You’ve probably seen it many times in movies: someone exposed to the vacuum of space—without the comfortable safety of a spacesuit between them and, well, nothing—explodes into many decorative pieces, freezes into an oversized fish stick, or their blood starts to boil.
That may all look spectacular and believable, but what really happens?
First: no, you would not explode. For a long time, a very common theory suggested this because our bodies maintain internal pressure to counter the external pressure here on Earth. In space, that external pressure disappears, and many believe the internal pressure would be enough to make a human explode. In reality, however, we are held together quite well by our muscles, tissues, and skin. As long as those remain intact, so do you.
Something similar applies to the idea of boiling blood. This is largely an invention of science-fiction writers based on the fact that liquids have lower boiling points at lower pressures. So most liquids in space would indeed begin to boil quickly. But not the blood inside a living body, because—as mentioned—it is part of a closed system, namely the circulatory system.
So what about freezing? Everyone knows the universe is a very cold place (about 2.7 Kelvin, which equals −270 °C). BUT to lose heat, you need something to transfer it to. This is generally known as heat conduction and can only occur when the body is in contact with something that can absorb the heat, such as air or water.
Now some of you may already be excitedly packing your bags, spending your inheritance, and booking the next flight to space for a little walk. I strongly advise against it—it’s far too expensive, and is better to spend your time doing other things like talking to a virtual girlfriend as trukait online.
First, any air in your windpipe and intestines would be sucked out by the vacuum through various bodily openings, no matter how hard you try to keep your mouth shut or your underwear clean. After about 10–15 seconds, you would lose consciousness, because that is how long it takes blood to travel from your lungs to your brain—and without oxygen, our brain unfortunately doesn’t function. Surface blood vessels, such as those in the eyes, would rupture. Any liquids directly exposed to the vacuum would indeed begin to boil.
We even have first-hand information about this. In 1965, during a vacuum chamber test, a person was exposed to a near-perfect vacuum due to a faulty spacesuit. After 14 seconds he lost consciousness. When the chamber was returned to normal pressure about 15 seconds later and he regained consciousness, he reported that the last thing he remembered was the saliva on his tongue beginning to boil.
OH—and if you happened to be naked (for whatever reason), you would get the most intense sunburn of your life… which, admittedly, wouldn’t matter much because you’d be dead.
