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In Lee Smolin's book, The Trouble with Physics, pages 15 and 16, he states:
Can someone explain how this works?
Does this mean that modifications to gravity causing tension at large intergalactic scales could account for the accelerating expansion of the universe as well?
Or there is a new form of matter—or energy—that becomes relevant on these very large scales: That is, this new form of energy affects only the expansion of the universe. To do this, it cannot clump around galaxies or even clusters of galaxies, This strange new energy which we have postulated to fit the data, is called the dark energy.
Most kinds of matter are under pressure, but the dark energy is under tension—that is, it pulls things together rather than pushes them apart. For this reason, tension is sometimes called negative pressure. in spite of the fact that the dark energy is under tension, it causes the universe to expand faster. If you are confused by this, I sympathize. One would think that a gas with negative pressure would act like a rubber band connecting the galaxies and slow the expansion down. But it turns out that when the negative pressure is negative enough, in general relativity it has the opposite effect. It causes the expansion of the universe to accelerate.
Can someone explain how this works?
Does this mean that modifications to gravity causing tension at large intergalactic scales could account for the accelerating expansion of the universe as well?