Outer space is an extremely hostile place. If you were to step outside a spacecraft such as the International Space Station, or onto a world with little or no atmosphere, such as the moon or Mars, and you weren't wearing a space suit, here's what would happen:
- You would become unconscious within 15 seconds because there's no oxygen.
- Your blood and body fluids would boil and then freeze because there is little or no air pressure.
- Your tissues (skin, heart, other internal organs) would expand because of the boiling fluids.
- You would face extreme changes in temperature: Shade: -148°F (-100°C); Sunlight: 248°F (120°C)
- You would be exposed to various types of radiation, such as cosmic rays, and charged particles emitted from the sun (solar wind).
- You could be hit by small particles of dust or rock that move at high speeds (micrometeoroids) or orbiting debris from satellites or spacecraft.
The human body could tolerate a complete vacuum for a few seconds at the most. So in the scene in "2001: A Space Odyssey" where Dave ejects from the pod into the vacuum of space and dives for the space station -- that might actually work. But beyond a few seconds, things would get ugly fast.