Quantum Theory – A Very Short Introduction
I have recently been in some discussions about the interpretation of quantum mechanics and the potential consequences of those interpretations. My chief opponent (we may call him) is a Copenhagen interpretation theorist. He has some rather odd views that are incoherent in themselves but apparently common among fysicists (as we will see).
My position has been one of realism+indeterminism. I came to this position some years ago after reading up on QT on a rather sporadic basis (mostly Wikipedia) and reading a paper by one of my favorit filosofers: Raymond Bradley.
Raymond D. Bradley – How to lose your grip on reality An attack on anti-realism in quantum theory (his paper)
It seems to me that Bradley is completely right about verificationism: it is an incoherent theory of meaning. However, i decided to take a closer look at the fysics involved. Admittedly, i did not want to learn everything that someone who takes a bachelor in fysics learns, so i decided to read some books written for laymen by experts. I decided on reading four books from the series A very short introduction to … series. These are: The Elements, Relativity, Quantum Theory, and Particle physics. QT is the third book. I probably shud have chosen another order so that QT was the last to read, but too late now.
What follows are some quotes from the book and my thoughts about them. I don’t bother to cite the page since i uploaded the ebook. Anyone wishing to find the page can just do a search in the pdf.
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The measurement problem continues to cause us anxiety as we
contemplate the bewildering range of, at best, only partially
persuasive proposals that have been made for its solution. Options
resorted to have included disregard (irrelevance); known physics
Darkening perplexities
(decoherence); hoped-for physics (large systems); unknown new
physics (GRW); hidden new physics (Bohm); metaphysical
conjecture (consciousness; many worlds). It is a tangled tale and
one that it is embarrassing for a physicist to tell, given the central
role that measurement has in physical thinking. To be frank, we do
not have as tight an intellectual grasp of quantum theory as we
would like to have. We can do the sums and, in that sense, explain
the phenomena, but we do not really understand what is going on.
For Bohr, quantum mechanics is indeterminate; for Bohm,
quantum mechanics is determinate. For Bohr, Heisenberg’s
uncertainty principle is an ontological principle of indeterminacy;
for Bohm, Heisenberg’s uncertainty principle is an epistemological
principle of ignorance. We shall return to some of these
metaphysical and interpretative questions in the final chapter.
Meanwhile, a further speculative question awaits us.
Notice how the author contrasts an antirealims+indeterminism view with a realism+determinism view. However, these are not the only options. At least, the option of indeterminism+realism is possible. I’m not sure about the antirealism+determinism position. It seems to be ‘claiming’ that everything that happens in the quantum world (or the world at large) has a cause, but that there are no subatomic particles before we measure them. This is odd. The first possibility i suggested is that one that i like the most.
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The EPR effect’s implication of deep-seated relationality present in
the fundamental structure of the physical world is a discovery that
physical thinking and metaphysical reflection have still to come to
terms with in fully elucidating all its consequences. As part of that
continuing process of assimilation, it is necessary to be as clear as
possible about what is the character of the entanglement that EPR
implies. One must acknowledge that a true case of action at a
distance is involved, and not merely some gain in additional
knowledge. Putting it in learned language, the EPR effect is
ontological and not simply epistemological. Increase in knowledge
at a distance is in no way problematic or surprising. Suppose an urn
contains two balls, one white, the other black. You and I both put in
our hands and remove one of the balls in our closed fists. You then
go a mile down the road, open your fist and find that you have the
white ball. Immediately you know I must have the black one. The
only thing that has changed in this episode is your state of
knowledge. I always had the black ball, you always had the white
ball, but now you have become aware that this is so. In the EPR
effect, by contrast, what happens at 1 changes what is the case at 2.
It is as if, were you to find that you had a red ball in your hand, I
would have to have a blue ball in mine, but if you found a green ball,
I would have to have a yellow ball and, previous to your looking,
neither of us had balls of determinate colours.
I agree that the analogy works from the pov of someone who thinks that antirealism about QM stuff is true. I still don’t. It’s going to be very hard to convince me i am wrong about this.
–
An alert reader may query all this talk about instantaneous change.
Does not special relativity prohibit something at 1 having any effect
Quantum theory
80at 2 until there has been time for the transmission of an influence
moving with at most the velocity of light? Not quite. What relativity
actually prohibits is the instantaneous transmission of information,
of a kind that would permit the immediate synchronization of a
clock at 2 with a clock at 1. It turns out that the EPR kind of
entanglement does not permit the conveyance of messages of that
kind. The reason is that its togetherness-in-separation takes the
form of correlations between what is happening at 1 and what is
happening at 2 and no message can be read out of these correlations
without knowledge of what is happening at both ends. It is as if a
singer at 1 was singing a random series of notes and a singer at 2
was also singing a random series of notes and only if one were able
to hear them both together would one realize that the two singers
were in some kind of harmony with each other. Realizing this is so
warns us against embracing the kind of ‘quantum hype’ argument
that incorrectly asserts that EPR ‘proves’ that telepathy is possible.
I have seen the claim before, that SR implies that no FTL communication is possible. I don’t see how it follows from the information presented earlier in the book or the introduction to relativity that i read last week.
I have thought up a method for FTL communication. Not sure if it works, probably doesn’t and i’m wrong about some fysical detail, not being a fysicist and all. One takes alot of these entangled particles. Then separates them into two boxes, such that all of those in one box are of the same type of spin, and the same for the other box. Then one ships the one box to out in space with a spaceship. To communicate, one changes the spin of the particles in the box, and the other party can see this change too (becus it is instantaneous). I’m thinking that this method doesn’t work becus of one of the following: 1) it is not possible to separate them into the boxes as described, 2) there are some problems with changing one of the particles and then having the other people measure this without destroying the signal.
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Positivism and realism
Positivists see the role of science as being the reconciliation of
observational data. If one can make predictions that accurately and
harmoniously account for the behaviour of the measuring
apparatus, the task is done. Ontological questions (What is really
there?) are an irrelevant luxury and best discarded. The world of the
positivist is populated by counter readings and marks on
photographic plates.
This point of view has a long history. Cardinal Bellarmine urged
upon Galileo that he should regard the Copernican system as simply
a convenient means for ‘saving the appearances’, a good way of
doing calculations to determine where planets would appear in the
sky. Galileo should not think that the Earth actually went round the
Sun – rather Copernicus should be considered as having used the
supposition simply as a handy calculational device. This face-saving
offer did not appeal to Galileo, nor have similar suggestions been
favourably received by scientists generally. If science is just about
correlating data, and is not telling us what the physical world is
actually like, it is difficult to see that the enterprise is worth all the
time and trouble and talent expended upon it. Its achievements
would seem too meagre to justify such a degree of involvement.
Moreover, the most natural explanation of a theory’s ability to save
appearances would surely be that it bore some correspondence to
the way things are.
Nevertheless, Niels Bohr often seemed to speak of quantum theory
in a positivistic kind of way. He once wrote to a friend that
There is no quantum world. There is only abstract quantum physical
description. It is wrong to think that the task of physics is to find out
how nature is. Physics is concerned with what we can say about
nature.
Bohr’s preoccupation with the role of classical measuring
apparatus could be seen as having encouraged such a positivistic-
sounding point of view. We have seen that in his later years he
became very concerned with philosophical issues, writing
extensively about them. The resulting corpus is hard to interpret.
Bohr’s gift in philosophical matters fell far short of his outstanding
talent as a physicist. Moreover, he believed – and exemplified –
that there are two kinds of truth: a trivial kind, which could be
articulated clearly, and a profound kind which could only be
spoken about cloudily. Certainly the body of his writings has been
very variously interpreted by the commentators. Some have felt
that there was, in fact, a kind of qualified realism to which Bohr
was an adherent.
Does everybody else see the glaring almost-contradiction in what Bohr wrote? One cannot both deny that there is a quantum world and then go on to claim that we can’t say anything about it. That is my interpretation of his words, altho he was a bit better in the above quote. He technically only wrote that it is not the case that the task of fysics is to find out how nature is. Since he made some claims about how the world is (in his case, isn’t), apparently he either got his information from fysics even tho that’s not fysics’ task, or he got his information from somewhere else. This is not a contradiction, just odd.
–
Not particularly related to any passage in the book, but building on the general idea of the problem of how to reconcile the determinism of the macroscopic world with the indeterminism of the quantum world. After all, the macroscopic world is made of quantum world stuff. The current thinking is that the world is only approximately deterministic. I have a question: suppose that there is a level below quantum world stuff. Is it possible that this level is deterministic? That is, is it possible to have a deterministic layer and then an indeterministic layer on top of it? It seems not. But, it is definitely possible to have a deterministic layer and then a layer that is epistemically indeterministic on top of it.
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I’m still not satisfied. I have not been convinced of antirealism in QM. Usually, the author talks about epistemic limitations, and then in some later passage talks about ontology, as if there were some connection, like the verificationism that Bradley criticized. I will read some more filosofical texts on the matter. Surely, if there is some way to make realism work, someone has thought of it.
http://plato.stanford.edu/search/searcher.py?query=quantum is where i must go.