Think of it this way:

Gravity itself is a field. So travel doesn’t apply. It’s like saying how fast is the ocean between SF and Tokyo. However, gravity waves, according to general relativity (and some pretty strong evidence), travel at exactly the speed of light.

Thanks. :-)

Why has no one mentioned the fact that this joker has it backwards and time flows SLOWER in strong gravity?

It's been mentioned at least once. By me.

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"I'm making wheatloaf. It's like meatloaf, only with wheat"
"Isn't that just...bread?"

I'm not sure if this link has been circulated on BABB before, if not, it's an interesting read (haven't read it all myself, but the pieces I've read are interesting), if it has, sorry for reposting it. Thought it fit into this topic though.

The Speed of Gravity

also: if the speed of gravity determines the speed of light, the size of the current universe is very, very wrong. as is the size of our solar system, etc. Is the speed of light determined by the speed of gravity at it's instantaneous location or at it's point of origin? That would make a huge difference in this theory also.

I'm guessing by the location it is travelling through, since it is apparently different on the moon than on earth, and neither is a source of light.

Perhaps this, tied with the car example will help clear things up. the speed of gravity on earth is this: when I am rock climbing, I use a rope because the instant I let go of the rock, I start to fall. For simplicity sake, let's say the time is 0.1 seconds (greatly exxagerated for the purpose of this illustration). I fall, accelerating at 9.8 m/s/s until I hit the ground and suddenly stop moving. That hurts really bad or kills me, which I don't want and so I use a rope.

Now, I am on vacation on the moon and climbing in some crater with a spectacular view. By this theory, I don't need a rope. On the moon, I would not start falling for .6 seconds, which is enough time for me to 1) realize I am slipping, and 2) grab another hold before i even start falling. Then I would only accelerate at 3+m/s/s (I didn't do the math, so shoot me!) which is not terribly fast. I can speedwalk that fast for the first couple seconds. That is enough reaction time to do plenty of grabbing and so on! I wouldn't need a rope if I were so bold.

It doesn't work that way though, the astronauts (and this requires believing we went to the moon...) didn't jump and hang for long times before they were affected by gravity. It didn't take the moon a longer time to "realize" they were floating and start pulling them back. The speed at which they were pulled changed, yes. But now the amount of time it took to affect them. Jumping off Mt Everest, you will start falling in the same amount of time as if you jumped off a dock at sea level. Or jumping off the shuttle, the time for falling is the same, the difference is the shuttle is also falling and neither of you ever reaches the ground.

The speed of gravity is constant, its power/strength changes.

Anyway, I don't want to make this too long, and many others have already laid out good scientific explanations. I am just trying perhaps to make it more vernacular. Going on would only whip the horse again.

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None to speak of

This isn't what is meant by "speed of gravity". Gravity doesn't just "kick in" the minute you leave go, it is there the whole time.

The way to view the speed of gravity issue is to consider a (presumably impossible) hypothetical situation: Imagine the Sun disappears. Its mass is complete removed. How long does it take the Earth to stop following it's curved path (relative to the fixed stars) and sail off in an approximately straight line. Based on current theory, this would be 8 minutes. If the theory is wrong, it might be some other amount of time.

Has anyone speculated that it isn't constant? I think the leading hypothesis are that the speed of gravity is infinite (ie, Newton), is equal to the speed of light (ie Einstein), or is equal to some other value. So far the data has supported Einstein, but I recall that some researchers claim the experiments were flawed.

edited to add last sentance

/pulls foot out of mouth...

wow.

i hate myself sometimes, just when i begin to think i understand something (doesn't happen often!) i go and eat toast with toe jam.

perhaps if you had a really REALLY big mountain to climb...

i know gravity is there the whole time, that's why...hmm. ok, i think i am beginning to see. in the same way of your earth flying off model, we would also see the light for eight minutes after the sun vanished. then all would be dark suddenly, and off we'd go?

i can see reason in that, though it requires a bit of rewiring in my noodle. (only a bit though...) in all i must say you make sense. i am thinking now!

edited to add: this theory would still throw off the size of the universe right? if the speed of light isn't constant but changes each time it passes an object...and i don't mean like it does by going through a glass of water!

even a small percentage change here and there would make a vast difference in our understanding of size on such an immense scale it seems...

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None to speak of

Hey, don't have a cow, man. Everyone on the board gets things wrong sometimes (there are even a few who own the much-desired "I-corrected-Jay-Utah" t-shirt. Visit the Lunar conspiracies forum if you don't understand that)

That's the great thing about the board --- there are knowledgeable people in just about every area --- we're all learning from each other

Two things --- first, the theory is that the speed of light doesn't change as it goes by an object, but certainly the light's path deviates from what an outside observer thinks is a straight line

So in a sense you're right --- if all light has been bending to and fro as it traverses the universe, the size of the observable universe may be different from what has been calculated. Loosely similar to the way that my house is 10 miles from work (straight line), but my car travels 12 miles on curved roads when I commute.

But that brings up the second point. First, light isn't bending that much as it "weaves" its way across the universe. Second, there are a lot of other uncertainties in calculating ages and distances that overwhelm that particular uncertainty.

Uhh.... This is the Lunar Conspiracies forum.

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Old laser physicists never die, they just become incoherent.
These days, every Tom, Dick, and Harry thinks he knows what a photon is, but he is wrong. - Albert Einstein

oh......., um......, ahem, yeah I did that on purpose to illustrate that we all make mista....oh never mind ops: ops: