The Many Worlds Interpretation of Quantum Physics

Remember the Schroedinger’s cat trick?

Put Mr. Whiskers in a box along with a quantum particle with a half-life of an hour. Hook up a detector to a vial of cyanide so that if the particle decays it sets off the detector which opens the vial and the cat bites the green weenie. Close the box and wait an hour.

Is Mr. Whiskers alive or dead?

The odds are 50/50.

Due to some weird principles of quantum mechanics that we don’t need to go into now (though we can if you want,)Mr. Whiskers is neither. The act of observation will seal his fate, and the cat is neither alive nor dead until somebody looks in and observes it.

Sounds pretty fishy doesn’t it?

The cat’s either alive or dead, right? There ain’t no in between.

What Shroedinger was really implying was that it was both.

Another way to look at it is like this:

Poke two holes in a piece of cardboard just big enough to let a photon pass through. Shoot 100 photons at the board.

50 photons go through hole A and fifty go through B.

Now cover up hole B. What you probably expect to happen is fifty photons will go through hole A, and 50 photons will crack their skulls against closed hole B, right?

Nope. All 100 go through hole A.

That was pretty smart for a stupid photon wasn’t it?

Let’s do it another way. Let’s randomly close one hole, so we don’t know which one is open. Let’s put a basket behind each hole, shoot our photons, and then we will go and see which basket our photons are in.

From our previous experiment we know photons are “smart” They know if one hole is closed and all pile through the other. Therefore we should expect to find either 100 photons in basket A, or in Basket B. Right?

We do the experiment check our baskets, and guess what? 50 of the photons are in basket A, and 50 photons are in basket B.

Holy &*%$ing @%&#!!!

That’s impossible. We know that one of the baskets has to be empty. If one of the holes is covered, there is absolutely no way a photon could get through.

Being reasonable people we go and slap our lab assistant upside his worthless head for playing a practical joke.

We do the experiment again, and this time we are really, really careful.

50 photons in basket A, 50 photons in basket B.

“Crap!!!” You shout. “I should’ve been an accountant,” and you go home.

Other scientists get the exact same results. There is nothing wrong with the experiment.

It took a lot of math to finally figure out what was going on.

Somebody WAS screwing with the experiment.

There are actually 200 photons.

“No way! Jose.” you say. “I was careful. I counted. There were only 100 photons.”

Sure. You are right. There were only 100 photons in YOUR universe.

Let’s pretend for a second that in an alternate universe (let’s call it France,) there is a French version of yourself conducting the same experiment with his bag of 100 Photons. Furthermore, we happen to know for purposes of this experiment that photons are very cosmopolitan particles. They know no borders, and are as comfortable here in our universe as they are in France. In short there is now no such thing as a French photon.

Let’s look at both of these experiments again.

In the first experiment we shut hole B. Somehow all the photons knew this and went through hole A. What we were expecting was 50 through A, and the rest to bounce off of closed hole B.

From our new perspective with knowledge of France, what happened was this:

We shot 100 photons at the board. 50 went through hole A. The other 50 found hole B, closed. These 50 instead of banging themselves against the closed hole, left our Universe and travelled to Alternate Universe France where the experiment was being run with hole A closed and B open. Finding a warm welcome in France, they proceeded through the open hole B to be counted by our French counterpart.

Meanwhile, 50 photons in France found hole A closed, so they switched over to our universe where the hole was open, and landed in our basket along with 50 of our photons.
Net result: 100 photons in basket A here, 100 photons in basket B in France.

In the second experiment where one of the holes is randomly closed, something similar happens. If a photon finds the hole closed here it just switches over to France where the hole is open. The French particles come through our open hole.

Both holes are open (one here and one in France).

Similarly Mr. Whiskers may be dead here, but he’s also alive and well and living in France!!

I’ve taken some liberties in altering the experiments for easy explanation. But, essentially, what I have explained above is what happens.

I think science needs to work harder on this subject. I think we should figure out a way to conquer France. Then I could bring my French self over here, and make him work. I could bring the French version of my wife over here, and make her cook and clean and such. Me and my wife could just stay home in bed.


“Don’t just stand there in Uffish thought!”
-The Caterpillar

So where is the debate?
Am I supposed to counter with the superposition theory?

Peace

Umm. let’s see now… Oh yeah, Everett was a yutz.

Makes you wonder if he even heard of the Copenhagen Interpretation.

BTW, very clever post, scylla. :slight_smile:

the cat will mutate into a huge photon

I am with Asmodean on this 1. I read the OP 3 more time. I don’t see the joke. What am I missing? :confused:

Peace

Um, I think you may be misunderstanding or misrepresenting or oversimplyfying a bit.It’s difficult to predict the results of QM scenarios without starting with the math and later simplifying for us humans. And it’s been a long long time since I did any of the math …

I think there’s a problem with your 100 photons scenario. The results of the experiment depend strongly on exactly how you shoot to photons at the target. For example, you might shoot the photos through a long straight fiber optic directly towards the A or B hole. The typical double-slit experiment first passes the photos through a single very small hole in another piece of cardboard, so the photons that leave that hole leave it random directions. Of course, most of these photons will not pass through either hole A or hole B, so you have to shoot lots of photons to get 100 through holes A and B.

In this scenario, covering either hole will decrease the number of photons that get to the final detector.

You also need to specify what you are detecting. I beleive that you have implicitly stated that you are detecting the presence of photons.

Here’s how I understand the weirdnesses of the double slit experiment, using the random-direction photon source:

  1. Open both holes and shoot a lot of photons. Measure the number of photons that arrive at a particular point in space beyond the double-hole plate. Repeat many times, each time moving the detector a little bit parallel to the plate. The number of photons detected will vary with detector position … in the classic interference pattern manner.

  2. Close one hole and repeat. The number of photons detected will vary with position, but not in the interference pattern manner; rather, there will be one peak when the detector is in line with the open holes (one in the source plate) and decreasing quickly as the distance from that line decreases.

  3. Open both holes, and repeat with a source that emits so few photons that there is only one photon in the apparatus at a time. Our intuition tells us that each photon must go through one and only one hole … but the interference pattern reappears!

  4. Add detectors that detect photons passing by, one beside hole A and one beside hole B. Repeat experiment 1. The interference pattern does not show up! You get a pattern that looks like the results of two different experiment 2’s, one with hole A closed and one with hole B closed.

  5. If that isn’t weird enough, replace the photon-passing-by detectors with ones that detect photons passing by with imperfect efficiency. Say each detector has a 50% probability of detecting a photon passsing by. Repeat experiment 1. The result is a pattern that looks like the pattern from experiment 1 multiplied by 0.5 plus the pattern from experiment 4 multiplied by 0.5!!

Of course, the space in this message composition box is totally inadequate to address all the subtlties … if you haven’t already read it, I strongly recommend QED : The Strange Theory of Light and Matter. It doesn’t require math to understand, but it does require slow and careful reading.


As to the many-worlds interpretation; I haven’t gone deeply into it, favoring as I do the Feynman interpretation (briefly, “it’s so weird that we don’t have a prayer of understanding”). I believe that the many-worlds interpretation says that alternate universes are created every time a choice or alternative occurrence comes up; your
shooting 100 photons at two slits creates 200 universes. In each universe that photon does something different. I have a little conceptual difficulty with this interpretation, and maybe I’m wrong in my initial statement.

jrf

JonR:

Yeah, I deliberately oversimplified. For our purposes, we just assume a photon goes through hole A or B. I think it’s still consistent within that framework.

The implications are sill clear that particles are interacting with other particles which shouldn’t exist. Because they shouldn’t exist, I call them “France.”

There are lots of great links available on the “double slit” experiment for anybody that wants to see for themselves.

The many worlds interpretation of quantum physics doesn’t recquire a new universe to be created each time a random event occurs. Rather it states that all possibilities must actualize… somewhere.

Here’s some links:
http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html
http://www.microscopy.fsu.edu/primer/java/doubleslit/

a tougher one:
http://physics.hallym.ac.kr/education/Math/tdr/apps/schroed.html
http://www35.kfunigraz.ac.at/imawww/vqm/pages/samples.html

tons of stuff out there.


“Don’t just stand there in Uffish thought!”
-The Caterpillar

Hmmm… “all possibilities must actualize somewhere.”

Would this indicate, for example, that abiogenesis, however unlikely, must actualize somewhere? Would that pretty much counter any argument about how abiogenesis is so unlikely that God must have been responsible? Does this principle provide enough of a “cause” to satisfy Pashley?

Stay tuned to another week’s worth of GD for the answers…


“It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.” - Adam Smith

Waterj:

I suspect that if we took a handful of sterile mud, passed some current through it, radiated it, etc. etc. and made it spontaneously assemble into a hamster right before his eyes, he’d still say it didn’t happen.


“Don’t just stand there in Uffish thought!”
-The Caterpillar

You know, I once asked Cecil a similar question, to see if he could verify anything. Instead, I was recommended to the boards. Well, here I am. mit Re
Anyway, I haven’t been taught all that much (read: nothing) about quantum physics, but I have managed to pick up a bit (read: enough to impress a horde of crazed monkeys.)
So, that first explanation basically verifies what I know (source: Timline, Micheal Crighton) Anyway, I’ll get to my point: has anyone heard of the science (not theory) of Chaos? I just picked up this great book on it (creatively titled <u> Chaos"</u> ) which talks more about the history and development of the science than the science itself, but a lot of it can be applied to Quantum physics.
The cat, for example. Chaos basically says that you can never predict if the cat will live. It also suggests other things; namely, that your results will be tainted. This is because it’s impossible to record everything exactly (too many decimals) and the small mistakes in your recording will become huge and will basically come back to bite you in the, err, rear. So…that was about as much of a question as the original post, but, whatever…
“When I think of that Cat, I get my shot gun”
-Steven Hawkins

No, you may not assume that a photon goes through hole A or hole B. It may, but assumingthat almost forces you into the many-worlds interpretation. All that you may assume is that a photon passed through the apparatus. Anything else must be measured or derived.

Well, I sure can’t find any discussion of it that doesn’t involve branching at every possibility. For example, from the Many Worlds Theory FAQ:


jrf

JonR:

What I’ve attempted to do here is create an Einsteinian thought experiment, similar to the famous “Dancing Giant” light years across.

I know that you can’t poke a hole in a piece of cardboard one photon wide. I know you can’t aim photons so that it’s an either A or B proposition. In short, I know that the experiment can’t be performed as stated. I ignored those limitations of reality that either did not have bearing on the thought experiment, or that served to confuse what is already a complex subject.

Indeed it was my attention to highlight those aspects that demonstrate the many worlds interpretation of quantum physics.

Of course it’s oversimplified. Gimme a break!

Feynman explains the experiment using machine guns for chrissakes and nobody gives him a hard time.!

The Schroedingers cat experiment isn’t exactly practical either.

I feel I have some precedent for simplifying to show my point. You’ll notice that’s why I didn’t venture into wave/particle duality, though it’s also a key to the experiment. Perhaps THE key.

Here’s a smiley to show I’m not really upset. :slight_smile:

The “baskets” I refer to represent interference patterns. The crux of the Double slit experiment is that there is interference with photons that should not exist, and yet are very very real. I fail to see how I have altered that.

France isn’t real either. :slight_smile:
One can interpret the the many-worlds theory in two ways as I see it.

#1 Is as you say. Each random event splits reality.

#2 There is already an infinity of realities. The potentialities of each random event actualize within that infinity.

In either case there is a seperate universe for each possibility of each random event that occurs.

In a quantum sense these are both two ways of saying the same thing.

Is the cat dead or alive before you open the box?

Does the alternate universe truly exist before the random event or is it created by it?

See?


“Don’t just stand there in Uffish thought!”
-The Caterpillar

Well, I’m unfamiliar with the photon experiment, but I’m quite knowledgeable about the cat experiment. But, based on what you’ve said, I would like to point out that there’s a significant difference between both experiments. The photon bit is about particles randomly choosing between two equal choices at once. The cat bit is about the probability of a living animal degrading to dead matter as time goes by.

Of course, if I read the OP correctly, you’re not really comparing the two experiments, you’re using both to demonstrate that there’s an alternate universe. I, for one, believe that each instant of time spawns an infinite number of alternate universes (univervi?), so it’s nothing special about the experiments creating an alternate universe. In one universe, the cat can spontaneously combust and die the second the box is closed… in another universe, the cat can live forever and rise to power as the unchallenged Emperor for all eternity. Similar results can happen with the photons.

However, I have a more likely scenario about the photons… the first part of the experiment determined that the photons are “smart”, right? (You said as such, Scylla… but I know that was half-facetious). Since they’re smart, I think it’s safe to assume that they like to have a little fun every now and then. So isn’t it possible that they all pass through hole A, but after passing through, half immediately jump back to where hole B was so as to wind up in basket B? Those darn photons… they’re just messing with our minds!! Kill 'em! Kill the photons!!


-SPOOFE

With what?

Everybody shouts in unison

"Photon Torpedoes!

When the wheels come off, it’s time to retire.

Beakeroni… that was just bad… but funny. Kudos!


-SPOOFE

I think I am cutting you a break. However, I do think that your disussion of the double slit experiment is oversimplified to the point where the key concepts have been lost. Have you read Feynman’s discussion? It’s wonderful on at least two levels; it’s comprehensible, and it’s rigorously correct (including his machine gun analogy) without any significant amount of math. An astounding feat.

Sure you can aim photons so it’s an A or B proposition (e.g. a finely tuned laser beam and a 50% beam splitter). Exactly how you do so affects the outcome of the experiment. You can also create tiny openings in metal foil that, while not one photon wide, have dimensions comparable with the wavelength of tte photon, and really perform the double slit experiment.

Please note that I haven’t contradicted your discussion of the many worlds interpretation; I’ve used phrases like “I believe” and “I sure can’t find any discussion”. I would love to see a reference to some discussion that does not involve branching …

I think that there’s a significant conceptual difference betwee branching and non-branching versions. I’d actually prefer the non-branching version, because it doesn’t require modifications to conservation of energy. But I don’t see any physicists discussing non-branching versions, so I suspect that there’s some theoretical reason why it can’t be.


jrf

No, if you read Scylla’s description in the OP carefully, you’ll see that there is a 50% chance that the cyanide capsule opens and poisons the cat, and a 50% chance that the cyanide capsule does not open and the cat lives. And the probability is based on the uncertainites in the actions of quantum particles, just like the double slit experiment.


jrf

JonR:
Arrrg! For purposes of the OP I was only interested in the double slit experiment as it applies to the Many worlds interpretation of Quantum physics. I hacked it to suit my purposes! I admit it! And I would have gotten away with it too if it weren’t for you meddling kids! HAHAHAHAHAHAHAHA!!!

Is there no poetry in your soul, man?

I throw down the gauntlet and challenge you to write a better explanation, both in readability and scientific accuracy.

Re: Many worlds

“Created” is a misnomer.

You could say that they are created in the same way that you could say opening the box and observing the cat determines its fate.

I wish I could draw a picture.

I’ve read explanations both “branching” and “parallel” Concerning MWI.

It is also my understanding that these explanations are insufficient to describe the phenomenom.

I’ve read both the “Choose your own adventure” branching universe theory, and the “Frames in a motion picture,” infinite slightly different parallel universe explanations.

These are really just two ways of looking at the same thing.


“Don’t just stand there in Uffish thought!”
-The Caterpillar

What’s the matter? Doesn’t anyone like pilot waves anymore?

Can anyone confirm an explanation of Schrodinger’s Cat that I heard? I heard it was actually Schrodinger’s parody of quantum physics, and that he considered it an illustration of the problems with quantum physics. In other words, he chose the “cat 50% dead 50% alive” thing as a way of showing how pure probability can’t really be applied to a single case. Is this true?

I suppose my biggest problem with advanced physics is that, physics students always seem to express concepts in the weirdest and most counterintuitive way possible. Top-notch physicists avoid this, since their goal is to attract more people to the field rather than to intimidate freshmen. The problem is, I don’t generally have Einstein or Feynmann or somebody to explain why a hockey puck shrinks when you whack it across the ice at near-light velocities. Instead, I have some physics student tell me the hockey puck actually shrinks at near-light velocities, but the hole in the ice shrinks as well, since it’s moving at near-light velocities as well. It takes a generalist with some knowledge of physics to point out that the shrinkage is apparent, not real (and that it only occurs along the axis of movement).

Anyway, the point is, I’ve grown wary of “here’s how counterintuitive physics can be” stories, since those usually just turn out to be a single paradigm among competing paradigms, gleaned for stuff to intimidate lay people with.