NS: Void that is truly empty solves dark energy puzzle

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NS: Void that is truly empty solves dark energy puzzle

Post by bystander » Thu Sep 02, 2010 12:17 am

Void that is truly empty solves dark energy puzzle
New Scientist | Physics & Math | 01 Sep 2010
EMPTY space may really be empty. Though quantum theory suggests that a vacuum should be fizzing with particle activity, it turns out that this paradoxical picture of nothingness may not be needed. A calmer view of the vacuum would also help resolve a nagging inconsistency with dark energy, the elusive force thought to be speeding up the expansion of the universe.

Quantum field theory tells us that short-lived pairs of particles and their antiparticles are constantly being created and destroyed in apparently empty space. A branch of the theory, called quantum chromodynamics (QCD) - which explains how gluons and quarks, the particles that make up protons and neutrons, behave - predicts that a vacuum should be awash with an interacting sea or "condensate" of quarks and gluons. This picture helps to explain how particles made of quarks get most of their mass.

This condensate carries energy, so it might be thought to be a candidate for the mysterious source of dark energy, which can be described by a parameter called the cosmological constant. The trouble is that when physicists use QCD to estimate the condensate's energy density, their calculations suggest it would pack a punch that is 1045 times the cosmological constant that we measure from observations of the universe's expansion.

Now Stanley Brodsky of the SLAC National Accelerator Laboratory in Menlo Park, California, and colleagues have found a way to get rid of the discrepancy. "People have just been taking it on faith that this quark condensate is present throughout the vacuum," says Brodsky. Instead, his team have assumed that the condensate exists only inside protons, neutrons, pions and all other quark-containing particles, collectively known as hadrons.
New perspectives on the quark condensate - SJ Brodsky et al

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