
Reality doesn’t exist until it is measured, quantum experiment finds - lermontov
http://www.anu.edu.au/news/all-news/experiment-confirms-quantum-theory-weirdness
======
Strilanc
The linked article is titled "Experiment confirms quantum theory weirdness".
Please don't exaggerate the title. These experiments do not show that "reality
doesn't exist until it's measured".

First, "realism" [1] is not the same thing as "reality". "Realism" basically
means "physical quantities have a definite value". "Reality" is that thing
that determines your experimental outcomes. Don't mix them up.

Second, interpretations of quantum mechanics disagree wildly about what kind
of weird you use to explain things. Some interpretations have "realism", some
don't. Some interpretations have retrocausality, some don't. Some
interpretations have FTL effects, some don't. Since all the interpretations
give (mostly) the same experimental predictions, it's misleading to single one
out and say just that particular brand of weirdness was confirmed.

We confirmed that there's weird there. We didn't distinguish what brand of
weird it is. Physicists widely disagree about which brand of weird to use,
with no position achieving even a majority [2]. The original title was better.

1:
[https://en.wikipedia.org/wiki/Na%C3%AFve_realism#Realism_and...](https://en.wikipedia.org/wiki/Na%C3%AFve_realism#Realism_and_quantum_physics)

2: [http://www.preposterousuniverse.com/blog/2013/01/17/the-
most...](http://www.preposterousuniverse.com/blog/2013/01/17/the-most-
embarrassing-graph-in-modern-physics/)

~~~
cristianpascu
A standard case of mixing (or actually confusing) epistemology with ontology.
That is to say that something doesn't exist until we get to know something
about it. Or, by all means, knowing something _about_ something is posterior
to us _being_ here AND that something _being_ there. Here lies the danger of
dismissing philosophy as a bag of words when compared with the Holy Science
that _works, bitches_.

~~~
bweitzman
I've been reading Thomas Nagel's "Mind and Cosmos" recently, and while I think
it's actually a really terrible book and Nagel is incredibly uninformed on the
theory of evolution, I do think he makes one really good point: the scientific
method presupposes that the universe can be understood/observed/measured. It
seems like such an obvious axiom, but I think it makes sense why we keep
brushing up with observation / consciousness when we push the boundaries of
science. It's sort of tautological in a way.

~~~
jgroszko
It will be interesting to see as we run closer and closer to the limits of
observation and consciousness if we're on the verge of another huge paradigm
shift in empiricism.

------
zw123456
And perhaps someday we'll get to meet the great programmer in the sky the
developed the simulation we are living in and we will ask him why he designed
it that way and he will say something like "oh I just wanted to optimize the
code so I simply excluded reality subroutines when there were no beings
looking. I just never thought you guys would notice. As soon as I saw that you
guys noticed the flaw, I was going to load a patch but then the confusion it
was causing with the simulated beings became interesting and so I just left it
in as an accidental feature of the game." Meh, but probably not.

~~~
antimagic
I always find it fascinating at just how much of our fundamental physics ends
up being constraints on information movement. The laws of thermodynamics are
about entropy, general relativity puts constraints on the movement of
information (for example, Spooky Action as a Distance(tm) is faster than
light, but you can't transmit information with it), the Uncertainty Principle
puts limits on how much information you can have on a given system.

Information information everywhere you look in fundamental physics. It does
make me wonder why.

~~~
joshuahedlund
I'm fascinated by such things also. I often can't help thinking of God as a
programmer, though I don't know how much of that is confirmation bias of my
priors as a theist and a programmer. But I've always thought the periodic
table and DNA both felt a lot like code...

~~~
orbifold
The masons thought about God as the great builder, I believe generally we make
gods in our own image.

~~~
anonbanker
As do the high-level masons.

------
hasenj
I'm not familiar with this particular experiment, but all my pondering on the
subject - as a layman - leads me to a simple conclusion.

The properties these experiments are measuring are simply bogus. They are not
well defined. The answer that comes out is not some intrinsic property of the
"particle", but the result of the environment in which the particle interacted
with the "measurement" system, so to speak.

The particle has some other properties, but what's being "measured" is not one
of those properties.

How can I explain?

Imagine someone who has never tried any Korean food, and you try to ask
him/her: what's your favorite Korean food? There's no answer. So you try to
"measure" it by feeding him some Korean items and recording his facial
expressions. He will like some items more than others, but it has nothing to
do with "his favorite Korean food", and has more to do with how the items were
prepared and his mood at the time.

A "point" location for a photon is never defined; it's not a property of a
photon that it exists in a point in space. When you fire a photon at a "wall"
and see a "blip", you're not seeing the position of the photon at some point
in time. You're seeing the rough position of the atom that had an electron
that absorbed the photon's energy, and I'm not even sure the atom has a well
defined point position either. The whole thing is an artifact (a side effect)
of some interaction between several systems and doesn't really tell you
anything fundamental about the photon (or the quantum object).

At least that's how I understand it.

~~~
Kequc
The topic outlined in the OP's article has been raised before, multiple times,
once every couple of years. It was even the focus of a cult indoctrination
propaganda piece called "what the bleep do we know".

[http://skeptico.blogs.com/skeptico/2005/04/what_the_bleep_.h...](http://skeptico.blogs.com/skeptico/2005/04/what_the_bleep_.html)

Essentially, yes, it's bogus science. Quantum physics are much more complex
than these articles ever bring on. But by explaining it simply, it sounds awe
inspiring and so it propagates across social media. Over and over again.

It isn't that particles exist in multiple states until they are measured. It
is that the mechanism by which you measure very small things affects the
outcome.

~~~
dghf
> It isn't that particles exist in multiple states until they are measured.

I thought it was exactly that. Or rather, particles exist in multiple states,
and when they are measured, _either_ those multiple states collapse into one
(Copenhagen Interpretation) _or_ you, the measurer (who also exists in
multiple states), gets entangled with them, causing each of your states to
perceive exactly one of the particles' states (Many-Worlds Interpretation).

Unless Bohmian mechanics is correct, in which case no, particles don't exist
in multiple states, but do depend on faster-than-light transmission of
information about the state of other particles.

~~~
Kequc
I'm personally a really big fan of the Many-Worlds Interpretation. Because a
brief abstraction would mean every person will live as long as is physically
possible. To outside observers, you may have died at any point along the way.

[https://en.wikipedia.org/wiki/Quantum_suicide_and_immortalit...](https://en.wikipedia.org/wiki/Quantum_suicide_and_immortality)

But, regardless. The copenhagen interpretation is from the 1920's. That isn't
to say it's wrong, it's just out of date. It has been expanded upon or
replaced since then so why hold onto it, what is the current understanding.

The most important takeaway here is that since measuring very small things
affects its outcome, it is currently impossible to know. Articles like this
one in the OP bother me because they don't know either. But it always becomes
a sensation and spreads misinformation.

~~~
eru
> Because a brief abstraction would mean every person will live as long as is
> physically possible. To outside observers, you may have died at any point
> along the way.

Though your `life' might not be pretty. It can be maximally awful as long as
you can still perceive.

------
westoncb
This is of course extremely interesting and probably important for
understanding our universe—but how is it helping anyone to say something like,
"...with scientists performing a famous experiment and proving that reality
does not exist until it is measured." The statement is like a distraction at a
magic show, drawing the reader to the glittery 'reality' and 'exist,' which
are totally undefined so the reader's imagination can rove without limit.

Maybe this is really just a fundamental challenge to our assumptions about
motion of particles or information transfer in the universe. Isn't that
interesting enough without these vague, human aggrandizing assertions about
creating reality?

~~~
epitomix
"Maybe this is really just a fundamental challenge to our assumptions about
motion of particles or information transfer in the universe."

Check out this TED talk on just that subject.
[http://www.ted.com/talks/donald_hoffman_do_we_see_reality_as...](http://www.ted.com/talks/donald_hoffman_do_we_see_reality_as_it_is)

Here's the punch line, space, time and matter are components of a user
interface produced through evolution. We don't take the desktop and icons of
our computer UI literally and we shouldn't take our evolved UI literally
either.

~~~
paxcoder
Fun to think about, but his argument is a non sequitur.

~~~
epitomix
Maybe, but my wording is not his argument. Here is a blog version of the same
idea. [https://edge.org/response-detail/25450](https://edge.org/response-
detail/25450)

------
flowctrl
The press around this experiment uses misleading language that leads people
like Deepak Chopra to think that we create reality through consciousness. It
has nothing to do with consciousness. This article explains it:

[http://theness.com/neurologicablog/index.php/more-quantum-
we...](http://theness.com/neurologicablog/index.php/more-quantum-weirdness/)

------
deciplex
John Wheeler's delayed choice thought experiment was already confirmed in the
lab over ten years ago. It's neat that they were able to get results with
baryonic matter, and it was definitely worthwhile to try to do that, but this
article seems to be implying that the results could have been anything else
than what they were, or that there is new physics here, and is wrong on both
counts.

Also the deference to the Copenhagen interpretation is annoying - it's wrong.
What they've observed is a consequence of how decoherence works, and
'observation' has nothing to do with it. Not faulting the researchers on this
but seriously, it's time to stop talking about mythical 'observation' as
though it's some integral part of quantum theory.

------
ghosthamlet
[http://www.simulation-argument.com/simulation.html](http://www.simulation-
argument.com/simulation.html) says: at least one of the following propositions
is true: (1) the human species is very likely to go extinct before reaching a
“posthuman” stage; (2) any posthuman civilization is extremely unlikely to run
a significant number of simulations of their evolutionary history (or
variations thereof); (3) we are almost certainly living in a computer
simulation. It follows that the belief that there is a significant chance that
we will one day become posthumans who run ancestor-simulations is false,
unless we are currently living in a simulation. A number of other consequences
of this result are also discussed.

COMPUTER SIMULATION vs HOLOGRAPHIC UNIVERSE

[http://www.crystalinks.com/holographic.html](http://www.crystalinks.com/holographic.html)
[http://thelaymansanswerstoeverything.com/2013/01/scientific-...](http://thelaymansanswerstoeverything.com/2013/01/scientific-
proof-we-live-in-a-simulation/)

~~~
exch
What does 'post human' mean? Unless we go extinct, we will always be humans,
regardless of what species we evolve into. Our current species is "Homo
Sapiens Sapiens", not "Human". Ergo, if we evolve into amorphous blobs of
space goo, we will still be Human but not "Homo Sapiens Sapiens". Which means
it is physically impossible for us to ever reach a "post-human" stage.

~~~
ceejayoz
I'd say you'd be posthuman if a current human wouldn't recognize you as being
part of the same species.

[https://en.wikipedia.org/wiki/Posthuman](https://en.wikipedia.org/wiki/Posthuman)

------
z5h
What does it mean to exist? A thing exists specifically when it affects
something else. What is measurement? It's a reciprocal affecting.

So does a thing which is not affecting anything else and not being measured
exist? No! QED

~~~
themgt
Right. This way of describing it is much closer to "zero-worlds" or relational
quantum mechanics, and to my mind is a far simpler, deeper way of
understanding what's really going on - reality is simply all entanglement.

What really still gets me is the way it's not simply that the atom wasn't
interacted with, but that if the information about the interaction never leaks
to the outside world - if it's "erased" _after_ the interaction takes place -
then the system still behaves as if the interaction never took place.

It undermines not just the concept that matter really exists, but time as
well.

~~~
dmvaldman
Do you have a source for this "information leaking" concept. I remember
hearing about an experiment confirming such an idea, but I can't recall what
it was.

~~~
themgt
I'm not sure the exact experiment performed in the article (which sounded
similar), but I've always thought the delayed choice quantum eraser was about
the best example of this, once you spend some time understanding the
experiment and results:

[https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser](https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser)

------
davidrusu
Clever optimization by our simulators, Big up

~~~
marwatk
I've always wanted to read (or write?) a book about us determining we are in a
simulation, but we find subtle flaws like this we're able to exploit in weird
ways. Kind of like breaking out of a VM through register flaws or something.
Anyone know of a story along those lines?

~~~
gall
Check out Greg Egan's Permutation City in which sort of the opposite happens.

~~~
nitrogen
I'm reading that book right now, and so far it's good. One can also read:
Anathem, Snow Crash, [http://qntm.org/ra](http://qntm.org/ra), or (extremely
NSFW) The Metamorphosis of Prime Intellect.

All of them explore the nature of reality and consciousness in some way.

To the parent commenter, please write your story. The world always needs good
fiction.

~~~
mhink
The Metamorphosis of Prime Intellect is one of my favorite sci-fi novellas.
But yes, extremely unsuitable for anyone with a weak stomach.

------
davej
I find it fascinating how the speed of light, quantum indeterminacy and
Planck's length could all be seen as allegories for computational
optimisations in a simulated universe.

This is something that I've thought about for some time, I posted a question
about this a number of years ago on Reddit:
[http://www.reddit.com/r/Physics/comments/g287k/quantum_indet...](http://www.reddit.com/r/Physics/comments/g287k/quantum_indeterminacy_a_computational/)

------
A_COMPUTER
If I'm standing here, all the stuff that the atoms in my body could
conceivably interact with have to be backfilled for me to interact with them
according to this experiment, but since I'm not special to the universe, atoms
three billion light years over, they are still interacting with each other,
just not with me. So am I decohered to them? Is this like a divergent
timelines theory such that coherence is defined as when different
possibilities converge while following possibilities, reducing them and then
so must necessarily collapse as other possibilities drop off? So what's the
difference between cohered and decohered reality then? It sounds then like it
would just be one of those paths, the one that we happen to be on that we only
notice because we're conscious so that's our arbitrary (to the universe)
observation point. That's the only way I can make sense out of this without
attaching significance to human observation.

~~~
mjfl
The philosophical interpretation of Quantum Mechanics is a very hard, unsolved
problem. There are many reasons why quantum mechanics is theoretically good
and philosophically terrible, and not just in a subtle, esoteric way. The
reason is that in Quantum Mechanics there are 2 main types of entities:
particles, "things" that evolve according to the Schrodinger equation, and
"observers". Observers are what deliver to us the results of randomly sampling
from the probability distribution defined by the squared amplitude of the wave
function by "collapsing" it, according to the Copenhagen interpretation.
However, there is no particle that acts as an observer, they all just follow
the Schrodinger equation, but nothing that exists isn't a particle. How could
"observers" exist and interact with particles then? The Copenhagen
interpretation is philosophically terrible. And it really pisses me off that
this article title seems to hint that they've really confirmed it. In a lab,
an experimenter can just point to his apparatus and say, "that's the
observer". Or, being more formal, they can say a _thermodynamically
irreversible process_ plays the role of an observer. But this is not really a
satisfying explanation because how could it be possible to generate these
large, discontinuous motions we call "collapse" on the macroscale if it is
impossible on the microscale? There are the multiverse theories that you seem
to describe, but they have their own problems. Rae's Quantum Physics:
[http://www.amazon.com/Quantum-Physics-Illusion-Reality-
Class...](http://www.amazon.com/Quantum-Physics-Illusion-Reality-
Classics/dp/1107604648/ref=pd_sim_14_1?ie=UTF8&refRID=1QMSE7ANN5CFTEC7XAEZ)

goes over a lot of them without getting to messy in the math. Other
interpretations of QM are in the book as well. There are many:

[https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...](https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics)

~~~
dghf
> Observers are what deliver to us the results of randomly sampling from the
> probability distribution defined by the squared amplitude of the wave
> function by "collapsing" it, according to the Copenhagen interpretation.
> However, there is no particle that acts as an observer, they all just follow
> the Schrodinger equation, but nothing that exists isn't a particle.

This is why proponents of the Many-Worlds Interpretation claim that Occam's
razor favours it: you don't need to posit "observers" or "collapses"; there's
just the evolution of the wave function.

~~~
stefantalpalaru
> Occam's razor favours it

Occam's razor is not a scientific principle, it's just a rule of thumb. I have
yet to see a proof that given a number of equal strength explanations for a
phenomenon, the simplest one is always true.

One other thing that's often forgotten is that in Occam's opinion the simplest
explanation for everything was God.

~~~
onnoonno
... and it should be added that having infinitely many worlds is maybe not
really the simplest explanation of reality.

------
hackinthebochs
Let us not forget about Pilot-Wave theory, where it has both particle and
wave-like properties simultaneously. In fact, I don't quite get why people are
so enamored by these fanciful interpretations when Pilot-Wave is so much more
down-to-earth.

~~~
madaxe_again
I came here to say the same thing - this behaviour is readily explained by a
pilot wave formulation of QM, and requires no spookiness. Increasing number of
physicists are re-evaluating Bohm and De Broglie's work - I for one think
we've been down a 60 year dead-end, which has yielded _models_ , but no
plausible mechanism.

~~~
orbifold
I'm fairly certain that you would have a very hard time extending pilot wave
theory to Quantum Field theory, although who kowns, maybe it is possible.

~~~
madaxe_again
It can be - did a graduate paper on the topic some years ago, looking at it
through the Dirac sea - and appears others are taking an interest in the topic
too - here's a nice paper which gives a good overview:

[http://iopscience.iop.org/1742-6596/306/1/012047/pdf/1742-65...](http://iopscience.iop.org/1742-6596/306/1/012047/pdf/1742-6596_306_1_012047.pdf)

------
db48x
Just remember that in quantum physics, any interaction between two particles
is a measurement.

~~~
Gravityloss
Something like this should be the top reply for every "quantum weirdness"
Hacker News link.

Schrödinger's cat thought experiment was meant to highlight the absurdity of
stochastic thinking by taking it to the extreme, not as a description of
reality.

[https://en.wikipedia.org/wiki/Quantum_decoherence](https://en.wikipedia.org/wiki/Quantum_decoherence)

------
nosuchthing
Observation does not exist until observed, experiment finds.

~~~
NeutronBoy
If a tree falls in the woods...

~~~
tarpherder
.. and nobody hears it, then is there even ground for it to fall onto?

~~~
iagooar
And is the tree really there?

------
graycat
We know that light bends near a gravitational field with a big gradient before
it is "measured".

Sounds like that light existed and generated and responded to a gravitational
field after it was emitted and before it was detected or measured.

~~~
tiatia
The light may be in a state of being bended and being not bended until you
observe it...

~~~
graycat
I doubt it: What is _bent_ is the _wave function_. There's no ambiguity there.

~~~
tiatia
It addresses the inability of the classical concepts "particle" or "wave" to
fully describe the behavior of quantum-scale objects. As Einstein wrote: "It
seems as though we must use sometimes the one theory and sometimes the other,
while at times we may use either. We are faced with a new kind of difficulty.
We have two contradictory pictures of reality; separately neither of them
fully explains the phenomena of light, but together they do"

------
vectorpush
armchair musings of a layperson physicist/philosopher follow:

the non-interference pattern is the optimized result of a deterministic
universe that requires the observation to occur. The measurement didn't reach
back in time, the results were specifically determined by the same causal
chain that determined an experiment would be performed.

------
jondubois
I always found the notion that "If you measure it, it behaves differently" to
be really confusing. When considering the double slit experiment - In both
cases (whether we are observing the particle going through a single slit or
otherwise observing the interference pattern left afterwards), we are in fact
simply measuring 'observable effects' in both cases - It's just that we are
measuring them in different ways.

If you didn't measure both cases, you wouldn't be able to compare their
outcomes. It seems that it is not about whether or not the event was
measured/observed but about HOW and WHEN it was measured.

In neither case do we actually 'witness it happen' \- In both cases, we are
just observing effects of those events.

The light which allowed us to 'directly observe it' is as much a byproduct of
the actual event as the interference pattern left behind on the surface.

------
agd
> "At the quantum level, reality does not exist if you are not looking at it"

So much physics reporting mistakes science for philosophy. It leads to so much
confusion among laypeople.

------
hkailahi
In the time of Empiricism, the philosophers George Berkeley and John Locke
proposed something similar. I believe it was called it immaterialism, or the
idea that nothing exists without being perceived. Berkeley went further saying
that objects only exist in the mind, or something like that.

~~~
fragsworth
They're not saying "nothing exists without being perceived", because the
probabilities of things at the quantum level all do exist.

It seems sort of unfortunate that physicists would call these quantum
probabilistic behaviors "not reality", because they are just as real as
anything else.

~~~
hkailahi
Right I'm aware of that. I just thought it was an interesting parallel.

Locke based his works off of the physics known at the time (Newton, etc). His
theories were later definitely refuted by advancements in physics. Though it
wasn't his intended meaning, it is interesting at least to see similar
language being brought back by physics.

------
facepalm
"If one chooses to believe that the atom really did take a particular path or
paths then one has to accept that a future measurement is affecting the atom's
past, said Truscott."

Is that equivalent to "reality doesn't exist until it is measured"? Because I
don't see the latter claim (which is the headline on HN) anywhere in the text?

Also, didn't Feynman explain in q.e.d. that it's not either a wave or a
particle, it's always a particle and the probabilities for the path the
particle takes behave like waves? (Something like that, I am foggy on the
details).

------
OscarCunningham
The jokes above that say that this was done by our simulators to save on
computation are amusing but wrong. Quantum computation is famously harder than
classical computation.

~~~
AgentME
That's assuming that the simulation is running on classical computers. The
simulation could be running on quantum computers or who-knows-what. Quantum
computers might not be so inconvenient to build to make in the host world's
physics.

------
dschiptsov
So, the Sun doesn't exist when experimenter is unconscious? I see.

It seems like at least Philosophy 101 should be mandatory to quantum
physicists.)

Reality doesn't depend on an observer (who distorts it by his observation).
Reality just is.

There are light and other temporary states of what we call "energy". That's
it. Time, space, relativity are human concepts - the hard-wired modes of
perception which conditions our experience. From a Photon's perspective none
of these exist.

~~~
jimhefferon
> at least Philosophy 101 should be mandatory to quantum physicists

Or perhaps quantum physics should be mandatory for Philosophy 101?

------
VonGuard
Reality is just a giant whirling layer of infinite View Master-like
multidimensional slides, overlaid one upon the other. Every slide locks into
place to be seen as we are looking in whichever direction, at whatever time.
I'd wager time travel is never discovered by humanity, but that some sort of
time or dimensional goggles are created, eventually.

Essentially, we're all watching our own multi-dimensional, multilayer,
composite TV channels and seeing shadows of each other across our screens.
Allegory of the Cave meets 3D Ray Tracing and such.

That's nothing, though. Not compared to the realization that every face is a
mirror, and we're all stuck here until we can treat each other as ourselves.

Maybe it's not true, maybe it's insane ramblings. But it does explain the
crazy doods muttering to themselves on the corner and those people in your
life who "just aren't watching the same channel as the rest of us."

Like me!

~~~
brador
But time may just be a human construct.

~~~
VonGuard
Absolutely! As is perspective. Time just translates to a whole series of
indexes for which planes of existence, in which dimensions are aligning into
the measuring perspective. It's the pointer for some such reflection, and
angle to see it.

Those planes of existence are these slides I mention. Whirling in time and
subject, but always a representation of some spherical center whole that is
the perspective of another. We're all just holes looking into this swirling
miasma of time/space/parallel-dimensions/etc, seeing shadows of holes.

~~~
brador
You are assuming a multidimensional universe. There may just be a single
dimension, with just a now, a single state solution, t=1, d=1. But physicists
like to ignore that solution because it doesn't get the juicy book deals.

------
derrickgrant
Guys I'm a total quantum physics noob but when I read this post I couldn't
help but think of Alan Watts and the Taoist definition of the theory of time
(quoted below). HN in your opinion how does this theory hold up to the to new
finding (if at all)?

Big thanks to anyone taking the time to humour me, I really appreciate your
time.

'So when you have this happening the other illusion that a Westerner is liable
to have is that it's determined in the sense that what is happening now
follows necessarily from what happened in the past. But you don't know
anything about that in your primal ignorance. Cause and effect? Why, obviously
not! Ha ha ha! Because if you're really na•ve you see that the past is the
result of what's happening now. It goes backwards into the past like a wake
goes backwards from a ship.'

~~~
derrickgrant
Here's the full transcript of the Alan Watts lecture

[http://thinkyhead.blogspot.co.uk/2013/09/alan-watts-
philosop...](http://thinkyhead.blogspot.co.uk/2013/09/alan-watts-philosophy-
of-tao.html)

------
DavidPlumpton
The Many Worlds Interpretation explains all of this quite intuitively
[http://lesswrong.com/lw/r8/and_the_winner_is_manyworlds/](http://lesswrong.com/lw/r8/and_the_winner_is_manyworlds/)

------
scotty79
For me the only way I can make wave-particle duality and associated
observations believable is to think that light and similar entities always
travel as a wave, but sometimes interact like particles.

This understanding is in line with this experiment without believing that
future affects the past. It's just that atom is never a particle until it
reaches detector at the end. Only there it displays ability to exchange
momentum with one other single atom as if two billiard balls hit. Throughout
the whole experiment it travels as a wave, both paths, grating or no grating.
It just either interferes if there was second grating or not if there was no
second grating.

------
obstbraende
Quantum Bayesianism [0] treats such effects explicitely as Bayesian belief
updates of the experimenter. This leads to an interpretation of quantum
mechanics free of such paradoxical/counterintuitive statements about reality.
I'd like to hear other physicists' opinions on minority interpretations like
this.

[0] layman-friendly article / interview:
[https://www.quantamagazine.org/20150604-quantum-
bayesianism-...](https://www.quantamagazine.org/20150604-quantum-bayesianism-
qbism/)

------
sosuke
If you could change how you measure it, could you change your reality?

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rrodriguez89
But , who was measuring before the big bang , and the millions of year before
we appear ? what is so special about measurement? I thought that our brain was
merely a quantum computer ?

------
bcheung
So that's why kids cover their eyes when they want to hide.

~~~
EarthLaunch
HN doesn't appreciate when you concretize their epistemology.

~~~
DanWaterworth
HN doesn't appreciate when you use words they don't recognise. It makes them
feel stupid and that is a Bad Thing™.

------
amelius
QM explained by a software engineer:

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

------
Moshe_Silnorin
Or, maybe, Everett was right.

~~~
deciplex
Most physicists or, depending on who you talk to, nearly half of physicists,
would appear to agree with you.

I'm convinced that the Copenhagen interpretation remains popular because by
making observation itself an integral part of the theory, you allow us to
postulate that there is something special about human brains. But 'mysterious
observation' is the luminiferous aether of quantum mechanics.

photonic29: I would like to continue our discussion, but HN has some kind of
stupid rule where I can't make more than five posts within a (I think?) 12
hour period. I don't know if this is a general rule that applies to everyone,
or simply one of the innumerable passive-aggressive account handicaps our
gracious mods will afflict us with if we catch them on a bad day.

At any rate, I can't post anymore for now, so our discussion about MWI and
Copenhagen interpretation can't happen. Sorry.

~~~
photonic29
Is that really the case though? An observation collapses a wave function. The
Copenhagen interpretation suggests that the collapsed state arises from a
probability distribution, but it does not address the "fundamental" origin of
that distribution. MW attempts to address it by suggesting that the rest of
the reality just went elsewhere, rather than disappearing or never having
existed at all, but it still does not explain why "we" get "this" reality.
Both rely on observations to collapse the wave function, and neither
specifically calls out a conscious agent as necessary for an observation to
occur. Observation is a measurement, whether intended and registered by a
brain or not.

~~~
pdonis
_> An observation collapses a wave function._

Not if the MWI is true. Talking about wave function collapse presupposes that
the Copenhagen interpretation is true. In the MWI, there is no collapse; it's
unitary evolution all the time.

------
hellbanner
How can you measure what doesn't exist?

~~~
photonic29
You can make an observation of a system whose state is undetermined. By
interrogating the system for its state, a state becomes determined. Suppose,
for example, that you have a flipped coin and sent it rotating in space, never
hitting the floor. Is it heads or is it tails? Until it is looked at, the
question doesn't really make sense. And for this case, we'll define "looking
at it" to mean sticking out your hand and catching it. There is a probability
that it's landed heads up in your hand, and a complimentary probability that
it's landed tails up. Once it's in your hand though, you can confidently say
which state it's in.

Now, you could definitely take issue with this example, because you could
argue that the rotation of the coin is well described, so with initial
conditions, you can predict its position at any given moment. But imagine a
microscopic quantum system, and, for the sake of this simple explanation,
believe that its "rotating through the air" state really does not have any
precise heads or tails definition. Until something gets in the way of that
system, creating an interaction that exchanges information about its
observable state, it's not meaningful to say that it's in one of the
observable states at all.

A superpositition of states, as such, is essentially the representation of a
state in terms of a basis set of observables. In the case of the coin, heads
and tails are the two observable states, they are orthogonal, and they fully
represent the state space of the coin. You could flip the coin, and put its
state vector into the form of sqrt(2)/2 * Heads + sqrt(2)/2 * Tails. This
state isn't observable, but it can be described in terms of observable
components, where the coefficients represent the probabilities that a given
observable state will be measured upon observation.

~~~
pdonis
_> You can make an observation of a system whose state is undetermined. By
interrogating the system for its state, a state becomes determined._

For QM, this is not correct, although it's a common misstatement. The correct
statement is this: you can make an observation of a system which is not in an
eigenstate of the measurement operator you are using. After the measurement,
the system is now in an eigenstate of the measurement operator--i.e., the act
of measurement changes the state.

Note that this is only true on a collapse interpretation, like Copenhagen. On
a no-collapse interpretation, like MWI, the "observation" is just an
interaction that entangles the state of the measuring device with the state of
the system being measured--it's all just unitary evolution.

 _> You could flip the coin, and put its state vector into the form of
sqrt(2)/2 _ Heads + sqrt(2)/2 * Tails. This state isn't observable*

Yes, it is; but it isn't observable by a simple method like looking to see if
the coin is heads or tails. But according to QM, every state is an eigenstate
of _some_ operator, so there will be _some_ observation that will distinguish
sqrt(2)/2 * Heads + sqrt(2)/2 * Tails from the state that is exactly
orthogonal to it, which is sqrt(2)/2 * Heads - sqrt(2)/2 * Tails.

~~~
photonic29
>The correct statement is this: you can make an observation of a system which
is not in an eigenstate of the measurement operator you are using.

I should have distinguished better, but what you're more rigorously calling an
eigenstate of a measurement operator, I'm calling an observable state. There
is something lost in translation to an audience unfamiliar with terms like
eigenstate, but that was my attempt. Would you suggest a better one?

>Note that this is only true on a collapse interpretation, like Copenhagen. On
a no-collapse interpretation, like MWI, the "observation" is just an
interaction that entangles the state of the measuring device with the state of
the system being measured

The greater point being addressed is that MWI is no more deterministic than
Copenhagen.

>Yes, it is; but it isn't observable by a simple method like looking to see if
the coin is heads or tails. But according to QM, every state is an eigenstate
of some operator

Some hermitian operator? But more to the point, if looking at the coin is the
only operator at our disposal in the simple example, then its eigenstates are
the ones we care about.

~~~
pdonis
_> what you're more rigorously calling an eigenstate of a measurement
operator, I'm calling an observable state._

Yes, but "observable" here is relative to the measurement you are making. If
you make a different measurement (i.e., realize a different operator), then
the set of "observable states" by your definition is different, because the
set of eigenstates of the operator is different.

 _> The greater point being addressed is that MWI is no more deterministic
than Copenhagen._

But this isn't true. The MWI is completely deterministic, because wave
function collapse never occurs, and wave function collapse is the source of
all the indeterminism in the Copenhagen interpretation.

 _> Some hermitian operator?_

Yes.

 _> if looking at the coin is the only operator at our disposal in the simple
example, then its eigenstates are the ones we care about._

If all you're interested in is that particular experiment, yes. But here we're
discussing claims that must apply to all possible experiments and all possible
measurements, not just the particular one in the example you chose. So we have
to consider all possible operators and all possible sets of eigenstates, not
just the ones in your example.

~~~
photonic29
> _But this isn 't true. The MWI is completely deterministic, because wave
> function collapse never occurs, and wave function collapse is the source of
> all the indeterminism in the Copenhagen interpretation._

For what useful definition of deterministic? If a measurement comes with
decoherence into multiple non-inteferring branches, then certainly the state
evolves in a predictable way from "god's eye", but not from the perspective of
the experiment occupying any given branch.

~~~
pdonis
_> For what useful definition of deterministic?_

The definition that says the future state is entirely determined by the
present state. That's the only definition I'm aware of.

 _> the state evolves in a predictable way from "god's eye", not from the
perspective of the experiment occupying any given branch._

The entire "god's eye" state is the one that appears in the dynamical laws of
QM (unitary evolution), so that's the one that's relevant for assessing
determinism.

 _> the state evolves in a predictable way from "god's eye", but not from the
perspective of the experiment occupying any given branch._

This "apparent randomness" of measurement results is equally true of chaotic
classical systems; it's not something that only appears in QM. Basically, it's
just a consequence of the fact that individual "observers" will in general not
have complete knowledge of the state. That doesn't mean the state doesn't
evolve deterministically; it just means the observers don't have complete
knowledge.

~~~
photonic29
> _This "apparent randomness" of measurement results is equally true of
> chaotic classical systems; it's not something that only appears in QM._

Is that a fair comparison? Yes, in either case, the experimenter is limited in
his predictive capability by the information available to him. But in a
chaotic system, your predictive power can be improved arbitrarily by surveying
more information with greater precision. As I understand it-- and hopefully
you can clarify if this is accurate-- decoherence forbids a measurement from
receiving information from a branched outcome, so even if you take a
measurement with arbitrary access to information _now_ and repeat the same
measurement in the future, there becomes a set of information that is
fundamentally off limits to the observer in a given branch.

~~~
pdonis
_> Is that a fair comparison?_

I think so. Perhaps it will help if you look at it this way: you repeat some
measurement multiple times, and get a sequence of results that looks random.
Is the randomness because of classical chaos, or because of quantum
"indeterminacy"? From the measurement results themselves, in many cases, there
will be no way to tell. The only case in which there would be a way to tell
would be if you specifically made measurements on entangled quantum systems in
order to test the Bell inequalities; if those inequalities are violated, the
measurements can't be due to classical chaos. But that just underscores my
point: looking at "apparent randomness" of measurement results is not
sufficient to tell whether they are due to "quantum indeterminacy.

 _> decoherence forbids a measurement from receiving information from a
branched outcome_

Once again, this is a misleading way of stating it. What is happening, again,
is that the observer evolves into a superposition, corresponding to the
superposition that the measured system is in. Decoherence just means the
branches of the superposition don't interfere with each other. But the system
is still in a single state; the "branches" are not separate states or separate
entities, they're parts of a superposition.

(Note, also, that decoherence does not guarantee that the different branches
will _never_ interfere with each other. Decoherence is not a fundamental
limitation; it's just a recognition of what happens in the usual case, where
no special measures are taken to isolate the system or to facilitate
interference. According to the MWI, there is in principle always a way to
cause the different branches to interfere, i.e., decoherence is never
absolute.)

 _> there becomes a set of information that is fundamentally off limits to the
observer in a given branch_

According to the MWI, the observers in different branches are not different
observers; they're different terms in a superposition that the observer is in.
Thinking of them as "different observers" with access to different information
implicitly assumes something like the Copenhagen interpretation.

------
ghosthamlet
There is no reality at all, like 3D cgi, if no man see it, it will not be
calculated, so no exists. It means another experiment: we living in a
computer-simulation, [http://www.telegraph.co.uk/news/science/science-
news/1045198...](http://www.telegraph.co.uk/news/science/science-
news/10451983/Do-we-live-in-the-Matrix-Scientists-believe-they-may-have-
answered-the-question.html)
[http://www.huffingtonpost.co.uk/2012/10/11/physicists-may-
ha...](http://www.huffingtonpost.co.uk/2012/10/11/physicists-may-have-
evide_n_1957777.html) [http://news.discovery.com/space/are-we-living-in-a-
computer-...](http://news.discovery.com/space/are-we-living-in-a-computer-
simulation-2-121216.htm) [http://listverse.com/2013/12/02/10-reasons-life-may-
be-a-com...](http://listverse.com/2013/12/02/10-reasons-life-may-be-a-
computer-simulation/) [http://io9.com/5799396/youre-living-in-a-computer-
simulation...](http://io9.com/5799396/youre-living-in-a-computer-simulation-
and-math-proves-it) [http://www.nature.com/news/simulations-back-up-theory-
that-u...](http://www.nature.com/news/simulations-back-up-theory-that-
universe-is-a-hologram-1.14328)
[http://thelaymansanswerstoeverything.com/2013/01/scientific-...](http://thelaymansanswerstoeverything.com/2013/01/scientific-
proof-we-live-in-a-simulation/)

------
sravfeyn
For us, Reality by definition, is what we perceive. Our
mind/brain/consciousness interprets the perceptions, draws conclusions makes
up reality by interfacing an Electromagnetic medium. When trying to explain
Popular Quantum Physics, one should avoid using the word Reality loosely.

~~~
sooheon
I think most people's definition of reality would be precisely _not_ that it
"is what we perceive", in that two people can and often do perceive the same
underlying reality differently. That there is an underlying reality at all may
be an incorrect assumption, but it is the intuition most people have.

------
sown
What does this mean? If there was a supernova eons ago in another galaxy and
I'm the only human who had been hit by a cosmic ray, does that mean it didn't
exist or happen until ... ?

Does measurement have to include an agent? Could measurement mean interaction
with other atoms?

~~~
photonic29
>Does measurement have to include an agent? Could measurement mean interaction
with other atoms?

Indeed it can. Roughly put, if information about the state left the
undetermined system, a measurement has been made. One of the most frustrating
interpretations of literature such as this is the idea that there is something
spooky, special, and reality-making about a conscious mind. Lots to think
about there philosophically, but the physics happens at lower levels of
abstraction.

------
Rapzid
Is it not possible that it could have been observed no other way? Is
observation driving the behaviour or behaviour driving the observation(or an
external factor driving both)?

------
sebringj
no.

[https://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat](https://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat)

and then...

[http://bigthink.com/dr-kakus-universe/physics-on-the-
fringe-...](http://bigthink.com/dr-kakus-universe/physics-on-the-fringe-dr-
kaku-answers-questions-from-viewers-of-the-science-channels-new-show)

clears it up for me.

------
jen729w
Deepak Chopra is going to have a field day with this one.

------
leeleelee
Most of these articles / experiments focus on the perspective of being the
observer...

What is the conclusion if you are the thing being observed?

------
omarchowdhury
Who or what is measuring all of the quantum building blocks that collectively
sustain and comprise the total universe?

------
hyperion2010
Ah, the old "now we have to figure out what 'measured' means." Thanks science
journalists!

------
sudioStudio64
It's too bad that this will be taken by Deepak Chopra fans as evidence that
consciousness is magic.

------
Ygg2
Um, this doesn't prove reality doesn't exist until it is measured. It just
proves that measuring and "decision" which state to appear in happens
simultaneously.

It could mean that time on quantum scale doesn't differentiate past/future.

~~~
david927
Sure it does because, while certainly quantum scale doesn't carry the same
sense of time, we do.

Everything we see, what we call reality, is made up of the Lego blocks of
electrons, protons and neutrons, and yet even at that level it makes no sense
to talk in concrete terms about, say, an electron's spin. We would expect that
the spin exists and we find out what it is when we measure it, but it's not
that. It's that talking about its spin is meaningless until you measure it.
What you can reason about the Lego blocks of everything we see, smell, touch
and taste, what gave birth to us and what will kill us, is indescribable until
it's asked to be described. Whether that's because it's locked-in to time or
not is irrelevant because it means the same thing: reality is not there until
it's there.

~~~
Ygg2
You can only conclude that "Physical reality doesn't exist until observed", if
you imply nothing can move faster than light.

Also hidden variable theory aren't yet categorically disproven. A fractal
theory could explain why we keep getting different results when measuring
reality in different ways.

~~~
david927
I will happily imply that energy/mass cannot move faster than light.

You know, I think a hidden variable theory is a crutch. To me, there's simply
a Planck's constant foundation that prevents infinite regression just as much
in terms of information as it does with radiation, etc.

~~~
Ygg2
What you imply is besides the point. It's what the finding implies.
Interpreting that as "physical reality doesn't exist" is far fetched.

~~~
david927
This isn't about relativity at all.

If you're measuring N-S electron spin, you will get 100% N spin or 100% S spin
but never any E-W spin. Period. If you're measuring E-W electron spin, you
will get 100% E spin or 100% W spin, but never any N-S spin. You can word
smith it how you wish, but electron spin is directly tied to the spin you look
at. To speak of the "reality" of the spin when you're not measuring it _makes
no sense_.

~~~
Ygg2
In my previous comment I didn't mention relativity.

> If you're measuring N-S electron spin, you will get 100% N spin or 100% S
> spin but never any E-W spin.

Ok, but not arguing against it. I'm arguing that there are alternative
interpretation to that event other than "reality doesn't exist until we look
at it". There are other explanations like: retroactive causality, many world,
informational based, etc.

Basically, just read the top comment, it summarizes my thoughts on the matter.

------
octatoan
Editorialized titles are irritating, random HN commenter says.

------
wanda
> Reality is a computer program

I'd like to issue a pull request..

------
dfragnito
"Truth" is ones version of Reality.

------
azinman2
Best headline ever.

------
rasz_pl
maybe time is not a one way street

------
dang
This experiment has been posted to HN a few times in recent weeks, but I'm not
sure it's had a real discussion yet.

The paper is at
[http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys...](http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html).
We changed the URL of this submission from [http://www.independent.co.uk/life-
style/gadgets-and-tech/new...](http://www.independent.co.uk/life-
style/gadgets-and-tech/news/reality-doesnt-exist-until-you-look-at-it-
pioneering-quantum-physics-experiment-finds-10305047.html).

------
andyl
Lazy instantiation.

~~~
has2k1
Just like python generators.

~~~
andyl
reality must be dynamically typed.

~~~
lucozade
Could just be an ADT. photon :: (Wave | Particle)

------
dazlari
So a bear doesn't sh*t in the woods.

~~~
ceejayoz
The bear itself is an observer, though.

------
codeshaman
Which is another way of saying that reality is invented.

"Measuring" is applying our sensors onto the external reality and producing a
map of what is observed in the form of thoughts, ideas, imagery -
'perception'.

But since the sensors are also part of reality, which does not exist before
sensing it, it can be postulated that what is perceived is not a consequence
of reality hitting the sensors, but the result of a new thought about reality
being perceived, or simply - an invention.

That is, reality (including your body, brain and you) is the product of a
thought process, but (here's the interesting part) the thinker is you and not
you at the same time, or rather - the thinker is you and every other being.

That thinker is called God. Or Universe or whatever you want to call the thing
or being that is the eternal recursive loop of self-invention / self-
perception.

Of course very hard to put into language, but easily grokked under
psychedelics.

It's interesting that science (and math) is slowly pointing towards this
conclusion too, a thing that many great scientists arrived at intuitively.

~~~
CatsoCatsoCatso

        Of course very hard to put into language, 
        but easily grokked under psychedelics.
    

Fantastic line.

