There is a theory that our universe has collided with other universes

There is a theory that our universe has collided with other universes

There is a theory that our universe has collided with other universes in the past and we can view the scars by studying the night sky

Relaxing on an idyllic beach on Grand Cayman Island in the Caribbean, Anthony Aguirre vividly describes the worst natural disaster he can imagine. It is, in fact, probably the worst natural disaster that anyone could imagine. An asteroid impact would be small potatoes compared with this kind of event: a catastrophic encounter with an entire other universe.As an alien cosmos came crashing into ours, its outer boundary would look like a wall racing forward at nearly the speed of light; behind that wall would lie a set of physical laws totally different from ours that would wreck

There is a theory that our universe has collided with other universes everything they touched in our universe. “If we could see things in ultraslow motion, we’d see a big mirror in the sky rushing toward us because light would be reflected by the wall,” says Aguirre, a youthful physicist at the University of California at Santa Cruz. “After that we wouldn’t see anything—because we’d all be dead.”There is a sober purpose behind this apocalyptic glee. Aguirre is one of a growing cadre of cosmologists who theorize that our universe is just one of many in a “multiverse” of universes. In their effort to grasp the implications of this idea, they have been calculating the odds that universes could interact with their neighbors or even smash into each other. While investigating what kind of gruesome end might result, they have stumbled upon a few surprises. There are tantalizing hints that our universe has already survived such a collision—and bears the scars to prove it.Aguirre has organized a conference on Grand Cayman to address just such mind-boggling matters. The conversations here venture into multiverse mishaps and other matters of cosmological genesis and destruction. At first blush the setting seems incongruous: The tropical sun beats down dreamily, the smell of broken coconuts drifts from beneath the palm trees, and the ocean roars rhythmically in the background. But the locale is perhaps fitting. The winds are strong for this time of year, reminding the locals of hurricane Ivan, which devastated the capital city of George Town in 2004, lifting whole apartment blocks and transporting buildings across streets. In nature, peace and violence are never far from each other.Much of today’s interest in multiple universes stems from concepts developed in the early 1980s by the pioneering cosmologists Alan Guth at MIT and Andrei Linde, then at the Lebedev Physical Institute in Moscow. Guth proposed that our universe went through an incredibly rapid growth spurt, known as inflation, in the first 10-30 second or so after the Big Bang. Such extreme expansion, driven by a powerful repulsive energy that quickly dissipated as the universe cooled, would solve many mysteries. Most notably, inflation could explain why the cosmos as we see it today is amazingly uniform in all directions. If space was stretched mightily during those first instants of existence, any extreme lumpiness or hot and cold spots would have immediately been smoothed out. This theory was modified by Linde, who had hit on a similar idea independently. Inflation made so much sense

There is a theory that our universe has collided with other universes that it quickly became a part of the mainstream model of cosmology.Soon after, Linde and Alex Vilenkin at Tufts University came to the startling realization that inflation may not have been a onetime event. If it could happen once, it could—and indeed should—happen again and again for eternity. Stranger still, every eruption of inflation would create a new bubble of space and energy. The result: an infinite progression of new universes, each bursting forth with its own laws of physics.In such a bubbling multiverse of universes, it seems inevitable that universes would sometimes collide. But for decades cosmologists neglected this possibility, reckoning that the odds were small and that if it happened, the results would be irrelevant because anyone and anything near the collision would be annihilated.At the Grand Cayman conference, Guth sounds somewhat sheepish that he ignored the possibility of cosmic collisions until recently. “It’s funny that we hadn’t thought about this seriously,” he says. “I hadn’t thought about it all, except maybe to think it was rare.”That changed a few years ago, after Guth received a chance phone call from an ABC News reporter. She was working on a story about global disasters and asked if a collision with another universe could destroy the planet. Guth’s response was apparently not dramatic enough—his interview did not turn into a TV spot—but the question inspired him. He decided that the risks of death-by-bubble should no longer be ignored, and he teamed up with Vilenkin and Jaume Garriga of the University of Barcelona in Spain to investigate.The team assumed that bubble collisions would be deadly and set out to calculate the odds of such a lethal run-in. Guth’s calculations showed that the likelihood of a fatal collision in our part of the multiverse is probably quite small. However, other research was starting to show that our universe could actually survive a run-in with an alien bubble—and in fact, there was a good chance that such a nonlethal collision had already occurred. “When you think about it, in an infinite multi­verse, with bubbles being formed all the time, sooner or later a bubble will form near the boundary of our bubble, and we will be hit,” Vilenkin says. “There’s the possibility of a benign collision when the cosmological characteristics of the alien bubble are similar to ours, so that it doesn’t destroy us but recedes away.”

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