Let's say that scientists somehow discover that the universe is infinite. In particular, they say that after the big bang, the universe expanded everywhere. In that case, if the universe is infinite and it takes up all space, does that mean that the multiverse isn't real and that our infinite universe is all there is? Or, could the multiverse still be true?

Could there be an infinite number of universes, all of which are infinite but are separated from each other?

  • $\begingroup$ This doesn't seem like a world building question. Can you explain how an answer might build your world or what you are looking to accomplish? $\endgroup$ – Trevor Mar 6 '19 at 14:29
  • $\begingroup$ Infinity is more of a concept than a hard number. After a quick google, something can have an infinite amount of things inside of it, but still be contained in a single object. An example that was used was the space in between the numbers 0 and 1. There are an infinite amount of points between 0 and 1, but the ends are clearly defined as 0 and 1. So there can be an infinite amount of universes with infinite space in them, it seems. I don't think my explanation is good enough to warrant an actual answer. $\endgroup$ – Jorgomli Mar 6 '19 at 14:31
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    $\begingroup$ I'd also add - isn't the point of a multiverse that the universes aren't literally sharing the same space? The question makes it seem like each universe is just really far away from each other but still laid out in the same space (somehow), whereas I always thought of a multiverse with each universe being a completely separate entity in a completely separate "box", if it were. So a universe can indeed be infinite and take up all space. That doesn't mean that another universe doesn't exist, since it has a completely different space it occupies $\endgroup$ – VLAZ Mar 6 '19 at 15:15
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    $\begingroup$ It is in fact totally possible for one continuous infinite region to contain multiple - even infinitely many - subsets which are themselves infinite. This has to do with the concept of cardinality. $\endgroup$ – Cadence Mar 6 '19 at 15:26
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    $\begingroup$ "The universe is infinite and it takes up all space": the universe by definition takes up all space. The universe is all there is, that why it is called the universe. To speak about a multiverse requires a special definition of existence and a special (and usually poorly defined) ontology. $\endgroup$ – AlexP Mar 6 '19 at 16:38


  1. Just because something is infinite doesn't mean that there's not room for other things. For example a line can be infinite, but there is room for a line next to it which is also infinite.
  2. The concept of a Multiverse was actually developed under the assumption that each universe in a multiverse would be infinite.
  3. All of the current hard evidence does actually point to our universe being infinite (in size). There is little evidence to support a multiverse theory, but no evidence against it either, and there are a lot of different forms that a multiverse could look like. So we just don't know if there is a multiverse, and if there is one we still don't know what a multiverse actually is. It really could be anything at this point.
  • $\begingroup$ Some further reading on the idea of the multiverse/universe and how they are connected for anyone interested. space.com/32728-parallel-universes.html $\endgroup$ – Tyler S. Loeper Mar 6 '19 at 16:37
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    $\begingroup$ And to blow the mind yet further: cosmologically speaking if you use the right set of assumptions then not only is our universe infinite it must, logically, also contain an infinite number of versions of itself at an infinite number of points in time. The ‘alternate universe’ is actually just ‘over there’, if you can go an infinite distance fast enough. $\endgroup$ – Joe Bloggs Mar 6 '19 at 18:22
  • $\begingroup$ Chiliocosm, dichilicosm, or trichilicosm, anyone? $\endgroup$ – nijineko Mar 6 '19 at 18:32

So lets say you have are the owner of The Hotel Infinity with infinite rooms and in a single hour you defy physics and book an infinite amount of guests in the infinite amount of rooms. During the next hour, another person arrives and asks if there is room at the inn... of course the answer is yes. Because the size of the hotel in rooms is infinite, the subset of booked rooms is infinite... as is the size of available rooms booked rooms. There's always room at the Hotel Infinity.

Now, we can really have some fun worthy of the TARDIS: Let's say we have the pleasure cruise ship the S.S. Infinity, with infinite space for infinite guests and luggage. As your booking the infinite guests, you get a call from the Captain of the S.S. Infinity's sister ship, the S.S. Universe I which is built in the same class as the S.S. Infinity and to the same dimensions. He wants to book a stay on S.S. Infinity, and he's checking the entirety of S.S. Universe I (Including the passengers and their own cargo) as his own personal cargo. We can allow this because the S.S. Infinity has enough cabins for one more to be berthed and enough room in the hold to house an infinite amount of space, including a second ship of the same exact class.

Or better yet, a Time Lord can park his TARDIS inside another TARDIS, which itself is parked inside another TARDIS and so on and so forth.

If universe is infinite, it doesn't mean that a multiverse is impossible. It just means that the multiverse has infinite space for infinite subsets of infinite space. For example, the set of all real numbers is an infinite set... which includes the infinite set of all real numbers between 1 and 2. It doesn't matter to us how big the gap between those real numbers are (1.2-1.3, 1.245-1.247 1.2899999-1.9) there are are still an infinite set of real numbers between those gaps. Infinity in this sense doesn't care about value of a single real number, but the total amount of those real numbers within that gap.


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