Although evolved sensibilities and communication technology will break down cultural barriers between species, physiological differences will be harder to conquer. A significant barrier is erected of biological time. To the best of our knowledge, almost all life comes equipped with an ingrained “master clock.” Located within the brain, this “clock” — built from a bundle of neurons — coordinates groupings of interacting molecules spread throughout the body. These molecules control circadian rhythms: physical, mental, and behavioral changes that respond to light and dark cycles. When these rhythms aren’t followed, problems arise. For example, humans forced to work at night and sleep during the day experience fatigue, general malaise, and increased rates of metabolic disorders like obesity and diabetes. A functional crew will need to minimize these issues. While Star Trek understandably glosses over the complications of circadian rhythms, on a real intergalactic starship, they will need to be dealt with. Not all of the crewmembers will be from planets with 24-hour day-night cycles, so duty schedules will have to be individually tailored and coordinated to fit their biological clocks.

Air conditions present a higher problem to hurdle. On the International Space Station, the matter is simple. Earth life is adapted to a pressure of roughly 14.7 psi and air composed of 78% nitrogen and 21% oxygen, so those are the conditions that suffuse throughout the orbiting station. But what will the conditions be onboard a starship of diverse life forms? After all, some crewmembers might breathe fluorine, or chlorine, or nitrogen… Moreover, high pressures that would squish some life forms might be perfect for others, and lower pressures that would boil the water in human lungs might be business as usual for other species. The only sensible solution would be to set the ship’s life support to a setting that would accommodate the most crewmembers. Everybody else, however, would need to don a spacesuit, though the atmosphere in their personal quarters could be tailored to their physiological needs.