View Full Version : Gravity/speed of light
It's known that information about an event cannot travel faster than the speed of light.
On the other hand modifications in the intensity of the magnetic force between 2 magnets or the gravity pull between any 2 objects is transmited instantaneously. How is that possible and why can't we use that as a mean of information transport (communication) ?
cripkd
HallsofIvy
Mar14-04, 04:02 PM
Originally posted by cripkd
On the other hand modifications in the intensity of the magnetic force between 2 magnets or the gravity pull between any 2 objects is transmited instantaneously.
Where did you get that impression? That's certainly not what most physicists believe!
:)
Sorry, I'm not a physicist and since posting this question i already found the statement that gravity isn't traveling faster than the speed of light.
Severian596
Mar14-04, 07:36 PM
It's weird to think that if the sun "blinked out" of existence we'd orbit around where it used to be for another 8 minutes or so! [:)]
And if there were a GRB "now" near Sag A* (the Milky Way core), aimed directly at the solar system, we'd have another 25,000 years or so before the surface of the Earth were sterilized ... [;)]
Originally posted by Nereid
And if there were a GRB "now" near Sag A* (the Milky Way core), aimed directly at the solar system, we'd have another 25,000 years or so before the surface of the Earth were sterilized ... [;)] And we'd have no advance warning.
In fact, maybe there was a GRB there 24,999 years 364 days 23 hours 59 minutes ago and we'll all die in the next minute.
[8)] [8)]
Originally posted by Cecil
And we'd have no advance warning.
In fact, maybe there was a GRB there 24,999 years 364 days 23 hours 59 minutes ago and we'll all die in the next minute.
[8)] [8)] Well, those of us lucky enough to be on the other side of the Earth would be OK until the effects of the GRB on the atmosphere worked their way round to us. And if we were in the deepest gold mine in South Africa, ... we'd possibly know the rest of the world was dead, but how much longer would we live?
:)
Sorry, I'm not a physicist and since posting this question i already found the statement that gravity isn't traveling faster than the speed of light.
Look and you will find reputable physicists who claim gravity is instantaneous to all measurable limits. They are outnumbered by those who say it travels at c, but I don't think the argument is necessarily over.
Njorl
Look and you will find reputable physicists who claim gravity is instantaneous to all measurable limits. They are outnumbered by those who say it travels at c, but I don't think the argument is necessarily over.
NjorlI'm not sure you'll find very many physicists who claim the former.
There have been a couple of attempts to actually measure 'the speed of gravity', but the results have been somewhat 'inconclusive' shall we say.
With LIGO and its sisters, esp LISA, some definite, unambiguous gravitational signals will advance the 'observational' side a great deal ... maybe within the next 3 to 5 years?
Longer term, somehow QFT/QM has to fit with GR, but how and when the dots will be joined is quite uncertain. Ain't it fun to be around now
:biggrin:
and here i was thinking that I was born too soon :)
After all we're all born in the same century as all the great discoveries, meaning electric current, internal combustion (ok, ok it was the 1800's but it's been put to use later), computers. But yes, it's a point, we're here to see at least part of the image about the universe being put togeather.
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