Time Will End in Five Billion Years, Physicists Predict
The prediction comes from the theory of eternal inflation, which says our universe is part of the multiverse. This vast structure is made up of an infinite number of universes, each of which can spawn an infinite number of daughter universes. (Related: "New Proof Unknown 'Structures' Tug at Our Universe.")
The problem with a multiverse is that anything that can happen will happen an infinite number of times, and that makes calculating probabilities—such as the odds that Earth-size planets are common—seemingly impossible. "Normal notions of probability—where you say, Event A happens twice and Event B happens four times, so Event B is twice as likely—don't work, because instead of two and four, you have infinity," said Ken Olum of Tufts University in Massachusetts, who was not involved in the study.
And calculating probabilities in a multiverse wouldn't just be a problem for cosmologists. "If infinitely many observers throughout the universe win the lottery, on what grounds can one still claim that winning the lottery is unlikely?" theoretical physicist Raphael Bousso of the University of California, Berkeley, and colleagues write in the new study.
Physicists have been circumventing this problem using a mathematical approach called geometric cutoffs, which involves taking a finite swath of the multiverse and calculating probabilities based on that limited sample. But in the new paper, published online last month at the Cornell University website arXiv.org, Bousso's team notes that this technique has an unintended and, until now, overlooked consequence. "You cannot use [cutoffs] as mere mathematical tools that leave no imprint," Bousso said. "The same cutoff that gave you these nice and possibly correct predictions also predicts the end of time. "In other words, if you use a cutoff to compute probabilities in eternal inflation, the cutoff itself"—and therefore the end of time—"becomes an event that can happen."
Universe Is One Bubble in a Boiling Pot. Despite this odd wrinkle, Bousso and colleagues think eternal inflation is a solid concept. Most of the theory's underlying scientific assumptions—such as Albert Einstein's theories of relativity—"all seem kind of innocuous, and it's hard to see what could replace them," Bousso said.
