Are you more likely to explode or freeze in space? - Tejal Gala

Due to an unfortunate teleportation malfunction, this mad scientist has just found himself in the vacuum of space. With no oxygen, he might be tempted to hold his breath, but this would only accelerate his demise. The air in his lungs is desperate to expand, so if he doesn't release it right away, his lungs will rupture. Our poor professor quickly exhales, and his skin’s tensile strength prevents the rest of his body from bursting, but things are still looking grim.

Without surrounding air pressure, his bodily fluids begin to vaporize in a process called ebullism. His skin swells, moist surfaces like his eyes start to boil, and bubbles form within his vessels, obstructing blood flow. This is all exceptionally painful, but while these nightmarish effects will take roughly 90 seconds to reach their deadly conclusion, he’ll mercifully pass out from lack of oxygen within about 15 seconds of arriving.

And even though space is barely above the temperature of absolute zero, our scientist won’t die by freezing. Because unlike on Earth, where body heat can transfer to molecules in the environment, in space it can only leave by slowly radiating away. It'll take hours before our professor becomes a human popsicle, and by then, he’ll have perished a long time ago.

Now, had our scientist planned his teleportation to space, he certainly would have dressed for the occasion. Let's imagine he arrived in a spacesuit instead. The suit’s pressurized air protects his body from ebullism, its oxygen tank keeps him breathing, and the insulation prevents him from freezing. But although these features thwart an immediate tragedy, space is still an incredibly dangerous place.

Outside the shield of Earth's atmosphere and magnetosphere, our scientist is bombarded by galactic cosmic rays—a form of radiation believed to come from distant supernovas. If he's exceptionally unlucky, he might be hit by solar energetic particles expelled from the Sun. Both these forms of ionizing radiation effortlessly pass through the scientist’s suit, damaging his DNA and increasing his risk of cancer.

But let's say our mad scientist isn't so mad at all. He’s planned a month-long research expedition, complete with a cutting-edge spacecraft to live in. This structure protects him from low air pressure and temperature, as well as some of the radiation bouncing around space. But even here, he's vulnerable to certain changes.

In addition to experiencing motion sickness and sleep disturbances, microgravity changes the distribution of his blood and cerebrospinal fluid, shifting roughly half a gallon of internal fluids to his upper body. As the weeks pass, his brain engorges and the sheath of his optic nerve swells. This not only compresses his pituitary gland but also flattens the back of his eyes, impairing close-distance vision.

Having very little gravity to work against also causes muscles and bones all over his body to gradually lose mass. And when bones break down, they release minerals like calcium. So our professor might get kidney stones too. Diet and exercise can help reduce the deterioration of his bones and muscles, but it’s harder to address the potential damage to his mental health that comes from being confined to a tiny spacecraft, far away from his loved ones.

Thankfully, this isn’t a one-way trip, and after a month in space, our adventurer happily teleports home. However, his journey has left him with some lasting effects. Back under Earth’s gravity, it’s initially hard to stand without fainting. It takes a few days for his fluids to redistribute back to normal, and it'll be months before his muscles completely regain their strength.

Meanwhile, full restoration of bone density will take at least a year. His vision might take several years to recover, and it may never return to normal. There’s still a lot waiting to be discovered about how space travel impacts human health in the short and long term. So for now, our scientist is content to use his teleporter for its original—and much safer—intended purpose.