Re: Would it be really noisy if the vacuum of space was filled with air . . .

Dear James:

You are really asking a philosophical question, as opposed to a strictly “scientific” question. But that’s all to the good. Science and philosophy have gone hand-in-hand ever since what we now call “physics” used to be called “natural philosophy.”

It turns out that, in some sense, you can “hear sounds” that have, in some sense, traveled through a vacuum. But the traveler is not sound waves (which require a physical medium such as air in which to move), but rather is electromagnetic radiation (in the form of “radio waves”). These waves must be “translated” into sound when they reach the earth by a special device known as a radio. There are special kinds of radios called radiotelescopes which translate electromagnetic waves generated from stars and galaxies (and other sources) into what they “sound like,” and with computer technology, you can also see what they “look like.” In that sense, you can actually “see” sound!

Now, an answer to your philosophical question might be: if space contains air, it can’t be a vacuum! Why? Because of the way we define “vacuum.” Someone said that the only statement that is completely true is a definition. The question you ask is kind of similar to watching a cartoon in which the cartoon character runs off a cliff, but doesn’t realize it, so he remains suspended in space. You know what happens when he looks down! So – can gravity exist and not exist at the same instant of time? You are essentially asking if a vacuum and a non-vacuum exist at the same time.

One of the fascinating aspects of the human mind is that it can entertain the possibility of the simultaneous existence of two completely opposite “realities” and not be disturbed about it (maybe that’s why dreams can be so neat). In fact, it was once thought by extremely famous physicists that light itself needed a physical medium (such as a gas) to travel from one place to another. They called it the “ether” (a.k.a. the “luminiferous aether”) and gave it fantastic physical properties to justify their theory. The problem was that all attempts to demonstrate its existence experimentally came to naught because of the famous Michelson-Morley experiment (http://encyclopedia.laborlawtalk.com/Michelson-Morley_experiment).

Regards,

PMF