[blake1]

The single most important assumption in this paper is that energy consumption will increase by 2% per year. This kind of exponential growth leads to outlandish estimates for the amount of tidal energy that society will demand.

Energy consumption has decoupled from population growth rates and economic growth.

How much energy will we consume in 1,000 years? Most projections of the population have it stabilizing at around 15 billion. But continuing at its current growth rate (an optimistic assumption I think), gets us to about 150 trillion humans in 1,000 years.

And at 2% growth rate, each of those humans will consume 20,000 times more energy than a circa 2023 human.

Now state of the art technology wastes about 80% of the energy consumed, so this is equivalent to 100,000 times more useful energy consumed per human.

So the physics in this page is a good examination of the surprisingly large compounding effects of unchecked exponential growth.

[RetroTechie]

> 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.

[onlyrealcuzzo]

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.

[hollerith]

>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.

[ricardobeat]

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.

[pmontra]

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?

[codethief]

> The single most important assumption in this paper is that energy consumption will increase by 2% per year. […] How much energy will we consume in 1,000 years

I keep posting this link here on HN but, once again, it seems very appropriate:

> The upshot is that at a 2.3% growth rate (conveniently chosen to represent a 10× increase every century), we would reach boiling temperature in about 400 years.

https://dothemath.ucsd.edu/2012/04/economist-meets-physicist...

[jl2718]

When the nuclear apocalypse has passed, and the last remaining humans are living underground on mushrooms, somewhere an economist will claim growth using a model updated to include the work done by ants, and somewhere a bureaucrat will update the tax code to collect on it.

[casparvitch]

If HN was reading Murphy the front page would look very different every day

[istjohn]

A global cooling system is easily conceivable. The ISS uses radiators to dissipate heat into outer space. We could do the same. We could concentrate heat with heat pumps and pump hot steam, molten salt, or plasma up a space elevator and radiate the heat away.

Edit: The link points out that in 1,400 years we'd be using energy at the rate produced by the sun and in 2,500 years at the rate of the entire Milky Way. Even if we solved the heat radiation problem, it seems unlikely we'd be able to obtain fuel for our fusion reactors at a sufficient rate given the speed of light and the density of matter in the universe.

[nvm0n2]

That's not a great argument by the physicist, the economist definitely won that debate. The physics guy only seems to realize that though when he wakes up the next day and has calmed down a bit.

Although the link is useful for the thermodynamic calculations, there are two major problems with the argument as presented:

1. Right up front the physicist arbitrarily bans space travel. The economist, being an agreeable man who'd probably rather be making smalltalk with a pleasant member of the opposite sex rather than defending his whole profession to a bolshie physicist, accepts this limitation, but he shouldn't have done. Nothing in economics is predicated on a space travel ban. We are already obtaining economic growth from space via satellites and that era has barely got started. None of the physics arguments work if you make the relatively small leap to putting factories, power plants etc on moons, asteroids, space stations or other planets. This doesn't require colonization assuming progress in robotics.

2. Much more seriously, the physicist doesn't understand what growth or wealth mean in an economic context. The economist tries patiently to explain this to him many times, and he just doesn't get it. This is a very common problem when talking about economics because people aren't used to the expansive definition of wealth economists use, so often conflate it with other things like money or (in this case) energy.

You can increase wealth indefinitely even with a stable population and stable energy/resource usage. This isn't controversial or weird, it's just part of how wealth is defined. The VR example is one attempt, dessert another attempt to explain this to him, but he just doesn't get it until the next day when he suddenly has an epiphany but decides it wasn't his fault because he personally distinguishes between "growth" and "development". No such distinction is recognized by actual economists for valid reasons. But you don't get to claim there's a problem with economics just because you failed to understand the lingo of the field.

[joak]

This boiling temperature conclusion makes the assumption that we continue using thermal power (steam engines, etc...), where waste heat is around 60%.

However photovoltaic and wind does not produce much waste heat. Arguably solar and wind cannot scale 1000x but then you could have non thermal fusion like Helion's https://www.helionenergy.com/technology/.

Btw, thermal power is already showing limits (rivers overheating in summers), we don't have to wait 400 years to see its failure.

[dredmorbius]

The lesson that constant percentage (that is, exponential) growth cannot continue endlessly is the fundamental message behind the concept of Limits to Growth. That is, there exist intractable limits to growth, and that no matter how convenient it may be to pretend otherwise, humans ignore this fact at their extreme peril.

Long-term ongoing economic growth, expressed as a constant percentage, is baked in to most current orthodox economics and economic policy. Even apparent mavericks such as Thomas Piketty assume that growth will continue interminably (noted in Capital in the Twenty-First Century).

Rather than being a critique of Liu, you've actually written a criticism of those he himself is generally addressing.

[kbenson]

> Long-term ongoing economic growth, expressed as a constant percentage, is baked in to most current orthodox economics and economic policy.

Whether it is or isn't, the optimal strategy for a nation is likely exponential growth until it can't, and then switch as quickly as can be done with the least problems.

Since nations are competing, and we're talking about exponentials here, the cost for cutting off exponential economic growth too soon is likely to become irrelevant to the future, which every nation is going to strive to avoid.

[xg15]

I think there is one escape from this, basically confining more and more "growth" to artificial numbers on paper (or in a DB).

Cryptocurrencies are kind of going in that direction, where the "value" that is reported as economic growth doesn't correspond to any kind of real-world matter or activity, but is simply assigned to some specific group of bits.

I can kind of believe that this virtual kind of growth could continue a long time without boiling the planet, but of course that doesn't make things less absurd, as the "value" would represent nothing objectively useful and would have to be maintained artificially - either through scarcity mechanisms like PoW etc, or through locked-down devices and ecosystems.

So that kind of "growth" could go on forever without burning the planet but would probably be a step back for civilization.

[snowwrestler]

Constant percentage economic growth is possible indefinitely because the economy is made up.

It’s like saying “you can’t imagine a bigger number than I can.” A person can always imagine a bigger number, and the marginal cost of doing so is merely what is necessary to store the larger number in a ledger.

[felipeerias]

> Long-term ongoing economic growth, expressed as a constant percentage, is baked in to most current orthodox economics and economic policy.

As a forecast which may or may not happen? Yes.

As an actual outcome that has been decided a priori? No, not at all. Only planned economies tried to do that.

[slt2021]

it is possible to have exponential growth with a brief period of financial crash/recession, when prices reset to previous bottoms and exponential growth continues (boom&bust cycle).

so far it has been the case with human economics across all countries/economies. yes some shareholders will be zeroed out during recession, but others will continue on the growth journey

[bobthepanda]

The UN has revised peak projections down several times; the peak is now expected at 10 billion.

[coldcode]

More countries are now sub-2.0 replacement, China is down to 1.09 so the peak is unlikely to get much more than that.

[quotemstr]

Almost every human population is under strong selection pressure towards having more people. This dip in fertility cannot and will not last.

[api]

20000X the energy of a current human shows how absurd it would be for growth and energy use to not decouple. I can’t even imagine what I could do on Earth using that much power. Fly my own 737 to a new city every day?

I suppose spacefaring humans might use that kind of power but if they are living in space they are no longer part of the biosphere of Earth.

[ben_w]

> I can’t even imagine what I could do on Earth using that much power. Fly my own 737 to a new city every day?

Sure, why not?

It's absurd today for the average person, but it's the kind of thing rich people get to do already, and looking at the rich today is a decent (though imperfect because inflation and invention don't work like that) hint for what normal people can afford in a richer future.

[rodgerd]

> Fly my own 737 to a new city every day?

That's literally the billionaire lifestyle.

Meanwhile cryptocurrency is seeing decades of power efficiency undone as miners bring old power plants online and want to burn tyres to power their scams.

[asah]

Consider modern use of energy vs ancient, and the ancients couldn't imagine our factories, power plants, data centers, etc. Now consider the crazy compression of energy in the conversation to LED lighting.

In the future, we might use a lot of energy for the we cannot imagine today.

In the future, we might stop using every the way we do today.

In the future, we may produce and consume substantial energy in places other than earth's surface.

In the future, the concept of energy itself might be different, much like people couldn't imagine the type of energy involved in nuclear fission.

[cryptonector]

With this analysis no energy source is renewable, and we'd even run out of sunlight (or surface area that can be dedicated to solar power anyways, or see demand exceed solar power were we to put solar panels on every square inch of the planet's surface).

In reality we're already certain to hit a population maximum in just two+ decades, and not only that but the world is very likely to be on a negative population growth curve after that for some time. And we're going to need some new tech revolution to drive energy demand in developed countries up much more than it is, and the developing world's per-capita demand will not likely exceed the developed world's once fully developed.

I.e., we're not growing forever, the end of population growth is around the corner, and the end of energy demand growth is not much further.

[svnt]

> gets us to about 150 trillion humans in 1,000 years

I realize the big issue is settled here but just to scope this detail: the total land area of earth is coincidentally approximately 150 million km^2

At 150 trillion humans each human would get just about a square meter. Many of those square meters are uninhabitable.

[midasuni]

That’s about the density of Kowloon walled city. And ignores the available space in the ocean.

[ChuckMcM]

Extrapolation is always a bad thing :-). That said, this guy has some interesting thoughts. Of course he misses out that if you pump the tides you can speed up the rotation of the earth and thus "renew" the lag (think moving your legs while swinging).

Similarly solar isn't renewable because at some point the Sun is going to run out of hydrogen, and if you made a dyson sphere to capture all of the Sun's energy you would wipe out life on earth.

[solalf]

Peak human population is expected to reach 10.4B in 2084 and slowly decrease from there. This is according to the UN[1] but other estimates envision a much earlier peak by the 2040s at 8.5B followed by a sharp drop to 6B by the end of the century[2].

[1] https://www.un.org/en/global-issues/population

[2] https://earth4all.life/news/press-release-global-population-...

[bufferoverflow]

1000 years is a loooong time. It's entirely plausible to have trillions of humans, if we create conditions for that. And not only on Earth.

For that to happen we need almost complete automation, which would provide cheap food, cheap housing, cheap healthcare, and lack of worry about the immediate future.

Even if you can sustain 1% increase in population per year, 1000 years of prosperity will result in

(8 billion)*(1.01^1000) = 167673 billion = 167 trillion people

(1% is roughly the current population growth, but it's slowing down)

[sidewndr46]

If you assume 2% increase per year, anything is irrelevant. Nothing can allow humanity to sustain unbounded energy growth on a single planet.

[georgeecollins]

15 billion as a stabilized population of the Earth is actually a very high estimate. Some estimate the curve will flatten at 10.5bn. But it is all a prediction, so who knows.

https://en.wikipedia.org/wiki/Projections_of_population_grow...