# Re: aiming to complete Everett's derivation of the Born Rule

`On Tue, Apr 26, 2022 at 2:02 AM John Clark <johnkcl...@gmail.com> wrote:`
```
> On Mon, Apr 25, 2022 at 8:08 AM Bruce Kellett <bhkellet...@gmail.com>
> wrote:
>
> * > That is true enough, but we do not always measure energy by comparison
>> with some reference energy. Sometimes we use other laws of physics. For
>> example, most of the energy in our immediate environment is mass energy,
>> coming from the relation E = mc^2. So we can consider mass as a surrogate
>> for energy. Mass can routinely be measured by weighing, assuming that the
>> gravitational constant does not change.*
>>
>
> The only reason we think the gravitational constant does not change is
> because when we measure the potential gravitational energy in something
> today against a standard calibration energy we find that we get the same
> number of energy units that we got yesterday when we measured the potential
> gravitational energy it was in against a standard calibration energy.
>

Sure, a spring balance needs to be calibrated against some standard mass.
But we do not calibrate every day. Once the scale is set, we assume that
the spring constant or whatever remains the same, so that recalibration is
not necessary. So if all energies (including mass) drop by 90%, we will be
able to detect this as long as the spring constant does not also change by
this amount. Springs tend to rely on the electromagnetic properties of
metals, and these will not change just because we measure a spin component
in the next room.

To take another simple example, I used a spring balance to compare a mass
against the gravitational field, where I assumed that Newton's constant
does not change on a spin measurement. If all energies (and masses) drop by
50% in each branch of the spin measurement, then the mass of the earth
decreases by 50%, and the local acceleration due to gravity, g, also drops
by 50%. Now consider a simple pendulum: the period of swing is T =
2*pi*sqr(L/g), where L is the length of the pendulum. If g drops by 50%,
the period of the pendulum increases by a factor of sqrt(2). This increase
can easily be measured against a clock that does not rely on local gravity,
such as a spring clock, or a crystal clock.

So the idea that a change in the energy of a branch is not noticeable is
false -- one can always devise an experiment that does not rely on
comparison with standard weights before and after the split. Other physics
comes into play, and there is no suggestion that Newton's constant, for
example, is influenced by our spin measurement, so the increase in the
period of the pendulum is certainly measurable, as is the change in weight
of our bag of flour.

Bruce

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