From Newsgroup: comp.arch

On 2026-08-05 22:27, MitchAlsup wrote:

[snip]

Sometimes, one also has to consider the speed-of-light problems as
separate from the speed-of-gravity {also known as the gravitational
anomaly. If the sun disappeared instantaneously the earth would leave
its orbit instantaneously, even though we could still see the light
from it for 8 minutes.}

Are you sure about that "leave its orbit instantaneously"?

AFAIK, one of the advances in general relativity over Newtonian gravity
is that in GR, gravitational interactions do not have infinite speed,
but propagate at light speed.

On "Speed of gravity", Wikipedia says (https://en.wikipedia.org/wiki/Speed_of_gravity):

"Suddenly displacing one of two gravitoelectrically interacting
particles would, after a delay corresponding to lightspeed, cause the
other to feel the displaced particle's absence [...]".

So a delayed effect, same as the delayed ending of the light from a
suddenly disappeared sun.

(The Wikipedia page also discusses why the apparent direction of a
constant gravitational field is /not/ aberrated by the finite speed of gravity, unlike the apparent direction of a light source, which is so aberrated.)

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From Newsgroup: comp.arch


Niklas Holsti <niklas.holsti@tidorum.invalid> posted:

On 2026-08-05 22:27, MitchAlsup wrote:

[snip]

Sometimes, one also has to consider the speed-of-light problems as
separate from the speed-of-gravity {also known as the gravitational anomaly. If the sun disappeared instantaneously the earth would leave
its orbit instantaneously, even though we could still see the light
from it for 8 minutes.}

Are you sure about that "leave its orbit instantaneously"?

When the question is phrased "the sun disappears instantaneously"
then yes, earth leaves orbit instantaneously.

When it is phrased "an arm reaches out and plucks the sun from
the center of our solar system" then yes, it takes 8 minutes
for the gravity gradient to disappear.

AFAIK, one of the advances in general relativity over Newtonian gravity
is that in GR, gravitational interactions do not have infinite speed,
but propagate at light speed.

The gravitational vector on the center of earth's mass points at
where the sun is right now--or the orbits would not be stable,
whereas the light vector points at where we see the sun in the sky.
This is known as either "the aberration of light" or the "aberration
of gravity" (I forgot).

On "Speed of gravity", Wikipedia says (https://en.wikipedia.org/wiki/Speed_of_gravity):

"Suddenly displacing one of two gravitoelectrically interacting
particles would, after a delay corresponding to lightspeed, cause the
other to feel the displaced particle's absence [...]".

So a delayed effect, same as the delayed ending of the light from a
suddenly disappeared sun.

(The Wikipedia page also discusses why the apparent direction of a
constant gravitational field is /not/ aberrated by the finite speed of gravity, unlike the apparent direction of a light source, which is so aberrated.)

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