity help

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I admit it -- I have a nasty habit of arguing with fundies of various sorts on the internet. There is a particular breed of fundie on a particular forum in a particular thread who keep going on and on about relativity just being an issue with the clocks (i.e. gravity is some how affecting the clocks, not time). Unfortunately my knowledge of relativity is really very superficial, and so despite my best efforts, I'm running into brick walls left and right because I really don't have a good grip on the math involved.

The essence of their argument boils down to:

The change in gravity affected the clock. Much the same way as gravity would influence a water clock being carried up a mountain. Much the same way as a change in gravity affects everything of mass.

.....

Two clocks show different times at different altitudes.

The majority assumes relativity, records the difference and uses it to calibrate the clocks for any gravitational change.

Pastor Enyart's article states that it is just as valid to assume gravity affected the clock.

This alternative assumption does not remove the ability to do the exact same calculations and it has the advantage of being testable.

and

None of this does anything except to show that the clocks were effected. It does not show that time itself acts differently. And the clocks were not going to remain in perfect unison. Not with that significant change in gravity.

This is, of course, in reference to the famous clocks on a mountain experiment. Any guidance from our resident physicists?

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What's the difference between time-intervals being "affected" and clocks being affected?

- If "clock" refers to any generic keeping track of time then it looks pretty equivalent to me.

- If clock really refers to say specifically an atomic clock then it makes me wonder: calculating planetary orbits in GR gives nice results. But the related (same spacetime geometry but simpler calculation) question of gravitational time dilatation does not work but instead accidentally happens to have the same value as the real effect: a yet-unknown influence of the gravitational field on atomic clocks?

Disclaimer: There's a very prominent way to introduce relativity with clocks. I never understood those introductions. I find them silly (because I do not understand them ). So perhaps I just don't get the point here.

Sidenote: Has anyone ever noticed that on internet discussions about relativity people always talk about if and whose clock goes slower and why. But seemingly no one asks how much?

- There is no unique time that it takes to get from one event to another. Similarly to the length of a path from city A to B depends on the road in relativity the time it takes from one event to another (note that event is a fixed space and time position) depends on the path taken.

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...Sidenote: Has anyone ever noticed that on internet discussions about relativity people always talk about if and whose clock goes slower and why. But seemingly no one asks how much?...

Knowing "how much" takes specific information. We do consider "how much" when we talk about the GPS satellites or 1G rocket rides to a particular location.

I see everything as a clock. The rate of decay of road kill measures time.

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I admit it -- I have a nasty habit of arguing with fundies of various sorts on the internet. There is a particular breed of fundie on a particular forum in a particular thread who keep going on and on about relativity just being an issue with the clocks (i.e. gravity is some how affecting the clocks, not time). Unfortunately my knowledge of relativity is really very superficial, and so despite my best efforts, I'm running into brick walls left and right because I really don't have a good grip on the math involved.

The essence of their argument boils down to:

The change in gravity affected the clock. Much the same way as gravity would influence a water clock being carried up a mountain. Much the same way as a change in gravity affects everything of mass.

.....

Two clocks show different times at different altitudes.

The majority assumes relativity, records the difference and uses it to calibrate the clocks for any gravitational change.

Pastor Enyart's article states that it is just as valid to assume gravity affected the clock.

This alternative assumption does not remove the ability to do the exact same calculations and it has the advantage of being testable.

and

None of this does anything except to show that the clocks were effected. It does not show that time itself acts differently. And the clocks were not going to remain in perfect unison. Not with that significant change in gravity.

This is, of course, in reference to the famous clocks on a mountain experiment. Any guidance from our resident physicists?

The thing is that the clocks do not change proportionally to the change in the gravity field, but change porportionally to the change in gravitational potential.

Or put another way, even if you put two clocks at different heights in a gravity field that does not change in strength with height, the higher clock will still run faster, even though it feels exactly the same force of gravity as the lower clock.

If you put a number of clocks at different altitudes, and compare them, you will find that the Results match what is predicted by a reliance on potential difference and not on gravity strength.

Also, experiments have been done with high speed centrifuges that confirm that g-force has no effect on the decay of radioactive isotopes.

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If it affects every possible measure of time by exactly the same amount, you might as well say that time itself was slowed.

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Blike, I'm going to go over the fundies' thread, but here's something that immediately popped into my eyes:

Well both special and general relativity require relative time.

That's not true. Special relativity doesn't require relative time, its application results in the fact that time dilates.

I just finished an Electromagnetics course that was an introduction to relativity. When we left Lorentz and Maxwell "behind" (not really) and started talking about actual Sepcial Relativity, the notion of time dilation didn't just "pop up".. we derived the situation of electromagneticism in motion, and concluded that there are two aspects to the resulting 'effect': Time dilation and length contraction.

It's not as if Einstein just popped up and said "Time must be relative! Now fit all your theories into mine." Special relativity is a direct derivation of Lorentz and Maxwell's laws. In fact, the way to see if a 2 events are "spacelike" or "timelike" (if it can occur simultaneously in some inertial frame or if it occur at the same spacial position at some inertial frame) is to use the "Lorentz invariant". Einstein did not make up special relativity, he "just" proposed that the Ether wasn't necessary and went on to produce General Relativity.

The statement that the theory "requires" time to be relative makes it seem like we first wanted time to be relative and then we came up with the theory. That's absolutely not true. We first examined the effects of electromangetism laws and movement, and out of THAT came the conclusion that there's time dilation.

Big difference.

~moo

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