About 13.7 billion years ago, our universe was born, and like some acne-ridden teenager going through puberty, it quickly expanded in size. Within hardly any time at all, the universe had gone from a little speck of nothingness to a vast wasteland of galaxies and Scientologists not much smaller than the universe today. (See Big Bang and cosmic inflation, respectively.)

Once we figured out the beginning, it wasn’t hard to guess the end. Inflation was done with, so it was all up to gravity. Basically, if the universe is dense enough (a lot of stuff in not too much space), then it should eventually collapse in a reversal of the Big Bang. Otherwise, space would continue expanding slowly into infinity and beyond. Or, if you’re an obsessive Albert Einstein, magical new quantities pop into existence and the universe, in turn, neither expands nor collapses.

(Un)fortunately(?), reality seems to be a little different. Instead of business as usual, or the universe heading toward the Big Crunch, expansion is accelerating. And eventually far-enough objects will be moving away from us faster than the speed of light. Ultimately, stars and galaxies will be moving away from us so quickly that light from them will never reach our eyes, as if they were never there to begin with.

Sad.

This places current scientists in a very interesting position:

Scientists in the far future, on some other planet without the benefit of our current knowledge, will see no evidence from their observations that the universe is expanding. After all, the only way that we know about it is by looking out at distant galaxies and tracing their motion. If they are out of sight, there will be no such tracers.

In other words, right now is the only time when both the expansion of the universe and its cause (dark energy) can be inferred. As the New Scientist article states, dark energy could not have been measured in the past, and the expansion will not be measurable in the future. And if we can predict that the sky will be a lot less informative for future scientists, what about today’s cosmologists?

We may never know if other fascinating and important aspects of our universe are hidden from us today, yet would have been visible had we been smart enough to evolve 5 billion years earlier.

Time travel never seemed more urgent.

One Response to “Nerd Alert: The past is disappearing”

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