Science
The Time Machine
By JOHN WILLIAMSON H. G. WELLs's time machine is a nice piece of Victoriana—perhaps the only machine ever described, except the first Centurion tank, about which no one has ever had the remotest idea how it might conceivably work, or what we would see happen if it did. With its comical patent leather and chromium glitter and its one lever, it was an intriguing and imaginative conception. What exactly would it be like, to travel in time? Is it an inconceivable thing to do; or is it merely something no one has yet thought of a way of doing?
It seems to involve detaching one person from the public Now, and providing him with a private Now which, no longer anchored to the kind of progress everyone seems obliged to make together in time frees him to make an independent progress or regress. It may be there is a palpable absurdity in this idea, like asking if God can create a rock that is too heavy for Him to lift, but nobody has ever been sure. The suspicion that it might be possible has been the germ of fantasies about spirits and visitations, Priestley plays, zany philosophies like Dunne's, sundry prophecies, predictions in dreams and advance information about the end of the world.
Not a propos of this, a lady in Sweden with the disturbing name of Madame Frankenhaeuser has been doing experiments on people in the best Wellsian manner. She found in 1957 that—with- out allowing mental or verbal counting— people's estimate of a time interval is quite accurate up to about 5 seconds, but above that tends to become more inaccurate, always by underestithating. The general rule is that the longer the time interval, the more we tend to underestimate, up to a period of 20 seconds, which was the limit in her experiments. Now she has found that this subjective inaccuracy in the estimate of time can be accentuated by centri- fuging people. People who had previously pressed a buzzer after about 16 seconds when they thought 20 seconds were up, pressed it on average after 13 seconds when they were subjected in a centrifuge to a gravitational stress three times that of the earth's pull, i.e., 3g.
Nobody knows what is going on in a man's brain, or in his mind, when he is judging an interval of time; but in spite of this ignorance, it seems an extraordinary thing that, whatever it is, it should be affected by gravity. It is well known that gravitational stress, as when a pilot pulls out of a dive, produces blackout, due pos- sibly to a fall in blood pressure in the top half of the body, with a reduced oxygen supply to the brain and eyes. Madame Frankenhaeuser's guess is that the consciousness of time depends on the ability to remember a previous time interval, and that gravitational stress in some way abbreviates the memory; though again, why this should happen is equally mysterious.
What is interesting is to speculate what effect this disturbance of the mind by a stress on the body would have on the men who might soon travel into space. A craft leaving the earth's gravitational field will be subject to this kind of stress, so it might be expected that its occupants would have their subjective sense of time altered. According to the results so far, the effect will be that the men's estimate of a time interval will err more and more on the short side as they accelerate more, so that objectively, time is going more slowly than they think. What looks like being a tedious journey anyway Will seem all the longer.
Not only that, but their objective time will be altered in any case. According to the special theory of relativity, a traveller A moving from an observer B at a velocity v will differ in his objective measurement of the time of his journeY on returning to B by an amount shorter by a factor of 1/1-04.2, where c is the velocity of light. This gives rise to the 'clock paradox,' since if all motion is relative, B can claim to have been the traveller, so his measurement of the journeY will be shorter than A's by the same amount that A's should be shorter than his. However, several learned gentlemen whom I couldn't quarrel with about this think that the paradoa is resolvable, and that the practical result is that the clocks of a space traveller returning t° the earth after having accelerated about a good bit among the stars will show his journey to have been shorter than we back home have measured it to be. And the ageing of his body will have obeyed his clocks, not ours.
The amount of the time difference depends 00 what speed he reached, which in turn depends 00 how long he can accelerate for. For travel N' tween the planets, this time effect is very small, but for bigger distances could become large, even astounding. A man accelerating at 10g. (i.e., 10 times the earth's gravity, or 10 times the acceleration of a falling stone) would reach Neptune in 5 days, by our time. By his 1inie, however, it would be 4 days 23 hours 581 r minutes. If he could accelerate even at lg. for long enough, a matter of years, he cou approach the speed of light, and then presumably a long stretch of earth time would pass by, while his clocks and the ageing of his body stood almost stationary. At this rate, it seems an objec- tive possibility that a man could come back t° the earth from space younger than his son. The obstacles are entirely practical. They are the difficulties of generating enough power t° keep accelerating for long enough to reach fast enough speeds and great enough distances, and the question of keeping the occupants alive dor ing the process. These are great enough barriers to ensure that we people here will never have to worry about seeing our fathers through unlver. sity, but the mere possibility of it is dismaying enough.
So we don't need a special Time Machine' ordinary rocket vehicles are enough to shift a man backwards in time relative to the earth. What is not possible is either to send a man into the future, or backwards into his own Past' Further, once a man has volunteered for a stint of this magnitude in space, and done it, there is no way of 'fetching him back' out of the Past' As for the subjective condition of anyone coming back from a really impressive journey, say of five or ten years, having felt as though it 05 fifteen, and not looking (or being) more than a year or two older than when he went, one can, Pljr way of doing a spell in gaol, especially if only surmise. Perhaps it wouldn't be such a ha°416, :dcas were in advance of your time, though there would be a legal problem of how much tineyou had succeeded in doing.
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