Hacker News Reader

Comment by dist-epoch | Hacker News Reader

We all know that life on Earth gets it's energy from the Sun.

But we also know that's an approximation we tell kids, really life gets low entropy photons from the Sun, does it's thing, and then emits high entropy infrared waste heat. Energy is conserved, while entropy increases.

But where did the Sun got it's low entropy photons to start with? From gravity, empty uniform space has low entropy, which got "scooped up" as the Sun formed.

EDIT: not sure why this is downvoted, is the explanation Nobel Physics laureate Roger Penrose gives: https://g.co/gemini/share/bd9a55da02b6

View on HN

Your question fascinated me. Googling "where did the Sun got its low entropy" I also came across these explanations:

"Solar energy at Earth is low-entropy because all of it comes from a region of the sky with a diameter of half a degree of arc."

also, from another reply:

"Sunlight is low entropy because the sun is very hot. Entropy is essentially a measure of how spread out energy is. If you consider two systems with the same amount of thermal energy, then the one where that energy is more concentrated (low entropy) will be hotter."

https://physics.stackexchange.com/questions/796434/why-does-...

Probably it's a bit of both. I'm not sure I understand your hypothesis about the Sun scooping up empty, low-entropy space. Wasn't it formed from dusts and gases created by previous stellar explosions, i.e. the polar opposite of low entropy?

I read the gravity explanation for the sun low entropy in the "Road to Reality" book from Roger Penrose. Asked Gemini to summarize the argument (scroll to end)

https://g.co/gemini/share/bd9a55da02b6

It's also in his previous book "The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics", along with a lot more. Strongly recommended (even though after reading a lot of Greg Egan, my views on consciousness somewhat shifted towards "classical computation can do it, too".)

Yes, the main argument in the Emperor's New Mind seems to boil down to 'consciousness is weird, and quantum stuff is weird, so consciousness needs to be quantum'.

If you can look past that, there's some good other material inside.

The universe was low entropy at the time of the big bang, and even though entropy is steadily rising, the universe is still pretty low entropy.

This is just a question about the origins of inhomogeneity in the universe. The prevailing theory is cosmic inflation, I believe: in the early universe a quantum field existed in a high entropy state and then the rapid expansion of space magnified small spatial inhomogeneities in the field into large-scale structures. What we see as "low entropy" structures like stars are actually just high entropy, uniform structures at a higher scale but viewed from up close so that we can see finer-scale structure.

The photons do not have entropy.

The photons from Sun are hot, the space around Sun is cold, the system has a low entropy.

If the space around Sun was as hot as the photons, the entropy would be high.

  But where did the Sun got it's low entropy photons to start with? From gravity, empty uniform space has low entropy, which got "scooped up" as the Sun formed.

From the Big Bang originally. We don’t know what caused the Big Bang.

The end of the previous Big Bang, a-la Big Bounce ;^)

"It's turtles all the way down."

Based on the theory of gravity in the article it's actually, "Archimedes Principle all the way down."

https://en.wikipedia.org/wiki/Archimedes%27_principle

One of the major challenges with "Big Bounce" that media coverage of it tends to overlook is that it is not entirely clear how the previous universe, which is presumably high entropy if it's supposed to be like ours, becomes the low entropy feedstock for the next universe. There's still a "And Here There Be Magic" step there.

I'm not saying there's no solution; indeed, this is the sort of thing where the problem is that the profusion of proposed solutions is exactly the thing that shows there's a problem there. I think people tend to intuitively think that "lots and lots of possible solutions" is somehow better than "no solutions at all" but they're actually nearly the same thing.

You’d have to explain how the steadily increasing entropy in our universe would revert to a low-entropy state again.

Reply on news.ycombinator.com