Expert: Tom Whiting - 12/13/2005

Question
If the sun suddenly collapses,then when would the earth feel it's effect? Instantly or after 8 minutes(at the speed of light)?
                     or
What is the velocity of gravitational waves?

Answer
Hi Aditya....
Good "trick" question from your instructor!  (Or textbook)
Answers:  #2 first.....

Velocity of gravitational waves....speed of light, we think,
and we're pretty sure, as those waves are just a longer
extention way down below radio waves,
at least according to Einstein (but realize we've never measured or "seen"  them, as yet...but that's what the  relativity theory says).

Question #1,  (the tricky one),
"If sun collapes, when would Earth feel the effect?......"  NEVER,  as all the mass is still at the center of the Solar System....it's just that the sun would become a condensed,
small black hole, so all the gravity and mass is still there, at the center of the Solar System, so from a gravitational standpoint only,  nothing has changed!
(You'll earn extra credit for that answer)!

Of course, 8 min and 20 seconds later, at light speed, there
would no longer be any light and heat, so within a few
hours, the Earth would be frozen like an ice cube.

{BUT,  if the question would have been....."If the sun could magically,  completely disappear...all its mass gone"...when would the Earth feel that effect?"    Answer.....8 min and 20 seconds later....the Earth (and all the planets, asteroids,
comets, etc) would fly out of orbit on a straight line tangent, just like swinging a bucket of water with your arm, and letting it go at some point.}
And all the light and heat would be gone at that time,
also.  So we'd all be frozen that way too....so it wouldn't really
matter what was happening to the Earth as we wouldn't be
around very long.
(few hours, at the most).
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA  USA