|Author Edgar Allan Poe, best known for his macabre poems and detective stories, proposed a solution to a paradox about the dark night sky.|
If the universe is infinite and uniformly filled with stars, then any line of sight, when we look up into the sky, should eventually hit some distant star. If so, then the night sky would be as bright as the face of the sun, rather than dark. How can this be?
This paradox vexed 19th-century astronomers, but today the puzzle is solved. The universe is simply not old enough for light from such distant stars to reach our eyes. Wait a billion years, and another billion light-years of galaxies will help to fill the gaps.
It’s not widely known that this solution was first proposed by Edgar Allan Poe, an author of horror and detective stories. In an essay called “Eureka: a Prose Poem” (1848), he speculates that stars are so distant that, for some, “no ray from it has yet been able to reach us at all,” and he reminds the reader that light travels at a finite speed. He assumed implicitly that “the universe of stars” has a finite age, and together these are the three ingredients of the present-day explanation.
Poe’s essay was more spiritual than scientific, his assumptions about the distances to most stars could not be tested by measurements of the day, and his implicit assumption that the universe of stars had a beginning was motivated by religious faith. This point about the beginning of time has always fascinated and frustrated humanity. Whether one starts by believing in a moment of creation or a universe that has always existed, one finds oneself asking either, “What happened before the beginning?” or “How did this uncreated world come to be?” It’s hard to be comfortable with either scenario.
In the early 20th century, the discovery that the universe is expanding came as a shock because many scientists at the time expected it to be without beginning and largely unchanging. Using general relativity, which relates the rate of spatial expansion to the matter and energy that fill space, the current best measurements point back to an absolute beginning of time 13.8 billion years ago. It seems as though science has vindicated all of Edgar Allan Poe’s beliefs.
However, extrapolating all the way down to a point of zero size, infinite temperature and infinite density goes beyond our present state of knowledge. Physicists are still learning how matter behaves at very high temperatures and energies, and the behavior of matter affects the expansion rate of space. The high energies currently being studied at the LHC, for instance, correspond to a temperature of quadrillions of degrees, which was the temperature of the universe a trillionth of a second after the naive Time Zero. If new phenomena appear at higher energies, then that first picosecond of history may need to be rewritten.
This distinction between the physics of the very early universe and the metaphysics of creation is something that I feel is important because it has led to misunderstandings. Physicists and journalists use the phrase “the big bang” in different ways: To physicists, it means the early expansion history and development of the universe as we know it, but in the popular press, it is often taken to mean creation itself. Using the physicist’s definition, it’s not wrong to ask, “What happened before the big bang?” In fact, this is an active area of scientific research.