How do you get a pressure wave in a vaccuum?

Answer 1

Light will create a "pressure wave" in a vacuum by the action of photons on an object in the way. Example: a solar sail for interplanetary travel would be dependant upon a "pressure wave of photons impacting upon the sail. The "pressure" of the wave will be dependent upon the intensity of the light energy being produced by the source. Higher the intensity greater the "pressure".

Gravity can produce a "pressure wave" but in the inverse. Gravity produces a force of attraction which diminishes by the square of the distance from the attractive source. So the "pressure wave" would be negative in action, pulling something toward it vs pushing something away.

Theroritically, there is another possibility where a compression of time is produced by the interaction of gravity and the space around it could produce pulses of time distortion. This is best observed on the inside of a Black Hole or on the event horizon.

Answer 2

Well, current theory says that space is a perfect or nearly perfect vacuum. I tend to disagree somewhat, since light needs a medium to propagate in if it's a wave. SOMETHING has to be there in order for it to wave...

But basically, pressure is a measure of the overall pushing power of atoms against other atoms. IE, if some particles are more energetic they will push harder against less energetic atoms.

So, if we're talking about a theoretical clasically "perfect" vacuum (IE, literally nothing existing within a void), there wqould be no "pressure" since there would be no atoms to do any "press"ing against any other atoms. You could ADD atoms to the vacuum. But then it would no longer be a "perfect" vacuum, because there would be particles in it, so one could theoretically say it was a gas or possibly a plasma (if the atoms were ionized).

So, yeah, theoretically no pressure IN a vacuum. Now, outside the vacuum, there might be atoms wanting to get in. So, the outside medium would be pressurized... But not the vacuum itself. I'd expect the vacuum to have 0 pressure. Of course the stuff outside would come rushing in, so the vacuum wouldn't stay a vacuum for long.

Answer 3

Pressure is force divided by area. So you need something to exert a force. A force is a change in momentum divided by a change in time. So you need something with momentum which can hit something else. Light has momentum, and when absorbed it will in fact exert a measurable force. So (in the absence of matter) you need a pulse of light.

Of course, the light itself is a "thing" in the vacuum. The same analysis will do for any pulse of field energy (gravitational, for example).

Answer 4

You don't. A pressure wave implies the presence of a fluid; a vacuum, by definition, has none.

Answer 5

I guess this is a trick question.... It is a vacuum, therefore void of any pressure!

Answer 6

You need molecules, so you'd have to introduce them
yourself.

Answer 7

You would have to split an atom