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. Polarisation is the property of a substance that polarises light that passes through it. This is similar to the manner in which 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.
Normal light is isotropic, it is oriented in all directions. When a light is shone through a vertical filter it takes away the vertical component of the light leaving only the horizontal component of the light. Therefore, the intensity of the light is reduced by fifty percent. If a vertical filter , also called the analyser, is placed in front of the original vertical filter 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 almost all of the light with the same polarization to pass through.
However, if 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.
This result is fairly cut and dried, when both the horizontal and vertical component of the light are blocked, no light can pass through and the entire light is blocked at the second filter or analyser, which blocks all of the light.
But, here is where the big mystery arises, classical physics although able to explain the phenomenon using statistics, has no physical explanation. If a third filter that is oriented at 45 degrees is placed between the vertical and horizontal filter, some of the light is again allowed to pass through. This is a complete mystery, in what magical way does the placement of a third diagonally oriented filter that is placed between the vertical and the horizontal filter, allow the light to once more pass through all of the filters? However, it should be noted that at each stage of the experiment, some percentage of the light is reduced. After passing through the first filter, the light is reduced by 50%, after passing through the diagonally oriented filter placed in the middle the intensity of the light is reduced to 25% of the original intensity and finally after passing through the horizontally oriented filter the light is reduced to 12.5 % of the original intensity. 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.
Both classical physics and quantum mechanics arrive at the same conclusion mathematically. However, while classical mechanics has no explanation for this phenomenon, quantum mechanics has an explanation that fits in perfectly with its doctrine. The quantum mechanics explanation for the phenomenon is that light can be in either of two states, vertically polarised or horizontally polarised. Therefore, when both states of polarisation are blocked; all of the light is blocked. However, when a diagonally oriented filter is introduced in between the vertical polariser and the horizontal polariser it puts the vertically polarised light into a state of superposition, where the light exists in an intermediate state and is both vertically and horizontally oriented. Superposition is one of the basic tenets of quantum mechanics.
The quantum mechanics explanation for this phenomenon of the third filter allowing a percentage of the light to pass through both filters 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 hope for the classical physicists, a simpler explanation exists. If one looks at the polariser as a linear 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.
So, what is considered to be one of the most esoteric results in quantum mechanics, is shown to be the result of a simple change in the direction of light and not due to superposition at all.
It should be remembered here, that polarization is not an intrinsic property of light. Polarisation is the property of a substance that polarises light that passes through it. This is similar to the manner in which 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.
Normal light is isotropic, it is oriented in all directions. When a light is shone through a vertical filter it takes away the vertical component of the light leaving only the horizontal component of the light. Therefore, the intensity of the light is reduced by fifty percent. If a vertical filter , also called the analyser, is placed in front of the original vertical filter 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 almost all of the light with the same polarization to pass through.
However, if 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.
This result is fairly cut and dried, when both the horizontal and vertical component of the light are blocked, no light can pass through and the entire light is blocked at the second filter or analyser, which blocks all of the light.
But, here is where the big mystery arises, classical physics although able to explain the phenomenon using statistics, has no physical explanation. If a third filter that is oriented at 45 degrees is placed between the vertical and horizontal filter, some of the light is again allowed to pass through. This is a complete mystery, in what magical way does the placement of a third diagonally oriented filter that is placed between the vertical and the horizontal filter, allow the light to once more pass through all of the filters? However, it should be noted that at each stage of the experiment, some percentage of the light is reduced. After passing through the first filter, the light is reduced by 50%, after passing through the diagonally oriented filter placed in the middle the intensity of the light is reduced to 25% of the original intensity and finally after passing through the horizontally oriented filter the light is reduced to 12.5 % of the original intensity. 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.
Both classical physics and quantum mechanics arrive at the same conclusion mathematically. However, while classical mechanics has no explanation for this phenomenon, quantum mechanics has an explanation that fits in perfectly with its doctrine. The quantum mechanics explanation for the phenomenon is that light can be in either of two states, vertically polarised or horizontally polarised. Therefore, when both states of polarisation are blocked; all of the light is blocked. However, when a diagonally oriented filter is introduced in between the vertical polariser and the horizontal polariser it puts the vertically polarised light into a state of superposition, where the light exists in an intermediate state and is both vertically and horizontally oriented. Superposition is one of the basic tenets of quantum mechanics.
The quantum mechanics explanation for this phenomenon of the third filter allowing a percentage of the light to pass through both filters 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 hope for the classical physicists, a simpler explanation exists. If one looks at the polariser as a linear 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.
So, what is considered to be one of the most esoteric results in quantum mechanics, is shown to be the result of a simple change in the direction of light and not due to superposition at all.
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