Physics Asked by user158802 on March 10, 2021
First of all my apologies in case my understanding turns out to be wrong and idiotic. Being a layman in physics and cosmology, i have just started reading Brian Greene’s book "The Hidden Reality". Now i am confused because of some passages from the book:
"Think of the universe as a gigantic block of Swiss cheese, with the cheesy parts being regions where the inflaton field’s value is high and the holes being regions where it’s low.
Taken together, the two processes yield an everexpanding block of cosmic cheese riddled with an ever-growing number of holes. In the more standard language of cosmology, each hole is called a bubble universe."
Is the "block of cheese" the Multiverse? Or is it our Universe, which wouldn’t make a lot of sense to me. If it is the multiverse, does it mean that the inflation field permeates throughout the multiverse, and is not limited to our universe?
Also, the "bubble" universes expanding "like in the cheese" don’t really make sense to me if some of the universes are flat, in this case infinite? How can an infinite universe even be located inside something? Wouldn’t it occupy all the space, instead of a "bubble"?
Edit: Also, are the laws of physics limited to our Universe, or the entire Multiverse?
The general problem here is that, while it is a nice analogy for picturing a bubble of our universe within the multiverse, it is far from perfect. To try and address your questions directly; it is the block of cheese that is the multiverse and our universe is a 'hole' inside this.
Your next question and the question in the edit are linked and relate to what I see as one of the nicest points of the multiverse theory. The laws of physics within each universe do not have to be the same. This can be used to explain why we happen to be in the universe with the right conditions to allow for life. There are very many universes with different physics and the one that allows for life is the one we are in. However, I think what the quoted text is getting at is that there is an inflaton field throughout the multiverse but with different field values in different universes.
Your final question is probably the most difficult to answer and hints at some of the more complex points about multiverse theories. I'd like to refer you to https://www.space.com/31465-is-our-universe-just-one-of-many-in-a-multiverse.html and the wikipedia on the multiverse, https://en.wikipedia.org/wiki/Multiverse which are both useful here. Essentially in this analogy we are only considering the observable universe which is not infinite and does form a nice bubble in the multiverse. If you want to try and picture universes of infinite extent in a multiverse it is probably more useful to think of sheets of paper lying on top of each other, so that they are separated by a distance in one (or more) extra dimensions.
Answered by Tom Clarke on March 10, 2021
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