[extropy-chat] MWI warms up (was cold fusion ..)

scerir scerir at libero.it
Wed Dec 27 16:57:51 UTC 2006

>> (Ok, there are even good physicists which believe in MWI,
>> not as an interpretation of quantum phenomena, upon
>> measurements, but as an _ontology_, that is: real worlds.
>> Simple experiments can show, imo, they are wrong).
Robert Bradbury writes:
> I will note the "imo".  This is good.  
> But how can one claim to assert or
> disprove something which by definition 
> is unassertable or disprovable? [...]

MWI is (often) said to be an 'ontological'(as opposed 
to 'epistemic') interpretation. That is to say, 
quantum states, in a superposition, are physical,
'ontic' states.  
But, of course, in MWI quantum states become 
real, evident, as 'relative' states only, as states
which are relative to measurement apparata ... 

|a>|detector_a> + |b>|detector_b> + |c>|detector_c> 
each quantum state, of a superposition, is
entangled with a specific state of the measurement
apparatus (a pointer in general, or whatever).

And here comes the 'branching', or the creation,
by decoherence or whatever else, of the famous
'many worlds'.

It is possible to show (at least imo) that the MWI, 
when considered as an 'ontological' theory, is wrong.

Imagine a source 's', inside a box, emitting, at time 't0', 
a charged particle, with velocity 'v' (v << c). This can be
done, and there is no relevant problem (here) due to the HUP, 
ie with the emission time 't0'.
|                  |
|                  |
|                  |
|                  |
|        s         |
|                  |
|                  |
|                  |

When the charged particle hits one of the faces
of the box, it produces a sharp flash of light,
because each face is made of scintillating stuff.
By seeing the flash of light an observer realizes 
that the particle has reached a face of the box.

Now we put, inside the box, at a distance 'r' from
the source, a little scintillating surface 'm'. 
This can be done. 
|                  | 
|                  |
|           m      |
|           |      |
|        s  |      |
|           |      |
|                  |
|                  |
There are, of course, chances that the charged particle
now hits the little scintillating surface 'm', and not
a face of the box. In this case, 'm' would produce a
sharp flash of light, at time t=r/v (v is the velocity
of the charged particle), and the observer will see this
flash (more or less at time t=r/v, since v << c).

The quantish description would be something like
|k(time)> = c1 |charged particle hits 'm'> + 
            c2 |charged particle hits a face of the box>

Upon measurements, according to the MWI, the branching

There are, of course, many more chances that the charged 
particle hits a face of the box and does not hit the little 
scintillating surface 'm'. In this case there is no interaction,
no scattering, no irreversible measurement between the 
charged particle and the little scintillating surface 'm'.
No flash of light at t=r/v. At t=r/v the observer only
_realizes_ that the charged particle, emitted at time t0 
by the source 's', did not hit the little scintillating
surface 'm'. But no measurement occurred at t=r/v.
Nevertheless the 'branching' _already_ happened all the same,
at t=r/v. 

This kind of reasoning (which is experimental, and 
not counterfactual) makes me think that MWI is not 
an ontological theory.

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