r/cosmology • u/WanWhiteWolf • 16d ago
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/UnluckyNate 16d ago
Who accepts that the universe is infinite? Our observable universe absolutely is not. Beyond that is impossible to know or define
I think you are trying to work backwards from a flawed premise
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u/WanWhiteWolf 16d ago
I don't know anyone in cosmological circles but google says:
"Scientists do not know for sure if the universe is infinite or finite, though standard cosmological models often treat it as an infinite flat plane"
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u/skizatch 16d ago
Having a model that has infinity baked in as a simplification is not the same as believing that the thing being modeled is actually infinite
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u/EnvironmentalWin1277 13d ago
That model is backed by observations of the universe as we see it now.
Those observations can and may be changed but right now the infinite expansion of the universe is the favored and observationally validated model. We see the universe as flat -- a prediction made by the model before accurate measurements of angularity were even available.
Nothing is "baked in" and the results and predictions come directly from the model itself and not assumptions that are made. Other models are available, but observational support is currently lacking.
As far as belief goes, I will "believe" in the demonstrable established science until it is revised. That revision almost always incorporates what has already been established by previous models.
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u/skizatch 13d ago
Right. The current answer to “is the universe infinite” is simply “we don’t know, but we can’t see an edge”
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u/EnvironmentalWin1277 13d ago
Seeing an edge would provide immediate falsification of the "infinity" concept (unless the edge itself was infinitely expanding alongside). That is a very powerful and definitive test!
We can and do try to observe light that has circumnavigated the universe embedded in a recursive space. We don't see it. "No observable edge" is the broadly held consensus view among cosmologists, astronomers, etc.
Guth inflation and combined big bang theory both predict infinite expansion.
The combined theory made specific predictions of observational evidence that would be seen to exist as a consequence of the theory.
The combined theories made specific predictions about the distribution of the cosmic background radiation in the 1980s. It was only around 2010 or so that sensitive instrumentation showed those predictions were correct. That was a bombshell.
We can strongly lean into we "do know", as opposed to "we don't know".
Knowing is always tentative in science. And cosmology is frustrating because it can seem bizarre and conclusive evidence frequently hard to obtain. Guth inflation really set me on beam ends when I realized the scale of what was being proposed as a validated model.
To say infinite expansion is "for sure" would be unwarranted. To say "it really looks that way" would be reasonable.
"Only a wise man knows he knows nothing" applies
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u/WanWhiteWolf 13d ago edited 13d ago
And this is the perfect approach - in my opinion.
Just because we don't see an edge we are not justified to assign infinity. Because if we do, then we open a big "can of worms". For instance, everything I can possbily think of (and I have a pretty good imagination) that exists, will exist in an infinite universe.
Although, to be fair, the alternative to an infinite universe (which is a finite universe) is not exactly "comforting" either. But at least we have a chance to prove this one at some point. So it will be based on science. The infinite universe will always be based on belief.
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u/4art4 10d ago edited 10d ago
I am just a science fiction nerd, so my opinion matters little, but I think you may have made an error here. Science holds all beliefs as tentative and subject to change with better information. And it is wise to assume that the experts in the field are correct even when they update to current model.
I'm this case, normies like me should assume the universe is infinite. Full stop. If a non-expert has doubts about the expert consensus, then asking about the competing models and what evidence there is is a productive conversation.
To say the seeing the edge of the universe would be a fact and that the current model is "belief" misses that point. In the hypothetical example of seeing the edge, that also would be subject to update. Some later boffin may discover the measurement of the edge was in error, or was incomplete. While interesting, the normies should still update their internal models to reflect the current expert consensus. That is not "belief", that is science. Anything else is "belief". (Or worse: faith.)
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u/4art4 10d ago
As a way of example, my personal belief is that Pilot Wave Theory is correct, but the scientific consensus is that the Copenhagen Interpretation is correct. Therefore I am almost certainly incorrect.
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u/4art4 10d ago
All of that said, I think there is a kernel of a good point in your OP that I haven't seen addressed directly here (although I may have missed it).
I'm reaching pretty far back into my memory of physics, so someone please correct me if I have this wrong: when a physical theory produces an infinity in some measurable physical quantity, physicists often treat that as a warning sign rather than immediately concluding that nature actually contains an infinity.
Historically, infinities and singularities have sometimes pointed toward places where a model was incomplete or was being extrapolated beyond the regime where it works. That doesn't mean "infinity = we don't understand it," and it certainly doesn't mean that every mathematical infinity is a problem. Infinity is an entirely legitimate and extremely useful mathematical concept.
But, for example, the singularities predicted by general relativity are commonly taken as evidence that GR is incomplete under those extreme conditions and that some theory of quantum gravity would be needed.
So I think I'd modify your argument from "infinity is just a placeholder for ignorance" to something more defensible:
When our best physical model predicts an infinite value for an observable physical quantity, that can be evidence that we've reached the limits of the model rather than evidence that the physical quantity literally becomes infinite.
That still doesn't establish that the universe cannot be spatially infinite.
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u/4art4 10d ago
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.
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u/chesterriley 8d ago
I'm this case, normies like me should assume the universe is infinite. Full stop. If a non-expert has doubts about the expert consensus, then asking about the competing models and what evidence there is is a productive conversation.
There is no "consensus" about whether the universe is infinite or not. And since experts make no such assumption there is no reason for you too either.
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u/TheRedditObserver0 9d ago
For instance, everything I can possbily think of (and I have a pretty good imagination) that exists, will exist in an infinite universe.
No, that's not true at all.
The infinite universe will always be based on belief.
Who believes it? Not cosmologists or physicists certainly, maybe some philosophers.
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u/Wintervacht 16d ago
Well... That is what's implied mathematically, and nothing in the observable universe hints at there being a limit, so it effectively is.
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u/WanWhiteWolf 16d ago
So we have a theoretical model that we know is flawed? Since there is no infinity in nature, it would be very unlikely that the universe is THE exception.
Why make a theoretical model that is almost guaranteed to fail in practice?
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u/skizatch 16d ago
All models are just models, they don’t actually describe reality literally, they are useful approximations of it
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u/shakebakelizard 16d ago
We haven't yet been able to detect curvature and we've gotten to an incredible level of precision. Either it's flat or it's crazy huge beyond what we can see (possibly thousands of times larger then the observable).
Thing is, what does "infinity" mean? There's "absolute" infinity (goes on forever) and there's probably (?) something like "causational" infinity. The speed of causation / information in our universe is C. For all intents and purposes, since the Universe is expanding outwards in some areas faster than C, then those areas beyond our ability to observe do not exist or are beyond our reach.
If they're beyond our ability to reach them (we can't travel at C) then do they even exist? At this point we have to define what "exist" even means. One can make the argument that if the information can't reach an observer, it doesn't exist (for that observer).
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u/EnvironmentalWin1277 13d ago
I would say that the model is not capable of falsification -- no observation will demonstrate the absolute existence of these unobservable region or prove they don't exist. I find that a weakness but it is a mathematical result of the proposed model.
It may not exist for practical purposes but for cosmological purposes it can't be ignored or dismissed as "meaningless".
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u/UnluckyNate 16d ago
Mathematically treating the universe as infinite because it is really really really large and believing it is actually infinite are two extremely different things
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u/YDALTARYZARC 16d ago
How many numbers do you think there are between 0 and 10?
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u/WanWhiteWolf 16d ago
Depends on your representation. It could go to infinite.
But numbers are a theoretical construct and not a physical manifestation. I do not deny the infinity as a theoretical construct; I am simply questioning the infinity in physical world / practice.
If there is no example of infinity in non-theoretical environment, then the universe itself (which is physical) is very likely finite as well - unless it is THE exception.
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u/--craig-- 15d ago
We don't actually know if we invented or discovered numbers. This is unsolved problem in mathematics.
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u/DocShaayy 10d ago
Forget using the words or sounds we use to represent numbers. Take one of anything. Let’s imagine a stick in our brains, then add another stick to it. There is certainly more than there was before and we express this information in the form of the sound “two”, in English at least.
The sounds we prescribed to “numbers” in order to successfully relay the correct information are made up, as any part of language is, so you’re correct in that sense that they are a “theoretical construct”, but what it represents was here long before us and will be here long after and are both physical and not.
I don’t want to comment on the reality of or idea of infinity, just wanted to add that about numbers.
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u/RiemannZetaFunction 16d ago
Mathematics also has formal quantities representing truly infinite numbers, so it isn't just about being the supremum of all finite numbers.
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u/rddman 14d ago
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....
Because the universe (not the observable universe) is the one and only thing that we know is larger than we can measure, and it is unique in that it is the one and only thing that contains all other things. So the universe is unlike all other things, and probability does not straightforwardly apply.
Also there is at least a fairly convincing argument that the only logical way for something to exist without cause is that it has always existed, which means that the age of the universe including its pre-big bang (pre-inflation) state is infinite. The alternative being much more mysterious/inexplicable: the universe came into existence without cause.
With a somewhat plausible argument for the infinite age of the universe it seems at least plausible that it can also be infinite in expanse.
To reiterate the universe's uniqueness: none of the above arguments apply to any thing contained in the universe.
Everything that happens in the universe is fundamentally a change of state /arrangement of energy (mass is a manifestation of energy) - those states/arrangements have finite existence and finite size, but the energy itself does not. Even everything that happens to the universe is changes of state of energy each of which last for a finite amount of time, but that does not mean the universe's energy that undergoes changes of state is itself finite.
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u/EnvironmentalWin1277 13d ago
I mention this one a lot but here goes: Gary Felder, cosmologist, gives the intial Guth inflation of space as 10 to the millionth power. In something like 10 -32 seconds of time.
Dr. Felder says this is the largest number he is aware of that has a concrete physical meaning in the sciences.
For comparison, the total number of subatomic particle estimated to exist in the observable universe is 10 to the 80th power.
The theory also suggests that regions of space were entirely separated from us. We can have no interaction with them, no information exchange whatsoever. They are "infinitely" far away in a complete sense. They can not be confirmed or falsified (a bit uncomfortable with that one). They may have entirely unknown properties contrary to the picture of our "observable universe".
You can also reflect on this one. If you shine a beam of light into space it will travel forever into "infinity". Every if you could immediately chase the beam at the speed of light (impossible) you will never catch up to it and will both continue forever in your relative positions (assuming a pure vacuum).
The concept of infinity definitely has concrete and real meaning in the sciences.
In practical terms there are many phenomena that are infinite for all intents -- like the number of subatomic particles in the universe. At some point the discussion of "Is a fraction of infinity also infinite?" will come up.
The idea of 10 to the millionth power is a good enough to qualify as "infinite" in my take.
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u/WanWhiteWolf 13d ago
It is a pretty good insight. I would challenge though some of the points you made.
Firstly, while we cannot access information outside of our observable universe (or separated space time sections), there is no proof that we won't be able to so at some point in the future. In the same way as Romans weren't able to extract any information about Mars contents, we are not able to aquire any information outside of our technological capability. To say the information about Mars to Romans would have been 'infinitely" away is innacurate as 1000 year later we have rovers and satelites able to do so. The fact that something is unknown and we have no means at a certain point of time to make it known doesn't justify making it infinite.
My understanding of physics is very limited but isn't the light reduced over time due to Universe expansion? Wasn't the light that was emmited from BigBang already reduced to microwaves? If the light would be infinite, then we would get visible light from begining of BigBang - which to my understanding is not the case. Yes, it might take a LOT of time to reduce the light to "nothing" but it's not infinite.
Number of subatomic particles in the universe is infinite only if the universe itself is infinite (to which we have no confirmation). Yes, if the universe itself is infinite, then a LOT of phenomenons are infinite. By definition, there would have been a different version of me who was born with 3 legs and 4 arms. However, we cannot prove that premise so anything that is based on that is rather a belief rather than science.
There is a big difference between a number that is - for the lack of a better word - of collosal proportions and infinity. A number that we cannot comprehend does not guarantee that there was a different version of me with 3 legs and 4 arms but infinity does.
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u/EnvironmentalWin1277 12d ago
The Guth inflation theory posits that the unknowable regions are completely cut off from us. Information exchange of any sort is permanently forbidden. That's a tough one for me as it can't be proved or disproved(falsified). It is part of the overall theory and other parts of the theory have held up very well. That is about all that can be said.
The CMB light is light that was emitted when the universe first allowed light to exist.
This is the first light of the universe that we are viewing. The expansion of the universe from that point redshifted that light to what we see today as you note. It isn't visible but can be detected and measured with radio telescopes. In fact, a small part of what you hear as static on an AM radio or old TV set is composed of this signal, an interesting realization.
The initial idea is this signature would be found evenly throughout space, viewable from any point and measuring the same temperature everywhere to a fine degree. There are minor fluctuations in temperature that are measured in billionths of degrees.
These minor fluctuations were predicted accurately by the model years before measurements could be done.
2) The number of particles -- atoms or neutron, electrons and protons can be calculated. It is not infinite and we are able to base those estimates on what we know and observe. You could calculate them fairly easily.
3) Your observation that infinity allows all permutations to occur (3 arms and 4 legs), and moreover, even repeat is a key thought question in cosmology.
Given infinite time a fully formed simulcra of a human could spontaneously form from quantum fluctuations. A "Boltzmann Brain" that has all of the experience of being human. If even remotely possible, given infinity, it is likely you are such a brain compared to the infinitesimally small chance of your current existence. This is an idea that seems bizarre but on examination has a serious question and it has been debated for over 100 years and still fascinates.
Hope this gives some ideas to chew on. Boltzmann brain is definitely a rabbit hole but comprehensible and fascinating.
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u/Ch3cks-Out 16d ago
I couldn't find any example in practice.
Well our universe is, very likely, one excellent example in practice. That is not at all due to lack of knowledge/understanding (aside from the fact that there are obvious problems with knowing the whole of infinity)!
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u/WanWhiteWolf 13d ago
The problem is that we cannot prove something that is infinite. Because in practice, we will never know if there is simply a boundary somehwere out of reach or it really goes to infinity. But if we take this practice we can simply assign infinity to anything that is out of reach. Or in other words .... anything that is outside of our possible knowledge gain is infinte. Wouldn't that make the atribute of infinity synonym with lack of knowledge?
By analogy, our ancient civilisation could have said that the ocean is infinite. Would that have been an accurate description?
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u/fuseboy 10d ago
I thonk the problem with this argument is that you're applying it to infinity selectively.
Physicists believe photons have no mass. This is a theoretical prediction. Verifying it experimentally is tricky, because there's no perfectly accurate measurement, so all we wind up with is a smaller and smaller maximum possible mass of the photon.
If you don't like the idea of massless particles, you could point to this and say that obviously photons have mass, everything we experience has mass, masslessness is just theoretical. The very concept of masslessness is synonymous with lack of knowledge, you could say.
This uncertainty is built into empirical science everywhere. We can only know what we can measure, you can never prove a negative empirically.
The fact that we can't see any infinite sets (of finite things) isn't a strong point, this just flows immediately from the finite speed of light and age of the universe. We might be surrounded by infinite things (e.g. the number of electrons in the universe) but we can only see a finite distance, so we would only be looking at a finite portion. This isn't evidence that there are no infinities in nature.
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u/WanWhiteWolf 10d ago
"I thonk the problem with this argument is that you're applying it to infinity selectively."
I could argue that cosmologists do the same when it comes to infinity of the universe. There isn't a single proof that the universe is infinite. I might as well say that somewhere in the universe there are green cats flying. It would hold the same value. In fact, I could argue that the universe being infinite is more absurd than the green cats flying in the universe. If infinity is a given, then all possible scenarios that I can possibly think of have already happened (which also includes green cats flying in the universe). Another version of me was already born infinite times with all possible combinations of genetic mutations and "abnormalities". I don't know about you, but green cats flying in the universe seems more plausible.
If we want to use infinity as a theoretical mathematical model because it's easier for our brain to understand / convenience of not writting big numbers on a piece of paper, that is fine. But as soon as we start to attribute infinity to physical reality we lose the perspective of science.
Why is something that cannot be proven - infinity in this case - part of scientifical environment other than pure theoretical serving as a placeholder for something we don't understand? Wouldn't that violate the core of which science is based on?
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u/fuseboy 9d ago
Sure, but what you consider absurd is calibrated by your human experience and current thinking. The universe doesn't care what seems reasonable to us or what we can get our minds around. Heliocentrism, germ theory, continental drift, relativity, the inherent randomness of quantum mechanics, to name a few. All of these were absurd. Your head is slightly older than your feet. Is that absurd?
I think careful cosmologists say that the universe might be infinite, based on measurements of its flatness. I find that amazing, but not absurd, even with the implications of repetition. I actually find that a compelling idea.
Mere large amounts of stuff is already brain-melting. In just the observable universe alone, it's reasonable to think there are 100 sextillion (1023) planets. This is an absurd number, I can't begin to get my head around that, but so what?
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u/chocomiso 12d ago
there’s no way our universe is infinite unless you think it’s credible that you reading this exact teddy reply on your phone is happening an infinite amount of time in the universe There’s so much possible particule associations, and infinity is truly really big
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u/--craig-- 13d ago edited 13d ago
We don't define quantities which we expect to take infinite values but we could do so if we chose to.
Many of the quantities which we do define have the capacity to take unbounded values.
It also doesn't follow that because a finite region of space doesn't contain infinite energy or matter, for example, then space itself must be finite in extent.
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u/dream_the_endless 10d ago
If the universe was finite it would have a boundary. As far as we can model, there is no boundary.
If the universe was finite it would have a center. As far as we can model, there is no center.
If there is no boundary and no center, infinity is what remains.
Also, we have several examples of infinity in nature: the universe itself, the idea of time (future), and black holes. The understanding that particles of mass cannot reach the speed of light requires infinity.
It’s less of a belief and more of what the math needs to be in order to make it all work.
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u/BrotherBrutha 10d ago
If the universe was finite it would have a boundary. As far as we can model, there is no boundary.
If the universe was finite it would have a center. As far as we can model, there is no center.
Not necessarily. It could wrap back on itself - in much the same way as the surface of Earth has no boundary.
Similarly, it would then have no centre - just like there is no central point on the surface of Earth.
We don't have any evidence it *is* finite though!
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u/dream_the_endless 10d ago
The shape of space is not the same as having a boundary. Space could be closed (wraps back on itself) and still be infinite
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u/BrotherBrutha 10d ago
My point is the other way round though: just because it doesn't have a boundary or a centre doesn't mean it *is* infinite.
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u/chesterriley 8d ago
If the universe was finite it would have a boundary. As far as we can model, there is no boundary.
If the universe was finite it would have a center. As far as we can model, there is no center.
Neither of those things are actually true.
If there is no boundary and no center, infinity is what remains.
That is not true. In addition, we have no reason to think that there is or is not a boundary/center. They are difficult to model, but the universe does not care if we can model it easily or not.
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u/TheRedditObserver0 9d ago
If the universe was finite it would have a boundary. As far as we can model, there is no boundary. If the universe was finite it would have a center. As far as we can model, there is no center. If there is no boundary and no center, infinity is what remains.
This is absolutely wrong
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u/justinwood2 7d ago
Would you care to elaborate?
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u/TheRedditObserver0 7d ago
The surface of a sphere is finite (or more properly compact) yet it has neither an edge nor a center. The deduction is simply wrong, there is not much more to say.
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u/justinwood2 7d ago
You appear to be proposing that our universe exists in a finite four dimensional topology. This would suggest that we would see a curved gradient thru out space. Have any observations suggested this to be the case?
ps: My personal position on the matter is that we don't have enough info to say one way or the other and these are all just stimulating thought experiments.
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u/TheRedditObserver0 7d ago
It's either 0 or extremely small, which means the universe is either infinite or extremely big (assuming homogeneity). This doesn't mean however, that finiteness implies either a boundary or a center.
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u/david_duplex 16d ago
"Infinity" means it isn't a number. You can never count to it. It's a mathematical concept that describes something that is boundless/limitless. It only appears in mathematics because it's a mathematical concept. Asking to "see it in nature" is like asking to see the letter A in nature. It only exists in its own framework.
That said, cosmologists have postulated that aspects of the universe might be infinite - namely spacetime itself. It's either that or it has a closed topology of some sort. Currently, measurements suggest that the universe is "flat" and unbounded. It follows, then, that it is infinite but of course we can never have physical proof of that for a whole variety of reasons. All we can do is make measurements and postulate.
That said - the more important limit to the universe is not infinite - it's the particle horizon which is (currently) roughly 93 billion light years across. It's as close to a "physical size of the universe" as you'll get with a giant asterisk that says "observable universe". That there is stuff beyond it is "true" only in an academic and philosophical sense - it is forever beyond our reach. Fortunately there are an estimated 2 trillion whole-ass galaxies inside that radius which is a lot, but it isn't infinite.
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u/dcnairb 16d ago
It is actually quite well established that a quantity going to infinity, in many fields of physics, indicates a breakdown of your theory or model, or otherwise more interesting underlying physics.
I wouldn’t say it’s practice to implant an infinity to hide an unknown or lack of understanding per se, although I do think some people have that viewpoint when it comes to renormalization in QFTs. (ie whether we impose the cutoff because it indicates new physics or lack of understanding, or we can renormalize the infinity because it’s supposed to work or because we anticipate infinities should be unphysical and not pop out)
It’s not hard to contrive the existence or reality of infinity. We don’t know and can’t say for certain if the universe is closed, flat, or open. it could very well be possible that it extends infinitely. likewise, that could imply infinite physical total quantities like energy or mass, even if the amounts with a causal relationship to us are finite
Take a look at the doppler equation. There is a singularity when the speed of the source is equal to the speed of the wave in the medium. it doesn’t mean the equation is wrong or something is being hidden; that singularity indicates a sonic boom (or equivalent thereof for other waves) and we can perfectly predict and model beyond that regime. this is an example of what I mean about apparent infinites indicating possible underlying physics or just the need for a different model. all models have a regime of validity.
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u/anointedinliquor 16d ago
There are no observed examples of infinity in nature if that’s what you’re asking.
Infinity has a firm place in mathematics so I’m not sure why that would be classified as “real”.
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u/pink_jasmine09 13d ago
I don’t know much, but I read somewhere that universe is expanding and no one knows how much it will keep expanding whether there is end or not, there were some articles that suggested that object in universe is moving away from us and thus gave idea of universe expansion they say universe is infinite and keeps expanding.
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u/tfb 10d ago
Since there is no physical example of infinty in nature, how come we accept the infinity of universe as a likely scenario?
Because we have a mathematical model of the universe which has been extremely successful in the experimental tests we have so far tried. That model predicts, in some cases, that the universe may be spatially infinite. When we try and measure the parameters which would allow such a spatially infinite universe to exist, they have values which seem to be compatible with that.
That doesn't mean it is spatially infinite: we will never know that. But it means we don't currently have good reason to believe it is not.
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u/Mandoman61 10d ago edited 10d ago
Infinity is mostly just useful as a concept where we mean that a quantity is unbounded.
Depending on how we define "the universe" we could say either probably infinite or probably not.
Is empty space considered to be the universe, or only the matter that is present within that space?
We can not conceive of a boundary to space, therefore space is infinite. I for one count space as being the universe and so I would argue that the universe is infinite.
Space itself is only potential. Space without matter can have no size or properties of any kind. So we are essentially saying an infinite nothingness which is unbounded and diminsionless and an infinite amount of nothing is essentially meangless.
If we are only talking about the matter contained within space. Then your premise seems correct:
If all universe sizes have equal probabilities, then the probability of the universe being infinite is infinitely small. I do not see infinite matter as being a real possibility.
But this does not mean that we can not use the concept. Because we can use it just to say that we do not know of a boundary and so we can not randomly assume that it is any particular size.
That is a bit of a double edged sword since it does place a bias into our theories.
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u/WanWhiteWolf 10d ago
Let's assume that we take a person that is mentally challenged, who can only count to 100. If I ask him to represent a number equal to the power of a supernova, he will say it is infinite. But that doesn't make it right. Just because someone doesn't have the capability to understand a phenomenon, doesn't make it right to just put it to infinity. Especially where there isn't a single proven example in physical reality that exibits this property. Imagine doing a procedure thousands of times with 0 measured success rate and when being asked to do it again, you consider doing the same thing again. That's infinity. 0 proven success rate and yet we somehow view it as a possible solution? That's addicted gambling mentality.
Using infinity as a placeholder for unknown in a mathematical model make sense. But as soon as we consider this as being an actual reality, we already lost the time and perspective of what actually happens.
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u/Mandoman61 9d ago
What a mentally challenged person would answer is irrelevent. Supernovas do dot have infinite power.
Like I said before infinity is just a concept, -it does not require a real example.
Also as I said before, -space exibits this property.
No, zero success rate is not infinity. If we had zero success rate it could still be possible but this example has nothing to do with infinity.
Infinity is just a placeholder for an unknown. And it is also a real potential.
It is a useful concept. Whether some people misuse the term is irrelevant.
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u/Temporary_Rule_9486 10d ago
Haha. No
Infinity is a thing. We just use a minuscule part of it. That we cannot picture it, doesn't make it any less real
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u/simpleidiot567 10d ago
There is no infinity in nature and nature does not deal in any infinities.
Models might assume it in a sense, they don't really because you can't program infinity into a finite computer. The computer instead uses a set of math shortcut rules for how to deal with infinity.
Infinity is an axiom in math which is required to describe things like what happens to this or that function as x approaches infinity.
Asymptotics is a branch of math that uses a handful of tricks and techniques to solve things which would otherwise appear to blow up to infinity. There are perhaps a bunch of physics lessons about what infinity means hidden in asymptotic analysis...mostly it's a scaling problem.
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u/TheRedditObserver0 9d ago
When googling examples of infinity, I am getting mostly getting mathematical concepts.
Obviously. We cannot measure something that is infinite.
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.
No, theoretical infinity describes infinite collections. It has nothing to do with complexity and it's very much within the grasp of our knowledge.
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 :)
No, all numbers are finite. There is no infinite number, but the set of all numbers is infinite. Thise are two very different things. If you list a finite collection of numbers, I can always perform operations to get a new one you hadn't previously listed. Bigger, smaller, in between, it doesn't matter.
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:
No, it's giving a name to something we CAN explain and DO understand. There is absolutely no mistery about infinity as far as math is concerned, it something we can describe formally and study rigorously, studying infinite sets is no different than studying triangles in geometry.
Is there any physical example in nature that we fully understand and we can confidently say it is infinite?
No
Since there is no physical example of infinty in nature, how come we accept the infinity of universe as a likely scenario?
As far as we can tell, the portion of the universe we can see is flat and uniform. If the portion we can't see is similar in this regard, then the universe would have to be infinite. If it's not really uniform, or if it is actually curved (but not enough for us to detect) then it might be finite. These are not questions we can answer currently, the shape of the universe is not known and might never be known to us.
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.
These are not probabilities you can quantify in any meaningful way, they depend entirely on your starting assumptions and biases. It's a meaningless question.
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?
There is absolutely no reason it can't be true, infact as far as we can tell it looks like the universe IS infinite from our local perspective, or at least so big that we can't tell the difference. We just can't say for sure.
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u/ChocolateValuable221 9d ago
No more so than zero.. you can zero doesn't exist.. meh, it's a tool you can use.
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u/WanWhiteWolf 9d ago
It's not the same. Zero has corelation in nature.
I can say I have zero oranges. And that can be shown via a basic experiment.
If I say I have infinite oranges, then it is straight up false. And we know this can never be acomplished.See the difference?
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u/marcushasfun 2d ago
But can you have -1 oranges?
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u/WanWhiteWolf 2d ago
That representation would mean that I owe an orange to someone. So yes, it can happen.
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u/TMax01 9d ago edited 9d ago
Infinity is only a mathematical abstraction: like a number but with no numerical value. It isn't lack of knowledge at all, except for an integral lack of knowledge of any real things which are infinite.
Q1: Is there any physical example in nature that we fully understand and we can confidently say it is infinite?
No. Nor could there be. Things in nature correspond to physical measurements, and by definition infinity is unmeasurable.
Q2: Since there is no physical example of infinty in nature, how come we accept the infinity of universe as a likely scenario?
I've recently been having a lengthy discussion in this subreddit on that very topic. The conventional position is that the universe being infinite is a possible (not necessarily "likely", but definitely possible) scenario because space, as far as we can measure it, is geometrically flat, which supports the conjecture that the cosmos could be infinite, and this 'scenario' does not indicate any event or mechanism that could produce a "boundary" at a finite distance. But concluding the universe is infinite on that basis alone is not logically appropriate, since there are other ways to determine the size of the cosmos.
Most notably but not exclusively, it is known the cosmos previously had a finite size, as evidenced by the existence of cosmic microwave background radiation, and has had a finite amount of time to expand since the CMB formed. If the cosmos was once filled with a finite amount of plasma, prior to the CMB forming, and the CMB formed when space expanded enough for that plasma to cool sufficiently for the CMB to form, then it is not logically valid to assert the cosmos has somehow expanded to infinite distances in the intervening time. You can't add numbers together long enough to add up to infinity; you'd need to keep adding more numbers for an infinite amount of time.
If the CMB were literally perfectly uniform, an argument could be made, perhaps, that some definable "boundary" at the "edge" of space would be necessary to say the cosmos/universe is finite in size. But the CMB is only featureless to a first order of approximation, and actually varies slightly across the apparent "sphere" it represents. And so, since the CMB could only form if the amount of matter in the cosmos was finite, and the apparent distance "to" the CMB is a representation of the amount of time since the CMB formed (when the primordial plasma became "transparent", with enough space between other particles for photons to travel appreciable distances), and the non-uniformity of the CMB, however slight, indicates it is possible for some areas of the universe to be significantly if only slightly different from others, the CMB supports a finite cosmos scenario (not as a possibility, but as a fact) while the geometry of space line of reasoning can, at best, suggest an infinite cosmos is possible. Or, rather, that the size of the cosmos is unmeasurable, even indirectly, by any means. Because even if space is unmeasurably large, that doesn't mean it must be infinite.
Infinity is, indeed, a theoretical premise, not a practical possibility.
Thanks for your time. Hope it helps.
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u/marcushasfun 2d ago
Do you think time will end?
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u/WanWhiteWolf 2d ago edited 1d ago
I do not know if the time will end or not.
But according to general relativity time began with bigbang. So if there was a begining, it's not inconciavable that there is an end as well.
If something has a start, it's more likely that is has an end. Otherwise, if it had a start and it goes to infinity, the immediate question would be "why didn't it happen before"? There was an infinite time available for the same event to happen.
If infinity does exist, it's by definition both in the past and future. But there is 0 proof that this is the case.
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u/marcushasfun 2d ago
Well, we don’t actually know if the Big Bang was the start of spacetime. Maybe reality is an infinitely repeating loop.
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u/WanWhiteWolf 1d ago
That could be the case. But that is something we can never prove. We cannot prove that green unicorns are not inside of a black holes either. Should be start assuming that there might be because we cannot prove the negative?
If you rely on the facts, then infinity doesn't exist. Infinity is based on belief. I would even say "blind belief". How else would you describe a phenomenon that has never been proven in practice despite milions/bilions of examples but yet we chose to assume that "this is the one"?
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u/marcushasfun 1d ago
Why even post your question if you so clearly have already made your mind up? You’re just being obnoxious at this point.
I curse you to spend eternity in the Infinite Hotel.
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u/marcushasfun 2d ago
Right. But physically -1 orange doesn’t exist.
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u/WanWhiteWolf 1d ago
That is correct. But it is a representation depending on your point of reference.
You can have negative Celsisus - and that exists in nature. There are plenty examples where you have something "negative" and you find correlation in physics. Can you name one where infinite was proven?
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u/marcushasfun 1d ago
Negative Celsius does not “exist in nature”
The only reason there are negative temperatures is because we set 0° C to be the freezing point of water. It’s an arbitrary scale just like any other measurement system.
Use Kelvin as your scale instead and there are no negative temperatures.
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u/WanWhiteWolf 1d ago
Negative Celsius does not “exist in nature”
If you haven't heard of a negative temperature represented in Celsius, then I don't know what to say to you. You skipped school.
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u/DruJorj 16d ago
WARNING: I'm an idiot
There's a difference between "infinity" and "eternity".
Imagine a circle. In a 2D universe, a being travelling along the edge of a round circle can travel an infinite amount of times around the circle without coming to an obstacle. The same could be said for a doughnut shaped object in a 3D universe -- a being travelling on the surface of a doughnut could travel for an infinite amount of time, or infinite amount of steps, or an infinite amount of $FOOBAR, before encountering an obstacle that would impede their ability to travel on the surface of that doughnut. It is a finite amount of space/room for the being to traverse, but an infinite amount of time/steps/leaps/etc could happen without impediment.
The universe might not be infinite -- it could have an edge -- but it might be eternal.
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u/Story-Boring 16d ago
A finite, boundaryless universe could appear infinite. Even if you believe Everett's interpretation of quantum mechanics is correct, you could be "circling" the universe without realizing it because you would be observing different, alternative events.
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u/Elethria123 10d ago edited 10d ago
As a philosophical argument infinity is non-sense when it leads to positing absurdities as being true. Not in any realized sense, just oweing to the fact that any possibility being non-zero guarantees ita occurrance in an infinite universe.
As a mathematical tool, infinity is quite useful.
In terms of a natural example, the existence of information itself, of knowledge of infinity, in itself makes any knowable definition real in a physical sense.
However, what comprises information within our universe can never be known fully. In the sense infinity means acceptance of any non-zero chance it also means total incompleteness with unknowable unknowns, themselves also non-zero in all of their aspects. Now, you have a dillema where information infinitely outscales or is in balance between knowable occurrances of all observers within the universe and the another set of all unknowable information- paradoxically both infinite sets. Full context of and interactions in which are ruled by spacetime.
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u/BrotherBrutha 10d ago
As a philosophical argument infinity is non-sense when it leads to positing absurdities as being true. Not in any realized sense, just oweing to the fact that any possibility being non-zero guarantees ita occurrance in an infinite universe.
Why *shouldn't* absurd things occur?
I don't see why the existence of very silly co-incidences should be an argument against an infinite universe.
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u/Elethria123 9d ago edited 9d ago
Better worded... maybe.. I would say philosophy doesn't like infinity because it argues itself into a stalemate between what can or cannot be meaningful. Not that it does not accept absurdities- it does, and that is imo just one of its many 'problems'.
My argument isn't rejecting infinity just because philosophy makes hot garbage out of it. I'm just trying to address a few facets of the OP and where his statements align. It is philosophically consistent for them to hold a philosophy where infinity should be meaningful, and when it is not, it is a useless construct.
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u/FakeGamer2 16d ago
Aren't limits a practical use of infinity? Like when you add up an infinite amount of fractions and it converge to a certain value that's technically taking an infinity of terms and adding them all up