September 13, 2006

Scientists Debate Size of Universe at Cornell

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As the semester moves on, does the walk to class every morning seem to get longer and longer? Rather than blaming a lack of sleep or a loss of motivation, blame the expanding universe. Millions of government tax dollars have been spent studying the phenomenon and the least you could expect in return is a good excuse to be running late. While this excuse may work on an unexpecting art professor, it may lead to a lengthy lecture if used unwisely on your physics TA.

While the expanding universe may not affect you tomorrow, it will definitely play an important role in your ultimate future, and it has already had quite an impact on your past. The Theory of the expanding universe explains the transition from a single big bang to the infinite expanse that is the known universe today. It also provides a set of scenarios for the distant future, including a wildly accelerating universe, in which everything is torn apart or even a universe that comes to rest and then starts hurtling inward to a final apocalyptic crash.

The expanding universe is a Theory with a capital T. Cosmologists cannot perform experiments with individual characteristics of the universe like biologists can in a lab. There is no way to view other possible universes to better understand our own either. This makes hypotheses more difficult to prove and gaps in our understanding harder to fill in. Despite this, astronomers and physicists have been able to passively measure the effects of the expanding universe and deduce much about its nature. Prof. Mark Trodden, Syracuse University, spoke about his research in the more theoretical and less understood portions of the field at the weekly physics colloquium Monday. While some of the Theory is considered physical law, other parts remain open to discussion and controversy.

The history of this Theory is embroiled in arguments that go far beyond the study of stars and into philosophy. It grew out of an attempt to answer the fundamental question, “How big is the universe?” Experts in seemingly disparate fields as religion, philosophy and science have tried to pin down the answer to this question. Two factions emerged. The first said that the universe extended infinitely outward in all directions, and the second said that it had finite size and shape.

In ancient Greece, philosophers debated whether something infinite could really exist but at the same time questioned what would happen if one stuck one’s hand over the edge of the universe. The paradox lasted for thousands of years with different historical geniuses lining up on different sides.

At the beginning of the 19th century, Heinrich Olbers claimed he had solved the riddle. He stated that if the universe were infinite and filled with stars, eventually every line of sight would reach a star; while the visible size of a star decreases with distance, its surface brightness does not. Therefore, in an infinite universe, the sky would be as bright as the stars, day and night; since this is not so, the universe must be finite in size.

Isaac Newton, the formulator of gravity, stands on the other side of the table. He claimed that if the universe were finite in size, it would have a center. And since everything has gravity, and gravity attracts, the universe would fall inward. Since his observations did not lead him to believe this was true, he supported the infinite universe theory.

Science today accepts a version somewhere in between those stated above. Albert Einstein and Edwin Hubble deserve much of the credit, but the Theory is still a work in progress. Olbers’ paradox is explained, because while the universe may be infinite in size, it is not infinite in age (approximately 13.7 billion years).

Light created at the far side of the universe just hasn’t had the time necessary to get all the way over here. Since the universe is expanding and in fact accelerating its rate of expansion, Newton’s concept of a collapsing universe simply hasn’t happened yet.

Observations have provided numerous checks to the Theory, and it is well accepted that the universe is indeed expanding, but future work needs to explain why. Trodden provided insight into possible gravitational explanations. Other explanations mentioned include buzzwords such as dark energy or multiple dimensions. All of these theories will require a high level math and critical thinking from whomever creates an acceptable explanation, but the future of the universe truly hangs in the balance.