An Exact Value for the Planck Constant: Why Reaching It Took 100 Years

http://blog.wolfram.com/2016/05/19/an-exact-value-for-the-planck-constant-why-reaching-it-took-100-years/

by _kcxz • 10 years ago

49 11 10 years ago

blog.wolfram.com

gsmethells• 10 years ago

If there ever was a need for a TL;DR, then this is it. Anyone care to take a crack at it?

WorldMaker• 10 years ago

It appears to be:

An abbreviated history of the SI system of measures told with interspersed jokes of arguable usefulness from a first person POV character of unnecessary abstraction.

Within this history are glimpses into the complicated history of experimentally verifying Planck's constant and the interest in moving to a Planck's constant-based kilogram rather that the previous kilogram definition.

It would seem these glimpses into said experiments and kilogram debates are the reason for this post to exist and key thesis of the chosen title/headline. However the majority of this content is nested deeply below the fold and surrounded by so many tangents and attempts at humor one can only question if perhaps the author or authors misstated their thesis in the title or are intentionally attempting to confuse potential audiences for some semblance of humor.

GrumpyYoungMan• 10 years ago

Yeah, the ghost of Jean-Charles de Borda is rather wordy, isn't he? It boils down to:

1) Fundamental units are the base units by which all other types of measurement units are defined.

2) The kilogram is the last fundamental unit that is defined by an arbitrary physical artifact. This is a problem because every time it's taken out to calibrate other measurements, the measurement process wears it out a little, making its mass change.

3) Other units are defined now by simple arbitrarily chosen values and the interrelationship between those values as defined by the formulae of physics. For example, a second is defined as "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

4) The particular physics formula chosen to use as part of the definition matters greatly because the precision of the definition depends on the least precise measurement of the other variables of the formula being used.

5) After long debate, the standard definition of the kilogram is about to be changed to a definition based on an arbitrarily chosen value of Planck's constant, which is good because it's now reproducible everywhere instead of being dependent on a physical object that's slowly being worn out.

rwallace• 10 years ago

It's an enchanting, well-written essay on the history of an area of science few people ever think about, a window into the past, containing quite a few things I didn't know before, and along the way a showcase of some pretty neat things Mathematica can do.

No, it doesn't need a tl;dr. It doesn't contain any data you're going to personally need today or tomorrow. It falls into the categories of intellectual curiosity and general education. If that's not your dish, skip it and move on.

But I am reminded of a Lewis Carroll quote:

"No, no!" she broke in merrily. "I didn't mean our Literature! We are quite abnormal. But the booklets--the little thrilling romances, where the Murder comes at page fifteen, and the Wedding at page forty--surely they are due to Steam?"

"And when we travel by Electricity if I may venture to develop your theory we shall have leaflets instead of booklets, and the Murder and the Wedding will come on the same page."

Successful prediction.

euyyn• 10 years ago

I mean, if you weren't going to tell the parent what it wanted, as others did, why bother?

cdumler• 10 years ago

Glancing through it, it almost appears that it's almost copy and paste. It has so many tangents and subject splices, it is hard to follow.

It appears to be arguing that the Planck constant is defined partially by mass, which has never had an high-precision value SI unit. The Avogadro project has determined a high-precision definition the Avogadro constant. The Rydberg constant is known to high precision; therefore, the two can be used to together to find a high-precision value of the Planck constant. Also, once a fixed definition of mass through physical constants is made, we will have an exact definition of Plank constant.

domdip• 10 years ago

This is unreadable.

scottshea• 10 years ago

It lost me with the opening spoof (?) of Sympathy for the Devil. Love the song but not remotely needed in the article.

brianpgordon• 10 years ago

Wow, is this an entire year's work? It just keeps going and going, and going.

outworlder• 10 years ago

Interesting advertising. It shouldn't be that long though, unless they expect us to spend 100 years too.

Someone• 10 years ago

"in 1889 the Romanian prototype was already 953 mg lighter than the international prototype kilogram"

Is that correct, or should that be 953 μg? I find it hard to believe that a carefully kept reference kilogram designed to keep its mass would lose almost a gram in a century.

μg Also seems more in line with what Wikipedia writes (https://en.m.wikipedia.org/wiki/Kilogram#Stability_of_the_in...)

An Exact Value for the Planck Constant: Why Reaching It Took 100 Years

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