why is the speed of light a precise value?

The speed of light exactly 299792458 m/s. It was set that value. This video looks how it got to this point and also explores some of the more recent attempts at measuring the speed of light, including Michelson and Eveson. I also explore how the meter definition was refined over time and led to its redefinition based on the speed of light.

Errata: A small typo in my title that appears briefly at 0:47. The last three numbers should be 458, not 568. Sorry - The T shirt is correct!!

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[paulvale]

I love learning stuff even at 63. Thank you for another well presented video.

[JungleJargon]

There are three rates to consider. 1. The diminishing effect or draw of gravity away from the center of mass. 2. The increasing rate of time away from the center of mass. 3. The increasing measure of distance away from the center of mass. Speed is measured by time and distance which change and that changes the speed of light and causation. Distance gets longer without gravity and time goes by faster, both of which speed up causation. The light has to arrive at a farther distance faster when distance is stretched *and* time also goes by faster. *Then* there is the first thing to consider and that is the diminishing draw of gravity which means things eventually slow down the farther away they are from the center mass of a galaxy. (It's not complicated.) 😎

[JohnSmith-tdhd]

The people who defined a meter must be really kicking themselves that they almost got it to be exactly 300, 000, 000 m/s.

[naelblogger]

What a relief that you use the metric system :D Great video!

[arijit]

on an another note as light is electromagnetic wave
light experiences a speed of
c=1/√(μ₀ε₀)
where, μ₀ is the permeability of space
& ε₀ is the permittivity of space

from the Maxwell's Eqⁿ

[cdouglas]

Facinating! Never would have guessed that tinkering with measurement criteria, (time and distance) would be a way to "determine" the speed of light. Altho I guess they are abstractions of humankind so why not define them at our convenience.

[theoriginaldrpizza]

Excellent video! Perfect for a flipped lesson.

[Zenaneh]

Its clear and easy explanation!
Tnx for remind me again.

[bernardwhipps]

Your t shirt says 299 792 458 but you asked the question why the speed of light is exactly 299 792 568? Huh?

[carinalexicon]

James Clerk Maxwell's estimate of 299, 792, 472 is significantly absent in spreadsheet at 10.03
Then they redefine both the metre and the second to 'correct' Maxwell by 14 metres.

[gerrymcerlean]

Why does it say '299, 792, 458m/s' on your T-shirt but '299, 792, 568m/s' on the overlay banner? Which one is correct?

[baberoot]

That number...is the two-way speed of light. Technically...we do not know the one-way speed of light.

[sergusy]

Wow. As far as I know the speed of light is 299792458+/-1.2 metres per second. It is not the exact number. Moreover, the direct quote of the Michelson work - “Measurement of the velocity of light in a partial vacuum”:

Series of measures 1-13 and 26-54, made from February 20 to July 14, 1931, gave 299775 kilometres per second. Series 14-25, made from March 25 to April 3, 1931, gave 299746 kilometres per second. The fact that these mean results differed from each other and from the value 299796 kilometres per second obtained on Mount Wilson necessitated additional readings.
Further readings made from March 3 to August 4, 1932, gave a mean value of 299775 kilometres per second. If, however, the readings be divided into two groups with an equal number of individual determinations of the velocity, series 55-110 give a value of 299780 kilometres per second, while series 111-158 give 299771 kilometres per second.
Readings were resumed in December, 1932 giving a mean high value of 299785 kilometres per second, which dropped to a mean of 299765 kilometres per second on January 15 and rose again to earlier value on February 28. The mean velocity for the 75 series was 299775 kilometres per second.
Attempts to explain these variations in velocity as a result of instrumental effects have not thus far been successful.

What clearly shows the speed of light can vary.

[Enegma]

The meter was an Egyptian invention not a French

[KrystelSpicerMindArkLateralThi]

A comparison:
If I have something important to do in a few days but it feels like I should be doing it now, is that comparable to when a deceased friend asks if you're ready for the show months after the fact?
✨If so, I wonder can we only see where we are by looking at ourselves from a long way away, & that this here is not as concrete as it gets. And then I think, is anything concrete?
✨And then I wonder that as universe expands, history might also, & everything changes beneath & including our own noses ..& truth moving faster than light knocks time as we know it off kilter by days or months eg.
This post may be useful to anyone wishing to measure the speed of light.

Krystel Spicer Mind Ark on Facey. I'm pretty sure light won't be told what to do.
👋😉

[levitheentity]

0:43
"why is the speed of light exactly 299.792.568 m/s?"
IT ISN'T!!!

[EGMAG]

if you square 186, 000 m/s you get 34, 596, 000, 000 ! What is up with that ? Please .

[grass]

is 300.000 000 just some fricción of dark matter

[casualcadaver]

High school level physics seems like post grad level physics in the early 1900's.

[rikkimiller]

Precision is a measure of the REPRODUCIBILITY of a series of measurements. A measurement can be precise, but NOT accurate. A number that is accurate is also precise. Your title is not correct. You are confusing people with the meaning between PRECISE and ACCURATE.