High School Is infinity truly infinite if it has something else in it?

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SUMMARY

The discussion centers on the philosophical and mathematical implications of infinity, particularly in relation to subsets. It asserts that an infinite volume, such as water, can still be considered infinite even if it contains finite objects like rocks. The conversation references Hilbert's hotel to illustrate that removing an infinite subset (even numbers) from a larger infinite set (natural numbers) still results in an infinite set (odd numbers). The participants emphasize that infinity is a concept that transcends physical limitations, suggesting that even with boundaries or finite elements, infinity remains intact.

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  • Understanding of mathematical concepts of infinity
  • Familiarity with Hilbert's hotel paradox
  • Basic knowledge of set theory and subsets
  • Conceptual grasp of cosmology and infinite volumes
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  • Research the implications of Hilbert's hotel in set theory
  • Explore the concept of infinite sets in mathematics
  • Study the philosophical interpretations of infinity
  • Investigate the role of infinity in cosmological models
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Mathematicians, philosophers, cosmologists, and anyone interested in the foundational concepts of infinity and its implications in both mathematics and the physical universe.

ddjj77
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Is infinity truly infinite if it has something else in it?
Put differently, say there's an infinite volume of water that has some rocks in it, is the volume of water truly infinite? Though there's a place where there's no water?
 
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Yes, a subset of an infinite set can also be infinite. For example, there is an infinite number of odd numbers even though you have to remove another infinite set (the even numbers) from the natural numbers to get the odd numbers. This leads to things such as Hilbert's hotel.
 
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What does "truly infinite" mean?

Certainly you can have infinite regions with boundaries - an infinite volume minus a finite volume is still infinite. I presume, since you're posting this in cosmology, that you're thinking of space or spacetime. This doesn't have any holes in it anyway, so far as we are aware.
 
Then when I use the term "infinite volume of water", this shouldn't mean there's water everywhere. Got it.
 
ddjj77 said:
Is infinity truly infinite if it has something else in it?
Put differently, say there's an infinite volume of water that has some rocks in it, is the volume of water truly infinite? Though there's a place where there's no water?
Infinity is a mathematical concept. If you can put rocks in it, you speak about something which exists within the universe, and then - in case it should be infinite - all rocks are already in it.
 
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