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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.
Well, thank you, Mr. Smarty Pants.
Scanning for sense of humor ... scanning ... no sign, captian.
Gravity: we all know it sucks, we just don't know how fast.
The speed of gravity has been redefined as to be the exact same amount of time it takes to deliver the slashdot effect.
In teh event of an actual emergency this space might provide useful information.
It's a very fine line between troll and funny. Wait, there's no line. There a lot of fine lines. One for each person. Each person has a different definition of troll or funny. Actually those denitions are kind of complex, so it's probably a n-dimentional plane between troll and funny. Yea, millions of n-dimentional planes define the different between troll of funny, now. Of course they chage with time, so they dynamic planes between troll and funny. That's it. Except these probably some uncertainty in there, so there should be error bars on the plains between troll and funny, or something.
The truly interesting question is whether the different lines are orthogonal according to the Sturm-Liouville theory, and what partial differential equation they are the solution of. I suspect you could get a Nobel prize for finding this out. Once you've done that, the fact that they change with time becomes easy to deal with thanks to perturbation theory.
Daniel
Carpe Diem
Wow. Where to begin. Your applying initial velocity and accelleration to the one ball, thats why it lands first. What does this have to do with the speed of gravity?!
__________
Love conquers all... except CANCER
comedy gold.
Vulcans don't have a sense of humour, this one would make mass suicide the only logical thing to do in a galaxy that produces such kind of joke (the parent and the grandparent posts, I mean)
It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
I consider trolls funny anyway. So there is no line to me.
What do you suppose the repurcussions would be if it could be shown that gravity was instantaneous, rather than propagating at the speed of light? Could we use that to transmit information instantaneously? Would that violate causality?
'Spose I were rooting for Einstein, then do I want an instantaneous gravity or one that takes time to propagate?
Eat at Joe's.
The time it takes to 'get' a joke.
Eat at Joe's.
--Mike--
IANAP
the question could be more fundamental. Does gravity have a speed? Consider this: light is a particle (wave) traveling along a many dimensional space-time membrane. Now, we've defined (more or less) what a photon is; and, how it behaves. We expect it to travel no faster than c. The problem is, we don't really undertand the space-time thing.
We have some theories as to how space is constructed. One of the things physics is trying to do is to create a theory that ties together space, time, gravity, energy, mass, quantum mechanics (basically everything). It's proving to be very difficult and gravity is the problem. Would a gravity wave have to obey all of the "laws of physics" as we know them? maybe not. Not if our theories are wrong. A lack of understanding wrt gravity might be why we need to make claims about "dark matter" and "dark energy" in order to explain the accelerating universe.
You have to remember that our "laws" are based on observation. The rules (like no speed exceeds c) are based on mathematical models created to explain the observations. What if the models are close, but wrong?
Just something to think about.
If gravity was instantaneous, how is it that we couldn't use it to transmit information? Surely it would be difficult in practice, but it seems pretty simple in theory.
"When we're ready, I'll start moving this ball'o'mass towards and away from you."
What's impossible? Moving the mass around, detecting the mass in motion, or detecting it instantaneously?
Let's not stir that bag of worms...
OMG, who modded this interesting?? Its not even related to the story! Do moderators read the comments, or just look for big words?
Two days from whose frame of reference?
So what you're trying to say is that the speed of gravity is 42?
Nothing to see here; Move along.
If there is a difference, the error was already recorded as a specific force constant. Obviously if a body is moving away the average force over a second is going to be less than if it sits still.
So we already recorded the difference without taking the speed of gravity into account. Our values are good to an extent, they fail where our theory is wrong.
The message on the other side of this sig is false.
Maybe we should throw you off a building and measure how fast you fall.
Contrary to popular opinion, the ability to travel or send information faster than light does not allow one to travel backwards in time.
Maybe not "travel", but you can send a message backwards in time. This assumes that you can send faster-than-light messages in two different reference frames that are moving with a high relative velocity - you bounce the message back and forth between the reference frames, and the net result is that it arrives at its point of origin before it was sent.
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.
Switching off my sense of humor for a bit, what he's saying is that 'speed' as we know it won't be a factor in the final equation, but a result of it. Some theories (heard this at CERN in 2001) say that the graviton is a 4D particle/wave. Therefore it would also 'travel' in the time dimension and to call the graviton a tachyon might not even be a silly idea.
/essential/ in coming up with the ToE (Theory of Everything). It'll require a new kind of thinking in the proportions the ToR was to Classic physics. The ToE will take the form of mutual dependency between variables where interaction is not a process, but a function.
Getting off the beaten path of time, velocity and momentum is
All rites reversed 2010
Wouldn't basic calculus seem to indicate that there should be a speed between "delay, slower than instantaneous" and "time travel, faster than instantaneous"? If at some message speed X that may be greater than C, communication between two points can be not only instantaneous, but as you say can allow the sender to receive a response before they send, then shouldn't there be a speed between X and C where communication between two points is "merely" instantaneous? Clearly, this is not true of C, where there is a time delay.
So as you can see, young Mr Kopeikin, the ability to measure gravity waves is dependant on your frame of reference. As Stuart (Look at what I can do) Samual points out, when you take into account the position of Jupiter and rotate your frame of reference, you cannot accurately measure the propigation effects of gravity with todays measurement instruments.
Mr Kopeikin:
Why do we have to learn this? We aren't really going to need this stuff outside school right? Like I'm really going to go to Jupiter in my lifetime! I don't live in China!
Ross Youngblood
This assumes that you can send faster-than-light messages in two different reference frames that are moving with a high relative velocity - you bounce the message back and forth between the reference frames, and the net result is that it arrives at its point of origin before it was sent.
But doesn't this argument assume that the special theory of relativity applies? 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. I think that if you work it out that this negative acceleration will cancel out the temporal paradox that is being suggested.
I've seen a persuasive presentation of this on the Web someplace, but it's too late to look for it now. Maybe a real relativity physicist could comment?
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.
I appreciate the reply, and would like to ask a follow up question. Remember, IAJADBG (I am just a database guy).
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.
But this would be communicating with gravity permutations, not light pulses. What would the equivalent of color or spectrum shift be for gravity?
No, quantum entanglement cannot transmit information. But there is some open debate as to whether quantum tunneling can. See
F TL /tunnelingftl.html
http://www.aei-potsdam.mpg.de/~mpoessel/Physik/
And for the reason entanglemnt doesn't cut the
mustard, I'd recommend reading the book "Quantum Reality" which should be easy to find. There may be better books by now.
I'm not sure if this has anything to do with anything, but aren't black holes so strong that they will inhibit any light to escape. This being said it would seem that gravity is faster than the speed of light. If light was faster, some light could escape because gravity would not have enough time to catch up.
-curious
Please forgive my ignorance, I am not a cosmologist.
/ hu bble_acs_020430-5.html
http://www.space.com/scienceastronomy/astronomy
These galaxies are colliding, but the one arm of the larger galaxy, the arm farthest from the smaller galaxy is undisturbed... undistorted by the presence of the other smaller galaxy. Is this the result of the speed of gravity having a finite value (the force not having had the time to reach the other side of the bigger galaxy)? Or is this the result of the smaller galaxy being too small to affect the larger one's distant arm?
Just curious.
Also on a related note, if the speed of gravity is finite, would that not help to make the expansion of the universe appear to accelerate at the point in time when the universe had grown so large that the masses at one end of this reality could not 'immediately' feel the pull of the masses at the other end due to the ever increasing distance between them? If the rate of expansion was fixed, then at this point in time a number of billions of years ago, there would have appeared to be a sudden 'kick' if my thinking on this matter are right.
Cosmology scares me sometimes.