Is time in our universe absolute?

[ailog]

When it is said that the universe is, for example, 9 billion years old, is it the same everywhere else in the universe? Do the distant quasars that we see know that they are the same age as we figure they are?

And what defines the “edge” of our universe. The most distance object that we can detect? How about the light from this object that travels away from us? If we spot an object say 9 billion light years away, then its light must have gone another 9 billion farther out and the light would be 18 billion light years from us. Am I thinking correctly?

 

[Nakisima]

The universe doesn't just pop up into existence when it expands, it takes the matter inside it with it to a degree - We know this because the galaxies are moving further apart. No one really knows how the universe can still be expanding, as it was once smaller than the size of a dust particle.
I can answer your second question more accurately.
The edge of our universe is the ever expanding big bang, like blowing up a balloon. The most distant object we can detect is in the "observable" universe, 140 Ym (Yottameters, (10 to the power of 24)m) in diameter. The universe as a whole is expected to be 930 Ym in diameter. The universe is 14,000,000,000 years old, so if something was more than 14,000,000,000 light-years away, it would take more than that amount of time for the light to reach us - more time than the universe has existed. It is also important to note that a light year is a measure of distance and not time - a light year is how far light travels in one Earth year, therefore your 9 billion light-year object will look to us on Earth exactly how it was 9 billion Earth years ago. If you're looking at a young star 9 billion light years away, it could well have died and we wouldn't know until the light catches up, which would be anything up to 9 billion Earth years.

 

[Nakisima]

I've only just realized the complexity of your second question, and I didn't quite answer fully. Light emitting from an object 9 billion light years away will inevitably send light out not just in our direction, however that light will keep on traveling long after it has reached us depending on how old it is. So say that something has just appeared in the night sky to us; how far away it is will also tell us how old it is. We can only see if anything is there if the light has reached earth, but in the other direction if you were far enough away, it wouldn't even be visible, not because the light's energy has ran out, but because (as is only too obvious), even light takes time to travel, and it won't stop going in the other direction just because we can see it. So we can see that it is 9 billion years old, and if there were any humans further out than Earth is in the other direction, they would be able to work out how old it is even though they are further away than we are, but they would only be able to see it if they were 9 billion light years away or less, and would appear to them later if they were more than 9 billion light years away.

 

[JesseM]

The edge of our universe is the ever expanding big bang, like blowing up a balloon. The most distant object we can detect is in the "observable" universe, 140 Ym (Yottameters, (10 to the power of 24)m) in diameter. The universe as a whole is expected to be 930 Ym in diameter. The universe is 14,000,000,000 years old, so if something was more than 14,000,000,000 light-years away, it would take more than that amount of time for the light to reach us - more time than the universe has existed.

The size of the observable universe is actually defined in terms of the current distance of the most distant regions we can see at any point in the past, which is much larger than 14 billion light years due to the expansion of space. See the wiki article Observable universe for details.

 

[bcrowell]

When it is said that the universe is, for example, 9 billion years old, is it the same everywhere else in the universe? Do the distant quasars that we see know that they are the same age as we figure they are?

There is no well-defined notion of simultaneity in relativity, so there is no inherently well-defined interpretation for the question of how old a distant galaxy is "now."

What you can do, however, is to imagine a clock that has existed since some early time and that has always been at rest with respect to the Hubble flow. This clock defines a time coordinate t at every point in space which is not the *only* possible time coordinate, but is in some sense a very natural one. Since the universe is approximately homogeneous, observers will always find that this local-comoving-clock-time correlates well with conditions like the average density of galaxies.

And what defines the “edge” of our universe. The most distance object that we can detect? How about the light from this object that travels away from us? If we spot an object say 9 billion light years away, then its light must have gone another 9 billion farther out and the light would be 18 billion light years from us. Am I thinking correctly?

In a closed universe without a cosmological constant, that light could actually have wrapped around.

 

[ailog]

Thanks to all of the responses. I am still of a mind that time has a universally fixed rate with local deviations due to relativity. The local deviations in our universe somehow add up to a null such that the universal time rate is invariant. If one could be a god and somehow observe our universe from outside, how old would are universe be? If we say 14 billion years, then what is that time interval relative to? I suppose relative to our everyday life on earth.

I do not believe that the age of our universe is relative to ones position in (or outside) the universe, especially if we assume that distant objects are made of the same types of particles that behave in the same way as particles do locally. Unless we take a guess that there exists different types of space and the particles we know of act differently in the different spaces, and the absolute times in these spaces are different.