The following Thursday morning, Gillian ascended the stage in the Navigation centre for a simulation exercise. She wore a Walker skin suit that had been tailored for her, one of several. She took off her shoes, dropping them next to the stage.

Gillian had now completed a significant amount of study. Mr Rogers and his team had introduced her to the complexities of astrophysics and Newtonian mechanics, followed by basic relativistic and macro-quantum theory. She had discovered that she preferred the Newtonian world. It was so simple, almost sweet in its common-sense practicality. Lumps of stuff bounced off each other, or whizzed around each other and it all made sense. It was the everyday world.

But the non-Newtonian world of the Walker was weirder, more alien than she had expected. She found the quantum universe hard to grasp. Mr Rogers had outlined the strange realities underlying ordinary matter: the randomness, the mysterious appearances and disappearances, the things that changed if you looked at them too closely, the invisible influences that might reach in an instant across light years. It was too bizarre.

 Finally, she had accepted Mr Rogers' advice: not to worry too much, nobody really understood this stuff. Everyone just did the mathematics and accepted its results. Then Rogers attempted to explain the implications of this incomprehensible physics for her as a Walker: how the interstellar Walking technology grew out of the abandoned theory of quantum entanglement and the identification of macro-quantum structures. What he and his team had described was, he told her, a crude, cartoonish depiction, and it was just background context for her.

"You should work towards harmony with all this - I'm giving you Abel's words, as I recall them. I don't know what they're going to mean to you in practice, but you have the abilities and the mind of a Walker, so I assume it will come to you eventually."

The astrophysics team had now completed a significant amount of mapping in the region that surrounded the ship. It was enough to prepare a short but realistic simulation session for Gillian. For this exercise, she would not experience any of the strange macro-quantum structures. They did not wish to overload her at such an early stage.

Gillian was excited to be in the Navigation centre again, in a Walker skin suit, alone on the stage. She glanced around the centre. Apart from Captain Xing and Abel, all the committee members were there. McWhirter was whispering with Mr Dryen, and Joan Rubilio looked as if she was explaining a point to Mr Barry. From his stellar observation instruments, Mr Rogers grinned up at Gillian. In the background, she noticed two male nurses.

Gillian pulled the Walk mask down over her head. She closed her eyes, clasped her hands, and opened her eyes again.

She was in interstellar space, but it was not like her first session. It smelt dusty and stuffy, with something unpleasantly damp and sweetish behind it. Dirty looking fuzzy clumps surrounded her, above and below: grey, brown, some darker, some black, a few yellowed like old paper. Here and there, stars glinted through the murk. In a few holes and fissures in the distant clouds, she even glimpsed an occasional glowing nebula and a single small star cluster.

"What is this?" Gillian asked. "It's like being inside a mouldy old wardrobe!"

Mr Rogers replied, "You're seeing our first mapping results. Those clumpy clouds are mostly carbon and a few silicates. They're dense concentrations of what's all around you - that is, around the ship. That's what might seem musty to you. There are ice particles too. We've tried to give that a nice wet smell. There's the usual hydrogen and helium, that should be a background sweetish odour, so you'll notice if it gets stronger."

"What do the different colour shadings mean?"

"Broadly, the proportion of carbon, ice and silicates. Let's not worry about that now."

Green galactic coordinates and orientation lines flashed up when Gillian turned her head, overlaying the scene before her. When she stopped, the green lines and flicking numerals vanished.

"You've added the instrumentation for me this time."

"Yup. We'll explain the bits you haven't learnt later."

"What do you think of it, Gillian?" Mr McWhirter asked.

Gillian couldn't hide her disappointment. "The view's not as nice as last time. I can't see as many stars because of these clumps of muck all around me. Everything's dull and sort of grimy. It's almost a bit ... sordid."

Mr Dryen said, "What's around you is a reasonable representation of the environment around the ship, for the scale you're working at. It's not quite as bad as it seems to you. We've dialled it up a little because we want to make certain you see and avoid the things that the ship needs to stay away from. But we can make the smell nicer, if you like."

"Well, you could tone it down a little, I suppose. But I don't want to start liking this stuff."

"How close together do the clumps appear to you?" Mr Rogers asked. "They're the dense areas it's important to avoid, and we've set the system to delineate them clearly for you. If they're too big, you could change the scale, so it's easier to step over them into the emptier regions."

"Wait a moment. I'll have a good look around." Gillian began turning around, also gazing up and down, trying to remember how to interpret the green coordinate information flashing before her. "I don't know if they're big or not, since I've never seen anything like this before. How far is it to the top of the galactic plane? That direction seems clearer. Maybe we should go up there, Walk across and come back down into the bubble."

Mr Dryen's voice answered. "It's too far, Gillian."

"I agree," Mr Rogers added.

"If you say so. Ooh! There's a scary looking black cloud in the distance. It's all jagged, with a nasty sheen."

"Yes, it's called a Bok globule," Mr Rogers said. "And we'll stay away from them. They have new stars forming inside."

"The clumps seem manageable to me. I won't need to jump between them."

"I hope not. Jumps are risky."

"Which direction is the nearest edge of the bubble?"

"Behind you. About one hundred light years off."

"That's a long way!"

Gillian turned her body around as the green coordinates information flashed. What she saw was disappointing.

"It all just the same everywhere!"

"Well, try Walking, anyway."

"Ok." She lifted a leg high, nearly horizontal, and, leaning forward and stretching a little, cautiously stepped over a cloud clump and into the gap between it and the next. She repeated the same movement, aware if its inelegance.

"It's not too difficult, I think."

 It was almost like stepping between puddles. She continued her high steps, until she heard a muffled sound from someone in the Navigation Centre.

"Is someone sniggering?" she demanded. "I guess I might look a bit odd."

"Sorry," Doctor Morris said. "I'll try to keep quiet."

"Thank you."

Gillian strode on, growing more confident. After she crossed ten or twelve cloud clumps, her growing experience made it not necessary to step quite so high. The Walk became less tiring.

"Easy-peasy!" she declared, pleased with herself.

Then she tripped. Her Walk suit twisted her legs and forced them into unnatural positions. She felt herself sprawl across the invisible stage in the Navigation Centre, "Shit! What was that?"

Mr Rogers' voice sounded sympathetic. "You stepped into a gap between the gas clumps that had a small clump at the bottom. It was shallower than the others. Your suit reacted to avoid it."

Gillian said, "Like a puddle you're not expecting. I'll remember that."

"It's difficult sometimes because you're up on that stage, and not actually out there in three dimensional space. You're facing the illusion that you're walking on something solid. Well, it's not an illusion, it's unfortunately reality, but it's creating an illusion within your illusion - if you know what I mean."

"Um," Gilliam said. She heard a few people laugh.

Mr Dryen added, "He means the simulation isn't completely accurate."

"Ok."

"Do you want to carry on, Gillian?"

"Yes."

"Good. But be careful. You fell right through a cloud. That could have set off a blizzard of nano-blasts if we'd been live and the system was slow to pick that you were falling." Mr Dryen paused. "Also, the Walk suit might break your legs trying to avoid a macro-quantum object, if one happened to be there."

Gillian Walked on for another five minutes without incident. This required her to turn around on the stage several times, using the shrug gesture. Twice, she avoided the trap that had caught her a few minutes before, after examining the space she was about to step into.

"Will it be like this all the way back to the bubble?"

"I wish it were that easy," Rogers said, "but we're sure to come up against more difficult problems than this before we reach clear interstellar space. Want a rest now?"

"Ok."

"What about practising a few gestures first?" Dryen suggested.

"Yes, good idea!" Gillian replied.

"Rotate?" Rogers said.

"Ok." Gillian brought her hands together in a prayer-like gesture, then moved both hands horizontally in clockwise circles, and watched everything spin around while green galactic coordinates flickered in her vision. She reversed the action and spun back to her original direction, facing in the direction of the bubble.

"It's just as easy to turn my own body around," she remarked.

"Not if you're in an awkward spot, perhaps," Rogers said. "Scale change?"

Gillian made swimming motions with her arms a few times and watched the dirty clumps recede until they almost vanished and she was standing in the middle of a dark, slowly swirling mist. As with the stars in her previous session, it was a swirling that she could perceive even though the mist was still. But she saw more stars, and she could even make out the elusive shape of the Orion-Cygnusarm itself, winding away into the remote distance.

She spread her arms and made beckoning motions, returning to the same scene she had started with.

"Try a vertical rotate? But be careful. Slow."

"Right." Gillian raised her hands and, drawing in a breath, slowly rotated them around each other, in a forwards roll. She felt relaxed, happy.

"Too fast!" she heard someone yell.

The universe tilted, the green coordinate lines twisted and spun, and Gillian gasped in terror. She had suddenly lost track of her subjective "up" and "down". Her stomach lurched. She cried out, overwhelmed.

They had warned her, described the effect to her, but it hadn't prepared her. The interstellar dust cloud wasn't thick in this new direction and the system gave her a full, realistic 3D panorama. She was skidding down the misty spoke of a vast, relentlessly revolving wheel of gas, dust and stars. Glimpsing this through fissures in the clouds emphasised the perspective, made it more terrifying. And she saw all the way down: down, down, down. As her legs buckled, Gillian saw all the way down to the edge of the galaxy, eighty thousand light years below her. She perceived its immense depth. For an instant, she glimpsed the tip of the foggy spiral arm itself as it thinned to a slim finger of desperate, twisting gas below her, swinging like part of a broken Ferris wheel. To comprehend all this for an entire galaxy was terrifying.

But it wasn't the end. Below the vast and inexorably swinging tip of the spiral arm, Gillian saw a colossal drop into a vast and empty abyss. A few minuscule galaxies gleamed whitely at the bottom, like tiny menacing blossoms, but even that wasn't the finish of it.

Naturally, she fell, drifting down like a speck of dust. Those watching gasped as she collapsed on the hard stage floor.