Quantum Mechanics is strange, and we
don't really have any idea of why it is as it is. We see particles
apparently communicating infinitely fast to produce apparently random
yet coordinated outcomes. We can predict with amazing accuracy the
probabilities of outcomes and yet it seems that no-one can predict
precisely what will happen. This mystery has led to a range of
models of what is actually happening with quantum states, and there
are more than just the two models that are widely known: Copenhagen
and Many Worlds, but I'll start with those.

The “Copenhagen” interpretation of
Quantum Mechanics says that quantum states remain undecided until
some kind of measurement takes place, and at that time of measurement
the state collapses into one of the possible outcomes. The mystery
with this interpretation is that no-one can say what “measurement”
actually means. It could be the interaction of the quantum state
with some laboratory equipment, or it could be as soon as there is an
interaction with a single atom or particle. This interpretation has
led to vast amounts of nonsense about “observer effects”, in
which the mind is supposed to have some role, but that's not a
sensible view of things – the human mind is a physical system which
is no more special than any other physical system when it comes to
interaction with quantum states.

The “Many Worlds” interpretation
says that quantum states don't collapse, because all the possible
outcomes always happen. We don't see all those possible outcomes
because we are physical systems like any other, and our existence is
split when we encounter an quantum state so that there is one of us
seeing each possibility. This interpretation is widely used in
physics, but I find it unhelpful, as it doesn't answer the question
of why THIS copy of me sees what I see – each copy of me will be
unable to predict which of the outcomes it sees.

Now, some other ideas:

The “Transactional” interpretation
says that as soon as a quantum state interacts with anything at all,
an interaction (“transaction”) back and forth through time occurs
during which one of the possible outcomes is picked (at random). The
link through time avoids the issue of instant communication through
space. There is no need for any idea of “measurement”, and there
is no “interaction at a distance”.

Roger Penrose's quantum gravity
interpretation says that quantum states can remain undecided only
while they are below the level at which there is a significant
difference in the gravitational effect of possible outcomes. Once
that level has been reached the quantum system is forced to collapse
into a single state.

I could go on and on. The point is
that there are many more ways of looking at quantum mechanics. It's
more than just a matter of either “observer effects” or “quantum
worlds”. Right now, we have no way to determine by experiment
which of these interpretations is correct, so anyone drawing any
conclusions from a particular view of quantum mechanics is on dodgy
ground!

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