… with
John Gribbin
i) Introduction
ii) What
is Interpretation?
iii) Shut
up and calculate!
iv) Limits
to John Gribbin's Pluralism
v) Only
Maths?
vi) Waves
and Particles
vii) Conclusion
This
piece doesn't claim to offer a conclusive case for the elimination of
all the interpretations of quantum mechanics (QM). It simply raises the
possibility of elimination and then offers a few arguments in that
direction.
The
prime motive here is that, at least at present, there's no way of
establishing which interpretation is the true/correct/etc. one.
Secondly, the multiplicity of interpretations both confuses the issue
and leads to scepticism towards many of them. Thirdly, some interpretations are so
convoluted and wacky that laypersons and even physicists themselves
have only aesthetic reasons to believe in them.
This
is particularly true of the Many Worlds Interpretation. I can see no
reason whatsoever for the layperson to accept it other than it can be
taken to “explain
the phenomena” (a phrase which is being used in contrast to
Bas van Fraassen's "save the phenomena"). That is, in the way that panpsychism,
idealism, Marxism, theism, etc. can all be taken to explain the
phenomena. However, explaining phenomena is often very cheap and easy, even if
it is neat and tidy. (Note Albert Einstein's rejection
of David Bohm's theory.)
The
first section introduces John Gribbin's position as well as a potted
history of positions (which features Paul Dirac, Richard Feynman, etc.) which can be taken to lead towards a possible
eliminitivism This section also deals with both the shutupandcalculate
mantra and instrumentalism and how they can be taken to lead to
eliminitivism. Then the simple question “What is Interpretation?”
is asked. After that, Gribbin's pluralism is tackled and seen to be
not very convincing (at least not from a philosophical point of
view). The section “Only Maths?” is selfexplanatory. Finally,
the issue of waveorparticles is discussed in the context of the elimination of interpretations of quantum mechanics.
What
is Interpretation?
To
state the obvious: the interpretations of quantum mechanics are,
well, interpretations.
Thus it's hard to grasp what kind of standing (philosophical or scientific) a particular
interpretation of quantum mechanics could (or should) actually have. Indeed the very word “interpretation” seem to deflate what it is that's
being done – at least from a strictly scientific perspective.
Does
an interpretation become something else when it is proven or simply
established to be true or correct? Do any interpreters of quantum
mechanics believe that their own interpretations can be proven or shown to be true? What
would that even mean?
When
it comes to all interpretations of QM, the
mathematical theory is taken as a given (or at least parts thereof).
Thus the interpretation is something that's over
and above
the mathematical theory. (This is complicated by many laypersons' views on what exactly scientific theories are.)
In
effect, the interpretation attempts to tie the mathematical theory to
the world (or to reality). This is even the case when that
(mindindependent) reality is rejected or simply seen as being
philosophically problematic.
In
the end, all interpretations ask and answer similar questions.
Nonetheless, not all of these questions are to do with "what is real”. They can also be questions of measurement,
determinism/what is random, and so on. Thus such questions aren't
always about things
– such as particles, waves, parallel worlds and so on.
Shut
up and calculate!
John Gribbin (an astrophysicist
who's been writing on quantum mechanics for over 40
years)
has an interesting and radical position on the interpretations of
quantum mechanics (QM). Thus, in this piece, I'll often bounce off
Gribbin's words. However, although Gribbin doesn’t cite a case for
the elimination of the interpretations of QM, he does strongly (for
want of a better word) deflate
them.
Following
on from that, there's no reason why an eliminativist position on QM
interpretations can't be advanced. By this I don't simply mean the
instrumentalist, technological or “philistine” position which is
best summed up by N.
David
Mermin's
wellknown quote, “Shut
up and calculate.”
Indeed
it may even be possible to recruit both Paul Dirac and Richard
Feynman to the eliminitivist cause.
Dirac,
for example, once compared particles to the pieces of chess. He
wrote:
“I
can describe the situation by comparing it to the game of chess. In
chess, we have various chessmen, kings, knights, pawns and so on. If
you ask what chessman is, the answer would be that it is a piece of
wood, or a piece of ivory, or perhaps just a sign written on paper,
or anything whatever. It does not matter. Each chessman has a
characteristic way of moving and this is all that matters about it.
The whole game of chess follows from this way of moving the various
chessmen.”
To
put it bluntly, Dirac's position seems to be eliminativist when it
comes to particles. Yet if it is eliminativist, then why did he speak of
“particles” at all? That's unless, of course, the word “particle” is
simply shorthand for specific types of behaviour or movement. Yet this simply raises the question:
What
is it that behaves or moves?
Richard
Feynman
also
had a problem with seeing particles as
particles.
He hinted at the possibility that we have a waveparticle
duality simply because there are no particles or waves in the first
place. He
wrote:
“Things
on a very small scale behave like nothing that you have any direct
experience about. They do not behave like waves, they do not behave
like particles, they do not behave like clouds, or billiard balls, or
weights on springs, or like anything that you have ever seen.”
Like
Dirac, Feynman was emphasising behaviour,
not particles or things.
From
a purely scientific point of view, it's easy to agree with Mermin's
wellknown phrase which was quoted earlier. (Although he wasn't
putting his own position.) So it's not a surprise that the science
writer Philip Ball says that “[s]ome scientists feel the same way
today”. Ball himself writes:
“Quantum
theory works. It allows us to calculate the shapes of molecules, the
behaviour of semiconductor devices, the trajectories of light, with
stunning accuracy.”
Thus
the “theory works”; though “without our knowing what it's
about”. And that, surely, wouldn't be such a bad thing if
physicists also believed that there's no real (or available) answer to the
whatisitabout
question. Perhaps some (or even many) physicists do believe that.
So
what do the words, “What the maths mean”, mean?
What does the maths describe? What is there beyond the maths (if
anything)? Does the mathematics alone give us a full understanding?
"new
interpretations [of QM] appear every year. None ever disappear."
Now
that's another reason to be sceptical of – or deflationary towards
– the many interpretations of quantum mechanics.
One
can also take a positive pragmatic (or instrumentalist) position on
these many interpretations of quantum mechanics. Alternatively, one can
take a pessimistic position on them.
The
theoretical physicist Steven
Weinberg takes
the latter option. He
writes:
“My
own conclusion is that today there is no interpretation of quantum
mechanics that does not have serious flaws. This view is not
universally shared. Indeed, many physicists are satisfied with their
own interpretation of quantum mechanics. But different physicists are
satisfied with different interpretations. In my view, we ought to
take seriously the possibility of finding some more satisfactory
other theory, to which quantum mechanics is only a good
approximation.”
Now
is Weinberg's position philosophical/ontological in nature? Is he
saying that it's not all about prediction, experiment, observation,
etc. – it's also about what
is?
In other words, is it a realist
position
on the interpretations of quantum mechanics?
The
physicist David
Finkelstein
also notes the problems with these different interpretations; though
he doesn't really hint at any metaphysical concern. He
tells
us
that “[q]uantum theory was split up into dialects” and that this
was the case because “[d]ifferent people describe the same
experiences in remarkably different languages”. Consequently, this
pluralism may seem fine except for the fact that all “[t]his is
confusing even to physicists”.
As
hinted at above, the philosophical position called instrumentalism
comes the closest to the position that rejecting all interpretations
(or the need for interpretations) of quantum mechanics is a good
idea. Yet it's still a philosophical
position, if not an actual interpretation
of quantum mechanics.
Having
said that, interpretation is not even an issue for the many physicists and technologists in white coats.
In quantum field theories, for example, the structures described are abstract (or purely mathematical). That is, they exist without
any clear interpretations of the quantities which are part of the
theory.
Yet, on
the other hand, just as we can deflate QM interpretations, so we can
also deflate the Technophile/Philistine Interpretation (as it were)
of QM. For instance, Gribbin says
that
"[j]ust
how an electron, or a beam of electrons, get from A
to B
does not matter to an engineer designing, say, a TV set".
Put
that way, it's hard to imagine any scientist not
being interested in how electrons "get from A
to B".
Of course we may not be able to speak of the in
between
of A
and B
 and that's a recurrent theme in QM. (This is a position best
highlighted by the relationalist

or
interactionist  interpretation of QM; such as that offered by Lee
Smolin
and Carlo
Rovelli.)
Gribbin himself highlights the problem
in
this way:
"If
you have a set of parameters describing the system in state A,
you can calculate the probability that it will be in state B
after a certain time. But there is nothing which tells you what is
going on in between."
Yet
to many quantum theorists there is (effectively/simply) no "in
between"!
Finally
and more relevantly, there may be a philosophical
case that can be given for eliminativism when it comes to the interpretations of QM. And this is something the shutupandcalculate
brigade
never offered.
Limits
to John Gribbin's Pluralism
Gribbin's
actual position is one of the “complementarity”
of all the different interpretations of QM. That is, no
interpretation (or no set of classical physical concepts) can refer
(at the same time) to a singular quantum system. This of course can
be traced back to Niels Bohr's theoretical stance on both the wave
and particle descriptions (see later section).
Prima
facie,
Gribbin's position seems to be one of relativism. Or, at the very
least, one of conceptual
pluralism.
For example, Gribbin believes
that
“none
of them [quantum mechanical interpretations] is anything other than a
conceptual model designed to help our understanding of quantum
phenomena”.
His
primary reason for stating the above is that all the interpretations
he considers “make the same predictions”. Sure, this is hardly an
original point. People have been saying this about all the
interpretations of quantum mechanics since at least the 1950s. Yet
surely even if we see the essential limitations of these
interpretations, and the fact that they don't offer us a complete
picture, that doesn't also mean that all of them must be treated
equally. That simply doesn't follow.
Take
a murder that hasn't be solved and which has engendered numerous
interpretations (or explanations). Does that mean that all interpretations should all be treated equally? Having said that, if
they're all in the same ballpark
(as, arguably, all/most QM interpretations are), then perhaps they are
all equal.
Gribbin
himself also believes that all interpretations of quantum mechanics
are effectively in the same ballpark. Thus can we also argue that all
the interpretations are in the same ballpark as purely
metaphysical/ontological theories? Or, more simply, that they're all
actually metaphysical/ontological theories? The fact that QM
interpretations are about physical (or scientific) realities doesn't
really seem to make any difference here. The fact is that they go beyond
the maths, predictions, experiments, observations, etc. And that
means that they're (almost by definition) philosophical in nature. (That's not necessarily a criticism.) However, can we say (as already stated) that
the interpretations of QM are also in the same boat as, say, panpsychism, monism,
idealism, theism, Marxism and whatnot? If they are, then the interpretations may never
be able to smoothly bridge the gap between the mathematical theory
and the interpretations.
As
stated, Gribbin is a pluralist (as are many scientists and
philosophers when it comes to scientific theories, concepts and
models). Gribbin, in the following, again talks
about
the interpretations of quantum mechanics:
“I
stress, again, that all such interpretations are myths, crutches to
help us imagine what is going on at the quantum level and to make
testable predictions. They are not, any of them, uniquely 'the
truth'; rather, they are all 'real', even where they disagree with
one another.”
This
is heavy stuff. Of course what's true of quantum interpretations (or
“myths”) isn't also true when it comes to mathematical theories.
(The above is certainly problematic for string theory, for example,
for the simple reason that Gribbin talks about such
theories/interpretations making  unique  “testable predictions”.)
Despite
all the above, Gribbin happily acknowledges that the quantum interpreters believe
that their interpretations are true. He
writes:
"[T]he
interpreters and their followers will each tell you that their own
favoured interpretation is the one true faith, and all those who
follow other faiths are heretics."
And
that passage comes straight after Gribbin
tells
us
that
"[a]t
the level of equations, none of these interpretations is better than
any other".
Thus,
logically, "none of the interpretations is worse than any of the
others, mathematically speaking". Though all this hinges on precisely
how we're to take the phrases "at the level of equations"
and "mathematically speaking". That, of course, is the main
issue of this piece.
Gribbin
also gets all psychological or aesthetic when he concludes (as
the very end of a book)
that we
“are
free to choose whichever one gives you most comfort, and ignore the
rest”.
Again,
there may well be an argument that all interpretations are
superfluous when it comes to predictions, technology, etc. However,
that certainly doesn't mean that all interpretations are “equally
good”. They may be equally good in the sense that they don't make
the slightest bit of difference when it comes to to mathematical theory, predictions and
(quantum) technology; though are they equally good in literally every
respect?
“literally
every version of mathematical concepts has a physical model
somewhere, and the clever physicist should be advised to deliberately
and routinely seek out, as part of his activity, physical models of
already discovered mathematical structures”.
Yet
even in Gribbin's case, it's still clear that a “mathematical
concept” comes first and only then is a “physical model” found
to square with it.
Only
Maths?
Do
mathematical physicists require (or need) Gribbin's “conceptual
models” or any interpretations of QM? It depends. It depends on what
they’re doing and what they want.
One
way of interpreting Gribbin's remarks is that only those who know the
mathematics can bypass QM interpretations altogether. Thus are all
these interpretations the result of commentators (or laypersons)
having a mathematical deficit? That can't be true for the simple
reason that many wellknown QM interpreters have also been adept
mathematicians and mathematical physicists. (Not all have taken the
eliminitivist position of Paul Dirac – see later section.) Thus if
the maths literally gives us everything, then why did all these
people feel the need to interpret QM in the first place? For a start,
they aren't simply telling stories to assuage the layperson. Yes,
they also believe that their own interpretations are true/accurate/etc.
In
addition, it may not be the case that knowing all (or much of) the
maths of QM (as, say, Richard Feynman did) automatically brings you
closer to the truth when it comes to interpretations. For example, say that I acquire literally
all the mathematical knowledge which is used and known by all the
believers in the Many Worlds Interpretation of QM. Would I then automatically see that this interpretation is the only true one? There will still be a leap from the mathematics to the
interpretation. That is, the links between the mathematics and the
interpretation will neither be (entirely) mathematical nor (entirely)
logical. Indeed it can be argued that they can't be (entirely)
scientific either.
On
the other hand, Stephen Hawking’s question as to “what
breathes
fire into the equations”
will always hover
over the heads of the physicists who don't endorse an interpretation.
The science writer Kitty
Ferguson
(in her The
Fire in the Equations)
offers a possible Platonist answer to Hawking's question by saying
that “it
might be that the equations are the fire”.
Alternatively, could Hawking himself have been “suggesting that the
laws have a life or creative force of their own?”. Again, is it
that the “equations are the fire”?
If
the maths is “only” a tool for predictions, experiments and
suchlike, then the maths alone can't possibly answer all the
questions raised by QM interpreters.
The
physicist John
Archibald Wheeler also provided a powerful riposte to such
Platonism (as it were) in physics. We're told that Wheeler used to
write arcane equations on the blackboard and stand back and say to
his
students:
“Now
I'll clap my hands and a universe will spring into existence.”
So
is the maths simply a tool which doesn't tell us what
is?
Sure, the “what is the case?” question may end up being bogus
(i.e., from an antirealist or instrumentalist point of view).
Nonetheless, surely there must always be something beyond the maths
and therefore beyond the predictions, the technological applications,
etc. of QM.
A
sharp and tothepoint antiPlatonist
(as it were) position is also put by the science writer, Philip Ball.
He
writes:
“...
equations purportedly about physical reality are, without
interpretation, just marks on paper”.
In
other words, what exactly (as Hawking put it above) “breathes fire
into the equations [to] make a world”?
The
Philip Ball quote above also highlights two other problems:
i)
The fact that we can make mistakes about physical reality.
ii)
That even if the equations are about physical reality, then they're
not one and the same as the physical reality.
Ontic structural realists (in the philosophy of physics), on the other
hand, would say that this distinction (i.e., between maths and the
world) hardly makes sense when it comes to physics generally  and it
doesn't make any sense at all when it comes to quantum physics.
Nonetheless, surely there's still a distinction to be made here.
Waves
and Particles
Niels
Bohr made it clear that only mathematics gives us a true picture of
the quantum realm. He
wrote:
"We
must be clear that when it comes to atoms, language can be used only
as in poetry. The poet, too, is not nearly so concerned with
describing facts as with creating images and establishing mental
connections.”
This,
again, is a roundabout of saying that only the mathematics is
adequate when it comes to describing subatomic phenomena. Thus, by
this definition, the words “particle” and “wave” simply can't
do the full job. Yes, they can do part of the job; though not the
full job. Indeed it's not just the word “particle” that's
problematic, thinking of particles as things
is too. Bohr
wote:
"Isolated
material particles are abstractions, their properties being definable
and observable only through their interaction with other systems."
In
other words, it can't possibly be about the world “as it is in
itself”. Every statement we make about the world comes with a lot
of contingent baggage. There is of course a causal set of relations
to any x
– though those very same relations can be described in an
indefinite number of ways.
At
the most basic level, “seeing” a subatomic x
as a particle or as a wave is an act of interpretation.
So is seeing them as both (i.e., within different experimental
contexts), as Louis
de Broglie
and many other did. Finally, seeing x
as neither
a wave nor a particle may also involve interpretation.
In
more general terms, Bohr argued that the reality behind our
measurements and experiments is that there is neither
a particle nor a wave. But we must still talk about something (his "poetry").
However, that something
isn't necessarily a thing
as such (this is grammar speaking here). And we give that x
(which doesn't need to be a thing,
only a something)
the name “wave” or “particle”.
So when de Broglie argued (in 1924) that that every moving particle
(yes, particle)
can be equally described as either a wave or a particle, that may
well be because this x
is neither
a wave nor a particle. Nonetheless, describing x
as
a wave or a particle still helps both physicists and laypersons.
In
more detail and to go back to the 1920s. Erwin Schrodinger was
committed to waves. Werner Heisenberg and Paul Dirac to particles.
(Heisenberg dealt with pure numbers in the form of arrays – i.e.,
matrices).
In the end and in a strong sense, all this didn't matter because
Dirac went on to show/prove that the wave and particle
interpretations are equivalent. That is, equivalent when it came to
the maths, experiments, predictions and, later, technology.
In
actual fact, we can go back to J.J. Thomson, when he showed that
electrons are particles. Then, 30
or
so years later, his son, George Thomson, showed that electrons are
waves.
The American philosopher
Ernest
Nagel
(in his
'The Cognitive
Status of Theories')
had a different (though related) take on particles and waves. Firstly
he discussed their “puzzling characteristics”. These puzzling
characteristics seem to be “incompatible”. (Though the word
“incompatible” isn't a synonym of “contradictory”.) More
precisely, electrons are “construed to have features which make it
appropriate to think of them as a system of waves”. Yet, “on the
other hand”, electrons “also have traits which lead us to think
of them as particles”. They're deemed to be particles because each
one has “spatial location and a velocity”. However, “no
determinate position and velocity can in principle be assigned
simultaneously to any of them”. It's here that Nagel appears to
deflate quantum mechanics. He does so by saying that
“many
physicists have therefore concluded that quantum theory cannot be
viewed as a statement about an 'objectively existing' domain of
things and processes... On the contrary, the theory must be regarded
simply as a conceptual schema or a policy for guiding and
coordinating experiments”.
It's
also the case that the words “particle” and “wave” carry far
too much baggage. After all, the original waveparticle experiments
had water waves in mind. Is that a good thing when it comes to talk
about happenings at the subatomic level? Yes, it is if it helps us
get of grip of things. The same goes for the word “particle”. So there are a host of good reasons as to why
x should
be seen as a particle. Yet there are also a host of equally good
reasons as to why we shouldn't
see it as a particle.
Gribbin himself takes an equally radical position on particles and
waves. He
writes:
“In
the world of the very small, where particle and wave aspects of
reality are equally significant, things do not behave in any way that
we can understand from our experience of the everyday world...all
pictures are false, and there is no physical analogy we can make to
understand what goes on inside atoms. Atoms behave like atoms,
nothing else.”
It
can of course be said that even if it's correct
that
“all
pictures are false, and there is no physical analogy we can make to
understand what goes on inside atoms”
then
it may still be the case that (at least for laypersons) that's all
we've got. Indeed without the mathematics, all we have are pictures,
images and analogies. So we'd better make do with all that. And
surely Gribbin isn't arguing that pictures, images and analogies
serve no purpose. Indeed he can't be arguing that because his books
make extensive use of them. Having said that, all Gribbin's pictures,
images and analogies do come along with words of warning (as can be
seen in the quotes above).
In
fact we can even say that the very use of the words “particle”
and “wave” may mean that Gribbin himself is also using pictures
or images and/or being analogical. That is, if “in the world of the
very small” it's the case that
“things
do not behave in any way that we can understand from our experience
of the everyday world”
then
why is Gribbin using the words “particle” and “wave” in the
first place?
Conclusion
One
thing is certainly the case: without the maths, we'd have almost (or
literally) nothing to "say" about the quantum world – real or
otherwise. When it comes to QM, the usual means of
ownership aren't available to us. That is, we can't observe, feel,
smell or (often) even imagine the quantum world. Thus the maths is
all we've got. This is excellently expressed in
the following passage from
John Horgan:
“[M]athematics
helps physicists definite what is otherwise undefinable. A quark is a
purely mathematical construct. It has no meaning apart from its
mathematical definition. The properties of quarks – charm, colour,
strangeness – are mathematical properties that have no analogue in
the macroscopic world we inhabit.”
If
maths is all we've got, then it's not really a surprise that many
physicists (i.e., the more philosophical ones) have said that quantum
mechanics doesn't really “say anything about the real world”. Or,
at the very least, everything that's said about the quantum world is
said by the maths. Thus, all the imagery, picture painting,
analogies, etc. aren't really about the quantum world – they're
simply the crutches we use in order to get a grip of that world.
So
when it's said that Richard Feynman, for example, could only do
“quantum theory” (i.e., the maths), then that's not a surprise.
That's because the maths may be all we've got. And when we stray
beyond the maths into “interpretation”, then we (perhaps by
definition) can't help but get things wrong... Or at least this is
one sceptical scenario we must consider.
Again,
it's not a surprise that Feynman didn't “know what the maths
means”. That may be because the phrase “what the maths means”
is (almost) meaningless. At the very least, there's a hint that we
can't go beyond the maths. Yet it's still the case that so many
philosophers, and somewhat less physicists, believe that the maths is
only secondbest to something far deeper – the interpretation (or
ontology) of quantum mechanics.
***************************
Afterthought
In many respects it can be argued that certain interpretations of quantum mechanics aren't really interpretations at all. Or, at the very least, they're less interpretational than their rivals. The Copenhagen Interpretation and QBism (quantum Bayesianism), for example, are good examples. The very fact that there are strong antirealist or verificationist factors to these positions surely limits the need for interpretation.
Take the electron's journey from A to B mentioned in the piece above. To quote John Gribbin again:
"Just how an electron, or a beam of electrons, get from A to B does not matter to an engineer designing, say, a TV set… If you have a set of parameters describing the system in state A, you can calculate the probability that it will be in state B after a certain time. But there is nothing which tells you what is going on in between."
If Niels Bohr, John Gribbin, QBists, etc. all deny that in between (or simply play it down), then surely there's little room left for interpretation.