Thursday, 06 February 2014

Gravity

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It’s the force that holds stars and planets together, and it’s the reason life evolved on Earth the way it did. Gravity’s absence will mean enormous challenges should our dream of interstellar travel and off-world living ever come to fruition.

Gravitation, or gravity, is a natural phenomenon by which all physical bodies attract each other. It is most commonly recognized and experienced as the agent that gives weight to physical objects, and causes physical objects to fall toward the ground when dropped from a height.

Wikipedia

Earlier this year, artwork for proposed colonies in space commissioned by NASA’s Ames Research Centre in the 1970s, were rediscovered and widely published. The artists’ impressions of what giant, free-floating toroidal, cylindrical and spherical colonies inhabited by humans in space suggested vast spaceships, almost Death-Star like in scale, floating through space, with familiar, terrestrial landscapes. Some saw rolling green hills and suburbs looking up to filtered sunlight during the “day” and an unclouded universe by night; others saw terraced houses and gardens, great long fields with grazing animals: entirely self-sufficient, terrestrial suburban dreams transferred to contained spaces and strange geometries. No blue skies.

We are a long way from these imaginary colonies, every new spacecraft and mission teaches us something about life in space. Commander Evan Hadfield’s recent biography talks at length about the training process for astronauts; how flight and simulation trains crew and engineers to think carefully about every step, every aspect of life in space. It’s not just about trying to successfully launch spacecraft, the purpose is to work out and cover every aspect of the processes involved in launching a spacecraft – and how to survive in space. Life in space, at least for now, is not merely transferring lifestyles from earth into a smaller capsule, a smaller space. It means a complete change about how we act and live on not just a day-to-day, but hour to hour basis.

In the zero gravity of space, simple acts taken for granted on earth require planning and precision. Teardrops do not trickle down faces but form spherical droplets and float off. Astronauts must exercise daily, not merely to keep fit for nonexistent racetracks but to prevent muscles wasting away. The kind of food one eats and how it’s delivered to you matters. Even sewing and crafting, as astronaut Karen Nyberg recently demonstrated through video, reveals the many acts we take for granted here on earth. To make a quilt patch in space, as Dr Nyberg found, is fraught with difficulties we don’t even conceive of on earth. There is nowhere to put the fabric down to cut it. All the items of a sewing box – scissors, needles, thread – must be fixed somewhere by Velcro or else float dangerously around the spacecraft. Instead of diamond-shaped fabric pieces, forming regular geometric patterns, the difficulty of cutting fabric without laying it on a surface results in a patch of slightly crazy (if not unpleasing) geometry. How would we resolve these issues? Detachable Velcro boards and patches for putting fabric down on, set squares to cut against. On earth, we would simply put the fabric down on the table or floor to cut it, hold it in our hands to sew it.

Gravity. It’s a constant force that holds the planet, the solar system and the universe together. We know that. But gravity is necessary for life on earth, indeed, it helped drive the evolution of life on earth.

In space, movement does not encounter resistance: not much friction in a spaceship, from air or anything else, low gravity or microgravity. On earth, we walk upright with ease, locomotion relatively unchallenging. Muscles in one leg contract and relax to put one foot on the ground, it pushes the earth away, literally, with each step, while the other leg partially rotates, bends at the knee, to form the next step. We have evolved groups of muscles attached to dense bones in our legs that allow us to walk and to walk upright, to propel ourselves forwards, backwards, to run. The muscles face resistance from gravity, the foot friction from the ground: it is this ability to overcome the resistance of gravity and friction that allows us to walk. And this resistance is what keeps muscles in shape and gives them bulk, or to even exist at all: without training, or without walking, they waste away. In space, you must go to the gym every day to survive.

If muscles require resistance to prevent wasting, even from the first cell, gravity has affected life on earth. The size of cells is limited by the force of gravity – the larger the force of gravity, the smaller the cell will be. There is an upper limit to the size of cells on earth. On other planets with lower levels of gravity, it’s possible that cells could grow larger, and then other limitations will come into play. Gravity affected the formation of complex organisms, limiting their size, their bones structures and densities. Gravity is also the reason why we evolved dense bones to support our musculature: for the purposes of walking upright on terrestrial gravity required many modifications to the mammalian system: the ability to sense that you are upright, a cardiovascular system to pump blood against the forces of gravity and so on. In the ocean, the buoyancy and mass of water overcomes some of the issues presented by gravity and atmospheric pressure, resulting in giant squid, whales, sharks with cartilage bones. On land, plants succumb to and defy gravity at once: in the sprouting seed, roots are driven by gravity to push through the soil in search of nutrients, while stalks and leaves shoot upwards in search of light and air. Plants do not have hearts as animals do, but have vasculature, or vessel systems, of their own, to transport water and nutrients along chemical gradients and both with and in opposition to the force of gravity.

Our studies so far show that in space, small but vital aspects of cell function in multicellular organisms are affected by low or microgravity. Immune cells in humans on earth usually differentiate into a complex subset of cells. Since many immune cells originate in bone marrow and thymus, the low levels of gravity in space affect their ability to migrate and differentiate. Multicellular organisms are made of many specialised cells: cells that form barriers and membranes, tissue, organs. In microgravity, metabolic processes and the ability of some cells to differentiate is affected, and if the ability of some cells to differentiate is affected, it’s possible that the reproduction of organisms can be affected as well. Studies are currently being carried out to determine whether animals can be successfully bred in microgravitational conditions. These studies will hint at what effects long term existence in space might have on humans.

We are some way off from the rolling green hills of the proposed toroidal space colonies, but each new mission and every experiment, whether involving spiders or plants, mice or humans, tells us more and more about what challenges we will need to overcome to make a life in space, let alone giant spaceship. The Death Star is still some time away.

This article is from the King’s Tribune Summer 2014 magazine, which includes an exclusive extract from Tim Dunlop’s book The New Front Page and articles from Brocklesnitch, Amy Gray, Jo Thornely, Stephen Herrick, Mat Larkin, Upulie Divisekera and many others. The full list of articles and contributors is here

You can buy the limited edition paper copy here Subscribers will received a $5 discount (select Summer Issue 2014 from the drop down membership list, available only until sold out) or the Kindle version here.

Upulie Divisekera

Upulie Divisekera is a cake-loving molecular biologist and science communicator with an evangelical interest in dinosaurs.

Follow her on Twitter @scienceupulie