this post was submitted on 27 Jul 2025
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I love shit like that.
We have this incredibly expensive machine that was made by incredible engineers and scientists who spent an ungodly amount of hours on it. And their solution to some kind of problem with the machine, was to wrap a part in kitchengrade alu-foil, probably from the employee kitchen.
Aluminum foil is very common in physics labs. And a main use for it is "baking"! To get ultra high vacuum (UHV)* you generally need to "bake out" your chamber while you pump down. Foil is used same as with baking food
keep the heat in and evenly distributed on the chamber.
Sadly, it's usually not food grade aluminum foil, as that can contain oils, and oils and vacuum are generally a big no-no.
*Just how good is UHV? Roughly: I live in San Francisco, which is ~7 miles by ~7 miles (~11km). Imagine you raise that by another 7 miles to make a cube. Now, evacuate every last molecule of gas out of it. Now take a family sedan's trunk, fill it with 1 atmosphere of gas, and release that into the 7 mile cube. That's roughly UHV pressure.
Thanks for the analogy, that really helps to put it in perspective. I was trying to work out the number of molecules per metre that would leave you with, but either my sense of scales is off kilter or I've got it wrong.
From what I can find, there are approximately 2.5e25 molecules per m^3^ at 1atm. Given an 11km cube has a volume of 1.3e12 m^3^, that gives around 2e13 molecules per m^3^ per m^3^ released. That sounds high, have I got the figures wrong somewhere?
Your numbers seem reasonable
more intuitive for me to work in terms of pressure. Atmosphere is (roughly) 1e3 Torr, good UHV can be around 1e-10, so that's 13 orders of magnitude, which is (roughly) the same difference that you calculated.