Where Was the Observer Detector in the Double-Slit Experiments?

[SDetection]

OK, here is my next question:
Is there a possibility that an electron could alter the state of any particle in its way from the emitter to the detector ?

 

[Fredrik]

Yes, definitely. That's actually the main reason why the photons in the standard double-slit experiment have to go through the slits.

 

[SDetection]

Yes, definitely.

OK, is this why the electrons take different paths in their way from the emitter to the detector ?. I don't think it's a mechanism of the emitter itself, right ?.

Thank you for your time.

 

[Fredrik]

OK, is this why the electrons take different paths in their way from the emitter to the detector ?.

No, it's just the reason why you can ignore all the paths from the emission event to the detection event that don't go through the slits. Technically you have to add up the contributions from all paths, but the contribution from a path that goes through a region filled with matter is going to be extremely close to zero because of interactions between the particle and the matter in the region.

I don't think it's a mechanism of the emitter itself, right ?.

Right. It's just how matter behaves. It's a pretty weird way to behave, but nature doesn't care what we think is weird.

 

[sokrates]

OK , I meant:
In the double-slit experiments, when there was an observer to determine which slit the electron passed through, that made the wave function collapse and the electron acted as particle, and there wasn't any interference at the detector, right ?.
But if the detector itself is an observer, this should also make the electron act as a particle, but there was actually an interference, which means the wave function didn't collapse.
Am I right ?, If so ,How could this happen ?

By the time you measured the wavefunction and "collapsed it" it has already interfered with different components of itself.

The interference pattern has already formed.

And the collapse of the wavefunction at the detectors is precisely the reason why they always come in "quantized" amounts. You always hear a single click in a Geiger counter. Not a weak click. Always one.

 

[SDetection]

No, it's just the reason why you can ignore all the paths from the emission event to the detection event that don't go through the slits. Technically you have to add up the contributions from all paths, but the contribution from a path that goes through a region filled with matter is going to be extremely close to zero because of interactions between the particle and the matter in the region.

But when the electrons were going though the slits, they were still interacting vertically with other free particles, as the slits were only horizontally narrow, right ?

 

[Matterwave]

@SD: the usual way we think about the double slit is in 2 dimensions, the third dimension isn't really thought about very much. But just imagine instead of a slit, a very small hole through which the particles can pass through.

So, I think an equally interesting question is, can you set up a standard double slit experiment with PHOTONS (not electrons) and get them to NOT interfere? I'd imagine shining a light wouldn't do the trick this time...

 

[SDetection]

@SD: the usual way we think about the double slit is in 2 dimensions, the third dimension isn't really thought about very much. But just imagine instead of a slit, a very small hole through which the particles can pass through.

So, I think an equally interesting question is, can you set up a standard double slit experiment with PHOTONS (not electrons) and get them to NOT interfere? I'd imagine shining a light wouldn't do the trick this time...

Yeah!, I was going to suggest that , as it's more practical because photons unlike electrons hit the detector at one position.
If no interference happens , then the HUP is violated, right ?

 

[SDetection]

...photons unlike electrons hit the detector at one position.

Maybe because photons don't spin ?.

 

[Fredrik]

Photons have spin 1, not 0. (Electrons have spin 1/2). And what's this about photons hitting "the detector at one position"? They certainly don't hit the same spot every time. A laser beam can hit a specific spot if you fire it directly at the screen, but if you put a screen with a single slit (or just a tiny hole) between the emitter and the target screen, the area on the target screen that gets hit by photons spreads out. The smaller you make the hole, that bigger you make the area that gets hit by photons. It's hard to explain why. Feynman's book "QED: The strange theory of light and matter" explains it pretty well, but I don't think I can explain it in a post here.

 

[DrChinese]

Maybe because photons don't spin ?.

As Fredrik says, photons do spin. Both photons and electrons - in fact pretty much any nuclei as well - will exhibit interference in a suitable double slit format. (Obviously, the slits must be spaced/sized appropriate for the relevant wavelength. For particles with a rest mass, you will use a wavelength proportional to the total mass/energy.)

The rule for interference in these setups is essentially: interference appears in the absence of the possibility of which-slit information. Experiments have even been done on molecules as big as fullerene (that's 60 carbon atoms).

 

[SDetection]

Photons have spin 1, not 0. (Electrons have spin 1/2). And what's this about photons hitting "the detector at one position"? They certainly don't hit the same spot every time.

I meant photons can be more concentrated at a tiny hole than electrons.

A laser beam can hit a specific spot if you fire it directly at the screen, but if you put a screen with a single slit (or just a tiny hole) between the emitter and the target screen, the area on the target screen that gets hit by photons spreads out. The smaller you make the hole, that bigger you make the area that gets hit by photons. It's hard to explain why. Feynman's book "QED: The strange theory of light and matter" explains it pretty well, but I don't think I can explain it in a post here.

So, you're saying that this experiment was also done using a tiny hole , and there was also interference/spread of photons ?.

 

[Vanadium 50]

I meant photons can be more concentrated at a tiny hole than electrons.

Why do you think this?

 

[SDetection]

Why do you think this?

Tell me first whether it's true or false, and after that I will tell you why I think so .

 

[Cthugha]

So, I think an equally interesting question is, can you set up a standard double slit experiment with PHOTONS (not electrons) and get them to NOT interfere? I'd imagine shining a light wouldn't do the trick this time...

Sure, just use incoherent light and a double slit with standard dimensions.

 

[Fredrik]

I meant photons can be more concentrated at a tiny hole than electrons.
...
So, you're saying that this experiment was also done using a tiny hole , and there was also interference/spread of photons ?.

What experiment? Are you asking if people have tried shooting photons through a tiny hole? Of course they have. (And yes, the beam spreads out).

I don't know if it's true or not that it's easier to focus a beam of photons towards a tiny hole than a beam of electrons, but it's not really relevant for the double slit experiment. I would guess that it's much easier to focus a beam of electrons, since their shorter wavelength should enable you to use a screen with hole in it to focus the beam. (If the size of the hole is just small enough to spread out a laser beam, it wouldn't spread out an electron beam significantly because their wavelengths are shorter).

 

[SDetection]

What experiment? Are you asking if people have tried shooting photons through a tiny hole? Of course they have. (And yes, the beam spreads out).

Using one photon at a time ?. Is there a reference for that ?.
Thanks.

 

[ZapperZ]

Using one photon at a time ?. Is there a reference for that ?.
Thanks.

This is no longer in the realm of exotica or needing "references" because it has become so common, it is done in undergraduate physics labs.

See this for example:

http://ophelia.princeton.edu/~page/single_photon.html

Zz.

 

[SDetection]

This is no longer in the realm of exotica or needing "references" because it has become so common, it is done in undergraduate physics labs.

See this for example:

http://ophelia.princeton.edu/~page/single_photon.html

Zz.

I'm sorry, this experiment is not clear for me. Was it done using vertical slits or tiny round holes ?.

 

[ZapperZ]

I'm sorry, this experiment is not clear for me. Was it done using vertical slits or tiny round holes ?.

Sorry, I was referring to slits.

Would round holes make any difference in what you're after?

Zz.

 

[SDetection]

Sorry, I was referring to slits.

Would round holes make any difference in what you're after?

Zz.

Yes, It's my last try to find Einstein's hidden variable .

 

[ZapperZ]

Yes, It's my last try to find Einstein's hidden variable .

And the round holes can do this but the the slits can't?

Zz.

 

[SDetection]

And the round holes can do this but the the slits can't?

Zz.

Yes, I think so. I won't rest until I do my best to clear Einstein's name. If only I can make a photon go though a tiny round hole without changing its momentum, then it's over for the HUP!.

 

[Hootenanny]

I won't rest until I do my best to clear Einstein's name, If only I can make a photon go though a tiny round hole without changing its momentum, then it's over for the HUP!.

Well, good luck with that ...

 

[DrChinese]

Yes, I think so. I won't rest until I do my best to clear Einstein's name. If only I can make a photon go though a tiny round hole without changing its momentum, then it's over for the HUP!.

Now that's funny!

 

[SDetection]

Come on people!, it's science not a religion. If the HUP is wrong, we all have to accept that, right? .

 

[DrChinese]

Come on people!, it's science not a religion. If the HUP is wrong, we all have to accept that, right? .

I don't think we are the "religious" ones - that appears to be you.

This experiment and a zillion other tests of the HUP have demonstrated it is indeed correct. Every day, new and sophisticated experiments are performed on entangled particles and their behavior must follow the HUP to obtain the expected results. So the scientific community is actually performing ongoing experiments in this regard daily. That is the exact opposite of what you are saying. None of them expect a violation of the HUP, but it could happen. And if it did, we'd be reading about it. (Have you heard about dark matter? That wasn't on anyone's agenda until recently.)

So until that time, exactly what is your point?

 

[SDetection]

I don't think we are the "religious" ones - that appears to be you.

This experiment and a zillion other tests of the HUP have demonstrated it is indeed correct. Every day, new and sophisticated experiments are performed on entangled particles and their behavior must follow the HUP to obtain the expected results. So the scientific community is actually performing ongoing experiments in this regard daily. That is the exact opposite of what you are saying.

Hi, I'm not saying that everything is wrong, somethings will just have to be changed somehow. Maybe the HUP will be called the Relative Uncertainty Principle.

None of them expect a violation of the HUP, but it could happen. And if it did, we'd be reading about it. (Have you heard about dark matter? That wasn't on anyone's agenda until recently.)

So until that time, exactly what is your point?

I'm still preparing my argument, as I don't want to rush it this time .

 

[SDetection]

I don't think we are the "religious" ones - that appears to be you.

I'm sorry DrChinese if you thought that "religion" was meant as an offense. I didn't mean it that way, I thought it would be funny ?.

 

[Hootenanny]

Hi, I'm not saying that everything is wrong, somethings will just have to be changed somehow. Maybe the HUP will be called the Relative Uncertainty Principle.

I'm still preparing my argument, as I don't want to rush it this time .

I think that it would be prudent at this point to remind you of the Physics Forums Global Guidelines, specifically the section concerning over speculative posts:

Overly Speculative Posts:
One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion. Posts deleted under this rule will be accompanied by a private message from a Staff member, and, if appropriate, an invitation to resubmit the post in accordance with our https://www.physicsforums.com/showthread.php?t=82301. Poorly formulated personal theories, unfounded challenges of mainstream science, and overt crackpottery will not be tolerated anywhere on the site. Linking to obviously "crank" or "crackpot" sites is prohibited.

 

[DrChinese]

I'm sorry DrChinese if you thought that "religion" was meant as an offense. I didn't mean it that way, I thought it would be funny ?.

No offense taken, I didn't think you meant it badly. I just don't get why you would argue against a principle that has already been studied 17 ways from Sunday. But if you like, do the experiment and publish. (That's what Afshar did.)

 

[SDetection]

I think that it would be prudent at this point to remind you of the Physics Forums Global Guidelines, specifically the section concerning over speculative posts:

Thanks, but I don't think I was over speculating. Some people think that I'm totally rejecting the QM/HUP, and I was responding to that. I had to do it, and I think I did it in the accepted range. As nothing is perfect, physics can be refined all the time, and it did happen before as with Newtonian physics. If the HUP could be violated, then things just have to be reconsidered.

 

[ZapperZ]

Thanks, but I don't think I was over speculating. Some people think that I'm totally rejecting the QM/HUP, and I was responding to that. I had to do it, and I think I did it in the accepted range. As nothing is perfect, physics can be refined all the time, and it did happen before as with Newtonian physics. If the HUP could be violated, then things just have to be reconsidered.

Physics gets "redefined" often, but not in ways that you are doing. It cannot be challenged simply based on a matter of tastes, or by being ignorant of it. From following this thread, it appears that you are still learning it, or simply didn't understand many different aspects of QM. So how are YOU going to be the one who would be able to do this when you haven't actually understand some of the basic premise of the theory?

Are there legitimate studies to push the boundary of the validity of QM? Sure there are! But these are done in peer-reviewed journals, not on here.

Zz.

 

[SDetection]

I just don't get why you would argue against a principle that has already been studied 17 ways from Sunday.

Yeah, but you know that we tend to challenge our intelligence and complicate things so we can be proud of ourselves, but things might be much more simpler than we think they are!.

But if you like, do the experiment and publish. (That's what Afshar did.)

Or you can cooperate with me to see if we can actually violate the HUP ?.

 

[ZapperZ]

This thread is done.

Zz.