Speed of Gravity

[bicyclebones]

I submit that may actually gravity travel faster than the speed of light. I have read that gravity might even be instanteous so when an event affecting gravity happend on the other side of the universe this side feels the affects at the same time. I read that even Einstein did not fully understand gravity so his theory does not give proof how fast gravity travels if travel even applies to gravity. When I ask if gravity travels at a speed equal to the speed of light squared I intend to say gravity could be way faster than light. Maybe gravity does not actually travel..maybe it is such a different force it can act across great distances in a way that seems instantaneous. We dont' know what gravity is yet, we don't know what dark energy or dark matter is. Einstein didn't know either and there is no proof that gravity travels at the speed of light. The speed of light depends on the medium it is traveling through..gravity affects all mediums that have mass...gravity seems different than light and would not necessarily travel like it. But who knows? I dont'. I am just wondering and wandering through all the awesome knowledge given for us to ponder by the superb people providing us with this forumn. Thanks APOD!

[apodman]

I have read that gravity might even be instantaneous so when an event affecting gravity happened on the other side of the universe this side feels the affects at the same time.

... When I ask if gravity travels at a speed equal to the speed of light squared I intend to say gravity could be way faster than light.

... Maybe gravity does not actually travel..maybe it is such a different force it can act across great distances in a way that seems instantaneous.

... I read that even Einstein did not fully understand gravity so his theory does not give proof how fast gravity travels if travel even applies to gravity.

... Einstein didn't know either and there is no proof that gravity travels at the speed of light.

I still think that gravity travels at the speed of light. I think gravity traveling at the speed of light is part and parcel of Einstein's General Theory of Relativity (GR). I think you need better sources.

We don't know what gravity is yet, we don't know what dark energy or dark matter is.

In the sense of having a photograph of gravity in action, interpreting it in terms of everyday non-physics concepts, or understanding its deeper meaning, we will never know about any fundamental parts of nature. But we do have an extremely accurate operational idea of how gravity works and how it can be expected to work on any collection of mass. Anyone who says different is a bad source.

gravity seems different than light and would not necessarily travel like it.

They are different and they travel differently. They just use the same roads and observe the same speed limits. Traveling on the back of Sputnick's moped is not the same as traveling in the back of apodman's tandem trailer. Actually we have a good model of "how" light travels as waves and photons, and we know the mathematical "mechanism" by which gravity travels, but the actual "agent" by which gravity travels is still unknown. (Loose terms in that last statement to be brief.)

[bicyclebones]

I am wondering if approaching theoretical cosmology in a artistic way might inspire the true physicist to think in a different way long enough to extend the boundry of knowledge so to see things in a different light...not the light measure in terms of velocity but the light Einstein saw when he had one of those great realizations. Maybe an artist could draw a picture of gravity that leads the number crunching physicists to see the answer. Theoretical Cosmological Art and theory and can work together to take us farther. I am looking forward to seeing the light pattern from a black hole penumbra..one of these days.

[apodman]

I am wondering if approaching theoretical cosmology in a artistic way might inspire the true physicist to think in a different way long enough to extend the boundry of knowledge so to see things in a different light...not the light measure in terms of velocity but the light Einstein saw when he had one of those great realizations. Maybe an artist could draw a picture of gravity that leads the number crunching physicists to see the answer.

The nature of inspiration, artistic or scientific, and the relationship between them you suggest are food for thought. Surely creative and brilliant minds don't have the Great Wall of China dividing logical from artistic thought, no matter what the left-brain right-brain people say. And one person's inspiration being built on the work of another surely happens all the time, even among seemingly unrelated subjects. Unconscious collaboration. So everyone exercising their creativity liberally in many directions is good for progress in general, in my humble opinion.

Check out this link:

http://en.wikipedia.org/wiki/G%C3%B6del,_Escher,_Bach

If something doesn't like the commas in the link, treat it as a copy-and-paste job.

The book was very popular in its day (1979).

I am looking forward to seeing the light pattern from a black hole penumbra..one of these days.

That day is today. Check out these (currently) 42 APODs:

http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... ional+lens

This one is the "Einstein cross":

http://antwrp.gsfc.nasa.gov/apod/ap070311.html

Tell me which one you like best.

Since the sun is relatively close to and bigger than the earth, the earth's shadow is cast by what amounts to a single wide patch of light. Of course, the pattern of light going past a black hole is made by discrete light sources (unless you have the universe's biggest searchlight), so the "penumbra" area is not quite the same.

[bicyclebones]

I like them all! Thanks for the excellent work!

[bicyclebones]

Not being a phyiscist I ask...What If there is a very hugh mass very far to the right of us and very hugh mass very far to the left of us both so far away that we see no light and have no idea they are there, yet these two sources would have a center of gravity nearby. What would the characteristics of the center of gravity be? Would it appear to be a dark energy source. I quess I am asking if a center of gravity has a reality other than just the point about which two masses interact gravitationally?

[apodman]

Standing here where the pull is equal in both directions, there is a separate direction to the center of gravity of each of the two masses. In the absence of other objects to confuse the issue, we could determine the direction and force of the attraction to each of the two masses, and we could determine the force and angle at which the two masses are pulling us apart.

Standing far away as an outside observer, there is a plane (perpendicular to the line joining the two centers of gravity) where the gravitational forces from the two masses are equal. Where the line joining the two centers of gravity passes through that plane of equal force, the forces are opposite as well as equal and you have the center of gravity for the two masses taken together.

It's hard to set up a realistic scenario exactly as you suggest (masses very far away and very massive). I guess the answer of how they would act upon an object in the center depends on how far and how massive. If you get the masses large enough and close enough to have an appreciable effect, you have an unstable system whose constituent masses will eventually collide (in the absence of other forces to keep them apart) due to their mutual gravity.

The center of gravity appearing as a Dark Energy source? My gut says no, but the question is really beyond me.

[bicyclebones]

Thanks! I appreciate your answer. I just imagined large masses beyond our view, possibly outside the area encompased by the big bang, affecting our universe and us not knowing it.

[apodman]

Oh, you mean really big masses. Well, two masses on that scale would make themselves apparent by attracting their share of galaxies. Beyond that, any effect such a setup would have on space is way beyond me.

[Chris Peterson]

I submit that may actually gravity travel faster than the speed of light.

GR requires that gravity propagate at c. This has been experimentally confirmed to a reasonable precision by assuming that GR is otherwise accurate. It has also been measured to moderate precision by another technique. People continue to work on methods of making this measurement, but there isn't much doubt about the speed of gravity.

[Chris Peterson]

I am wondering if approaching theoretical cosmology in a artistic way might inspire the true physicist to think in a different way long enough to extend the boundry of knowledge so to see things in a different light...not the light measure in terms of velocity but the light Einstein saw when he had one of those great realizations.

In my opinion, science is the most creative discipline there is. Conventional artistic expression (painting, sculpture, etc) pales in comparison. The kind of insight that leads to great new theories can very well be thought of as a form of art. It is a myth that science is a purely mechanistic process.

[bicyclebones]

Well said! Then gravity takes a long time to propagate across the universe. We can see light waves even though they travel at that speed but we can't see gravity waves. I wonder what gravity waves disturb that we can see?

[Chris Peterson]

Well said! Then gravity takes a long time to propagate across the universe. We can see light waves even though they travel at that speed but we can't see gravity waves. I wonder what gravity waves disturb that we can see?

We have, in fact, developed instruments to "see" gravity waves. These instruments are only now becoming sufficiently refined to have a reasonable chance of recording gravity waves. Even more sensitive instruments remain under development. Not many scientists doubt that such waves will be recorded in the next few years at most, adding even more evidence in support of GR, modern cosmology models, and our understanding of black holes and neutron stars.

Gravity waves, not surprisingly, disturb masses, so gravity wave detectors are conceptually simple: you set up a couple of test masses and observe their relative motion as a wave passes through. The devil is in the engineering details, as the motion is exceedingly small: less that the diameter of a proton!

[bicyclebones]

Less than the diameter of the space the wave like particles a proton is made of occupy! Less than the diameter the space an elusive graviton exists in? Once we slice up a quark we might find the diameter of a protom to be very large relatively. A photon propagates though a medium in space that has electic and magnetic properties. I was wondering if there are other properties of that medium other than electro-magnetic.