'Conversely, an observer inside a freely falling elevator in Earth's gravitational field would observe no effects of gravity inside that elevator. He could stand on a scale, and would register no weight. Liquid would not pour from a glass. It has been stated that no mechanical experiment could ever reveal the presence of Earth's gravitational field in the interior of any such frame of reference moving freely in this field of gravitation. We have accepted this assumption for a long time.
'There are good reasons for accepting it, good, sound mathematical reasons. Yet we have not empirically exhausted all possible means of detecting a gravitational field under such conditions, and it is foolish to exclude the possibility.
'So — Dykstra has made a good point in his fairly rigorous; demonstration that a mechanism such as Dunning's would demand the abandonment of the postulate of equivalence. It may well be that the postulate is an unwarranted assumption, based upon inadequate data. If so, that's a good starting point. What the next step might be, I don't know.'
'Is gravity a kind of a something that can be identified otherwise than as a mathematical symbol — or through the observation of a falling apple?'
'No. That's all it is, actually. A symbol in our formulas that stands for an unidentified something which manifests itself in the attraction between masses.'
'How about a flowing something, like this stream?5
'Could be. Nobody knows.'
The water eddied about a projecting rock near the bank. Berk threw in a handful of sticks he had been idly breaking, in his hand. Swiftly, they flowed together and converged in the centre of the whirlpool by the rock.
'Might be a point of view,' he said, 'in which it could be postulated that those sticks gravitated towards each other under a mutual attraction.'
'It wasn't attraction in them,' said Mart thoughtfully. 'It was forces pushing and pulling on them. Gravity — a pushing and pulling, maybe. But a pull or a push of what? That Dunning! He knew!'
Sitting on the porch in the dark, after dinner, Mart had a feeling of satisfaction, a vague sense of having accomplished something during the day. He didn't know what, but it didn't matter. It was something-
'You know,' he said suddenly, 'the thing we need to know, and that you psychologists ought to be able to tell us, is where ideas come from.
'Take the first cave man with two brain cells big enough to click together. Where did he get the idea to put a fire in his cave? I think that's the problem you and I tried to solve a long time ago. Where do they come from — inside or outside?' He paused and gave the mosquitoes his attention.
'Keep going,' said Berk.
'I haven't any further to go. I'm thinking about gravity again.'
'What are you thinking?'
'How to get a new idea concerning it. What does a man actually do when he cooks up a new theory, a new mechanism? I feel like I'm being sucked into
'Well, what are you doing? You're trying to cook up a new idea-'
'I'm thinking right now about this afternoon. Something flowing — but it would be something you couldn't get a picture of- like space-time. Now that it's been brought into the open, I think I really have never liked the postulate of equivalence. Just a feeling knocking around through a few molecules in my cranium. The postulate is wrong.
'Then I try to picture something flowing through the dark of space. It couldn't be a three-dimensional flow like a river.'
He sat up straighter and slowly withdrew the cigar from his mouth. 'It couldn't be- But it
Berk's cigar tip brightened in a long, glowing moment. 'Don't mind me,' said the psychologist.
Berk had no idea what time Mart went to bed that night. In the morning he found him in the same position working furiously, and had the impression Mart had not retired at all. He observed he'd changed clothes, at least.
'The fish are calling,' said Berk.
Mart glanced up. 'Give me another half hour. Look, the fish can wait. I've got to get back to the office as soon as possible. There's something here I want to keep on with.'
Berk grinned agreeably. 'Go to it, boy. I'll get the car packed. You say when.'
In town he went directly to his own office without seeing anyone. There, he continued the work begun the night before. As he proceeded, some of his initial enthusiasm waned. It would be two or three days before he would be ready to invite inspection. One of his manipulations several pages back turned out to be in error. He retraced slowly through the maze.
A little after three there came a knock. He looked up in irritation as Dykstra walked in.
'Dr Nagle! I'm glad you're in. I tried and couldn't find you yesterday.'
'I took a day off for fishing. Can I help you?'
