
Einstein’s Parable of Quantum Insanity - treefire86
https://www.quantamagazine.org/20150910-einstein-insanity/
======
graycat
Physicists, here is a related question:

We have a gun that shoots electrons one at a time due north. A little ahead of
the gun and in the path of the electrons we have a _beam splitter_ , that is,
a flat plate of material with horizontal normal along the line from south east
to north west.

So, we fire the gun. The electron hits the beam splitter. The wave function
splits with some going east and the rest passing through the beam splitter and
going north.

One mile to the north of the beam splitter and in the line of the path of the
wave function we have a very good electron detector. Similarly for one mile to
the east.

So, we fire and some fraction of the time we get a detection from the north
detector and the rest of the time, from the east detector.

Now, let's move some of the mass of the electron faster than the speed of
light: A little ahead of each detector we have a very sensitive detector of
gravity (or, maybe charge).

So, as the two parts of the wave function pass the gravity detectors, we get a
signal from both. If the beam splitter sends 10% of the wave function north
and the other 90% east, then from the north gravity detector we should get a
signal of 10% of an electron, and from the east, 90% of an electron.

Then, soon, one of the electron detectors gives a signal, of 100% of the mass
(and charge) of an electron. So, 90% or 10% of the mass (and charge) of the
electron moved instantly, faster than the speed of light. along the line
between the two detectors.

Is this wrong? Why?

In more detail, what about the electromagnetic field from the moving parts of
the wave function? E.g., if the electron is detected at the east detector, is
there an electromagnetic field still from the path of part of the wave
function to the north?

~~~
joefkelley
My understanding is that the gravity detectors would not detect 10% or 90% of
an electron. One would detect 0% and one would detect 100%. You cannot measure
the wave function directly. Attempting to do so collapses it.

When that waveform collapse happens, everything about the quantum state
collapses: electromagnetic field, gravity, etc.

~~~
graycat
Thanks.

Sounds like when the wave function of the electron is moving, likely it is
following the local geometry of space-time but otherwise is essentially _lost_
to the universe.

Then whenever we do detect a field, gravity, electro-magnetic, strong, weak,
etc., necessarily we are detecting just collapsing wave functions, each of
which happens at essentially just a point in time. Then after the point in
time of the collapse, the electron is just a wave function again off on its
way to another collapse.

E.g., when an electron accelerates going around a circle and radiates photons,
each photon radiated is from a collapse of the wave function of the electron
at which time the electron creates a new wave function and continues on?
Sounds like that.

Hmm ... So, all we are seeing, feeling, detecting, observing, measuring, etc.
are just high rate point processes of collapsing wave functions? Gads. Why
didn't they tell me that back in high school?

Where am I going wrong?

~~~
joefkelley
You're getting closer.

Regarding your electron-emitting-photons example: I would describe the photons
being emitted as themselves in a quantum superposition of having been
emitted/not emitted/emitted at different times, etc. It is when we detect or
observe the photon that the state of the whole system collapses! The electron
and the photon are entangled. Continue this line of thinking and you arrive at
the famous Schrodinger's cat... it's a cascading entanglement of larger and
larger groups of particles until you open the box and the waveform of every
particle in the whole cat collapses to either alive or dead.

The waveform is not really a physical object; I think of it as a probability
distribution about the state of the system when observed. These probabilities
can be highly correlated; in this case, the probability of observing the
electron at one energy level or another is 100% correlated to the probability
of observing or not observing the photon at all - which is the definition of
entanglement.

Yes, you are constantly observing collapsing wave functions. It might be some
solace that most of said wave functions have highly-degenerate probability
distributions. By this I mean that 99.999...% of the "mass" of the
distribution lies in something reasonable happening. For example, each
particle in a tennis ball is so highly entangled to every other particle, that
when you throw it against a wall, it's exceedingly likely that the ball will
bounce back. A single unentangled atom may have been able to pass right
through the wall, but the tennis ball's "waveform" is much more stable and
localized such that it's better approximated by classical mechanics.

------
GregBuchholz
For the opposite take, some may like the article, "Clearing Up Mysteries - The
Original Goal" by E.T. Jaynes:

[http://bayes.wustl.edu/etj/articles/cmystery.pdf](http://bayes.wustl.edu/etj/articles/cmystery.pdf)

>While it is easy to understand and agree with this on the epistemological
level, the answer that I and many others would give is that we expect a
physical theory to do more than merely predict experimental results in the
manner of an empirical equation; we want to come down to Einstein's
ontological level and understand what is happening when an atom emits light,
when a spin enters a Stern-Gerlach magnet, etc. The Copenhagen theory, having
no answer to any question of the form: What is really happening when - - - ?",
forbids us to ask such questions and tries to persuade us that it is
philosophically naive to want to know what is happening. But I do want to
know, and I do not think this is naive; and so for me QM is not a physical
theory at all, only an empty mathematical shell in which a future theory may,
perhaps, be built.

...and maybe chapter 10 of his book, "Probability Theory: The Logic of
Science".

>We are fortunate that the principles of Newtonian mechanics could be
developed and verified to great accuracy by studying astronomical phenomena,
where friction and turbulence do not complicate what we see. But suppose the
Earth were, like Venus, enclosed perpetually in thick clouds. The very
existence of an external universe would be unknown for a long time, and to
develop the laws of mechanics we would be dependent on the observations we
could make locally.

>Since tossing of small objects is nearly the first activity of every child,
it would be observed very early that they do not always fall with the same
side up, and that all one’s efforts to control the outcome are in vain. The
natural hypothesis would be that it is the volition of the object tossed, not
the volition of the tosser, that determines the outcome; indeed, that is the
hypothesis that small children make when questioned about this. Then it would
be a major discovery, once coins had been fabricated, that they tend to show
both sides about equally often; and the equality appears to get better as the
number of tosses increases. The equality of heads and tails would be seen as a
fundamental law of physics; symmetric objects have a symmetric volition in
falling.

>With this beginning, we could develop the mathematical theory of object
tossing, discovering the binomial distribution, the absence of time
correlations, the limit theorems, the combinatorial frequency laws for tossing
of several coins at once, the extension to more complicated symmetric objects
like dice, etc. All the experimental confirmations of the theory would consist
of more and more tossing experiments, measuring the frequencies in more and
more elaborate scenarios. From such experiments, nothing would ever be found
that called into question the existence of that volition of the object tossed;
they only enable one to confirm that volition and measure it more and more
accurately...

>Biologists have a mechanistic picture of the world because, being trained to
believe in causes, they continue to search for them and find them. Quantum
physicists have only probability laws because for two generations we have been
indoctrinated not to believe in causes - and so we have stopped looking for
them. Indeed, any attempt to search for the causes of microphenomena is met
with scorn and a charge of professional incompetence and "obsolete mechanistic
materialism." Therefore, to explain the indeterminacy in current quantum
theory we need not suppose there is any indeterminacy in Nature; the mental
attitude of quantum physicists is already sufficient to guarantee it.

[http://www.med.mcgill.ca/epidemiology/hanley/bios601/Gaussia...](http://www.med.mcgill.ca/epidemiology/hanley/bios601/GaussianModel/JaynesProbabilityTheory.pdf)

~~~
eli_gottlieb
For being the top purveyor of maximum-entropy methods, Jaynes really should
have been more willing to accept a probabilistic theory of fundamental
physics.

~~~
OscarCunningham
Jaynes believed that the only kind of probability was that caused by
uncertainty about the true state of the world. So he was advocating MAXENT as
a way to summarise one's (lack of) knowledge about some system.

In fact, this point of view probably made him less likely to accept a
probabilistic theory of fundamental physics. If you've discovered how a
deterministic universe can appear random, and how probabilities can still be
useful for measuring one's ignorance, then it's reasonable to suspect that
these are the only kinds of probabilities and that the universe really is
deterministic.

~~~
eli_gottlieb
And how can states of knowledge be probabilistic if the mind isn't made out of
something related to its function?

------
FrankenPC
Charlton Einstein: "You'll pry my determinism from my cold dead hands"

~~~
rubidium
Determinism is dead. Long live an in-deterministic (and free) universe!

But seriously, why many scientists are so attached to wanting a deterministic
universe is beyond me. Even at the highest levels, I'm amazed that physicists
have an near moral repugnance to the idea that there's randomness inherent in
the universe. They even go through such lengths as inventing the many worlds
theories to try and recapture determinism.

~~~
omalleyt
If you accept that all effects have causes, you accept determinism.

Also, determinism will be resurrected. Look at Pilot Wave theory. It explains
quantum weirdness with a deterministic worldview, but everyone would prefer to
hype voodoo theories.

~~~
FrankenPC
Well..not really.

"But pilot wave theory could still be important, because it has a different
conceptual formulation, so if you set out to modify the theory, you get
different modifications. In that sense, it is a good new idea. I personally
think that you can produce a truncation of pilot-wave which doesn't coincide
with ordinary quantum mechanics, but which is mostly the same as quantum
mechanics when you are dealing with only a few particles only slightly
entangled. In this case, you need the wavefunction to be a complicated
function of the hidden-variables (the particle positions) which only obeys the
Schrodinger equation approximately. This type of thing is a true modification
of quantum mechanics, but I was never 100% sure that it works. I described the
idea roughly in my answer to one of 'tHoofts questions on physics
stackexchange."

Source: [http://www.quora.com/Why-dont-more-physicists-subscribe-
to-p...](http://www.quora.com/Why-dont-more-physicists-subscribe-to-pilot-
wave-theory)

~~~
omalleyt
The predictions of pilot wave theory are the same as any other interpretation
of quantum mechanics, and the theory isn't new it's been around 80 years

------
yakult
Wild guessing from someone who has no background in physics:

1\. Simulating QM-level events is NP-complete.

2.Assuming P=/=NP, a machine that simulates a volume of size X in QM-correct
terms must be exponentially larger than X.

3\. This includes X itself.

4\. Therefore, the universe is taking sweeping shortcuts that look like
classical mechanics at large scale. These are not 'our' computational
shortcuts, they're actually how things work at a fundamental level.

5\. ...maybe if we build a big enough quantum computer we can overflow the
universe's buffer.

~~~
spacehome
You're missing step 0, which is assuming that our universe is a simulation.
Also, you're making a lot of assumptions about the laws of physics and what is
computationally feasible in the universe that that computer is running in.

~~~
yakult
I'm not assuming simulation. It's more of "if the universe can pack something
that can predict the outcome of an NP-complete system (that is, the universe
itself) in real-time into a relatively very tiny space, then either it's
cheating or P=NP."

As for the assumptions, I agree. Hence it's wild guessing.

~~~
spacehome
Then I misunderstood originally.

If you're not assuming the universe is simulated and is instead "fundamental"
(whatever that means), then who are you to put limits on its processing
power?'

I think you have a level-confusion here - the universe isn't packing
computational machinery into itself. Remember that space-time is a part of
this universe. If something is computing our universe, it has to hold the
representation of space-time, too. The computation machinery isn't in here
with us.

~~~
yakult
If 'fundamental' stuff gets to break P=/= NP, then I don't see why we can't do
it in a computer, if only by aping the design. But then P=NP and things get
weird.

~~~
spacehome
I'm not sure why you keep mentioning NP and P. A problem being exponential
doesn't mean it can't be computed. Maybe the universe does the calculations
the hard way.

------
coldcode
Physics is a game best played by madmen.

------
spacehome
Einstein had amazingly good intuition for the character of physical laws, i.e.
what shape the laws of physics must necessarily take. And in this case he was
right, too. God doesn't play dice; the universe _is_ deterministic.
Unfortunately, he didn't stumble upon the right answer, Many Worlds. I
sometimes wonder how much longer it will take popular science writers to
stumble upon it, too.

~~~
trhway
>he didn't stumble upon the right answer, Many Worlds.

i hope you're joking. Many Worlds to treat the alleged indeterminisity is like
cutting the head off to treat an acne.

~~~
spacehome
Haha, no, not joking.

Many worlds is by far the best hypothesis to date.

~~~
anigbrowl
I have known about MW for 25 years or more, thanks to popular science writers.
I don't see it getting more traction than it already has absent some way to
falsify it. It's stylish from a distance, but like imaginary numbers, you
should tidy up your multiverse when you are done playing with it.

~~~
spacehome
That's a common criticism, but many-worlds is a consequence of a theory, not a
theory itself. Plus all the other candidates are worse. (And Copenhagen isn't
really a theory at all since it never gets around to defining what a
'measurement' is.)

~~~
millstone
Many worlds requires postulates (Everett's word!) that are not a consequence
of theory, in particular that the wavefunction is an objective property of a
particle. This is very much in dispute, and is rejected by the ensemble
interpretation, consistent histories, etc.

I don't agree that those interpretations are inferior to MWI. In particular
those theories postulate that the world is essentially probabilistic, and so
do not have MWI's trouble with predicting probabilities.

