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Why we think there's a Multiverse, not just our Universe. “Every true, eternal problem is an equally true, eternal fault; every answer an atonement, every realisation an improvement.”

Why we think there's a Multiverse, not just our Universe

-Otto Weininger The best measurements of the distant Universe — out beyond our galaxy — have led us to the current picture of exactly what our Universe is doing: expanding and cooling, with its galaxies progressively getting farther and farther apart. Image credit: Molly Read for the University of Wisconsin-Madison. But what does that mean for our past? If we’re expanding and cooling, that means our past was less expanded and less cooled, or as we like to think of it, denser and hotter. Now, if you’re thinking like a scientist, you don’t just want to know what it’s doing. And the answer is actually straightforward: if general relativity is your theory of gravity, the Universe’s expansion rate is determined by what type of energy dominates your Universe.

Welcome to the Multiverse. Theoretical cosmologist isn’t one of the more hazardous occupations of the modern world.

Welcome to the Multiverse

The big risks include jet lag, caffeine overdose, and possibly carpal tunnel syndrome. It wasn’t always so. On February 17, 1600, Giordano Bruno, a mathematician and Dominican friar, was stripped naked and driven through the streets of Rome. Then he was tied to a stake in the Campo de’ Fiori and burned to death. The records of Bruno’s long prosecution by the Inquisition have been lost, but one of his major heresies was cosmological. These days, cosmologists like me may be safer, but our ideas have grown only more radical. Also like Bruno, cosmologists are reaching far beyond what observational evidence can tell them. The extent of what astronomers can see is frustratingly limited by the speed of light: one light-year (about six trillion miles) per year.

Everybody talks about the multiverse, but nobody does anything about it. MIT: "New Universes are Being Constantly Created" In this view, “nature gets a lot of tries — the universe is an experiment that’s repeated over and over again, each time with slightly different physical laws, or even vastly different physical laws,” says Jaffe.

MIT: "New Universes are Being Constantly Created"

Some of these universes would collapse instants after forming; in others, the forces between particles would be so weak they could not give rise to atoms or molecules. However, if conditions were suitable, matter would coalesce into galaxies and planets, and if the right elements were present in those worlds, intelligent life could evolve. Some physicists have theorized that only universes in which the laws of physics are “just so” could support life, and that if things were even a little bit different from our world, intelligent life would be impossible. In that case, our physical laws might be explained “anthropically,” meaning that they are as they are because if they were otherwise, no one would be around to notice them.

The Daily Galaxy via MIT News Office. How to spot a multiverse. How can we tell if another universe has collided with our own?

How to spot a multiverse

Physicists in Canada and the US believe they have the answer – it would leave "a unique and highly characteristic" imprint in the microwave background that pervades the cosmos. The physicists claim that the prediction can be tested using existing and future space telescopes, which contradicts a widespread view that the existence of a multiverse is untestable. Chuck Bennett, an astrophysicist at Johns Hopkins University in Maryland, US, who was not involved with the study, believes the prediction helps bring multiverse theory into the realms of conventional, falsifiable science.

"Science relies on being able to falsify ideas through experiment or observations of nature," he says. "The fact that these potentialities exist enables us to call this 'science'. Time and the multiverse. This article first appeared on the FQXi community website, which does for physics and cosmology what Plus does for maths: provide the public with a deeper understanding of known and future discoveries in these areas, and their potential implications for our worldview.

Time and the multiverse

FQXi are our partners in our Science fiction, science fact project, which asked you to nominate questions from the frontiers of physics you'd like to have answered. This article addresses the question "What is time? ". Click here to see other articles on the topic. "You must remember this, a kiss is still a kiss, a sigh is just a sigh. The fundamental things apply, as time goes by... " For many of us, this song from Casablanca evokes memories of romance. Mersini-Houghton's view of time comes from looking at the bigger picture — the biggest possible picture, in fact. Womb to tomb We travel through life from womb to tomb, not vice-versa, yet physicists have no real explanation for why time flows in only one direction.

Is our universe inside a bubble? First observational test of the 'multiverse' The theory that our universe is contained inside a bubble, and that multiple alternative universes exist inside their own bubbles -- making up the 'multiverse' -- is, for the first time, being tested by physicists.

Is our universe inside a bubble? First observational test of the 'multiverse'

Two research papers published in Physical Review Letters and Physical Review D are the first to detail how to search for signatures of other universes. Physicists are now searching for disk-like patterns in the cosmic microwave background (CMB) radiation -- relic heat radiation left over from the Big Bang -- which could provide tell-tale evidence of collisions between other universes and our own. Many modern theories of fundamental physics predict that our universe is contained inside a bubble.