Vacuum

Outer space is a whole bunch of nothin’. Most of it is a near-perfect vacuum — far emptier than anything we can produce in a laboratory on Earth. Yet it’s not completely empty. It contains a few atoms and molecules. It’s filled with the afterglow of the Big Bang. And it may produce its own energy.
The quality of the vacuum depends on where you are. A couple of hundred miles above Earth, for example, the vacuum is fairly densely populated. Wisps of Earth’s outer atmosphere exert a drag on orbiting satellites. They have to fire their engines from time to time to keep from falling down.
The space between the planets is less dense — perhaps 5 to 10 atoms or molecules per cubic centimeter. Most of that consists of particles of the solar wind. Venture out between the stars, and the number drops to about one atom per cubic centimeter. And between galaxies, it’s only a fraction of that — mostly atoms of hydrogen and helium forged in the Big Bang.
Space also is filled with a type of energy know