It's time to attempt some sort of summing up. We've left the Special Theory so far behind that I'm not going to return to it now. Anyhow, since it's so generally acknowledged as a well-established theory that lies at the roots of so much of today's scientific thought, what is there to discuss? The General Theory is a more interesting topic–still subject to active controversy.

Let's begin with a limitation. It never lived up to its title, with the suggestion of a great all-round generalisation of the Special Theory. It turns out, as I said in the Introduction, to be only a theory of gravitation, and as such we must judge it. So let's start by comparing Einstein's theory of gravitation with Newton's at a philosophical level. You'll know by this time where my preference lies.

Please reread §§26.46–7. There we have one reason for preferring Einstein's outlook: at the most basic level it involves one assumption fewer than Newton's. And so (although technically more complicated) it is simpler in principle. And most of us would agree (though it's hard to say precisely why) that simple explanations are philosophically preferable to complicated ones.

We can't, of course, blame Newton for being more complicated–the Einstein approach was inconceivable in his time. But we can note what caused him to be so. And that is simply that his theory begins by saying, in essence, ‘If there were no gravity’, things would behave in such and such a way. That's unsatisfactory, because you can never find true no-gravity conditions in which to test its truth.