Examining the Slit Experiment

[IDMclean]

Taken from the light particle duality article

As I have placed as objection in the past, why must I accept that the photon, electron, etc went through the slit at all?

This seems an easy question to answer: because when you cover the slits, no photons, electrons, etc. appear on the other side at all.

 

That would seem to be the easy answer, but if you ask the question of if the barrier is massed, and mass is 90% empty space, then why doesn't the photon merely pass through the barrier?

 

This of course is without getting into the whole dual nature of the barrier itself or the absorption of the barrier.

 

What I mean is that one can not simply neglect the influence of the barrier in the experiment. It has mass, and energy. It curves the trajectory of the photon/electron/etc. It has a measurable effect on the surrounding space. So once again, I must ask why must I accept that the photon passed through the slits? Also in the case of a closed barrier, why must I accept that the photon is still contained within the experiment area?

[Boerseun]

Well, simply put, if you close the slits, nothing goes through. This is easy enough, a torch and your hand should do the trick.

 

How, and why, or rather, why not the photon passes through the mass barrier, when that mass 99% empty space, is a matter for optics. The slit experiment is about light exhibiting interference patterns under certain conditions, putting the 'wave' part of light's 'wave/particle' duality on display. And the freaky thing is that a single photon will interfere with itself. Now that's just plainly weird.

 

What I want to know, seeing as we're discussing this particular experiment, is how on earth do they guarantee that a single photon was released in order to produce the results? Who counts photons? How do you count photons? I think there's a lot to the physical structure and properties of light that we don't fully understand yet. I'm actually of the opinion that light is completely different than what we think it is. But that's just me.

[freeztar]

I suppose they have a highly callibrated photometer for measuring photon(s)...

 

I agree with you though Boer...I think light is something entirely different than we think and it will be a long time, if ever, before we fully understand it.

[pgrmdave]

So once again, I must ask why must I accept that the photon passed through the slits? Also in the case of a closed barrier, why must I accept that the photon is still contained within the experiment area?

 

Well, when we set up the experiment, we have something that produces photons, the slit, and a detector. When we have a slit present, we are able to detect the photon on the other side. When we don't have a slit present, the photon is not detected. Clearly the presence of the slit allows the photon to travel from the producer to the detector. Perhaps there are reasons other than the possibility that the photon travelled through the slit, but then why would the presence of a slit have an effect? Why the photon doesn't travel through the barrier doesn't really have any bearing on the question - the fact is that it stops the photon.

[Qfwfq]

That would seem to be the easy answer, but if you ask the question of if the barrier is massed, and mass is 90% empty space, then why doesn't the photon merely pass through the barrier?

Sure, especially if you use a barrier made of glass! :hihi:

 

Perhaps there are reasons other than the possibility that the photon travelled through the slit, but then why would the presence of a slit have an effect?

Excellent! :shrug: This is exactly the matter of the whole issue: If we hypothecically consider that the particle went through one of the slits, then why does the other have any effect?

 

Essentially, what the experiment shows is that there is something non-local about how the outcome is determined for each single particle. Quantum formalism describes this with great success but we don't understand exactly how the observable outcomes are determined.

 

What I want to know, seeing as we're discussing this particular experiment, is how on earth do they guarantee that a single photon was released in order to produce the results? Who counts photons? How do you count photons?

Basically, knowing the nature of the source and the typical duration of each emission, it's enough to have few enough emissions per unit time so that, given the length of the apparatus and therefore the time of transit, the great majority of them won't be overlapping. It's a statistical consideration. Today there's a variety of possible techniques for counting photons, when I was in fourth-year lab we used an old photomultiplier tube cooled with liquid nitrogen and a spectrometer to cast away most of the "noise" i. e. triggerings not due to a photon coming in. Technology does however offer some more refined things today.

 

I think there's a lot to the physical structure and properties of light that we don't fully understand yet. I'm actually of the opinion that light is completely different than what we think it is. But that's just me.

It isn't just a matter of light, it's about anything. Quantum formalism describes the way reality is, when things are in a coherent state.

[LaurieAG]

Essentially, what the experiment shows is that there is something non-local about how the outcome is determined for each single particle. Quantum formalism describes this with great success but we don't understand exactly how the observable outcomes are determined.

 

Hello Q,

 

If a photon is a particle that orbits in a very small radius around its center while moving in a fixed direction (like an electron orbit), this width, the width and depth of the slits, and the actual direction of the spin (relative to its proximity to either side of the slit) would have to be taken into consideration in any experiment, conceptual, quantum or otherwise.

 

A clockwise orbiting photon would be blocked by the barrier while an anti clockwise orbit would deflect inside the slit (on the slits side) if they were both shot at the slit from the exact same location (i.e. within one radius length of rotation of the slits edge).

 

If your measuring equipment (or experiment) couldn't determine, or didn't consider the radius of rotation of the photon the result would appear uncertain. This is also consistent with the photon being a particle which produces a wave when you plot the forward motion of its orbit over time. (i.e. the particle is now (no orbit considered) and the wave is the orbiting particles path over time).

[Erasmus00]

What I want to know, seeing as we're discussing this particular experiment, is how on earth do they guarantee that a single photon was released in order to produce the results?

 

This is actually a topic of much debate in the world of quantum optics. However, we could just as easily do this experiment with electrons, where it is much easier to deal with the particle nature.

-Will

[IDMclean]

Well. I suppose that helps to clarify the details of the experiment, however it does not statisfy my sense of reasoning.

 

I understand and accept that the medium the photon is passing through/by/around/under/over/etc has an effect. Elementry, matter bends the path of light through space-time.

 

What I am questioning is whether or not the interpertation of the outcome of the experiment is correct, within reasonable certainty. There are, in my mind and observation, many possible explinations for the experimental outcome.

 

In my own view, I do not see why it is not possible, if not reasonable, that the photon does not merely leave the detecting area when the slit is closed. Following the path of least resistence/action. For that matter why does the interferance pattern have to be the result of the (same) photon impacting the surface of the detector?

 

I primarily think of things like Faraday cages, and other similar electromagnetic phenomena in this regard. Like I said, how can one neglect the matterial barrier, or the matterial observation equipment in this experiment?

 

As I have attempted to explain previously on this site, what if fundamental matter is point-like, and without mass-energy. In and of itself? What if mass-energy is the measurement of a ray between fundamental matter?

 

This question is non-trivial. If photons interact only approximately to how we would think and calculate then it is possible that the whole results of the experiment are thrown into question. Whether it is done with a photon or an electron.

 

Eitherway, assumptions are being made in the interpertation of the data which may not be entirely justified. Common-sense, sure. Scientifically, logically and mathematically sound, maybe not.

[Drum]

Well. I suppose that helps to clarify the details of the experiment, however it does not statisfy my sense of reasoning.

 

I hope I am not intruding here. This is my very first post and I don't know a lot about Science or Maths .... but perhaps I may be able to go a little way towards satisfying your reasoning. In your original thread #1 you had a problem with the barrier.

 

Originally Posted by KickAssClown That would seem to be the easy answer, but if you ask the question of if the barrier is massed, and mass is 90% empty space, then why doesn't the photon merely pass through the barrier? ......

 

Just for the moment forget about the photon and replace it with an electron. Electrons have negative charge .. The barrier is made from cardboard, steel or anything else you like and it doesn't matter if it is 99% space. The fact is that the barrier is a substance made of molecules locked together within an electron field. It is stable, it has the correct electron count in its shells around the positive protons and it does not want any more. The charge is balanced. You are also made of the same electron binding. Negative charges repel. This is why you cannot walk thru a wall, when you get close, the wall's negative electron field repels you as much as your negative electron field repels the wall, not the fact that the wall is solid, nor that it is 99.999% space. A bullet can tear through a cardboard wall because its electron field is tighter and 'locked' in a more stable 'matrix'. It has enough acceleration (increased mass) to literally overcome the negative repulsion and breaks the electron bonding. Remember, this is not Science, just rough understanding. The next thing in your thread was that you cannot ignore mass

 

Originally Posted by KickAssClown What I mean is that one can not simply neglect the influence of the barrier in the experiment. It has mass, and energy. It curves the trajectory of the photon/electron/etc. It has a measurable effect on the surrounding space.

 

Unfortunately, in Quantum Mechanics you do have to ignore mass. The mass that effects the curvature of space is to do with Classical maths. That is, the maths of Newton and Einstein. Einstein's principle of equivalence states, and very elegantly proves, that gravity and acceleration can be considered as one and the same thing. Lets not go there yet. Very, very basically classical maths says that to leave one location and arrive at another you need to travel a trajectory that can be calculated. In other words, you know where and when you are at any particular point and you can prove it with math. This enables us to build tall buildings and travel faster than the speed of sound. It ensures that commercial flights arrive at their destinations on time. It governs our Macro world.

 

Quantum mechanics says that if you want to know, with any degree of accuracy, the location at any point you cannot know with certainty the trajectory taken because all possible trajectories have a probabilty of being correct. Lets not go there yet.

 

You cannot introduce gravity (acceleration) into quantum mechanics. It turns into nonsense. Sounds weird I know, but without our grudging acceptance of Quantum mechanics there would be no computers, no smoke detectors, no internet and so on. We have to live with it.

 

These two forms of mathmatics do not agree and yet the results of QM never break Einsteins rules of relativity. String theory bridges these two, but because it can never be proven it is relegated to an Hypothese along with religion etc

 

We are now talking about QM only: You shine a torch on the dual slits and the hot filament inside the bulb ejects trillions of electrons at much less than the speed of light, many of which strike the first barrier and each electron gives off one photon of light. They take no further part in the experiment. Those that pass thru the slits are unaffected by the negative charge of the barrier. (Trust me) They strike the second barrier in a bar pattern and each electron gives off one photon of light which enables us to see the pattern.

 

Of course its obvious (or is it) that the trillions of electrons pouring through the two slits are colliding and jostling each other and therby form a bar pattern as they strike the wall.

 

We close one slit. Now all the electrons have to pass through one slit only and of course there is no bar pattern, just a blur on the wall. This too, is obvious.

 

So now we slow the electron emission rate to only one every ten seconds. (very easily done) Now there can be no jostling and elbowing for position. Each electron has ten seconds to himself to get to the wall. With only one slit open, and after recording where each electron strikes with a geiger counter, the same blur pattern is built up slowly but surely. This too, is obvious.

 

Now we are entering the really weird part of QM. We open the second barrier and allowing each lonely electron 10 seconds to arrive at its destination we set the geiger counter to record and head of to make a brew (coffee). When we get back after a cigarette and a brew the geiger counter gleefully tells us that the bar pattern is back.

 

How can this be ?? The electron had to go through one or other of the slits, there were no others electron to create wave interference ?? What the fuk is going on. One particle cannot create a wave. If the particle is a wave then what the fuk is it waving with ?

 

And there you have QM in a very simple nut shell. Everything is a wave. How does it wave ?

 

Turns out it is a very special wave..... not like a water wave or tsunami, nor a mexican wave like at the football. Its a probability wave.

 

Whats a probability wave. QM tells us that prior to striking the second barrier the electron particle/wave had a probability of going through either slit in the first barrier. In other words there are 2 paths, each with a probability of 50%. QM says that each probability is a possibility.... further ... if its a possibility it WILL happen. In other words it must always equal 100%.

 

Remember you can never know 100% trajectory if you know the arrival point. In other words the particle/wave went through both slits with a probability of 50% and waved with itself. True. If there were 3 slits it would have gone through all 3 with a 33.333% probability. and so on if there were 4, 5 .... remove the first barrier and you have an infinite number of paths each with a probability.

 

If you put the geiger counter on one of the slits to determine its path by detecting it (or not detecting it) you simply change the arrival point to that location and from there to the wall it travels with 100% known trajectory and forms the blur again as opposed to the pattern. The same as if there was only one slit.

 

Quantum mechanics says that all matter has this wave particle duality. This means that prior to observation/interaction all things have a probability of being absolutely any where in the universe. Another way of thinking about it is that the particle is spread like a giant elastic sheet throughout the whole universe, thinnest where the probablity is least, thickest where its most probable. The instant you interact with the observed particle its location is now known 100% and therefore its probability of being anywhere else collapses to zero. This really means that the particle could have been in a distant galaxy, of course with a very very very minute extremely small probability immediately prior to your observation

 

In general, the highest probabilities for anything are where they are most likely to be. Thats why life always behaves as we expect, The odd hiccup, such as a Tyranosaurus Rex, appearing in front of your eyes for a nano-second is passed of as 'I must have been seeing things'. :) But if you set out to walk through a wall and you keep at it for an enternity, no matter that the probability is an infinity to one... given an infinite numbers of tries you will appear on the other side at least once. Wow, I am very sorry if this post has gone on too long... Remember its only a rough explanation and I hope it helps

 

cool bananas ...... drum

[IDMclean]

I quite enjoyed your explanation, Drum. It hit some of my points of contention, but missed a few others. Obviously missed two of my major points of contention. Kudos though.

 

Just for the moment forget about the photon and replace it with an electron. Electrons have negative charge ..

 

Drum, I know you haven't been here at hypography long enough to necessarily read my other posts regarding the nature of mass-energy, space-time, charge and matter.

 

Consider a simple correspondence fact about the photon and electron. They both have mass-energy and thus are identified as forms of matter. The difference between them is minor when you go into it far enough. They both have net charge, mass-energy, spin, etc (same property-types).

 

Now consider that the detector, the slits, and the barrier are all composed of material, that is they all have the properties of net charge, mass-energy, spin, etc.

 

By identity the electrons, photons, neutrons, and protons have no formal property differences from one another. That is they all have the same properties, though different variances in the values of those properties.

 

Why is this all important? Well if we conjecture for a moment that our emitted particle, box, barrier, slit and detector are a homogeneous soup of matter varying only in values of properties, how are we to discern that the particle we shoot is the particle we catch?

 

Which I surmise in my question of "why must I accept that the particle went through the slits at all?"

 

Classical physics sees the particle as one single piece (or collection of tightly held pieces); Quantum physics retains but refines this picture of the particle. I question the very validity of that model.

 

What I am questioning is the results of a material experiment within which I believe that certain key factors are being neglected, such as the very structure of matter at it's fundament.

 

Neither Classical physics, nor Quantum physics give a satisfactory explanation (theory) of matter. Here is a challenge. Give me two seperate theories of matter. One classical and one quantum. Preferably from the standard model.

 

Thanks for listening and I look forward to your reply.

 

-sign

The Klown.

[Buffy]

Trying to understand what you're doing so here goes:

Quantum physics retains but refines this picture of the particle. I question the very validity of that model.

Why?

 

This is not a facetious question: I'm trying to get you to be explicit about what bothers you about Quantum Mechanics. Knowing you, I know that this is probably much more sophisticated than "it just doesn't make sense from my macroscopic experience of the world."

What I am questioning is the results of a material experiment within which I believe that certain key factors are being neglected, such as the very structure of matter at it's fundament.

 

Neither Classical physics, nor Quantum physics give a satisfactory explanation (theory) of matter.

What makes Quantum theory's explanation unsatisfactory?

 

I think anyone who's studied it will agree its hard to grok that is well attested to by Feynman, and many others. There are certainly unknown boundaries of the standard model, and it definitely is hole prone when it comes to trying to integrate gravity, but claiming that its description of matter is incomplete is attacking it at its strongest and best-supported-by-data point!

 

So expound a bit KAC: what's your beef?

 

A wavy particle,

Buffy

[Drum]

Kickass ....

Thanks for your kind words. Its true that my last post was my first and that I have read very little of yours, or others posts on this forum.

 

I am not a Scientist and I know very little about maths. I will try a little more detail

 

..KickAss ..Consider a simple correspondence fact about the photon and electron. They both have mass-energy and thus are identified as forms of matter.

 

If you consider the electron as occupying an 'orbit' or 'blur' around a nucleus, then only certain 'orbits' are allowed. A raw description of allowable 'orbits' would be that the 'diameter' of the electron must divide into the circumference of the orbit exactly, whether it be 10, 20 or 11 times. if an allowable orbit had a circumference = (ten electron diameters) then the next larger allowable orbit would be a circumference = (11 electron diameters)

 

Of course this is an explanation that does not exist in reality.... but it is conceptual.

 

Each time an electron gains or loses energy it 'jumps' to the next available orbit. Remember this 'jump' is not really describable as it is part of the probability of all possible paths. However, each time the electron does this it gives of exactly one Photon.

 

Electrons are massive objects, while Photons have zero mass (at least zero invariant mass ... which for our purposes is the same).

 

This difference can not really be considered minor. The reason I suggested electrons in the double slit experiment is that they are 'heavy' and travel 'slow' whereas a Photon, having zero mass zips along at Light(-ening) speed. Electrons are very easy to keep track of, look at the example of your TV screen or computer monitor if you still have the CRT type. if there was no barrier at all and we fired a single electron at the target it will register.

 

The double slit experiment was first performed many years ago, 1801-2, I think. Since then many, many times it has been proven. it has been followed by the Delayed-Choice double slit experiment...... If you have a problem with the double slit then be prepared to be outraged by the delayed choice. The most shocking implication is that the past can effectively be altered by the future.

 

All this culminated in an alienation between two camps ... On the one side Einstein, Podolsky and Rosenberg, known as EPR ... and on the other, all the new hot, young quantum physicists.

 

The EPR side threw up a challenge that absolutely stymied the QM camp in their tracks. The best answer they could come up with was that 'in the world of the Quantum such questions are not allowed' .... pretty lame, but from a scientific viewpoint perfectly valid.

 

The along come an unknown guy called Bell. He suggested a way that the EPR Paradox could be tested ... up to this point it had been thought impossible to test. In the early 1960s (or possibly late 60s) this test was conducted and guess what .... it proved absolutely beyond doubt 100% that the universe is not local, and that Classical mathematics is no longer the most valid description of our Universe.... it also spawned many false religions and cults as people read mystical things into it.

 

Once you have a handle on Bell's Theorem you will never look at reality in the same way again. You can be assured that Bell and the other physicists that successfully bought his ideas to experimental conclusion are people of immense skill and integrity. They can easily detect particles used in experiments from amongst the particles making up the machinery of the experiment..

 

 

KickAss ..Here is a challenge. Give me two seperate theories of matter. One classical and one quantum. Preferably from the standard model.

 

I am afraid that it will take someone a lot better than me to do that.

 

From my own personal opinion, I believe that in the beginning there was a fundamental substance (matter) that was somehow put in motion (energy) ... The Universe is the result. Once you have matter in motion you only need a Newton to say F=MA, an Einstein to correct the absolutes by fixing the Speed of Light relative to all observers, then go on to say that Gravity is nothing more than Acceleration and it is also fixed relative to all observers.... but finding out what that bastard fundamental substance (matter) is ... you will need Quantum Mechanics .... and there goes the neighbourhood..!!

 

Drum

[Fatstep]

Keep in mind I know nothing about this topic.

But is the answer not because it isn't a single layer of atoms?

The hundreds/thousands/millions of layers of atoms form a barrier and stop any/everything from coming through?

[CraigD]

… if you ask the question of if the barrier is massed, and mass is 90% empty space, then why doesn't the photon merely pass through the barrier?

…

in the case of a closed barrier, why must I accept that the photon is still contained within the experiment area?

For the first question, “why doesn’t the photon pass through the barrier”, we should start by noting both that, in a classical sense, any barrier is much more than 90% empty – if you consider an atom’s nucleus (classical diameter about [math]10^{-14}[/math] m) and electrons ([math]10^{-18}[/math] m) to be “solid”, and the atom ([math]10^{-10}[/math] m) to be “hollow”, a typical carbon atom (6 electrons) is about [math]1 - \frac{6 \cdot (10^{-18})^3 + (10^{-14})^3}{(10^{-10})^3}[/math] = 99.9999999999 % empty. Even densely packed carbon atoms – diamond (3513 kg/m^3) or graphite (2267 kg/m^3) add about another division by 2 to its density, so a typical dense solid is about 99.99999999995 % empty. Using this figure, we can calculate the “classical” probability of a small, uncharged particle passing through a 1.5 m slab of graphite ([math]10^{10}[/math] packet atoms), and get a surprising (and strongly contradicted by observation) [math]0.9999999999995^{(10^{10})} \dot=[/math] 99.95 %.

 

From this, we should conclude what early 20th century physicists did: there’s something very wrong with viewing photons and sub-atomic particles as tiny little classical objects.

 

A detailed explanation would recapitulate most of modern physics, so jumping to the end, we explain why even a thin (1 mm, about 3000000 atoms) layer of something like graphite appears to allow effectively 0% of photons of visible light to pass through it as follows:

The electrons in the carbon in graphite are free to assume many different energies. For every frequency of visible light an electron is available to change energy, absorbing the photon. The electron then emits one or more photons, most of them either virtual photons of magnetic force that carry the energy to it’s atom’s nucleus and electrons in surround atoms in a phenomenon known macroscopically as heat, or if the electron’s energy is great enough to allow it to reduce its energy by a great enough amount, as one or more photons of visible or invisible light, in a phenomenon known macroscopically as glowing. If the electron emits a photon of the same energy as the one absorbed, the phenomenon is known as reflection. Graphite doesn’t reflect much.

 

On the scale of photons and electrons, and other fundamental particles, the idea of classical size and collisions isn’t useful. Instead, we must consider their interaction to be a summation of the wave functions of the photon and a superposition of the electron at various energies. Mathematically, this is very complex, but despite the difficulty we humans have calculating it, appears to be what huge numbers of photons, electrons, and other fundamental particles do to produce macroscopic phenomena, such as opacity to visible light

 

For the second question, “why must I accept that the photon is still contained within the experiment area?”, referring to the preceding explanation, we can see that the photon is not contained by the opaque barrier. It is absorbed, ceasing to exist, by an electron, which then emits photons of other than visible light.

 

Note that none of these explanations require consideration of gravity. The whole of observed macroscopic optics is explained by quantum mechanics, and would work about the same if gravity did not exist.

 

(All of the data used in this post is available in numerous references, such as wikipedia)

[silverslith]

Love to hear you describe the

Delayed-Choice double slit experiment......

Drum.

:)

[IDMclean]

I quite enjoy hearing all about the various facets of the double slit experiment, with different variables and all.

 

However, I reconginze that my beef as Buffy says, is not understood in full.

 

The reason I gave the challenge to present the classical and quantum theories of matter is because I know within reasonable certainty that there exists no such theories. Not formally anyway. My physics book has a chapter early on that describes basic concepts such as mass-energy and matter, but no where in it does it contain a standard theory of mass-energy or matter.

 

What it does explain is this, Mass-energy are properties of the object matter. It further explains that these properties are the device by which we detect the underlying object, matter.

 

Now I have a hard time expressing concisely why this fact bothers me in the context of the double slit experiment but I do know that if someone takes a little time and effort to sit and think about the structure of the experiment both microscopicly and macroscopicly they will realize, at least to some degree, that the experimental results are reflective of a structure. What is neglected in all this discussion and interpertation is that the experiment in total is matterial. Everything about it.

 

Wheather we talk about electrons and their orbits, photons and their phantom rest mass, wheather we are using carbon, cardboard or steel for the barrier. We are using matter for the entire construction. Now in classical experiments regarding non-quantum scale experiments we could neglect such things as the truely fundamental structure of matter, however what this experiment does goes far beyond that scale. It obviously enters into a different realm of scale.

 

Take for instance CraigD's comment:

On the scale of photons and electrons, and other fundamental particles, the idea of classical size and collisions isn’t useful.

 

CraigD here asserts, implicitly, that what is being played with is fundamental particles, I would assert that what is infact being played with is not fundamental, though I would conceit that it is made up of fundamentals.

 

I am not necessarily saying that the experimental results are incorrect, what I am disputing, what I am remain skeptical of is the interpertation of the results.

 

My reasoning for remaining skeptical arrises from the simple fact that these interpertations, by even the most knowledgable, come about without a real scientific basis. There is no theorem of mass, no theorem of matter, no theorem of energy.[math]^1[/math] [math]^2[/math]

 

As such what can be really said about the interaction of matter particles/waves? When the term matter, mass, and energy are all so ill defined?

[Erasmus00]

My reasoning for remaining skeptical arrises from the simple fact that these interpertations, by even the most knowledgable, come about without a real scientific basis. There is no theorem of mass, no theorem of matter, no theorem of energy.

 

As such what can be really said about the interaction of matter particles/waves? When the term matter, mass, and energy are all so ill defined?

 

Note: I abridged the above. What do you mean by a "theorem of mass, matter and energy?" I ask, because as far as I know, mass, and energy are very well defined in standard theory. What is not known is WHY certain particles have certain masses.

 

However, once experimentally measured, mass is a very well defined property, as is energy.

-Will