

Macroscopic quantum objects cannot exist if P ≠ NP? - sleepysort
https://medium.com/the-physics-arxiv-blog/the-astounding-link-between-the-p-np-problem-and-the-quantum-nature-of-universe-7ef5eea6fd7a

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Dunnorandom
For anyone interested, here's Scott Aaronson's response to the paper:
[http://www.scottaaronson.com/blog/?p=1767#comment-103591](http://www.scottaaronson.com/blog/?p=1767#comment-103591)

~~~
awhitty
I understand that people get a little passionate about their fields of study,
but the tone of Aaronson's response is wildly inappropriate. Phrases like "a
common novice mistake" and "as if he just emerged from a cave" are unnecessary
and entirely condescending. This style of discourse fosters a really awful and
exclusive atmosphere, and I wish it wasn't the norm.

I don't know this guy at all, and I'm guessing he's pretty respected in his
field, but at the end of the day, he doesn't have to be a jerk to get his
point across.

~~~
soganess
I find the dismissive tone and holier and thou attitude that Aaronson has
garnered more that bit of notoriety for really detrimental to the growth of
both our collective understanding of QM and our understanding of
computability. if knowledge is truly power, lording your knowledge over a peer
is paramount to oppression. A bit dramatic, of course, but not completely
without warrant.

This maybe a bit of a kumbaya, everyone hold hands argument, but I'm going to
make it. Its not as if the number of people that have the ambition to collect
the wealth of knowledge required to characterize(even incorrectly) any
perspective overlap between computation and quantum is exactly a huge working
set. I don't consider it reasonable to shit on someone's work so
indiscriminately in this space where its rather hard to be right and quite
easy to be wrong.

Prima facie, the paper was accepted for publish in a peer reviewed journal
(Physical Science International Journal), and. from all the terse looks of it
I've encountered, is likely erroneous on a fundamental level. Highlighting
this is not meant to imply that peer-review is a good/bad measure of academic
muster, but rather an indicator of how complex comprehending and qualifying
such theories might be.

My point is, even in its incorrectness, a bravo for thinking so wildly is
likely in order.

Disclaimer: I'm a quantum chemist and computer scientist. I'm also not the
biggest fan of Scott Aaronson, so I might be harder on him that is likely
deserved.

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raverbashing
I'm not buying it

1 - P=NP is a mathematical problem. It has nothing to do with Physics. Physics
has to do with Mathematics but one should be _very careful_ when extrapolating
(range, constraints, etc).

2 - Nature has no problem whatsoever solving complicated equations. Our
mathematical models are the ones who suffer to model simple everyday stuff in
Physics. Turbulence and Navier-Stokes equations, electromagnetic propagation,
the way lightning goes through the air, etc.

~~~
swombat
Unless, of course, our entire reality is running on a very powerful, but not
infinitely powerful computer, and the Great Programmers in the Sky decided to
cheat by putting in a hack that cuts off quantum behaviour at a larger
scale...

Unlikely, but cute...

~~~
cstross
_Or_

The granularity of the simulation of our reality is the Planck length. This
constraint does not apply to the real, underlying, reality within which our
simulation is embedded.

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wcoenen
We can't directly observe superpositions (macroscopic or otherwise) because
when doing so, we become entangled with the state of the observed object. The
only thing special about macroscopic objects is that it is difficult to
prevent or postpone their entanglement with the environment.

Think about Schrödingers' gedankenexperiment from the cat's point of view. It
finds itself to be either comfortable or dying by toxic fumes; it can't see
the superposition because it is _inside_ of that superposition. The same thing
happens to any observer trying to look at a quantum superposition.

~~~
JulianMorrison
Box closed: two cats, one scientist. Box opened: two cats, two scientists,
each sees one cat. Entangling yourself with the superposition pulls you into
it.

~~~
trhway
>Entangling yourself with the superposition pulls you into it.

following that logic and taking cat as the observer, Mr.Cat PhD, the
superposition is that doubles the number of cats (and PhD's :).

Yet it works in the other direction - entangling a cat (a macro-object with
macro-state) with superposition had already destroyed the superposition well
before box is opened.

>> it can't see the superposition because it is inside of that superposition.

it can't see the superposition because the superposition is gone because he
got entangled with it.

~~~
JulianMorrison
The cat is pulled into the superposition by interacting with the results of
the detector and the poison vial. There are two cats from the "outside", but
from each cat's perspective it sees only a single "random" outcome.
Superpositions _aren 't_ destroyed - you are subsumed within them.

~~~
trhway
>There are two cats from the "outside", but from each cat's perspective it
sees only a single "random" outcome.

in a given Universe there is only one cat. A human observer just doesn't know
what the state of the cat in his Universe. The cat knows.

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kazinator
This hypothesis seems to rest in the flawed idea that quantum processes must
unfold as if by a step by step calculation which consumes time, in the
ordinary temporal dimension. And so certain complex state changes are
impossible simply because they don't have enough time to execute within some
predetermined slot, or something like that. Time in the simulation is not the
same as time in the simulator. Come on, this is not even basic science as much
as basic sci-fi! :)

~~~
sambeau
Surely Schrodinger’s Paradox implies cause and effect?

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tomp
Wait what? What this article is arguing is totally absurd - just because we
can't model certain physical objects, they cannot exist?! That's like saying
that since we can't model three gravitational objects interacting (i.e. the
numerical solutions diverge, therefore to properly model the system, we would
require increasing amounts of memory and time), therefore they cannot exist.

I'm not saying that the physical claim is wrong - I'm just saying that the
explanation in the article is severely lacking/logically inconsistent.

~~~
SnacksOnAPlane
I'm a simulationist. I believe that the universe we're experiencing is a
simulation made by a far-advanced civilization. So in my reality, if something
can't be modeled, it can't exist.

Not saying that this is the truth, just the way I choose to understand things.

~~~
mdxn
I think you would have to be assuming that the far-advanced civilization's
simulator has the same complexity as the models of computation we can
construct. I think that's a huge leap to make. We might not be able to model
something due to issues with, let's say, Turing decidability. Unlike us, the
advanced civilization's might be able to because their constructable models of
computation are strictly more powerful.

~~~
drdeca
I think you described what I wanted to in a much better and more concise way.

Thank you for doing that.

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pndmnm
Interesting and semi-related:
[http://www.opticsinfobase.org/oe/abstract.cfm?id=140598](http://www.opticsinfobase.org/oe/abstract.cfm?id=140598)

Essentially, solving the traveling salesman problem in quadratic time using
photon interference -- however, since the photons scale up as N^N, the
Schwarzschild radius of the effect means it's not observable in less than
exponential time.

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kipple
One part I didn't like is towards the beginning the author says: "Nobody knows
why we don’t observe these kinds of strange superpositions in the macroscopic
world. For some reason, quantum mechanics just doesn’t work on that scale. And
therein lies the mystery, one of the greatest in science."

But I thought the reason we dont see macroscopic events exhibiting quantum
superposition behavior was because of quanutm decoherence? It's just so hard
to get a macroscopic situation that hasnt already been observed and collapsed.

But then the author kinda hints at this point later when he mentions:
"Physicists have become increasingly skilled at creating conditions in which
ever larger objects demonstrate quantum behaviour."

Am I missing something, or is he blowing the problem (and the impact of
Bolotin's computational limit theory) way out of proportion?

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Strilanc
I hope Scott Aaronson blogs about this article, because it espouses several of
the wrong-facts he complains about _and then cites him_.

\- Limitations on computers _within_ physics are not limitations on _physics
itself_. Analogously, you can simulate system so simple that a computer can't
be made in them without your computer unmaking itself. Relevant: xkcd.com/505

\- We do understand why we don't observe superpositions. It all comes down to
this thing we call "quantum mechanics", which precisely describes those sorts
of situations.

\- The article consistently mixes up NP-Hard and NP-Complete.

> "And how does the universe decide whether a system is going to be quantum or
> not?"

Seriously, is this article a satire?

~~~
PeterisP
An interesting point is that limitations on math (i.e., things that would be
true regardless of the details of the physical world) would put limitations on
_any_ physics simulations - including hypothetical physics simulations done by
someone outside of our universe with potentially different physical
limitations.

So the point of the article is something like - if phenomenon-X can't be
simulated by anyone, no matter how good their computers become; and if our
universe is a simulation (which is a possibility), then our universe won't
contain phenomenon-X.

~~~
TheLoneWolfling
The problem is that there is no proof that there is any such thing as
something that would be true regardless of the details of the physical world.

------
ctdonath
This is radiantly insightful. It makes perfect sense to me. The effect of
reading it is like drinking a _Pan Galactic Gargle Blaster_ : feeling like my
brains were smashed out by a slice of lemon wrapped round a large gold brick.

Yes, in real physics solves vastly complex equations fast. That's not enough
to discount the point here. There _are_ limits on _physics itself_ : the
particles in a cat (presumably one owned by Schrodenger) are so numerous that
for all of them to express, within a reasonable time, superpositioning the
effects of a single radioactive atom's unobserved state would require particle
interactions occur _way_ faster than Planck time.

Nothing moves faster than light. There are a finite, albeit large, number of
particles in the universe. Nothing can be smaller than Planck length, and no
particle interaction can occur faster than the time light takes to move one
such unit. Upshot: macroscopic superpositionining effects cannot occur because
it takes too long for full propagation among particles numbering on the
magnitude of Avagadro's number.

There's an upper limit to what can happen, because there's only so much stuff
and "happen" can only be so fast.

------
jjgreen
The Navier-Stokes equations are also hard to solve, that does not stop fluids
from obeying them.

~~~
kazinator
Also, how can N bodies orbit each other? Don't they know there is no analytic
solution to their problem? Sheesh! (Maybe they are using floating-point?)

------
bcbrown
An interesting assertion. I don't think it's valid to object that this is just
about hard-to-solve equations. As I understand the article, this is the
argument:

1) It's not possible to directly observe a macroscopic quantum object. This is
because the act of observation collapses the wave function.

2) It's possible in theory to describe macroscopic quantum objects in the
solutions to Schrodinger's equation

3) That solution for macroscopic systems is NP-hard

4) A physical theory that can neither be observed nor modeled is "nothing more
than [a] nontestable empty [abstraction]"

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baddox
> What’s interesting about NP-hard problems is that they are mathematically
> equivalent. So a solution for one automatically implies a solution for them
> all.

That's a mistake. The author is describing NP-complete problems, which are all
roughly equivalent (reducible in polynomial time). NP-hard includes all NP-
complete problems, but also includes problems much harder than those in NP-
complete, including undecidable problems like the halting problem which aren't
even in NP.

~~~
pcvarmint
> That's a mistake. The author is describing NP-complete problems...

Correct. I think that quote basically killed the whole article for me.

~~~
baddox
It didn't kill the whole article for me, although it seems to be a consistent
misconception rather than an isolated typo. To be fair, the naming convention
is pretty tricky, considering NP-hard contains things outside NP.

~~~
icodestuff
And the diagram did get the terminology right. The author may need a (better)
proofreader, but it wasn't impossible to see what the author meant. They only
conflated the names, not the concepts.

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snake_plissken
I thought you could observe quantum effects but only when it was the
superposition of all the eigenfunctions? You never observe the ones with a low
probability density because they are dominated by the others. And also does it
matter if you could solve numerically all of the functions for a macroscopic
group of particles if in the end all you would care about is the average value
(due to Planck's constant and the uncertainty principle)?

------
Iftheshoefits
I think the explanation for why we don't observe macroscopic quantum phenomena
is rather more simple than that, and likely has more to do with the results of
a superposition of a large ensemble of possible states than some fairly
strained analogy with computation (think of it as something like fourier
decomposition of a function).

------
TheLoneWolfling
An interesting tidbit:

If the smallest proof for something takes up more than ~10^123 bits, or the
fastest proof requires more than ~10^120 operations, it cannot be proven in
our universe.

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dllthomas
_" Nobody knows why we don’t observe these kinds of strange superpositions in
the macroscopic world."_

Yeah, why can't we observe processes that rely on lack of observation?

~~~
bcbrown
We can observe processes that rely on lack of observation in the microscopic
world. Look up the one-slit and two-slit experiments[0]. In the two-slit
experiment, we don't observe which slit the photon takes, but we can observe
the interference pattern on the screen.

The two-slit experiment works with photons, but not with bullets, or cars, or
baseballs.

[0]:
[http://en.wikipedia.org/wiki/Two_slit_experiment](http://en.wikipedia.org/wiki/Two_slit_experiment)

~~~
dllthomas
Hmm, probably fair.

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typon
This is such a poorly written article. I can't even begin to point out the
mistakes. I'm sure Scott Aaronson will write a response and strike this down.

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agorism
This is almost the same as the free-will vs determinism problem. Our universe
is deterministic, but computing into the future is NP-complete.

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lfuller
By this logic, shouldn't the existence of the universe be impossible since
simulating it mathematically in its entirety is infeasible?

