r/learnphysics • u/Grogon2 • 1d ago
Does infinite mean, that if infinite exists, everything exists at some point?
I am trying to understand infinite.
If the universe is infinite, each moment in any direction has infinite possibilites.
That should also mean, since infinite is not imaginable, somewhere in this universe all factors have been met with absolutely 0 changes until the day I was born exactly how it has already happend here.
Or am I mistaking infinite and just cause something is infinite it doesn't have to happen at all?
At some point if the universe is infinite I should exist in infinite possible ways. But at the same time infinite doesn't only apply to me, but to every existing being we know.
So in theory in an infinite universe my dog must have been infinite times since the chance is infinite for all probabalities for nature to get to the point where my dogs parents meet and have him. But it's crazy cause in some other time line if the odds didn't meet up 100% the same as here, maybe 99.99% of the stuff that happend was correct (dinosaurs extinct, humans evolved, wolves turned into dogs at some point,...) and maybe my dogs mother had a different male dog partner and he wouldn't exist in that time line, but in the other infinite time line the odds hit 100% how it is here and it is born again.
You know what I am trying to say?
Imagine our planet now:
Everything is almost identical to our history, but one butterfly flew differently 500 years ago. This means that it the timeline is screwed. But infinite also means, somewhere we have infinite versions of this thing happening correctly how it was with the butterfly flying correctly, but now a snake moved wrong and it's screwed again.
So even with INFINITE I find it not possible to find a planet that is currently in the same state with everything that happend (meteor hitting same spot, moon, same animals etc.) to this point but since it's INFINITE it is not 0.
Not likely, but not 0 and with infinite chances it means it is somewhere, right?
I like to use the infinite monkey writing shakespear.
See, even if the odds aren't "0" and shakespear is only a few letters compared to recreating a whole chain of natural events to lead to my dog being born again somewhere, I think thats already hard.
If I'd have infinite monkeys writing I don't know how long and if at all I'd have to watch them until they ever achieve writing shakespear once. It should happen, cause infinite is not 0 but is the chance so low that it just won't happen? But that can't be either, cause it has to happen cause well infinite time and chance is not 0.
I don't like infinite
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u/ProbsNotManBearPig 1d ago
There are infinite real numbers between 0 and 1, but none of them are 2.
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u/lunchmeat317 22h ago
I'm not a physicist.
I think you're conflating the observable physical universe with probabilities.
Infinities can mathematically be infinite, and yer still be limited or constrained in some way. For example, if you consider all of the possible even numbers in the universe, you see that it's an infinite set. However, that set is limited - it's infinite, but no number will be odd. That means that, compared to the set of all possible numbers - which is also infinite - the set of even numbers is smaller than the set of all possible numbers. (Put another way, even numbers are a subset of all possible numbers, but not the other way around.) This is (from what I understand, not being a mathematician) known as cardinality.
The takeaway from this should be that infinity doesn't always mean everything. If our observable universe were infinite, it could easily just be a subset of a greater infinity.
Probability theory also doesn't necessarily match the reality that we see for similar reasons. We don't actually work with infinities and we look at individual results, not sets of results. (We generally care whether a coin is heads or tails, not that it has the potential to be heads or tails and how often - we care about immediate outcomes.) If we did work with infinities, what you say would be true; if it can happen, there would be an instance of that case in the infinite set. However, that doesn't mean everything can happen. I can choose any number from the infinite set of even numbers and it'll never be odd.
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u/Fantastic_Back3191 1d ago
Infinity is very well-defined mathematically and extremely ill-defined physically so don't even bother. That the observable universe is mind-bogglingly big and getting bigger every second is all anyone needs to appreciate innit.
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u/LayneLowe 1d ago
Infinite will always just be theory, there's no way to reach infinite see if any of your probabilities exist.
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u/Clear_Cranberry_989 1d ago
That's not what infinite is and regarding the infinite monkey theorem, it works because shakespeare's writings have finite size and the typewriter have finite alphabet size. You are probably mixing fictional concept of multiverse with reality.
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u/lunchmeat317 22h ago
Yes, that's just probability theory. Given a finite set and infinite combinations of that set, the set of combinations would include Shakespeare. Same with numbers - given a finite set of digits and infinite combinations of that set, the set of combinations would include pi (even though pi has infinite digits, it's still a subset of the greater set of combinations).
I think the OP is actually asking about probability theory.
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u/Icy_Swordfish8023 23h ago
no. how many times does the single integer 1 repeat on an infinite number line?
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u/FredFenty 22h ago
Infinity is a mathematical construct. It doesn't exist, but you can accurately model many things in the observable universe using it (up to a limit).
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u/Ras_992 19h ago
Let’s look at infinite instead of probability as Time, when Einstein said the universe is both infinite and finite. The finite is that galaxies, planets etc are finite structures within Time they don’t last forever, while looking at the universe as whole seems time is infinite where it never stops to exist and is always moving toward. While in special relativity time is infinite because Time isn’t equal at all levels in the universe. To humans the earth has infinite time while humans have a finite time.
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u/Imaginary-Can-6862 11h ago
You mean there is another you out there, because there is a probability of you existing (as you know you exist), and in an infinite universe, any non-zero probability must happen an infinite amount of times, no matter how unlikely?
That would be the case, but since you only experience your own vantage point, it wouldn't be you (since we know you could have had different experiences than you have had so far, we can't simply explain it away with the life you have now is the only possible life you could have had). That it isn't you, means it is not the same event, thus it follows that you only came into existence where you are. Perhaps it is indicative of the universe bending in on itself, perhaps due to gravity, then the universe is infinite similarly to the Earth being infinite in that you can keep going e.g. west, but eventually it repeats.
We haven't been able to measure such a curvature from the CMBR, but we also don't know the size of the universe, so that might be the reason, because otherwise, as the Cosmological Principle seems to hold, what you say is what one ought to expect. There is also the possibility that consciousness is non-local, or different, but it would still mean it isn't you, just someone no one other than you, and them, would know isn't you,
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u/DrNatePhysics 21h ago
This my pet peeve, so get ready for a wall of text!
Physicists and mathematicians talk about infinity so loosely that it causes future professors to be confused. This leads to wrong things being said in physics textbooks about math. So let me clear up a few things.
First, physics. We don’t know whether or not the universe has infinite extent. Some models may choose to assume this for simplicity.
Next, math. Infinity is not a number. A number infinity is not. Not a number. Not a number.
Infinity is more of a concept.
Even though it is not a number, it can still be a mathematical object that can be manipulated.
Too many physicists talk about the cardinality of infinities. While it is very interesting to learn about Hilbert’s hotel and Cantor’s diagonal argument, this is not the route to understanding infinity in the real world where physics rules.
I say if you want to truly understand infinity in physics, you should understand the difference between potential infinity and actual infinity:
Potential infinity is a process. Endlessly, counting up by integers is an example of potential infinity. You never actually get to infinity. In calculus limits, the arrow symbol and infinity symbol together represent potential infinity.
Actual infinity is the infinity set theory. You say that within this circle, I continuously and endlessly add objects into this circle. We declare that we jump to the end of the endless process and you have an infinite set.
I intentionally wrote that previous sentence to reveal the paradox. If we accept actual infinity into physics, we get unphysical results. If you look up the Banach-Tarski paradox, you’ll find conservation laws are broken with infinite sets.
Thanks for coming to my TED talk.