Why is the universe's expansion accelerating despite gravitational forces?

[LeeJeffries]

I say inflation, I might possibly not mean it. I've read that the expansion of the universe is accelerating, and it's a mystery why, but my question is why isn't it expected to appear that way?

If the masses of galaxies are spiralling towards the center where gravity is highest, and as more mass moves towards the center, space-time becomes more and more warped quicker and quicker as gravity increases, why wouldn't the space-time between galaxies curve quicker and quicker, redshifting the light?

In my head I picture it as the back of a chesterfield sofa, where galaxies are the studs and space-time is the leather inbetween

Where have I gone wrong? I admit "dark energy" just seems too stretched of an idea for me

 

[Naty1]

You mean the universe is expanding. Inflation was the very brief theoretical period in the big bang model right after the big bang when things got much bigger really,really fast...briefly faster than the speed of light.

Everywhere we look, more distant galaxies are receding at greater speeds than closer ones. Nobody knows why for sure but Einstein's equations suggest, despite Einstein's initial interpretation that things "just had to be stable", that the universe should be expanding or contracting. As you point out, it was discovered that not only is the universe expanding but is doing so at an accelerating rate.

As far as is known, the universe is quite isotropic and uniform over vast distances, NOT curved, but flat or very close to flat. In other words, there do not seem to be concentrations of mass or energy so vast as to curve much of the universe except locally, as perhaps within a galaxy or a massive black hole. Spacetime "between galaxies" would be some of the least curved as there isn't much there to curve it.

You can find more here:
http://en.wikipedia.org/wiki/Expanding_universe

and maybe try "cosmological constant" if you are interested.