Galactic-Scale Energy (2011)

https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/

75 58 4 years ago

dothemath.ucsd.edu

akira2501• 4 years ago

Thankfully, the planet contains abundant stores of Uranium.. and we are nowhere near peak efficiency in commercial and industrial processes. These one dimensional analysis of the problem are particularly useless, especially when their only conclusion is "we must stop growth."

The average power usage may well be 2000W, but how many average consumers are there? If we're facing a multi-mode distribution of those users, then this "stop growth" strategy instantly creates new "castes" from this distribution. As a long term strategy, it seems doomed in one way or another.

api2• 4 years ago

These analyses have been predicting doom for decades. They just keep moving the goal post.

Arthur8• 4 years ago

Huh, I had to re-read the article.

"But let’s not overlook the key point: continued growth in energy use becomes physically impossible within conceivable timeframes." (conceivable timeframes ~ few 100 years)

As far as I understood, the argument is not "we are doomed" but that there is a natural limit to the growth of energy consumption in the not too distant future using some naive assumptions. In any case, it is implying that 2.9% growth per year is a lot! if it is extrapolated by just a few 100 years. Do I misunderstand something? Why is this controversial?

But I did not yet read all the linked later posts.

lumost2• 4 years ago

The article accounts for this in average earth temperature. The earth’s surface would be hotter than the sun in 1000 years, and would generally be uncomfortable after 200. The only way around that would be a substantial change in the thermodynamic efficiency of our energy use and/or a non radiative means of disposing of heat.

Granted, if we did have the equivalent energy of a sun - we are unlikely to be spending it all on earth. Escaping earths gravity would be a trivial expense.

whatshisface3• 4 years ago

That thermodynamic argument was the least convincing part. If you wanted to, you could beam your power plant's infrared radiation towards space, or put the plant itself in space and have it beam its waste heat away from the planet. The idea that heat dissipation is limited by the black body radiation of the Earth assumes that your house is part of the power plant's radiator, which itself implies that you will be living in a power plant's radiator. :-)

TheOtherHobbes2• 4 years ago

Large parts of the Earth's surface are going to be generally uncomfortable within 10 years, never mind 200.

AtlasBarfed2• 4 years ago

There's no way we achieve the higher powers of ten without a big infrastructure migration to space. Really that's the promise of those higher powers, you move from a terrestrial to a at least a solar civilization.

AtlasBarfed2• 4 years ago

Only a small fraction of Uranium is usable for fission without breeding. There is (IIRC from a LFTR youtube) 4-10x as much thorium as uranium.

The other issue is most designs are solid fuel rod, and they waste a huge percentage of the fuel once "spent".

Nuclear isn't price competitive with existing wind/solar, and any new nuclear project is 10-20 years away, and with wind/solar in substantial/active cost improvement and economies of scale, nuclear may never be competitive.

I loved those LFTR presentations, and I would like to think a scalable LFTR solution could be made price competitive with wind/solar once it stabilizes, but right now probably not.

LFTR can use thorium (still needs a fissile uranium starter plug), and can probably breed non-fissile uranium, I've heard it can breed existing nuclear waste into usable fuel as well. It uses 99% of the fuel according to the sales brochure, which I view as a massive huge advantage: it takes all the handwringing and NIMBY about waste storage out of the equation. IMO that should be a table stakes for any "new nuclear" design.

It's basically meltdown proof with the plug, isn't pressurized, and somewaht self-regulating in temperature if I understand the neutron economy and expansion/contraction of salts. Also a "table stakes" aspect of any new nuclear project IMO.

Scalability is probably the biggest path forward to competitive fission as well, the original MSR at ORNL was allegedly closet-sized. Massive concrete dome designs lend too much to boondoggle management and cost overruns. Scalability would enable nuclear to compete with the current kings of scalable power generation: wind and especially solar.

Maybe pebble bed can get a lot of the same table stakes as LFTR. Maybe a LFTR could serve as an onsite fuel reprocessor for a more economical design if LFTR isn't broad market feasible. I'm not a nuclear engineer, I'm just a fan of the ultracool engineering and science.

But the economics don't line up for nuclear currently.

pdonis• 4 years ago

The article leaves out a crucial point: the main driver of growth in energy usage is growth in human population. The human population of Earth is expected to level off this century. So any projection beyond that that assumes continued energy growth at the same rate is not realistic.

zamalek• 4 years ago

The article does mention this:

Chiefly, continued energy growth will likely be unnecessary if the human population stabilizes.

aaaaaaaaaaab• 4 years ago

In other words: the exponential function grows very fast.

NickM• 4 years ago

I don’t think most people advocate for indefinite growth of energy usage; when people talk about sustainability of growth they are typically referring to economic growth. This has often been correlated with energy usage in the past but there’s nothing that says it has to be that way, and indeed there are a number of countries that have shown that decoupling the two is possible: https://ourworldindata.org/energy-gdp-decoupling

api2• 4 years ago

It tends to be tightly correlated to energy use up to a certain material standard of living. At that point they start to decouple.

mbbutler2• 4 years ago

They don't even decouple at high material standards of living. Recent increases to GDP produced emissions too but those new emissions were offset by reductions in emissions of existing industries.

This "decoupling" gets us basically nothing because it's not like we can just stop emissions tomorrow since GDP and emissions are "decoupled".

jillesvangurp2• 4 years ago

There's nothing wrong with energy. It's just that certain ways of producing energy are destroying our planet. Now that we have better and cleaner ways of generating energy, we can resume coming up with creative ways to convert energy into useful things like food, transport, computing power, clean water, etc. There is no shortage of ideas on that front. But we've kind of been sitting on our hands here because energy is an expensive bottleneck.

Transitioning all of that to sustainable processes, is the game changing transition that is defining this century. It's happening very rapidly now. And yes, I do believe we are going to see an unprecedented economic boom as well. Last century was nice. This one is going to be better.

Jweb_Guru2• 4 years ago

This article (and site) are pretty great, and helped shape a lot of my worldview. It tends to throw a bucket of cold water on a lot of the arguments regularly made on this website, though, so I'm surprised to see it here.

epistasis2• 4 years ago

What sort of arguments do you see made on this website that this would refute?

rimeice• 4 years ago

Presumably that much of the tech industry and the way it’s funded is built on the assumption of boundless growth.

yrgulation• 4 years ago

I have always been impressed by the fact that as much solar energy reaches Earth in one hour as we consume in a year. What hope such a statement brings! But let’s not get carried away—yet.
The abundance of deuterium in ordinary water would allow us to have a seemingly

I mean isn't it obvious that we are missing opportunities here? Are we really that complacent that we can't achieve anything on a grand scale anymore? Plant solar panels everywhere that there is not agricultural land and meets the criteria for energy efficiency. Fill in the all the roofs. It's vacant space. Spend billions more on fusion research.

The merciless growth illustrated above means that in 1400 years from now, any source of energy we harness would have to outshine the sun.

Hopefully by that time we'd be an interplanetary species. Unless we imagine we can keep digging all the way to the core to extract resources down here. When all the good stuff is literally sitting out there waiting for us to plunder.

Chiefly, continued energy growth will likely be unnecessary if the human population stabilizes.

I doubt our insatiable hunger for more, more, and more will stop anytime soon - even if the numbers stagnate, our egos will grow bigger and bigger and we'll want more and more. It's in our nature. So why not go beyond our planet for that never-ending "want"? Consumer everything that's out there and turn into shiny new crap for down here. Once we are done, eject it into the sun and keep the earth tidy.

tener• 4 years ago

Feels like a similar methodology here https://xkcd.com/605/

iso16312• 4 years ago

It does, and you can see at the end of his list a tapering of the growth. US energy consumption has grown 1% in the last 10 years, not 1% per year, 1% in total. Now sure, some of that is offset by some shift to imports (energy is expended in China, for the benefit of the US), but not all of it.

However had energy use increased at 2.9% since 1990 it would be nearly twice as high as it really is (4.2GToe vs 2.3 in 2018)

The Earth as a whole, with rapidly industrialising countries like China and India, global energy use from 1990 to 2018 only increased about 1.5% per year.

The world is becoming more efficient, and ultimately there is a limit to consumerism - I personally use less energy today than I did 20 years ago, and I'm sure that's the same for many people in the west. As transport becomes more efficient, there's only so many times you can go on a plane in a year (144 was my own record, but lets say it's 1000), after that point energy use on airplanes can't increase - there just aren't enough hours in the day.

mlsu2• 4 years ago

Filling in the roofs and spending billions amounts to linear growth. (Spend $1, get $1 worth of energy; fill 1 roof, get that area in energy). The argument of the article is that the exponential growth will outshine whatever linear coefficients we throw at it.

Even going interplanetary; that is only linear growth -- go to 1 new sun, get 1 new sun of energy!

Exponential wins in the end no matter what.

chii• 4 years ago

Its only linear because the process is linear as you described. There's no reason why we can't have exponential growth - produce a machine which manufactures more of itself. This machine also contains solar panels (and other appendages) to collect resources to replicate itself.

Then very soon, the earth will be overrun with such machines, and we can go interplanetary, then consume the sun to go interstellar. At least, whoever that remains after the grey goo takes everything else would go interstellar...

ncmncm• 4 years ago

Once we get too big for our britches, the ancient aliens in our way will put us in our place.

carapace• 4 years ago

See also: "Exponential Economist Meets Finite Physicist" which covers the same material in the context of economic growth.

Some while back, I found myself sitting next to an accomplished economics professor at a dinner event. Shortly after pleasantries, I said to him, “economic growth cannot continue indefinitely,” just to see where things would go. It was a lively and informative conversation.

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

cletus• 4 years ago

This is just a bad analysis. You have to go to the comments to find relevant terms like "Dyson swarm" and "Kardashev scale". The worst mistake is limiting energy collection to what hits the Earth.

Here is (IMHO) the likely course of humanity, assuming we don't descend into fascism with the upcoming climate-change caused mass migration and starvation or otherwise wipe ourselves out.

We will build Dyson swarms. What are Dyson swarms? They are nothing more than a collection of orbitals that orbit the Sun. The most basic form of these is an O'Neil Cylinder, which is about 3 miles in diameter and 10-20 miles long. You put solar power collectors on these things and they're pretty much self-sufficient.

Why this size? Because you can build that with a material no stroner than stainless steel. Any larger and the centrifugal force will of rotating for spin gravity will tear it apart. If mass production with graphene ever goes anywhere, it opens the door to building McKendree Cylinder, which could get to ~300 miles in diameter and thousands of miles long.

So the question is why. Several reasons:

1. You can effectively collect all the energy the Sun outputs;

2. This is only predicated on solar power, something we can already build. It isn't predicated on nuclear fusion power generation, for example. I'm personaly not convinced fusion will ever be commercially viable. It might and that'd be great but it's not a pre-requisitie for that and that's what's important;

3. It requires no new physics or no magical new materials; and

4. Here's the big one: it's super-efficient in creating living area per unit mass. I think I saw an estimate that you could build a complete Dyson swarm around the Sun with ~1% of the mass of Mercury. Such a Dyson swarm could comfortably house more than 10^15 people with an energy budget per person orders of magnitude than what we have now.

So a brief note about the Kardashev scale. This is an approximation but a Kardashev-1 ("K1") civilization is defined as using the entire energy output of a planet. This is estimated as 10^16 Watts. A K2 civilization uses the entire energy output of a star, estimated at 10^26 Watts. A k3 civilization is the entire galaxy at about 10^36 Watts.

Humans use about 10^11 Watts (IIRC) of energy. So a K2 civilization might have 10^15 people but have access to 10^26 Watts of power. That's 10^11 Watts of power per person.

The scale of a K2 civilization is almost beyond comprehension.

Firmwarrior• 4 years ago

I'm glad that a few of the influential billionaires out there nowadays calling the shots think along the same lines as you. I grew up under this dark cloud of thinking there's no future for humanity, we all have to tighten our belts and cut way back to survive at all, blah blah blah.

Yet here we are, right on the cusp of realistically exploiting the ridiculously vast resources of the solar system! I'll bet that 50 years from now, humanity will be so rich that even stingy red state welfare will pay for a lifestyle I can barely afford nowadays on my fat tech salary.

ETH_start• 4 years ago

This analysis excludes geothermal and nuclear, which have massive energy potential. Yet even limited as it is, based on its assumptions, we could grow at these rates for centuries, at least, before having to worry about physical limits even within the solar system, so why fret about it now.

Focusing on realizing that growth now would save monumental amounts of energy from being wasted, as the sun radiates it into space, and allow trillions to live who otherwise wouldn't have.

jillesvangurp2• 4 years ago

Yes, growth is logically not going to continue forever. But we are nowhere close to the point that growth will inevitably have to stop.

There's a moral undertone here of course that that growth is coming at a price and that therefore we need to show some restraint. It's a very elaborate argument against energy gluttony. That's a particular world view that seems to never really catch on with the wider public. At least judging from their waste lines.

What does seem to happen is that we are rapidly transitioning to more guilt free forms of energy generation. For example, put solar panels on your roof and you get free kwh for your Tesla and you can turn your AC on as long as you want. Problem solved. That's a consumerist version of reality that is a bit more real in the sense that that is actually something that a lot of people aspire to do at a scale that matters.

Not all energy usage is bad. Energy production growth is fine as long as we do it sustainably. And now that that seems to become the default, the next interesting thing for humanity is to figure out what to do with all that clean, plentiful energy.

mgsouth3• 4 years ago

Forgive me, for I am doing an end-run around a HN rule (replying to a reply to a reply). But it seems an entertaining question...

What if you radiated a Sun's worth of energy (10^26 Watts) out of 1 square meter?

* Blackbody temperature: 2 x 10^8 K.

Peak blackbody wavelength: Wolfram didn't like that question. However, it did helpfully note that it was twice the temperature needed for controlled nuclear fusion, and 5e7 K above the temperature at which the triple alpha process occurs inside stars.

It also noted that it was equivalent to 17 keV. This would, suprisingly to me, be X-rays and not gamma; the cut-off is 100 keV. 17 keV is a photon wavelength of 73 picometers (7.3e-11 m); a helium atom's diameter is about 62 pm.

* Luminosity would be about 4e15 lux. It would, of course, be twice as bright as the sun (equivalent to seeing both solar hemispeheres at the same time.) You would be able to see the Earth from lightyears away.

* Radiation pressure would be 730 x 10^12 newtons (80 gigatons).

* This would accelerate the Earth by 1.2e-10 m/s^2. Even if sited at one of the poles, that's only 4 millimeters/sec over one year. Not useful for jaunting around the Solar System except on geologic timescales.

* Asteroid Apophis is a whole 'nother matter. It's estimated to be 6 x 10^10 kg. Assuming we left its destruction to THE VERY LAST SECOND (i.e., distance 0), the radiation pressure would accelerate it at 36 km/s^2. (Yep. You try it: [0]; it's x 2 because it is reflecting) Of course, it would melt it in about half a nanosecond (literaly).

* Mars' moon Phobos would fare better. Assuming the radiator is a 73 picometer X-ray laser with 1.1 m diameter (1 m^2 area), beam divergence (based on no-doubt-poorly-applicable-in-reality formulas) would be about 2e-11 radians. At conjunction, the Earth and Mars are a maximum of 400 million km apart. Wolfram thinks (it ain't easy calculating the sine of 2e-11) the beam would diverge to about 8 meters wide at that distance. Phobos masses about 1e16 kg. It would only accelerate at 0.14 m/s^2, or 12 km/s/day. And it wouldn't melt for at least 80 milliseconds.

[0] https://www.wolframalpha.com/input?i=730e12+newtons+*+2+%2F+...

taneq2• 4 years ago

sin(2e-11) is almost exactly 2e-11 since sin(x) ~= x for small x. :)

Galactic-Scale Energy (2011)

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