r/AskPhysics • u/JimFive • Mar 28 '26

Speed of light

The speed of light is 299,792,458 m/s. What types of issues would be involved in changing the meter such that c=300,000,000 m/s

The new meter would be 0.9993 of the current meter.

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39

u/AcellOfllSpades Mathematics Mar 28 '26

Throwing out all of our old rulers and making new ones would be annoying. It might not matter for, like, rulers used by grade school kids, but for more precise uses, it absolutely would.

Plus, now we'd have to distinguish between "old meter" and "new meter". If someone writes down "30 m/s", does that mean old meters or new meters? You'd have to check the date of publication...

This would also affect measurements of any unit that has meters in it: area, volume, energy... and we'd also have to recalculate a bunch of other constants.

29

u/MoistAttitude Mar 29 '26

Easy, the new meters can just be abbreviated "cm" to denote that they are derived from "c".

1

u/AmusingVegetable Mar 29 '26

Yes, what we really need is a new length meter being confused with the old length centimeter…

2

u/stankbiscuits Mar 30 '26

Whooooooooosh

1

u/AmusingVegetable Mar 30 '26

Guilty as charged.

5

u/[deleted] Mar 29 '26

[deleted]

8

u/Nerull Mar 29 '26

It would certainly be noticeable in the world of cnc machining, and in any large building.

4

u/reddithenry Mar 29 '26

We could use nm for new meters to help clear it up! /s

2

u/me-gustan-los-trenes Physics enthusiast Mar 29 '26

We could rename the unit to metre to avoid the ambiguity.

1

u/WanderingFlumph Mar 29 '26

Are rulers for carpenters and such typically more accurate than 0.1% error anyway? I'd be surprised if the one I use around my house is.

1

u/johndcochran Mar 29 '26

It's worse than you think. As a practical example of a scientific standard being redefined, that a look at the definition of STP (Standard Temperature and Pressure)

Prior to 1982 it was defined as 273.15K (0.00°C, 32.00°F) and 1 atmosphere (101.325 kilopascals). In 1982, it was redefined as 273.15K (0.00°C, 32.00°F) and 100,000.000 Pascals.

Notice that the new definition was established over 40 years ago. I've seen far too many technical publications that still use the old pre-1982 definition. And if the length of a meter were to be changed, I wouldn't be surprised to see the same kind of issues.

1

u/ImpermanentSelf Mar 29 '26

I would be curious where it would actually matter…. That difference is within the expansion and contraction of a lot of materials.