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The Speed Of Gravity Revealed
redwolfoz writes "New Scientist is reporting that the speed of gravity has been measured for the first time. 'The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.' Researchers made the measurement of the fundamental physical constant with the help of the planet Jupiter. One important consequence of the result is that it will help constrain the number of possible dimensions in the Universe."
I'm sorry, I don't mean to ask the stupidest question ever, but how does gravity have speed? The last I was taught on the subject (and believe me, it was a while ago) was that gravity was a force, but didn't have mass. Doesn't something need to have mass in order to have speed?
...a topic like this to be a bit more precise in the summary. There's a signifigant difference between .95 times the speed of light, and the speed of light. Not to mention the large .25 margin of error. Which theoretically shouldn't be able to get to +.25 anyhow.
"Kopeikin found another way. He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity."
The theory of relativity was appearantly used to detect the speed of gravity. This would be fine if the theory of relativity didn't assume a speed of gravity. Basically, all he did was prove his given. So, if eggs are green, then eggs are green!
Karma Clown
The sun couldn't suddenly disappear, although that scenario works for the purpose of explaining the speed of gravity. Consider this alternative.
Take the sun and instantly accellerate it to almost the speed of light, toward a collision course with Earth. For most of the 8 minutes between acceleration and collision, nobody would notice anything, as light, all other energy, and gravity would all present the sun as occupying its original location.
However, brief moments before the collision, the sun's change of accelleration toward earth will be noticed. Of course, you're noticing the change that happened 93 million miles away, even though the sun is about to impact. However, one second later, the sun will appear to be almost 186000 miles closer, and it will FEEL like it's 186000 miles closer. Suddenly the gravitational accelleration has increased to reflect the new position of the sun. But within that second, you get all the accumulated influences of gravity over a much larger stretch of space than just the 186000 miles it travelled in that time. Since the sun is moving at almost the speed of light, let's say 99% of it, after 99 seconds, the influence of the sun's gravity will only be 1 second ahead of the sun. However, within that one second between the position of the sun and the gravitational influence of the sun is contained the gravitational influence of the sun over the last 99 seconds. You get the combined force in 1 second that you normally would have gotten in 99. So when the Sun's influence is finally felt by Earth, you will not get a force that implies a steady rise in gravitational force of a sun massed object until impact, you'll get a very quick rise in force of an object that is, generally, about 99 times as large as the sun.
And if you remember relativity, when an object is travelling near the speed of light, the mass increases. So the theory at least makes sense. Here's another thing to ponder. If an object the size of the sun suddenly acquired the 99x its mass, would it not either collapse upon itself, or expand rapidly, nova, and the core would collapse upon itself, causing the same result, a singularity, with a small event horizon. And it will be this singularity that will collide with Earth, ripping through it in a fraction of a second, and the sudden, combined gravitational effect on earth will cause it to very suddenly pull out of it's orbit toward the origninal center of gravity of the sun, with a nice city sized hole carved through it.
Ok, this had no purpose at all, but it was interesting to think about. Go on with your business... nothing to see here. Rant over.
-Restil
Play with my webcams and lights here
Gravity waves have been used in many stories as a FTL communication system, now that's all out of date.
Venus is a big swampy planet, eh guys ?
If Gravity's speed is equal to that of the speed of Light, then how do you explain the pull descrepencies between blackholes and low graivty environments? Go to the moon, you'll notice that the gravitational pull there is much lower than that of Earth's. And Earth's is far far less then a blackhole's gravitational pull.
:)
So how can one say that Gravity's pull is as fast as the speed of Light when Gravity itself doesn't stay constant in different environments? I never heard light not traveling the "speed of light" so it's a bit confusing.
Ao, from what I gather, blackholes have so much gravitational pull that even light can't escape. Which suggests to me that Gravtiy is stronger than light. It would also suggest to me that gravity is is faster than light because of this. I don't have any sources to back this up, all of this is just my train of thought in words here.
I'd appreciate a simple-as-possible answer as to why my train of thinking is wrong, as i said, i'm no scientist, but this topic is interesting none the less
A Penny for my thoughts? Here's my two cents. I got ripped off!
I have a question:
If they have confirmed that gravity travels at the speed of light, how does gravity escape a black hole? obviously it does because the only energy that escapes a black hole is in the form of gravitational waves, but if the escape velocity is higher than than the speed of light, how can it get out?
Jeremy
Actually, you got the order wrong.
:).
Strong, Electromagnetic, Weak, Gravitational
This depends strongly on the distance you choose to measure the force at. At a distance of 1m, as opposed to 1e-15m, the original ordering may be correct.
And as long as we're being nit-picky, I'll point out that human-observable phenomena tend to be larger than 1e-15m
The mass of photons is very real. Try this experiment, which a professor did at one of my Engineering Physics classes:
Take a relatively large gong. Make sure it is reasonably well polished.
Next, take a professional-class camera flash and set the intensity to "fry".
Third, fire the flash at the gong. As the photons bounce off the (polished) gong, it will resound as if having been struck with a solid object.
This was a very awakening demonstration to me...