Huge cosmic structures of unknowable matter tug at the edges of our universe. The wind lifting the hem of Beth’s skirt is a gesture of gravity pulling at the air around us. Our universe is flowing outwards at a velocity that just keeps on increasing. We are made of the aftermath of supernovae.

Beth pushes her daughter, Rosie, on the old plastic and rusting chain swing in the neglected children’s area of the municipal park. She counts the beat of time elapsing during swings. She lets go of Rosie: one, two. Rosie reaches the point nearest the earth: three, four. The little girl powers through gravity’s grasp: five, six. She’s back at the apex: seven, eight. She’s back at her mother: nine, ten. Irresistible forces return the daughter to her mother and keep everyone’s feet on the ground. Except Mary’s.

For every action there is an equal and opposite reaction. Beth had a theory that a similar rule applied to sisters. Specifically her little sister, Mary. The sisters differed in temperament. Beth was analytical, calm, competitive, and Mary was warm, impulsive, relaxed. Beth had a wryly curved mouth, double-helix curls of thick brown hair and meditative grey eyes. Mary was half-moon smile, helter-skelter ringlets of thick brown hair and restless grey eyes. Over many arguments and tussles for sibling supremacy the two debated and attempted to define their differences.

Beth could remember their Dad refusing to speak to either of them for over a week when a teenage row had become physical. Mary had bruises up her arm, Beth had a black eye. Even now Beth’s stomach knots in indignation that their Dad punished them both for that. But she’s a mother now herself, although not a lone parent like her Dad, and she has begun to understand him more. He was trying to bring up, on his own, two wild girls who could never agree. I just have Rosie, she thinks, watching the back of her daughter’s head approach and recede. Dad didn’t live long enough to meet you, she thinks to her daughter.

He was there to see Beth graduate from Durham university, though. He looked on proud but frail in his new suit with Mary holding onto his arm in the crowd. Beth became a respected astrophysicist lecturing at Cambridge, how proud would you have been of that Dad? Mary would not be outdone, of course. She became a theoretical physicist specialising in controversial theories about the properties of nothingness. Bringing the pendulum of her daughter’s swing to a stop, Beth feels a familiar jar of irritation at her younger sister. It was never enough to be just different from Beth, Mary had to follow an almost identical path to her and then put a crazy twist on it.

Their dad had refused to pick a favourite despite the sisters’ best efforts to force him to choose. Now without him the sisters existed in separate worlds. They continued their colloquia of confrontation in irregular bursts. Mary lectured at Monash University in Melbourne – half a world away from Beth’s cosmic practice in England. Twice so far the sisters had given papers at the same conferences. Beth had sat self consciously at the back of her sister’s presentations, hoping that people wouldn’t make the familial connection between them. She’d try to control her expression when colleagues would politely say, “Doesn’t your sister look just like you?”

“Not really,” Beth would mumble, fumbling with artificial clumsiness through her file of notes until the well-wishers left her alone.

Beth straps Rosie into the child ‘bike seat and hoists the bicycle up onto its axis. Bringing it to an improbable balance she manoeuvres her daughter’s shifting weight back home.

In the kitchen Beth takes a carton of chocolate milk out of the fridge for Rosie. She looks in the glass fronted cupboard for a beaker and sees her reflection. The curly hair, the grey eyes. For a moment she sees Mary there in the light bouncing off the glass. Beth opens the cupboard door and the ghost holds her gaze even while the reflection slips away. As the cupboard door closes, the image slides back. Her face is her own again. Beth remembers one of the last arguments she’d shared with her sister. Mary had started talking to Rosie about the future contraction of the universe.

“What do you think it would be like, little bean?” She asked. “Would we all get squashed?” Rosie had just looked at her aunt, confused, as Mary slowed her voice down to a cartoon pitch, “Would time slow down?” Beth had told Mary to stop it, that there was no evidence that the universe would ever stop expanding. Mary had told her to calm down. Beth hadn’t appreciated being told to calm down.

Beth looks at her daughter and pictures her sister sitting next to Rosie. It is not hard to imagine a shadowy outline at the kitchen counter, the air trembles with the potential presence of the absent sister. Beth strokes the soft mess of Rosie’s higgledy piggledy hair and takes down the landline ‘phone from the wall. Six weeks remain before the end of the academic year. Beth wonders if Mary has even begun to think about coming over to visit in the summer break. Rosie adores her aunty Mary, as everyone does. If Mary could make it over, even for just a few weeks, Rosie would be ecstatic.

Calculating the time difference in her head, Beth dials Mary’s home number. The ringing on the other end is a flat chirrup. Beth thinks it is odd the way that ‘phones ring differently overseas. When Mary answers there is a little echo on the line, syncopating her voice.

“Professor Gerson speaking,” Mary says, her voice whirling in the cross-continental radio static. She either refuses to get a ‘phone with caller id, or this is how she introduces herself to everyone, Beth thinks.

“Mary, it’s Beth. Is this a good time for you? I needed to ask if you are planning to come over here at all this summer?” Beth counts the time lag between speaking and Mary’s response, just like Rosie counts between lightning flashes and thunderclaps.

“Beth. How are you? I’m just about to go to bed. This line is terrible! You should record this noise as evidence of cosmic fallout from the big bang,” Mary says, with her habitual lightness. Beth thinks, Is Mary avoiding my question?

“How are Ian and little Rosie? You know it’s winter here, not summer.” Mary says, avoiding the question. Beth listens to the clicks and pops in the busy air between them. For just a moment she feels the universe contract. The nothingness in the gaps between matter becomes infinitesimally small and, just for a second, Beth’s sister is right there in the kitchen, next to her.