Experiment confirms quantum theory weirdness
The bizarre nature of reality as laid out by quantum theory has survived another test, with scientists performing a famous experiment and proving that reality does not exist until it is measured.
Physicists at The Australian National University (ANU) have conducted John Wheeler's delayed-choice thought experiment, which involves a moving object that is given the choice to act like a particle or a wave. Wheeler's experiment then asks - at which point does the object decide?
Common sense says the object is either wave-like or particle-like, independent of how we measure it. But quantum physics predicts that whether you observe wave like behavior (interference) or particle behavior (no interference) depends only on how it is actually measured at the end of its journey. This is exactly what the ANU team found.
"It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it," said Associate Professor Andrew Truscott from the ANU Research School of Physics and Engineering.
Despite the apparent weirdness, the results confirm the validity of quantum theory, which governs the world of the very small, and has enabled the development of many technologies such as LEDs, lasers and computer chips.
The ANU team not only succeeded in building the experiment, which seemed nearly impossible when it was proposed in 1978, but reversed Wheeler's original concept of light beams being bounced by mirrors, and instead used atoms scattered by laser light.
"Quantum physics' predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness," said Roman Khakimov, PhD student at the Research School of Physics and Engineering.
Professor Truscott's team first trapped a collection of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them until there was only a single atom left.
The single atom was then dropped through a pair of counter-propagating laser beams, which formed a grating pattern that acted as crossroads in the same way a solid grating would scatter light.
A second light grating to recombine the paths was randomly added, which led to constructive or destructive interference as if the atom had travelled both paths. When the second light grating was not added, no interference was observed as if the atom chose only one path.
However, the random number determining whether the grating was added was only generated after the atom had passed through the crossroads.
If one chooses to believe that the atom really did take a particular path or paths then one has to accept that a future measurement is affecting the atom's past, said Truscott.
"The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behavior was brought into existence," he said.
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It isn't that reality doesn't exist when we don't look at it. It's that certain quantities only become well defined in the context of particular measurements. The moon is still there when we look at it. It's just that if we attempted to measure the spin of one of the photons reflected from its surface, we would only be able to confidently confidently measure its value along one axis of our own choosing.
Furthermore, quantum measurements happen without intelligent agents. For example, a decaying radioactive isotope in an asteroid might still emit a particle capable of starting a chain reaction, in say, interstellar gas.
now, although whether CI has most aptly explained things or not may never be settled, I don't think this is the greatest trouble.. we can continue to excavate and explore the depths of the unseen and come up with various explanations for what we can see, but it will always only be a scratching at the surface until we step out of the particular field of physics and look at the broader implications..
if the metaphysical and physical are really just figments of our knowledge and imagination linked by our epistemology, a making out from the haze, or, an ultimate pragmatism, then we can say whatever we want, but it's how we say it which makes the difference
http://phys.org/n...ent.html
which I offered a comment and if indeed we converge to the predominant information theory view then we have an interesting philosophical conundrum that arises, in that substance becomes more ethereal and has no fundamental basis other than probability fields impressed on the singular core idea of energy of which matter as we perceive particles is none other than probabilistic exclusions of the greater probabilities of empty space re quantum foam & virtual particles becoming 'real'.
The more attention I give to the dilemma of issues such as wave/particle duality and seemingly separate issues of the dark-matter conundrum suggest these two are emergence and therefore not directly understandable except by immense permutations of their irreducible components eg per the link I offered in the linked post:-
http://en.wikiped...mergence
Hmmm... Cheers
Now for the personal speculation part. The evolution of these equations is entirely deterministic, at least in theory. However, in the Copenhagen interpretation, we speak of random wave function collapse as a fundamental part of reality, and this should, in turn affect the evolution of the wave function, but if you look at the wave equations of QM, they leave no room for this phenomenon. Rather, it is always tacked on in an ad-hoc fashion when we transition from talking about quantum phenomena (wave function evolution) to actual measurement.
There are some problems with this, though. First, presumably, the measurement apparatus is really just part of the quantum system, so, really the difference between measurements and quantum phenomena seems artificial. Second, as far as I know a measurement is just a macroscopic reaction to a quantum phenomenon. (to be continued)
Now, if you look at the equations of QM, you'll see that as you increase the number of particles, classical quantities go from "smeared" to "well defined". In the limit of an infinite number of particles, you get perfectly "sharp" quantities. In a hand wavy sense, mathematically when you combine sharp quantities with smeared ones, the sharp quantities tend to override everything else. It's sort of like a more sophisticated version of multiplying by zero or infinity. So, in my mind wave function collapse really just comes from this interface between the macroscopic and microscopic. (to be continued)
Indeed, there's good reason to believe (from arguments involving entropy which I won't get into in the interest of conciseness), that systems consisting of a large number of particles tend to have expected values that behave more like classical objects than quantum ones.
In this light, this all sort of has an anthropic flavor to it. Namely, our world appears to be classical because we are macroscopic beings who rely on macroscopic values to interpret the world, and it isn't that the outcomes of measurements are random, but only appear that way because the configuration space of the Hamiltonian is unimaginably immense, and tends to be dominated by classical behavior.
Well, that was a surprisingly long comment. Sorry for all the speculation, but this stuff has been on my mind for a while.
Maybe, though I am inclined to believe it isn't so much a matter of there being a third thing or anything at all, but more of a matter of that the question being asked is inaccurate in the first place. It's sort of like stereotypical children asking where the lap goes when you get up.
As I said in that horribly long comment I just left, all forms of measurement in QM are just the macroscopic (think large part of the wave function) interacting with the quantum (think tiny part of the wave function). When you have large non-linear systems, you get emergent phenomena that can't easily be recognized without looking at the big picture. In this case, I would argue that classical quantities are really just emergent from the evolution of the wave function.
This experiment is further evidence that the Quantum scale universe is imprecise until we force it to be. As always this has very deep and complicated philosophical implications, but the truth has a funny way of doing that :-)
My view:
When multiple histories of a "particle" are simple, the effects of history interference is easily measured and histories can even be recombined.
But once a particle's multiple histories impact many particles, the interference between these complex superpositions become statistically impossible to detect and the histories impossible to recombine.
When we "observe a collapse", we are just being split into superpositions whose interference is now so statistically complex as to be undetectable.
Multiple histories continue, but each history is now independent (illusory from a fundamental law perspective but very real from a thermodynamic perspective).
If any particle is an quantized bit of angular momentum in the superfluid (a toroidal vortex), with pressure oscillations allowing it to be stable given the higher local energy and pressure, then those oscillations provide the basis for the pilot wave determining which paths through space the particle might take. And, the pilot wave would be impacted by the 2nd grating. Certainly this is speculative, but it's also quite conceivable and is reason to hold off on claiming the CI must be true.
Collapse then becomes an emergent law in the second sense, while wave equations are laws in the first sense. If this is correct then there will never be a measurable line between systems where superposition is easily detectable and where it is not.
There will always be more elaborate experiments that can demonstrate interference between more complex histories, but as a practical matter this will get so hard that lots of particles will always effectively "collapse" their superposition very quickly from our perspective.
Wow, charlimopps, you don't seem to have read my comment at all, seeing that what you said is one of the things I was arguing. But, I guess we'll never know or certain, as I am now on your ignore list.
@nevermark
What do you mean by simple? Do you mean that most of the paths it takes don't happen to involve interactions with other particles? I confess that I am not yet at the second-quantization point in my understanding of QM (or even the path integral formulation point), but it seems like this is just a different version of what I was saying.
Basically, the interaction of one particle with a large number of particles in a coherent manner leads to what seems like WF collapse, due to the sheer amount of contribution to the expected value these interactions make. (to be continued)
I am inclined to agree with your assessment of dividing the laws of nature into emergent and fundamental ones, though I guess one question to ask is whether wave-function collapse can ever happen on quantum scales. Namely, can one particle ever measure the property another particle on its own without the intervention of some classical system. To me, it would seem very strange for this to happen.
I suppose, though, if we ever discovered a particle that happened to behave classically, that might happen. For example, if we discovered a fundamental particle with a mass of 1 gram, that might make everything around it behave classically, too.
An interesting take on those misconceptions about QM as describing reality I found at:
https://questforn...-quanta/
Discussion about TR weirdness as commonly perceived I found at:
https://questforn...ativity/
And interesting reading about general problem of experimental interpretation of theories:
https://questforn...reality/
The issue is that of "observation" and rests with what many take as the "definition" of "observation", namely, acted upon by another particle in a way that can cause a reaction.
But, the fact of the matter is that all particles are, according to "science", supposedly always being subjected to these interactions! There are particles of all sorts everywhere, always, real photons; virtual photons, which supposedly transfer the electrostatic force; real matter; virtual matter popping in and out of existence during Planck intervals; gravitons which "science" has not supplied virtual counterparts. So particles always "exist" in that way.
If there is any appropriate nuancing, perhaps it is in the sense of a being with a soul monitoring the event.
By simple I mean particle arrangements that can be isolated and controlled. That could be a small number particles with a limited number of possible interactions or it could involve a lot of particles confined and correlated in some way.
Complex arrangements are when enough particles with enough freedom are involved so that interference between superpositions becomes too subtle and complex to control or measure.
My view is that "collapse" is just the statistical loss of recognizable interference between histories. Large objects like us obviously cannot be controlled at the particle level, so even though we may be interfering with millions of counterparts, those other histories will be indistinguishable (in a psychological sense, not necessarily experimental) from any other statistical source of noise.
Perhaps virtual particles are the points where largely uncorrelated histories happen to pseudorandomly constructively interfere for small moments of time.
I think that is the correct epistemological interpretation,.... more specifically ... that the underlying reality (objective) is conceptually formless,... that the experimental arrangement, necessarily macroscopic, supplies that conceptual form.
This corresponds well with the Hilbert space formulation where the axis basis of the state-vector and operator Defines the possible conceptual values that are observable. The underlying reality is a-priori necessarily forced to "take on" a conceptual form,... if it is to be observable at all.
It is a bit irresponsible to say this especially with using the word 'proves'. It does not prove that there is no objective reality prior to measurement as obviously there must be an objective reality that says "no" to arbitrary theories in the first place.
What it lends evidence to, imo, is that "scientific realism", ... that 'particles', 'waves', locality,... exist independently of observation (by mind and by extension scientific apparatus),... is untenable.
It exists, it just has no conceptual form, until the apparatus supplies it (ultimately mind).
But that's what I (and I think Nevwermark) ARE suggesting, though. The wave function doesn't actually collapse, but only appears to as a consequence of having a macroscopic system interact with a quantum one., or are you saying that wave-function collapse definitely happens?
Everything should be made as simple as possible. But not simpler. - A. Einstein
Okay, I see. That is a good explanation of the emergence of classical behavior,…. the loss of off-diagonal terms causing the quantum interference effects,… a coherent state being a superpostion… however, how do you get a specific conceptual value during a quantum measurement? They are not random and arbitrary, but discreet and subsequent qm measurements can be performed prior to decoherence occurring.
I don't think the wave-function is a physical entity, it is not observable as such, so yes, operationally it collapses into a particular conceptual value upon observation.
Yes, thanks for putting the right words to the concepts.
@Whydening Gyre,
Agreed. Particle waves functions don't have single positions they are 3D objects. It is simply the interaction with another particle that happens at a point.
Its like blindly finding a water balloon with a pin. You will only ever know the definite point where you popped the balloon, but the fact that there were many potential balloon popping points doesn't mean that the balloon wasn't real. The event point didn't exist until the event, but the balloon existed as a non-point before that.
To put it simply another interpretation is that the way you measure determines the result
Except that every time a measurement is made in a different way, it's the same result.
What nonsense.
Please leave the stupid at home, and strip these fools of whatever credentials they supposedly have.
We don't need more of this idiocy hijacking science and sending it down yet another rabbit trail.
Your stupidity is beyond measure, yet it definitely exists as evidenced by your pathetic work in the field of science fantasy.
http://arxiv.org/.../0412182
Have to admit I am rather partial to that one, as it nicely explains why the common approaches to unification cannot work.
Not necessarily.
When you view a Hologram, the objects in the hologram (given the details of the hologram) appear to have volume and shape - but the reality is, it's a sort of illusion.
Perhaps it's not the state of a system that we're confused about, but rather the source of the system.
Until something happens, nothing can be said about what existed before beyond the superposition of possibilities with probabilities given by the Schrodinger equation (or equivalent statement.) I don't understand why this trips people up.
Agreed but it needs some clarification. The conceptual form of "objective reality" acquired through experimental settings may as well have no relation to objective reality as thing in itself but rather may be reflection of concepts of experimenter acquired through inception rather than detection of stimuli stemming from objective reality. The central issue here is concept of existence itself, which is most likely of our own making (by knowing subject) perhaps not even applicable to objective reality. It this sense objective reality does not exists only its numerous representations materialized within our concepts.
https://questforn...reality/
A simplified example, if I may;
This article was here. I read it and went away.
I came back, it was still here and more "pontification" had been added.
Those comments were "measurements" made by others, thereby modifying my observational perception of the article's content, even if only subtly. I even made "measurement" of my own.
Reality is - the article concept (wave) is still here. Not collapsed, just "measured".
When I 'see' that you've high 5'd all the comments then (and only then) you are compelled (by some 'scientific' sorcery) to initiate the action. Really?
The proof of the pudding is in the pie.
The explicate being wave or particle...
I'm not suggesting that the conceptual structure is derived from or through 'independent objective reality', for otherwise I would be a 'realist',.. but rather indeed is a-priori for knowledge to be possible to begin with, given the nature of mind. Yes, it is mind dependent.
However,….
We do not agree on that. As with I. Kant, … I kan't follow this reasoning into idealism. There must be an objective reality existent independently of mind. As I mentioned above, there must be a 'something' that 'says no' to arbitrary theories, even if in itself it is formless. On this basis I reject any metaphysics, especially in science.
Your blog appears anti-science in tone, … yet when in fact, Kant's entire point was to delimit valid knowledge to the realm of science…. i.e. meta-physics cannot be a source of knowledge.
The realm of science is 'phenomenal reality'. As contrasted with 'Noumenal reality', this means that it necessarily contains a component which is mind dependent. Despite that this component, our conceptual structure, renders an artificial synthesis of 'objective reality', … science is still a valid source of predictive knowledge. It's just that that knowledge is of Experience rather than of 'Independent Reality'.
EDIT: "there must be a 'something' that 'says no' to arbitrary theories, even if in itself it is [conceptually] formless."
I do not see how metaphysics, highly speculative in its nature can be against science that is subject to stringent empiricism. These are two different fields. However, science is widely using or misusing metaphysical concepts and assumptions never proven by experiment and Kant clearly pointed it out by formulation of his categories of thought as a part of apriori knowledge that is innate to our mind and not stemming from experience.
Existence is one of those metaphysical concepts or categories widely adopted and used in science without questioning. What I am questioning are problematic assertions when "scientific" speculation level dangerously approaches that of metaphysics while still insisting on authority of stringent experimentally supported scientific inquiry purportedly into true nature of reality. When in fact it may just be an inquiry solely into scientific theory itself.
As long as that science allows for predictions and one does not expect that science to conform to our a-priori forms of thought for the intuitive understanding, it is valid within the delimited realm of 'phenomenal reality' - defined above,.... i.e. that one does not expect that science to explain how things 'are' independent of experienced. (The 'realists' are routine guilty of this). The above article experiment supports this view.
Quantum mechanics is a non-intuitive science for this reason, at least wrt the Copenhagen Interpretation.
.....
That's correct, which is why Kant made the Phenomenon / Noumenon distinction. As long as science operates within the context of 'phenomenal reality' which as I mentioned above contains a mind dependent component (Kant's forms of thought, or categories), it is valid knowledge.
Again the above article describes an experiment that shows that the results are not independent of mind operating at the macroscopic scale where our minds evolved its forms of thought,.... the experiment is not independent of the act of observation, ultimately by mind.
As DarkLord points out above, a realist can still take a different interpretation,... however (s)he would be need to be willing to enter into metaphysics,
Following Rene Descartes, I think we have to start somewhere, .... that a "something" says "no" to arbitrary theories [d'Espagnat] is imo allegorical to 'Cogito ergo sum' and valid with 'phenomenal reality'.
To that extent I have been questioning the 'scientific realists' position here since 2007. However, science is perfectly valid predictive knowledge of 'phenomenal reality' as defined above.
No one said they are the center of the universe in this article.
Also, experimental data has been confirming since around the 1920's that, at least at the quantum level, matter is observer-dependent.
If you would like links to peer-reviewed articles to research this for yourself, I have a library for you.
Are you implying that since you disagree with their results, that they should be "Stripped ... of whatever credentials they have"?
Also, you sound pretty certain that these people are "stupid". Do you have data of your own that refutes their results? I'd really like to see it. I'd also like to see what substance you have to support the claim that these people are "stupid".
That "reality does not exist until we measure it" is a stupid, meaningless statement. What is more accurate is that we don't know what we will measure until we measure it. Whatever has the potential to produce a measurement certainly exists before we measure it. It is simple to express its "before-measurement" reality mathematically. How can a science site post such editorial garbage! 0 to the article. +10 to the experimenters.
The answer is:
There is no Mime if nobody see him
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