Naked Science Forum
On the Lighter Side => New Theories => Topic started by: McQueen on 26/03/2024 04:35:37
-
If the results of The Double Slit Experiment sound weird, there is yet another experiment that demonstrates quantum mechanics effects, that trumps everything else. As far as proofs of quantum mechanics goes, the 3 polariser experiment may be considered to be the ace in the hole.
It should be remembered here, that polarization is not an intrinsic property of light per se. Polarisation is the property of a substance that polarises light that passes through it. This is similar to saying that a laminar flow, is not an intrinsic property of water, a laminar flow of water is the result of certain conditions being imposed on the water as it passes through a space. Historically, the polarisation of light was first observed in naturally occurring crystals such as calcite or quartz. These crystals both demonstrate the property of birefringence, or changing of the direction of the incoming light. Later, the same effect was duplicated by stretching plastic like materials causing the molecules to form into long lines or chains. When iodine was added to the molecules, they effectively absorbed light falling on the chains of molecules blocking it, while allowing orthogonally oriented light to pass through. If the polariser is effective, it blocks 50% of the light.
The experiment is as follows, three polarisers are used, hence the name of the experiment.
(https://imgbb.host/images/Qk3hE.jpeg)
When a light is shone through a vertical filter (let's call it Filter 1) and then through another vertical filter (Filter 2 also called the analyser in QM), all of the light that passes through the first filter will also pass through the second filter. This is because both filters are aligned with the same orientation, so they allow light with the same polarization to pass through.
(https://imgbb.host/images/QkMES.jpeg)
However, if the polarisers are good and a horizontally oriented filter is put in place after the vertical polariser, it is found that light passing through both filters is completely blocked. No light passes through to the other side of the horizontally oriented filter.
(https://imgbb.host/images/QkQNM.jpeg)
This big mystery arises from the fact that if a third diagonally oriented polariser is placed between the first two polarisers, light is again allowed to pass through. Although the intensity of the light is reduced in keeping with malus law where the intensity is equal to the square of the cosine of the angle made between the transmission polariser and the analyser polariser is multiplied by the initial intensity.
(https://imgbb.host/images/Qka0I.jpeg)
The quantum mechanics explanation for this phenomenon is superposition, and it is deemed to be the final proof of quantum mechanics. Therefore, according to this explanation, light has a definite polarisation (a) horizontal or (b) vertical, when it undergoes diagonal polarisation it is in a superposed state, having elements of both vertical and horizontal orientation, and hence can pass through either the vertical or the horizontal with its intensity reduced according to malus law.
However, there is a simpler explanation if one looks at the polariser as a diffraction grating. The size of the molecules forming linked chains make this alternative a distinct possibility, as they would diffract the light without dispersing it. One result of this is that the vertical component is blocked or absorbed by the chains of molecules, while the remaining vertical component of the light is diffracted in a horizontal direction. Therefore, only the horizontal component of light is present after it passes through the vertical filter (i.e., chains of molecules oriented in a vertical direction) . If a horizontal filter (i.e., chains oriented horizontally or orthogonal to the first filter) is now placed in the light coming from the vertical filter all of the light will be blocked and no light shall pass the horizontal filter.
What happens when a diagonally oriented filter( i.e., chains of molecules oriented diagonally) is placed between Filter 1 and filter 3? Some of the light coming through Filter 1 is blocked by the diagonal chains of molecules but the remaining light undergoes diffraction at a diagonal angle and the light reduced according to malus law, makes it not only through the diagonally oriented filter but through the horizontal filter, although undergoing a further reduction in intensity in the process.
So, it is not due to super position at all. Finally it all depends on the direction of the light as mentioned at the beginning of the post.
-
If you set up a radio transmitter with a simple dipole antenna, the polarisation is the axis of the dipole.
If you move towards that antenna very quickly, the radio waves are blue-shifted into light.
So you are wrong to say "it should be remembered here, that polarization is not an intrinsic property of light per se. "
-
I have just managed to upload the images that go with this post. It might make more sense now.
-
As far as proofs of quantum mechanics goes, the 3 polariser experiment may be considered to be the ace in the hole.
Theories such as quantum mechanics are never "proven", theories are considered viable if they are consistent with observation and experimentation.
However, there is a simpler explanation if one looks at the polariser as a diffraction grating.
Quantum mechanics explains the 3 polarizers results. It also gives the exact intensity of light that results. This means that the quantum theory is a good theory to use in this situation.
You have a conjecture that it is a diffraction effect, but you can only back up your claim with vague arm waving. If you had some mathematics that supported your conjecture then it would be worth considering, but you don't so it isn't worth considering.
Unsupported conjectures are not theories, they're just guesses.
-
Theories such as quantum mechanics are never "proven", theories are considered viable if they are consistent with observation and experimentation.
Strictly speaking your statement is not true. Take, as an example one of the earliest experiments, namely Galileo′s experiments to prove that bodies picked up speed at a constant rate, or that they had constant acceleration. No-one since then has been able to prove Galileo′s conclusions wrong or to imply that the results of his experiments were due to some other cause. Therefore, it should be clear from the above that for an experiment to be viable, it cannot (must not) have two or more causative factors. This is in spite of whatever mathematical justifications that may be put forward, in its defence.
Quantum mechanics explains the 3 polarizers results. It also gives the exact intensity of light that results. This means that the quantum theory is a good theory to use in this situation.
You have a conjecture that it is a diffraction effect, but you can only back up your claim with vague arm waving. If you had some mathematics that supported your conjecture then it would be worth considering, but you don't so it isn't worth considering.
Unsupported conjectures are not theories, they're just guesses.
My claims might be unsupported but in effect the ′claims′ were also predictions. I had predicted that if the lines of the polariser were oriented vertically that it would block out the vertical component of light leaving only the horizontal component. This conjecture turned out to be right. Following this reasoning, in order for the vertically oriented lines of molecules to produce horizontally oriented light, the only possible explanation is that the light is diffracted horizontally. This conclusion is also correct.
Earlier polarisers were made by imbedding little pieces of crystal (Herpathite) in a plastic substrate to form the lines of the polariser, this was difficult to achieve, hence not only were these early polarisers rare they were also expensive and (comparatively) inaccurate. Modern polarisers use poly-vinyl alcohol molecules that can be stretched, the molecules are doped with iodine or some other such substance that absorbs light. If one looks at the size of these PVA molecules, one finds that they are the perfect size to diffract light without dispersing it (i.e., splitting it into component colours.). They are also the right size for diffracting light in a direction orthogonal to the lines of molecules. Therefore, the physical explanation of the linear polarisation of light (as used in the 3 polariser experiment) is much as I had described in the OP. Since the polarisers diffract light in an orthogonal direction, a diagonally oriented polariser would diffract light diagonally. Light oriented in such a manner would be able to pass through both vertical and horizontal polarisers. The mathematical percentage of light passing through each orientation according to malus law is very accurate.
The main point is that an alternate explanation is presented to that of the rather eerie super position theory of quantum mechanics. That being so, one can no longer state that this experiment proves once and for all the quantum mechanics theory of super position and by association of quantum mechanics itself.
There is also the example of Occam?s razor: The simplest explanation is preferable to one that is more complex.
-
Strictly speaking your statement is not true.
I disagree.
Therefore, it should be clear from the above that for an experiment to be viable,
I was talking about theories.
They are also the right size for diffracting light in a direction orthogonal to the lines of molecules. Therefore, the physical explanation of the linear polarisation of light (as used in the 3 polariser experiment) is much as I had described in the OP. Since the polarisers diffract light in an orthogonal direction, a diagonally oriented polariser would diffract light diagonally.
You are simply repeating your claims without evidence.
Quantum mechanics explains mathematically what is happening. Your idea would need to do a better job than QM. Your idea is just a guess with no math or compelling evidence, so it is not worth considering.
-
Hi.
There were several posts about polarisers and polarised light recently (let's say within the last 2 years).
It might be possible to dig these up with a bit of searching if you were interested. However, it's not essential - you can start a new thread and discuss similar things again.
I'm not entirely sure what your proposed explanation is. Please re-examine this phrase:
One result of this is that the vertical component is blocked or absorbed by the chains of molecules, while the remaining vertical component of the light is diffracted in a horizontal direction.
Is that a minor error in the typing? I may be mis-understanding what is written here. As I understand it the vertical component is absorbed - so there isn't any remaining vertical component for the last part of the sentence.
Many of the conventional classical models for polarising filters become interesting when you consider very low intensities of light where we would effectively only have a single photon. We have experiments like the photo-electric effect suggesting that light does come in discrete packets, which I'll call a photon.
Most classical models will only produce or predict the results we see at high intensities of light. They fail to predict the results at very low intensities of light. When you're down to just one photon, you can't have a 45 degree filter knock out one half of it - photons don't come in halves, you either let it all through or you absorb all of it. The model ought to predict that you get all the light through half the time and none the other half of the time, instead of suggesting you get half the incident intensity transmitted every time. Does your model, involving some sort of diffraction, handle low intensities differently to the higher intensities? If your model would always predict that Malus' law applies, so that you'll always get half the intensity from a 45 degree polariser, then it doesn't accurately predict the results at low intensities.
The QM model does predict the appropriate behaviour at very low intensities of light and also reproduces the usual relationships at higher intensities (because statistical averages take over and produce those results). So it explains or models all the behaviour we can observe at any intensity.
Anyway, the classical models are useful and in many situations it's all you need - but the QM model seems more capable and handles more situations.
.... one can no longer state that this experiment proves once and for all the quantum mechanics theory of super position and by association of quantum mechanics itself....
I don't think a lot of people do state that. It's a useful experiment, it's another one where QM makes sucessful predictions but it's not necessarily the most important experiment.
Best Wishes.
-
However, there is a simpler explanation if one looks at the polariser as a diffraction grating.
One could, with equal validity, look at an elephant as a fish, and thus explain all the mysteries of the universe.