Monday, April 29, 2013

How Many Universes Are There In a Multiverse?

Andrei Linde is Professor of Physics at Stanford University and the author of several important theories, including the inflationary universe theory, the inflationary multiverse theory and the theory of eternal inflation. These theories taken together envisage a multiverse with an eternally growing fractal structure in which universes continuously arise, with different laws of low energy physics operating in each of them.

In a 2009 paper (1) Linde and Vanchurin attempted to calculate how many universes there are in a multiverse. The initial calculation came to 10^10^10^7, a very large number and one which they admit could be wrong by many orders of magnitude. But they quickly point out that a multiverse has no meaning without an observer, if correctly viewed by quantum physics. 

“One of the implications of this result is that one can talk about the evolution of the universe only with respect to an observer. In the limit when the mass of the observer vanishes, the rest of the universe freezes in time. In this sense, the number of distinct observable histories of the universe is bounded from above by the total number of histories that can be recorded by a given observer. And this number is finite.”

Their calculation takes into account the total amount of information that can possibly be absorbed by a human brain during its lifetime, which they deem to be about 10^16 bits, “which means that a typical human brain can have about 10^10^16 different configurations, which means that a human observer may distinguish no more than 10^10^16 different universes.” From this number they hope to calculate the probability of a universe in which the laws of physics would allow intelligent life to evolve, the so-called anthropic principle.

So how many parallel universes are there in a multiverse? As many as your brain can fathom.