On 10-04-2022 06:15, Bruce Kellett wrote:
On Sun, Apr 10, 2022 at 10:25 AM smitra <smi...@zonnet.nl> wrote:
On 09-04-2022 07:03, Bruce Kellett wrote:
On Sat, Apr 9, 2022 at 11:28 AM smitra <smi...@zonnet.nl> wrote:
On 08-04-2022 07:19, Bruce Kellett wrote:
Permanent records do follow from entanglement and decoherence.
There
is no reason to suppose that algorithms processing information
are
going to produce permanent records. Unless they do, they are
useless
as a model of observation. In the words of David Albert
(paraphrased):
"The task of fundamental physics is to explain the manifest
image
."
Decoherence is never complete it can in principle be reversed.
No. Measurements are in principle irreversible. Whenever you have
a
result entangled with the environment (by decoherence) you
inevitably
have low energy IR photons that escape into space. Since these
vanish
at the speed of light, they cannot be reversed. The records of
results
are permanent, not just FAPP, but in principle, according to the
laws
of physics.
These IR photons have nothing whatsoever to do with observation.
But the have everything to do with the fact that the formation of
records is irreversible.
Which just shows how nonsensical invoking records as a criterion for
observations taking place is.
And
it's FAPP, not in principle, anyway.
In principle means that the laws of physics forbid any violation.
The laws of physics are reversible, so they don't guarantee the
formation of permanent records at all.
If I observe something then that's
due to my brain processing information, so, it's the processing of
information by a particular algorithm that's the key thing here, not
that decoherence happens and that IR photons would make this
irreversible.
Your brain can only process external records of the result. The making
of these records is irreversible because the laws of physics do not
allow you to reverse them.
No, the laws of physics are known to be reversible.
That this is FAPP and not in principle, follows from the fact that
IR
photons can be reflected back.
You are ignoring some important laws of physics here. Even if one
could put an appropriate reflecting mirror in the path of the photons
so that they are reflected back, that mirror would impart a change of
momentum, so would be slightly heated, and would emit its own IR
photons in response. No escaping those pesky IR photons.
When a photon reflects off a mirror, the quantum state of the mirror has
a large amplitude for staying the same. This is because the wavefunction
of the mirror is very wide in momentum space compared to the momentum of
the photon. This is also why you can have interferometers with mirrors
without losing the interference pattern die to momentum of the photons
getting transferred to the mirror causing which way information to move
into the state of the mirror.
There are, of curse, losses, there is a probability that a photon will
be absorbed, but this can be made arbitrarily low. what matters is that
the laws pf physics do not have a lower bound on how low you can make
the losses.
So, as I claimed, you are appealing to FAPP.
So, one can consider a closed system
within which an observer exists. If we impose reflecting boundary
conditions at some distance, then the number of modes of the
electromagnetic field below a certain energy E is finite.
There is no such reflecting boundary. And no such boundary is relevant
to the measurement. It would still not make the process reversible.
The emission of the IR photons is a probabilistic process, so merely
reflecting them back does not ensure that they will be exactly
reabsorbed -- that is a process of zero probability measure.
No, what matters is that in principle the initial state can be restored.
It doesn't matter if that requires astronomically large amounts of
resources. What matters is that it is in principle possible.
And the amount
of information carried by photons with wavelength much larger than
the
size of the experimental system is small, as for those photons that
are
emitted, there are only a small number of distinct photon states.
Not relevant, since there is no enclosing reflecting boundary.
Yes there is. One can also consider an observation inside the event
horizon of a supermassive black hole. No photons escape from there. The
escaping Hawking radiation is so small that it doesn't contain much
information.
And since you are attempting to promote a FAPP argument to an in
principle argument, you also have to consider that the space environment
is not a perfect vacuum, so photons do not travel at exactly the speed
of light. This means that in principle one can retrieve the escaping
photons
Saibal
Bruce
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