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Speed of Gravity Experiment Challenged
An anonymous reader writes "The previous hoopla over the discovery of the speed of gravity has an opponent from the Lawrence Berkeley National Laboratory. Read about the latest calculations."
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That is not what they are trying to prove. The speed of gravity they are referring to is the speed of propigation of a change in gravity. If I am a giant mass which you are being influenced by gravitationally, and I move to a different location, does the force you feel change instantaneously? Or does it change after some set amount of time? Is that amount of time dependent on the distance you are from me? If so, then there is a speed of gravity that is not infinite. These scientists think that is is c, others do not. THAT is the controversy.
You would want gravity that moves at the speed of light. This is what most reasonable scientists expect, and probably what they assume.
All sorts of strange things can happen if it is instantaneous. According to Einstein, two people can disagree about what happens first if they are moving. A person at rest can see that event A happens at the same time as B. A person moving one direction will argue that A happens before B, while a person moving the opposite direction will argue that B happens before A. The strange thing is that everybody would be right!
Let's assume that gravity can travel at faster-than-light speed, and can be used for communication. Now, a person who is moving can see A happening, and call the operator at "B" and tell them to stop event "B from happening. The person moving in the opposite direction can see B happening and tell the operator at "A" to stop event A from happening. Who is right? Clearly, they both cannot be right!
It is possible that I am missing something here. Does anybody with more experience in this stuff have more insight?
"-1 Troll" is the apparently the same as "-1 I disagree with you."
--Mike--
IANAP
Just as interesting, is does the speed of gravitation propogation (the rate of change in local gravitation measurements) follow Einsteinien physics? As I remember, he was interested in that question also, but there still doesn't seem to be an answer to it.
If gravitational changes propogate faster than c, it could have all kinds of interesting effects on our understanding of physics. Robert Forward started experiments on gravity "waves" back in the 60s, but still, as far as I know, nobody has demonstrated whether or not gravity follows EMR laws, or whether it has it's own laws.
I'm way out of the physics world nowadays, but I'd love to learn more.
SB
It's old. The more humans I meet, the more I like my cats. At least they are honest.
Quantum entanglement would be a possible way to have relativity hold true, yet allow superluminal information transport. Essentially, the states of two similar particles become, for a lack of a more definate word: "entangled" and changes made to one of the particles occurs instantaneously with the second.
I once shot a man who posted too many, "Imagine a beowulf cluster of these"
But doesn't this argument assume that the special theory of relativity applies?
Yes, this scenario assumes SR.
Because if you look at the general theory of relativity, you have to account for (speaking from the point of view of one reference frame only) the massively negative acceleration as the message is stopped and bounced back.
That's not an issue if you're only dealing with messages, rather than people (e.g. the "twins paradox"). To send a message between two reference frames, all you have to do is send a pulse of light between them. The light may be a different color when it's received, but the information content will be the same.
I'm sure there's a better description somewhere, but the basic concept is:
Two pairs of spaceships: A,B ; X,Y.
A and B are at rest relative to each other, and are some horizontal distance L apart (in their reference frame).
X and Y are at rest relative to each other, and are some horizontal distance L apart (in their reference frame).
The XY pair is moving horizontally past the AB pair. When A and X are next to each other, A sends a message to X (using "normal" methods). X then relays the information to Y using some faster-than-light channel. Some time after Y receives the message (from Y's perspective), Y and B are next to each other. Y relays the message to B (with normal methods), then B relays it to A using a faster-than-light channel.
For appropriate numbers, using the standard coordinate transformations, it will turn out that the time of arrival at A is earlier than the time at which the message left A. This is pure SR (except for the faster-than-light channel), in flat space, with no acceleration required.