## torsdag 12 januari 2023

### Not Natural New 2019 SI Definition of Unit of Mass

The Kibble balance is an impressive instrument used to specify a new of unit of mass.

The 2019 SI definition of units gives a new specification of the unit of mass as kilo $kg$ based on Einstein's formula $E = Mc^2$ where $E$ is energy in joule $J$, $M$ is mass in $kg$ and $c$ is the speed of light in meter $m$ per second $s$, with

•  1 kilo = 89875517873681764 J     (*)
and by SI definition $c=299792458\, \frac{m}{s}$

Here second $s$ is defined as the duration of exactly 9192631770 periods of certain radiation from a Cesium atom, and meter $m$ in terms of the distance traveled by light per second assumed to be exactly 299792458 meters. The new choice of units connect to old units but the exact values are assigned by definition.

Further,  $J$ is defined in terms of jouleseconds $J\cdot s$ by specifying Planck's constant $h$ to be exactly equal to $1.054571817\times 10^{−34}\, J\cdot s$, which by a special electromechanical instrument named Kibble balance gives the value (*).

We see that the unit of mass is defined in terms of second, meter and Plancks constant $h$ assuming Einstein's formula $E=mc^2$ together with Planck's light/photon energy formula $E=h\nu$ to make a connection through the Kibble balance between (gravitational) mass and electric/light energy.

Many other possibilities of replacing the International Prototype of the Kilogram (IPK) in Paris, named Le Grand K (The Big K), were discussed before settling on using Planck's and Einstein's formulas arguing that they are the most fundamental relations of all of physics.

In other words the new SI  definition of unit of mass is a hommage/tribute to Planck and Einstein representing modern physics with Le Grand K simply old physics.

But is it natural? The result is that the energy of a mass of 1 kg is equal to the energy of a collection of photons with frequencies summing to $1.356392489652\times 10^{50}$, which is not very illuminating.

In other words, insisting on Einstein's $E=mc^2$ has very little to do with actual physics. We know that energy can take different forms as kinetic, potential, chemical energy and nuclear energy with possibly a connection to $E=mc^2$ in nuclear energy. But not else, and so the present SI unit of mass lacks good reason as long as controlled nuclear fusion is far into the future, if ever.

Further, Planck's key formula $E=h\nu$ for photon energy with $\nu$ a natural number, expresses that energy can only take discrete values as multiples of a smallest quanta of size $h$. Planck did not like this idea, which he used only as a last resort in a hopeless situation as explained in Computational BlackBody Radiation offering a new theory in the form of continuum wave mechanics without smallest quanta. Compare with What, exactly, is a photon?

A more natural definition of a unit of mass would be in terms of a certain number or atoms (the Avogadro project) of e.g. gold as a new gold standard of physics. But that would be classical physics, which has to be replaced by modern physics, even when it does not make sense, to motivate continued funding...and it seems to work...