Saint Augustine was, of course, quite correct. The celestial bodies measure time for us; they do not tell us its nature. Like all too common words, “time” has developed a multitude of meanings. We use it in one sense if we say, “The time has come,” and with a slightly different meaning if we speak of “time and tide,”–to give only two examples out of thousands; therefore philosophers have sought to define the nature of time, and differentiate its meanings. From Aristotle and Saint Augustine to the superb treatment offered by Thomas Mann in the Magic Mountain philosophers have tried to solve their own problem; and from Thales to Herschel the astronomers have been content to measure this aspect of the universe and scorn its nature.
Not until our generation have the two problems touched each other; but recent scientific theories indicate a close bond between the two. When Einstein announced to the world his fourth dimension, the philosophers looked up with startled eyes. Einstein was a physicist and a mathematician. They had not expected to find in him so close an ally. “But that is what we have been trying to say for two thousand years,” the philosophers announced, rather modestly to be sure, for philosophers like astronomers have fallen on evil days. “We have not stated it as well, and we could not point to mathematical proof behind us; but surely we have told something of the sort. Don’t you remember that in the Republic, Plato said that the studies of three dimensions would not, by themselves, completely explain the world. Surely you remember that?” No one answered; no one remembered. “This fourth dimension,” said the world, “is a new idea, and because it is new we must investigate it.”
So far as mathematical proof and manner of statement are concerned, it is indeed new. As often happens, the ideas of philosophers were so far ahead of their time that no one understood them, and the thinkers could not substantiate their theories. Not only the philosophers, but the writers of fiction, have hit at one time or another on some aspect of the fourth dimension, and there have been numerous tales of going back in time. The scientists too, since they learned that light had a finite velocity, have loved to play with a theory of retracing time which involves neither dreams nor miracles. Of course their idea is even more theoretical than the ideas of philosophers and it requires a greater flight of fancy than even the novelists demand; but at least it is couched in mathematical terms and, in a way, it helps us to understand how time and space are related. If only it were possible for us to fly through space faster than the speed of light, then we might be able to see time backward.
A second is a short period of time in our lives. One hundred and eighty-six thousand miles is a long stretch of space. Yet light covers that distance in a single second; and all our calculations are dependent upon its speed. The Moon is 240,000 miles from the Earth, therefore we do not see the Moon as it is, but as it was a little over a second ago. The Sun is separated from the Earth by 93,000,000 miles, so light takes eight full minutes to cover the distance. If the Sun should be snuffed out like a candle flame, we, on the Earth, would still live in complete ignorance and bliss for another eight minutes of time.
The distances are much longer in interstellar space. Our little family group gathered around the Sun can at least follow one another’s actions from day to day; but a message from our nearest neighboring star would take three years to reach this planet, and beyond it the stars stretch out over distances so vast that their light may take as much as 150,000,000 years to reach us. The star, Arcturus, a close neighbor, which received a good deal of publicity a few years ago, is forty light-years away. The rays which left their home in Arcturus when the old Chicago World’s Fair was in progress, were used to start the illuminations of the Century of Progress Fair forty years later. In the same way the Sun’s light, reflected off the surface of our little planet, is traveling outward in space.
Einstein says that nothing can travel with the speed of light, yet in imagination at least we can take a journey backward through time. In imagination we can do almost anything, so we shall provide ourselves with a comet plane, sit upon its tail, and place a telescope before our eyes. The new telescope which is just being completed is two hundred inches in diameter; but ours would make it look like a doll’s plaything. “Go as fast as the speed of light,” we say to the pilot. Then we settle ourselves comfortably, adjust the eyepiece and take a look.
The world which we should see under such imaginary conditions, would be as strange as the one which Alice found through the looking-glass, and in many respects similar. We start off with what seems to be terrific speed, but our comet plane takes some time to accelerate properly. “Faster, faster,” we cry, as the White Queen cried to Alice. Everything upon the Earth we have left appears to be moving more and more slowly, as if it were under the spell of a slow motion camera. The faster we go the slower the inhabitants of the Earth seem to move. “This is the speed of light,” calls the pilot, and we look again.
“I wonder if all the things move along with us,” thought poor Alice. . . . She looked about her in great surprise. “Everything’s just as it was!”
“Of course it is!” said the Queen. “What would you have it?”
“Well, in our country,” said Alice, “You’d generally get somewhere else if you ran very fast for a long time as we’ve been doing.”
“A slow sort of country,” said the Queen. “Now here, you see it takes all the running you can do to keep in the same place. If you want to get somewhere else you must run at least twice as fast as that.”
And so we must, in any looking-glass or interstellar country; for if we are leaving Earth with the speed of light, then the light rays around us are not changing. They stay with us constantly, and no matter how far we progress, so long as we continue at the same speed, everything on the Earth will appear the same.
“Do you want to go faster than light?” the pilot calls.
“Yes, please.”
Now, as we look through our giant telescope things seem to be changing indeed. We are catching up with the light rays which left Earth before us. Time appears to be turning backward. As we catch up with the years we see ourselves as children, growing smaller and smaller until we disappear entirely. Horses jump with their hind feet foremost over a fence.
In a great stadium a boy picks up a football from the goal line, holds it tightly in his arms, and fights his way backward to the center field. “There’s the King’s Messenger,” said the White Queen. “He’s in prison now, being punished: and the trial doesn’t begin till next Wednesday: and of course the crime comes last of all.” Since we are flying faster than light, that is the order of events.
Still we can hardly believe our eyes. “Pilot, pilot, turn back. Something terrible is happening. I must get back to Earth before everything is destroyed.”
“Pray don’t disturb yourself, good people. That is the Fire of London. It happened over two hundred years ago.”
