this post was submitted on 03 Apr 2026
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Microblog Memes

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The speed of light (lemmy.world)
submitted 2 days ago by The_Picard_Maneuver@lemmy.world to c/microblogmemes@lemmy.world
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[–] wolframhydroxide@sh.itjust.works 1 points 1 day ago (1 children)

I was unaware that the person to whom I was replying, who claimed to be intimately familiar with the complete works of Feynman, needed instruction in how to "make use of" a fundamental constant of nature. If that is something you think is necessary, perhaps you should see to their instruction in such matters, as you are so confident in your faculties of condescending instruction.

Furthermore, I am acutely aware of the existence and nature of dimensionless constants, thank you very much.

[–] Natanael@slrpnk.net 1 points 1 day ago* (last edited 1 day ago) (1 children)

For somebody who claims to be acutely aware, you really seem to have no idea what goes into calibrating measurement devices to be able to measure physical constants. In particular you have no idea how many other units go into calibrating them, and how you fundamentally can not get an accurate reading of a physical constant without that calibration. And for somebody claiming I'm the condescending one, you're awfully rude yourself

Just see the definition of the kilogram, and how it's now defined in relation to time, c, and the planck constant.

While the second is the only base unit to be explicitly defined in terms of the caesium standard, the majority of SI units have definitions that mention either the second, or other units defined using the second. Consequently, every base unit except the mole and every named derived unit except the coulomb, gray, sievert, radian, and steradian have values that are implicitly at least partially defined by the properties of the caesium-133 hyperfine transition radiation. And of these, all but the mole, the coulomb, and the dimensionless radian and steradian are implicitly defined by the general properties of electromagnetic radiation.

https://en.wikipedia.org/wiki/Caesium_standard

When the atom is irradiated with electromagnetic radiation having an energy corresponding to the energetic difference between the two sub-levels the radiation is absorbed and the atom is excited, going from the F = 3 sub-level to the F = 4 one. After some time the atom will re-emit the radiation and return to its F = 3 ground state. From the definition of the second it follows that the radiation in question has a frequency of exactly 9.19263177 GHz, corresponding to a wavelength of about 3.26 cm and therefore belonging to the microwave range.

Oh so now we need to measure electromagnetic fields and charge to be able to hit the atom with light of the right energy to be able to measure time? And to verify the emitted frequency (both in and out) is right we need to define either energy (Joule, circular via either kilogram or Volt) or wavelength (directly circular)? Huh...

Everything meaningful is defined as relative properties, as ratios to other forces and properties of nature.

[–] wolframhydroxide@sh.itjust.works 2 points 1 day ago* (last edited 1 day ago)

Again, I think you're replying to the wrong person. I never disagreed with any of this. I literally learned all of this years ago. I appreciate your attempt to educate, but I'm unclear on its purpose. The dude claimed that the speed of light is defined based on the meter, and that that makes it a tautology. That is simply, provably false. Then the dude tried to move the goalposts. Never did I say that our measurements are anything less than relative. Never did I suggest that our derived units are not based on fundamental constants the nature of which can be only guessed at. Now, you've said that the statement I made didn't tell the dude "how to make use of" dimensionless units, which is a complete non sequitur. If you feel that that lecture is an important one when a dude demonstrates a fundamental misunderstanding of what c even is, that's your own affair, and I invite you to give this lecture a few comment levels up to the guy who thinks that c is defined based on the meter.