The Fate of the Universe - All Life Could End

Today's generally accepted view of the distant future has been that today, there is more matter than radiation in the universe and ordinary matter particles - protons and neutrons in particular - will gradually decay into radiation over trillions upon trillions of years, leaving a universe in which radiation once again dominates over matter; a universe lacking the material structures that are necessary for life.

Two physicists, Lawrence Krauss and Robert Scherrer argue that there might be still good news. They claim that matter as we know it will remain as the universe expands at an ever-increasing clip. That is, the current status quo between matter and its alter ego, radiation, will continue as the newly discovered force of dark energy pushes the universe apart.

In physical cosmology, dark energy is a form of energy that permeates all of space and tends to increase the rate of expansion of the universe. The existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total energy of the universe.

Ironically, dark energy causes expansion because it has strong negative pressure.

A substance has positive pressure when it pushes outward on its surroundings. This is the usual situation for fluids. Negative pressure, or tension, exists when the substance instead pulls on its surroundings. A common example of negative pressure occurs when a solid is stretched to support a hanging weight.

"The discovery of dark energy has changed everything, but it has changed the view of the future more than the past. It is among the worst of all possible futures for life," says Krauss, who has spent the last few years exploring its implications. In an eternally expanding universe there is at least a chance that life could endure forever, but not in a universe dominated by vacuum energy, Krauss and CWRU collaborator Glenn Starkman have concluded.

As the universe expands, the most distant objects recede at the highest velocity. The faster that objects recede, the more that the light coming from them is "red-shifted" to longer wavelengths. When their recessional velocity reaches light speed, they disappear because they are traveling away faster than the light that they emit.

The process of disappearance has already begun, claim the two physicists: there are objects that were visible when the universe was half its present age that are invisible now. However, the process won't become really noticeable until the universe is about 100 billion years old. By ten trillion years, nothing but our local cluster of galaxies will be visible.

Regarding the fate of future civilizations, this process puts a finite limit on the amount of information and energy that will be available to maintain life. Assuming that consciousness is a physical phenomenon, this implies that life itself cannot be eternal, Krauss and Starkman argue.