# RE: Speed of Light/Gravity

Vandergraaf, Chuck (vandergraaft@aecl.ca)
Tue, 28 Apr 1998 00:47:30 -0400

Bill,

I've often wondered about the speed of gravity, but I have never heard any
reasonable argument that information (e.g. gravity) can be transmitted
faster than the speed of light.

The hypothetical question I have posed to physicists is the following: if
the sun all of a sudden disappeared, it would take ~8 minutes for us to be
engulfed in darkness. Would it also take 8 minutes for the earth to fly off
in space (and would we have 8 minutes to see the sun become progressively
smaller, or would it happen sooner?

For that matter, is there any reason, physical or otherwise, why nothing can
go faster than the speed of light? I understand that mass approaches
infinity as the speed of light is approached, but does this apply to gravity
as well? (whatever gravity is, anyway)

Chuck Vandergraaf
Pinawa, MB

> ----------
> From: Bill Payne[SMTP:bpayne@voyageronline.net]
> Sent: Tuesday, April 28, 1998 12:03 AM
> To: Glenn R. Morton
> Cc: asa@calvin.edu
> Subject: Speed of Light/Gravity
>
> 27 Apr 1998 20:40:26 -0500, Glenn R. Morton wrote:
>
> > Nothing
> > travels faster than light and to travel 1000 light years in one year
> would
> > violate the speed of light.
>
> I'm only going to respond to this one point in Glenn's excellent post.
>
> I understand that gravity travels much faster that light, almost
> instantaneously. If it did not, then the planets would be unstable in
> their orbits.
>
> I think it works like this. When sitting still in a car while it is
> raining, you can see the rain outside falling vertically down. When you
> begin to move, the rainfall appears to slant back. Likewise, because
> the earth is orbiting the sun, the light rays from the sun slant in the
> direction of the earth's travel relative to the sun, and the sun's disk,
> as observed from the earth, is the sun's apparent position, not it's
> true position. During a total solar eclipse, the moment of totality
> comes either before or after (I can't remember which) the gravational
> maximum exerted on the earth by the sun and moon combined.
>
> Hopefully someone else can shed more light on this, the speed of
> gravity.
>
> Bill
>