question-so it has been observed at some parts of the universe that the expansion rate is faster than the speed of light!! can you please explain when, where, and how ...this was observed..
answer by jesmul-Mr , I will try to have a discussion on this very interesting Question....There are two big things to remember about the expansion of the universe. First, the universe doesn't expand at a particular speed, it expands at a speed per distance. Right now it's about 70 kilometers per second per megaparsec. That means that galaxies that are about 1 megaparsec (1 parsec = 3 lightyears and change) away are presently getting farther away at the rate of 70 km every second, on average. Galaxies that are 2 megaparsecs away are presently getting father away at the rate of 140 km every second, on average.
Notice the awkward phrasing there: distant galaxies are "getting farther away", but oddly enough they are not "moving away".....................
abdullah's comment-iam pretty sure u get the answer from comment! that is exactly right! navnit, get the concept from there, and for ur '' where did u read that '' question, I read that from national university of Australia through Professor Brian Schmidt (noble prize winner) !!
jesmul continued-......ok , If you allow me to leave the calculation part....i think the answer would a lil bit easier to understand.....The Universe is expanding more than the speed of light......How, cause Light travels at 3 Hundred Million per sec.......but many galaxy are more then 25 billion Km apart from each other......To answer the broader question in detail, we need to specify what we mean by the universe "expanding faster than the speed of light." The universe is not a collection of galaxies sitting in space, all moving away from a central point. Instead, a more appropriate analogy is to think of the universe as a giant blob of dough with raisins spread throughout it (the raisins represent galaxies; the dough represents space). When the dough is placed in an oven, it begins to expand, or, more accurately, to stretch, keeping the same proportions as it had before but with all the distances between galaxies getting bigger as time goes on.
The bottom line is that different pairs of galaxies are moving at different speeds with respect to each other; the further the galaxies are, the faster they move apart. So when we ask whether the universe is "expanding faster than the speed of light," I am going to interpret that to mean, "Are there any two galaxies in the universe which are moving faster than the speed of light with respect to each other?"
So how do we measure this? As discussed in a previous question, the universe's expansion is determined by something called the Hubble constant, which is approximately equal to 71, measured in the technically useful but conceptually confusing units of "kilometers per second per megaparsec." In more sensible units, the Hubble constant is approximately equal to 0.007% per million years -- what it means is that every million years, all the distances in the universe stretch by 0.007%. (This interpretation assumes that the Hubble "constant" actually stays constant over those million years, which it doesn't, but given that a million years is extremely short on cosmic timescales, this is a pretty good approximation. It also assumes that when we talk about the "distance" between two galaxies, we are referring to the distance between them right now -- that is, the distance we would measure if we somehow "pressed the freeze-frame button" on the universe, thereby stopping the expansion, and then extended a really long tape measure between the two galaxies and read off the distance. There are many other distances that can be defined in cosmology, but this is the most useful one for the current question.)
If we use the definition of distance given above (and only if we use this definition and no other), then the Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second. Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
So we have reduced the original question to a much simpler one: Are there any two galaxies in the entire universe whose distance (as defined above) is greater than 4,200 megaparsecs?
