On 13 Nov 2017, at 22:40, [email protected] wrote:
On Sunday, November 12, 2017 at 11:50:00 PM UTC-7,
[email protected] wrote:
On Sunday, November 12, 2017 at 11:24:15 PM UTC-7,
[email protected] wrote:
On Sunday, November 12, 2017 at 11:15:33 AM UTC-7, John Clark wrote:
On Sun, Nov 12, 2017 at 1:01 AM, <[email protected]> wrote:
> What is your definition of non-realistic?
Nonrealistic means when something is not being observed it doesn't
exist in any one definite state.
You have to be careful here. For example, when the Earth-Moon system
formed, it existed in a definite state, but was NOT observed. So not
everything in a definite state must be observed, by detectors or
conscious entities. OTOH, when an electron is prepared for a double
slit experiment, it is in a superposition of states; that is, NOT in
a definite state. If it were in a definite state, we'd observe the
classical probability distribution. So quantum experiments, and QM
in general to the extent it relies on superposition of states, is
NONREALISTIC, whereas the macro world is generally REALISTIC. I
can't speak to why the macro world is realistic.
FWIW, I left out an important reason why some systems are in
definite states, like macro systems, and others not, such as quantum
systems prepared for measurements. It's likely related to whether
the systems in question are ISOLATED.
If you find collapse of the wf anathema, instead of the MWI why not
just assume the branches that aren't measured in this world,
dissipate into the environment as I think Decoherence theory
postulates?
In the MWI (= multiverse, = non-collapse), the dissipation is a (bad)
terming for "entanglement with the environment". If you have a
superposition of some particle up + down, and that particle interact
with some unknown passing particles, that you lost, from your point of
view, the superposition is lost, as you would need the other particle
to recover the interference of the initial particles. That is why it
is hard to make macroscopic object interfere: they leak to easily to
the environment, including to you, which is akin to a measurement. I
use the expression "the superposition is contagious to the
environment": the "dissipitation" is about the pure state, which
behave like a mixed state when it has not been isolated enough.
Bruno
MWI doesn't tell us what will be measured in this or any other
particular world, so what's the downside to this hugely simpler way
of avoiding collapse?
A photon hits a horizontally polarizing filter and the universe
splits in two if Many Worlds is right, in one the photon makes it
through the filter and the inhabitants of that world conclude it is
100% horizontally polarized , in the other world it doesn't get
through the filter and they conclude it must have been 100%
vertically polarized, but in the world before the split, before it
hit the filter, the inhabitants of that world would conclude (if
they believed in Many Worlds) that the photon did not have any one
definite polarized state at all.
>> That is not unique to the MWI. In a accelerating
Einsteinian universe such as ours energy is not conserved at the
cosmological level.
> There was some unique condition that gave rise to our
universe.
The multiverse may have always existed, if so then nothing, unique
or otherwise, gave rise to it,
You're conflating Multiverse with the MWI. In the former, OUR
universe emerged due to unique, unknown initial conditions from an
entity which, if it exists, is likely infinite in age and extent. In
the MWI, universes allegedly emerge when Joe the Plumber shoots an
electron at a slitted screen. The two situations are in no way
comparable, and the latter seems hugely overblown IMO. So where the
energy comes from in the MWI cannot be easily dismissed by the lack
of global energy conservation in GR, or by referring to unknowns
related to the emergence of our universe from a hypothetical
Multiverse.
> MWI has it happening wily-nily when someone performs a slit
experiment in a lab (and uncountably many times). Hardly a
conservative interpretation IMO.
Many Worlds is very conservative if the mathematics doesn't
say anything about a wave collapse. And it doesn't.
>> they can't even say what is observation is.
> I can. They can. In a SG experiment, e.g., an observation
occurs when the electron's spin state is aligned, or anti-aligned to
the magnetic field.
Observation is the wrong word if no observer is involved, then its
just a change and a change is the criteria Many Worlds uses.
Agreed that "observation" is misleading when there is no
consciousness involved in a quantum experiment. We should speak of
detectable changes recorded by instruments; aka "measurements".
In MWI everything that can happen does happen, so when a photon
approaches 2 slits the universe splits and one photon goes through
the right slit and one goes through the left slit. If after that the
photons hit a photographic plate (or a brick wall) then the photons
no longer exist in either universe and so they merge back together
into one universe and this merger causes the interference lines. If
instead after passing the slits there is no photographic plate (or
brick wall) and the photons are allowed to continue on into infinite
space then the 2 universes remain different and remain separated
forever.
So if David Deutsch takes a right turn at an intersection, there's
another identical David Deutsch in another identical universe who
takes a left turn? I can't disprove it, but why would anyone of
sound mind want to assert it?
The universe splits because there is a difference, in one the photon
went through the left slit and in another it went through the right
slit, and the wave function never collapses it just keeps on going.
And there is nothing special about me, I split just like everything
else in the universe, the fact that I am conscious is irrelevant.
That's another great advantage of Many Worlds, unlike Copenhagen it
doesn't need to explain what consciousness is or how it works
because consciousness has nothing to do with it.
As I previously pointed out, the alleged collapse of the wf has
nothing to do with consciousness regardless of what Bohr or others
might have speculated in the early days of QM. As Feynman clearly
explained, you can have a detector recording outcomes, and if the
detector is designed to determine which-way, the interference will
be destroyed. In other words, we can have quantum observations
without any conscious "observer".
>> Can only a person make a observation or can a cockroach
collapse the wave function too?
> Feynman is conclusive on this point. No person or cockroach
needed; just an instrument to record the result.
If an instrument is anything that can exist in at least 2 states
then I would be fine with that, but that sounds much more like Many
Worlds than Copenhagen. All that's needed is a change, any change,
it need not be anything as dramatic as a change in something as
complex as a brain.
> Does every event require an observer or instrument to witness
it? I think not.
I think every observation requires a observer to witness a change,
and Copenhagen requires an observation to trigger the collapse of
the wave function.
Not for macro events as pointed out above, or even quantum events.
Detectors to record changes are sufficient as "observers".
Many Worlds just requires a simple change to trigger a split, a
change in anything, and nothing triggers the collapse of the
wave function because the mathematics doesn't even hint at such a
thing happening, the Copenhagen people just tacked that on.
Not exactly true IMO. When the measurement occurs, the probability
becomes unity for the value of the measurement, implying collapse of
the probability density to a delta function.
Somebody said that Many Worlds is cheap on assumptions but expensive
in universes and I think that's true, I'm a fan because universes
are cheaper than assumptions.
Thanks for an interesting discussion.
John K Clark
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