Standard Weights and Measures 1

[rb1957]

I couldn't think of which forum for this, but figured most would come here at some time.

I was watching a TVO (like PBS) show (probably from the BBC/ITV) about standard weights and measures, dealing with time and meter length standards and creating hyper accurate standards.

1) If we're measuring time by the frequency of atomic emissions (I think we are), yeah it's easy to count peaks and infer the period of time from the number of peaks (from the frequency of the emission), but isn't the frequency of the emission dependent on some physical parameter (planck's constant?) ? Do we Know that constant to such an amazing degree of accuracy ?

2) Is the flow of time here on earth affected by the earth's gravitational field ?

3) The speed of light (used to measure a meter) is dependent on the medium it travels through (yes?). If so, how do we make a perfect vacuum ? (if we're making hyper-accurate measurements)

4) Is the distance here on earth that this light travels affected by the earth's gravitational field ?

another day in paradise, or is paradise one day closer ?

 

[dik]

Planck's constant is neat... if you were to change it dramatically, temperature changes in a room wouldn't be a 'continuoum' but the temperature would change in stepped values, like 18C to 20C to 22C, etc. It was a neat concept.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[IRstuff]

1) Yes, but ... ;-) atomic time standards are stable to something like 1 second in a billion years, so frequency is quite stable, assuming tolerably stable environment

2) Yes, gravitational time dilation is a factor; GPS has a time dilation correction factor on the order of 50 nanoseconds

3) Vacuum, yes, perfect, not necessary. They've built atomic fountains with the vacuum technology currently available

4) How would you even tell? ;-) presumably, the answer is yes, but it's "relative" ;-) What the photon sees as distance isn't necessarily the same as distance that we see, I think.

Sorry, my quantum is pretty rusty and I sucked at it the first, and second, time around

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[TigerGuy]

Besides, how does this all affect Han Solo making the Kessel Run in 12 parsecs?

 

[IRstuff]

Besides, how does this all affect Han Solo making the Kessel Run in 12 parsecs?

It's explained in

https://starwars.fandom.com/wiki/Kessel_Run

;-) There are more than enough nerds in the world to retcon that tidbit.

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[1503-44]

They get to where they're going so fast, they're not really bothered by distance. NY to London in 0.025s Who cares if you forgot your wallet, just pop back and get it.

https://spie.org/news/photonics-focus/novdec-2020/what-exactly-is-a-photon?SSO=1

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[Tomfh]

There are more than enough nerds in the world to retcon that tidbit.

Do you think it was a script error that nerds eventually “fixed”, or was actually correct from the start? I quite like the idea of the ships “speed” being a function of how tightly it can travel through hyperspace.

 

[IRstuff]

Do you think it was a script error that nerds eventually “fixed”, or was actually correct from the start? I quite like the idea of the ships “speed” being a function of how tightly it can travel through hyperspace.

The script was written by Lucas intentionally incorrect as a way of telegraphing that Han was a BSer. The nerds came along later with a concocted scenario where Han would have been mostly correct.

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[dik]

was unaware of the... I remember the movie because of the 'old day westerns' where there were 'white hats' and 'black hats', and 'good' triumphed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[IRstuff]

The first Star Wars segment is loosely inspired by a samurai movie called "The Hidden Fortress" starring Akira Kurosawa, although Lucas took away from the movie the princess in distress and the two bumbler side characters.

Speaking of Westerns in space, Battle Beyond the Stars is basically The Magnificent Seven shifted in time and space; in fact, Robert Vaughan plays the exact same character in both movies, although they have different names. Sybil Danning is in BYTS, so it also has that going for it. Otherwise TMS is a way better movie. Oh, and Magnificent Seven is likewise based on a samurai movie, "The Seven Samurai," naturally ;-)

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[Tomfh]

The script was written by Lucas intentionally incorrect as a way of telegraphing that Han was a BSer.

Ahh, that makes more sense. He was originally more of a crook and a scammer. "Han Shot First" and all that.

 

[rb1957]

well that took three posts to get hijacked !

back to the last on subject reply, thx IRStuff ...

1) Yes, I know atomic clocks are hyper accurate. But do we know the frequency to that accuracy ? Isn't frequency derived from some physical constants (like Planck's constant) ? How accurately do we know these ?? And yes I know that if Planck's constant were a little different then the universe would be very different.

2) Yes, I know this . I'm suggesting that this'll impact hyper accurate measures. Unless we are defining the Terrain meter and second. Of course what else are we sensibly doing here on Terra, but the program seemed to be suggesting these would be universal measures.

3) and 4) yes, I know these are tiny effects but when you're trying to be hyper accurate, then molehills become mountains.

another day in paradise, or is paradise one day closer ?

 

[IRstuff]

1) Yes, I know atomic clocks are hyper accurate. But do we know the frequency to that accuracy ? Isn't frequency derived from some physical constants (like Planck's constant) ? How accurately do we know these ?? And yes I know that if Planck's constant were a little different then the universe would be very different.

We essentially define the frequency and time together; Planck's constant or any other constants are bypassed.

The second is equal to the duration of 9192631770 periods of the radiation corresponding to the transition between the hyperfine levels of the unperturbed ground state of the 133Cs atom.

What this means is that when the cesium atom is at the right temperature, etc., and excited with the appropriate radiation, the transition of the hyperfine levels has a frequency of 9192631770 Hz.

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[cranky108]

Would most of us be able to determine if an atomic clock is correct, or off by a fraction of a second? On a human scale, does it matter?

 

[IRstuff]

Sure, it would; the second and speed of light determine the accuracy of the measurement of accuracy of military rangefinders, and just the error of using vacuum speed of light vs. air speed of light throws off the rangefinder verification by a few meters over 20 km, so roughly 0.001%. Teensy, but if you're trying to drop a round on a T72, missing by even a meter means they get to shoot back. Likewise, GPS depends on the secondary time standard, which is the rubidium clock, and even grossly NON-relativistic speeds of the GPS satellites, the time dilation effect would throw off your location by roughly 50 ft, putting you possibly on the opposite side of the freeway.

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[Alistair_Heaton]

i still haven't ever seen a standard for a mozzy's/midgies cock or chuff. Which was a very common requirement in Scotland in my day.... Surpassed metric and imperial

hey tam go skim a midges cock off that mate would ya...

 

[btrueblood]

" Isn't frequency derived from some physical constants (like Planck's constant) ? How accurately do we know these ?? "

As IR said, we don't need to know it, we only have to assume it's constant in the area where the standards are used. Which suggests that there should be a footnote in all standards to that effect (akin to the lawyer-speak in TV medication adverts, "your mileage may vary, not applicable in areas where h is non-constant...")

 

[btrueblood]

It is interesting to see that the international mass standard kilogram was reported to have changed since the last time it was measured...thus the push to create a non-artifact standard for mass.

 

[Alistair_Heaton]

As long as everything the same it doesn't matter

Its a bit like imperial going metric. Its all been metric for years.

 

[Eufalconimorph]

The bootstrapping problem in Metrology is certainly an interesting one (though probably not for this particular subforum).

You can get *very* deep in the weeds.

For measuring time & frequency, I recommend reading the NIST Handbook of Frequency Stability Analysis.

For measuring basic mechanical quantities (flatness, straightness, roundness, concentricity, etc) I recommend Foundations of Mechanical Accuracy by Wayne R. Moore. Or watching a bunch of Tom Lipton's Youtube channel, eg how to measure a straightedge with a precision level. More modern devices like electronic autocollimators and interferometry are also used.

Most of the fundamental properties of the universe don't seem to vary much (if at all) on a local scale. It's possible to measure a few varying, such as the effects of gravitational time dilation due to differences in the Earth's mass, eg as [Tom Van Baak did by carrying an atomic clock up Mt Rainer and leaving a twin at home](

http://www.leapsecond.com/great2005).

But most of the constants do seem to be constant within the local region (Earth & near surroundings), not variable.