'YES, that's it,' said the Hatter with a sigh. 'It's always tea-time and we've no time to wash the things between whiles.'
This sounded pleasant enough, but, of course, odd too, which was due to the fact that Alice lived before 1908. Since that time, and especially since 1913, a number of gentlemen wearing glasses and looking wondrous wise, and no doubt as wise as they look, have proved to us that it can always be teatime if we care to figure it out properly and get away from a commonplace three-dimensional existence.
To-day any budding physicist can tell you without cracking a smile that 'a conception of the physical world in its objective four-dimensional scheme would merely be an abridged statement of the correspondence of the subjective time-space experiences in the realm of the various senses, and nothing more.' Remember, it is not the Hatter speaking now, but the average serious-minded young man or woman at college, who has been taking notes of the lectures on Relativity given by the Professor of Mathematical Physics. The words used above happen to be those of an Oxford Don, but the professors at almost any other University can put the case just as succinctly. Perhaps at the University on the Cam they discuss gravitation, space, and time more than elsewhere, which is natural when we recall that Sir Isaac Newton himself and Lewis Carroll were once undergrads there and, later, professors. The Cambridge Professor of Astronomy is easily a leader in demonstrating the new Einsteinian theory of gravitation. Sir Isaac never had a theory of gravitation, only a law; but Einstein has both theory and law.
Our professor says that if we would only let him 'interpose some kind of dispersive medium, so that light of some wave-length could be found traveling with every velocity and following every track in space-time, then, if we were looking at a solid which suddenly went out of existence, we should receive at the same moment light-impressions from every particle in its interior, supposing them self-luminous. We actually should see the inside of it.' Now, this would surely have satisfied Alice, for she did so want to know what the flame of a candle looked like after it was blown out. But even Alice did not yearn to see the insides of things-in-themselves; and besides, if it is to be always tea-time, as these professors can easily bring about, it will perhaps be more pleasant not to see more than the insides of the tea-cups.
Alice's friend the March Hare had a watch which he looked at gloomily. He had used butter on it, the best, too; but, as the Hatter said, 'Some crumbs must have gotten in as well.' But that is a trifling matter compared with the six clocks that our professor has on his mantel, all good time-keepers and set right. Yet he can make you view them in such a way that the clock on the extreme left indicates noon, the clock next to it points to eleven, the third clock to ten, and so on. If the mantelpiece were long enough and he had clocks enough, he could turn to-day into yesterday; and, we could all say together, 'How queer everything is today, and yesterday things went on just as usual.'
On this side of the Atlantic, a professor at Columbia tells us in a snappy little volume that, if we could only look far enough straight before us, we would in time see our back hair, if we had any. Or if a man goes to the top of a high mountain and aims a gun in any direction and shoots, provided the bullet goes fast enough, it will whiz round the world and on its return hit him behind the ears. Which goes to prove that it may be dangerous to stand back of some marksmen.
Or, again, let a man start for Arcturus. By terrestrial chronology, it will take one hundred years, traveling at the rate of one hundred and eighty-six thousand miles each second. When he arrives at Arcturus, some professor of mathematical physics at the leading University will say, 'How do you do? I timed your start. Of course you have not had breakfast yet?' The explanation is that, traveling with the speed of light, the yard-stick or light year shortened almost to zero in the line of travel. Now here we have one way of getting eternal youth.
Alice longed to be able 'to shut up like a telescope'; and she thought she could if she only knew how to begin. That's just it. One must know how to make the right beginning. And the modern theory of general relativity does seem to prove that we have never started right on earth. We thought we were standing still, while all the time we were hurrying so fast that it makes one's hair stand up on end just to think of it. Why, since you began this article, say five minutes ago, you have flown through space thirty-eight hun-dred miles.
And that is not all. For no one can be sure of his shape now; because size depends upon speed. All motion is relative. If Alice had moved fast enough she could have diminished her weight. All students of physics to-day know mass and energy are essentially same thing.
Einstein's law is practically this: 'The gravitational mass of a body is equal to its inertial mass.' If, when we were reading Alice long ago, we had in a moment of forgetfulness written the above on our final examination papers in mechanics, it is a certainty that would have cost us our degree. What distress of mind it would have our old instructor if we had said things—that is, assuming that professors really feel keenly such errors! And to-day the point of view has changed. If a conscientious old instructor in mathematics insists that a straight line is the shortest distance between two points, he will soon be enlightened. Or if someone quotes Herbert Spencer's dictum that the proposition concerning parallel lines not meeting at infinity is undemonstrable, because no one could go there, mathematical proof forthcoming to show that the lines may meet because of a warp in space which makes them geodesics. Up to now lived in a three-dimensional world, but the coming generations will be only with a fourth.