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Cake day: February 1st, 2024

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  • 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.












  • That’s…not really a cogent argument.

    Satellites connect to ground using radio/microwave (or even laser), all of which are electromagnetic radiation and travel at the speed of light (in vacuum).

    Light in a fiber travels much more slowly than in vacuum — light in fiber travels at around 67% the speed of light in vacuum (depends on the fiber). In contrast, signals through cat7 twisted pair (Ethernet) can be north of 75%, and coaxial cable can be north of 80% (even higher for air dielectric). Note that these are all carrying electromagnetic waves, they’re just a) not in free space and b) generally not optical frequency, so we don’t call them light, but they are still governed by the same equations and limitations.

    If you want to get signals from point A to point B fastest (lowest latency), you don’t use fiber, you probably use microwaves: https://arstechnica.com/information-technology/2016/11/private-microwave-networks-financial-hft/

    Finally, the reason fiber is so good is complicated, but has to do with the fact that “physics bandwidth” tends to care about fractional bandwidth (“delta frequency divided by frequency”), whereas “information bandwidth” cares about absolute bandwidth (“delta frequency”), all else being equal (looking at you, SNR). Fiber uses optical frequencies, which can be hundreds of THz — so a tiny fractional bandwidth is a huge absolute bandwidth.







  • I feel old…when I was learning how to run Linux I started with an old 386 (maybe 486?) my dad wasn’t using. I think it had 32MB RAM, which was fancy for those machines.

    We had dial up at the time, so only one machine could be on the Internet. So, I set up a modem on the x86, plugged into an Ethernet hub (switch?), and learned enough ipchains (this was before iptables) to share a connection. It also ran Samba, an AFP server, and probably FTP and HTTP (just for local access) — but it worked for filesharing.

    It could also run MP3 streaming software which amused me because the machine itself was too slow to decode MP3 (but that’s not necessary to stream).