
Experimental rejection of observer-independence in the quantum world - lisper
https://arxiv.org/abs/1902.05080
======
comboy
Here's a dumbed down version:
[https://outline.com/7Ckkqa](https://outline.com/7Ckkqa)

Also not directly related video if you like your mind being blown:
[https://www.youtube.com/watch?v=8ORLN_KwAgs](https://www.youtube.com/watch?v=8ORLN_KwAgs)

Especially given how our understanding of the world changed during the last
200 years, I would say we are still very much clueless. I find that exciting.

Btw, no idea why did researchers get "freedom of choice" involved.

~~~
keyle
> It begins with a single polarized photon that, when measured, can have
> either a horizontal polarization or a vertical polarization. But before the
> measurement, according to the laws of quantum mechanics, the photon exists
> in both polarization states at the same time—a so-called superposition.

Pardon my basic understanding, but doesn't it meant that it's both simply
because it hasn't been measured - and therefor we don't know? Meaning it's
either one or the other; at a very fast rate, it's both.

~~~
chii
> it's both simply because it hasn't been measured ... Meaning it's either one
> or the other

A common misconception about quantum superposition is that the particle "has"
some state, and we only use superposition to model that we "dont know". This
is called the hidden-variable theory ([https://en.wikipedia.org/wiki/Hidden-
variable_theory](https://en.wikipedia.org/wiki/Hidden-variable_theory)). It's
been proven that this hidden variable theory can't be true because of
[https://en.wikipedia.org/wiki/Bell%27s_theorem](https://en.wikipedia.org/wiki/Bell%27s_theorem).

This is completely non-intuitive. See this video for a laymen's explanation:
[https://www.youtube.com/watch?v=z-s3q9wlLag](https://www.youtube.com/watch?v=z-s3q9wlLag)
(you may also need to watch the prev. video about the EPR paradox
[https://www.youtube.com/watch?v=5HJK5tQIT4A](https://www.youtube.com/watch?v=5HJK5tQIT4A)).

Edit: actually, this is a much better video
[https://www.youtube.com/watch?v=ZuvK-
od647c](https://www.youtube.com/watch?v=ZuvK-od647c) \- less technical and
more visual.

~~~
keyle
Brilliant, thank you!

------
ikeboy
Just going to repeat from the HN thread a few days ago[0]

[https://www.scottaaronson.com/blog/?p=3975](https://www.scottaaronson.com/blog/?p=3975)

Here's Scott Aaronson arguing that the theoretical work underpinning this
experiment is flawed.

[0]
[https://news.ycombinator.com/item?id=19369655](https://news.ycombinator.com/item?id=19369655)

~~~
Cybiote
I don't think that blog post is referring to the same paper. This new paper is
about an experimental demonstration of Wigner's Friend:
[https://en.wikipedia.org/wiki/Wigner's_friend](https://en.wikipedia.org/wiki/Wigner's_friend).
Scott's blog post is talking about a more controversial extension to it, which
combines Wigner's Friends with Hardy's Paradox to attempt to construct a
reflective or meta limitation on the applicability of QM. The wiki link also
discusses:
[https://en.wikipedia.org/wiki/Wigner's_friend#An_extension_o...](https://en.wikipedia.org/wiki/Wigner's_friend#An_extension_of_the_Wigner's_friend_experiment)

~~~
ikeboy
This paper cites the one Scott argues against.

~~~
tsufe
Yes it does and yet you are still wrong AFAIK. Citing a paper does not
necessarily mean that said paper would form the theoretical basis of the
citing paper.

This paper about the experiment is trivially true, there were no surprises
regarding to what QM predicts.

Here is a direct quote from Scott: >My comments about the Frauchiger-Renner
paper never doubted for a second the result predicted by QM. So an
“experimental demonstration” of their setup—by which one really means an
experimental demonstration of Hardy’s experiment, since the Frauchiger-Renner
one would require superposed conscious observers (!)—has zero effect on any of
those comments.

And here is a prescient direct quote from Craig Gidney: >I wonder how long it
will be until someone 1) executes the circuit from Hardy’s paradox (which has
very few qubits and very few gates, so you could run it on a NISQ machine), 2)
confirms that of course the results match the predictions of quantum
mechanics, 3) frames the result in terms of Frauchiger et al’s variant, and 4)
journalists telephone-game it into something like “quantum researchers prove
decisions aren’t real”.

Please see also the relevant discussion in comments here:
[https://www.scottaaronson.com/blog/?p=4147](https://www.scottaaronson.com/blog/?p=4147)

~~~
ikeboy
The experiment is uninteresting, as far as I can tell, without the
interpretation from Frauchiger-Renner.

My point in linking the original article was that the media discussion of this
(in part driven by the paper's own framing) as disproving objective reality is
wrong, something Scott clearly agrees with.

------
pdonis
It is quite an exaggeration to talk about this experiment as actually
realizing a "Wigner's Friend" type scenario. In the Wigner's Friend thought
experiment, the friend--an actual conscious macroscopic human being--is put
into a superposition of different, mutually exclusive conscious experiences
that Wigner, from the outside, is able to measure as such a superposition.
Nothing like that is being done in this actual experiment: the only things
being placed into superpositions are microscopic systems that have no
experiences.

This experiment is certainly interesting, and it realizes the basic structure
of the multiple Wigner's Friend scenario that a number of theoretical papers
have been written about recently, but I don't think it comes anywhere close to
probing the actual issues raised by those theoretical papers. The kinds of
real measurements that would have to be realized in order to probe those
theoretical issues are many orders of magnitude more complex than those in
this experiment.

------
paraschopra
There’s an interpretation that keeps observer as the central element. It is
not as popular as many worlds or Copenhagen but I find it very intriguing.
Check out QBism:
[https://en.m.wikipedia.org/wiki/Quantum_Bayesianism?wprov=sf...](https://en.m.wikipedia.org/wiki/Quantum_Bayesianism?wprov=sfti1)

In QBism, the Born rule is normative in that it tells the observer which
observations to bet on, and observations are data points to update the
observer’s subjective assessment of outcomes. Taking this perspective, a lot
of paradoxes in QM seem to get resolved trivially. It’s controversial for sure
but mathematically it’s rigorous.

------
everdev
> Wigner can even perform an experiment to determine whether this
> superposition exists or not. This is a kind of interference experiment
> showing that the photon and the measurement are indeed in a superposition.
> From Wigner’s point of view, this is a “fact”—the superposition exists. And
> this fact suggests that a measurement cannot have taken place.

> But this is in stark contrast to the point of view of the friend, who has
> indeed measured the photon’s polarization and recorded it. The friend can
> even call Wigner and say the measurement has been done (provided the outcome
> is not revealed).

A bit of a stretch saying that protons lose their superposition based on the
content of a conversation.

~~~
mlthoughts2018
From a Many Worlds point of view at least, they absolutely could, because the
superposition represents ignorance in the mind of infinitely many Wigners, but
once you remove the ambiguity you are just dealing with one specific Wigner,
who would then know which Everett branch he is actually on (at least ip to the
ambiguity of this particular experiment).

~~~
gus_massa
In this experiment, in both branches he receives the same information "A
measure has been done.", so it doesn't remove the ambiguity, and it doesn't
destroy the superposition.

~~~
mlthoughts2018
I was talking about the case when the friend is told the outcome of the
measurement, that’s the only part relevant to what the parent comment said.

------
cromwellian
Ron Garrett gave a presentation at Google years ago on Quantum Information
Theory that kind of demystified a lot of spooky stuff (like quantum eraser),
and I'm wondering how much of this is merely an artifact of the way we're
interpreting the math.

[https://www.youtube.com/watch?v=dEaecUuEqfc](https://www.youtube.com/watch?v=dEaecUuEqfc)

~~~
pishpash
As they say, the only mystery in QM is the Born rule.

------
p1mrx
If you're reading this, congratulations for observing a universe that contains
this experiment.

~~~
charlesism
And condolences to our selves in parallel timelines where this experiment was
never conducted.

------
badrabbit
I am very far from even understanding quantum physics theories but for all
this experiment to be valid to begin with,the idea that superpositions exist
must be true, correct?

What if what they're proving is really the abscence of a superposition state?
I never understood how superposition can be verified independent of
assumptions. In this case,how can Wigner measure the photon has veritcal and
horizontal polarity at the same time?

Lastly,could superposition be explained by human's limit of sampling reality?
For example audio recorded at 10Hz means 10/samples of audio a second,a sort
of audio-resolution. If our reality-resolution is low,some things might
require ability to measure their state at a better time-space resolution than
what humans can currently sample (or build equipment that can measure this)?
But with limited time-space resolution it can appear as if the object is in
two states at the same time. Sort of like watching a movie at a very slow
frame rate and you capture a moment where half the screen is of one frame but
the rest is of a different frame since the display is only half finished
rendering the raster/rows.

Apologies if I am being absolutley clueless.

~~~
phayes
> for all this experiment to be valid to begin with,the idea that
> superpositions exist must be true, correct?

Depends what you mean by "exist". All that needs to be true - and is true - is
that QM provides an accurate model of the experiment. For many of us, QM is
just probabilistic mechanics; i.e. probability theory applied to mechanics[1],
and so long as you maintain the distinction between (epistemic) probability
space states and (ontic) configuration space states (something the article
under discussion here unfortunately fails to do), no ontic existence of
[superposition] states is ever assumed in the first place.

[1] More precisely, a natural and necessary generalisation of the classical,
Kolmogorovian probability theory you might be familiar with (necessary because
of the noncommuting random variables):

[https://news.ycombinator.com/item?id=19315457](https://news.ycombinator.com/item?id=19315457)

See also:
[http://blogs.discovermagazine.com/cosmicvariance/files/2011/...](http://blogs.discovermagazine.com/cosmicvariance/files/2011/11/banks-
qmblog.pdf)

------
datenwolf
If I were to review this paper, my critique would focus on this little
paragraph:

> We note that, although Bell’s mathematical machinery [9] is used to show the
> result, the set of assumptions considered here — and therefore the
> conclusions that can be drawn from a violation of inequality (2) — are
> different from those in standard Bell tests.

That statement contains a lot of handwavium and in fact the interpretation of
the results depends a lot on, if this experiment may be interpreted as another
test on locality. Which I strongly presume, it does.

------
amai
"they seem to assume that all the photons' degrees of freedom are described by
pure states according to both observers. This seems wrong to me. The
observation of the photons by Wigner's friend creates an entanglement with the
degrees of freedom in the friend's body, so the state of the photons
themselves become mixed according to Wigner (I mean the external observer),
not pure. So I think that when these things are done correctly, it's not
possible to find this kind of a "contradiction" in practice."

[https://motls.blogspot.com/2019/03/six-photons-claimed-to-
pr...](https://motls.blogspot.com/2019/03/six-photons-claimed-to-prove-
that.html)

------
westurner
Objective truth!? A question for epistemologists to decide.

How could they record their high entropy (?) solipsistic observations in an
immutable datastore in such as way as to have probably zero knowledge of the
other party's observations?

Anyways, that's why I only read the title and the abstract.

Wigner's friend experiment:
[https://en.wikipedia.org/wiki/Wigner%27s_friend](https://en.wikipedia.org/wiki/Wigner%27s_friend)

------
powera
This is an ARXIV pre-release. Has anyone peer-reviewed this?

~~~
lisper
If this turned out to be wrong it would be bigger news than if it turns out to
be right. This result is 100% expected.

------
jliptzin
Not a physicist but I was under the impression we already knew this. For
example if someone is falling into a black hole, to an outside observer they
never cross the event horizon, just fall asymptotically slower towards it. But
to the person falling in, he gets ripped to shreds. But I guess we haven’t
tested that out.

~~~
akvadrako
That's the general relativity world, not the quantum world. They are different
models, which is where these things are being proven.

------
SubiculumCode
An interesting thing about deterministic systems. If the deterministic system
ever enters into a state exactly like a prior state, then from then on, that
system will be in an inescapble loop destined to repeat forever.

If there ever was a repeatable state, I'd bet it would be at thr big bang,
though i am no physicist.

------
naasking
It actually doesn't reject observer-independence unless you agree to certain
axioms that an observer-independent interpretation of QM wouldn't feature.
Bohmian mechanics is still perfectly viable, for instance.

------
bookofjoe
[https://news.ycombinator.com/item?id=19366854](https://news.ycombinator.com/item?id=19366854)

------
internet_user
Does this imply Leggett's inequalities have been proven?

------
dooglius
Did the results of this experiment differ from what quantum mechanics
predicts? No? Then what is the point of publishing it? It's not as if
different interpretations make different testable claims, or else they would
be theories rather than mere interpretations.

~~~
wilg
You don't want people to publish experimental results that confirm
predictions?

~~~
dooglius
Quantum mechanics has already been experimentally confirmed ad infinitum. If I
experimentally verify predictions of Newtonian mechanics with some new
configuration of billiard balls, would you consider that worthy of
publication?

~~~
empath75
If it’s a brand new configuration of billiard balls that nobody has ever seen
before, sure.

~~~
wilg
And even if not, it never hurts to double check.

Certainly not hurting anyone to publish a "repetitive" paper. Worst thing that
happens is more people have a chance to hear about it.

------
8bitsrule
Meanwhile, the world could sure use more kinds of biodegradable containers. If
these philosophers could spare a minute.

~~~
anonytrary
Meanwhile, people complain about quantum theory research on a device that
exists thanks to years of quantum theory research.

