Talking About Vacuums

darkchild

Why do scientists say that certain conditions hold in a vacuum despite the fact that no vacuums exist or are known to have ever existed?

Vanadium 50

The same reason we talk about frictionless planes, stretchless ropes, massless pulleys...

darkchild

Interesting. I'd never thought about it that way before. I remember working on those introductory physics problems in which we were supposed to ignore things like rope mass and surface friction and thinking, 'oh, they're just leaving things out to make the problem easier for beginning physics students.'
When it came to statements about x or y being true in a vacuum, I thought, 'oh, this is just some random assumption.' Now I see that both reflections are true in both situations: both the ideas about phenomena in vacuums and the massless ropes etc. are simplifications, and the act of solving problems with those simplifications is based on the assumption that we can meaningfully and accurately solve problems involving physical conditions that we do not and cannot have experience with.

SteamKing

It's easier to create a hard (although not perfect) vacuum than it is to create a nearly massless rope or nearly frictionless mechanism.

I like Serena

There is something more.

Take for instance the speed of light.
By now we know it has a fixed value, but only in vacuum!

Whenever we do a measurement, we will find another value, since real vacuum does not exist.
To compensate, a number of measurements have to be made.
Then the lack of real vacuum has to be taken into consideration, meaning the measurements need to be extrapolated to the point where we would have a perfect vacuum.