[lisper]

A pithier way to introduce this topic: the first law of thermodynamics, a.k.a. the law of conservation of energy, is that energy cannot be created nor destroyed, only transformed from one form to another. In light of this, how can there ever be a shortage of energy?

[Note that this is intended to be a rhetorical question advanced for the purposes of pedagogy. If you find yourself wanting to post an answer, you have missed the point.]

[dahart]

Why is this pithier than the video? I’m not entirely sure I see added pedagogical value. Asking the rhetorical question how can there be a shortage of energy sounds a little like someone sort-of intentionally misunderstanding what that phrase “energy shortage” means in any practical economic context. “Energy shortage” is an economics phrase, not a physics phrase. The first law of thermodynamics doesn’t suggest there can’t be energy shortages on earth, because the phrase “energy shortage” is not used to suggest a loss of energy to the universe, energy shortages are all about not having enough specific forms of energy in specific places at specific times [1], and it’s no surprise that we can’t capture dissipated heat, or that a local power system has a maximum limit at any given time, for example.

Something similar could perhaps be said for the video’s approach; “what do we get from the sun?” is an ambiguous question, not necessarily a fair setup to ask a lay person when you have entropy in mind as the answer. We do get energy from the sun, that is a correct answer, and we use some of it before it goes away. But, there is the nice a-ha that all the energy from the sun eventually leaves the earth, right?

[1] “An energy crisis or energy shortage is any significant bottleneck in the supply of energy resources to an economy.“ https://en.wikipedia.org/wiki/Energy_crisis

[JumpCrisscross]

It’s pithy, but in the way of word play. Energy, colloquially, means useful energy. The question collides the conventional and technical definitions to create the illusion of profundity.

[lisper]

Pithy != profound. The intent was to get people to think about the fact that the word "energy" means different things in different contexts, and that the thing that actually has value is not energy but the absense of entropy.

[JumpCrisscross]

> intent was to get people to think about the fact that the word "energy" means different things

But the question posed is weaker at prompting that than the sequence of questions posed by the video. It's a strange response that doesn't add to the discussion.

[lisper]

> But the question posed is weaker at prompting that than the sequence of questions posed by the video.

You really think "what do we get from the sun" is a better prompt? I guess we're just going to have to agree to disagree about that.

We get all kinds of things from the sun. Tides. Light. Tans. But there is only one correct answer to why we worry about "energy production" and "energy shortages" when energy is supposedly conserved.

"What do we get from the sun?" has a lot of correct but off-point answers, which makes it IMHO more a prompt for the questioner to exhibit their superior knowledge than a well-designed Socratic question.

[dekken_]

> how can there ever be a shortage of energy

I think it's not so much a shortage of energy, but that there thermodynamic equilibrium and thus no available energy to do anything.

I don't think this will ever happen tho, it's pretty clear to me that making energy more dense is a universal process.

[sghiassy]

Not really - look up “heat death” of the universe.

[jjaken]

Heat death doesn’t mean “no heat” or that energy has depleted. It just means that energy is fully dispersed. All kg the hear exists, it’s just that no one place has any more than anywhere else, and so there is no longer any transfer of energy.

[A_D_E_P_T]

> so there is no longer any transfer of energy.

Ah, but there is.

The Second Law is a statistical law, not an absolute law. On long enough timescales, low-probability fluctuations in local entropy will allow for energy transfer. These fluctuations will also allow for the formation of structures. (Boltzmann himself was of the opinion that the low-entropy universe emerged from a higher-entropy background state. And indeed there's nothing in physics to rule out the emergence of Boltzmann Brains and even Boltzmann Galaxies from homogeneous and maximally entropic universes in "heat death." This is a philosophical problem of the highest order, because it implies that we're not necessarily going from "less likely to more likely states" as the video implies, but rather from a relatively deterministic state to a probabilistic state.)

[jjaken]

Oh interesting, I didn’t know that

[credit_guy]

The "heat death" of the universe is a concept that deserves to die. The second principle of thermodynamics is true only if you ignore gravity. In the presence of gravity, systems tend to go towards lower entropy, just see how a planetary system can form out of a gas cloud.

[consilient]

> In the presence of gravity, systems tend to go towards lower entropy, just see how a planetary system can form out of a gas cloud.

This isn't correct: the entropy (and energy) of the gas cloud goes decreases as it collapses, but the entropy of its surroundings increases faster as it radiates.

[credit_guy]

Is that a fact? Or just a hypothetical way that could save the second principle?

[consilient]

It's a fact. See for instance https://arxiv.org/pdf/0907.0659.pdf

[mNovak]

Not my area of expertise, but in the video at least, they indicate that black holes have very high entropy. So if we imagine gravity eventually pulling all those planetary systems together into some number of black holes, isn't gravity indeed pulling the system towards a high entropy state?

The video actually directly addresses the gas cloud question, saying basically that a gas cloud is actually a highly improbable distribution of matter, whereas the eventual planetary system is much more probable. The claim being, that trend towards expected state is entropy increasing.

[dekken_]

I think of it as a death cult. Thinking we know all that there is to know about the universe to the point where we can declare with 100% certainty that any particular thing will happen is not scientific.

[kergonath]

Really? We are far from really understanding gravity, but I can very confidently tell you that if I kick a ball its trajectory will be a parabola (roughly, as a first order approximation and ignoring things like friction, which we can also calculate to a decent approximation). We can say where it will fall and give some confidence interval depending on the conditions and such. There is nothing unscientific about it.

Thermodynamics is not magic. In the same way that we can predict the evolution of climate without knowing where every single cloud will be, we can make statements about the evolution of large systems even though our knowledge of their state is imperfect. Again, nothing unscientific about it.

[dekken_]

If you read what I said, I said nothing about predictions. Predictions are fine. Stating things as certainties, not so much.

[sghiassy]

Usable energy is different than total energy. If energy isn’t concentrated (say something like gasoline) it’s not usable

[uoaei]

Energy is actually a red herring -- what's relevant here is work.

Useful work, aka information, is work that can be employed in dynamics vis a vis processing. Useless work, aka heat, is the devil's share of the energy expenditure which is lost as entropy when undergoing a process.