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from the will-this-help-me-win-the-lottery? dept.
A team in Australia turned thought experiment into lab reality by using lasers. Their subject matter was not a photon but a helium atom. The lasers they used served as a pair of grates, one before the other, with the second grate randomly dropped in.
What they found is weirder than anything seen to date: Every time the two grates were in place, the helium atom passed through, on many paths in many forms, just like a wave. But whenever the second grate was not present, the atom invariably passed through the first grate like a particle. The fascinating part was, the second grate's very existence in the path was random. And what's more, it hadn't happened yet.
In other words, it was as if the helium particle "knew" whether there would be a second grate at the time it passed through the first.
Also covered at: phys.org. An abstract is available; full report is pay-walled. The original news article is at Australian National University
Original Submission
(Score: 2) by Zinho on Friday June 12 2015, @10:17PM
the atom's interaction with the detector is sufficient in itself to cause the waveform collapse
That is a perfectly reasonable assumption, but I can't think of any way to create a falsifiable hypothesis to test it. Can you? If the entire apparatus remained in a superposition until consciously observed, the outcome would be indistinguishable from an immediate collapse, would it not?
Fair point. Your question flirts with solipsism, which I also reject as highly improbable and unnecessarily complicated as a hypothesis. In this case I don't see either hypothesis as useful, since the experimenter isn't putting his own eyeball in the line of fire of the lasers or helium particles; instead, there's a screen being illuminated or a counter being incremented, and the researcher reads those. I'm fine with discussions about at what point in the apparatus up to and including the detector the waveform has collapsed, but I learned when I was 2 years old that things still exist when I don't look at them. [wikipedia.org] My failure to observe the output display of a Geiger counter should not change its count, provided that I'm not somehow interacting with its inputs.
Also "macroscopic" is an arbitrary a line to draw for quantum effects as "conscious". Massive neutron stars, are postulated to be heavily influenced by quantum effects, and the behavior of even more degenerate theoretical quark stars should be heavily dominated by quantum effects on scales that would make a laughingstock of our concept of macroscopic.
I think we're getting into the realm of "things I never said", but I'll go with you on this. I don't know whether quarks, atoms, rocks, trees, planets, or neutron stars are "conscious" or not. They've never spoken to me, so there's that, but what does it even mean to be conscious? Could we, in theory, test whether an object can cause a quantum waveform to collapse through "observation" as a guideline? If so, then there are some laser beams in quantum computing labs that count as conscious. Since philosophers can't even come up with a definition for consciousness that includes all humans (see solipsism again) I find it to be a useless metric in quantum physics.
this would force us either to conclude that our decision to measure the particle's path affects its past decision about which path to take, or to abandon the classical concept that a particle's position is defined independent of our measurement
This is where I've gone in my analysis of quantum physics. I give up on imagining atoms and their subatomic components as billiard balls or bullets, and accept that from emitter to detector they are unlike anything I see on a daily basis. I accept that, when they start moving, knowing their momentum prevents me from saying anything meaningful about their position; and that they may not even have a "position" the way I think about for things sitting on my desk. I'm more OK with this than the idea that they are somehow gaining clairvoyance and the mystic ability to determine whether something looking at them is "alive".
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by Immerman on Saturday June 13 2015, @07:26PM
I fail to see how the idea that waveform collapse occurs on observation is "flirting with" the idea that the self is the only thing that can be known to exist. I know perfectly well that their is a quantum waveform at with a given probability distribution in my box, I'm simply arguing that it might not collapse into a single concrete state until someone looks at the counter, rather than immediately upon interacting with the larger but still fundamentally quantum system of the detector .
Ah and, I seem to have dropped a word and changed the meaning of a paragraph. That should be
"Also "macroscopic" is as an arbitrary a line to draw for quantum effects as "conscious".
I didn't mean to suggest that stars are conscious*, but rather that any sort of "measurement" that relies on interacting with a macroscopic (and hence presumably non-quantum) system is challenged by the concept that entire classes of stars should exist in a state that can only be adequately described by their quantum wavefunctions. If an entire star can only exist as a non-classical quantum system, what makes you thing a Geiger counter is fundamentally different?
* The consciousness of stars would be a completely different discussion. I do happen to currently subscribe to the school of thought that consciousness is a fundamental quality of the universe rather than an emergent phenomena, but that's generally irrelevant to most discussions, probably even this one unless we can postulate a manner in which a star with a coherent consciousness could meaningfully observe our instrumentation.
(Score: 2) by Zinho on Monday June 15 2015, @02:42AM
The solipsism connection comes from the fact that "consciousness" is so poorly defined and understood that there are philosophers even today who claim to be unsure that anyone besides themselves even exists, let alone is capable of independent thought. If that's the case, how are we to determine what is and is not conscious? If we can't cleanly define consciousness, what kind of basis is that for a useful scientific theory?
"Macroscopic" can at least benefit from tautology - define it as the point at which quantum effects cease to dominate, and leave it at that. :P
Also useless as a guideline, especially given your very valid point regarding neutron stars.
For me, the essence of "observation" is interacting in a way that can determine the quantum state. In our labs that usually involves a destructive read - absorption and re-emission in the case of Young's screen, leaching some kinetic energy to create a cascade of freed electrons as in Geiger's counter, etc. Our detectors in the lab generally transduce the quantum state we want to read into a classical interaction that we can see, feel, hear, record electronically, etc. I would argue that the act of performing such a transduction is sufficient to count as "observation" in a meaningful sense and collapse the waveform, even if we figured out how to make it non-destructive.
The alternative you suggest is fraught with problems, not the least of which is deciding what counts as "observation" of the transducer. If I had a blind researcher listening for a Geiger counter's clicks, does the device fail to click if he leaves the lab to use the restroom? We are now exactly back to the question of "if a tree falls in the forest and no one is there to hear it, does it make a sound?" Pointing out that we don't have a meaningful way to test whether that is the case or not (because how can we know happens if the result looks the same either way?) is exactly the problem I have with solipsism - it posits an unnecessarily complicated world for no better reason than questioning "how can I know any different?"
I'll leave you a thought experiment which I hope would illustrate how we'd tell, extending the case of my blind researcher. Let's imagine that he's blind and deaf, and that the Geiger counter's output is a set of mechanical wheels (like a car's odometer) instead of a click, which the researcher reads by touch. If the system of quantum event -> detector -> counter were in a state of quantum superposition where for each possible nuclear decay even the wheels both turn and don't turn until the researcher reads the output then we enter a state of paradox. The wheels are not quantum devices; their state is overwhelmingly determined by the Brownian motion of the air around them and other classical interactions they experience, so how can their position be entangled with the uncertain quantum events being measured? They certainly aren't remaining stationary until just before being touched and then spinning rapidly to catch up; at some point that would require some portion of them to exceed the speed of light (depending on how long the researcher lets it run). The many-worlds hypothesis makes quick work of this paradox, creating parallel universes for each event detected; the researcher doesn't know which universe he's in until he reads the counter, but for each universe the counter wheels advance via classical mechanics based on whether or not an event was detected in that universe and are already in their appropriate state when the researcher touches the dial.
I'd love to keep this discussion going, I'm finding it invigorating. Unfortunately, I'm about to leave on a week-long trip in the mountains and won't be able to make any replies until next Saturday. Please follow up with another post, but be patient for my next reply ;^)
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by Immerman on Tuesday June 16 2015, @03:56PM
Well, if you want to bring philosophers into a scientific discussion you'll be there all night and probably never reach any conclusions - regardless of the topic. Modern philosophy has largely degenerated into mental gymnastics - it's great for developing strength and flexibility, but isn't actually directly useful for much. It just hasn't been the same since science and religion split off and took most of the practical questions with them.
Just because philosophers can't agree on whether anything beyond themselves doesn't mean there's no meaningful definition to be found - in fact it's a largely orthogonal question. Even if we had a perfect definition, we'd still run afoul of Descarte's evil-demon hypothesis and be unable to claim with certainty that anyone else even exists, much less is conscious.
You seem to see my point though -we could as easily define consciousnes by tautology: "a system which causes quantum wavefunctions to collapse when interacted with". In fact if we could find some way to detect exactly when the wavefunction collapsed, that might form the basis of a consciousness detector.
As for your cog-driving Geiger counter, of *course* the wheels are quantum devices - *everything* is a quantum device - what we call "classical physics" is the unexplained anomaly. How does combining a bunch of tiny quantum systems into ever-larger quantum systems eventually create something that appears to be governed by much simpler rules to a degree far beyond what can be explained by statistical averaging?
As for your speed question? If my preposition is correct then there would be no issue - the wheels would themselves would be in a superposition of states, having both rotated and not rotated as they interacted with the superposed measurement signal. The question is only whether the superposition collapses when it interacts with some poorly defined "macroscopic system", or if it continues to expand until it interacts with something conscious, or some other criteria is met, or even if it never actually collapses at all. There have been researchers who have managed to create mm-scale superpositions, so clearly it's not just "too many atoms involved", but as yet we really don't know what that criteria may be - it's *all* speculation. But clearly it doesn't simply end with the interaction of the initial superposed particle - far too many experiments have managed to transfer that superposition to other, often much larger, systems.
Enjoy the mountains, it's been too long since I spent a good chunk of time in them. I'll be around.
(Score: 2) by Zinho on Monday June 29 2015, @08:28PM
Thanks for the well thought-out answer! And your patience as well; I've been back for over a week now, but too busy catching up to spend time giving your response the consideration it deserves.
From what I read in your last post, I believe you and I are very close to each other philosophically, and perhaps talking past/around each other. I like your idea of a consciousness detector based on quantum waveform collapse; I even am open to the idea that we'll make startling discoveries, with many things we consider "inanimate" being detected as conscious. That would make for interesting news headlines, and perhaps a few amusing activist groups. [schlockmercenary.com]
That being said, I think I'm expressing myself poorly regarding my attitude towards consciousness. There are plenty of people willing to talk about consciousness who have more scientific street cred than philosophers; neuroscientists are a prime example. Even for them, though, it is a "hard problem". [livescience.com] Quantum mechanics is a difficult enough field to research, study, or understand; we do ourselves no favors be importing intractable problems from other fields. As a result, I find consciousness to not be useful as a tool in quantum mechanics.
Even if it were true, though, that conscious observation were the determining factor in waveform collapse, the mechanism by which that occurs would fall deeply into the field of untestable metaphysics. To restate one of my earlier ideas, how does the decaying atom know whether or not Schrodinger's cat is conscious? If the cat is asleep would it not be poisoned? If the cat doesn't count as conscious, how does the system know when/how/if/by whom it has been observed? If this is what's real, testing could/should be performed to determine its limits and explore it as a possible means of long-distance communication. If such testing is not possible, though, then it again isn't very useful as an analytical tool or avenue of research.
I mentioned Occam's razor in a different discussion thread, and I want to use (perhaps over-use?) it here. Instead of "observation" I prefer "measurement" as the collapsing action. Quantum entanglement is a delicate state, short-lived and easy to destroy. Certain types of interactions with an entangled system result in a determination of its state (e.g. measurement of polarization), which forces the waveform to subsequently act in a coherent manner for the entire entangled system (assuming that many particles are entangled). It is easy for me to believe that components of entangled systems behave consistently when measured because their entanglement requires it - if the measurements were going to be inconsistent, the particles wouldn't have been entangled in the first place. This is where the razor comes in - if I believe that the system is internally consistent from the beginning of the experiment, there is no need for me to be spooked out by measurements of widely separated entangled particles being consistent with one another.
Back to the article topic, my over-use of the razor in this case leads me to believe that the atoms of the experiment didn't need prescience or metaphysical awareness of the experimenter. If there are two grates and a detector, then the atoms will interact with grate A the same way every time that interaction takes place. If grate B is lowered, then the atoms interact with it; if it isn't, then they don't. At the detector, the atoms interact with the detector in a manner consistent with their history of previous interactions. This only causes problems if I want to believe things like that the atom has a specific position or path that it's following between grate A and the detector. That specific incorrect belief is what is disproved by this experiment. I am perfectly wiling to believe that grate B's interaction with the atom shifts it later behavior to be more wavelike than particle-like, and that there may not have been a specific path from grate A to detector in the first place.
Please understand that I'm not ruling out large-scale entangled systems. I'm actually quite looking forward to commercialized quantum computing systems, which rely on just such mass entanglements. I'm also looking forward to quantum cryptography, which may be needed to protect our privacy in a world with ubiquitous quantum computing; since good Q. crypto requires long-distance transmission of entangled pairs, I rather hope that entanglement over long distances (as has been repeatedly demonstrated) is not only possible, but practical and that we understand it well. I'm simply skeptical of interpretations of lab results which imply overly-complicated and untestable concepts of how the world works when much simpler explanations are readily available.
(Score: 2) by Immerman on Tuesday June 30 2015, @03:00PM
If we are talking about "useful tools", then yes, I agree - for the time being at least discussions of interactions between consciousness and QM are unlikely to be terribly productive. That does not mean it's inherently untestable however, only that nobody has yet thought of the tests needed. If, however, someone *does* think of such a test (and a testable link is discovered) it's likely to have far-reaching implications for both QM and consciousness research. But that requires that someone with a suitably subtle intellect not dismiss the possibility out of hand. There may even be non-dimissive conversations with peers required.
I have no answers as to the mechanism and limits of such an interaction, at the moment I can't even think of any well-formed speculations. But then formulating and testing such hypotheses is the whole point of scientific research, is it not? Though I will admit I have my doubts that the addition of consciousness would have any impact on the potential for long-distance communications.
> Instead of "observation" I prefer "measurement" as the collapsing action.
And as a practical short-term matter, that is likely the most productive approach. I think it's important though to remember that that is a completely untested preference, a matter of faith, and should be treated as such in a scientific discussion, lest your confidence spread and discourage the explorations that might yield definitive results.
Occams Razor is a wonderful tool for formulating useful explanations, but I think it's important to consider that in a scientific context it has pretty much invariably led to false, or at least incomplete, theories. Arguably often among the best theories that could be reasonably expected to emerge from the constraints of the culture and technology of the time, but nevertheless theories that have since been proven fundamentally flawed.
(Score: 2) by Zinho on Tuesday June 30 2015, @05:34PM
I completely agree with everything you just said, I think we're talking the same language now.
There is plenty of room for speculation on what is and is not going on in QM, and plenty of areas where we're really not sure what's happening because our efforts to measure anything change the systems we're measuring. Research into those areas of our ignorance will require subtle minds open to new ideas and careful consideration of new possibilities.
As long as we know that's where our discussion is sitting, I have no problem with that. Given that I am an amateur in this field (I took the course in college, but that's not what I'm paid to do today) I tend not to have a lot of discussions at that depth. In most discussions of QM I try to restrict myself to things that I firmly understand (or at least, think that I do) and theory that is at least consistent with my textbooks if not widely accepted in the field.
As a result, I do tend to get a bit snippy in tone on occasion. As an example, when someone finds a way to test for quantum entanglement being passed to measurement instruments and/or requiring a conscious observer for the expanded entangled system to collapse there will literally be a pair of PHDs waiting for them at the end of the project, plus a mention in two different fields' textbooks. I'll be honest, I get a bit nervous about how people with a shaky grasp of the topic will interpret speculation along those lines when discussing things like that in public forums. Thanks, by the way, for pointing out how I was coming across; it gave me an opportunity to think through why I was reacting the way I did and consider better ways to express myself. Hopefully this paragraph is a more tone-neutral way of expressing the same sentiments.
Speaking of faith, I've actually found this conversation a bit surreal; I often find myself at the other end of it. I'm a man of faith, and believe that the universe we inhabit is a large-scale engineering project created to make a home for conscious beings like ourselves. I suspect, based on other components of my faith's philosophy, that it is possible that animals, the earth, and even sub-atomic particles may possibly have intelligence of a sort at a level we don't fully understand (as if we even understand our own intelligence or consciousness). Discussions of such things in scientific circles generally elicits immediate derision and out-of-hand dismissal on the basis that my beliefs are based wholly upon superstition and must therefore be false. In our conversation I feel like I've been playing devil's advocate, struggling to balance between respectfully (and, regretfully at times, silently) agreeing with your sentiments and trying to point out where they over-reach the current state of the art as I understand it.
Thanks again for taking the time and patience to have a well thought-out discussion. I'm not sure that I have much more to contribute to this one, so respond or not at your leisure. I'll be watching for your future posts, and look forward to more engaging conversations when the opportunities arise.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin