Robin Hanson and Bryan Caplan are having a cross-blog debate, or at least discussion, about Robin's book Age of Em. Without going into the specifics, I get the feeling that there is a certain disconnect right from the start.
Robin thinks that the em world will develop so quickly, and contain so many people compared to the outside meatspace world that we can treat the latter as static and uninteresting; and besides, the em world is what the book is about!
Bryan on the other hand finds it hard to think of the ems as people at all. After all, they are just computer programs interacting through software; the whole em world is just one big video game. The real people are the ones on the outside.
Allow me to propose a scenario which I think has at least a chance of engaging both points of view. Let's assume a level of technology roughly equivalent to that in Age of Em, i.e. the ability to scan a brain down to a level where you have captured all the essential detail. Below this level we will assume that we have studied the structure of neurons etc in general all the way down to the molecular level. But we will also assume that we have a fabrication ability to match. So when we have scanned a brain, we will simply rebuild it, molecule by molecule.
What do we do with such a brain? Why, we put it in a vat, of course, and let it think. We put the vat (it's only 1.5 liters) in a giant factory-like building along with lots of pipes and pumps and tanks of nutrient fluid, and enough computing hardware to run a virtual world simulation for each brain. Note that the level of understanding of our neural circuitry (and amount of computation) necessary is just the same as in Robin's em world.
Now are these BiVs ("Brain in a Vat") really people? After all, we could instead of copying them molecule for molecule, simply have taken actual human brains and put them in the same BiViac (sorry). Furthermore, we now have a situation on which philosophers from Descartes to Bishop Berkeley have weighed in for centuries. BiVs think; therefore they are.
The BiV world has many, but not all, of the features of Robin's em one. A reasonable level of nanotech lets you build a brain in well under an hour. One obvious place to get the material is deconstructing a previous brain, copying off a record of its fine structure if you care to. Everbody gets to live in a fantastically splendiferous virtual world, shared or not at their whim. You can teleport, you can fly, you can have a city with a million flying cars and no traffic worries, because the cars simply go through each other.
The big difference would be the lack of a brain-speed control knob.
How are we to measure the income and wealth of a BiV? Each one can have, to all apparent physical purposes, anything he wants. In the real physical world, all he needs is a fixed supply of "juice" (under which rubric we will include both nutrients and electricity for the VR system, pumps, etc). "Fixed" is the operative word; in some sense it is not possible to make him any better off, physically, than he is at a "subsistence" level.
What is subsistence level? One easy way to guess is the energy input, some of which is direct power and some of which gets backed out into the manufacturing process for the nutrients. Grand total for a full human body is 100 watts; nanotech manufacturing brings the capital cost down to a level we can ignore for the moment. So the BiV at current typical power prices needs 24 cents per day, or less than $100 per year.
So that's subsistence, in a virtual world of limitless luxury. The main reason a BiV would want more money would be prestige, status, to have things others didn't that were only valuable because they were rare, and things in the real world. So he might work hard for that, if he were ambitious. But given that people need so little for the baseline, it's hard to imagine how they could be so unproductive as to have to work more than a few days a year if they didn't want to.
The average American (including children, the elderly, etc) produces nearly 500 times as much in economic value than the BiV subsistence. If we start with a selection of motivated, intelligent people, one can guess that they would be at least 5 times as productive on average. A factor of 2500 is a long way to fall in productivity, even if most BiVs spent most of their time sending pictures of cats to each other.
On the other hand, one can sink a virtually infinite amount of time into software. A large part of the internal effort in a BiV (or em, for that matter) world would be spiffying and decorating the virtual worlds, which would do nothing as seen from the outside in the real world. I think that the real question in either formulation would be how much of the effort went into really useful productivity enhancement tools, and thus tended to counteract the diminishing returns to adding more brains.