understood-or where it still held mysteries, they were not such that sapped the mind. But the thing beneath their feet defied all reason and all logic.
They waited, lost in their own thoughts and saying nothing, merely listening for the first sound of Discovery's beacon as she came up over the horizon. Luckily for their peace of mind, she was exactly on time; still without a word, they jetted themselves up toward her and, ten minutes later, were jockeying themselves through the airlock.
Astronauts are somewhat addicted to harmless practical jokes; it is one of their ways of asserting superiority over the Universe, which has no sense of humor. Kaminski and Hunter might, for a moment, have thought that the others were pulling their legs, but their doubts lasted no more than seconds.
Two orbits later, they went down themselves, taking cameras with long-focus lenses to record the star- patterns at the bottom of the shaft. Within minutes, Kaminski had an additional piece of information. He timed the movement of the stars across the opening, and calculated that it took fifteen hours for a complete revolution-as against Jupiter V's ten. It seemed that, by some magic of space or time, they were looking out into a strange universe through a window in the surface of a world that turned upon its axis once in every fifteen hours.
Kaminski was almost half a mile down the shaft when with shocking abruptness, the window looked upon a different scene.
SOMETHING IS SERIOUSLY WRONG WITH SPACE
Hunter, up on the surface, heard and recorded every word.
'I'll try a long exposure with the thousand-millimeter lens,' Kaminski began. 'I hate to confess it, but this is the first time I've ever done any astronomical photography. … Hello!'
'What's happening?'
'The end of the slot's getting lighter. Yes, there's no doubt of it. There's a very faint glow along one side. You know, it looks like-my God-that's what it is!!'
'What, for heaven's sake?!'
' Sunrise ! Sunrise ! Leave me alone-I want to watch.'
There were maddening minutes of silence, during which Hunter could hear only Kaminski's heavy breathing and, occasionally, the sound of instruments and controls being operated. Then, at long last, the astronomer spoke again, his voice full of wonder.
'It's a sun, all right. And it's enormous-it's completely filling the view. If I could see it all at once, it would look as big as Jupiter.
'And it's not a G-zero type like our sun. It's very dull and red-I don't even need dark filters on the telescope. Must be a red giant, like Antares. That's an idea-maybe it is Antares. Ah, here comes a sunspot-looks pretty small, but it could be as big as our whole sun….'
His voice trailed off into silence and again Hunter possessed himself in patience until at last Kaminski said: 'Still no change-that sun's still blocking the view. It'll take hours to move out of the way. Let's get back to the ship-I want to study these photos. And I'd like to try an experiment, if I can talk Dave into it.'
'What sort of experiment?'
'We still have most of our instrumented probes. This is the place to use them.'
When they returned to the ship, Bowman was at first reluctant. If anything was dropped down the shaft, he pointed out, even this low gravity could give it a terminal speed of over a hundred miles an hour. There was no telling what damage it might do-or what reactions it might produce.
Kaminski finally settled the argument by pointing out that the designers of this place would certainly have protected their handiwork against such trivial accidents. Every few centuries, a large meteor must plunge into the chasm at a far higher speed than any falling probe could attain.
Once the project had been agreed upon, Kimball acted as bombardier. Since the orbiting Discovery could track the probe only during the few seconds while it was passing directly over the slot, space capsule Alice was fitted with receiving gear. Kimball dropped the probe at the exact center of the chasm, then flew to the edge and waited on the brink, Alice 's receiving antenna jutting out over the abyss.
At first the probe fell with the lethargic slowness to be expected in Jupiter V's gravity field. Its instruments recorded a very slight temperature rise, but nothing else of importance. There was no radioactivity, no magnetic field.
And then, five miles down, it began to accelerate. Its signals started to drop rapidly in pitch, indicating a Doppler effect of astonishing magnitude. Kimball had to continually retune the receiver in order to keep track of the signals, and the radar started to indicate impossible ranges and velocities. In a few seconds, the probe was two hundred miles away-which, taken at face value, meant that it had gone right through Jupiter V and out the other side. Thereafter, it became more and more difficult to detect, and swiftly passed beyond the tuning range of the receiver. On the last contact, it had descended nine thousand and fifty miles down a hole which under no circumstances could be more than a hundred miles deep-the diameter of the tiny moon.
The radar was working perfectly; Kimball checked it with the utmost care as soon as he got back to the ship. The trouble must lie in Jupiter V-and Hunter neatly summed up what everybody was now beginning to suspect.
'I'm afraid,' he said, 'that there's something seriously wrong with space.'
'A long time ago,' said Kaminski, 'I came across a remark that I've never forgotten-though I can't remember who made it. 'Any sufficiently advanced technology is indistinguishable from magic.' that's what we're up against here. Our lasers and mesotrons and nuclear reactors and neutrino telescopes would have seemed pure magic to the best scientists of the nineteenth century. But they could have understood how they worked-more or less– if we were around to explain the theory to them.'
'I'd be glad to settle without the theory,' remarked Kimball, 'if I could even understand what this thing is-or what it's supposed to do.'
'It seems to me,' said Bowman, 'that there are two possibilities-both just about equally impossible. The first is that Jupiter V is hollow-and there's some kind of micro-universe down there. A whole galaxy a hundred miles across.'
'But the probes went thousands of miles, according to the radar readings.'
'There could be some kind of distortion. Suppose the probes got smaller and smaller as they went in. Then they might seem to be thousands of miles away, when they were still really quite close.'
'And that,' said Kaminski, 'reminds me of another quotation-one of Niels Bohr's. 'Your theory is crazy– but not crazy enough to be true.' '
'You have a crazier one?' asked Hunter.
'Yes, I do. I think the stars-and that sun down there– are part of our own universe, but we're seeing them through some new direction of space.'
'I suppose you mean the fourth dimension.'
'I doubt if it's anything as simple as that. But it probably does involve higher dimensions of some kind. Perhaps non-Euclidean ones.'
'I get the idea. If you went down that hole, you'd come out hundreds or thousands of light– years away. But how long would the journey really be?'
'How long is the journey from New York to Washington ? Two hundred miles if you fly south. But twenty-four thousand if you go in the other direction, over the North Pole. Both directions are equally real.'
'I seem to remember,' said Bowman, 'that back on Earth you once told me that shortcuts through space-time were scientific nonsense-pure fantasy.'
'Did I?' replied Kaminski, unabashed. 'Well, I've changed my mind. Though I reserve the right to change it back again, if a better theory comes along.'
'I'm a simpleminded engineer,' said Hunter rather aggressively. 'I see a hole going into Jupiter V, and not coming out anywhere. But you tell me that it does come out. How?'
Everyone waited hopefully for Kaminski to answer. For a moment he hemmed and hawed, then he suddenly brightened.
'I can only explain by means of analogy. Suppose you were a Flatlander, an inhabitant of a two– dimensional
