What is faster, light or gravity?

Question

Speaking hypothetically: Which would be faster, light or gravity? Light is the fastest known speed in the universe, but has anyone ever measured the speed of gravity? Let's say that the sun were to instantly disappear... again, speaking hypothetically... what would cease to be? The light emitted from the sun to reach our eyes, or would the planet be blown off orbit around the sun before the light even reaches us?

Answer 1

They both travel at the exact same speed. This was recently verified here : http://www.newscientist.com/article.ns?id=dn3232

Answer 2

Thanks for asking. It's definitely not a stupid question.

What is KNOWN about it:
Actually until now nobody has been able to measure the speed of gravity, because it is a very weak force (the reason that the earth has a gravity worth talking about is that its mass is HUGE as is the mass of the sun, but the gravitational force between two 1 kg masses for instance is very, very small).

WHAT MOST PHYSICISTS BELIEVE TODAY:
Gravity is moving at the speed of light. There is a well established theory about it - namely Einsteins general theory of relativity. According to that gravity is described as a geometrical effect on space and time. In that theory gravity propagates as so called gravitational waves which are fluctuations in space. This is a little bit like light which is consisting of electromagnetic waves propagating in space. The speed of light is the highest possible speed anything can have without violating the physical laws. You can say that light moves at the speed of light because it cannot move any faster - and so do gravitational waves! So LIGHT AND GRAVITY ARE MOVING AT THE SAME SPEED.

There are a couple of physicists worldwide who are trying to detect gravitational waves from distant, massive stars. Until now it hasn't been possible, but it is not unlikely that they will succeed within a few years which would be a big scientific breakthrough.

Hope the answer helps.

Answer 3

I have read an article that says gravity waves travel close to the speed of light. If the sun would hypothetically disappear, I think the light would fade out before we felt the affects of the sun not being there.

Answer 4

It baffles me that so many people have absolutely no idea what they're talking about. Someone claimed to have a degree but doesn't even know anything about physics outside of highschool newtonian mechanics.

I always knew stuffing newtons theory of gravity down kids throats was a bad idea.


I suggest ignoring a lot of what has been said so far. Gravity absolutely has a speed and does not act instantly.


Gravity and Light travel at the exact same speed.


The foundation of much of modern physics revolves around the theory of General Relativity, which was Einsteins proposal. Here, gravity has to propage at exactly the same speed as light.

This has been confirmed on several experimental accounts.

Answer 5

OK, ACTUAL physicist here. Degrees and everything.

Light has a finite speed, but gravity acts instantaneously. If the Sun were suddenly gone, we would still get light for another 8 minutes, but the Earth would stop it's orbit and just go off in a straight line in whatever direction it was heading at the time, as would all the other planets. This is because gravity warps the space around it - no gravity, no warping.

Answer 6

What I know that light is the fastest thing in the universe, even gravity. I'm not a real physics know it all, but I'm taking a class right now. What I learned so far that gravity has a constant of 9.8m/s on Earth. (Of course everywhere else is different but I guess you're talking about gravity of Earth).

Imagine this. If you are on top of a tall building and you have a flashlight (or spot light so you can see the light at the bottom) and a ball and turn on the flash light and drop the ball down, you know that the light will get there first while gravity acts downward at a slower speed.

Thank goodness light is faster than gravity... because if gravity is faster than light we will be squashed LOL

Answer 7

That's one of the main arguments in favor of the "rubber sheet" theory of gravity. Classical physics was unable to resolve this question, but the "rubber sheet" theory suggests that the effects of gravity are instantaneous.

Edit: Am I the only person here who actually understood the question? He wants to know whether, when something happens to change the gravitational force on an object, the object experiences the change immediately, even when the change took place several light-minutes away, or whether there is a delay because, according to the Theory of Relativity, an event that takes place x light-seconds away can't possibly affect you until n seconds have passed.

It's not that complicated, people! (Well, the answer is, but the question isn't.)

Answer 8

gravity acts instantaneously only according to Newton

the Einstein General Relativity predicts that any disturbance in the gravitational field propagates with speed c. These gravitational waves are yet to be detected experimentally.

Answer 9

I think the effects of gravity travel at the speed of light. Down here on the earth it all looks instantaneous. But if the sun were to disappear, I think it would take seven or eight minutes for Earth to fly out of its orbit, just like it would take seven or eight minutes for the light to stop hitting us.

Answer 10

Gravity has no speed, so your question doesn't really make sense. Gravity is a force, and I'm sure you know it is equal to -GMm/r^2. At the surface of the Earth it reduces to mg. There is no velocity in either form.

I don't think some of you understand, gravity is a force, it exists between EVERY body in the universe, if the universe had edges, one body at one end would excert a force on another body at the other end, although the magnitude of the force will depend on the masses of the bodies. That force would exist even if light from one end has not reached the other. Gravity has no velocity.

Answer 11

Light