The most confusing and baffling in science? (QuantumMechanics\Double Slit experiment)

[sanoj688]

So if you have no clue what the double split experiment is, go watch this very clear and understandable video!

Now, from now on I assume that you know what surprising results came out of the experiment.

Apparently, when tiny particles are shot at the screen with two slits, but they are shot ONE AT A TIME... there is STILL an interference pattern!

It get's crazier though, as can be seen in the video. As soon as scientist place a detector at one of the slits and the experiment is repeated... the interference pattern is gone, and the usual 2 stripe pattern can be seen.

Now.. from watching another video I heard a scientist say that when they unplugged the detector, but left it at one of the slits.. the interference pattern came back!

How spooky is that.. (

)

So, what's my point? Well I made this topic more to ask a question. I can't think of another place to ask right now, so here it goes.

Question

When the particle emitter fires the particles one at a time at the screen.. what exactly is it aimed at? The spot in the middle of the two slits? Just the screen? Will the particles come out at an angle randomly? What's going on?

A bit further..

If you are really interested in this, try watching this video:

This one is quite hard to follow for me, but what I could understand (I think) is that the fact whether the light goes through slit 1 or 2, is established after the light has even hit the screen where it will create a pattern. And there is a 50% chance of them knowing which slot it went through, and 50% where they don't know. I think that whenever they COULD (they didnt even check, but the mere fact that they could check) which slit it went through, there was a 2 slit pattern, and whenever they could not establish the fact, there was an interference pattern. This is mindboggling because the experiment setup did not change! This means that putting a detector at one of the slits has no effect on the behaviour of the particle!

So what the peep is going on? I think the guy in the last video gives some explanation but understanding that as well was too much for 1 video.. also I think he's not really a scientific scientist so to speak, but more a philosophical.

Anyway, besides all this I'm curious if there are people here who actually know a thing or two about this. I've seen some people writing smart stuff about physics before on these subforums

Cheers!

[N_las]

Imagine that Particles propagate as waves, but interact as particles:

The canon shoots a particle that propagates as wave at the wall with the slits. Dependend on the amplitudes of the propagating wave one can determine the probability of the particle to interact with the wall. For the sake of argument: Say the probability is 80%. If that is the case, than it obviously doesn't travel further. In the rest of the cases (20%) the particle won't interact with the wall but propagate throug the slit. Since it hasn't interacted with the wall, it still resembles a wave originating at the canon, and an interference pattern will form. The Amplitudes of the interference pattern at the back wall now determines the propability were the particle will interact with the wall. If you repeat the experiment with many particles, the pattern becomes visible.

If you place a detector at the slits, you force the particle to interact with the detector. There is now way of detecting a particle, without interacting with it. So the particle interacts with the detector at the two slits. Now it will propagate as a wave further to the back wall, but the wave doesn't have its origin point at the canon anymore, but at the point were the detector interacted with it, in front of one of the slits. A wave originating from that point doesn't create an interference pattern.

So just keep in Mind: Particles ALWAYS propagate as waves, but interact as particles. (obviously that ist just a simplification)

[lajoswinkler]

I won't comment on the last video (it smells fishy, but let me allow others speak about it), but I will comment the first one.

It's a clip from one of the stupidest and most harmful movies of our ages.

It implies that electrons are conscious and know when they're being watched by a sentient being, which is a complete fabrication. This piece of lie is the cornerstone of modern quackery which claims not only that people can affect the outcomes of such experiments simply by watching the apparatus, but that the mere presence of people can modify the outcomes of any macroscopic phenomenon.

One example of a literary excrement that uses these things is this, unfortunately popular, book.

It's like almost no laymen knows the real truth behind these claims, that it's the act of measuring (by apparatus) that creates the phenomenon exclusively on quantum scales. The harm has been done, and it corrodes our society on a daily basis.

[K^2]

Question

When the particle emitter fires the particles one at a time at the screen.. what exactly is it aimed at? The spot in the middle of the two slits? Just the screen? Will the particles come out at an angle randomly? What's going on?

Center point between the slits is your best bet to get a nice pattern, but it doesn't have to be that precise. That's kind of the whole point. Particle propagates as a wave packet, so you aren't aiming a point object. But if you get center of the packet aimed at the center point between the slits, you get the nicest overlap between the wave packet ad the general area where the slits are. If you are off, your interference pattern ca be a little uneven, because intensity through one slit is greater than through the other.

[MC.STEEL]

For me its this penomenon until you find that the triangles are not proper 60 by 90 by 30 degrees.

http://cdn.themetapicture.com/media/funny-gif-math-triangles.gif

EDIT: if you dont see a gif its because hates me or I am doing something wrong,and for that matter

Edited February 1, 2014 by MC.STEEL

[lodestar]

It's like almost no laymen knows the real truth behind these claims, that it's the act of measuring (by apparatus) that creates the phenomenon exclusively on quantum scales. The harm has been done, and it corrodes our society on a daily basis.

Frankly, I think unrestrained scientism corrodes our society much more than anything else. You don't have to go as far as electrons being sentient beings. By replacing the cartesian metaphysical premises of modern science with thomism you can simply say that subatomic particles exist as pure potency, and gain act during the interaction. The apparatus obviously has act gained from its constructor, who is the ultimate observer. Simple as that.

Recommended reading: anything by Wolfgang Smith.

[sojourner]

It's simple really. Our entire universe is a simulation being run on a computer. The slit experiment just exposes a flaw in the simulation.

[N_las]

Frankly, I think unrestrained scientism corrodes our society much more than anything else. You don't have to go as far as electrons being sentient beings. By replacing the cartesian metaphysical premises of modern science with thomism you can simply say that subatomic particles exist as pure potency, and gain act during the interaction. The apparatus obviously has act gained from its constructor, who is the ultimate observer. Simple as that.

Recommended reading: anything by Wolfgang Smith.

Wolfgang Smith is a geocentrist and believes in intelligent desing. He tries to weave as much religion into his interpretation of quantum mechanics as possible. 'Unrestrained scientism' has lead to less wars, less poverty, less sickness, more knowlege and stronger social liberties. Thats quite an 'corrosion' ...

[lajoswinkler]

Frankly, I think unrestrained scientism corrodes our society much more than anything else. You don't have to go as far as electrons being sentient beings. By replacing the cartesian metaphysical premises of modern science with thomism you can simply say that subatomic particles exist as pure potency, and gain act during the interaction. The apparatus obviously has act gained from its constructor, who is the ultimate observer. Simple as that.

Recommended reading: anything by Wolfgang Smith.

I can't take you serious. This guy believes Earth is in the center of the universe. Crackpot. Case closed.

[lodestar]

Wolfgang Smith is a geocentrist and believes in intelligent desing. He tries to weave as much religion into his interpretation of quantum mechanics as possible. 'Unrestrained scientism' has lead to less wars, less poverty, less sickness, more knowlege and stronger social liberties. Thats quite an 'corrosion' ...

You're obviously criticizing without ever reading anything, because not only his book on quantum mechanics doesn't weave religion into anything, his books that actually deal with religion are philosophical, not scientific. As to his belief in geocentrism and intelligent design, I don't see how that's a problem, except for someone with the naive scientistic belief that these are unscientific.

Edited February 2, 2014 by lodestar

[lodestar]

I can't take you serious. This guy believes Earth is in the center of the universe. Crackpot. Case closed.

Well, the beauty of living in a free country is that I am free to believe in anything I want, and you are free to take me seriously if you want.

Anyway, just to clarify, I don't believe Earth is in the center of the universe, I simply know for a fact that there's no scientific evidence favoring a frame-independent model over a preferred-frame model since both provide satisfactory explanations to current observations. If that makes me a crackpot, then the most brilliant physicists of the 20th century are crackpots, from Einstein and Eddington to Hawking and Ellis.

[K^2]

A preferred-frame model that properly treats field theory does not exist. Experiments that demonstrate preferred frame do not exist. Saying that there is a preferred-frame theory is the same as saying that intelligent design is a scientific theory.

[Aphobius]

Saying that there is a preferred-frame theory is the same as saying that intelligent design is a scientific theory.

That's what he said earlier. xD

As to his belief in geocentrism and intelligent design, I don't see how that's a problem, except for someone with the naive scientistic belief that these are unscientific.

[K^2]

We really need to do something about that education system.

[lodestar]

A preferred-frame model that properly treats field theory does not exist.

Neither it does for frame-independent, so what's the problem? Anyway this is subject to time, funding and publication bias, not a perennial truth. Science advances one funeral at a time, as Max Planck used to say.

Experiments that demonstrate preferred frame do not exist.

Neither there are any experiments for a frame-independent model that also won't fit a preferred frame model well. The gravitational fields we can actually experiment with are too weak for that. To quote Clifford Will, "General Relativity has passed every solar-system test with flying colors. Yet so have alternative theories.â€Â

Saying that there is a preferred-frame theory is the same as saying that intelligent design is a scientific theory.

That analogy doesn't make sense, since the first proposition is contingent, while the second is a contradiction. I guess you think I believe intelligent design is a scientific theory and tried to be sarcastic?

[lodestar]

That's what he said earlier. xD

Is it? Read again... carefully...

[magnemoe]

Imagine that Particles propagate as waves, but interact as particles:

The canon shoots a particle that propagates as wave at the wall with the slits. Dependend on the amplitudes of the propagating wave one can determine the probability of the particle to interact with the wall. For the sake of argument: Say the probability is 80%. If that is the case, than it obviously doesn't travel further. In the rest of the cases (20%) the particle won't interact with the wall but propagate throug the slit. Since it hasn't interacted with the wall, it still resembles a wave originating at the canon, and an interference pattern will form. The Amplitudes of the interference pattern at the back wall now determines the propability were the particle will interact with the wall. If you repeat the experiment with many particles, the pattern becomes visible.

If you place a detector at the slits, you force the particle to interact with the detector. There is now way of detecting a particle, without interacting with it. So the particle interacts with the detector at the two slits. Now it will propagate as a wave further to the back wall, but the wave doesn't have its origin point at the canon anymore, but at the point were the detector interacted with it, in front of one of the slits. A wave originating from that point doesn't create an interference pattern.

So just keep in Mind: Particles ALWAYS propagate as waves, but interact as particles. (obviously that ist just a simplification)

This, there is no huge mystery just travel as wave and interact as particle.

And you can not do measurements of an particle without interacting with it, this typically take away energy from it. Again no mystery just that the particle is so small and weak and anyway to measure it will be far larger than an atom.

Yes many who work with this want it to seems mysterious as it grant prestige.

And yes its weird, however quantum mechanic is not designed to be intuitive.

[Dunbaratu]

It implies that electrons are conscious and know when they're being watched by a sentient being, which is a complete fabrication. This piece of lie is the cornerstone of modern quackery which claims not only that people can affect the outcomes of such experiments simply by watching the apparatus, but that the mere presence of people can modify the outcomes of any macroscopic phenomenon.

I too find this annoying but I think the first blame lays with theoretical physicists' love of using oversimplified explanations and terms for situations in which a correct explanation requires a bit more verbosity. The claim that observation *causes* the experiment to give different results comes right out of that tendency for oversimplification. It's not that the observer's mind causes the change to the results, but that there is no physical mechanism to detect something without changing it.

Take vision for example. For an object to be visible it has to reflect light and the act of reflecting that light that alters the material of the object. It's not the fact that you put an eyeball attached to a human brain in front of that ray of reflected light that caused the change to the object. The change already happened *prior* to the observation. The change happened at the moment the light got reflected off of it.

What the observer effect is really saying is that all the physical means by which any phenomena may be detected are things that must cause a change to the thing being detected. But the way it's always *phrased* is to act as if it's the act of observing (meaning a conscious mind is doing it) that causes the change. And that's horse****. If you measure a phenomenon with a machine and then throw away the results without looking at them then you never observed the phenomenon, and yet the "observer" effect was still happening because it had to in order for the non-thinking non-observing machine to be able to take that measurement.

To say otherwise is to violate space-time - because the act of observation occurs AFTER the thing it's measuring.

It's not that the act of observing a phenomenon changes it.

It's that whatever it was that caused the phenomenon to become observe-able changed it. Whether you choose to make use of that observability or not.

Edited February 2, 2014 by Steven Mading

[Z-Man]

This, there is no huge mystery just travel as wave and interact as particle.

While that does explain the double slit and photoelectric effect nicely, it does not explain electron behaviour in atoms. That requires electrons to stay waves all along even though they interact with the nuclerus' electric field.

And you can not do measurements of an particle without interacting with it, this typically take away energy from it.

The delayed choice experiment nicely demonstrates that the influence of the measurement on the particle has nothing to do with it. As the measurement is done on the idler photon, the signal photon is not disturbed one bit.

Yes many who work with this want it to seems mysterious as it grant prestige.

Yes, claiming something is mysterious and beyond mere mortals' comprehension is... harmful. But it's also not simple. The fact that experts of the field have been arguing since a century over the fundamentals should be a small hint Well, the fact that the more advanced and amazing experiments only became possible in the last 30 years or so also has something to do with it.

Recommended watching:

. Title is just clickbaiting, no actual conspiracy inside

TL;DW: measurement is entanglement. That is a simplification that works because it explains the seemingly simple thing that is not well understood with a complicated thing that is well understood.

[sanoj688]

OP

So a particle travels as a wave and interacts as a particle.. okay, I can take that for granted. But is there no way to make a wave detector instead of a particle detector?

Or if you detect a particle in its wave-form, you will make it a particle in a particle form.. meaning you can never detect any waves without transforming them to particles?

I'm probably looking at this in a too simple classic kind of view.. can anyone recommend some good youtube videos for people that want to dive into this?

[ZetaX]

It's not that the act of observing a phenomenon changes it.

It's that whatever it was that caused the phenomenon to become observe-able changed it. Whether you choose to make use of that observability or not.

That's not fully correct, only a part of the truth. You can transfer quantum information, and thus you can also transfer that uncertainty, i.e. (under the right conditions) that photon's existence is still only determined if you watch it, not after it hits the object to be observed. The problem is actually deeper and not that simple at all, a catchword is "decoherence".

Speaking from my experience in teaching high level science, I can assure you that to convey complicated concepts you will have to simplify or explain by "images" (in a broader sense). The alternative is to slowly step up, then you can avoid such things, but it is in overall slower and only recommendable if time is not an issue (you won't be able to do that in a 2h lecture, often not even in a short series of such).

But I agree that some of the early quantum physicists are to blame on misnaming and miscommunication.

[lajoswinkler]

You're obviously criticizing without ever reading anything, because not only his book on quantum mechanics doesn't weave religion into anything, his books that actually deal with religion are philosophical, not scientific. As to his belief in geocentrism and intelligent design, I don't see how that's a problem, except for someone with the naive scientistic belief that these are unscientific.

Well that makes you a kind of a crackpot, too. It's simple as that. NHF

I too find this annoying but I think the first blame lays with theoretical physicists' love of using oversimplified explanations and terms for situations in which a correct explanation requires a bit more verbosity. The claim that observation *causes* the experiment to give different results comes right out of that tendency for oversimplification. It's not that the observer's mind causes the change to the results, but that there is no physical mechanism to detect something without changing it.

Take vision for example. For an object to be visible it has to reflect light and the act of reflecting that light that alters the material of the object. It's not the fact that you put an eyeball attached to a human brain in front of that ray of reflected light that caused the change to the object. The change already happened *prior* to the observation. The change happened at the moment the light got reflected off of it.

What the observer effect is really saying is that all the physical means by which any phenomena may be detected are things that must cause a change to the thing being detected. But the way it's always *phrased* is to act as if it's the act of observing (meaning a conscious mind is doing it) that causes the change. And that's horse****. If you measure a phenomenon with a machine and then throw away the results without looking at them then you never observed the phenomenon, and yet the "observer" effect was still happening because it had to in order for the non-thinking non-observing machine to be able to take that measurement.

To say otherwise is to violate space-time - because the act of observation occurs AFTER the thing it's measuring.

It's not that the act of observing a phenomenon changes it.

It's that whatever it was that caused the phenomenon to become observe-able changed it. Whether you choose to make use of that observability or not.

Yes, exactly. The problem with most scientists is that they suck at explaining stuff. Not many people know stuff and have the ability to teach.

It's mindboggling how much damage has this done already. Those physicists need to get their ***** together.

[Z-Man]

So a particle travels as a wave and interacts as a particle.. okay, I can take that for granted. But is there no way to make a wave detector instead of a particle detector?

In that simplified and limited picture: No, that would be impossible.

Yes, exactly. The problem with most scientists is that they suck at explaining stuff.

Steven Mading was complaining about oversimplification. Sorry to break it to you, but the full picture or any reasonable approximation requires knowledge of Hilbert spaces, differential equations and, ideally, the Hamiltonian formulation of classical mechanics. If you know those, the principles of QM can be taught in maybe an hour. And pretty much every worker in the field will be able to give you that lecture, many of them without preparation. If you don't have that background, simplifications, analogies and baffling results are all your teacher can work with, and in the case of QM, that will not even get you to the point where you can ask interesting questions. They'll just point to the holes in the simplification most of the time.

The only way to simplify QM is to go finite dimensional. If you understand basic probability and complex numbers and linear algebra, I could write a simple "Over here are classical dymanics. Over there in somewhat similar structure, QM." cheat sheet kind of thing.

[K^2]

I too find this annoying but I think the first blame lays with theoretical physicists' love of using oversimplified explanations and terms for situations in which a correct explanation requires a bit more verbosity. The claim that observation *causes* the experiment to give different results comes right out of that tendency for oversimplification. It's not that the observer's mind causes the change to the results, but that there is no physical mechanism to detect something without changing it.

Take vision for example. For an object to be visible it has to reflect light and the act of reflecting that light that alters the material of the object. It's not the fact that you put an eyeball attached to a human brain in front of that ray of reflected light that caused the change to the object. The change already happened *prior* to the observation. The change happened at the moment the light got reflected off of it.

What the observer effect is really saying is that all the physical means by which any phenomena may be detected are things that must cause a change to the thing being detected. But the way it's always *phrased* is to act as if it's the act of observing (meaning a conscious mind is doing it) that causes the change. And that's horse****. If you measure a phenomenon with a machine and then throw away the results without looking at them then you never observed the phenomenon, and yet the "observer" effect was still happening because it had to in order for the non-thinking non-observing machine to be able to take that measurement.

To say otherwise is to violate space-time - because the act of observation occurs AFTER the thing it's measuring.

It's not that the act of observing a phenomenon changes it.

It's that whatever it was that caused the phenomenon to become observe-able changed it. Whether you choose to make use of that observability or not.

You are on the right track, but I would like you to take a good look at Delayed Choice Quantum Eraser experiment. In a nut shell, it says that you can make a measurement, but then if instead of taking a look at results, you quickly erase the results, it is as if the measurement has not taken place. (Yeah, there is some of that famous over-simplification.) Worse! The data can be erased after inteference pattern has already been recorded. Now, there are some restrictions on all of that, but at the face value, it contradicts everything you've just said above.

At the end of the day, what you say is absolutely correct. It's the interaction between measurement apparatus and the object of study that effects a change. But interaction between observer(s) and measurement apparatus are also measurements. And the underlying objective reality itself is just a touch more complicated, because when all's said and done, what we're really dealing with are fields, and we have to be talking about a field theory. The cool thing about your basic Quantum Mechanics is that it helps you step around a lot of these issues by introducing a few nifty axioms, making sure that math works out even if you haven't figured out exactly what sort of a thing you're studying.

Does it contradict your normal, every-day understanding of causality? Yeah. But why shouldn't it? Actual locality is not violated within Quantum Mechanics. Information is still local, and causality is preserved. But if you aren't careful about your choice of interpretation, you end up with "spooky action at a distance". It really is just a problem of interpretation, however, and isn't the problem of core theory.

[lodestar]

Well that makes you a kind of a crackpot, too. It's simple as that. NHF

Intelligent design is ultimately a philosophical problem regarding final causes, and I don't see how taking either side on that makes one a crackpot. In the end of the line, the choice is between the preferred frame of geocentrism or Dark-Matter, and the degree of crackpotness of either one is merely cultural.

So, what you're saying really doesn't make sense. If that's really your best excuse for not reading Wolfgang Smith, too bad. Your loss.