Expert: Courtney Seligman - 4/15/2011

Question
QUESTION: I just wanted to know what is the biggest things right away?  I thought that would a universe.

ANSWER: It depends upon what you mean by "thing". The Universe isn't an actual object, in the normal sense of the word -- just the space occupied by everything, everywhere. So if you were on a quiz show, they might count that answer as right, or they might not.

If the question allows you to include large groups of things, like galaxies, which although they contain a lot of empty space are gravitationally held together by the mutual interaction of their individual stars, then the largest thing would probably be a cluster of galaxies, or a relatively dense "supercluster". If you leave out the requirement that gravity can hold the structure together, and just require that the structure be significantly different from its surroundings, superclusters would certainly qualify; but if gravity has to be able to hold the structure together, not all superclusters would qualify, because their gravitational force might not be able to overcome the local expansion of the Universe. In that case, a cluster of galaxies would be the largest grouping of things.

And of course, the person posing the question might not even allow "galaxies" as an answer, because even though they are essentially permanent structures, they are mostly empty space. They might mean the largest object which is a single object, in which case "red giants" should be the answer.

So unless I've let the morning fog cloud my memory, I'd say that the largest "individual" objects are red giant stars, but that galaxies and clusters of galaxies are the largest generally stable collections of objects, superclusters are the largest collections of objects more or less distinguishable from their surroundings, and the Universe is the largest expanse of space and its contents (being everything there is, was, or will be, here and everywhere else). But whether any of these answers would satisfy the person asking the question would depend upon exactly what they mean by "things", and whether they really want an answer, or to just frustrate your effort to provide one.



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QUESTION: What is everything that exists? I am leaning toward multi-verse that is the largest.

ANSWER: Ah. I see your point now. In that case, most cosmologists would probably agree with you. The only problem with that answer is that although we can't observe all of our Universe, we can at least tell that it exists, whereas even if the Universe is part of an infinity of Universes (as is generally thought), there is no way to tell whether that is actually correct, since none of those Universes would be connected with any of the others. So if we allow ourselves to venture into "meta-physics", or the physics of unprovable probabilities, then the multiverse would be the answer. But if you are required to restrict yourself to absolutely provable existence, then the Universe would be it.

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QUESTION: Is there anything bigger than a multi-verse?
What is all that exists in the multi-verse? Can you lists it?

Answer
As I explained above, it isn't possible to tell if the so-called multiverse even exists. So whether there is something even bigger than that would be pure speculation. As for listing what might be in the multiverse, that depends upon who you talk to. Some cosmologists suppose that there are (unknown) fixed laws underlying the nature of existence, which would require all universes in the multiverse to have similar laws of physics, and if so, presumably similar contents to our Universe. Other cosmologists suppose that the laws of nature could be different in every universe, in which case there would be no way to know what, if anything, might exist in any one of them, let alone all of them. In other words, no one knows or can know if the multiverse exists, no one knows or can know if any larger structure exists, and no one knows or can know what the contents of any universe other than ours might be. So although your question might be interesting, it has no answer.