Exploring a universe where nothing isn't empty

We appear to live in a universe where getting rid of all ordinary matter still leaves a fabric full of quantum fields and virtual particles—and getting rid of that turns out to be energetically unfavorable.

By John Timmer | Last updated June 26, 2009 6:20 AM CT

In our last bit of World Science Festival coverage, we discussed how inflation has produced an expanding, inhabitable universe. That still leaves the question of why that universe seems to be filled with strange stuff like virtual particles and dark energy. A different panel tackled that question and, in true quantum fashion, the session that described the contents of the universe came before the one that described its creation.

The session, which was moderated by radio host John Hockenberry, started out with a historical perspective on the fabric of the universe from Cambridge's John Barrow. Barrow described various views of whether it might be possible for a space to exist that was devoid of the sorts of matter we're familiar with. Reactions to the prospects, from the time of Aristotle onwards, were mixed, but they were primarily based on philosophical grounds. Things really didn't get close to our modern conception of a vacuum—one with states that could change over time—until the time of James Clerk Maxwell. The advent of quantum mechanics finally made the description and study of vacuum states a quantitative science.

The panel discussion featured Paul Davies, George Ellis, and Frank Wilczek. The latter described how quantum mechanics changed our view of what constitutes a vacuum by analogy: imagine you're an intelligent fish. You'd probably develop physics that are appropriate for your environment, which is water. What quantum mechanics has done, Wilczek suggested, is show us what sort of physics operates once you do the equivalent of taking the water away. What's left, in the case of our universe, is space that isn't really empty—instead, it's filled with quantum fields (notably the Higgs field) and virtual particles that pop briefly into existence before being annihilated by collisions with their antiparticle counterparts.

The striking thing about this, in contrast to the multiverse, is that we actually have evidence for the existence of these vacuum fields and virtual particles. The clearest the authors described comes in the form of the Casimir effect, in which two plates are brought close to each other in a vacuum. Their proximity excludes the existence of some of the quantum fields in the space in between them, leaving that area, in effect, more empty than the vacuum outside the plates. The net result is a pressure that drives the plates together, and that force has been experimentally verified.

more:

http://arstechnica.com/science/news/2009/06/exploring-a-universe-where-nothing-isnt-empty.ars