a vortex pulls to the center

Why, when you stir a cup of tea, do the tea leaves all move to a neat pile in the center? Why doesn't it simply mix everything up and distribute the leaves evenly throughout the volume?

replicators

I've mentioned here before about those devices variously called 3d-printers, replicators, fabricators, and 3d prototyping machines. Contrary to what you might think, they already exist, and have done so for quite a few years. I saw one in operation at Swinburne Uni in Melbourne many years ago. A quick Google search will turn up a lot of 3d prototyping companies whose business revolves simply around receiving 3d files and using their machine to create a solid object. MIT is currently trying to create a fairly cheap version that can be distributed. NASA uses such a machine to make a lot of its parts because it often can't use off-the-shelf pieces. There is a project in UK to create a very cheap replicator that will even be able to build copies of itself.

One of the limitations of such a device is the material you feed it to create the final objects. There are various kinds of source material in use, but the most promising seems to be a polymer in powder or liquid form. If you wanted to use one of these machines you'd have to buy this stuff. This would prevent it spreading to the parts of the world where it is needed most -- the poorest places.

But when I say that the next big step will be in creating the stuff out of air, people can scarcely contain their need to roll their eyes. Well, it seems I had underestimated the amount of time till we're able to do this. It is already being done. There are pilot projects working right now that take exhaust fumes from power plants and convert them into oil, using the sun. It should be no great surprise. This is precisely what plants have been doing for hundreds of millions of years: creating stuff out of thin air. (In fact the pilot operations use algae in tanks.)