Why the universe is most likely not infinite – Part 5: Popular argument against infinity

in #hive-1635212 months ago

Ein beliebtes Argument, die Unendlichkeit des Universums zu widerlegen, lautet ungefähr so: Wenn das Universum uendlich (groß) wäre, warum ist der Nachthimmel dann nicht weiß statt schwarz?

Wenn es unendlich viele Sterne in allen Richtungen gäbe, müsste der Nachhimmel doch weiß erstrahlen. Das Licht der unendlich vielen Sterne würde sich summieren und den gesamten Nachthimmel ausleuchten. Das ist aber nicht der Fall. Captain Obvious.

Nicht schlecht, aber ganz so einfach ist es auch wieder nicht, die Unendlichkeit zu widerlegen. Das Argument macht nämlich drei weitere implizite Annahmen, erstens dass das Universum isotropisch und homogen sei (das ist wahrscheinlich wahr, Universum in allen Richtungen ähnlich strukturiert), zweitens Licht sich unendlich weit bewegen kann (Licht kann tatsächlich sehr große Distanzen zurücklegen) und drittens das Universum bereits ewig lange existiere (Steady State Universe), damit uns das Licht von fernen Sternen überhaupt erreichen könne.

Sollte eine dieser Annahmen falsch sein, würde der Nachhimmel großteils schwarz sein, unabhängig davon, ob das Universum unendlich groß ist oder nicht.

Die Lichtgeschwindigkeit ist jedenfalls endlich (nicht unendlich schnell) und in kosmischen Dimensionen eigentlich ziemlich langsam und der limitierende Faktor, wenn das Universum laut herrschender Big-Bang-Theorie vor 13.8 Milliarden Jahren entstanden ist und sich seitdem ausdehnt, hat das Universum einfach nicht genug Zeit gehabt, damit uns das Licht von (un)endlich weit entfernten Sternen überhaupt erreicht.

Das Argument funktioniert nicht ganz so gut wie erhofft, ist aber auch kein Beweis für die Unendlichkeit und schließt zumindest ein unendlich altes, unendlich großes Steady-State-Universum aus.

Der Nachhimmel ist schwarz und nicht weiß.

Was sagt ihr dazu?

ps. es gibt übrigens noch ein weiteres Problem des Weißen-Nachthimmel-Arguments und zwar dass die Helligkeit der Sterne quadratisch mit der Distanz abnehmen und Sterne das Licht von dahinterliegenden Sternen teilweise blockieren. Ein weißer Nachhimmel wäre selbst bei unendlich vielen Sternen unrealistisch.

sd-universe-finite-or-infinite-2.jpg

Is the universe infinite or rather finite? AI-generated illustration (Stable Diffusion)

English

A popular argument to refute the infinity of the universe goes something like this: If the universe were infinite (infinitely large), why isn't the night sky white instead of black?

If there were an infinite number of stars in all directions, the night sky would have to be white. The light from the infinite number of stars would add up and illuminate the entire night sky. But that is not the case. Captain Obvious.

Not bad, but it's not quite that easy to disprove infinity. The argument makes three further implicit assumptions, firstly that the universe is isoptropic and homogeneous (this is probably true, the universe is structured similarly in all directions), secondly that light can travel infinitely far (light can really travel extreme long distances) and thirdly that the universe has already existed for an eternity (Steady State Universe) so that the light from distant stars can reach us at all.

If one of these assumptions is wrong, the night sky would be mostly black, regardless of whether the universe is infinite or not.

In any case, the speed of light is finite (not infinitely fast) and actually quite slow in cosmic dimensions and the limiting factor, if according to the prevailing big bang theory the universe was created 13.8 billion years ago and has been expanding ever since, the universe has simply not had enough time for the light from (im)finitely distant stars to reach us at all.

The argument does not work quite as well as hoped, but it is also not a proof of infinity and at least rules out an infinitely old, infinitely large steady-state universe.

The night sky is black, not white.

What do you think?

ps. by the way, there is another problem with the white sky argument, the brightness of stars decreases quadratically with respect to distance and stars partially block the light of stars behind them. A white night sky would therefore be unrealistic even with an infinite number of stars.

Finite or infinite universe

Part 1: Definitions https://stemgeeks.net/hive-163521/@vikisecrets/why-the-universe-is-most-likely-not-infinite-part-1-definitions-reply-with-infinite-or-finite

Part 2: Scientific question or not? https://stemgeeks.net/hive-163521/@vikisecrets/why-the-universe-is-most-likely-not-infinite-part-2-scientific-question-or-not

Part 3: Infinity as a placeholder for ignorance https://stemgeeks.net/hive-163521/@vikisecrets/why-the-universe-is-most-likely-not-infinite-part-3-infinity-as-a-placeholder-for-ignorance

Part 4: Everything we measure is finite
https://stemgeeks.net/@vikisecrets/why-the-universe-is-most-likely-not-infinite-part-4-everything-we-measure-is-finite

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As we all know this is a small place where we live and the rest is all water around us. This is the system of nature and it has to run like this for the rest of life

I think that our Universe is one of many multiverses (with different constants). Our Universe is not infinite. Matter in general originated and expands in a limited volume. The number of atoms in our Universe is finite.

Unendlich könnte für mich nur sein, wenn man an einem Ende ankommt, kommt man am anderen Ende wieder rein, also wie eine schleife. Sonst wäre für mich unendlich unmöglich, wenns unendlich wäre würde es sich ja auch nicht ausdehnen.

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Wenn's endlich wäre stellt sich doch die Frage von was es umgeben ist und wo dieses etwas dann endet.
Ich hatte als Kind diese Vorstellung, es sei ein großes Aquarium, das im Wohnzimmer Gottes steht

These are some information that we never searched about that.

I think there's a theory by Albert Einstein that says the universe is expanding away at the edges at the speed of light. If this is true then the universe is not infinite since it has edges and expands. This is an interesting lesson in astrophysics. Thanks for sharing and have a wonderful day.

I’m just beginning to think of why the sky is not always white even though we usually have so many stars in the sky

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Too soon to call... It may be infinite but as finite creatures we are unable to comprehend it at our point of evolution. The universe seems to be expanding faster and faster, so there is much yet to be understood.
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If, as some argue, the universe is expanding, then it could not be infinite. I think.

Does infinity even exists? Is there anything truly infinite?

Does infinity even exist?

A very good question. I think, this is nothing we can answer. We have a mental concept of infinity but nothing else. I even think it is not relevant to know if it exists. Can you think of a relevant theme?

No, yes, perhaps it could be relevant in some subjects, due to the fact that the assumption of infinity has repercussions in other areas, such as the nature of the universe in which we live. There are things that don't seem practical at all, but then end up changing the way we see the world, and thus, changing us.

There are things that don't seem relevant, but then help us a lot in indirect ways.

Can you think of a relevant theme?

That depends on what you consider relevant. Maybe you can help me here and think of one.

Cheers!

"The nature of the universe", what do you mean by that?
If you mean that we as earthlings assume that our part of the universe does not exist infinitely, then we have made a prediction about its finiteness. How would that help you personally, for example? How would that differ from your knowledge that your own life is finite, regardless of the nature of the universe?

That depends on what you consider relevant. Maybe you can help me here and think of one.

I have no idea about that, hence my question. There's actually nothing I can think of.

Well, you presuppose that our own life is finite. If we ask ourselves: What was I before this life? We can think, for example, that all the matter that forms our body existed before we were what we call "us" today. All that matter was previously part of food and other things that later, at the moment of our birth, formed us. So, materially speaking, everything we are made up of probably preexisted what we call ourselves. In the same way, if we believe in souls and spirits, perhaps we can apply a similar logic, and it is possible that the substratum of all that we are may, in one way or another, have existed before. I am not saying it is so, but it is a possibility.

In the same way, and applying the same logic, we may continue to exist, in every sense, after our death. What would that existence be like? That would be another question, but one way or another it would be existence. Whether or not we identify ourselves with that other previous or future existence, is another matter, but in reality it could be said that we are that too.

Probably everything we are, including our mind, has always existed and will continues to do so.

The way I see it, believing that there is only the present and that it is somehow eternal. Things don't "existed" neither "will exist". Things simply exist. Now. And it cannot be otherwise. Things will not be, nor were, but are.

Thinking about this may cause us to see everything differently, and even not to see, neither birth as the beginning, nor death as the end. Everything that has a beginning, I think, has an end. But that which is uninitiated, properly eternal, has no end.

I have no idea about that, hence my question. There's actually nothing I can think of.

It's fine.

Well, you presuppose that our own life is finite.

My dad died. My mom died. A friend of mine died. My grandparents died. And so on and so forth. Objective reality, in the same way I age and am a woman.
Now, if my parents are leading some other form of existence or they were being born again, I cannot say with certainty. I need not. It shall satisfy me to have faith.

If we ask ourselves: What was I before this life?

It is language or synonyms for "life after death" ( a contradiction, actually:). I once asked myself all these questions and I have left them behind me; sort of ;)

neither birth as the beginning, nor death as the end. Everything that has a beginning, I think, has an end. But that which is uninitiated, properly eternal, has no end.

Agreed.
It's a matter of cultural expression, though. We have the need to find a common one. Christianity is not he worst, if those are the roots of your parents and grandparents, for example. I tried Buddhism for quite a while and recognized that it does not work for me.

If you get too mixed up in various religions, you might lose more than you win.

Do you think that people simply cease to exist? As if they had disappeared or been disintegrated?

But I think you are right and we have no certainty about this.

Sure, I know that they disappear and are disintegrated. Their bodies sure do and I see them never again.
How they once were is gone, in fact, and they will never again be together alive in this exact body with the exact same people.
I, when I die, will not take my body with me, so there is no similarity in sight which carries what might be left of "me", into another form of existence. I don't have any specific thoughts or imaginations about what there might be after my death. I don't think I need to know. If I happen to live long, I guess I will part from life willingly, since becoming old is not much fun and one day you are happy to receive the end of it.

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What I would like to know is that the universe expands infinitely.

What about black light?! :P

I love theories about the universe. Very interesting stuff that I hope to get to know much more!

Actually everything has a limit, but the universe is huge. But there is an end. The stars are so far away that the sky appears black

I tend to think that it isn't infinite but I do think it's large enough for most people to think that is is infinite. We are just a small part of the universe.

Very interesting.

This argument does not work quite as well as hoped, but the Big Bang is also not a proof of infinity and at least rules out an infinitely old, infinitely large steady-state universe.

This would be the case if you make the assumption that the universe started with the Big Bang. However, the Big Bang is not the origin of the universe, but the earliest state that we have evidence of. It is like the highest point of a mountain, which is not the beginning of the mountain, but the place where it starts to descend. The Big Bang describes how the universe evolved from an incredibly dense and tiny point, but it doesn't account for the laws of physics and other things. More and more cosmologists are moving away from the idea that the Big Bang was an absolute beginning and consider it a sort of "first moment of time", as Sean Carroll puts it.

I would say that this argument reminds me of another argument that apologists use to defend the existence of God using science to make philosophical points, such as in the Kalam cosmological argument. William Lane Craig is one of the main defenders of that argument but he was was critiziced by top physicists and mathematicians such as Sean Carroll, Roger Penrose, Carlo Rovelli, Adrian Moore and others on the plausibility that the universe may be eternal and and therefore, actual infinities may exist. The documentary is on Youtube.

Sean Carroll, Roger Penrose, Carlo Rovelli, Adrian Moore and others on the plausibility that the universe may be eternal and and therefore, actual infinities may exist.

Do you think the universe can be eternal? This, I think, brings many aporias.

If the past is infinite (rather uninitiated), we can go infinitely backwards, right? But if the past is infinite, it would take an infinity of time to elapse (the past), wouldn't it? But an infinite time would never end, precisely because it is infinite. However, the past has already end because we are, obviously, in the present. So, how can the universe be eternal?

Yeah, I'm pretty sure that's answered in the documentary too. You should watch it. There are several ways to approach it.

Given that there will be an infinite number of present times, then it is logically conceivable that an infinite amount of time has elapsed for each one of them. The limit of the past present time doesn't have to be the present time that you want to pick up, because that would be confusing and switching the necessary condition with the sufficient condition. I know, it gets confusing, that's how the logic works. This is only by resorting to Logic and Philosophy, not Physics. You can watch the documentary for more information.

I don't think I'm going to watch it. But thanks for the recommendation.

Given that there will be an infinite number of present times, then it is logically conceivable that an infinite amount of time has elapsed for each one of them.

I think this does not solve the problem, but multiplies it. As I see it, an infinite time can never end, precisely because if it ends it would have an end, i.e., it would not be infinite.

If we were to accept, just by imagination, that infinite time could elapse, then we could go back to the past, elapse infinite time, and arrive at the "beginning" of the universe. Does that make sense? Just as infinite time could elapse into the present, we could also do the opposite and travel into the past.

But then again, the infinite is that which has no end, and I don't see how anything infinite could end.

Thanks for your attention. I will take the video into consideration.

Cheers!

I think this does not solve the problem, but makes it worse. As I see it, an infinite time can never end, precisely because if it ends it would have an end, i.e., it would not be infinite.

We're never going to reach the end of the beginning of the infinite time. It's just a concept, just like the sum of infinites or a Zenonian progression, that's why I said it is logically conceivable. To resolve that paradox, for example, you need to take into account that the size of the set of infinite present times is also infinite, it's just that today can't be the last moment, there are infinite present times. This makes more sense in the context of the tenseless theory of time, where there's no difference between the past, present and future. This issue is more complicated than it looks and the paradox you're raising is well known. Bear in mind that a finite time also creates counter-intuitive situations. For example, what was there before the beginning?

Thank you for your attention. I will take the video into consideration.

Sure, I'm glad you're interested in the topic. If you want to hear it from leading physicists and philosophers instead of me, then you should watch it.

To resolve that paradox, for example, you need to take into account that the size of the set of infinite present times is also infinite, it's just that today can't be the last moment, there are infinite present times.

Why do you say there are infinite present times? I am not a fan of Ockham's razor, but it seems much simpler to say that there is only one present time that does not end, than to say that there are infinite present times that end one after the other. Am I missing something?

This makes more sense in the context of the tenseless theory of time, where there's no difference between the past, present and future.

It's interesting. As I see it, one could also say that there is only the present, and that it is eternal.

Bear in mind that a finite time also creates counter-intuitive situations. For example, what was there before the beginning?

Yes, I am also aware of some of the obstacles that this brings. Some, like creationists, would argue that something of a different nature than the universe pre-existed. But it is a tricky issue.

I think most of these paradoxes can be solved if we change our perception of time. And if we stop seeing time as something linear. As you say, a tenseless time takes a step forward in this direction, I think.

Paradoxes, in general, teach us, I think, that we are considering things in an inadequate way, and that therefore, we must employ another path. These are not unsolvable problems, but just an indication that something needs to change in our approach.

Thanks and regards!

Why do you say there are infinite present times? I am not a fan of Ockham's razor, but it seems much simpler to say that there is only one present time that does not end, than to say that there are infinite present times that end one after the other. Am I missing something?

It used to be common to think like this in the past but now we know better.

I think most of these paradoxes can be solved if we change our perception of time. And if we stop seeing time as something linear. As you say, a tenseless time takes a step forward in this direction, I think.

Yes, it is philosophical, but it is also logical. Now, with the advent of physics, it's also scientific. There are models of the universe with and without a beginning. Both types are mathematically consistent and empirically adequate. We just don't know which model is the right one, if any. All of this is covered in the documentary.

Thank you.

good point, at least we have good evidence of the Big Bang, but we have no idea what happened before the Big Bang and why it happened in the first place, but those questions are meta-physical, pure speculation, non-scientific in the sense that we cannot test theories that are outside of our universe.

I agree, but it's still mathematically consistent. Many cosmologists regard the Big Bang as an open boundary, so there are both models of the universe with a beginning and models of eternal universes. Also, as a general principle, metaphysics should conform to physics, so it's not unscientific necessarily. Anyway, the main point was that actual infinities might exist and it's a widely accepted view among the experts in the relevant fields. Thanks for bringing up this topic.