I believed in the Big Bang until I heard universe expansion is accelerating

[bupkus]

I believed in the Big Bang until I heard universe expansion is accelerating.

Why?

1. Imagine going back into time. Isn't it fair to say that the rate of expansion would appear to be decelerating? As we approach the BB event the rate of expansion would either approach a constant or stop. Wouldn't it?

2. Also, I have heard that at the time of the BB the expansion occurred at such a high velocity that it surpassed the speed of light.

If the second statement is true then how could the first.

Note: I am not interpretating my 2nd statement (which I am just repeating from what I recall hearing) to mean that the matter inside the universe moved faster than the speed of light, only that the rate of universe expansion briefly was greater than the speed of light.
Again, to suggest "briefly" would require a period of rapid deceleration before, once again, the universe would begin to accelerate its expansion.

Fickle universe?

I, admittedly, am not a Physicist, so I am hopeful for illumination from one.

 

[beginner99]

I believed in the Big Bang until I heard universe expansion is accelerating.

Why?

1. Imagine going back into time. Isn't it fair to say that the rate of expansion would appear to be decelerating? As we approach the BB event the rate of expansion would either approach a constant or stop. Wouldn't it?

2. Also, I have heard that at the time of the BB the expansion occurred at such a high velocity that it surpassed the speed of light.

If the second statement is true then how could the first.

Note: I am not interpretating my 2nd statement (which I am just repeating from what I recall hearing) to mean that the matter inside the universe moved faster than the speed of light, only that the rate of universe expansion briefly was greater than the speed of light.
Again, to suggest "briefly" would require a period of rapid deceleration before, once again, the universe would begin to accelerate its expansion.

Fickle universe?

I, admittedly, am not a Physicist, so I am hopeful for illumination from one.

The expansion rate would not just get smaller. There needs to be a force to stop it. This force is gravity. Currently it's tought that the gravity is not strong enough to stop the expansion (= not enough matter in the universe).

For further read see wiki:

http://en.wikipedia.org/wiki/Accelerating_universe

and the links in that article.
Basically it says that if the cosmological constant is positive, empty room leads to further and faster expansion:

A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa. If the energy density is positive, the associated negative pressure will drive an accelerated expansion of empty space. (See dark energy and cosmic inflation for details.)

 

[silverpig]

The rate of expansion of the universe hasn't been constant.

1. At the time of the big bang, the universe expanded quickly, but less than the speed of light.
2. Shortly after, a scalar potential decayed (fancy way of saying add a bunch of energy to the expansion), and space expanded very quickly. No matter moved locally faster than light, but the space between points didi increase faster than light could traverse it. Imagine if every distance you know just doubled in 1 second. The moon is 1.3 light seconds away right now. Double that to 2.6 in one second, and you'll find that the moon moved away from the earth faster than light speed. All you're doing is just increasing the size of space. Yes this period was very brief. It is known as inflation.
3. After that, gravity started slowing things down.
4. The expansion rate changed again once matter dominated over radiation as the main form of energy in the universe.
5. Just recently (from a cosmological perspective), this vacuum energy began to dominate matter as the dominant form of energy in the universe and the expansion rate changed again and is now accelerating.