Ok, the current rules of the universe (as we understand them) state that nothing can exceed the speed of light. However, in papazaru’s thread “The Big Bang” it is pointed out that there are stars and galaxies apparently moving away from us at a speed greater than that of light. This is explained by the space in-between us and the object we are observing increasing; they are not moving faster than the speed of light where they are, just where they are is moving away from us fast enough to make it look that way.
This brings up my question: Speed is a relative term, correct? You cannot just say an object is moving at a million kilometers per hour without specifying in relation to what. On Earth we assume we are referring to the Earth, but when talking about other objects in space we have to explicitly state our point of reference.
If what I have said up until now is correct, then when it is said that nothing can exceed the speed of light, what is the reference point? We have already shown that there are points of reference that make it appear that objects are exceeding the speed of light, so how do we pick an acceptable place to measure from?
As an aside question, how did scientists decide that more space was being created at all times? You bounce some light off of an object and it takes more time to get back than it took to get there; how do you decide that space was created instead of assuming the object is moving?
Yep, speed is relative and light always travels at the speed of light, but when you bring in GR and very different reference frames it doesn’t mean that light always appears to travel at the speed of light.
For example the remote observer co-ordinate speed for light travelling radially away from a Schwarzchild black hole, at the event horizon is actually zero., in otherwords it appears to hover on the event horizon.
The reason why the expansion of space itself was proposed is that the expansion was uniform in all directions. As preferred frames of observation is forbidden by the Copernican cosmological principle it was concluded that the hole of space must be expanding inthis manner.
So… nothing can reach the speed of light, but if you are looking at it in a particular manner it seems as if they do. How is a viewpoint where things appear to exceed the speed of light wrong? This seems to clash with the idea that all points of reference are equally valid.
We cannot measure the rate of expansion like this for a couple of reasons. For difference in the travel time to be measurable, the object would be too far away to wait for the signal to return. Also, you don’t know the time it takes to get there and the time it takes to return; you only know the time for the round trip.
Expansion is inferred from other sources. More distant object have greater red shifts.
In Special Relativity, c is the maximum velocity and light always travels at c. But in General Relativity, c is not the maximum velocity, nor does light always travel at c. If we take a (general) reference frame attached to the rotating earth, Pluto is traveling faster than c, but not faster than light.