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Comment by sixdimensional | Hacker News Reader

"after trillions of years the universe will enter a dark age when there are no stars with visible light left".

Ok but, armchair amateur here, the scale of space is not known to humans, right? We cannot comprehend the actual limit of the universe, can we? How can we know that the universe entering a dark age is not a local effect in our known universe, and that other, incomprehensibly distant parts of the universe will keep doing just fine?

For that matter, if the universe enters a dark age, what is it that caused the universe to be in a "light age" in the first place? There has be a force that causes the universe to exit a "dark age" otherwise it would always have been dark.

These kinds of things perplex me.

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There are two different effects at play here. On the one hand, there will be a dark age because all the stars will burn out. This has nothing to do with the cosmological event horizon.

The cosmological event horizon is caused by the accelerating expansion of the universe. Space is expanding uniformly, so the more space there is between us and some object, the faster it is moving away from us. Objects that are farther than the Hubble Distance from us are receding faster than the speed of light, and so their light will never reach us. Over time, everything that isn't gravitationally bound to us will recede into the distance, redshift and disappear, leaving only our galaxy within the observable universe.

This isn't the answer you're looking for, but I'm reminded of the book of Genesis:

> "[1:2] And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. [1:3] And God said, Let there be light: and there was light.

If you'd like to read more, here you go: https://www.blueletterbible.org/kjv/gen/1/1/s_1001

I will note that in the above it says "morning" and "evening". In some sense, the writing is old enough that we assume that is what the original hebrew meant, but we don't actually have context to say. I've heard that the word for "morning" (erev) could have meant "order", and "evening" (boker) could have meant "disorder".

So what you get is 7 days (depending on who you ask) where the second law of thermodynamics is "wound up", if you will, which resulted in an ordered universe that isn't just a homogeneous soup.

>So what you get is 7 days (depending on who you ask) where the second law of thermodynamics is "wound up", if you will, which resulted in an ordered universe that isn't just a homogeneous soup.

Please... please don't imply that the book of Genesis, or any similar religious work, holds some hidden insight into modern science. The authors of Genesis, whoever they were, did not know what thermodynamics was, and were not writing about it when they came up with the Genesis account.

> Please... please don't imply that the book of Genesis, or any similar religious work, holds some hidden insight into modern science.

I didn't. Nor was that my intent. I only wanted to point out that there was something interesting and relevant to the above post.

This quotation demonstrates that man has been pondering this same quandary for a great many years. How does one conceive of that which is out of our comprehension? This is where the fields of logic, philosophy, religion, science, etc. try to help build a model for understanding. However, I find that no model we have is sufficient to truly understand, not yet at least.

Religion may have started building a model for understanding - but has been failing for at least 5000 years.

> but has been failing for at least 5000 years.

I encourage you to take some time and study the Christian church during the Middle Ages. Much of what we consider 'modern' learning, teaching, and method came about because there were monks an nuns who were very serious about their work.

Likewise, I encourage you to study Islam since its inception; there also clerics (I don't know the proper terms) sought to increase understanding in literature an science some 500 years before the church in Europe.

Also take some time to look into various religious orders (Hindu, Buddhism, and others) throughout Asia that, in very similar fashion, worked to preserve and expand knowledge within their orders and in their surrounding communities.

If anything, religion has been a driving force towards foundational methods of understanding, knowledge acquisition, and preservation.

I would like to know from those who down voted my comment: why down vote?

My intent was to add an extra dimension to the conversation.

"dark age" is just something I came up with. By "dark age" I meant that there are no thermonuclear processes left providing light for us. After trillions of years the last Red Dwarf will run out of fuel and there will be no light-emitting stars left.

We don't know the scale, that's why we usually say "observable universe", but we do know the rules which apply everywhere.

"light age" or whatever you call it in this context means that there are still stars left which emit light.

After the "dark age" there will be the heat death of the universe.

Your comment prompted me to re-read The Last Question by Asimov (https://www.multivax.com/last_question.html).

Your comment prompted me to re-acknowledge my fear of mortality

Wow, I've never read that but I will do so now!

There's also "The Last Answer" by Asimov, and if you're into these types of stories I can also recommend The Egg (by the writer of The Martian).

I remember Étienne Klein explaining that one of the theory why the universe is flat (if you take 3 galaxies and draw a triangle using them as points the sum of the angles will always be 180) is that we might be like an ant sitting on a ball. The ant only sees so much of the ball and from its perspective everything is flat. But in reality the ball is round.

Or the ball is projected from a 3D surface infinitely far away :D (holographic universe theory)

Not a physicist, but at a guess: Occam's Razor, plus the existance of simpler theories which explain our current observations.

I think this (Occam's Razor) clearly illustrates the limit of our perception/comprehension though. It is entirely possible that due to our comprehension of the complexity involved with dimensionality, we can be only vaguely aware (if at all) of a more complex system than the one we can perceive/comprehend. I'm reminded of the book Flatland[1].

It is fine to attempt to apply our rubrics, but I am not sure how to quantify the limits of our perception. Perhaps Occam's Razor and current simpler theories give a useful working tool for us to reason within our local known (or perceived/comprehended) universe.

The best way I can think of to ask this is, how do we factor in the "unknown unknown"? It is maddening not to be able to.

[1] https://en.wikipedia.org/wiki/Flatland

I mean, that's why people do theoretical physics in higher dimensions and then search desperately for ways to test their theories. We can extrapolate with mathematics in infinite ways, but until we can find ways to test things it's hard to do better than "find the simplest explanation that accounts for what you can observe".

Slightly off-topic, but how robust is Occam’s Razor as a principle for judging the likelihood of a theory being true?

Occam's razor is the search heuristic with bottommost priority. It works well because it's easier to falsify simpler things than more complex things. It's a technique to avoid adding epicycles and not very effective further up from there.

If you have other reasons to believe a more complex hypothesis may be likely those should generally override Occam's Razor.

I started typing a reply, but as usual Wikipedia has a better response than I do:

https://en.wikipedia.org/wiki/Occam%27s_razor#Justifications

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