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My question is, If space is a vacuum, how can that happen without being encased inside something? So could we be inside something we can't see or detect?

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    $\begingroup$ There is no reason why a vacuum has to be encased in anything : to be a bit simplistic about it, you don't need something to put nothing in. If you edit your question to explain why you think the vacuum of space needs a container, it might help us help you. $\endgroup$ – StephenG Feb 14 '18 at 0:51
  • $\begingroup$ The normal state of things in the universe is a vacuum. However, in a very few places in space, there are astronomical bodies that are large enough to "trap" an atmosphere due to their sufficiently high surface gravity, and earth is one of those places. And, of course, if that wasn't true, I wouldn't be typing this reply and you wouldn't be reading it. $\endgroup$ – David White Feb 14 '18 at 1:21
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    $\begingroup$ I do not see how the situation would be different (from your perspective) if space wasn't a vacuum. $\endgroup$ – Stéphane Rollandin Feb 14 '18 at 10:27
  • $\begingroup$ -1 Not clear what you are asking. Why does a vaccum need to be enclosed? $\endgroup$ – sammy gerbil Feb 14 '18 at 21:01
  • $\begingroup$ I watched an experiment on tv with DR Brian Cox, where they dropped a bowling ball and feathers at the same time, then they did the same thing after sucking all the air out of the building. That's why I thought to create vacuum, (such as our universe), must be enclosed. Thanks. $\endgroup$ – Fleegle Feb 15 '18 at 1:46
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It rather depends on how you conceive the situation. Space is indeed inside something - that thing being the "universe", which contains everything.

And because the universe encompasses all things by definition, there is no need for the universe itself to be contained (because there exists no outer area into which anything inside the universe can move, or into which the universe can expand).

Also, the existence of space is, broadly speaking, the counterpart to the objects in it. That is, you cannot have objects without having space between them (because objects without space between them cannot sustain any division between each other, and a single object simply becomes equivalent to "the whole universe"), and you cannot have space without any objects in it (because that simply becomes "nothing"). Space itself sometimes takes on the form of an object in physics, to which properties are ascribed (i.e. it's not truly treated as "empty space", but as an object in itself which fills the area between all other non-space objects, as water fills the gaps between fish).

Objects and space are, to a certain extent, self-referential in their definitions (with each defined in terms of being what the other is not), and they form a set of basic axioms about how we see the world. At this level the question ceases to be a physical one, but a very general philosophical one, and is not something that a physicist or any natural scientist would (in that capacity) be in a position to address or contribute any expertise.

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  • $\begingroup$ -1 This answer is philosophical, and does not say anything useful about physics. $\endgroup$ – sammy gerbil Feb 14 '18 at 23:16
  • $\begingroup$ @sammygerbil, that's pretty much what I said about the situation, because the question is philosophical and more basic than physics! $\endgroup$ – Steve Feb 15 '18 at 0:05

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