One of the fundamental ideas that the confluence of Quantum Theory and Modern Cosmology has posed is that there is not one, but many many Universes. String Theory is based fundamentally on the idea that matter/energy exists in not just one Universe but in multiple ones simultaneously – it uses that property to explain the observed matter/energy spectrum of elementary particles.
Of course once you stop thinking about a Universe and instead of a Multiverse, you start wondering if there’s a limit, an upper bound to the number of Universes.
A pair of researchers at Stanford have worked out a methodology for approximating the total.
“Their answer goes like this. The Big Bang was essentially a quantum process which generated quantum fluctuations in the state of the early universe. The universe then underwent a period of rapid growth called inflation during which these perturbations were ‘frozen’, creating different initial classical conditions in different parts of the cosmos. Since each of these regions would have a different set of laws of low energy physics, they can be thought of as different universes.
What Linde and Vanchurin have done is estimate how many different universes could have appeared as a result of this effect. Their answer is that this number must be proportional to the effect that caused the perturbations in the first place, a process called slow roll inflation, and in particular to the number ‘e-foldings’ of slow roll inflation.
Of course, the actual number depends critically on how you define the difference between universes.”
And their answer? Actually the answer has two parts. First is the number of Universes that we can observe. (Which is limited because of the criteria they use for “discernible” and the limitations of the human brain and human lifetime.)
Which is bigger than a Googol but smaller than a Googolplex.
How many Universe in principle, discernible or not?
A “humongous” number. (10^10^10^7) Which is way big.
And now you know.