Category Archives: Quantum Electrodynamics

Quantum Weirdness – A Matter of Relativity? Part 2

Quantum Weirdness

A Matter of Relativity? 

 

Copyright 2006/2007 James A. Tabb 

Part 2 – Double Slit Weirdness

When a proper light source (coherent – light from a single source all at the same frequency) is placed in front of a screen with a narrow slit, the light is diffracted (spread out) as it goes through the slit and appears as a shaded band centered on a screen or photographic film. The light is scattered and/or bent by the edges of the slit as shown in Figure 3.

Single Slit Diffraction
Figure 3. Single Slit Diffraction

 If we add two more slits located side by side between the first slit and the screen, the light passing through each of the new slits is diffracted again such that the photons from each slit are bent across each path and combine to reinforce or cancel each other where they strike the screen.

 Double Slit Diffraction

Figure 4. Double Slit Interference

The result is an interference pattern (light and dark bands) on the screen as shown in Figure 4. If you block either of the two middle slits, the interference pattern disappears. If a photographic film replaces the screen and the intensity is reduced so that only a few hundred photons are sent through the double slits before the film is developed, the interference pattern will be made up of individual dots organized in a pattern that duplicates the interference pattern. Keep the film in place long enough and the patterns become more complete. Put a cover over one of the slits and the film still shows dots, but no interference pattern, only a diffraction band. Put a detector in one of the slits and the interference pattern also disappears.

Now if the light source is reduced in intensity enough to send only one photon at a time, a weird result can be seen if the photographic film is left long enough (days or even months in a very dark box) where both slits are left open. The interference pattern continues to develop on the film, even though there is no possibility of interference (or even photon bumping) unless the individual photons go through both slits somehow.

Part of the current explanation is that the photon goes both ways, but any measurement (putting a detector in the path) always disturbs the measurement. In fact a whole class of quantum theory has developed around the inability to make precise measurements due to the measurement disturbance problem. How do we explain this quantum weirdness?

A Matter of Relativity

There are two processes going here. One process is the real time that our experimenter sees, about 1 nanosecond per foot of photon travel. The photon is traveling through the experiment with real and measurable delays from the emitter to the first slit and from there to the double slits and from there to the film. The other process is that the photon’s relativistic path is zero so it is in contact with the film and the emitter at once and all of its paths in between are of zero length and require zero time. All paths that can lead to the same path are conjoined. Time of flight and distances for the photon expand only as it passes through the setup. The photon and the observer see simultaneous events differently. All the events are simultaneous to the photon, but none are to the experimenter.

All the elements of our experiment have no depth and seem to be congruent as if they were paper cutouts that have been bonded together with the emitting source. As observers, we can’t see it. As the photon leaves one element of our experiment, such as the first screen with one slit, the double slits are squeezed down to a point and plastered across its nose. The photon easily fits across both slits of the second screen as the distances to them are zero and thus the distance between them is also zero. Indeed it fits across the entire second screen, but the edges are less distorted. Since the photon is also plastered across the slits, everything behind the slits is also plastered there – the entire path is available at one instant as in Figure 5 a. The photon is able to take all paths (even simultaneously) that lead to a common point because they are all in front of it as it enters our experiment, and zero distance separates all the paths. No amount of fiddling with flipping mirrors or detectors will fool the photon into disclosing its path because the mirrors and detectors are also plastered to the photon’s nose throughout its (instantaneous) flight. The mirrors and detectors are in place when the photon makes its decision or they are not. The result is path shut or open.

As the photon moves from the first screen to the second, the second screen moves with it (attached to its nose) until it reaches its normal (real world as we see it) dimension and then expands as the photon moves into the slits as in Figure 5 b. Portions perpendicular to the path of the photon become normal size and atoms from the edges again buffet the photon.  Everything behind the photon is of no consequence, gone – vanished.

Relativistic Double Slit

Figure 5. – Relativistic Double Slit

 From the relativistic point of view, the photon has a number of crisis points such as within the first slit. As it passes through the first slit, the atoms at the edge of the slit buffet it and the photon’s path is randomly diffracted from the original path.   The slit has grown to normal size (perpendicular to the photon’s travel) but now the photon is virtually attached to the entire screen containing the double slits in the background that represent the next crisis point or wakeup call. If neither slit is blocked, it has an opportunity to go through both.

Photon Recombining

Figure 6. Photon Recombining

I see the photon as being a packet of energy that obeys the laws of conservation of energy. It flows around the barrier between the two slits only if it can recombine on the other side without ever completely breaking into two separate pieces. It behaves almost like a perfect fluid and leaks through where it can, but unlike a perfect fluid, it cannot separate into multiple “drops”.

If the packet can meld behind the slit spacer as in figure 6, it does so before it separates in front of the spacer. The melding process takes place an integral number of wavelengths from the slits and results in a change in path that leads to an impact in the interference pattern, a pattern that can be calculated using the methods of QED.  As soon as the melding takes place, the photon separates in front of the slit spacer and begins joining the rest of the body already melded together, so that the photon is always a full packet of energy

If melding does not take place because of a blocking detector or some other shield, then the photon pulls itself into whichever slit passed the bigger portion of its packet and slips through that slit whole.  If it is the blocked slit, it is destroyed there.  If it is the unblocked slit, it comes though whole but does not interfere with itself because it did not meld around the slit due to the blockage in the other slit.  It may also be destroyed by the slit itself.   The photon is destroyed in the blocked slit or on the film behind the open one, never both. It makes no choice. In the case of a blocked slit, there is no recombination. The side with the larger energy pulls the photon through an opening if there is one and if that opening has a detector or blockage, it dies there.

The answer to the weirdness of photons seeming to interefere with itself is that it is due to the forshortening of the experiment due to the effects of relativity.

Next:  Polarized Light Weirdness Explained

Quantum Weirdness in Entangled Particles

Entangled Particles

Selecting which atom we use with careful attention to its excitation states can create entangled particles.  Some atoms emit two photons at a time or very closely together, one in one direction, the other in the opposite direction.  These photons also have a property that one spins or is polarized in one direction and the other always spins or is polarized at right angles to the first.  They come in pairs such that if we conduct an experiment on one to determine its orientation, the other’s orientation becomes known at once.   They are “entangled”.

Link to image EPR 

Figure 10 – Entangled Particles   

All of this was involved in a famous dispute between Einstein and Bohr where Einstein devised a series of thought experiments to prove quantum measurement theory defective and Bohr devised answers. 

The weirdness, if you want to call it that, is the premise that the act of measurement of one actually defines both of them and so one might be thousands of miles away when you measure the first and the other instantly is converted, regardless of the distance between them, to the complement of the first.   Action-at-a-distance that occurs faster than the speed of light?

Some would argue (me for instance) that this is more of a hat trick, not unlike where a machine randomly puts a quarter under one hat or the other, and always a nickel under a second one.  You don’t know in advance which contains which.  Does the discovery that one hat has a quarter actually change the other into a nickel or was it always that way?  Some would say that since it is impossible to know what is under each hat, the discovery of the quarter was determined by the act of measuring (lifting the hat) and the other coin only became a nickel at that instant.   Is this action at a distance? 

It is easy to say that the measurement of the first particle only uncovers the true nature of the first particle and the deduction of the nature of the second particle is not a case of weirdness at all.   They were that way at the start.

However, this is a hotly debated subject and many consider this a real effect and a real problem.  That is, they consider the particles (which are called Einstein‑‑ Podolsky‑Rosen (EPR) pairs) to have a happy-go-lucky existence in which the properties are undetermined until measured.   Measure the polarization of one – and the second instantly takes the other polarization.

A useful feature of entangled particles is the notion that you could encrypt data using these particles such that if anyone attempted to intercept and read them somewhere in their path, the act of reading would destroy the message.

So there you have it – Weird behavior at a distance, maybe across the universe.

Next:  Some Random Thoughts About Relativity

Quantum Weirdness for Tilted Glass

  Photons That Hit Tilted Glass

Individual photons directed at tilted glass have an option of being reflected or going through.  They can’t do both because they can’t be divided, or so we are told.  Yet some experiments seem to imply that they sometimes take both paths unless a detector is in place. 

Tilted GlassTilted glass acts like a sort of beam splitter.  It either goes through or bounces off  (or sometimes absorbed). 

QED can easily compute the probability dependent on the angle.  Some go through and some reflect and the angle makes the difference.  You can adjust the angle to get a 50-50 chance of reflect or go through.   

If you use other beam splitters to put the two beams back together you can get an interference pattern, not unlike the one depicted in the double slit experiment.   The beam goes both ways, but one path is longer and so when they come back together, they interfere with each other.

However, if you turn the light down so only one photon at a time goes through you still see the same effect, implying the photons go both ways.   If you leave the single-photon-at-a-time beam on long enough and have a good film in an exceptionally dark room, the outcome will be a well defined interference pattern. 

How can single photons being emitted minutes apart interfere with each other?   How can a photon that can only go one way or the other interfere with itself?   QED cannot explain this quantum weirdness for single photons.  It can predict the pattern but cannot explain it.  Every indication is that when no detectors are present, the individual photons somehow split.

There are some very sophisticated delayed choice experiments involving beam splitters.  There are super fast detectors that can be switched into the photon beam after it goes through the splitter. In other words, spit a photon at the splitter, calculate when it reaches it (about 1 nanosecond per foot of travel) and then switch the detector into the path behind the splitter.

The idea is to try to trick the photon into “thinking” there is no detector so it is ok to split, then turning on the detector at the last moment and try to catch the photon doing something it is not supposed to do, breaking laws along the way.  If it arrived at a detector in the reflected path and was also seen by the detector behind the splitter, some law has been broken and the mystery solved – figure out a new law. You do this randomly. If the photon goes both ways, it can be caught by the detectors.   It never does.

The physics says that if you try to make the measurement, it will disturb the experiment. And so every test seems to verify that fact. Whenever a detector is present there is no interference pattern. Whenever the detector is absent, the pattern reappears.

There is an argument that the photon must go through the glass whole since the photons transmitted through the glass are actually retransmissions within the glass, not the same photon that impacts it.  That argument then says that the other path has to either have had no photon or a whole one also (creation of energy not allowed).   It also says that the photon must retain a whole packet of energy.   Yet single photons seem to interfere with each other.  QED cannot explain why.   I hope to do so.

Next:  Entangled Particles

Polarized Light Weirdness

  Polarized Light Weirdness

Polarized CrystalsThe same weirdness problem arises when we pass light through polarized devices as in the figure at the left.  The devices are calcite crystals in which the light is split into two parts, a horizontal (H) and a vertical (V) channel.  If we try to send individual photons through, they go through only one channel or the other, never through both, and those that come out of the H channel are always horizontally polarized, those that come out of the V channel are always vertically polarized as we might expect.  

It is possible to orient photons to other angles at the input.  One such arrangement is to adjust them polarized so that they are tilted 45 degrees right or left as illustrated in the same figure.   If we orient the input to 45 degrees, tilted right, we get half of the photons coming out the H channel and half out of the V channel, one at a time, but these are always horizontal and vertical polarized, no longer polarized at 45 degrees right.  

Reversed Crystal setupNow comes the weird part.  See the figure at the left.  If we put a second calcite crystal in line with the first one, but reversed so that the H channel output of the first goes into the H channel of the second and the V channel output of the first goes into the V channel of the second, we expect the output to consist of one photon at a time (and it is), but since the first crystal only outputs horizontal or vertical polarized photons we expect only horizontal or vertical polarized photons out of the second crystal.  

 Quantum Weirdness at work.

However, if we test the polarization of the output, we find that the photons coming out are oriented to 45 degrees right, exactly like the input.  Individual photons go in at 45 degrees right at the input, are still individual photons but horizontal or vertical oriented in the middle, but come out oriented 45 degrees right again at the output!  Somehow the two channels combine as if the individual photons go through both channels at the same time, despite rigorous testing that detects only one at a time.  Quantum Weirdness at work. 

The polarization problem, like the double slit problem, is often called a quantum measurement problem.  An often-quoted theory is that the photon does go both ways, but any attempt to detect/measure one of the paths disturbs the photon such that the measurement results in a change in the path of the photon.

My theory reafferms the idea that it does go both ways, but in a manner you would not expect.  We will get to that later.  Next I want to mention  Quantum Weirdness in Glass

Double Slit Weirdness

Double Slit Weirdness

Single Slit ExperimentWhen a proper light source (coherent – light from a single source all at the same frequency) is placed in front of a screen with a narrow slit, the light is diffracted (spread out) as it goes through the slit and appears as a shaded band centered on a screen or photographic film.  The light is scattered by the edges of the slit as shown in the first figure.

Single Slit Diffraction. 

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Double Slit Setup

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Double Slit Setup

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Double Slit InterferenceIf we add two more slits located side by side between the first slit and the screen, the light passing through each of the new slits is diffracted again such that the photons from each slit are bent across each path and combine to reinforce or cancel each other where they strike the screen.    The result is an interference pattern (light and dark bands) on the screen. 

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If you block either of the two middle slits, the interference pattern disappears.  The diffracted light from the forward slit is diffracted again by the open slit in the second screen, but no interference pattern emerges because the other slit is blocked.

It can be shown that when both slits are open, the interference pattern seen can be duplicated by drawing the photon as a wave at the frequency of the source at each of the second screen slits and then combining the resulting waves by addition and subtraction of the waves where they mix behind the slits.  This addition and subtraction of the waves into the interference pattern seems to prove that the light is a wave.   Indeed, if the light is a particle, it would imply that their interaction cancels particles in the dark areas or at the very least, they bump each other into specific areas on the screen.   We know that does not happen. 

However, if you replace the screen by a photographic film and reduce the intensity so that only a few hundred photons are sent through before the film is developed, you will find that you can see the individual places the photons hit as dots on the screen.  You can also see that the individual dots are organized so that they fall into the bands of the interference pattern and duplicate it.  Keep the film in place long enough and the patterns become more complete.  Put a cover over one of the slits before you start and you will find that the film still shows dots, but no interference pattern, only the diffraction band. 

The dots seem to prove that the light is indeed a particle, not a wave, but yet they seem to interfere with each other like a wave when both slits are open.   A mystery, but not necessarily weird.

Quantum Weirdness at Work

Now if the light source is reduced in intensity enough to send only one photon at a time, a weird result can be seen if the photographic film is left long enough (days or even months in a very dark box) where both slits are left open.  The interference pattern continues to develop on the film, even though there is no possibility of interference (or even photon bumping) unless the individual photons go through both slits somehow. 

A test for this is to remove the film and put a detector behind the slits.  But then we find that the detectors only detect one photon at a time and only through one slit or the other, never both.   The interference pattern never develops if either slit is covered.  Quantum Weirdness at work.

There have been some very inventive tests such as using super-fast mirrors behind the double slits that switch in and out of the path between the time the photon leaves the slit and before it arrives at the screen.  The results are the same.   When either slit is covered, the interference pattern disappears but when both are open it reappears, even if the photons arrive only one at a time.

Since the photographic plates seem to prove that the light is a photon and never goes through both slits, the quantum weirdness problem arises and part of the current explanation is that the measurement (putting a detector in the path) always disturbs the measurement.  In fact a whole class of quantum theory has developed around the inability to make precise measurements due to the measurement disturbance problem.

Quantum Electrodynamics (QED) explains this behavior using simple diagrams to show the probabilities of where the photons will land.  It cannot predict where any one photon will land, but given enough photons, it can predict the pattern very accurately.   QED does little to explain the weirdness of it all.

I have a simple theory on how all this works that I will get to eventually.  Next I want to talk about Polarized Light Weirdness.