The Twin-Slit Experiment
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The Twin-Slit Experiment
Feel free to comment on or critique the below. I've numbered the paragraphs for ease of reference. If you disagree with, or want clarification on, anything written below please say so with reference to the paragraph number.
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1
Consider a sealed glass tube with almost no air in it. (It's been sucked out by a pump). At either end of the tube there are two electrodes (they're conventionally called the cathode and the anode) and a voltage is applied across those two electrodes by attaching a battery outside the tube.
2
An electric current is seen to be flowing around the circuit. We know from past experiments that electricity doesn't flow through glass. So the current must be flowing through that near vacuum between the cathode and the anode.
3
If the anode is moved closer to the cathode, so that the arrangements is as shown below, and a special coating is applied to the end of the tube, the coating glows when the current is flowing and stops glowing when the current isn't flowing. For brevity, we'll call that coating "the screen".
4
If an object is placed in the tube, as shown below, a shadow of that object appears on the screen. So the current flowing across that near vacuum must be causing that glowing, and it must be blocked by solid objects placed in between. We could call the thing flowing across that vacuum, and being blocked if there's something in the way, "cathode rays". It's as good a name as any, for now. We could also, for brevity, call the cathode/anode system a "ray gun". It's a lame name, but it'll do.
5
If the anode part of the "ray gun" is shaped so that there is only a small hole for the thing that's causing the current to flow ("cathode rays" we're calling it) to get out, the glow is confined to a small dot on the screen. So the metal housing of the anode must stop these "cathode rays" from flowing.
6
If we place a powerful magnet on the outside of the tube, the dot on the screen moves. If we apply an electric field across the tube, the dot on the screen also moves. So the cathode rays must be influenced in some way by magnetic and electric fields.
7
If air is allowed into the tube, the glow/dot rapidly gets dimmer and fuzzier and then goes away. As the air is gradually removed, the glow/dot gradually comes back and becomes sharper. So air must also stop the cathode rays, a bit like solid objects did. Perhaps the rays bump into the air molecules? There are various reasons why a vacuum pump can't literally remove every single air molecule. (Vacuum physics/engineering is an entire subject in itself.) That's why we've called it a near vacuum. But it seems that when we've pumped out enough of the air for that dot to appear on the screen, we can say that we've done enough for most of that cathode ray to continue unimpeded to the screen.
8
If, instead of air, we allow a particular type of low pressure gas into the tube, we see a glowing line going from the ray gun to the dot on the screen. We could theorise that as the cathode rays flow from the ray gun to the screen, some bits of them hit the gas molecules and cause them to emit light. And that way, if we want to, we can see the path of the cathode rays (or at least, the ones that don't hit the gas molecules and carry on). Maybe it's a bit like when you shine a laser across a room and can only see it crossing the room if there are dust particles or smoke for it to hit along the way? Otherwise you just see the dot on the thing that you're pointing the laser at. Maybe.
9
If we reduce the voltage, the brightness of the dot on the screen reduces. So whatever it is that is flowing (whatever these "cathode rays" are), more of it flows when the voltage is higher and less when the voltage is lower.
10
If we reduce the voltage so that it gets very low, there comes a point when the dot brightness is no longer constant for a constant voltage but starts to vary, apparently at random.
11
If we reduce the voltage still further, the dot starts to flicker on and off. When it's off it is completely off. When it's on, it's always the same brightness. Reducing the voltage further doesn't reduce the brightness when it's on any more. It just increases the average time for which it is completely off. The lower the voltage, the bigger the gaps between the times when it is briefly glowing. But the length of any individual gap appears to be random.
12
We can never know for sure what underlying mechanism might be causing the behaviour described in (11) but one model that would fit the observed behaviour so far would be the thing which flows from ray gun to screen arriving in discrete lumps. And since the flashes are all the same brightness, those lumps could be all the same size. Or at least we can say that whatever property they have which causes the coating to glow exists in equal amounts for each lump. We get lumps, all with equal amounts of that property, punctuated by nothing.
13
Of course, we don't yet know anything more about those lumps. They could be composed of several other things. They could be complex, composite things that can break apart into bits. Or they could be simple, single things. We don't know yet. All we can say so far is that they don't (so far) seem to break up. They always come together in one piece. Or at least, they hit the screen in one piece. Maybe they leave the ray gun in several pieces and come together later? Maybe they leave the ray gun in one piece, split into several pieces and then somehow come together again at/before the screen? We don't know yet.
14
We could now place a barrier between the ray gun and screen (a bit like we did in (4)) and make two holes in that barrier, close together, and see what happens on the screen. From past experience, we might expect the cathode rays to go through those two holes but be blocked by the solid parts of the barrier. Perhaps they'll cause two dots to appear on the screen?
15
With the voltage turned up high again, we don't see two dots. We see a pattern of bright and dark "fringes" on the screen. We don't yet know why, but they remind us of a similar pattern that we've seen when waves travel through two holes and then re-combine. We've seen something similar looking happen (in previous experiments and observations) with sound waves and with ripples on the surface of water.
16
With those sound waves and ripples, after a bit of experimenting, we concluded that the reason for the fringes was that waves pass through both holes, and after that happens the waves from hole 1 "interfere" with the waves from hole 2. So if, at the equivalent of our screen, a peak of one of the waves meets a peak of the other (or trough meets trough) we get a lot of wave - a lot of energy. But if peak meets trough we get no energy. In between, we get some energy. In the case of ripples and sound waves, at least, this doesn't mean that some object is flying through those two holes. It just means that the oscillating motion of the air or water - of the "medium" - passes through the holes. That's what a wave is, as far as we have seen before. You need that "medium" for those kinds of waves to make any sense. And those waves can be represented by various pieces of mathematics.
17
Since the pattern on our screen looks like the pattern for ripples and sound, maybe these cathode rays can be thought of as waves in the same way? Maybe they pass through both holes at once and interfere on the other side to create the fringes on the screen? But the waves we're used to (ripples, sound etc) all require a medium. If these cathode rays are waves like those, what's the medium? Perhaps we better investigate some more.
18
What happens now if we turn the voltage back down again? Previously, when we did that (11, 12), we started to see those "lumps" - almost as if the cathode rays come in discrete packets of some kind. When we do it now, we get the lumpiness, just like before.
19
But if, every time there's one of those flashes on the screen, like we saw in paragraph (11), we record its position, we can build up a pattern. What gradually emerges is that the flashes gradually build into the interference pattern. What possible physical model could we create to describe that?
20
We could start by trying to investigate those "lumps". If they hit the screen as all-or-nothing lumps, do they go through the twin holes in the same way? Does a single lump go through a single hole? Or do they perhaps split up, the two halves go through different holes, and meet up again at some point before reaching the screen? Maybe that, somehow, causes these interfere fringes to build up? How might we find out?
21
One thing we could try is looking a bit closer at each of the two holes to see if we can spot something going through them. If those flashes on the screen are caused by a lump of something or other hitting it, maybe we can see that lump going through one of the holes, or perhaps splitting up and going through both, or perhaps two lumps going one through each hole which then come together to make one lump on the screen. Or something.
22
How can we do that? It's not as simple as just "looking" at the vicinity of the holes. We know from past experience that we can't see these cathode rays unless they bang into something. Previously we've had them bang into the screen and bang into gas molecules. (If we think about it, it's the same with any object. We see objects because photons of light bang into them and then bounce into our eyes. But we rarely think about that.)
23
We'll have to put something near the holes for the cathode rays to bang into. Perhaps a mini-screen or other detector of some kind. If we do that for each hole, what we find is that we sometimes get a "lump" at hole 1, the same size as the lump we got on our original screen, and sometimes at hole 2 but never at both holes at the same time. So whatever it is that's coming out of the cathode, it doesn't appear to be the case that it's several things at once that go through both holes and then somehow interfere with each other. It seems to be just one lump of stuff through one hole then one through the other. If we like, we can turn the voltage right down so that those lumps come very, very infrequently, just to show that for sure. So how can that thing that resembles the interference patterns of waves appear on the main screen? If the resemblance to an interference pattern in waves means that what we're seeing is an interference pattern in waves, what exactly is interfering with what?
24
What happens when, as described in (23), we look at the hole through which the lump seems to have travelled, is that suddenly there is no interfere pattern on the main screen! Why? Well, presumably what happened is that our little screen, in measuring the lump passing through one of the holes, stopped that lump from reaching the main screen.
25
So how can we measure which hole the lump passes through but still see the interference pattern on the main screen? Perhaps we could find a way to more gently detect the lump, at the hole, but still allow it to go on its way afterwards?
26
It turns out that however we try to do this, it always ends up messing up the interference pattern. If we look "gently" enough such that the interference pattern remains, we can no longer see clearly which hole it went through. But as soon as we can see which hole the lump went through, the interfere pattern disappears. It's almost as if the very act of looking at these lumps somehow means that they go through only one hole, but as soon as we're not looking, they behave as if there is some sense in which they went through both holes at once and thereby the interference happened.
27
After a lot of thinking and experimenting, the physicists decided that the question of which hole the lump went through actually makes no sense until we measure it. Until that point, the only thing we can talk about is the probability of the lump going through hole 1 or hole 2.
28
The strange part is that it is this probability that they propose causes the interference pattern. In some sense, the probability goes through both holes at once and interferes. It's as if this probability is the thing which is acting like a wave. If that's the model that we work with, it seems to work. It seems to accurately describe and predict what is observed.
29
This might seem mad, but it fits perfectly with what is observed.
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30
So the question is: If something fits perfectly with what is observed and breaks no rules of logic, yet it seems mad and breaks what we might think are the rules of common sense, what do we think of it?
If we don't like it, do we have a better model? One that fits both observation and logic and common sense? Not just observation and logic?
- Terrapin Station
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Re: The Twin-Slit Experiment
"Some object(s) flying through those two holes" and "oscillating motion of the air or water" aren't actually separable. You can't have the "oscillating motion only" pass through the holes. Because the oscillating motion doesn't exist on its own. The oscillating motion supervenes on the motion of water or air molecules. Maybe what we'd want to say is that a wave isn't a "single set" of water or air molecules that travel from point A to point B (at least it's not that in most cases). But the wave passing through the holes IS molecules passing through the holes in a wave pattern.
Now, it's not impossible for something to move in a wave pattern where it is the same set of particles (or molecules or whatever) moving from point A to point B. That's just not usually how water or air waves work, especially not on larger scales. The way this would work is simply that the motion of one particle causes the particles near it to travel slightly ahead or behind--slight pushes and pulls, where that would occur in a wave pattern as those same particles travel across "space."
Of course, it's also possible that it's working like a traditional wave where among other possibilities, we simply aren't aware yet of the particles that fill the tube, and our attempts at creating a "near vacuum" don't affect the particles in question.
If the particles emitted by the cathode are moving in a wave pattern as above (for either scenario), it's possible that (a) for each wave, only a small portion of it is visible at the anode--re the type of particles we're dealing with relative to our detection methods, at least, that could easily be the case, (b) emitting wave after wave results in an interference pattern as we'd expect, (c) only a particular portion of the wave is detectable at the holes (just as at the anode), and (d) the physical manipulation necessary to detect the detectable portion of the wave at a particular hole (rather than at the anode) is sufficient to interfere with the wave pattern--with the pushes and pulls, so that the wave pattern breaks.
- Papus79
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Re: The Twin-Slit Experiment
Eric was stating, rather boldly early in the interview, that what we're seeing with the double slit is the result of the interaction of principal and vector Hopf fiber bundles. I could see where the behavior your describing seems to fit within a schema where you have a couple different orders of governance, something like the behavior of the photon (which as far as I understand it is a discrete minimum packet of light - you're encountering that when the single dot starts strobing I believe due to low voltage and impedance) being governed by a containing space that we somehow impinge on by measurement.
Do I believe Eric by default? While he's an incredibly intelligent guy there seems to be no shortage of pop physicists who'd declare x interpretation of qm or x interpretation of collapse to be the right one so he could be having similar epistemic humility issues, or he could be right, just that I haven't seen much out there to make sense of how Hopf fibration and bundles would get the job done. Admittedly I'm not a mathematician, I program and I'm thinking if the Hopf fibration is really that important a concept I probably should do more reading on it to see what we understand about these bundles and what their behavior is like in relationship to each other.
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Re: The Twin-Slit Experiment
Ok. I see your point. So let me put it like this: Wave motion in such things as water and air is an oscillation, and the defining feature of an oscillation is that the thing which is oscillating moves, but returns continually to an equilibrium position. So there is no long term movement from that equilibrium position. If we imagine a wave like this passing through a gap, or hole, then we have particles of air, or water, or other medium, which are close to the hole, either moving back and forth through the hole and back again (longitudinal waves) or moving side to side next to each other on either side of the hole (transverse waves).Terrapin Station wrote:"Some object(s) flying through those two holes" and "oscillating motion of the air or water" aren't actually separable. You can't have the "oscillating motion only" pass through the holes. Because the oscillating motion doesn't exist on its own. The oscillating motion supervenes on the motion of water or air molecules. Maybe what we'd want to say is that a wave isn't a "single set" of water or air molecules that travel from point A to point B (at least it's not that in most cases). But the wave passing through the holes IS molecules passing through the holes in a wave pattern.
So, for those kinds of waves, the wave is not identically equal to the medium, but the wave cannot exist without the medium and without the movement of the medium. A sound wave is not an air molecule. A sound wave is not a property of an individual air molecule. A sound wave is a collective feature of the movements of groups of air molecules. That feature can be described by various mathematical equations. (But, as we know, the mathematical equations are not the wave. They are the language used to describe the wave.)
I don't see how that fits with the definition of a wave moving through a medium. One of the defining features of such a wave is that the particles through which the wave moves return to equilibrium positions. The particle moving at the end point of the wave is not the same particle that is moving at the start point of the wave. For sure, those equilibrium positions could all be moving, in unison, relative to something else. For example, if I'm driving in my car with the windows closed, talking to the kids in the back, the equilibrium positions of all those air molecules are all moving with respect to the road. But that doesn't alter the fact that the sound waves are oscillations of air molecules about equilibrium positions. The other type of air movement is not called a sound wave. It is called wind.Now, it's not impossible for something to move in a wave pattern where it is the same set of particles (or molecules or whatever) moving from point A to point B.
That's not how they ever work. That's how wind and water currents work. As I said, waves can travel through air or water that is moving in unison relative to something else. But that movement relative to something else is not a wave. It is not an oscillation.That's just not usually how water or air waves work, especially not on larger scales. The way this would work is simply that the motion of one particle causes the particles near it to travel slightly ahead or behind--slight pushes and pulls, where that would occur in a wave pattern as those same particles travel across "space."
Could you think of a way to test this theory?Of course, it's also possible that it's working like a traditional wave where among other possibilities, we simply aren't aware yet of the particles that fill the tube, and our attempts at creating a "near vacuum" don't affect the particles in question.
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Thanks. But, no, I don't think that helps right now. I don't know what "principal and vector Hopf fiber bundles" are and, as far as possible, I would like to try to keep our analysis simple, at least for now. So let's park that idea for now.Papus79 wrote:I don't know if this will help ... Eric was stating, rather boldly early in the interview, that what we're seeing with the double slit is the result of the interaction of principal and vector Hopf fiber bundles.
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Re: The Twin-Slit Experiment
That's where the idea of probabilities and wavefunctions having an ontological function gets discarded, along with the Copenhagen interpretation. Probabilities and wavefunctions are really just abstract mathematical treatments which (so far) perfectly describe the results of the experiments. But they themselves are almost certainly not what's "actually" happening.
As science progressed, the world turned out to be bigger and bigger and bigger, and maybe QM just continues this pattern, adding at least one more dimension or whatever to existence. Maybe particles really do take every possible path at the same time, and/or can be broken down infinitely, and so they do literally go through both slits and interfere with themselves.
I think Occams's razor clearly favours this scenario (just more of the "same"), instead of adding an "abstract" or "non-real" or whatever realm to existence, leading to an insoluble duality.
And after this, we can try to look at the Measurement problem, which has now been transformed into something that makes a little more sense. How and why are we always part of this "classical" island that's part of an infinitely larger reality? In a way it turns the original problem inside out.
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Re: The Twin-Slit Experiment
I think all such considerations are for much later in the topic. For now, I'm concentrating on defining exactly what we mean when we refer to a wave in the classical sense of oscillations of particles in a medium. It's only after doing this, and doing a lot more consideration of what is observed in the experiment described in the OP, that I want to go on to discuss what it is about the behaviour of those flashes on that screen that might make anyone use the word "wave" in connection with them. At this stage, I don't think we're ready for the concept of a probability wave.Atla wrote:...That's where the idea of probabilities and wavefunctions having an ontological function gets discarded, along with the Copenhagen interpretation....
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Re: The Twin-Slit Experiment
Oh okay.Steve3007 wrote: ↑January 30th, 2020, 7:26 amI think all such considerations are for much later in the topic. For now, I'm concentrating on defining exactly what we mean when we refer to a wave in the classical sense of oscillations of particles in a medium. It's only after doing this, and doing a lot more consideration of what is observed in the experiment described in the OP, that I want to go on to discuss what it is about the behaviour of those flashes on that screen that might make anyone use the word "wave" in connection with them. At this stage, I don't think we're ready for the concept of a probability wave.Atla wrote:...That's where the idea of probabilities and wavefunctions having an ontological function gets discarded, along with the Copenhagen interpretation....
- Papus79
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Re: The Twin-Slit Experiment
That sounds good, and I'll see if I can do some more digging on that. I did find a math video with a prof talking about what 'fibrations' are and I think it would still need steps to unpack how that math translates to physics and what it means.
I do think what I'd go with - when you get single dots hitting the back screen and over time building a wave pattern - that's at least for me the most curious part of it and what seems most intuitive is that may very well be multiple dynamics interacting or perhaps containing each other, a bit like the light is contained within rule sets but that those rule sets may very well not be something you can derive from interaction with particles. Sure it's not a simpler explanation but it offers some restoration of common sense intuition.
I'm also wondering, if a similar film was put on the blocker to monitor how the straining works, would the light seem to hit that stop and disappear as the photon packet goes through the slit and hits the screen in the back (like a strand of spaghetti falling through a strainer), ie. is it congealed to itself strongly enough to pull whatever hit the stop through the hole and bring it all to the back screen. The strict on-off behavior of low voltage would suggest a certain likelihood of yes at a single photon level but it would be interesting to see if there's any confirmation of that.
- Terrapin Station
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Re: The Twin-Slit Experiment
The important thing is not that something fits a particular traditional definition of wave here, but that the phenomenon in question is sufficiently wave-like to produce both the interference pattern and the "points" we detect.
I explained how this could work, but it would be easier to explain it if I could produce an animation or at least use something like balls to demonstrate. A way it could work is that particles travel in groups, and they have a push and pull effect on other particles that results in a wave shape. Think of something like this, where the circles are the particles in question (and I'm only focusing on the black circles for this--the lines in this case would just be to better illustrate the resultant wave shape, and the particles of course might be packed many more a lot closer together):
The particles could interact, as they're traveling through space, so that the leftmost three particles (in the picture) are pushing each other ahead, the fourth particle is temporarily in an equilibrium state, then the next six particles pulling back on the particles ahead of them, then the next ones are pushing forward, etc. This would vacillate--pushing and pulling on the adjacent particle in a wave pattern, with the peaks and troughs being particles in a neutral or equilibrium state, with different particles, perhaps all of them (or perhaps only certain ones not too close to the ends) taking turns as the peak versus the trough, etc.
This of course is something like how waves work in general, just that with water or sound waves, particles are bumping into other particles and transferring momentum to them, which is how the wave continues.
In a situation where there aren't particles (or the right type at least) to bump into and transfer the momentum to, as there is with water or sound waves, a set of particles simply moves across space in this pattern.
The points we detect are a wave peak, where (a) there's something about the physical properties of a photon or electron etc. wave, or (b) at least there is relative to our detection abilities at present, so that either (a) there's just one peak at a time and we can only detect that--perhaps because detecting it is sufficient to immediately break up the wave, or (b) for some reason there's only one peak that we can detect at a time.
So one at a time we see "dots." But over time, after releasing many, we see what looks like a wave interference pattern, because that's really what it is, it's just that it takes many dots to make the full picture.
It's not something we could test either way. We'd be talking about something we haven't discovered yet (aside from concluding it's the case as an upshot of what we're observing in the experiments we're describing).Could you think of a way to test this theory?Of course, it's also possible that it's working like a traditional wave where among other possibilities, we simply aren't aware yet of the particles that fill the tube, and our attempts at creating a "near vacuum" don't affect the particles in question.
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Re: The Twin-Slit Experiment
- Papus79
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Re: The Twin-Slit Experiment
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Re: The Twin-Slit Experiment
True, but to find out whether it does produce that interference pattern we need to look at the form of that pattern and the way that it gets created by a "traditional" wave.Terrapin Station wrote:The important thing is not that something fits a particular traditional definition of wave here, but that the phenomenon in question is sufficiently wave-like to produce both the interference pattern and the "points" we detect.
If we do an experiment with ripples on the surface of a tank of water (an experiment that is often done in high school physics classes), or with any other kinds of waves, we get this kind of pattern representing the amplitude of the waves hitting the backstop/screen:
There is a band of high amplitude in the middle with successively narrower bands as you go from the middle to the edges. The exact characteristics of these bands - their widths and intensities - are precisely determined by the relative distances from each of the two slits to each point on the screen and by the wavelength of the waves. For any given point on the screen, if the difference between the path length from slit 1 and the path length from slit 2 is an integer multiple of the wavelength of the waves being used, then that point will experience maximum wave amplitude. If it is shifted by half a wavelength then that point will experience minimum wave amplitude.
So if we call the path lengths r1 and r2, and the wavelength w, and if n is an integer, the middle of the maxima are at positions such that (P1 - P2) = nw and the middle of the minima are at positions such that (P1 - P2) = (n + 1/2)w.
This gives us the precise angles to the middles of each interference fringe.
This is exactly the type of interference pattern that we get in our experiment with the cathode ray tube. So any explanation of that pattern needs to be able to describe the details of the pattern - the positions and widths of each of the fringes - in the same way that a "traditional" wave model does.
I'll see if I can work out whether your proposed model appears to do this in a separate post.
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Re: The Twin-Slit Experiment
It would be very handy to be able to easily draw diagrams in here without having to just link to whatever we can find on the internet. And it would be very handy to be able to edit posts. But unfortunately we can't do either of those things.
- Terrapin Station
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Re: The Twin-Slit Experiment
The pattern would simply be waves that fit the data (barring evidence that they couldn't occur in those waves).
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Re: The Twin-Slit Experiment
2023/2024 Philosophy Books of the Month
Mark Victor Hansen, Relentless: Wisdom Behind the Incomparable Chicken Soup for the Soul
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Rediscovering the Wisdom of Human Nature: How Civilization Destroys Happiness
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