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," National Geographic News quoted Ken Olum of Tufts University in Massachusetts, as saying.
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 wrote 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, Bousso's team noted that this technique has an unintended and, until now, overlooked consequence.
"You cannot use [cutoffs] as mere mathematical tools that leave no imprint.
"The same cutoff that gave you these nice and possibly correct predictions also predicts the end of time," said Bousso.
In fact, many physicists think eternal inflation is a natural extension of the theory of inflation, which solved some of the problems with the original big bang theory.
Eternal inflation is a next step in inflation theory, and it allows scientists to avoid some other tricky cosmology questions, such as what existed before our universe (answer: other universes) and why our universe appears to have properties fine-tuned for life.
"Although we don't have a theory [to explain the earliest moments of the universe], we have some pretty good ideas about what such a theory would look like ... and these ideas seem to necessarily include other universes," said Charles Lineweaver, an astrophysicist at Australian National University.
If probabilities are to work in a multiverse, there must be actual cutoffs that bring various universes to their ends, study leader said Bousso.
According to the formulas used to calculate cutoffs, a universe that is 13.7 billion years old will reach its cutoff in about 5 billion years, his team concludes.
For most people, the idea that a mathematical tool could be elevated to a real-world event might seem strange, but there are precedents for it in physics.
Scientists think our sun-now a middle-age star at about 4.57 billion years old-will be reaching the end of its life in about five billion years.
At that point in time, the sun will run out of fuel in its core and will start to shed its outer layers of gas, inflating to become a red giant and ultimately a planetary nebula.
Earth's exact fate during this event is unclear, but few scientists would argue that life on the planet could survive the sun's death.
The story was published at the Cornell University website arXiv.org. (ANI)