Galactic-Scale Energy

[jamesr]

Here’s an interesting write-up on the absurdity of continued energy usage growth on Earth
http://physics.ucsd.edu/do-the-math/2011/07/galactic-scale-energy/

[Matt M]

Be that as it may – half of the people on the planet still heat their homes and
cook using either wood or dung.

[jamesr]

Even if we all cooked & heated our homes that way, it doesn’t change the argument – just delays it slightly.

A large part of the historical growth is down to population increase rather than per capita usage. So, even if our average usage was burning 500W of wood rather than 2000W of fossil fuels then we would still reach resourse limits, just a few years later.

Although, of course, since we’re not going to be able to cover the whole world with solar panels, and still have space for food we will reach the limits much sooner, and the population will plateau around 2070, or even go into catastophic collapse.

All new technologies like fusion power will do is push back the dates a little.

So I guess the question is: If we manage to get to a sustainible population level, so energy use only grows with the supply of new resources (deeper mines, asteroids etc) and improvements in energy production/efficiency. When do we outstrip the Earth/Sun etc. ?

eg. if of (using his figure) the 2.3% historical growth in energy half was due to population growth, then rather than 350 years before the resultant heat from our energy use heats the Earth significantly, maybe it gets pushed out to 600 years.

If we use anything other that Solar for our energy source, and since if we use it to do work then it ends up as heat eventually, then it will heat up the Earth.

[dennisp]

Stewart Brand’s new book Whole Earth Discipline talks about population. He says the world is urbanizing very rapidly, and when people move to the cities they have a lot less kids. Kids are an asset on the farm, a liability in the city.

Right now humanity is a little over 50% urban. We’re rapidly progressing to about 80%.

The replacement rate is 2.1 children per adult. Many countries are below that now, some well below…I think the lowest he mentioned was 1.3. Many of these countries still have a lot of kids around, but as those kids get older and even more urban, their populations will drop rapidly. By 2050, the global population will start crashing.

(Only two countries are urbanized and maintain population growth: France, because they have extensive social programs to support parents, and the U.S., because it has immigration and lots of religious families who have kids because the bible says to be fruitful and multiply.)

On the other hand, with cheap fusion we’ll probably use a lot more energy per capita.

I think the answer is that we’ll expand into space. With compact fusion available that’s a lot easier to do. Expanding throughout the solar system gives us a lot of growing room.

Nevertheless, the article makes a good case that some time in the next few thousand years, even the solar system will run out of room. Hopefully within a thousand years or two we’ll be able to figure out how to put the economy in a steady state.

Or, maybe by then, people feeling crowded will put themselves in deep freeze and head for other stars. By the time the whole galaxy gets crowded, they’ll ramp up to a high percentage of the speed of light so the time dilation kicks in strong, and head to other galaxies. It might take billions of years to get there, but if you’re going close enough to lightspeed the shipboard time could be only a few years.

Nevertheless, from the POV of the people left behind it’s still a billion-year trip, so the rate of energy expansion drops enormously.

In short, as long as we get off this rock I don’t think this is going to be a problem.

[jamesr]

Have you seen this interesting TED presentation by Prof Geoffrey West on the scaling laws inherent in urbanisation

http://www.ted.com/talks/geoffrey_west_the_surprising_math_of_cities_and_corporations.html

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