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Author Topic:   Black Holes, Singularities, Confusion
nwr
Member
Posts: 6412
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.3


Message 18 of 60 (351000)
09-21-2006 12:05 PM
Reply to: Message 17 by Silent H
09-21-2006 6:13 AM


Re: more Questions..
Now here's a lame example. Say we use a quartz crystal for keeping time, current convention (as I understand it) is that as it approaches c it begins to slow down to an outside observer (and indeed does so in a measurable way).
But wouldn't that make sense by assuming that it is the result of energy limits within the system? The quartz crystal marks time by oscillations which is itself movement, and so involves energy. Moving in a direction also involves energy (or at least an input of such). If there is only so much energy that can be part of a system then as it nears c, less energy can be devoted to movement in other directions (oscillations).
No, that does not work at all.
Let's leave the quartz crystal alone, sitting in some suitable protective module. But you get on a space ship, and speed up to near c. Relative to you, the quartz is seen as moving at near c. You still observe the same slowdown. But we have left the quartz crystal alone. Nothing has changed in that system which could account for the change.

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 Message 17 by Silent H, posted 09-21-2006 6:13 AM Silent H has replied

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 Message 19 by Silent H, posted 09-21-2006 1:25 PM nwr has replied

  
nwr
Member
Posts: 6412
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.3


Message 20 of 60 (351074)
09-21-2006 2:18 PM
Reply to: Message 19 by Silent H
09-21-2006 1:25 PM


Re: more Questions..
Isn't the observational difference from the vantage point of the person in the ship because of the speed of the "information" from the quartz crystal? That is it will take longer to reach and so appear to slow down?
That would be the doppler effect time dilation.
When you correct for the doppler effect, the relativistic time dilation remains.
From what I understood most time dilation experiments focused on moving the object itself and seeing that time rate is changing there.
It is far easier to move the clock, than it is to move the observer.
In fact if time dilation happens in both directions why must it be accounted for in GPS measurements, wouldn't their mismatch sync?
There isn't much doppler effect with GPS, because you are remaining at about the same distance from the GPS satellites. The time dilation is relativistic. There is an additional complication here. The GPS satellites are in a gravitational field, so one has to use GR, not just SR, to fully account for the effect. (Note, I'm far from an expert in GR).

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nwr
Member
Posts: 6412
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.3


Message 22 of 60 (351108)
09-21-2006 3:33 PM
Reply to: Message 21 by Silent H
09-21-2006 3:01 PM


Re: more Questions..
But if what you said was true, that for a spaceman moving to c the clock he observes outside his ship slows down, why wouldn't scientists just accelerate something and see if our clocks slow down?
As far as I know, most of the experimental data is with orbiting satelites. The situation is not symmetric, due to the different involvement of gravitation for the satellite and the ground based point. For a pure SR test, where there is symmetry, the two bodies rapidly move so far apart that measurement becomes difficult. The exception is in particle accelerators, where one can observe relativistic effects on the rapidly moving particles. But that's only possible for objects light enough to be accelerated to near c.
I expect that cavediver knows more about what has actually been measured, and maybe it it will turn out that the kind of test you would like to see has been done.

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nwr
Member
Posts: 6412
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.3


Message 58 of 60 (359466)
10-28-2006 9:52 AM
Reply to: Message 57 by jaywill
10-28-2006 8:09 AM


Is there a non physics explanation to help people understand how space (which I thought is nothing) could be curved?
Will you accept a mathematics explanation?
"Curvature", as the term is used in relativity, is a mathematical term. It is defined in terms of the distance metric (as generalized to include time).
To illustrate, consider a cylinder (the surface, not the solid). On the cylinder, we would measure distances as the shortest path along the cylinder. Mathematically, the cylinder is flat, so not at all curved. This corresponds to the fact that you cut cut down along the cylinder, and open it up so that it is flat, and you could do this without changing any distances (not counting those where the shortest path crosses the cut-line).
Take out your atlas, and look at a Mercator projection map of the world. It is really an unwrapped cylinder. Think of it as a cylinder, with the left and right side taped together where they match. Now, let's suppose that we scrap our current way of measuring distance on earth. And, as a new distance metric, we use the old distance between the two places on the Mercator map. We could scale it, say one inch on the map = 100 miles on Earth. This will be a different distance metric than we ordinarily use. With this new metric, the north pole and the south pole will be an infinite distance away. With this new distance, the earth is flat.
When physicists talk about curvature of space (or space-time), the metric they are using is based on light travel. The distance between two points is determined by the time it takes for light to travel between them. This was adopted as the standard for distance, following the Einstein conclusion that the velocity of light is the same for all observers.
I hope that helps.

Compassionate conservatism - bringing you a kinder, gentler torture chamber

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