First speed of gravity measurement revealed

NewScientist.com ^ | 01/07/2003 | Ed Fomalont and Sergei Kopeikin

[Ernest_at_the_Beach]

Thanks for the ping!

How did Einstein figure all of this out, just amazing!

[Gary Boldwater]

If gravity travels at the same speed as light is it an electromagnetic wave or is it the medium that it travels through that limits the speed of propagation of all forces?

[muffaletaman]

You are confusing instantaneous with continuous.

The effect of Gravity as a field is based on a continuous "warping" of space based on the presence of mass. And mass such as the sun does not instantaneously dissappear, as in the thought experiment cited of a vanishing sun. Every "now" is based on the influence of where everything elsewhere "was" at this moment's light-horizon...

If the sun exploded from its center in an emmense explosion such that all the remaining mass of the sun was accelerated into a spherical shell expanding at near light speed from the center of the sun, once this shell of matter passed the earth, what was left of the earth would proceed in an essentially straight line - no longer an orbit - based on the long-recognized zeroing out of the gravitational attraction of matter outside a sphere, modified by the reaction of the collision of the expanding debris impacting the earth, and physically propelling it in a slightly different direction...

[forsnax5]

Perhaps there is a minimum distance -- a quantum of space -- and a minimum amount of time -- a quantum of time.

I gave myself a headache on one rainy saturday thinking about the ramifications of quantum time. It's a very interesting idea.

If you imagine a quantum of space like a square in a checkerboard (and make it a cube so it's 3-dimensional) and a quantum of time as how long it takes a quantum of light to pass from one quantum cube to the next, and then you imagine that space can be deformed, so that one quantum is not the same physical size as the next, and that the time quantum doesn't change with the space quantum, then...

HEADACHE!

[facedown]

I love gravity!

It keeps the salt in the shaker.

[Semper911]

Only one tiny thing they forgot to mention in the article: No one knows what gravity is.

[DoctorMichael]

........they worked out that gravity does move at the same speed as light.......

Okay, I'm confused.

We are always shown the picture of the Einstein space/time continuum: a marble (representing a planet) rolling around on a cross-hatched sheet, circling a steep central drop-off (representing a black hole). The momentum of the marble keeps it from falling inward.

Gravity, in this model, is the curvature of the sheet (the space/time continuum).

Isn't the curvature "felt" instantaneously by the marble because gravity is embedded in the very "fabric" of the space/time continuum?

Damnit Jim, I'm a biologist, not a physicist!

[Semper911]

perhaps all that they really measured was the speed of the radio waves...

Yes, you are on the right track, since radio waves travel at the speed of light.

Isn't that a co-inky-dink.

[muffaletaman]

Likewise the importance that as near as it can be measured, inertial mass and gravitational mass are exactly equal.

In the supposed experiment measuring the weight of an object suspended over a rapidly spinning superconducting disk, and finding the claimed finding that weight of the object is lessened...

(1) either a repulsive electromagnetic effect is generating a force upward... normal action/reaction is occuring, nothing more...

(2) or a method of shielding the gravity field is being generated, which if true can be engineered into a warp drive someday allowing interstellar travel vis-a-vis star trek (i.e. if gravitational mass and inertial mass can be caused to become different and the difference manipulated, then perhaps an inertial bubble can be created, and the bubble accelerated by a generated polar flux in the universal G-field - one direction of the entire universe attracts, the opposite direction repulses. Thus, though the object within the bubble never exceeds local light speed within the bubble, the bubble itself can be moved at warp speeds, multiples of the speed of light)...

(3) or... (fill in the blank yourself...)

[Semper911]

Of course I should add my usual disclaimer:

What I don't know about physics could fill a book. (Hundreds of them, actually)

[longshadow]

gravity speed bump!

[Sawdring]

But the assumption of light-speed gravity has come under pressure from brane world theories, which suggest there are extra spatial dimensions rolled up very small. Gravity could take a short cut through these extra dimensions and so appear to travel faster than the speed of light - without violating the equations of general relativity.

Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.

How fast do the "Brane World" theorists think light might travel? Could gravity travel at 1.20 times the speed of light for them to be correct? Or would it be 10,000 or 100 times the speed of light for them to be correct?

[forsnax5]

We are always shown the picture of the Einstein space/time continuum: a marble (representing a planet) rolling around on a cross-hatched sheet, circling a steep central drop-off (representing a black hole). The momentum of the marble keeps it from falling inward.

I saw a model of this in the Los Angeles County Museum of Science and Industry, many years ago. At the time, I thought that showing a model that used gravity to demonstrate the concept of gravity was cheating. ;)

Gravity and magnetism are two of my favorite puzzles. They embody "spooky action at a distance" for me...

[MHGinTN]

Is there a graviton responsible for propagation of mass attraction? With what does the graviton interact to deform spacetime? If two masses attract each other (deform spacetime in a way to influence each other's relative inertial existence), to what location of a mass or spacetime are the gravitons focused? Could it be that gravity is a temporal force/effect not strictly a spatial effect?... Might mass warp the planar 'smoothness' of present time rather than the volume of spatial spacetime?

[null and void]

[vannrox]

Very interesting, especially if all the current proposals that the speed of light is variable is true. The implications are stunning!

[commish]

OK someone has to say it :

Gravity Sux! ;-)

[Godfollow]

Yes but we won't ever get our anti-gravity boots unless we can find out "why" gravity pulls us down. Maybe if we could creat something upon which the mass of a foreign body like the moon would zero in on, therefor countering the the pull of earth, and give us a lift... kind of like a magnifying glass pulling in the reys of the sun, a device could be created that would magnify the gravity pull of the moon.

[Oberon]

Gravity, in this model, is the curvature of the sheet (the space/time continuum).

Yes. And if you pull the sheet down a little farther in that spot, the curvature won't readjust itself instantaneously across the whole sheet... instead, the increased curvature propagates as a wave outward from the place you pull on, at some measurable rate.

[Physicist]

Sorry I'm late to the thread! I had to come all the way over from the "I-told-you-so" Department.

;^)