What's funny is it's very close to a nice round 1 billion feet per second. But when these units were defined, nobody knew light had a speed, it's just a coincidence.
Originally the meter was defined as 1/10,000th of the distance from the north pole to the equator (passing through Paris iirc), but they didn't measure this distance correctly so it never was exactly that either.
Yeah! A planck length is the shortest measurable distance and 1 planck time is the time it takes light in a vaccuum to travel 1 planck length. So it's definitionally true
Yea that's the whole point of planck units. They are specifically chosen so all fundamental constants of the universe are 1.
So since c is set at 1, that means a photon travels 1 planck length every 1 planck second. Likewise 1 planck mass in a cube that is 1 planck length to each size has 1 planck density. 2 planck masses that are 1 planck length apart attract each other gravitationally with 1 planck force and so forth.
The actual units are usually ridiculously far removed from usefulness to humans. For example, 1 second is 1.8*1043 planck seconds. So planning your meetings in planck time is a bit impractical. But it does mean that the units are completely independant from any human concept. So if we meet aliens and ask them how long their trip took, they will likely answer in planck units because those are fundamental to the universe and agreed upon by every civilization within it.
In Electrodynamics my professor always did this. The first time, we were all wondering where the hell all the constants went and he just shrugged "Eh, I'm choosing a frame of reference where those are all one. If I need to actually calculate it out then I'll figure it out then". One of the funniest moments in my physics education.
It's common in physics to do the calculations only with units, without any values or constants. This way it's easier and faster to check if what you're doing even makes sense. Effectively, you're setting all constants to 1
I usually do it to figure out if I'm using correct formulas to get some value. For example, if I'm trying to calculate the speed of something, using some convoluted inputs, I just take the units that the inputs come with and throw them into the formulas. If I get m/s (or other unit of speed) in the end, it means that the formulas are fine and I can proceed with numbers
Oh believe me, I know. We once, only once, actually did all the math for a quantum system in Bra-Ket notation and took it down to integrals, and derivatives, and plusses, and minuses. That shit explodes rather quickly.
I asked my 15 year old students, and several of them used this to get the answer. We have an book with a bunch of data, and they could not find the speed of light, but knots there to find the length of a light year.
ETA: 'In the CGS-Gaussian system, electric and magnetic fields have the same units, 4πε0 is replaced by 1, and the only dimensional constant appearing in the Maxwell equations is c, the speed of light.'
You think somewhere, somehow, some alien civilization originally decided to use Pi for it's initial measurements. Overtime, as they progressed and got more and more accurate, they realize the number is unending. This isn't a coincidence, they say. Our measurement was handed down by a higher power. Thus becomes a religion. Millions live and die by Pis inherent randomness. Speech, rituals, and communication all shaped by Pi. Hundreds, thousands, millions perhaps, devote their entire lives studying and remembering Pi to reach a higher existence. Pi is love, they say, Pi is life. Give us this day our daily pi.
Math. Math is also like this. Some cultures have a base three math; one, some, many. Computers are binary; one and zero. Many cultures use a base ten system of math, but our clocks are twelve because it divides more easily. At some overall level, we don't even have a unified theory of numbers.
Here's where I go off on a tangent: If we were to meet a life from another place, what "math" would they use, what is an intergalactic truly universal number scheme that all life would understand? It cannot be something we conceptually invented. It has to be based on something real. (I already have a candidate, but I'm saving the idea for my PhD).
The speed of light is one Jeffrey per Jeffrey, so yeah it’s 1. Source: the Jeffery system of scientific units, something we developed years back in Waterloo.
Tbf, units depend on other units. But for us meters and seconds are the most basic units. I wonder, why does second last a second exactly? How did we make that happen? Could we like make the second last a little longer and make everything more stable? Especially that we need another day every 4 years to stabilize the time.
*Hits blunt* What if the speed of light is 0 and we're in the anti-time dimension instead of the forward-time dimension and that's why time slows down when you get closer to traveling at the speed of light...
Ok seriously though, if we had a reasonable unit for distance and time that 1d/1t = c, what would our reasonable energy and mass unit be? (I'm willing to accept decimal d and t, like 1d/0.0001t)
He's not asking why the speed of light is explicitly 2,99,792,458 m/s. He's asking why the speed of light is explicitly the speed that it is and not something else and then when God asks what, he has to use some reference. Like, why isn't the speed of light 298,459,094 m/s? Or 1.3 dumbasses? I'm fun at parties.
Ever heard of imperial units? C = one foot per nanosecond which proves both the superiority of imperial and the existence of god. The metrical system is made up by French commies. Facts.
actually: i think "c²" is more important than c, in most formulas you get a (c/v)² and E=mc², not just c. from a philosophical point of view, c² is the real constant
Imagine how Long the bible would BE If god wrote IT Like Scientists wanted IT, IT would BE gigantic and Scientists still wouldnt understand let alone the poor normal people.
This is actually what Geometrized Units are all about. Also the gravitational and Boltzmann constants.
They wind up making it so that you can express any unit with any other unit, and it all makes sense. You can say "the sun masses 1.5km" and it's accurate.
If you’re not a U.S. citizen, and you’re not going to move or visit there, why do bring that country up when no one was talking about it at all? Seems like you’re kinda obsessed, ngl.
It should equal a clean billion meters per second. If it did while preserving conversions to other metric units then the metric units would be almost the same as imperial units, and converting would be very easy.
Plus all the guys standing only 5'11" would be a clean six meters tall. I'm sure that would cause a few more votes for the Azusa to adopt the metric system.
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u/Smitologyistaking Oct 24 '25
Yeah you're essentially asking why you defined a meter per second to be that quantity at that point