Just watching a doco on reality which inevitably describes the double slit experiment and the illustrations have raised questions. If detectors are placed along the path of the photon before the slit haven’t you effectively built in deflection coils as you would find in a cathode ray tube? Which introduces basic laws of conservation of momentum, once the photon is measured it is limited to that measurement until another force either restricts it to another measurement or allows it to return to the unbound state that allows the wave pattern??

What is the paradox in this experiment again?

I do not understand the question

I thought that anything that interferes with the slit experiment marrs the experiment. There is no way of being near the experiment without interfering with the interference or photon wave pattern or something like that yeah?

ratty one said:

I do not understand the question

I thought that anything that interferes with the slit experiment marrs the experiment. There is no way of being near the experiment without interfering with the interference or photon wave pattern or something like that yeah?

——

Boris will explain;)

A related question would be wouldn’t a photon travelling in an electromagnetic environment be more likely to travel as a wave? Would a double slit experiment in an environment without a measurable EM field produce a non-wave result?

Postpocelipse said:

A related question would be wouldn’t a photon travelling in an electromagnetic environment be more likely to travel as a wave? Would a double slit experiment in an environment without a measurable EM field produce a non-wave result?

doesn’t the double slit experiment prove both things about photons…wasn’t that the point of the findings of that experiment?

ratty one said:

Postpocelipse said:

A related question would be wouldn’t a photon travelling in an electromagnetic environment be more likely to travel as a wave? Would a double slit experiment in an environment without a measurable EM field produce a non-wave result?

doesn’t the double slit experiment prove both things about photons…wasn’t that the point of the findings of that experiment?

a photon not being able to create the wave pattern in an environment without significant EM field would be additional data as I understand it….

you can’t detect the photons before they go through the slits. because if you do then how can they go through the slits as well?

ChrispenEvan said:

you can’t detect the photons before they go through the slits. because if you do then how can they go through the slits as well?

cos you interfere with their pathway otherwise – yeah?

if the experiment is set up to detect photons as particles then they will behave as particles. if the experiment is set up to detect photons as a wave then they will behave as a wave.

yes, you can only detect the photon once. the screen that is behind the slits is the detector in the experiment.

ChrispenEvan said:

if the experiment is set up to detect photons as particles then they will behave as particles. if the experiment is set up to detect photons as a wave then they will behave as a wave.

that is what I understand about the test… the interference pattern show the wave and an intermittent straight photo firing one after the other shows a particle

ChrispenEvan said:

yes, you can only detect the photon once. the screen that is behind the slits is the detector in the experiment.

unless you use detectors that measure the photons velocity seeing as the screen is measuring it’s position…..

Those bastards at Crown have packed the corkscrew.

that is the funny part. the particles hit the screen as particles but display a wave effect when enough have hit. mind you i don’t really understand it. PM is the guy.

Postpocelipse said:

ChrispenEvan said:

yes, you can only detect the photon once. the screen that is behind the slits is the detector in the experiment.

unless you use detectors that measure the photons velocity seeing as the screen is measuring it’s position…..

doesn’t the em field just control the trajectory similar to what the lhc does with the protons? or is this different?

how will you measure its velocity with affecting it?

photons aren’t affected by an em field. you can’t deflect them with a magnetic or electric field.

ChrispenEvan said:

how will you measure its velocity with affecting it?

presumably you meant with OUT affecting it.

yep. without.

ChrispenEvan said:

yep. without.

the whole crux is that you cannot come near the photon field without affecting the experiment that —- true?

yes. i think there has been an experiment where they measured the photon after the slits but before the screen. there was some special condition. was only a few years ago. can’t remember the details and don’t have enough data to do a search.

dv said:

Those bastards at Crown have packed the corkscrew.

—-

Keep your spirits up.

The double-slit experiment is my candidate for the most significant physics experiment of all time, because it’s still giving us new, unexpected information more than 150 years after it was devised. Thomas Young, who devised it, was a brilliant polymath who also laid the groundwork for the decoding of the Rosetta Stone.

The single-photon form of the experiment, in its basic form, shows that light passes through both slits, and so must still be a wave. If detectors are placed over each slit and the photon’s path monitored, the interference pattern disappears, showing that light is a particle. As has been observed, the only way to observe a photon is to absorb it, so this part of the experiment was done with electrons – which also exhibit interference patterns in the basic form of the experiment. A fundamental result of quantum mechanics holds that light is both a particle and a wave – but not both at the same time, so in the single-photon form of this experiment the photon would seem to make a choice to be one or the other at the time it passes through the slits. What happens, then, if we measure which slit the photon passes through after it’s made its choice? American physicist John Wheeler posed just that question in a series of papers between about 1978 and 1984 (see also the Delayed Choice Quantum Eraser). The experiments were first conducted in 1999 by Kim at al; the result is similar to the result obtained when the detectors are at the slits. Although the experimental apparatus was small, some of the experiments suggested by Wheeler involved (practical) cosmos-sized laboratory (see the wiki article), with photons travelling for billions of years before being forced to make a retrospective choice.

Wheeler believed that the photon was in a superposition of states, and therefore neither particle nor wave, until measured; if not, these experiments seem to violate causality. The researchers who have conducted the experiments have also accepted Wheeler’s view.

ChrispenEvan said:

you can’t detect the photons before they go through the slits. because if you do then how can they go through the slits as well?

One thought experiment I’ve seen is to place a parallel-sided glass prism between the source and slit. As the photon passes through the glass it is not destroyed and you can still detect it’s passage by the force applied to the prism (very sensitive measuring equipment is assumed). It turns out that as the photon travels through the prism its momentum is changed just enough to cancel out the interference effect. So even with that strategy you can’t both detect which slit and get the interference.

mollwollfumble said:

ChrispenEvan said:

you can’t detect the photons before they go through the slits. because if you do then how can they go through the slits as well?

One thought experiment I’ve seen is to place a parallel-sided glass prism between the source and slit. As the photon passes through the glass it is not destroyed and you can still detect it’s passage by the force applied to the prism (very sensitive measuring equipment is assumed). It turns out that as the photon travels through the prism its momentum is changed just enough to cancel out the interference effect. So even with that strategy you can’t both detect which slit and get the interference.

If a photon passes through glass without being absorbed/re-emitted, then surely it doesn’t apply any force to the glass at all.

If the photon changes direction then a force has been imparted.

What is a parallel sided glass prism then?

Dropbear said:

What is a parallel sided glass prism then?

Fair point

i guess not all prisms are triangular. maybe a rectangular prism.

ChrispenEvan said:

i guess not all prisms are triangular. maybe a rectangular prism.

my point is, if a photon goes through glass unabsorbed / re-emitted then it cannot be said to have interacted with the glass in any way – prism or not

KJW did give a good explanation of how diffraction works and i don’t think the photon being absorbed and re-emitted figured in it. I don’t have that saved anymore though.

woot. lucky i posted it here and google found it for me

I really dislike this common explanation as it fails to take into account the role of the medium. When an electromagnetic field propagates through a medium, the charges in the medium move in response to that electromagnetic field. The electromagnetic field associated with the charges adds to the propagating electromagnetic field in such a way as to produce a phase delay in the propagating electromagnetic field. Thus, the change in the speed of light (which is a change in the wavelength, but not the frequency) is the result of the ability of the changing electromagnetic field to alter the charge distribution within the medium. Media with a more easily polarisable electron density therefore have a higher refractive index. The refractive index also depends on the frequency of the propagating electromagnetic field. In the visible range, only the electron density can be deformed, whereas at frequencies lower than the infrared, the charge distribution can also be altered by deforming the shape of the molecules.

KJW’s explanation of refraction.

ChrispenEvan said:

KJW did give a good explanation of how diffraction works and i don’t think the photon being absorbed and re-emitted figured in it. I don’t have that saved anymore though.

That would be good to read..

That’s above my pay-grade, Boris..like most of what KJW says … as a smart guy he was a shit lay-communicator.

damn, i was hoping you’d explain it to me.

Dropbear said:

That’s above my pay-grade, Boris..like most of what KJW says … as a smart guy he was a shit lay-communicator.

so was I in high school, but at uni the college girls just made it that much easier…

diddly-squat said:

Dropbear said:

That’s above my pay-grade, Boris..like most of what KJW says … as a smart guy he was a shit lay-communicator.

so was I in high school, but at uni the college girls just made it that much easier…

:)

This may be what molly was trying to describe

Dropbear said:

This may be what molly was trying to describe

where’s the cross hilt????

ChrispenEvan said:

Dropbear said:

This may be what molly was trying to describe

where’s the cross hilt????

lol.. stop it …. it still hurts :)

I’ll sort this thread out later.

Bubblecar said:

I’ll sort this thread out later.

Stenger had things to say about popular misconceptions of the double split experiment, but I can’t remember what. I’ll look him up after dinner.

Bubblecar said:

I’ll sort this thread out later.

phew

Isn’t the thread title a porno movie as well

mollwollfumble said:

ChrispenEvan said:

you can’t detect the photons before they go through the slits. because if you do then how can they go through the slits as well?

One thought experiment I’ve seen is to place a parallel-sided glass prism between the source and slit. As the photon passes through the glass it is not destroyed and you can still detect it’s passage by the force applied to the prism (very sensitive measuring equipment is assumed). It turns out that as the photon travels through the prism its momentum is changed just enough to cancel out the interference effect. So even with that strategy you can’t both detect which slit and get the interference.

What I am proposing is that the interference pattern is not an expression of the photon but the electromagnetic field that is acting on it. Whilst the photon is only effected by the EM field it retains global symmetry(as much as the EM field maintains global symmetry). Other methods of measurement break global symmetry and introduce localised deflection, creating a ‘locally focussed’ particle. Is this simply saying the same thing in other words or is it an alternate explanation?

Bubblecar said:

I’ll sort this thread out later.

sounds of apprentices tuning dulcimers and a busy kitchen echo through the halls of the forum………..

ChrispenEvan said:

woot. lucky i posted it here and google found it for me

I really dislike this common explanation as it fails to take into account the role of the medium. When an electromagnetic field propagates through a medium, the charges in the medium move in response to that electromagnetic field. The electromagnetic field associated with the charges adds to the propagating electromagnetic field in such a way as to produce a phase delay in the propagating electromagnetic field. Thus, the change in the speed of light (which is a change in the wavelength, but not the frequency) is the result of the ability of the changing electromagnetic field to alter the charge distribution within the medium. Media with a more easily polarisable electron density therefore have a higher refractive index. The refractive index also depends on the frequency of the propagating electromagnetic field. In the visible range, only the electron density can be deformed, whereas at frequencies lower than the infrared, the charge distribution can also be altered by deforming the shape of the molecules.

KJW’s explanation of refraction.

thanks CE. I think this lays my question to rest.

that is purely to do with photons passing through a medium. nothing to do with the double slit experiment where there is no medium.

ChrispenEvan said:

that is purely to do with photons passing through a medium. nothing to do with the double slit experiment where there is no medium.

I think a no medium double-slit experiment would have to be technically thought experiment anyhoo……

KJW has provided an explanation that describes the variables involved which is what I was looking for. Cheers again ;)

no, there isn’t a medium involved, except the air the beam goes through. but this experiment has also been done in a vacuum with an electron beam. so you explanation would have to apply to all particles not just photons.

Postpocelipse said:

KJW has provided an explanation that describes the variables (and constants) involved which is what I was looking for. Cheers again ;)

ChrispenEvan said:

no, there isn’t a medium involved, except the air the beam goes through. but this experiment has also been done in a vacuum with an electron beam. so you explanation would have to apply to all particles not just photons.

The universal EM field is the constant medium for photons. Could a vacuum containing an EM field be considered a true vacuum?

doesn’t matter what constitutes a real vacuum, em propagation requires no medium.

ChrispenEvan said:

doesn’t matter what constitutes a real vacuum, em propagation requires no medium.

except photons?

emr is photons.

ChrispenEvan said:

emr is photons.

As I understand it an EM field is many photons in phase.

i would imagine the field is made of virtual photons.

ChrispenEvan said:

i would imagine the field is made of virtual photons.

There is no observable field as such. It’s a statistical convention used by QM.

http://en.wikipedia.org/wiki/Electromagnetic_field

dunno.

Stenger says (bear with me, I have to type it out :))

ChrispenEvan said:

i would imagine the field is made of virtual photons.

Electromagnetism is phased radiation so not virtual photons.

Postpocelipse said:

ChrispenEvan said:

i would imagine the field is made of virtual photons.

Electromagnetism is phased radiation so not virtual photons.

Unless you want to get into the holographic universe theory….

…And so not only photons but also electrons and ultimately all particles have wavelike properties. This is known as the wave-particle duality. However, here we have another physics result that is widely misunderstood, even among physicists. You often hear, “An object is a particle or a wave depending on what you decide to measure.” This is wrong. No-one has ever measured a wavelike property associated with a single particle. Interference and diffraction effects are only observed for beams of particles and only particles are detected, even when you are trying to measure a wavelength. The statistical behaviour of these ensembles of particles is described mathematically using equations that sometimes, but not always, resemble the equations for waves.

yes Bubblecar, the result of fourier analysis. a single particle would have an infinite wavelength.

Aside from the local EM fields phasing any laser involved has it’s own phasing. The simplest explanation is that the interference pattern is the presence of phasing in the photon. It is easily possible to deflect a phased photon but more difficult to return a deflected photon to phase…….

He goes on: If you do an interference or diffraction experiment in which you detect individual photons, youwill not see the effect until you accumulate a large number of detections. For example, you could do a double-slit interference experiment with a beam of photons of one per day. Watch it for a year, and you will see the interference pattern develop. Note that the photons can hardly be said to be “interfering with each other,” which is often the way the effect is described.

Bubblecar said:

He goes on: If you do an interference or diffraction experiment in which you detect individual photons, youwill not see the effect until you accumulate a large number of detections. For example, you could do a double-slit interference experiment with a beam of photons of one per day. Watch it for a year, and you will see the interference pattern develop. Note that the photons can hardly be said to be “interfering with each other,” which is often the way the effect is described.

…. that suggests that phasing is time dimensional……??

that is how i understand it Bubblecar. i have seen the experiment run with individual particles. that is the weird thing about the experiment.

Postpocelipse said:

Bubblecar said:

He goes on: If you do an interference or diffraction experiment in which you detect individual photons, youwill not see the effect until you accumulate a large number of detections. For example, you could do a double-slit interference experiment with a beam of photons of one per day. Watch it for a year, and you will see the interference pattern develop. Note that the photons can hardly be said to be “interfering with each other,” which is often the way the effect is described.

…. that suggests that phasing is time dimensional……??

oh of course…. FoR is any common momentum….

And continues: Let me make this as explicit as I can: It is incorrect to say, “this photon has a frequency f” or “this electron has a wavelength lambda”. The correct statements are: “this photon is a member of an ensemble of photons that can be described statistically as a wave of frequency f” and “this electron is a member of an ensemble of electrons that can be described statistically as a wave of wavelength lambda.”

And continues: Let me make this as explicit as I can: It is incorrect to say, “this photon has a frequency f” or “this electron has a wavelength lambda”. The correct statements are: “this photon is a member of an ensemble of photons that can be described statistically as a wave of frequency f” and “this electron is a member of an ensemble of electrons that can be described statistically as a wave of wavelength lambda.”

which is what i said a few posts ago.

Jolly good, but I thought I’d better post some Stenger since I said I would :)

Bubblecar said:

He goes on: If you do an interference or diffraction experiment in which you detect individual photons, youwill not see the effect until you accumulate a large number of detections. For example, you could do a double-slit interference experiment with a beam of photons of one per day. Watch it for a year, and you will see the interference pattern develop. Note that the photons can hardly be said to be “interfering with each other,” which is often the way the effect is described.

coming back to this…. the preceding photons interfere with the ones that follow simply through commonality of origin. The source shapes the photons path and repeating a path creates a phasing of that path so the path becomes it’s own FoR. Would that suggest that if you could force a contained environment into phase with a source of radiation you might be able to communicate within the FoR of the radiations source?

Postpocelipse said:

Would that suggest that if you could force a contained environment into phase with a source of radiation you might be able to communicate within the FoR of the radiations source?

ie, if you put a particle into phase with a distant source of radiation could you force a similar particle(or group of particles) within the sources FoR to mimic your particles momenta?

Postpocelipse said:

Postpocelipse said:

Would that suggest that if you could force a contained environment into phase with a source of radiation you might be able to communicate within the FoR of the radiations source?

ie, if you put a particle into phase with a distant source of radiation could you force a similar particle(or group of particles) within the sources FoR to mimic your particles momenta?

You’ll have to ask one of the boffins.

Bubblecar said:

Postpocelipse said:

Postpocelipse said:

Would that suggest that if you could force a contained environment into phase with a source of radiation you might be able to communicate within the FoR of the radiations source?

ie, if you put a particle into phase with a distant source of radiation could you force a similar particle(or group of particles) within the sources FoR to mimic your particles momenta?

You’ll have to ask one of the boffins.

the implications for the plans of lurking Evil Genii could be quite destructive…… yikes!!!

Postpocelipse said:

Bubblecar said:

Postpocelipse said:

ie, if you put a particle into phase with a distant source of radiation could you force a similar particle(or group of particles) within the sources FoR to mimic your particles momenta?

You’ll have to ask one of the boffins.

the implications for the plans of lurking Evil Genii could be quite destructive…… yikes!!!

you could do wierd shit to stars!!!

oooooook! the concept of intergalactic warfare just got a little realler for me. Glad it’s not highly likely in the order of things……..

Dropbear said:

This may be what molly was trying to describe

Yes. That’s it.

mollwollfumble said:

Dropbear said:

This may be what molly was trying to describe

Yes. That’s it.

A different approach to the question… if instead of a reflective surface a prism is place behind the slits, is the interference pattern imposed on the prism? ie: is the interference pattern only presented in reflection?