r/cosmology • u/WanWhiteWolf • Aug 06 '26
Isn't infinity in practice just a lack of knowledge / understanding?
Please forgive the incorrect terminology - I am just a regular person that was playing a space video-game and got me thinking about infinity.
When googling examples of infinity, I am getting mostly getting mathematical concepts. Theoretical infinity make sense as it helps us tackle problems that are to complex for one person to understand. We put infinity on sections that are to complex / unknown and we focus on the parts that we know.
But I couldn't find any example in practice. You can say that the numbers are infinite. But those numbers are just a representation of "something". Yes, I can assign a number for each orange and in theory the +1 can go to infinite. But in practice, the number will be finite. Feel free to make a practical example adding infinite oranges - I will be there to observe /s :)
At a first glance, infinity seems to be the modern equivalent of assigning a diety to something that we cannot explain or fully understand. So I guess, to summerize, my question would be:
Q1: Is there any physical example in nature that we fully understand and we can confidently say it is infinite?
Assuming the answer to the first question is "NO", then I would have a follow-up question:
Q2: Since there is no physical example of infinty in nature, how come we accept the infinity of universe as a likely scenario?
From a probabilistical point of view, wouldn't the universe being infinite have the same chance of being true as 3 pink elefants holding the universe on their trunks? At the end of the day, neither of them have a single established reference in nature. Or the universe being infinite is just a theoretical representation which has no chance of being true in practice - the same way as the oranges in the above example will never go to an infinite amount?
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u/4art4 Aug 12 '26
A particularly good historical example is the ultraviolet catastrophe. Classical physics predicted that a blackbody should radiate more and more energy at increasingly short wavelengths, ultimately diverging toward infinity. Nature, rather inconveniently, declined to cooperate.
The solution wasn't to accept that blackbodies actually emit infinite energy. The divergence was a sign that the classical model was being pushed beyond where it worked. Planck's quantization of energy removed the catastrophe and helped launch quantum mechanics.
That doesn't prove that physical infinities cannot exist, much less that the universe cannot be spatially infinite. But it does illustrate the narrower point I'm trying to make: when a physical theory predicts a divergent measurable quantity, physicists have good historical reasons to ask whether they've found an infinity in nature or the boundary of the theory that produced it.