If I understand correctly your analogy in the last couple of paragraphs and if I also understand light cones, expansion, and multiverses (these are of course big “if”s) then I think your soap bubble analogy is deeply misleading. Here is why:

Our observable universe is as you correctly say a function of our past light cone; that is, the amount of light that can reach us from objects that are not yet separating from us at a cumulative velocity greater than the speed of light. As expansion accelerates our past light cone will effectively contain fewer and fewer photons from distant objects as each in turn passes the light cone boundary because of expansion.

This is not at all the same as soap bubbles. In the soap bubble analogy each bubble (in our case, each light cone) is actually totally separate with a fixed boundary. But in the case of an expanding universe this is not at all the situation. To see why, imagine three observers. OA is on Earth, OB is about 2/3rds of the way to the edge of our light cone, OC is about 2/3rds of the way to the edge of OB’s light cone. Thus OA can see OB but not OC, while OB can see OA and OC. There is thus no boundary but rather an overlapping set of light cones permitting OB to see the two other observers. With a bubble analogy this would not be possible as each bubble is entirely separate from every other bubble.

You may be thinking of bubble nucleation in the case of eternal inflation, where indeed the newly nucleated universe is separate from the “parent” universe and separate from subsequent nucleations. But that’s got nothing to do with the inflation phenomenon that is the subject of your article here, because inflation occurs within the same universe. The term multiverse refers to universes that nucleate and are forever separate, not to that part of the universe we live in that simply happens to be beyond our light cone.

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