|
Post by buckleymanor1 on Jan 28, 2011 0:19:48 GMT 1
Except the Shapiro effect is a time-delay effect, caused by the route near a gravitating body being that bit longer than when the body is not there. But we aren't measuring the flight time of light from distant sources -- we don't know precisely when it started out, after all. To measure it, you'd need something like a pulsar, which emits regular signals -- then you can measure a delay, relative to the last pulse, if you like. This is what was done for pulsars: physicsworld.com/cws/article/news/2644But for signals without this regularity, and where these isn't a variation as to what the light passes through (as there is in binary pulsar systems), you wouldn't know it was happening. I am not sure if the light takes a longer route if it travels between two massive objects or it just slows down because it has fallen into and out of a gravity well. It could also be that two massive objects curve space just like one object and therefore the light takes a longer path.The link you gave and the one I supplied seem to give different explanations for the same effect. They are probably two ways of explaining the same.
|
|
|
Post by speakertoanimals on Jan 28, 2011 3:09:21 GMT 1
The wording is a bit confusing! If you didn't know that anything was happening to space, you'd just say --I know how far away the source is, the light took longer than I expected, hence it must have, in effect, slowed down.
The real explanation (but which involves curved space) is that light always travels at the same speed, just that the route gets a bit longer when there is a massive body (like the sun), almost in the way!
Think of the rubber sheet. To go from one side of the frame holding the sheet to the other takes a certain time for an ant crawling at constant speed. When you curve the sheet by dropping a steel ball in the middle, the sheet stretches, and it's a longer path for the ant, hence it arrives a bit later than expected.
|
|