Light wave/particle duality mystery

[Jklint]

Aren't waves mostly the classical aspect of said phenomena and particles/photons it's quantum manifestation. Please correct me if I'm wrong, but would the "wave" aspect of light, or EM in general even have much relevance in QM and if not what could be so paradoxical about this distinction?

[Steve3007]

Jklint:

This is how I understand it:

As a rule, what happens is that a theory is invented which accurately describes a set of possible observations to a certain level of accuracy. Then, when a new theory comes along, it doesn't so much replace the old theory as envelope it. It describes a larger super-set of observations to a greater level of accuracy. The old theory then becomes a special case of the new one. i.e. When certain simplifying assumptions are made, and certain factors are assumed to be small enough that they can be ignored, the new theory is shown to collapse back down into the old one. The new theory, in order to be valid, must contain the old one.

This is often referred to using the word "limit". The old theory is a "limiting case" of the new one. Physicists often use phrases like "in the classical limit" meaning the point at which classical physics emerges as a special case of quantum physics.

So, in the case of waves versus photons in electromagnetic theory: the wave-like behaviour of light, with all the associated classical wavey behaviour (diffraction, refraction, interference etc) emerges from the theory that uses photons in the "limiting case" of a very large number of photons.

All this, at least to my understanding, means that you're right in a sense to place waves in the classical camp and photons in the quantum camp. But that doesn't mean that EM waves don't exist in the quantum world. It can be shown that Maxwell's equations - those archetypal equations of classical EM wave theory - can all be derived as a special case from the Standard Model of Particle Physics. They're all still there. The waves exist just as they did before. We just have a more subtle and far-reaching description of them now.

[Jklint]

Jklint:

As a rule, what happens is that a theory is invented which accurately describes a set of possible observations to a certain level of accuracy. Then, when a new theory comes along, it doesn't so much replace the old theory as envelope it. It describes a larger super-set of observations to a greater level of accuracy. The old theory then becomes a special case of the new one. i.e. When certain simplifying assumptions are made, and certain factors are assumed to be small enough that they can be ignored, the new theory is shown to collapse back down into the old one. The new theory, in order to be valid, must contain the old one.

This is often referred to using the word "limit". The old theory is a "limiting case" of the new one. Physicists often use phrases like "in the classical limit" meaning the point at which classical physics emerges as a special case of quantum physics.

So, in the case of waves versus photons in electromagnetic theory: the wave-like behaviour of light, with all the associated classical wavey behaviour (diffraction, refraction, interference etc) emerges from the theory that uses photons in the "limiting case" of a very large number of photons.

All this, at least to my understanding, means that you're right in a sense to place waves in the classical camp and photons in the quantum camp. But that doesn't mean that EM waves don't exist in the quantum world. It can be shown that Maxwell's equations - those archetypal equations of classical EM wave theory - can all be derived as a special case from the Standard Model of Particle Physics. They're all still there. The waves exist just as they did before. We just have a more subtle and far-reaching description of them now.

Steve3007~

I do realize that older established theories become subsets of more encompassing theories which in turn become subsets of even more all-inclusive theories which is the goal of Unification. Every time a higher level of incorporation is achieved the energy levels increase and the distances decrease in conformity. So it is clear to me, from that standpoint, that EM wave theory can be derived from that with incorporates it meaning from its higher energy super-set. That, as you mentioned, is Standard Model of Particle Physics which denotes the forces of what we so far have been able to theoretically and experimentally unify.

That's the reason why I reasoned, somewhat simplistically because it gets more complicated, that the photon/particle of QM underpins the EM waves of Classical Mechanics. But this merely re-emphasis that I can't see any contradiction or paradox between the two same entities except in how they're measured meaning at what distance and energy level they're measured at.

I'm not at proficient in the subject as you are so I may expect deficiencies in my understanding to be corrected.

[Obvious Leo]

I'd go along with your balanced interpretation of a scientific theory, Steve, and add this. When physicists speak of particles, waves, fields, etc they speak of mathematical entities, not physical ones. Physicists make their observations of the world and they then describe their observations in the language of mathematics. Although I was rather pejorative in my use of language and the put-down of the mathematical gimmick I don't actually suggest that physics can be done any other way. However we must exercise great caution in the conclusions that we draw from this method because it becomes all too convenient to mistake the map for the territory. Sometimes light behaves as if it were a particle, sometimes it behaves as if it were a wave, sometimes it behaves as if it were moving through a geometric medium etc.

The point was well made earlier that experimental protocols are designed to predict what the observer will observe, because it is from observation that the models are derived and then constants are inserted as required. Therefore we can hardly feign amazement when the observer duly observes what the models have predicted. The flaw in this method lies in the observers interpretation of his observation and in the case of light this is doubly so because the observer can never see light moving. Light simply moves too bloody fast for the observer to observe it, which means the observer can only ever see it after it has already moved. Thus he models his observation on frozen light, not moving light, and lo and behold he observes that the speed of light is a constant. Sure it is. It's a constant zero by the time he observes it because it's completed its journey. How would you measure the speed of your car after you've parked it? If you've got enough information about it's previous journey you could calculate it but you can't observe your car retrospectively and this is essentially what physicists are trying to do with light. In fact the observer can't observe anything actually moving, not just light, because by the time he has observed it, it is no longer where he has observed it to be. The light has taken a finite time to reach his eye, by which time the moving object has moved on. Thus his observation is not an observation at all, but rather a CALCULATION.

As I've stressed many times in other threads the observer does not observe reality but a frozen tableau of it. Reality is what is happening all around us RIGHT NOW and when we observe it our observation is precisely analogous to watching a movie on a delayed telecast. The frames of our movie are being projected to our senses at a rate of 5.4 x 10⁴⁴ frames per second, but we only need to see the occasional frame to make sense of the world around us because we simply fill in the gaps with our consciousness. We make our own map of the world by calculation and no two observers will make the same map because our calculation depends on the a priori assumptions we have already made about the nature of our observation. In the language of Kant we would say that our cognition of the object is confirming our cognition of the object, which is insufficient for truth. This is exactly what the mathematical models in physics also do and thus we must exercise extreme caution in the conclusions we are free to draw from them.

In the early days of quantum mechanics this salutary caution went recklessly unheeded and the helpless layman was confronted with the nonsensical proposition that a physical entity could be in two places at once. Only rarely would a physicist be heard to say that quantum mechanics is a mathematical model that models reality as if a particle could be in two places at once. An electron, for instance, doesn't move as fast as light but it very nearly does. It can't occupy 5.4 x 10⁴⁴ discretely different positions every second but it manages to get through almost that number. Near enough is good enough in physics, when it comes to making predictions which only the artefacts of mere mortals can confirm, thus if the physicist were to model his speedy electron as if it were everywhere at once then in every practical sense he's going to be able to make astonishingly accurate predictions, because it very nearly is everywhere at once. However near enough is never good enough when we're speaking of the true nature of physical reality so quantum mechanics is not in fact a model of the real world.

Luckily nowadays very few physicists are continuing to make the preposterous claim that it is.

Regards Leo