What does a vacuum not have?
matter
Where does the word come from?
vacuus
What language is that?
Latin
what does it mean?
vacant or void
Is that an adverb?
no
What is it?
adjective
What do physicists call vacuum?
a perfect vacuum
What else?
free space
What do they call a vacuum that's not perfect?
partial vacuum
How does pressure in a vacuum compare to pressure in the atmosphere?
it's lower
What does a household vacuum do to air pressure?
reduces it
by how much?
20 percent
Is outer space a vacuum?
yes
How many hydrogen atoms or in a cubic meter out there?
just a few
would something be empty if there was no matter in it?
no
Why not?
phenomena in quantum physics
Is vacuum one of them?
yes
What's another one?
cosmic rays
What did they once believe was in a vacuum?
aether
When did they think this?
in the 19th century