Comments about the article in Nature: A World without cause and effect

Following is a discussion about this article in Nature Vol 546 29 June 2017, by Philip Ball
In the last paragraph I explain my own opinion.


Introduction

The events have happened in a sequence right?
All events, all changes in the Universe, have a cause in the past.
Walter's lab in the University of Vienna. Walters group has shown that it is impossible to say in which order these photon's pass through a pair of gates as they zip around the lab.
It is easy possible that the processes in nature are much more detailed than what we humans can observe.
It's not that this information get lost or jumbled - it simply doesn't exist.
In principle it exist but we humans can not unravel it.
Walter's experiments mash up causality, the idea that one thing leads to another.
The only thing that what these experiments show is that we cannot observe the nitty gritty details.
And by creating systems that lack a clear flow of cause and effect, researchrs now think they can tap into a rich realm of possibilities.
You can only investigate new roads if you understand the details of the underlying concepts. Otherwise it becomes pure speculation.

"Tangles in Time"

The Copenhagen interpretation insists that the outcome of a quantum measurement - such as checking of a photon's plane of polarization - is determined at random, and only in the instant that the measurement is made.
There is nothing wrong that when you measure the polarization of a photon that in 50% of the cases you get +x and in 50% of the cases -x. Also that the outcome of each experiment is random. What is wrong to assume that before the measurement the state of the photon was not fixed . Most probably the state was already fixed. Why should the direction of polarization of a photon change continuously?
No reason can be adduced to explain that particular outcome.
If you perform experiment 1000 times and you get 50% a 1 and 50% a zero randomly, there is nothing specific involved in each individual experiment.
But in 1935 Einstein and his young collagues Boris Podolsky and Nathan Rosen described a thought experiment that pushed Bohr's interpretation to a seemingly impossible conclusion.
Thought experiments are tricky in the Quantum Realm.
The EPR experiment involves two particles A and B that have been prepared with interdependent or entangled properties.
IMO it is impossible to do this as a thought experiment. You need at 1000 real experiments to explain what entangled particles are.
For example if A has an upward pointing 'spin' than B must be 'down' and vice versa.
Again you need real experiments to back this up. I expect that most of the experiments considered there is no correlation and that only in a small subset there exist such a correlation. This subset involves entangled particles. Very interesting when discovered but in principle nothing special.
Both pairs of orientations are possible. But researchers can discover the actual orientation only when they make a measurement on one of the particles.
That seems logical. Nothing special.
According to the Copenhagen interpretation, that measurement does not reveal the particle's state; it actually fixes it in that instant.
There is physical nothing wrong if this correlation already exists for al "long time". It is probably physical the most logical explanation (assumption).
That means it also instantly fixes the state of the particle's entangled partner - however far away that partner is.
It is important to observe that here is written entangled partner. You only know that when you have performed 1000 similar experiments which have demomstrated this physical correlation. Again the most logical asumption is that this correlation is permanent. It does not happen ad hoc (compared with similar experiments which do not show this correlation).
But Einstein considered this apparent instant action at a distance impossible, because it would require faster than light interaction across space,
correct
which is forbidden by his special theory of relativity.
SR has nothing to do with this i.e. entanglement.
Measurements of entangled particles show, however, that the observed correlation between the spins can't be explained on the basis of preexisting properties.
The author should give (point to) the details of these measurements.
Quite how the realtionship arises is hard to explain in any intuitive cause and effect way.
What you should do is test these correlations at a distance of 10m, 50m, 100m, 500m etc My prediction is that the correlation is always there. The most obvious explanation is that the correlation is born in the process which created the two (entangled) particles.
For event A to have any effect on event B, A has to happen first.
In this case ther are two event's B which are correlated. The vent A happens inside the reaction process.
The trouble is that this logic has unravelled over the past decade as researchers have realized that it is possible to imagine quantum scenarios in which one simply can't say which of the two related events happens first.
It is easy possible that there are reactions in which it is at quantum level difficult to say based on all the generated particles what the details are and exactly the sequence that internally took place.
Often (I expect) by making small changes, you can learn more.

"Ambiguous action"

Superpositions of quantum states are well known: a spin for example can be placed in a superposition of up and down states.
Based on the following sentence apperently they mean one particle. The issue is what is the difference between an experiment where the particle is in superposition versus an experiment were the particle is not in superposition.
And the two spins in the EPR experiment are in a superposition - in that case involving two particles.
And what does that mean? When on is up the other one is down?
It's often said that a quantum object in superposition exists in two states at once, but more properly it simply cannot be said in advance what the outcome of a measurement would be.
This is an interesting sentence It shows two different opinions. The first is more strict. The second more open.
Can one coin, being thrown, in a superposition state? What is the answer from both points of view?

Trippy Journeys

If the Qubit set in a superposition of 1 and 0 it is impossible to say whether the train goes through A or B first.
If the whole experiment depents on this superposition state, then it seems logical that you cannot predict the outcome.
Any attempt to measure the path of the train destroys the superposition and the train only follows only one defined path.
That seems logical.
The whole issue is that this whole experiment does invalidate the standard cause / effect rule (concept)


Unity in the Universe

It's not terrible complicated to build the necessary quantum circuit architectures either - you just need quantum switches similar to those Walther has used. "I think this could find applications soon" Brukner says.
I think this is all too overly simplistic. In general when you perform one experiment (quantum computation) the next time when you repeat that same experiment the outcome should be the same. If it does not what 'value' has each.


Reflection

The whole experiment with the train is very clever. The whole point is what does it really proof.

Feedback

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Created: 4 July 2017

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