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speed of forces

Hi was just watching this vsauce video on YouTube and it got me thinking. If light takes 8 minutes to reach us from the sun. How long does it take for us to feel the effect of the sun's gravity ? Is it instantaneous or does it take time, like light.
For example if the sun suddenly vanished we would still see is light for 8 minutes but would the gravity go away instantly or slowly fade away like the light ???
And if it's instantaneous does that mean it's faster than light?:eek::eek:




What do you guys think
The quick and simple answer is that the gravitational field cannot spread its influence faster than the speed of light.
So if the Sun suddenly ceased to exist you would also have to wait 8 mins for the Earth to fly off at a tangent. Almost certainly at the same time as the Sun disappeared from your point of view.
Nice question and the real answer to that is there are several 'theoretical' answers but NONE have ever been proved by direct measurement. That gravity travels at the speed of light is an assumption - albeit one that is derived from a good pedigree of reputable scientists.

For example: In Einstein's General Relativity theory, gravity travels at the speed of light - great pedigree as Einstein has not been shown to be wrong so far. Every experiment linked to date has not contradicted the theory of General Relativity, it's assumed gravity will not contradict it either even though no measurement directly exploring the speed of gravity has ever been successfully made. i.e. the velocity of gravity has never been independently proven.

Experiments are ongoing right now; such as trying to detecting gravitational waves from supernovae explosions (LIGO http://www.ligo-la.caltech.edu/LLO/overviewsci.htm) and others such as VIRGO, GEO600, LISA etc. experiments.

One theory says it should be possible to detect neutrino radiation and gravity waves some time before the light from the supernovae is visible. This would be strong evidence that gravity has a finite velocity.

Another theory is that gravity is mediated between masses by the hypothetical 'Graviton' particle as part of the wider Quantum Field Theory and String Theory.

However this is now deep within the realms of theoretical physics!

So for now, it's assumed the effects of gravity travel at the speed of light. (I am sure William Hill would give you odds if you want a punt on that!)
(edited 11 years ago)
Reply 3
Avatar for brummie786
brummie786
OP
thanks guys some nice responses hope the scientists can find out for sure

:smile::smile::biggrin::biggrin:

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