Galileo’s Dream. Kim Stanley Robinson

of nothing but a field of the darkest blue imaginable, a blue so deep and pure that it captured Galileo’s eye, and exhibited small reticulations and lighter gleams, revealing perhaps that it was an icy slush. It gave him much less information than the other rectangle, the brilliant colours indicating temperatures as he was informed they did.

      Down, down, down some more. The blue outside the window flowed upward more swiftly, and darkened even more. The temperature ‘picture’ likewise flowed. Otherwise there was only the hum of the vessel’s machines, the brush of its air. Once Galileo had dreamed of falling off a ship and sinking into the Adriatic. Now they were all dreaming together.

      Ganymede hated the necessity of this dive, hated the very idea of an intrusion into the ocean under the ice, and it soon became clear that his crew shared his opinion. They eyed their pictures with grim expressions, and said little; Ganymede strode back and forth nervously behind them, consulting with them in turn.

      On the rainbow panel a green potato-shaped patch moved upward; it looked like a boulder. Galileo asked about it.

      ‘A meteorite,’ Ganymede replied. ‘Space is full of rocks. The shooting stars you see in your night sky are rocks, often as small as sand grains, burning very brightly.’

      ‘Friction with air is enough to ignite rock?’

      ‘They are moving really very fast. Here on Europa there is no atmosphere, however, so whatever it encounters crashes straight into the ice. It happens a lot, but impact craters in ice quickly deform and flow back toward flatness.’

      ‘No atmosphere? What about the air we were breathing up there?’

      ‘We live inside bubbles of air, held in place by forces or materials.’

      Their vessel stopped in its descent; it was interesting to Galileo how clearly he could feel the halt, subtle though it was.

      Ganymede said, ‘Pauline, is everything going well?’

      ‘All is well,’ said a woman’s voice, apparently from within the walls of the vessel.

      ‘How soon will it be before we reach the ocean?’

      ‘If we maintain this speed it will be thirty minutes.’

      ‘Is the Ariadne thread unspooling cleanly?’

      ‘Yes.’

      Ganymede said to Galileo, ‘The Ariadne thread is also a heating element, and will keep the central line of our flue liquid, to ease our return.’

      They waited, absorbed in their thoughts. The light downward pull of Europa made the crew’s movements around the bridge fluid and slow, like dance in a dream. Galileo found it hard to keep his balance, it was somewhat like floating in a river.

      He drifted to Hera’s side and said, ‘All these machines have to work for us to stay alive.’

      ‘Yes, that’s right.’

      ‘It seems risky.’

      ‘It is. But because it is, we engineer for safety. Materials and power available are terrifically advanced compared to your time. And there is a principle called redundancy at the criticalities, do you know this term? Replacement systems are available in case of failures. Bad things still sometimes happen. But there you are. They do anywhere.’

      ‘But on Earth,’ Galileo objected, ‘on Earth, in the open air, the things you make don’t have to work for you to survive.’

      ‘Don’t they? Your clothing, your language, your weapons? They all have to work for you to stay alive, right? We are poor forked worms in this world. Only our technologies, and our teamwork, allow us to survive.’

      Galileo pursed his lips. There might be some truth to what she said, but still he felt it obscured a real difference. ‘Worm or not,’ he said, and she was a rather magnificently shaped worm, he did not add, ‘you could stay alive on Earth, by breathing, eating, and staying warm. Granted these take effort, but you could make the effort. You have tools to help you, but they don’t have to remain unbroken for you to survive. A single man alone on an island could do it. There are no mechanical contrivances that surround you and protect you, like a fortress, that have to function successfully forever or else you very quickly die.’

      She shook her head. ‘It’s like a sea voyage. You could not have your ship sink and survive.’

      ‘But you people never land. You sail on forever.’

      ‘Yes, that’s true. But it’s true for everyone, always.’

      Galileo recalled standing in his garden at night, in the open air, under the stars. It was an experience this woman had never had. Possibly she could not imagine it. Possibly she had no idea what he was talking about. ‘You don’t know what it is to be free,’ he said, surprised. ‘You don’t know what it is to stand free in the open air.’

      She shook her head impatiently. ‘Have it your way.’

      ‘I will.’

      Again her amused glance, as if she were looking down on a child. She said, ‘You were famous for that, as I recall. Until…’

      The voice Pauline interrupted to announce they were near the bottom of the ice layer, and were in what she called brash ice. They could hear floating chunks and clinkers striking the hull, a grinding noise full of scrapes and thuds.

      Then they were moving freely, in water. Galileo had spent so much time on barges and ferries, and on a few well-remembered trips out into the Adriatic, that he recognized the feel in his feet. Such kinetic sensations were so slight as to disappear when one focused on them, but when focusing attention elsewhere, one became aware of the totality of the effect.

      Ganymede said, ‘Pauline, search for the Europans’ flue, also any other vessels, of course. And give us an analysis of the water, please.’

      Pauline reported the water was nearly pure, with trace amounts of salts, floating particulates, and dissolved gases. Some of the crew began tapping madly at glyphs on their desktops. Outside the window was omnipresent black. They might as well have been deep in the bowels of the Earth. Only one’s sense of movement suggested they were in a liquid.

      Thus it was a great surprise to see a brief flash of cobalt blue in the window, like the random blue spark one sometimes saw crossing the inside of the eyelid.

      ‘What was that!’ Galileo said.

      ‘We call that Cherenkov radiation,’ Ganymede said.

      ‘Somebody’s patron?’ Galileo inquired, glancing at Hera.

      ‘The discoverer of the phenomenon,’ she said firmly.

      Ganymede ignored their fencing. ‘There are tiny particles called neutrinos, which pour through our manifold in great numbers but very seldom interact with anything. Once in a while one hits a proton, which is a small but substantial part of an atom-hits a proton in such a way that the proton releases a muon, which is a very small component of a proton. If that happens in an ocean like this, the muon will fly through the water in such a way as to spark a short trail of light in the blue wavelength. We will see a few per minute.’

      Another little flare of blue appeared, again like the flaws that plagued Galileo’s vision. ‘Like shooting stars,’ he noted.

      ‘Yes. A very subtle fire.’

      ‘A fire in water.’

      ‘Well, a light, let us say. Though some fires will burn in water, of course.’

      Galileo tried to imagine that. Of course there were different kinds of fire. Blue streaks in blackness…This dream was testing him in all sorts of ways: could he find a way to test it back? Maybe answer the basic question: was this really happening? He looked around to see if there was something small that he could take and conceal in his coat. Stealing ideas from dreams-perhaps it wasn’t so unusual. Perhaps it was a fundamental mode of thought.

      The next flick of blue light was followed