Quote:
Originally Posted by joglynne
OK. <, sigh>> Skip to my final comment and don't feel you have to read/reply to this as it's probably a silly question and, as before, being totally irrelevant.
If there was a straight line from A through B & C to
point D. (Have I lost you yet)
1) I am on point A with a speedometer oh and a mahoosive telescope.
2) If I were able to see points B & D, point C being invisible (big bang or whatever) and .......
..... I can see B & D are moving apart from each other at the speed of light what would my speedometer register as the relative speed that they were travelling apart...... I am assuming super dooper planets could move that fast 
Give up reading now unless you want the same headache as I have.
3) My head is seeing 2 cars, driving in opposite directions, passing at 30 mph surely they would be moving apart at 60 mph
Off to go and lie down in a dark room.
Add// Just realised I'm probably confusing the speed of light with the speed of sound but I have spent so much time pondering about all this that I blowed if I'm going to delete the sodding post!!!!!!!!!! |
I’m getting a headache but only because I don’t know why I’d be able to see B and D but not C, if A, B, C and D are all in a line together
As for point 3, yes, two cars traveling through town at 30mph in opposite directions are increasing the distance between them at a rate of 60mph, but neither car is traveling at 60mph and so neither car is breaking the speed limit.
Likewise, two galaxies traveling in opposite directions at 75% of lightspeed are increasing the distance between them at 1.5x lightspeed, but neither galaxy is actually traveling faster than light and therefore neither of them is breaking the universal speed limit.
If you were an observer located in either one of these galaxies, you would never be able to see the other galaxy because the light emanating from each could never reach the other (the light would have to travel at 1.5x lightspeed in order to do so, and it can’t).