Comment by RetroTechie | Hacker News Reader

Comment by RetroTechie | Hacker News Reader

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> The single most important assumption in this paper is that energy consumption will increase by 2% per year.

There's a 2nd big assumption:

That tidal energy extracted is additional Earth's rotational energy loss above what Earth does by itself.

According to the paper, tidal energy is dissipated through friction between ocean water & the seafloor. This dissipated energy subtracts from Earth's rotational energy. And some rotational energy is transferred to the moon (which makes the moon move further out). Ok so far.

Author's 2nd assumption is that as tidal energy is tapped, this is extra energy that subtracts from Earth's rotation.

But is it? It might also be that tidal energy extracted by humans, comes out of some fixed 'budget', and the remainder is dissipated naturally. More tidal energy extracted by humans -> less tidal energy dissipated through ocean vs. seafloor friction.

Kind of like solar influx: it's a huge but (apart from fluctuations) fixed amount. We can tap some % of that potential, but what's available doesn't increase. And what humans don't tap, gets absorbed / radiated out by other natural processes.

I won't even hazard a guess. But it would be interesting to figure out which of those applies.

It's a bit absurd the idea that humans living on earth are going to produce more energy than the Sun.

Maybe I'm naive and simple minded. But that just seems insane.

If I'm doing the math right, at 2.3% growth = we produce more energy than the Sun in 4500 years.

It doesn't matter how many years it is. It's never happening.

Just look at how damn hot and inhospitable the sun is. We're not producing more energy here!

It'd be infinitely more plausible to build a Dyson sphere around the Sun, and call me naive on that, too, but I'm skeptical that's ever gonna happen either.

And it’s been said that the mass requires to build a Dyson sphere around our sun would necessitate destroying all of the planets: not gonna happen.

The estimates I've seen suggest maybe just Mercury.

Which is good, because Mercury is mostly metal, whereas e.g. Mars is mostly rock and thus not useful for this kind of work

Would Mercury be a good candidate, given how far in the sun's gravity well it sits? Perhaps better to start with the asteroid belt.

Not a Dyson sphere, a Dyson swarm makes more sense and its doable since it can be very sparse at the beginning and grow denser with time.

Satellites (points), swarms, rings, sails along a spherical plane (e.g. spherical lune w/ axis along ecliptic)… seems like ”realistic” progression.

In a far-future where a TNG-inspired Dyson structure were somehow feasible (1AU size, habitable surface on interior, etc.), it’d be incredibly disappointing if we applied the (unrealistic) science and (unrealistic) resources towards building such a thing, rather than interstellar efforts. Buuuut maybe I’m just projecting my disappointment with our planet’s current approach to science and resource utilization.

100-500 years from now is enough time for AI to develop small nuclear and/or laser sail micro spacecraft that can colonize other systems at a good fraction of the speed of light.

Which would leave 4000 years or so to colonize every system with 1000 light years.

In each system collecting and engineering with low gravity material (asteroids, centaurs, smaller moons, etc.) and using that to capture solar energy will get routine.

Gas giants are basically massive hydrogen nuclear energy depots.

Earth and even our solar system don’t form any kind limit to resource growth on time scales like that.

>Author's 2nd assumption is that as tidal energy is tapped, this is extra energy that subtracts from Earth's rotation.

Not so. The calculation of the 1031 years is equation 19 and assumes the decrease in rotational energy all goes to human purposes.

The flaw in the OP is the assumption that human consumption keeps rising at .02 per year for 1031 years: we would probably boil the oceans away because of the waste heat from using that much electrical power.

> we would probably boil the oceans away because of the waste heat from using that much electrical power.

Which would slow the earth due to the change in angular momentum

Yes, the assumption seems to be that any energy extracted is in addition to the friction with the ocean floor and continental plates, as those will continue to exist.

Your observation seems to make sense.

Intuitively, if we extract energy from the tides, tides will be less tall and the speed of water will be smaller. Ocean currents will slow down too.

What I don't know is, less friction on the seafloor means that we would actually make Earth slow down less faster than it would do if left alone?

It’s a bit odd to extrapolate to this level. It’s like thinking, yes, I can set one tree on fire and release energy, but look how crazy it is if all the trees in North America burn at once!!

And currents are also affected by the rotation of the Earth, temp differences, and salinity differences so they might not change dramatically.

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