Another take on the split-beam interferometer paradox

Suppose instead of using stable particles like *photons, you use unstable ones like muons. Based on their half-life a portion of them would spontaneously decay while traversing the interferometer. So what would you observe? I suppose that the most mundane result (and probably what happens) is that we see decay particles emerging from points along one path of the split beam or the other.

But if I’m interpreting descriptions I’ve read of split-beam experiments correctly, you cannot strictly say that a photon takes one path or the other. The photon’s location is indeterminate until a measurement pins down it’s location. And my point in specifying unstable particles is that they decay spontaneously, without any external measurement being necessary. So how does a particle “on it’s own” decide to undergo a wave-function collapse and localize itself? Or is the very question of did it decay indeterminate until we see if the muon made it to the interference fringe detector or not?

*Caveat: Yes, I know that photons are bosons and muons are fermions, so strictly speaking the split-beam interferometer doesn’t work the same. I meant broadly “an experiment analogous to the photon interferometer”.

Morning, Lumpy. Er, cough I have no clue, actually, but I’ll be happy to bump this from Page 2 for you, to let the Thursday Morning Group take a shot at it.

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So…you’re trying to combine the two-slits experiment with the Schroedinger’s Cat thought experiment? You’re weird. :slight_smile:

Your latter supposition (Or is the very question of did it decay indeterminate until we see if the muon made it to the interference fringe detector or not?) I believe is the correct one. I guess I don’t see how introducing more uncertainty into an uncertain relationship makes things more certain. The particle may decay (whether it does not without our observation is irrelevant), but we don’t know about it until we measure it, thus collapsing the wave function.

That’s the way I understand it, as a non-physicist. I’m sure someone will come along and contradict me.

OK, so instead of muons, we can look at Z bosons, if it’s important that they be bosons. Of course, the experiment works with electrons, too, so it should work with muons.

I think that the key here is that you don’t have two different particles interfering with each other: You have one particle interfering with itself. You send your muons through the detector, one at a time. Some won’t make it, having decayed en route, and the ones that do make it, will form a standard interference pattern on the screen.

Yeah, Chronos, you could do the same thing with electrons–just eat the green ones instead of sending them through the slits.

To expand on Chronos’ answer (which I agree with BTW), the nature of the particle is not important in this experiment. The fundamental principle is still that we do not know the exact location of the particle until it registers on the CRT or photomultiplier tube or whatever you are using to measure the location with. For some reason, the individual particles will still interfere with themselves in a wave-like manner. You could think of the particles which have decayed as having never been there in the first place, since the experiment doesn’t require particles to be continually bombarding the detector. It would work the same if you shot single particles through the slits once a year or a thousand times a second. They are not interfering with each other.

Now I will go away from fact. :stuck_out_tongue:

I have always been intrigued with this experiment. I think if we figure this experiment out, it will provide a wealth of knowledge into quantum…well quantum whatever you believe in. :wink: There are two explanations that immediately occur to me:

On one hand, to me, it suggests that each particle in the universe has an “awareness” of what is around it. I’d like to believe this and believe that we exist in a “matrix” where everything that is affects, and is aware of, everything else.

OTOH, we have the (widely accepted) measurement problem. i.e. that whenever we measure particle interactions, they are intrinsically flawed, due to the interaction with the detector material. I don’t give a lot of creedence to this problem due to the field I work in (nuclear medicine) where we rely on data of this sort that has been proven statistically correct.

But the flaws are limited, too, so just because you get useable results in nuclear medicine, doesn’t mean that the “measurement problem” doesn’t exist.

I’m looking over (“reading” would be an exaggeration) Bohm’s 1951 Quantum Theory, the book that is often said to be the finest description of the Copenhagen interpretation of quantum mechanics (even though Bohm repudiated it the next year). It describes the path of an electron through a cloud chamber (p.137!), where the electron wave packet starts to spread as it enters the chamber, but each interaction with gas atoms (that become water droplet nuclei) restarts the process.

In that description, each exchange of energy with a gas atom is a “measurement,” and the electron exhibits its particle nature. It’s not hard to see why Bohm turned away from the Copenhagen interpretation (where some people were even doubting the existence of the moon if you were not looking at it), and to something like the implicate order.

According to the Copenhagen interpretation this is the correct explanation. A trifle more exact would be to say that the allowed states are in superposition until a measurement is made.

The implicate order, many worlds, etc. theories are all mathematically correct but for the most part they are hidden variable theories and unfalsifiable

But as unfalsifiable as the Copenhagen interpretation.

If you can contradict the Copenhagen interpretation, you’d be able to contradict (or support!) the others.

You can’t contradict the Copenhagen Interpretation. It simply states the facts and says nothing else is knowable. And it is falsifiable – all you have to do is prove that Quantum Mechanics is wrong.

Of course this is from a guy who posted that a cross could be described two dimensionally. (God, I’ll never forget that one)

The Copenhagen Interpretation is not equivalent to Quantum Mechanics.

If it were, we probably wouldn’t need two different names for the same thing. The clue in Copenhagen Interpretation is the word “interpretation.”

Hey, you could show the implicate order stuff was falsifiable too, by proving Quantum Mechanics wrong. The distinction we’d like to make is being able to choose between the many interpretations–not just the facts of QM, which they’ve all adopted.

Well, I guess I have to agree with that. The Copenhagen interpretation pretty much restricts itself to uncertainty, complementarity, probability and the collapse of the wavefunction via a measurement.

Bohm, goes quite a bit further and states that the world is explicitly non - local and that there is no collapse as a real world exists independent of observation. Even though Bell’s inequality and the Aspect experiment have pretty much shown that some sort of non locality is inevitable neither one goes so far as to say that the world in inherently non - local.

I guess you buy your ticket and you take your chances. The choices aren’t very appetizing; either the world isn’t real until it is observed (supposedly by a conscious mind ala Von Neumann) or the world is explicitly non local ala Bohm and the Transactional Interpretation.

Decoherence is gaining popularity but I don’t see where you draw the line that distinguishes the quantum world from the macro world, and how do you stop quantum systems from forming superpositions with anything other than a conscious mind?

I personally prefer the Copenhagen Interpretation.

So a single photon ‘shot’ through a dual slit board shows up twice, three times??? Don’t know why. See it leave and see it hit but miss its travel? Then when the equipment is moved closer it ‘acts’ normal? Other words, it has traveled its life span.The answer, at least to my humble thinking, lays in life itself. Like life and death. In other words the photon dies from a further distance than close. The single photon is still ‘alive’ when it is close to the split window board. Consider a person at death, has it not been proved (although not certain what it is) that 24 grams of weight “disappears”? It happens to everything at death. We leave this so-called realty. What happens is we actually return to the origins (hologram).It is the actual entity, not the non-reality, the reflection, the not real part ‘returning’. So we see whats not real!

Are Zombies a wave or a particle?

They’re both!

No, and I don’t know where you got this idea. Shoot one photon through a double-slit experiment, and you’ll get one spot show up on your detector. Shoot 2 or 3 more photons, you’ll get 2 or 3 more spots. Shoot a bunch of them through, and you get a bunch of spots. The spots will clump around a few different locations, rather than a single location like you’d classically expect, but you still need multiple photons in order to get multiple detections.

As I’ve remarked before, I really don’t understand this business people have with only looking at particles passing through a screen with two slits and asking “does the particle pass through one slit? Or Both? And how can it interfere with itself?” The situation, in general, is much more complicated.

For instance, you can use a screen with three slits. The resulting interference pattern will be different from the pattern for a single slit, or for a double slit. You don’t ask “did the particle pass through slit 1? or slit 2? Or slit 3?” Cleatly information from the whole screen is responsible for the diffraction pattern. You can repeat the experiment with a four-slit screen, or a five-slit, and so on. Heck, you can repeat it with a diffraction grating with the equivalent of thousands of slits, and with its unique pattern. At that point you stop asking which of the many faces of the grating a single photon passed through.

Or you can carry it in the other direction – use a screen with only one slit. Now there’s no question about which slit the particle passed through – there’s only the one slit. But you’ll find (as is rarely explained in these sorts of popularizations) that the interference pattern on the distant screen varies depending on the width of the slit. A narrow slit will produce a broader pattern than a broad slit, and both will have “ringing” at the edges, where bands of shadow alternate with bands of intensee regions, which decrease in peak intensity as you move awy from the center of the pattern. So you have to ask how one particle knows just how wide the slit is – does it brush both sides of the slit? Surely aan electron, muon, or photon is much, much smaller than the slit it passes through. (Actually, it’s still more complicated – the interference pattern also has features, in general, along the perpendicular direction, especially if the height is not much larger than the width. Not only does your particle “know” how wide the slit is – it knows how high it is, too.)

You can try to account for it by thinking of your particle as a fuzzy ball with a very small but non-zero presence that extends across the screen and “senses” the edges, but that’s imposing an inappropriate macroscopic model on the microscopic world. The diffraction phenomenon is an ensemble effect of a large number of particles (even if spread out over time and distance) interacting with a broad expanse of screen orders of magnitude larger than any meaningful measure of the particle size. Asking “which hole did the particle pas through ?” is not only asking the wrong question, it’s misapprehending the situation.

I did this as a project in my final year at Uni back in 94. I used a CCD camera as the screen and filters to reduce the intensity so that I could capture a single photon at a time. I ended up with hundreds of photos of single dots which I then superimposed on top of each other. The result was the classic diffraction pattern.