from Hacker News

Ask HN: Something that you learnt and made you go Wow

by boca on 9/22/23, 2:58 PM with 17 comments

• by eureka-belief on 9/22/23, 3:05 PM

  I recently went down the fighter plane dogfighting rabbit hole. I guess I used to think that dogfighting was just about reaction times and handling the plane. But because of the subtleties of airplane performance parameters and how they interact with energy management, it’s much more tactical than that. And while the pilots are calculating tactics they might be putting in 6+ Gs.

  https://youtu.be/kV391POGaV4?si=__YKqs4OdYzt1BgK

• by mikewarot on 9/22/23, 7:16 PM

  I helped a friend repair a few HP Cesium beam clocks. Once I understood how they actually work, including the Zeeman lines, I was amazed. I love explaining it to others.

• by 7373737373 on 9/23/23, 6:41 AM

  Roger Penrose - Why Did Our Universe Begin? https://www.youtube.com/watch?v=ypjZF6Pdrws

  tl;dw: It is well known that the universe expands, tracing this back in time leads to the singularity called the Big Bang. But is it possible to ask for a "before" the beginning of time? What is time? Time is what we measure with clocks. What are clocks? Something that returns to the same state (say, a pendulum, or the earth orbiting around the sun - a "year"). To be able to build a clock you need mass. Only objects with mass, moving below the speed of light, experience time. In the very far future, after all stars have burned out, the only objects remaining will be black holes. Eventually, even they will decay due to Hawking radiation. So in the end, there will be only expanding space, and radiation that "travels to infinity". Photons themselves do not experience time as they move with the speed of light. Without mass, without anything that has a notion of time, the concept of distance becomes meaningless. The universe will become spacelike. Without distances, the universe may as well be a singular point. Like the Big Bang :)

  I've listed some more here: https://icebergcharts.com/i/Things_that_blew_my_mind

• by ian0 on 9/23/23, 2:08 AM

  Grady from the youtube channel practical engineering [0] released a book recently called "Engineering in Plain Sight" and I preordered it for my son but end up hogging it myself!

  It explains how different infrastructure (electrical grid, roads, trains etc) are built and arranged. A beautiful book, with everything simply explained - chock full of wow/ah-ha moments.

  0. https://www.youtube.com/@PracticalEngineeringChannel

• by kwant_kiddo on 9/25/23, 8:45 PM

  Silly, but getting comfortable with vim macros.

  Not really wow, but makes me smile when I parse +100 lines in under 10s. Coworker might be impressed if you can pull it off on the spot. Too bad some editors are not emulating it too well.

• by mstipetic on 9/23/23, 1:11 PM

  For me it’s the elixir/erlang OTP library. Main point being - wherever I worked each team invented their own bespoke solutions and approaches to the problems solved with OTP, and it turns out we had battle tested building blocks all along, had we bothered to look back

• by CableNinja on 9/22/23, 3:45 PM

  Time, in relation to computers (and all tech really). A company i worked for wanted systems to have no more than 2ns of time drift between each other, in a network of +10 devices. NTP and the like, can only do so much, and the overhead is compounding. During my research i fell down a rabbit hole... A crystal oscillator, even from the same batch of crystal, will have a very slightly different frequency, which means oscillator A and B from the same batch will eventually drift. To solve that, newer tech steps in, MEMS oscillators. These are microscopic tuning forks that vibrate. These give precision oscillations, *however* movement of a MEMS device (ex picking up a machine and moving it, shaking it, etc), like in the case i was exploring, will also cause time drift because the device movement can cause the fork to ping off one of the sides, causing an early, or late, clock tick. Any movement can cause one or more mis-ticks, and a device constantly in motion will cause lots of drift. Crystals at least arent subject to drift as a result of motion (not entirely true, because at a certain speed you can start to have to deal the laws of physics like the analogy of a photon bouncing between two mirrors as you travel toward C). Theoretically, although i havent seen anything about it, you could cause time drift in a MEMS or Crystal oscillator, by yelling at the oscillator (at a certain frequency). Now, we come back to crystals, and discussing temperature, as these oscillators are supposed to be kept at a certain temperature during operation. Any temperature difference between optimal and actual temperature will cause the oscillator to slow down or speed up, causing time drift. MEMS are not susceptible to this, *however* they can be, if you can cause a temperature difference between the fork and the base, you could make the fork expand and hit more quickly, or shrink, and hit slowly. MEMS are also a wild device because the area between the parts is just large enough to allow helium atoms to get stuck between them, and to top it off, helium can squeeze through almost anything, which includes the IC packaging of the MEMS chip, which was discovered when an iphone was left in the vicinity of an MRI machine that was leaking helium.

  And thats the rabbit hole of time in relation to electronics. I honestly was never really curious about the whys of "its impossible to have zero time drift over an extended time between two or more electronic devices", i knew it was physics related, but wasnt really curious as to what about it. I know now, and i sorta wish i didnt because i feel like im having a Pepe Silva moment when i have to explain or remember any of this.

• by notsurenymore on 9/22/23, 4:54 PM

  I watched this a while back and it was one of the few videos I’ve seen recently that really impressed me:

  https://youtu.be/mdKst8zeh-U?si=cvD_1d6vmwEzxDas

• by b20000 on 9/23/23, 9:26 PM

  I studied CS and graduated top of my class and have 20 years of experience and learnt the past couple of years that now all that matters is grinding leetcode and my degree and experience are mostly ignored.

• by metaloha on 9/22/23, 4:03 PM

  Rice cookers. Damned clever. I wish toasters worked on a similar concept.

• by behnamoh on 9/22/23, 9:18 PM

  Lisp, Lambda Calculus, SICP's example of encapsulating data in closures