The Day the Universe Froze

About 11.5 billion years ago, when the universe was a quarter of the size it is today, it did freeze. Solid as a stone. Image at right  shows such a cosmic ice cream bar as visualized by Chandra/NASA.

This according to researchers exploring a new model for dark energy. The model, published online May 6 in the journal Physical Review D, was developed by Research Associate Sourish Dutta and Professor of Physics Robert Scherrer at Vanderbilt University, working with Professor of Physics Stephen Hsu and graduate student David Reeb at the University of Oregon.

“One of the things that is very unsatisfying about many of the existing explanations for dark energy is that they are difficult to test,” says Scherrer, “We designed a model that can interact with normal matter and so has observable consequences."

The model proposes that space itself is the source of the repulsive energy that is pushing the universe apart, and attributes dark energy to an entirely new field dubbed quintessence.

Quintessence is comparable to other basic fields like gravity and electromagnetism, but has some unique properties. For one thing, it is the same strength throughout the universe. Another important feature is that it acts like an antigravity agent, causing objects to move away from each other instead of pulling them together like gravity.

Image: Chandra/NASA

Would an antimatter apple fall up?

Shaun Saunders sends in an article with some real meat on it! An article in New Scientist online ask the seemingly innocent question: How would antimatter react in a gravity field? As the article points out: Physicists have studied antimatter, the mirror version of ordinary matter, for decades. They know, for example, that antiparticles have the same mass as ordinary particles, but opposite charge. But no one knows what effect gravity will have on such particles.

Now several groups want to measure exactly how the Earth will pull on antimatter. The tests would create a horizontal beam of anti-particles and measure how much gravity deflects it.

The test may show no difference between the way matter and antimatter fall. But some researhers are holding out hope that they may see something completely unexpected, which could point the way to new gravity-like forces, or perhaps even anti-gravity.