Does the force of gravity "travel" like energy (see below)?

Question

My dad read this theory in a book that I'm not so sure about.

Picture this: the sun instantly ceases to exist (I'm aware this cant happen). With it's mass gone the earth ceases to be in its orbit, and heads off on a tangent in the direction it was travelling at the moment the sun disappeared. So far, so good.

It would take eight minutes (earth being eight light minutes from the sun) for the sun's light to disappear from the perspective of earth. My dad says it would also take at least this length of time for the force of gravity to stop acting on the earth, because it too must "travel" from sun to earth, and nothing goes faster than light.

I say gravity doesnt "travel", so when the sun disappears, the earth immediately escapes orbit. Am I right?

Answer 1

Yes, the force of gravity "travels" like all other forms of energy, and the fastest that it can travel is at the speed of light in vacuum. So if the Sun were to disappear this instant, we would not know about it until about 8 minutes later.

Gravity between any two mass is communicated via an elementary particle called the graviton, which must obey the same speed limit as all other particles.

By the way, all forces are communicated via an elementary particle. This is a very well established fact. That is why physicists are very confident in saying that gravitons exists even though they have not yet been observed in particle accelerators. The reason gravitons haven't been observed is because current operating particle accelerators can not produce high enough energy collisions to create gravitons. However, the LHC at Cern due to begin operations sometimes in 2007 will be able to verify the existence of gravitons.

PS - the electromagnetic force is communicated via the photon, the strong force is communicated via the gluon, and the weak force is communicated via the weak gauge boson. All these particle has been verified to exist, particularly the photon.

Answer 2

Your dad is right apparently. The "speed" of gravity has been demonstrated using the gravitational lensing effect of Jupiter on a distant quasar within the last 2 years.

In fact you don't need the Sun to disappear instantaneously for the effect to be measured, theoretically anyway. The Sun loses about 4 million tonnes of mass every second, converting it to energy output. This means that if you had a sufficiently sensitive detector in a probe orbiting the Sun within the orbit of Mercury, which could measure its own motion very accurately and so calculate the mass of the Sun from the relevant formula, it could transmit this information to another probe orbiting further out. The second probe would do a similar calculation and compare results. If gravity travels at the same speed as the signal (speed of light) then the 2 mass calculations are going to be the same. If gravity were transmitted instantaneously then the outer probe's mass calculation would give a lower value because of the amount of matter converted to energy in the time interval between the 2 measurements (ok, space-time interval).

Answer 3

It's a bit of an non-question. Gravity is a force that is generated by the effect of a mass. Since a mass cannot be created or destroyed instantly (apart from on an atomic scale) but can only move within the laws of physics (I.e.) less than the speed of light, then gravity can only change at a rate less than the speed of light.

However, if we say that gravity carrys information, as in it can be measured to give information about the mass and distance of an object, then it would be fair to assume that the information could not be sent faster than the speed of light as this would contradict the theory of relativity. So I think that your dad is right, at least until somebody works out a way to prove it otherwise

Answer 4

No, it would take eight minutes for space to un-warp due to the Sun disappearing. Newton thought "gravity" acted instantaneously throughout space. Einstein proved him incorrect.
See the earth is traveling along in a straight line. The Sun's mass curves space around it. So, the earth's line of travel is straight through curved spacetime. I can't recall how many shows say it, but here goes....
Imagine a really really big trampoline. Now, roll a bowling ball out onto it so it settles near the center. The surface of the trampoline is warped by the bowling ball. Now, take a marble and roll it just to the side of the bowling ball. Don't throw it or it will go right off the other side. Just easily roll it to the side of the bowling ball and it will start going around the ball or orbiting it. If you could fill the material of the trampoline with ink [like a stamp pad], it would put a line on the marble and not completely cover up the marble. That's all the earth is doing, rolling along the curvature of space around the sun. Eventually, if the Sun wasn't going to evolve into a red giant, the earth would roll right into the sun--just like the marble does when it loses all the energy of your starting roll.
Lastly... if you were to make the bowling ball disappear by picking it up, the surface of the trampoline would bounce back. Well, for spacetime to bounce back, the contracting would happen at the speed of light.

Answer 5

All masses are attracted to each other, the larger the mass the greater the attraction, you may not believe it but the moon is attracted to the earth and is falling toward it, just as the earth is falling toward the sun, and the sun is falling toward the centre of our galaxy. (presuming it has a large mass at its centre.) If you take away the mass of sun, the earth will fall towards the next largest mass, centre of our galaxy? The effect would happen as soon as the mass was removed. This can not happen without converting the mass into energy Energy = Mass x the speed of light squared E=MC2 such a conversion would take the earth out like a massive atomic bomb about 8 minutes after the earth started moving towards the next largest mass.

Answer 6

Nobody knows, because noone understands gravity.

Many people have tried to detect "gravity waves," and so far they have failed.

If gravity is "really" a curvature of space, and the whole universe expanded in size faster than light-speed during the Big Bang, then conceivably gravity could as well.

Answer 7

This same question was discussed earlier today. Yes, your dad is correct, and gravity does take time to travel. Whether or not gravity is carried by any sort of particle is still a question, but regardless, gravity's effect will only travel at the speed of light.

Answer 8

Science is not clear on this. No data to prove or disprove. Gravitron some people mention is an imaginary matter. Dont exist.

Answer 9

No, your Dad is right.....picture this...if you are hanging in the air suspended from a crane...then the crane releases you...for a very small instant you will "hang" in the air with no velocity..then gravity kicks in and its all over.....

Answer 10

intresting question im not one to answar this question but when that happends ill be sitting on my roof waiting for marz to plumit into us :P