Re: Why does Physics have two different theories: Classic and Quanntum (+SRT)?

On Jul 2, 6:44 am, socratus <israel...@xxxxxxxxxxxx> wrote:
What is the reason for these differences?

Noone ever said there were two *different* theories. The microscopic
world is described by quantum physics. The macroscopic world is mostly
described by classical physics.

These two facts are *not* in contradiction!

In fact, along the spectrum of possible theories in "theory space" it
is even possible to have hybrids that are between classical and
quantum physics -- an entire continuum of selections to choose from
and fit to the world. The key concept is "superselection". The
extremes of a (a) purely classical or (b) purely quantum system are
those, respectively, where for the superselection sectors of the state
space (a) every sector is 1-dimensional and there are as many sectors
are there are degrees of freedom to (b) there is only one sector.
Anything in between is possible.

Anything in between is also almost certain! In particular, the vacuua
corresponding to two mutually accelerating frames lie in different
sectors. Consequently, the states corresponding to two different
setting of the gravity field (each defining its own field of inertial
frames) lie in different superselection sectors. Therefore, there is
no coherent superposition of two states corresponding to two different
gravity fields.

Gravity creates superselection.

A striking way to see this is to take the so-called Schroedinger Cat.
Not the fictional one of thought experiments, but a REAL one. That is,
put a lever arm inside a box on a spring-loaded lock, attach it to a
radiation-activate spring-release trigger.

Outside the box, put a Cavendish balance. Then, start the process.

Does the balance swing gradually over reflecting the "average" of the
different "coherent superpositions" of the states inside the box, or
does it swing abruptly with the event?

It swings abruptly.

There are no coherent superpositions in the box. The mere existence of
a force that (a) is universal, (b) is long-range, (c) is unshieldable
ruins the prospect of macroscopic coherent superpositions. The box is
completely and utterly transparent and might as well not even be
there. There's decohence and the macroscopic world is essentially
classical.

.