What happens if you float in space without a suit?
The Real Answer
Exposure to the near-vacuum of space would become life-threatening within seconds, mainly because you would no longer have breathable oxygen or enough pressure to keep body fluids behaving normally. You would rapidly lose useful consciousness from hypoxia. Very low pressure can also cause ebullism — water in tissues forming vapor — which can produce swelling. Expanding gas can injure the lungs, especially if someone holds their breath during rapid decompression. You would not instantly explode or freeze solid, and your blood would not simply erupt into a rolling boil inside your vessels. A very brief exposure may be survivable if repressurization happens quickly, but prolonged exposure is fatal.
You know space is a vacuum and still picture the movie version where a person instantly freezes or explodes because slow oxygen loss is not theatrical enough. You will remember the exploding-head scene long after you forget what decompression actually does.
The Dunce Dynamics Institute Examines Why People Ask This
This usually comes from airlock scenes in science fiction, where people freeze, explode, or instantly disintegrate depending on the movie. Real vacuum exposure is still extremely dangerous, but the physiology is different: oxygen loss and decompression are the immediate problems, while several famous movie effects are exaggerated.