ximerical (November 30, 1999 at 12:00 am)

Because that is not true :) As far as I know, you'd need a pretty weird charge distribution to get an effect similar to what we are observing, and such a charge distribution would surely be very unstable (like charges repel, unlike attract). Likewise, perturbations in the charge distribution will, over time, smooth themselves out because of this and so we have very good reasons to believe that the universe is on large scales electrically neutral.

spitneybeeers (November 30, 1999 at 12:00 am)

so why do not we simply say that the universe is not electrically neutural, and that causes the acceleration. Actually, i do not know if we have an experiment to support the assertion that the universe is electrically neutral on large scales.

ximerical (November 30, 1999 at 12:00 am)

What happens is that one takes Einsteins equation of gravity, and considers what happens when you have a constant energy density. You do the calculation and find that the expansion accelerating. I would assume that this is then what leads people saying that dark energy generates a repulsive gravitational field... However I am not sure how helpful that is. Atleast it's not the way I think about the problem.

spitneybeeers (November 30, 1999 at 12:00 am)

I still do not understand. I mean, I see that the universe has a vacuum expectation value which is not zero but some kind of constant. But what does that have to do with acceleration? As far as I understand this constant energy, called the Dark Energy, has some kind of gravitational field which is not attractive, but repulsive. Is that the fact? Otherwise I cannot explain how the acceleration is related to dark matter. Thanks for the answer, by the way! and thanks in advance for next answer :)

ximerical (November 30, 1999 at 12:00 am)

The probable source of the acceleration is what phycisists call 'dark energy', ie. an energy density constant throughout our universe. Where it comes from, no one knows, but that seems to be the way our universe is built. :)

mendesnipplesucking (November 30, 1999 at 12:00 am)

There is one thing I did not understand. Dr. Carroll said that the universe is expanding with an acceleration. What does that mean? What is the source of this acceleration? Thanks in advance!

IronCladBen (November 30, 1999 at 12:00 am)

whoah

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AntaresInScorpius (November 30, 1999 at 12:00 am)

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