When the multiverse and many-worlds collide

[crazynutsx]

 

TWO of the strangest ideas in modern physics - that the cosmos constantly splits into parallel universes in which every conceivable outcome of every event happens, and the notion that our universe is part of a larger multiverse - have been unified into a single theory. This solves a bizarre but fundamental problem in cosmology and has set physics circles buzzing with excitement, as well as some bewilderment.

 

The problem is the observability of our universe. While most of us simply take it for granted that we should be able to observe our universe, it is a different story for cosmologists. When they apply quantum mechanics - which successfully describes the behaviour of very small objects like atoms - to the entire cosmos, the equations imply that it must exist in many different states simultaneously, a phenomenon called a superposition. Yet that is clearly not what we observe.

 

Cosmologists reconcile this seeming contradiction by assuming that the superposition eventually "collapses" to a single state. But they tend to ignore the problem of how or why such a collapse might occur, says cosmologist Raphael Bousso at the University of California, Berkeley. "We've no right to assume that it collapses. We've been lying to ourselves about this," he says

 

In an attempt to find a more satisfying way to explain the universe's observability, Bousso, together with Leonard Susskind at Stanford University in California, turned to the work of physicists who have puzzled over the same problem but on a much smaller scale: why tiny objects such as electrons and photons exist in a superposition of states but larger objects like footballs and planets apparently do not.

 

This problem is captured in the famous thought experiment of Schrödinger's cat. This unhappy feline is inside a sealed box containing a vial of poison that will break open when a radioactive atom decays. Being a quantum object, the atom exists in a superposition of states - so it has both decayed and not decayed at the same time. This implies that the vial must be in a superposition of states too - both broken and unbroken. And if that's the case, then the cat must be both dead and alive as well.

 

 

To explain why we never seem to see cats that are both dead and alive, and yet can detect atoms in a superposition of states, physicists have in recent years replaced the idea of superpositions collapsing with the idea that quantum objects inevitably interact with their environment, allowing information about possible superpositions to leak away and become inaccessible to the observer. All that is left is the information about a single state.

 

Physicists call this process "decoherence". If you can prevent it - by tracking all the information about all possible states - you can preserve the superposition.

[swansont]

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Moderator Note

You claim to run a discussion forum, so you should know that copyright violation is a bad thing™ and the plagiarism is surprising from someone in such a position. It's against the rules of this forum, at least.

http://www.newscientist.com/article/mg21028154.200-when-the-multiverse-and-manyworlds-collide.html