[piaste]

It's good that you are aware it's a crazy thought :) Nothing wrong with looking into it though. Wikipedia offers:

> Movement of tides causes a loss of mechanical energy in the Earth-Moon system: this results from pumping of water through natural restrictions around coastlines and consequent viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the Earth (length of a day) has increased from 21.9 hours to 24 hours;[10] in this period the Earth-Moon system has lost 17% of its rotational energy. While tidal power will take additional energy from the system, the effect is negligible and would not be noticeable in the foreseeable future.

and there is some simple math in the [Tidal acceleration] page [0] that you may want to read. Basically, the tides slow the rotation of the Earth, with some of the energy being transferred to the Moon but most of it going into friction. The natural friction is estimated at a (surprisingly low, IMO) 3.64 TW, and at this rate the Earth will stop rotating in 50 billion years, long after the Sun has blown up.

So if we want to keep the Earth spinning (albeit slowly) until the Sun goes red giant, we can afford to cut that time down to a tenth, meaning we can produce 36 TW (before conversion to electricity, i.e. ignoring efficiency).

If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency.

(Global electrical energy production is currectly about 28 PWh per year, equivalent to a constant 3TW or so.)

[0] https://en.m.wikipedia.org/wiki/Tidal_acceleration

[lloeki]

> If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency.

I think you're touching on the problem very nicely here: the problem is not "how much raw energy is there" (because there's an absolute fuckton of it) but "when does the impact of capturing this energy - thus removing it from a complex ecosystem whose stability may depend on it - and turning it into something else - thus adding to a complex ecosystem in other ways - becomes a problem", which may or may not come well before the theoretical raw energy cap.

[piaste]

I'm not sure those considerations are applicable. There is no "ecosystem" that depends on the rate of slowdown of Earth's rotation - we do need to leave some rotation to keep flora and fauna alive, but that's a "reservoir" problem, to use the OP's formulation, not an intensity one.

As for the addition of energy (heat) to the planet, sure, but there's nothing specific about tidal energy here. All energy sources except solar (and wind/hydro which are direct solar derivatives) add heat to the planet that would otherwise have stayed sequestered. But it's many orders of magnitude less than the heating from solar energy, which is why increasing Earth's absorption factor by a few points is an infinitely bigger problem than all the energy we are directly producing or can hope to directly produce in the next few centuries.

[zaroth]

Also worth noting that trying to extrapolate the effects of current technology at this timescale is pointless.

There will be tide changes in human’s technological capabilities long before there could be any reckoning for over-extraction of the Earth’s rotational energy.

For example, in our ability to bring mass into orbit. Add a couple orders of magnitude in that capability, and humans can start directly tuning the Earth’s total solar irradiance by shooting lunar dust into a Lagrange point, reducing the amount of sunlight hitting the Earth by fractions of a percentage.

The Lagrange point is not perfectly stable, so the dust naturally dissipates over a 10-20 year timescale. If you don’t keep sending more dust, the “planetary sun-shade” naturally dissipates, so there’s zero risk of overdoing it.

Basically, within the next ~50 years, I predict we will gain the ability to turn down the planet’s thermostat in a very safe and predictable fashion, without having to pollute our own stratosphere. Overheating the planet becomes a total non-issue.

[ComputerGuru]

How much dust would you need to shoot up to affect a statistically significant change in the amount of sunlight getting through?

[zaroth]

A fuckton.

Roughly 100 million tons annually of lunar regolith launched into L1 by railgun.

https://journals.plos.org/climate/article?id=10.1371/journal...

[ComputerGuru]

:blink:

And this was being discussed credibly as "something we'll be doing in the near-term future?"

[SoftTalker]

> within the next ~50 years

Very optimistic. We haven't even been to the moon again in 50 years.

500 years, maybe.

[bbor]

With all seriousness, I’ll throw in “the unexpected breakthroughs in intuitive AI will aid this effort.” I sincerely think that LLMs will at least make R&D cheaper.

Beyond that, “we haven’t been to the moon” isn’t a fair summary of our tech imo - a HUGE portion of that is political in origin, and private companies have invented reusable rockets which is pretty damn important

[tremon]

I sincerely think that LLMs will at least make R&D cheaper.

How, exactly? Because to me it's just as likely that LLMs will hallucinate alternative solutions based on their flawed world model which will send numerous unfortunate researchers on wild goose chases that turn out to be exactly that. And I expect the volume of impossible-yet-probable-sounding solutions will dwarf the actual costs saved by using an Automated Induction system.

[lloeki]

> There is no "ecosystem" that depends on the rate of slowdown of Earth's rotation

I mean, raise acidic/temperature levels only so slightly and it kills off coral reef, which in turn destroys fauna that depends on it, leaving huge areas barren.

What I'm getting at is that small changes can have dramatic domino effects. Mass-scale tide dampening could have unforeseen effects.

Not saying any of the solutions are going to be a problem, merely that it's better to ask crazy questions about what happens when they ramp up at scale than handwave things away with uniform spherical cows.

[Karellen]

> at this rate the Earth will stop rotating in 50 billion years,

That's not what the link you posted says. It states that that's when the Earth-Moon system will be tidally locked, so that the Moon orbits the Earth at the same rate that the Earth rotates around its axis.

Kind of if the earth slowed so that one "day" took the equivalent of 28 days now. The earth would be locked with one side always facing the moon, so there would be no tides, but it would still be rotating. Except it will end up be a longer "day" than that, because as energy is transferred to the Moon its orbit is raised, which slows it down.

[piaste]

You're right, my mistake.

Ignoring for a second both the human factor and the Sun having gone red giant much earlier... I wonder what kind of ecosystem that would create. If the Earth were tidally locked to the Sun (which is what I was picturing in my confusion), it would clearly end up as two deserts with a tiny strip of life along the twilight circle. But how would complex life evolve to adapt to a 28*24h day/night cycle? We do have decently-sized ecosystems in caves so long nights aren't insurmountable, but being baked to really high temperatures for a month and then cooling down to freezing for another month sounds like quite a challenge.

[dylan604]

This is nice and all, but in 50 billion years, the moon's distance from the Earth will much greater which means it's gravitational effect on Earth will be much smaller.

[Karellen]

OK. Do you have any reason to suspect that the people making their calculation didn't take that into account? Of all the things that will vary over time, including the distance between the Earth and Moon, do you really think they'd have missed the fact that the Earth's gravity varies with distance?

If you've got what you think is a more accurate number, and can show your working, I'm sure the wikipedia editors would be willing to take a look at it.