Nice experiment, but they are still measuring neutrons, that are quite small. I don't understand why they try to sell this as a macroscopic experiment. Bell inecuality can be also measured at long distances, but it doesn't make it a macroscopic experiment.
I have learned to pay special attention when the phrase 'in a sense' is being used - sometimes it is in a relevant sense, sometimes not. Unfortunately, I'm not knowledgeable enough to make the call on this one.
I would argue that the neutrino is relatively large compared to the quanta typical of these kinds of tests, but in the abstract they suggested a basketball!
I think most test of bell inequality are made using photons. I'm not sure about this inequality. Neutrons are much bigger than photons [1], but somewhat similar experiments of interference have been made with helium atoms and even small molecules (with 10 atoms or so).
So if they say it's big in the quantum word, I expect at least a molecule. And the article saying macroscopic everywhere really sugest basketballs.
From the initial description, I was optimistic and I was expecting small dots of "dust", or a tiny thin membrane. There are some experimental results with extremly small object, but I guess they have a lot of thechnical problems and are difficult to use them in complex measurements.
I agree. (I missed the "ino".) It's also important that (as far as we know) the neutrino is an elementary particle, but the neutron is composed by three real quarks and a lot of virtual quarks and gluons, it's a huge mess of smaller particles together.
Much better if they use a proton beam, and combine it with similarly split electron beams. Then, collect the resulting hydrogen in two bottles and measure the resulting mass. Boom, quantum gravity.
Physicist working on QM here. At the macroscopic scale we are led to believe that the properties of a system have a value regardless of whether that value is “known” externally to the system. Then a measurement process would simply reveal the pre-existing value. But we can concoct a QM system such that it is impossible to assign a pre-existing value of a property in a consistent way (look for GHZ game to know more). This leads to true randomness in the most literal sense possible: there can exist no cause for a given value. That value materialized out of thin air.
This article describes one in a long, long series of experiments demonstrating that particles don’t exist and our intuition is simply wrong.
Imagine a gigantic, epic mountain of evidence tall enough to crush the resistance of even the most recalcitrant physicists. Particles are not real. Quantum fields are, which contain excitations, which because of conservation laws cannot simply disappear on their own and therefore in many common circumstances appear to persist and maintain an identity.
There’s our “particles”. But it isn’t hard at all to devise an experiment that breaks our intuition like a dried up stick.
I'm not in QM but electronics, still I accept QFT on evidence. Had to give up intuition/bad training when coming to grips with Aharonov–Bohm and related. Still, on bad days when (4kRTΔf)^0.5 or such gets in my way, I default and accuse my noisy little 'charges' of being too big and that they rattle around like large ball-bearings in an empty oil drum.
It is my belief that there is no reason to believe that elementary particles are ever point-like objects with momentum and location.
They are fuzzy objects that always evolve in time according to wave equation. It's just that in case of very narrow, sharp waves they equation simplifies to Newtonian (or special relativity) equation of motion.
Measurement is just exchange of momentum and energy between that fuzzy objects that happens very quickly and in quantized amount and the equations governing it simplify for narrow, sharp waves to equations of two balls bouncing of each other.
Our intuitions developed for macroscopic objects which are a very peculiar form of matter, tightly bound by interactions, which make the constituent elementary particles very sharp and narrow all the time. They are just wrong for anything else. Newtonian mechanics is attractive because it's simple but it's equivalent of gas laws, that while very simple, only statistically capture the complexities of what actually happens in ideal gas and don't reflect nothing physically real.
There are many kinds of quantum weirdness. One of them is this: we think classically of the past as definite and the future in terms of possibilities- but in reality both the future and the past are indeterminate in exactly the same way (it’s just that typically there are a lot more possible futures for the current state than pasts, because of entropy). In fact you could define the past as being the direction in configuration space with the smallest uncertainty, and the future as being the direction with the most uncertainty. In this view, at the Big Bang since there is no direction with less uncertainty, there is no past at that point.
That’s not the only quantum weirdness, but it’s a big one.
And, another big quantum weirdness is that matter has not only a probability but also a phase angle, so different possibilities can add but they can also cancel out, which is not how classical probability works where probabilities always add together.
> we think classically of the past as definite and the future in terms of possibilities- but in reality both the future and the past are indeterminate in exactly the same way
This has nothing to do with quantum theory. It's from classical physics already, from chaotic systems. For conservative systems, both predicting and retrodicting them is equally hard, due to high sensitivity of both to initial condition which we do not know exactly.
> it’s just that typically there are a lot more possible futures for the current state than pasts, because of entropy
This holds only in special cases, like when entropy of an isolated system increases (e.g. evolution towards equilibrium). When the system gets into equilibrium, entropy then remains constant, and both past macrostates and future macrostates have the same number of microstates, so for any state after that, "the number of futures" is the same as "the number of pasts".
> In fact you could define the past as being the direction in configuration space with the smallest uncertainty
In other words, you suggest to define future as that direction in which entropy increases. This is consistent with the usual meaning of future for an isolated thermodynamic system in a non-equilibrium process, evolving towards equilibrium; 2nd law implies entropy cannot decrease when comparing to the past macrostate, and entropy often increases when the new macrostate is reached.
But this is not usable definition in general. Earth, Solar System, Galaxy interact with their neighborhood; they are not such isolated systems in a macrostate, moving towards equilibrium. We do not know how to measure their entropy, to find out whether they move towards past or future. And if we somehow found entropy of Earth decreases, nobody would seriously suggest Earth is moving towards the past.
Instead, everything moves towards the future, just by definition, because that is how we think for ages. If spilled milk somewhere is observed to jump back into a cup, nobody will think the milk went back in time; instead, we will say that a very improbable thing just happened, violating prior experience and 2nd law, but that process would happen in time just as everything else, from the past towards the future.
Redefining "future" as that direction of a process in which "entropy is increasing" is really an unnecessary and flawed idea of future. We knew what future was before people invented kinetic theory and entropy; it's those events which we approach, anticipate, and when they come, we label them with a number for date and time on the clock, which (if it is running correctly) never decreases, only stays the same or increases. What entropy did in the meantime does not matter at all; a good clock does not care.
“ This has nothing to do with quantum theory. It's from classical physics already, from chaotic systems”
Not exactly. What’s important here is that every past is real. In the sense that different paths a particle can take can interfere with each other. It’s not indeterminate in a some fuzzy intuitive sense of “something we don’t know.” every past that matches the current known state of a system is real. That’s something that is included in the package of “quantum weirdness.”
And, if you make the assumption that every future is real in the same way, that’s the many worlds/decoherence interpretation.
You are using "real" in a way I don't recognize. In my view, the past that is real is that which corresponds to and is consistent with records of past events. This allows for many different pasts, and many can have some plausibility. But if my diary on a given date says I popped my knee, then any past which is inconsistent with this record is not real.
In orthodox quantum theory, past events, even those that happened in experiments showing quantum effects, such as double-slit experiment with single particle, are determinate in the sense they can sometimes be retrodicted from the present knowledge, even when they could not have been predicted before they happened (e.g. which hole the particle went); only future events are not determined by psi.
No, that’s not correct- there are no hidden variables such that a particle really took only one path to a point and we just don’t know which one it was. It really did go through all of them. All the ones that are consistent with the current state of the system. (So, no I’m not talking about pasts that are not consistent like your popped knee).
And that’s super cool, and something not many people understand! It’s the basis of the schrodingers cat experiment- you’ve heard of it. The cat is really, actually both alive and dead before the system is opened to the world, assuming that no information leaves or enters the box. It’s not that we just don’t know. It’s actually in both states. And although it’s practically speaking impossible to do the experiment, you could throw different versions of the cat through some diffraction grating a zillion times and prove that yes, the live and dead version interfere with each other. They’re both real.
I hope I’m blowing your mind a little bit with this, or if not at least being entertaining :). It’s super counterintuitive!
> there are no hidden variables such that a particle really took only one path to a point and we just don’t know which one it was.
We don't know that. It is a statement of your belief in such interpretation of quantum theory.
But I wasn't suggesting hidden variables predict which path will be taken - that is a different idea. I admit my description was somewhat confusing. My point is that retrodiction of trajectory is much easier than prediction of trajectory, because of records of the past. In other words, past is constrained by existing records of the past, while future is not constrained by records of the future, because those do not exist yet.
This retrodicted past is still loaded with uncertainty stemming from the records having uncertainty, and is speculative and not experimentally testable, of course.
> It really did go through all of them. All the ones that are consistent with the current state of the system.
This is also a speculative statement that is experimentally untestable. And I agree it is consistent with quantum theory, if we add "...and consistent with records of the past". So both stances are just an interpretation of what is going on, there is no experimentally testable idea here.
>We don't know that. It is a statement of your belief in such interpretation of quantum theory.
No, Bell’s Theorem conclusively proved it.
From Wikipedia: “To date, Bell tests have consistently found that physical systems obey quantum mechanics and violate Bell inequalities; which is to say that the results of these experiments are incompatible with any local hidden-variable theory.”
Bell's Theorem does not prove that. It is a theorem itself, so this theorem has been proven using quantum theory and other assumptions in Bell's paper.
In the quote, notice "Bell tests...have consistently found" and the word local. So not the Theorem, but the "Bell test" experiments' results, when interpreted using theorems like the Bell theorem and similar, show nature manifests non-local behaviour. They do not prove your belief that hidden variables do not exist.
Also, I recommend using more reliables sources than Wikipedia to argue a point about physics. It is not a reliable source, even though it is useful for discovery and occasionaly is correct.
Oh ok. So bells theorem is wrong and I have to cite scientific sources to convince some random person on the internet.
Look: i have a degree in physics, and I also don’t have time to argue with you. You don’t want to learn? Your loss.
You’re one of those people for whom “winning” is more important than the truth, I think.
You know what? You win. You’ve outlasted me. You’ve successfully learned nothing, and nobody will ever care about your statements about bells inequality because they’re laughably wrong and nobody will read this anyway. Victory is yours!
I didn't say that, and I think that statement is wrong.
> i have a degree in physics
Oh my. You lose credibility in an argument about physics when you fall back on authority, and even more, when that authority is supposed to be you.
> I also don’t have time to argue with you. You don’t want to learn? Your loss.
But if you don't have time to argue your point, why did you post it and defended it, and only pull this lack of time now? I would like to learn something from your posts, but so far, you regurgigated the usual incorrect/misleading claims about quantum theory and what the Bell theorem and related experiments imply. So then I thought it is you who may learn something new - please check the article I gave you above. If you do not want to take it from me, take it from people in academia who are better experts on this topic.
> You win. You’ve outlasted me. You’ve successfully learned nothing, and nobody will ever care about your statements about bells inequality because they’re laughably wrong and nobody will read this anyway. Victory is yours!
I disagree, because my aim was to learn or make you learn something I know, and so far I think I didn't succeed in any of those. So, please check the article in the link, if you have genuine interest in this topic.
Centimeter sized neutron beams are not really macroscopic because neutrons in them are not interacting with each other. Macroscopic objects consists of huge number of elementary particles that connect through interactions.
AFAIK the concept of a “particle” is kind of a construct, or at least every bit as much as a “wave.” What’s really happening down there is whatever the math says is happening and it does not have direct physical analogies to much of anything we experience microscopically on a day to day basis.
We're really looking at two (or more) different maps here, not map vs territory.
One of the maps is hey there's these little balls called particles, they bounce around and interact in ways X, Y, Z, etc.
Another is a big page of math that involves excitations of fields that interact. The point is that _this_ one is the best we currently have, but it doesn't let you simply, intuitively and correctly talk about particles interacting (or other things we intuitively want to understand the world in terms of), because those aren't real in the model. They're just an abstraction that usually works at the scale we experience day-to-day.
So yeah, the territory is the territory and neither of these are it, but even getting past that, our best map is just a bunch of math that you just have to take at face value if you want to be as correct as our maps currently allow.
This is meant to address questions like "is light a particle or a wave?" The answer is: No.
It's (according to our best model/map) this bunch of math that doesn't correspond to either one of those, have fun calculating.
No, but pilot wave theory is a bit weird since the wave contains all the same decoherent timelines as in many-worlds.
They can both be true. Then there’s a single timeline which happens to have particles following it around, but everything else is still there and there’s no way from the inside to determine where the particles are, other than the assumption that only the particles create conscious scientists.
