Here's Marshall Brain's response:

The conventional wisdom says that the economy will create 50 million new jobs to absorb all the unemployed people, but that raises two important questions:

What will those new jobs be? They won't be in manufacturing -- robots will hold all the manufacturing jobs. They won't be in the service sector (where most new jobs are now) -- robots will work in all the restaurants and retail stores. They won't be in transportation -- robots will be driving everything. They won't be in security (robotic police, robotic firefighters), the military (robotic soldiers), entertainment (robotic actors), medicine (robotic doctors, nurses, pharmacists, counselors), construction (robotic construction workers), aviation (robotic pilots, robotic air traffic controllers), office work (robotic receptionists, call centers and managers), research (robotic scientists), education (robotic teachers and computer-based training), programming or engineering (outsourced to India at one-tenth the cost), farming (robotic agricultural machinery), etc. We are assuming that the economy is going to invent an entirely new category of employment that will absorb half of the working population.

Why isn't the economy creating those new jobs now? Today there are millions of unemployed people. There are also tens of millions of people who would gladly abandon their minimum wage jobs scrubbing toilets, flipping burgers, driving trucks and shelving inventory for something better. This imaginary new category of employment does not hinge on technology -- it is going to employ people, after all, in massive numbers -- it is going to employ half of today's working population. Why don't we see any evidence of this new category of jobs today?

I don't find some of his examples (robotic scientists?) particularly persuasive, but the idea that many low skilled jobs will be destroyed while few high skill jobs created... seems at least plausible to me. That this has never happened before isn't a particularly good argument why it couldn't happen in the future.

I fear that this argument is too sci-fi to be taken seriously by the overly literal personalities that tend to dominate HN, so let's make it clear: he's not actually saying that "robot scientists" are going to take over. Brain is performing a reductio ad absurdum -- he's taking the other side's argument to the extreme to demonstrate the fundamental logical fallacies involved.

We don't need to wait for robot scientists to see the consequences of automation -- it's happening right now. Smaller numbers of skilled laborers are replacing larger numbers of unskilled laborers. To make the argumentative leap that this is a sustainable process, you have to prove that somehow, we will dramatically reduce the number of people who depend on unskilled labor to to make a living. I have yet to see a convincing proof that this is occurring. At best, we seem to keep shifting the kind of unskilled labor that we need, and paying less for it.

I do agree with your arguments, but regarding robotic scientists: automation is pretty strong also in science. combinatorial chemistry is used a lot in chemistry and chip fabrication r&d. And there's even a robot called ADAM that does biology research: he raises hypotheses , plans and executes experiments , analyzes results , and decides how to continue. the whole research loop.

What I don't get is the difference of timelines in his argument. Considering all the fields where supposedly humans are to be replaced by robots we are talking about a point in time probably still a 100 years off. (And we just cannot say for sure that all those activities ever can be sufficiently performed by robots, probably until it happens.) So how are we supposed to know what kinds of jobs there will be in a 100 years time?

My (imaginary) farming and livestock-holding greatgrandfather probably didn't ever imagine someone could make a living out of Search Engine Optimization. Still, despite machines ploughing our fields, we still have jobs. So we probably will have jobs in 100 years time. We just have no idea which ones.