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zanderbaxa · Sep 30, 2011, 07:14 PM

The evacuation is of a 1 m plastic tube 1" in diameter.

Unknown008 · Sep 30, 2011, 11:12 PM

Use a pump?

zanderbaxa · Sep 30, 2011, 11:56 PM

I want to get rid of all matter in the tube. If I shine a light through the end of the tube, no light should be reflected by any matter in the tube.

Unknown008 · Oct 1, 2011, 04:45 AM

In theory, I guess that no light will be reflected.

Though the plastic tube might cause some light to reflect... well, you'll see if you do the experiment :)

zanderbaxa · Oct 1, 2011, 03:11 PM

The idea is to show that light is a local phenomenon. Interpretation of the electromagnetic waves impinging on the opitical senses. Light is not perceived unless the EMW is reflected. If there is no matter in the tube to reflect the EMW, nothing will be seen.

jcaron2 · Oct 1, 2011, 07:59 PM

There's no way you'll be able to rid the tube of ALL molecules, but with a good vacuum system you can get the pressure low enough that the mean free path between molecules is much, much greater than one meter. That means you need to get down to high vacuum or ultra high vacuum range. You won't be able to reach the latter inside a plastic cylinder. The vapor pressure of most plastics is far too high. Stainless steel is typically used for vacuum chambers at those pressures.

By the way, when I said "vacuum system" above, I mean a system of pumps. This would typically involve some sort of roughing pump such as a rotary vane pump, followed by a high vacuum pump such as a turbomolecular, diffusion, or cryogenic pump. These aren't things you're going to find at your local hardware store, but they can be found at many universities and labs.

zanderbaxa · Oct 1, 2011, 08:12 PM

Thanks.

jcaron2 · Oct 1, 2011, 08:38 PM

By the way, glass has a very low vapor pressure too, so that would probably be the way to go if you need to see inside the tube.

zanderbaxa · Oct 2, 2011, 01:08 AM

Thinking more about it; it will not be necessary. There is another way, and there are plenty of witness of the phenomenon. During a full moon the EMWs from the sun can not be seen, as a beam of light when we look around the moon to the horizon' Wh only see the light from the sum when it is reflexted into our eye. Also ISS and Apollo missions did not see shafts of light bypassing their craft, only when they saw the light being reflected.

jcaron2 · Oct 2, 2011, 05:38 AM

Exactly!