Well, bugger.
De Broglie insisted that everything at the quantum scale was perfectly normal and above-board. He devised a version of quantum theory that treated both the wave and the particle aspects of light, electrons and everything else as entirely tangible. His “pilot-wave” theory envisioned concrete particles, always with definite locations, that are guided through space by real pilot waves — much like the waves propelling Couder’s bouncing droplets.
Couder discovered by chance that tiny oil droplets bounced when plopped onto the surface of a vibrating oil bath. Moreover, as the droplets bounced, they started to bunny-hop around the liquid’s surface. Couder soon figured out that the droplets were “surfing on their own wave,” as he put it — kicking up the wave as they bounced and then getting propelled around by the slanted contours of the wave.
Straightaway, they saw the droplets exhibit surprisingly quantum-like behaviors — only traversing certain “quantized” orbits around the center of their liquid baths, for instance, and sometimes randomly jumping between orbits, as electrons do in atoms. There and in bouncing-droplet labs that soon sprang up at the Massachusetts Institute of Technology and elsewhere, droplets were seen to tunnel through barriers and perform other acts previously thought to be uniquely quantum. In reproducing quantum phenomena without any of the mystery, the bouncing-droplet experiments rekindled in some physicists de Broglie’s old dream of a reality at the quantum scale that consists of pilot waves and particles instead of probability waves and conundrums.
The article contains links to the papers which have movies as supplementary material. I can't access the one about tunnelling, though there are numerous results if you Google "oil drop tunnelling". I'll have to check those out later.
After recording the trajectories of 75 bouncing droplets through a double-slit barrier, Couder and Fort thought they detected rough stripes in the droplets’ final locations — an interference-like pattern that seemed as if it could only come from the pilot wave. Double-slit interference, considered “impossible to explain in any classical way,” was happening without mystery before everyone’s eyes.
Drawn by the potential quantum implications, the fluid dynamicist John Bush started up a bouncing-droplet lab of his own at MIT and led others to the cause. Tomas Bohr heard Couder talk about his results in 2011 and later discussed the experiments at length with Bush. He teamed up with an experimentalist colleague, Anders Andersen, to study bouncing droplets further. “We really became fascinated with, in particular, the double-slit experiment,” Andersen said.
After perfecting their experimental setups, getting rid of air currents, and setting oil droplets bouncing on pilot waves toward two slits, none of the teams saw the interference-like pattern reported by Couder and Fort. Droplets went through the slits in almost straight lines, and no stripes appeared. The French pair’s earlier mistake is now attributed to noise, faulty methodology and insufficient statistics.
I'd like to hear from Couder and Fort. Most individual studies claiming that something has been proven or disproven turn out to be wrong. I don't mind quantum mechanics making the universe fuzzy and unknowable because it's like that anyway. No, what I want from quantum mechanics is :
- No need for an observer to collapse wavefunctions, because that is plainly silly.
- No need for multiple universes to kill a cat, because that's even sillier.
(I guess I could try and justify why I find these things silly, but I ain't gonna do that)
Originally shared by Eli Fennell
Pilot-Wave Alternative to Quantum Wave-Particle Duality a Bust
Ever since the dawn of Quantum Physics, there have been those who felt that somehow, eventually, it would be reconciled with a conventional Newtonian-Relativistic causal framework.
Einstein spent a large part of his later years trying to banish Quantum indeterminacy and entanglement (which he derisively called 'Spooky Action At a Distance'), only to fail miserably. Despite his insistence that God does not roll dice with the universe, the dice keep falling and no one can rationalize them.
A recent attempt to overcome this issue involved an analogy with the dual-slit experiment, wherein a photon can be shown in different conditions to behave as either a particle or a wave, but never both at once, depending upon how it is observed (or measured). As a particle is an object with a given mass at a given point in space moving in a particular direction with a particular velocity, and a wave is at best only some of those, this seems irreconcilable with our sense that reality must exist independent of observers.
More than a decade ago, some imaginative researchers suggested a theory based on observations of a stream of oil droplets surfing on their own wave, a pilot wave as it's called, which seemed to reproduce the effects observed in the dual slit experiment. This led to optimism that Quantum Physics could finally be brought back into the fold of conventional causation. Particles would be particles again, but sometimes behaving wave-like due to being acted upon by a physical pilot wave (think more-or-less a droplet of seawater being carried on an ocean wave, and you'll get the general idea).
Alas, research since 2015 has not only failed to support this, but has even debunked the original observation, showing that the droplets do not, in fact, behave like photons in the experiment they were meant to replicate.
Interestingly, one of those who helped put the final nails in the coffin of this approach was Thomas Bohr, grandson of Niels Bohr, the Father of Quantum Physics itself, and a Physicist like his grandfather.
Thus, yet another attempt to rationalize the Acausal, Uncertain, Observer-Dependent Reality described in Quantum Physics with the Causal, Determinate, Observer-Independent Reality pictured by conventional Physics and our general post-Enlightenment Era intuitions about reality has failed. While there are still efforts along these lines, they are vanishingly few, and increasingly arcane and difficult to disprove (thus lacking strong falsifiability).
As unsatisfying as it may be to some people, it appears Quantum Physics is correct in its core premise: though our macro reality may appear to be Causal, Uncertain, and Observer-Independent, its roots run into a more fundamental reality in which none of this is true, or is weakly true at best.
#BlindMeWithScience #QuantumPhysics #PilotWaveTheory
https://www.quantamagazine.org/famous-experiment-dooms-pilot-wave-alternative-to-quantum-weirdness-20181011/
Rhys Taylor, do you know if there is any update on whether Bohm's interpretation of QM is consistent with relativistic QM? I had read that it is with non relativistic QM.
ReplyDeleteI sort of got through the first chapter of The Undivided Universe and love the approach but I am very slow at math and there are so many other things for me to work on.
Dean Calahan I'm afraid not. It's been years since I understood even the basic mathematics of QM.
ReplyDeleteI'm afraid that, if you want Quantum Physics without the Observers, then what you want is not Quantum Physics. That's like saying you want Relativity without Masses changing with Velocity.
ReplyDeleteI, for one, have come to conclude that it is, in fact, our sense that anything can exist independently, i.e. without interactions/observations/measurements, that is what it is silly. After all, we cannot in fact find a single instance in all of nature where a thing exists that isn't the end result of infinite interactions of particles observing/measuring/interacting with other particles, or anything for that matter where observation doesn't alter that which is observed. That goes for our macro reality as well as our quantum one.
Granting, the search for 'Quantum but without the Weirdness' is nothing new, but to-date all such Searches have ended as unsuccessfully as all Searches to replace Newton and Einstein's Theories. Just because we don't intuitively like certain Theoretical concepts, does not make them untrue.
ReplyDeleteRhys Taylor You can think of the Copenhagen interpretation as simply a predictive model that permits nonlocal correlations and that sits within the framework of Bayesian statistics. In that sense, a conscious observer is clearly required because a wavefunction is simply a way for a conscious observer to try to predict probabilities of various outcomes.
ReplyDeleteAs a professor of mine used to say, nature doesn't care about physics. Only humans care about physics.
Gopindra Hannigan Again, that seems like a version of the Freedom of Choice Paradox, which has not held up in testing.
ReplyDeleteI'm not familiar. What prediction does the Copenhagen interpretation make that has not held up?
ReplyDeleteIn general, identical mathematical formalism leads to identical experimental predictions.
Or is this a Bayesian vs. frequentist objection?
Gopindra Hannigan I think you're misinterpreting the Copenhagen Interpretation when you say "In that sense, a conscious observer is clearly required because a wavefunction is simply a way for a conscious observer to try to predict probabilities of various outcomes."
ReplyDeleteOn the one hand, "conscious" is not a requirement for Observer in Quantum Physics. In fact, if we used that yardstick, there's no experiment in Quantum Physics proper that would permit us to show Observation. Quanta, after all, are too small for our senses to apprehend. The Observers in these experiments are actually Measuring Apparati, like Quantum Switches. The idea that Consciousness has some special role in Quantum Observation is a basic misconception of the Copenhagen Interpretation, and one which has been bastardized by plenty of Quantum Gurus to peddle notions that are ludicrous to anyone who really understands what Observation entails in the Quantum realm and when and where it actually matters (i.e. it doesn't and can't change anything that is already Determined).
On the other hand, more fundamentally, Observation or Measurement are both really just a way of saying interactions involving exchange of Quantum State information between things, where the 'exchange' actually in itself helps Determine it into a definite state from what was a sort of fuzzy probability cloud with no Deterministic outcome path. Think of it like having the ability to speak an unlimited variety of words at the start of a conversation, versus how the pathways of a conversation narrow with each word uttered out of the mind and through the mouth... the exchange doesn't share what exists independently, because nothing exists independently, rather it shares either/or what has already been determined or what hasn't been determined yet, and in the latter case, the exchange itself helps determine the outcome.
The Copenhagen Interpretation definitely doesn't say a wave function is simply a way for an observer to predict outcomes. And the evidence to-date suggests anything but that, and suggests instead that there are no Determined outcomes of an Indeterminate state until it Interacts/Is Measured By/Is Observed By Something Else. Mind you, the 'Something Else' is usually some other part of the same system, like Atoms interacting within Molecules, etc..., which is where the Schrodinger's Cat analogy gets confusing, since by any sane measure a cat is complex enough to be a Self-Observer, yes, even if it dies and therefore has no mind left, its own particles interacting with each other being more-than-sufficient.
Eli Fennell The Copenhagen interpretation treats the (modulus squared of the) wavefunction as a probability density. So, in a direct sense, it provides a predictive model.
ReplyDeleteOf what use is a predictive model to anything that isn't a conscious observer? As I said before, nature doesn't care about such things. Whatever happens will happen. Quantum physics is an attempt by humans to understand something about nature. We shouldn't confuse our models for nature itself.
It appears that some people prefer to call what I'm talking about Quantum Bayesianism, but my adviser characterized it as simply a version of the Copenhagen interpretation.
I am not making any claims about what is required to cause a change in a quantum system. Phenomena like spontaneous emission occur precisely because quantum systems interact with the environment, not just with degrees of freedom controlled by a person.
As a matter of practicality, each person attempting to model a quantum system will construct a wavefunction for that system to try to describe it. That wavefunction will depend on the particular information available to that person. If two people participate in an EPR experiment they each measure the particle local to them and collapse the remote particle into some specific state as a result.
It sounded like you were going to offer some falsification of Bayesian statistics as an approach to quantum mechanics. I would be most interested in hearing about that.
Relevant: plus.google.com - Why Quantum 'Spookiness' Doesn't Scale It is so commonly known as to almost ...
ReplyDelete