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[Xris]

Men once expected the gods to come down to earth and realise all our dreams but we forgot the golden rule. Heaven is for dreamers and gods. Earth is for humans and reality. We foolishly believe we are becoming godlike and can imagine ruling both heaven and earth. It is time for another reality check, when we can not explain the simplest of observations without turning ourselves in to gods or inventing millions of alternative existences. Flying too near the sun is dangerous.

[Teh]

Men once expected the gods to come down to earth and realise all our dreams but we forgot the golden rule. Heaven is for dreamers and gods. Earth is for humans and reality. We foolishly believe we are becoming godlike and can imagine ruling both heaven and earth. It is time for another reality check, when we can not explain the simplest of observations without turning ourselves in to gods or inventing millions of alternative existences. Flying too near the sun is dangerous.

Does that mean you favour the "Many Worlds" interpretation of quantum mechanics?

[Xris]

(Nested quote removed.)


Does that mean you favour the "Many Worlds" interpretation of quantum mechanics?

No. I am against the concept of particles in explaining this experiment. In fact I am like Mach, against the concept of particles in explaining what we can not observe directly. Metaphysics is an exercise that should be left to philosophers to ponder, not direct the path of science. The acceptance of this one simple experiment has enormous consequences for theoretical science. We appear incapable of even looking for an alternative to the seemingly dual nature of particles. Photons or electrons are concepts that change their characteristics to fit the desires of the theory. Even when they defy logic they are still referred to as particles. This experiment should be telling us we are wrong not that we are altering reality by simply looking, nor should it indicate the unbelievable idea that reality constantly alters to accommodate the dual nature of the quantum universe.

[Teh]

No. I am against the concept of particles in explaining this experiment. In fact I am like Mach, against the concept of particles in explaining what we can not observe directly. Metaphysics is an exercise that should be left to philosophers to ponder, not direct the path of science. The acceptance of this one simple experiment has enormous consequences for theoretical science. We appear incapable of even looking for an alternative to the seemingly dual nature of particles. Photons or electrons are concepts that change their characteristics to fit the desires of the theory. Even when they defy logic they are still referred to as particles. This experiment should be telling us we are wrong not that we are altering reality by simply looking, nor should it indicate the unbelievable idea that reality constantly alters to accommodate the dual nature of the quantum universe.

So, how do you explain Brownian motion?

[Logicus]

No. I am against the concept of particles in explaining this experiment. In fact I am like Mach, against the concept of particles in explaining what we can not observe directly. Metaphysics is an exercise that should be left to philosophers to ponder, not direct the path of science. The acceptance of this one simple experiment has enormous consequences for theoretical science. We appear incapable of even looking for an alternative to the seemingly dual nature of particles. Photons or electrons are concepts that change their characteristics to fit the desires of the theory. Even when they defy logic they are still referred to as particles. This experiment should be telling us we are wrong not that we are altering reality by simply looking, nor should it indicate the unbelievable idea that reality constantly alters to accommodate the dual nature of the quantum universe.

This is perhaps the most cogent and intelligent thing I have ever seen you post. I am quite impressed.

This "explanation" is, of course, the Copenhagen Interpretation. It is still taught, and it satisfies no one. It lies at the heart of the current inability of science to "put it all together". While adopting the attitude of "take the readings of your instruments, and get on with the calculations" they are ignoring a greater mystery they are either unwilling or unable to explore. We all operate on some set of assumptions, but science needs to be more careful about the assumptions it makes and how it defines them. I can't help but think there is something missing in their basic premises at this level.

I do not intend these statements to be critical of science, or disprove it in any sense. I just think it could be better served by a different interpretation of some phenomena. I think you agree.

[Xris]

(Nested quote removed.)


So, how do you explain Brownian motion?

Ignorance does not indicate a particle. We must ask, do you believe in pure energy? The point where energy expresses itself as a particle is the question. Sand is particle that we can observe and understand. Complex molecules or simple energetic particles are all just terms we use to explain what we can not observe directly. If we start believing in the concept of particles like sand we loose the plot completely. Energy of the universe and all the mass it creates is electromagnetic. If we understand that and keep it as a constant reminder of what we are trying to understand it might stop this constant misunderstanding of the quantum universe.Electrons with spin, frequency and an ability to communicate instantaneously can not be what we imagine, a very small grain of sand. Well it can if you believe the quantum universe has no reliable laws we can refer to. If it is so Alice in wonderland why not put a foolish imp there or a arogant god? Just look back at that naive link that is used to inform the uninitiated about the double slit screen experiment. Electrons fired like bullets one at a time. Electrons as individual particles are accepted even before we try to explain the duality of the experiment.

[Teh]

(Nested quote removed.)

Ignorance does not indicate a particle. We must ask, do you believe in pure energy? The point where energy expresses itself as a particle is the question. Sand is particle that we can observe and understand. Complex molecules or simple energetic particles are all just terms we use to explain what we can not observe directly. If we start believing in the concept of particles like sand we loose the plot completely. Energy of the universe and all the mass it creates is electromagnetic. If we understand that and keep it as a constant reminder of what we are trying to understand it might stop this constant misunderstanding of the quantum universe.Electrons with spin, frequency and an ability to communicate instantaneously can not be what we imagine, a very small grain of sand. Well it can if you believe the quantum universe has no reliable laws we can refer to. If it is so Alice in wonderland why not put a foolish imp there or a arogant god? Just look back at that naive link that is used to inform the uninitiated about the double slit screen experiment. Electrons fired like bullets one at a time. Electrons as individual particles are accepted even before we try to explain the duality of the experiment.

I agree, ignorance does not indicate a particle, but Brownian motion and the photoelectric effect do. Also electrons are particles and it is quite clear that light is quantised. If we except there are quanta, then isn't that synonymous with "particle".

Some people believe the "quantum universe" i.e. reality is subject to deterministic and comprehensible laws. Nothing, by the way, can communicate instantaneously. That idea is completely unphysical and wrong.

[Xris]

(Nested quote removed.)


I agree, ignorance does not indicate a particle, but Brownian motion and the photoelectric effect do. Also electrons are particles and it is quite clear that light is quantised. If we except there are quanta, then isn't that synonymous with "particle".

Some people believe the "quantum universe" i.e. reality is subject to deterministic and comprehensible laws. Nothing, by the way, can communicate instantaneously. That idea is completely unphysical and wrong.

Brownian motion indicates particles but not electrons nor photons. As I have said, at some point energy does become mass. I am not saying the point of mass requires an observable image.

Can you give me the precise description of an electron or a photon that indicates it has the necessary requirements to be called a particle. How do you explain quantum entanglement other than instantaneous ?

[Steve3007]

I've just looked at that "Dr Quantum" cartoon and I have to say, if I was basing my view just on that, I would probably be siding with the sceptics. I think it is a terribly flawed account. The particular part that stands out as being particularly misleading is this, near the end:

The electron decided to act differently as though is was aware it was being watched ... what does an observer have to do with any of this? The observer collapsed the wave function simply by observing

I think this is a needlessly confusing and misleading way to present these ideas to a non-specialist audience. It introduces the technical term "wave function" with no explanation and says nothing about what it means by "collapsing the wave function."

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The point that it completely fails to mention is the mechanism by which the electron "decides to act differently". The point is that observing the electron has an effect on it because observation is an action. In the normal visual sense of the word, it is an action that involves bouncing light off something. And it is no mystery that bouncing things off of other things affects them!

Observing the slit through which the electron goes with light is limited by the wavelength of the light. The resolving power with which you can use light to measure something is related to its wavelength. Longer wavelength = less resolving power. Shorter wavelength = greater resolving power. So clearly you need to use a wavelength of light that is short enough to resolve the distance between the two slits. But, with light, shorter wavelength = greater energy. And greater energy = a bigger kick to the electron.

It turns out that as soon as you increase the wavelength to a size such that it is sufficiently docile not to disturb the electron too much, it becomes too long to tell which slit it went through. And that is the start of the interesting part.

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I think this goes to show that providing a little bit of inappropriately targeted information can do more harm than good. Communicating ideas is difficult. I know. In the time I have been on this forum I have consistently failed to effectively communicate ideas to Xris.

[Logicus]

To make it more confusing: The wave in "wave function" is a probability wave, not a physical wave. It is an indeterminate location of the particle until something external to it "collapses" the wave by, in some way, determining where the particle has to be. This is the explanation for why it changes by observing it: observation collapses the probability wave. All that says, though, is that when you "see" the particle, that's where it is. The mystery is why that changes the outcome. They are essentially saying that defining the location alters the path of the particle which then alters the outcome of the experiment. I don't know if you noticed, but the cartoon was also stating that the indvidual particles go through both slits at the same time and interfere with themselves "in some way". That sounds more wave-like. In fact, I would say they are trying to express the behavior of the particles using an analog to the behavior of waves.

Is this a real problem, or a problem of how we are able to express it with language? The results would seem to indicate it is real. What does it mean? This has been an unresolved problem for decades.

[Xris]

I am told without the need for us looking, these pesky fellows also bounce of the structure of the screen. Is that a result of their frequency as wave or a particle? Steve if the truth was really told you and many others are as confused as me. So many questions remain unanswered throughout these exchanges, I have little faith they will ever be resolved. When the best can only give silly cartoons to explain the impossible we are all doomed. Doomed I tell you, doomed.

[Quotidian]

The point is that observing the electron has an effect on it because observation is an action. In the normal visual sense of the word, it is an action that involves bouncing light off something. And it is no mystery that bouncing things off of other things affects them!

However, in Brian Greene's Fabric of the Cosmos, we read

The explanation of uncertainty as arising through the unavoidable disturbance caused by the measurement process has provided physicists with a useful intuitive guide as well as a powerful explanatory framework in certain specific situations. However, it can also be misleading. It may give the impression that uncertainty arises only when we lumbering experimenters meddle with things. This is not true. Uncertainty is built into the wave structure of quantum mechanics and exists whether or not we carry out some clumsy measurement.

(p98.)

The other thing you're not acknowledging is that this is 'the measurement problem' or 'the observer problem', which gave rise to the Copenhagen interpretation, in the first place, and then to other theories, including the Everett Many World's Interpretation. As we have discussed already, Everett's interpretation of QM, which posits innumerable branching universes to rationalise the situation, is a popular alternative to the Copenhagen 'consciousness causes collapse' theory. So if there is 'no mystery', why this vast body of theorization? What problem was Everett trying to solve? Why did Neils Bohr say 'if you have not been shocked by quantum theory, you haven't understood it yet?' I think this is where your instrumentalist view is challenged, actually.

The wave in "wave function" is a probability wave, not a physical wave.

Right. Where he says 'the electron interferes with itself', it is because if you fire them one at a time, the result you get is exactly the same as if they were all fired simultaneously. So the individual 'particles' are tracing the path outlined by 'the wave', even though there is only one of them in motion at any given time during the period. The 'superposition' notion is that, prior to being measured, the 'particle' is not actually in any location. So before you measure it, you can say that it really exists. That is the essence of the 'consciousness causes collapse' issue, which is probably the biggest philosophical challenge posed by physics.

In fact, I think 'they' are neither particles, nor waves. Both particles and waves are the nearest real-world analogies that we can come up to what we are dealing with.

[Xris]

To make it more confusing: The wave in "wave function" is a probability wave, not a physical wave. It is an indeterminate location of the particle until something external to it "collapses" the wave by, in some way, determining where the particle has to be. This is the explanation for why it changes by observing it: observation collapses the probability wave. All that says, though, is that when you "see" the particle, that's where it is. The mystery is why that changes the outcome. They are essentially saying that defining the location alters the path of the particle which then alters the outcome of the experiment. I don't know if you noticed, but the cartoon was also stating that the indvidual particles go through both slits at the same time and interfere with themselves "in some way". That sounds more wave-like. In fact, I would say they are trying to express the behavior of the particles using an analog to the behavior of waves.

Is this a real problem, or a problem of how we are able to express it with language? The results would seem to indicate it is real. What does it mean? This has been an unresolved problem for decades.

Logicus. I realised the first time I read of this experiment, something must be wrong with our preconceptions. We must have missed something from the very start of our reasoning. What an experiment though. We have to admire the mind that conceived of such a worrying and magnificent quandary. There is nothing wrong with the experiment and nothing wrong with stating what we believe. What i find wrong is the constant juggling to certify what was seen as a proof of the concept of particles.

[Steve3007]

Clearly quantum mechanics involves very complex, subtle and difficult to understand ideas. It's a complicated story and, for that reason, I think it is important, if you want to have any hope of any understanding of the plot (mine is certainly nowhere near complete, and the earlier parts are getting rusty. A bit like the Forth Bridge.), that you read it from as close to the start of the book as possible and try not to skip too much. The video gives half a dozen or so of the more exciting and sensational sentences from some of the later chapters. That is why I said in my previous post:

It turns out that as soon as you increase the wavelength to a size such that it is sufficiently docile not to disturb the electron too much, it becomes too long to tell which slit it went through. And that is the start of the interesting part.

In my view, the route in, for an unfamiliar audience, is the mechanism for the uncertainty in this particular case - the electron being disturbed by the light that is used to observe it. The general principle of the uncertainty, including the relatively extremely abstract mathematical concept of a "wave funtion", comes in later chapters and is, ideally, built on lots and lots of prior experience. When I was studying this at University it was the culmination of at least two years of mathematical foundations (on top of high school), including, for one thing, learning vector calculus and then how to re-frame the subject of classical Newtonian mechanics into a thing called Hamiltonian and Lagrangian mechanics, as preparation for the mathematical "shape" of the Schrodinger wave equation.

As I said, the part at the end of my post is where the interesting stuff is just beginning. And that interesting stuff starts with the curious fact that nature appears to be conspiring to stop us from simulataneously measuring the position and the momentum of the electron through the mechanism of the light that illuminates it:

As I said, what you find when you do this is that, as you increase the wavelength, and therefore decrease the energy of the photons of light, just as you get to the point when the light is un-energetic enough not to disturb the movement (momentum) of the electron too much, you find that the wavelength is too long to measure its position accurately enough to tell which slit it went through. So this is the mechanism for the uncertainty principle in this particular case.

Just as, in more conventional familiar situations, you find all sorts of different and apparently unconnected physical mechanisms which express other general principles, like, say, conservation of energy.

My point is this: to understand and believe what you are being told you have to start from the solid, individual physical situations, and only then move on to abstract general principles. Talking about the uncertainty principle and the wave function without first discussing examples of mechanisms for these principles is like asking somebody to believe in the principle of universal gravitation when they have never seen an object fall to the ground! It's too abstract. This, I think, is at the heart of the objections which are exemplified by the understandable disbelief of the sceptics who cry: "It's all just an abstract mathematical fairy tale!"

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Quotidian:

Bearing in mind what I said above: I don't deny the interesting mysteries of Quantum Mechanics. I just think it is important not to dive right into the middle of those mysteries and just be completely directionlessly bemused by them. I think it's best to see how the mystery evolved, in a continuous unbroken process, from ordinary-ness. Apart from anything else, I think that is the only way to fully appreciate what a mystery it really is.

I'm reading a book on String theory by Brian Greene now, and I'm sure he's a hugely greater authority on the detailed plot of this entire story than me, with my half remembered wine-softened physics degree. But, dare I say it, I disagree with his wording in the passage you have quoted.

It is absolutely true that uncertainty appears to be a deep, fundamental principle of nature, like the conservation of energy (or, in later chapters of the book, mass/energy) but it is important to understand the individual mechanisms by which this principle is established.

[Logicus]

As I said, the part at the end of my post is where the interesting stuff is just beginning. And that interesting stuff starts with the curious fact that nature appears to be conspiring to stop us from simulataneously measuring the position and the momentum of the electron through the mechanism of the light that illuminates it:

As I understand the experimental setup when this experiment was originally carried out, the component used to "observe" the electron passing through one of the slits was not optical in nature. It was some sort of device to detect the motion of a particle through the slit, but it did not use light waves to do it.

I can understand the argument about clumsy scientists and crude measuring tools but even when the tools seem more appropriate to the task, it still seems to maintain its enigmatic results. Quotidian may be onto something when he says it might be something we haven't imagined properly, so we don't see it properly: There may be a greater more encompassing view that demonstrates the merging of the two modes of thought.