Doing the math backwards

Charlie Stross writes great science fiction and a blog which usually leaves me wondering how I can enjoy so much the novels of a man with whom I agree so little. In a recent post he linked to an article by UCSD associate professor of physics Tom Murphy to explain why space colonisation will not happen. Since the site is called "Do the Math" I was expecting some numerical analysis of space colonisation. Instead the article contains lots of reasons why space travel is hard and slow and requires lots of energy and is not likely to be done much more by NASA, but nothing that suggests it violates the laws of physics.

I like physicists. They do real science that gets answers from proper observations. So I was a bit disappointed by the space article and went in search of goodness. There must be some good insight that a physicist like Murphy can offer.

He analyses the growth of energy consumption. Since 1650, total energy usage of the United States has increased by about a factor of 10 every 100 years. If energy production continues to accelerate at this rate, we'll heat the atmosphere to 100C in 450 years. Murphy is not saying this will happen, he is saying that there is a limit to how much energy we will want to produce. So far so good. But how much energy can a person use? Why does it matter?

Once we appreciate that physical growth must one day cease (or reverse), we can come to realize that all economic growth must similarly end. This last point may be hard to swallow, given our ability to innovate, improve efficiency, etc. But this topic will be put off for another post.

So this is to be a Limits To Growth argument. In this other post Murphy talks a lot about the limits to how energy efficient things can be. He is right that it will always take a certain amount of energy to heat food, for example, and that there are processes that can not be improved beyond physical limits. But he seems unable to imagine economic growth without growing use of energy. Doing the same task with half the energy, something that is a routine advance in computing technology, is economic growth. Murphy admits this, but gets hung up on the fact that these other things can not improve. This is a problem, because

As long as these physically-bounded activities comprise a finite portion of our portfolio, no amount of gadget refinement will allow indefinite economic growth. If it did, eventually economic activity would be wholly dominated by us "servicing" each other, and not the physical "stuff."

To which I say: what is wrong with that? Here is what Murphy thinks is wrong with that, and here we get to what may be his fundamental error:

The important result is that trying to maintain a growth economy in a world of tapering raw energy growth (perhaps accompanied by leveling population) and diminishing gains from efficiency improvements would require the "other" category of activity to eventually dominate the economy. This would mean that an increasingly small fraction of economic activity would depend heavily on energy, so that food production, manufacturing, transportation, etc. would be relegated to economic insignificance. Activities like selling and buying existing houses, financial transactions, innovations (including new ways to move money around), fashion, and psychotherapy will be effectively all that's left. Consequently, the price of food, energy, and manufacturing would drop to negligible levels relative to the fluffy stuff. And is this realistic—that a vital resource at its physical limit gets arbitrarily cheap? Bizarre.

This scenario has many problems. For instance, if food production shrinks to 1% of our economy, while staying at a comparable absolute scale as it is today (we must eat, after all), then food is effectively very cheap relative to the paychecks that let us enjoy the fruits of the broader economy. This would mean that farmers' wages would sink far lower than they are today relative to other members of society, so they could not enjoy the innovations and improvements the rest of us can pay for.

The first paragraph simply lacks imagination, but the second one is almost unforgivable. Food production has already gone from being nearly 100% of the economy to a much smaller proportion of it. Are farmers poorer as a result? Of course not. There are fewer of them and each one produces food for more people. This is how food has got cheaper in the first place. A human body needs 100 Watts to work. We could completely automate food production using some multiple of 100 Watts per person which is only a small proportion of each person's energy budget, and there is your almost free food. With this kind of material abundance economic activity can be completely intellectual, no problem at all.

Can growth continue forever after that? It is possible that we will hit some limit of how much computation, and therefore intellectual activity, can be done with the available energy. Ray Kurzweil has tried to calculate the physical limits of computation and his answers are in units of how many entire civilisations can be simulated per second. So the limits are quite high.

This is Murphy's other error. He writes, "I am unsettled by my growing concerns about the viability of our future". In response to these concerns he proposes abandoning growth, not having kids and not eating meat. But he has gone the wrong way. He calculates that there are limits and is afraid of attempting to reach them. If you flip the argument around, what physics tells us is just how much wealth is possible. I have already described how material abundance can be had for very little energy. There is plenty of energy for a much larger population to live a much longer life with no material concerns and as much entertainment and intellectual stimulation as a person could want. Perhaps Murphy knows this, and it is the source of his cognitive dissonance when he writes, "such worrying is not consistent with who I am."