The quantum theory of parallel universes is not the problem, it is the solution. It is not some troublesome, optional interpretation emerging from arcane theoretical considerations. It is the explanation - the only one that is tenable - of a remarkable and counter-intuitive reality.

Is the human race a universal constructor?

To me quantum computation is a new and deeper and better way to understand the laws of physics, and hence understanding physical reality as a whole.

Like every other destruction of optimism, whether in a whole civilisation or in a single individual, these must have been unspeakable catastrophes for those who had dared to expect progress. But we should feel more than sympathy for those people. We should take it personally. For if any of those earlier experiments in optimism had succeeded, our species would be exploring the stars by now, and you and I would be immortal.

The brain is the only kind of object capable of understanding that the cosmos is even there, or why there are infinitely many prime numbers, or that apples fall because of the curvature of space-time, or that obeying its own inborn instincts can be morally wrong, or that it itself exists.

Where we have good, testable explanations, they then have to be tested, and we drop the ones that fail the tests.

The most important application of quantum computing in the future is likely to be a computer simulation of quantum systems, because that's an application where we know for sure that quantum systems in general cannot be efficiently simulated on a classical computer.