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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?

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  • $\begingroup$ You might find what you're looking for in answers to this question : The meaning of multiverse. And please ignore the incredibly rude answer you got from another user - Physics SE does not allow that sort of behavior and I've flagged it for moderator attention. $\endgroup$ – StephenG Jun 11 '17 at 16:09
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    $\begingroup$ You should keep in mind, while reading the book, that these multiverse ideas remain quite speculative and may be entirely wrong. Certainly there is no direct evidence for them, and the indirect evidence (CMB anisotropies) can be explained in other ways, for example by asserting that they originate in the Planck era. $\endgroup$ – Andrew Steane Jun 5 '19 at 13:28
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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.

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    $\begingroup$ I think your phrase "This can be used to explain" is here unscientific because unfalsifiable. If a theory suggests that there are many different things that exist, and all the things we detect are exceptional rather than typical, then the word "explain" is being used in a way different to the way it is ordinarily used in science. $\endgroup$ – Andrew Steane Jun 5 '19 at 15:10
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Whenever anybody broaches the subject of multiverse, the phrase "Deus ex machina" keeps jumping out at me.

The wiki definition of "Deus ex machina": a Latin calque meaning 'god from the machine'. The term was coined from the conventions of ancient Greek theater, where a machine was used to bring actors onto stage who were playing gods. It is a plot device whereby a seemingly unsolvable problem in a story is suddenly and abruptly resolved by an unexpected and seemingly unlikely occurrence, typically so much as to seem contrived.

Sounds familiar? Go figure.

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