In “When the multiverse and many-worlds collide” (New Scientist, 01 June 2011), Justin Mullins explains,
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.
Cosmologist Raphael Bousso at the University of California, Berkeley, accuses his community of “lying to ourselves,” by assuming that superpositions between particles (= here and there, both at once) eventually collapse into a single state. Maybe they don’t. Maybe information about one state leaks away, leaving only information about the other one.
If you can prevent it – by tracking all the information about all possible states – you can preserve the superposition.
This echoes the quantum Zeno effect – the watched elementary particle really doesn’t decohere. But bringing in many worlds and multiverses seems a radical way of resolving the quantum Zeno effect. Still, pressing on,
What Bousso and Susskind have done is to come up with an explanation for how the universe as a whole might decohere. Their trick is to think of the volume of space that encompasses all the information in our universe and everything it might possibly interact with in the future. In previous work, Susskind has dubbed this region a causal patch. The new idea is that our universe is just one causal patch among many others in a much bigger multiverse.
The leak of information from our causal patch causes the universe that we observe.
So Bousso and Susskind also link their interpretation to “many worlds” theory, which, Mullins says, is newly popular in the last decade:
According to this strange idea, when a superposition of states occurs, the cosmos splits into multiple parallel but otherwise identical universes. In one universe we might see the cat survive and in another we see it die. This results in an infinite number of parallel universes in which every conceivable outcome of every event actually happens.
They have proposed a mathematical framework in which“the alternative realities of the many worlds interpretation are the additional causal patches that make up the multiverse.” Reaction is, of course, varied.
We also learned recently,
Physicists seeking to understand the deepest levels of reality now work within a framework largely of Susskind’s making. But a funny thing has happened along the way. Susskind now wonders whether physicists can understand reality.
Thought: If they were wrong, how could they know?
Hat tip Dave Coppedge