Spontaneous collapse theories
The most referenced of which being The
Ghirardi–Rimini–Weber theory, or GRW.
Such theories have 4 main problems:
Problem with relativistic invariance
According to Precedence
and freedom in quantum physics (Lee Smolin, May 2012),
spontaneous collapse theories would have troubles to be defined in a
relativistic invariant manner. However Giancarlo Ghirardi's article
seems to be replying to this point. I still have to figure it out...
Problem with conspiracy
"That said, we presently have no theoretically good
reason why the parameter [exact rate of collapses per particle]
should be in the range that allows this explanation to work. It
might seem a little conspiratorial of nature to give us the
impression that quantum theory is correct, while tuning the
equations so that the crucial features that give rise to a
definite physical reality are – with present technology –
Problem with conservation laws
General Relativity proves that the laws of conservation of mechanics
are absolute logical necessities.
Quantum mechanics has is strange,
twisted but coherent way to satisfy these conservation laws.
But with physical mechanisms of spontaneous collapse, these logical
necessities may be broken. As this article reports "Another
interesting characteristic of all the collapse models is that a
narrowed wave function increases its energy because of uncertainty
principle: this leads to a violation of energy conservation". But this
problem may have been solved as presented by another article.
Since the core of the mathematical contradiction in the idea of a
violation of conservation laws is a matter of how it relates with
gravity, this would suggest a link between spontaneous collapse and
quantum gravity. Penrose had that kind of suggestion. But the nature
of such a link and how it can resolve the above problem, is far from
clear. In particular, physical
quantities would suggest that quantum random outcomes can be
consciously observed by humans (imagine, just a pack of photons
coming on a retina and then just a nerve impulse reaching the brain
! and a nerve impulse is a very microscopic move, much lighter than
a Planck mass) before they make the first graviton of difference.
This leads us to the philosophical problem:
Problem with too slow collapse
In his article The Quantum
Measurement Problem: State of Play (p.39), David Wallace wrote
the following remark on expected requirements for a spontaneous
collapse theory :
The other constraint — that macroscopic
superpositions should collapse quickly — is harder to quantify.
Maybe, would the motivation to see the idea of a slow
collapse “embarrassing”, come from an implicit feeling that the collapse
must have something to do with consciousness ?
How quickly should they collapse? Proponents of
dynamical-collapse theories (...) generally require that the
speed of collapse should be chosen so as to prevent “the
embarrassing occurrence of linear superpositions of appreciably
different locations of a macroscopic object”. But it is unclear
exactly when a given superposition counts as “embarrassing”. One
natural criterion is that the superpositions should collapse
before humans have a chance to observe them. But the motivation
for this is open to question. (...)
Now suppose that the collapse is much slower, taking several
seconds to occur. Then the cat-observer system enters the
α |dead cat> ⊗|observer sees dead cat> + β |live cat>
⊗|observer sees live cat>.
Who knows what it is like to be in such a state? But no matter:
in a few seconds the state collapses to
|dead cat> ⊗| observer sees dead cat> or | live cat>⊗|observer
sees live cat>.
Once again, the agent is in a state where he remembers seeing
either a live or dead cat, and the probability is |α|2
that he remembers seeing a dead cat — since his memories are
encoded in his physical state, he will have no memory of the
superposition. So the fast and slow collapses appear
But we can go further : since the condition of decoherence is
emergent and cannot be explicitly written in the fundamental
equations of laws, and the collapse needs to be slow to not be
measurable, the collapse "mechanisms" that were proposed are not
100% effective : alternative possibilities, not "chosen" by the
collapse, only see their "probability" (or "amount of reality", as
with the many-worlds) fall to a value that is close to zero but not
exactly zero. Now, here is a thought experiment I propose to analyze
: do you think that the following proposition can make any sense,
The next experiment has 99% chances to give "yes" and
1% to give "no"... Now done, let us look at the result. We
get... "No". Hum, but the collapse of the wave function is slow
and not complete yet, so we are now in a branch of the
multiverse that has 1% chance of staying real and 99% chance of
being annihilated in the next minute. So, just wait a minute and
the branch of reality we are now in, is most probably going to
be annihilated... One minute later... Uh what, we still exist,
what happens ? Ah of course, it is because the collapse is not
totally complete, the amplitude of our branch of reality most
probably fell but not exactly to zero, only to 10-100,
but so our annihilation is probably almost done, and thus most
likely to become... even more close to completeness, still one
An ontology in fact very close to that of the many-worlds, to be
compared to what we can tell there about "shrinking the size of
One reference I found: Killer Collapse:
Empirically Probing the Philosophically Unsatisfactory Region of GRW
by Charles Sebens
Challenge to all supporters of the plausibility of a
form of spontaneous collapseProvide a clearly expressed and philosophically justified
statement on the question whether or not the hypothesis of a slow collapse,
as described above (taking seconds, minutes or hours after conscious perception), is a reasonable possibility
Some deeper, more precise questions:
Admitting it was, for some yet undetermined reason, "metaphysically natural" to have a universe as described by the
spontaneous collapse interpretation of quantum physics, that is, with wavefunction collapse slow enough to have been still
undetected in our experiments, then, woudn't it be equally "metaphysically natural" to have a similar universe with an even
smaller value of the collapse rate, so that it would take a while after conscious perception to occur ?
In such a universe, would it be expectable that the perception of "likeliness of existence" of each possibility, was naturally
the same or different from before to after the collapse ? In other words, do you expect
the shares of "amount of existence" between "branches" of a non-collapsed wave-function, as I described about the the many-worlds interpretation to conform
to the probability distribution defined by the Born's rule ?
- If the slow collapse hypothesis has any problem, then which problem is it exactly ?
- If the slow collapse does not have any problem, then can you be happy with the many-worlds
interpretation as well (as it is the limit of very large collapse times), otherwise what is the problem with it ?
Finally, does the spontaneous collapse have to break relativistic invariance, and therefore, isn't the many-worlds interpretation much more elegant than spontaneous collapse, by
its respect of relativistic invariance, and how it gets rid of some of the difficult questions of making up arbitrary limits and processes for a reality
that is anyway unobservable how to make reality fit with subjective perception as if it ever mattered ?
- If yes then do you agree that, as a result, the collapse has "strictly no effect for all practical purposes", in the
sense that, then, the Many-worlds interpretation just fits to "explain" probabilities, and therefore should be favored, by
Occam's razor, eliminating any assumption of collapse as artificial ?
- If no, then it would seem to imply indeed that we can "observe that the collapse is fast" by the fact that otherwise,
at any time, existence would be spread out across recently appeared branches of possibilities not conform to Born's
rule and not yet eliminated by the collapse process obeying Born's rule. But then wouldn't it be reasonable to reply to
such an observation report by the following objection : "So, I see you as having written a moment ago, that you noticed
all things kept behaving in conformity with Born's rule, but this is only because, while that time actually blossomed
with versions of you with a dominance of some where you actually saw everything wildly running upside down, all those of the
latter kind finally turned out to vanish from existence before I had a chance to observe your report of them; only the then lucky versions
closest to Born's rule made it to me, or maybe I'm just myself in such a lucky branch of existence, the one you're
going to read back from me, while the rest of the versions of me with opposite observations, and myself also seeing all
things wildly running upside down, are going to vanish from existence until then".
Please answer this question in Quora
About an answer I find unsatisfactory
The answer that the spontaneous collapse would be explained as a necessary consequence of
quantum gravity, leading to specific values of collapse rates which do not let superpositions persists at the
scale of a working brain.
I cannot find this answer satisfactory because of the gross contingencies it is based on,
unworth of the much more fundamental nature of the question.
Namely, what if by some super new nanotechnologies we could engineer a system working like a
brain but much smaller and faster ? Is there any fundamental impossibility for another universe
to exist with different laws of physics, or different values of physical constants, working much the
same as our universe except that it would lead to slow collapse ?
Other Quora questions
When is a quantum superposition state broken?
the wavefunction in Quantum Mechanics collapse instantaneously when we measure an observable or is there a transition time between states?
How do measurements collapse quantum wave functions?
What exactly does it take to collapse a wave function?
Why does observation of a quantum wave function cause it to collapse into a discrete quantum state? QBist answers there
Can you uncollapse the wave
function by killing an observer who did the measurement?
What is currently the best
explanation for how and why the quantum wave function
In the double slit experiment what
constitutes as "measurement" causing the wave function to
What is the difference between
quantum decoherence and wave function collapse?
To what extent is there still
disagreement today among physicists regarding how to explain
the collapse of the wave function in quantum physics?
What hypothesis explain the collapse of a wave function?
an observer is required to collapse a wave function, how does the observer exist?
can 'measurement' or 'observe' in relation to collapsing the wave function in quantum mechanics be defined?
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