[stouset]

Even if the computer does perfectly-efficient computer things with every Joule, every single one of those Joules ends up as one Joule of waste heat.

If you pull 100W of power out of an electric socket, you are heating your environment at 100W of power completely independent of what you use that electricity for.

[spyder]

Only true for our current computers and not true with reversible computing. With reversible computing you can use electricity to perform a calculation and then "push" that electricity back into a battery or a capacitor instead of dumping it to the environment. It's still a huge challenge, but there is a recent promising attempt:

"British reversible computing startup Vaire has demonstrated an adiabatic reversible computing system with net energy recovery"

https://www.eetimes.com/vaire-demos-energy-recovery-with-rev...

https://vaire.co/

Short introduction video to reversible computing:

https://www.youtube.com/watch?v=rVmZTGeIwnc

[flave]

Actually pretty cool - I was about to comment “nice perpetual motion machine” but looked into a bit more and it’s much more interesting than that (well, a real perpetual motion machine would be interesting but…)

Thanks for posting. Pretty cool.

[tatjam]

This kind of stuff could trigger the next revolution in computing, as the theoretical energy consumption of computing is pretty insignificant. Imagine if we could make computers with near-zero energy dissipation! A "solid 3D" computer would then become possible, and Moore's law may keep going until we exhaust the new dimension ;)

[thegrim000]

I read it as the inefficient part isn't the compute efficiency, the inefficient part is dumping all the resulting heat into the environment without capturing it and using it in some way to generate electricity or do work.

On a related/side note, when there's talk about seti and dyson spheres, and detecting them via infrared waste heat, I also don't understand that. Such an alien civilization is seemingly capable of building massive space structures/projects, but then lets the waste heat just pour out into the universe in such insane quantities that we could see it tens/hundreds of light years away? What a waste. Why wouldn't they recover that heat and make use of it instead? And repeat the recovering until the final waste output is too small to bother recovering, at which point we would no longer be able to detect it.

[oasisaimlessly]

All energy inevitably changes into heat eventually, and in the steady state, power in = power out.

There is no way to get rid of heat. It has to go somewhere; otherwise, the temperature of the system will increase without bound.

[thegrim000]

For example, why couldn't you use the waste heat like a power plant? Use it to boil water, to turn turbines, to generate electricity, which gets sent and consumed elsewhere? Adding to the heat wherever the electricity is finally consumed. (Ignoring various losses along the way).

[stouset]

“Elsewhere” is still somewhere on the Dyson sphere.

Or if you magically beam 100% of the captured energy somewhere else, now that place gets to deal with shedding the heat from however many 1e26W+ of power were consumed. God help the poor planet you aim that ray of death at.

[stouset]

> but then lets the waste heat just pour out

There is no other alternative! If I build a perfect Dyson sphere and capture the energy output of a star, all of that energy will become heat. The average surface temperature of my Dyson sphere will be (IIRC) the ratio of the surface area of the sphere to that of the contained star, multiplied by the star's effective surface temperature.

"Recovering heat and making use of it" requires a heat differential. You need a cold side and a hot side to use energy. Using that energy causes the cold side to heat and the hot side to cool, until they reach equilibrium. The further the difference, the more usable work you can do. The closer the two sides are, the less work you can do.

Someone else here said it best: waste heat is the graveyard of energy. Once you have used energy, it will become high-entropy, low-grade, diffuse heat which is difficult-to-impossible to extract further work from.

[tasuki]

> every single one of those Joules ends up as one Joule of waste heat.

Yes it ends up as heat, but with some forethought, it could be used to eg heat people's homes rather than as waste.

[TheSpiceIsLife]

You can say that about any waste heat.

In really, it’s not convenient to move all waste heat to where it’s more needed.

[m4rtink]

Modern industrial scale insulated hot water district heating systems can do dozens of kilometers with the water cooling down only by a degree Celsius.

[tremon]

It's always more convenient to ignore externalities. That doesn't mean we should be okay with only bottom-of-the-barrel solutions.

[agumonkey]

These days it's not rare to have data center heated buildings. I guess crypto bros are just not thinking about this. But technically if could be done there too.

[KellyCriterion]

There was a startup in EU which explicitly sold heat from crypto mining to the local energy provider. IIRC it was also here on hacker news some time ago.

[agumonkey]

Qarnot maybe

[KellyCriterion]

I meant this team:

https://terahash.space/en/

[agumonkey]

oh nice, i didn't know about them

[robkop]

Interesting question - how much will end up as sound, or in the ever smaller tail of things like storing a bit in flash memory?

[Workaccount2]

Heat is the graveyard of energy. Everything that uses energy, or is energy, is actually just energy on it's way to the graveyard.

The energy of the universe is a pool of water a top a cliff. Water running off this cliff is used to do stuff (work), and the pool at the bottom is heat.

The "heat death of the universe" is referring to this water fall running dry, and all the energy being in this useless pool of "heat".

[devsda]

Do thermophotovoltaic cells operate on different kind of heat?

Is it impossible to convert heat into other forms of energy without "consuming" materials like in the case of steam, geothermal or even the ones that need a cold body to utilize thermoelectric effect.

[LiamPowell]

TPVs don't rely solely on the temperature of an object being high, they instead rely on two objects on either side having different temperatures. As heat moves[1] from one side to the other some of the energy from that movement is turned in to electricity.

[1]: Technically the movement itself is heat, the objects don't contain heat, rather they contain internal energy, but the two get mixed up more often than not.

[supermatt]

That movement is effectively “consuming” the differential.

[ajuc]

What thermal energy sources actually exploit is temperature difference, not heat. And in the end that difference averages out.

[phil21]

Almost none. A long time ago a friend and I did the math for sound, photons (status LEDs), etc and it was a rounding error of 1% or something silly like that.

And that’s ignoring that sound and photon emissions typically hit a wall or other physical surface and get converted back to heat.

It all ends up as heat in the end, just depends on where that heat is dumped and if you need to cool it or not. Most watts end up being even more than the theoretical heat per watt due to said cooling needs.

There is literally no way around the fact that every watt you burn for compute ends up as a watt of waste heat. The only factor you can control is how many units of compute you can achieve with that same watt.

[Terr_]

Well, at least until somebody devises a system that transports or projects it so that the heat ends up somewhere not-Earth. It'd still be heating the universe in general, of course, even in the form of sprays of neutrinos.

That reminds me of a sci-fi book, Sundiver by David Brin, where a ship is exploring the sun by firing a "refrigerator laser" to somehow pump-away excess heat and balance on the thrust.

[mrDmrTmrJ]

All sound will end up as heat.

[csomar]

Theoretically, if your computation is energy efficient, you won't need any electricity at all since the real computation costs zero energy.

[majoe]

That's not correct. For ordinary computers there is Landauer's principle, which gives a theoretical lower limit for the energy needed for computation [0].

I say "ordinary computers" because other comments mentioned "reversible computers" for which this limit doesn't apply.

According to the linked wikipedia page, this theoretical limit is around a billion times smaller than current computers use for an operation, so you may call me pedantic.

[0]: https://en.wikipedia.org/wiki/Landauer%27s_principle

[anthonj]

This violates energy conservation principles. Some power will be "wasted" into heat, some other will be used for some other work.

[stouset]

If I use energy to move a block one foot over, I have performed useful work. But 100% of the energy used to perform that work is either already heat or shortly will be.

[anthonj]

If you launch a rocket at escape velocity the momentum and potential energy you create never dissipates.

Certain chemical reaction endotermic reaction require energy to start. This energy is absorbed to generate molecular bond.

Also in the generation and absorption of high energy radiation there are non-thermal processes that can transfer energy.

Even something like bending a metal bar is not 100% a thermal process.

[usrnm]

If I turn my fan on and 100% of the electricity is converted to heat, where does the kinetic energy of moving fan blades come from? Even the Trump administration cannot just repeal the law of conservation of energy.

[numb7rs]

Even if most of the energy goes into kinetic energy of the air, that air will lose momentum via turbulence and friction with the surrounding air, which will end up as... heat.

[jo909]

While spinning, the blades store a miniscule amount of kinetic energy.

After removing power even that small amount ends up as heat through friction ( both in the bearing but mostly in the air turbulence). And the blades end up in the same zero energy state: sitting still.

So it is correct that a 100% "end up" as heat

[usrnm]

Most of that energy gets transfered to the air that's being moved by the blades, and who knows what that air does eventually. And we're not even talking about the plant growing light that might be sitting in my room near my house plants literally creating new life from electricity.

[stouset]

> who knows what that air does eventually

We do know what that air does eventually. Given no further inputs of energy, it swirls around generating friction, raising its temperature (heat!) as the currents slow down to nearly nothing.