
Quantum darwinism - scalio
https://arxiv.org/abs/0903.5082
======
scalio
Found here: [https://aeon.co/essays/the-quantum-view-of-reality-might-
not...](https://aeon.co/essays/the-quantum-view-of-reality-might-not-be-so-
weird-after-all)

 _Zurek and his colleague Jess Riedel have been able to calculate how fast and
extensive this proliferation of quantum copies is for a few simple situations,
such as a dust speck in a vacuum flooded by sunlight. They find that, after
being illuminated for just one microsecond, a grain of dust a micrometre
across will have its location imprinted about 100 million times in the
scattered photons.

It’s because of this multiple imprinting that such objects seem to have
objective, classical-like properties at all. Ten observers, say, can
separately measure the position of a dust grain and all agree that it’s in the
same location. Each observation consumes a different replica of the grain in
the reflected photons. In this view, we can assign an objective position to
the speck not because it truly ‘has’ such a position (whatever that means),
but because its position state can imprint many indistinguishable replicas in
the environment. What we take as obvious common sense turns out to have secure
yet far-from-obvious underpinning in quantum theory.

There’s a seemingly bizarre corollary to this picture. When we measure a
property of a system by probing its replica in the environment, we destroy
that replica. Might we then potentially use up all the copies by repeated
measurement, so that the state can’t any longer be observed? Yes we can: too
much measurement will ultimately make the state seem to vanish.

What Quantum Darwinism tell us is that, fundamentally, the issue is not really
about whether probing physically disturbs what is probed (although that can
happen). It is the gathering of information that alters the picture. Through
decoherence, the Universe retains selected highlights of the quantum world,
and those highlights have exactly the features that we have learnt to expect
from the classical world. We come along and sweep up that information – and in
the process we destroy it, one copy at a time._

