particle location

[DParlevliet]

then the only conclusion is said photon upon arriving at a slit somehow knows there's another slit close by, works out what sort of pattern might be produced

That is because photons has both particle and wave properties. The particle goes one path, but the wave goes both paths and the wave determines the propability of detection of the particle, even with a single photon.

 

Now I think it's safe to say that Quantum Mechanics and the behaviour of subatomic particles can behave in ways that are contrary to millions of years of human experience, but for a individual photon to be able to act in such a way seems to me to elevate credulity to the stratosphere.

That is because you look to it as classical particles, while a photon has particle (and wave) properties

 

I'm sorry, but I think you're missing the point in your example. As said, it involves a least one interaction mid journey, and as I understand it that'll be with an atom of the slit material - you know, effectively the reverse of it's creation when being emitted from an atom in the first place. Presumably the atom then re-emits this energy in the form of another (what we call) photon which we view as continuing toward the final target. Similar if not identical to peeking and destruction of the interference pattern in the two slit experiment.

Reflection is not absorption/emission, but reflection on electrons, without making the photon non-coherent.

Look to cystal diffraction, based on reflection and interference.

Mirrors give interference pattern, like http://en.wikipedia.org/wiki/Lloyd%27s_mirror

Read Feynman and you see mirrors and interference.

The above measurement is an interference example I used from Brain Green's "The fabric of the cosmos"

 

There's also the question of measurement. As I think sb635 also mentioned, the possibility of being able to measure a single photon in such a way may not be within the bounds of the physics of QM and Uncertainty. In other words, it can't be done because it can't happen.

That is on much smaller (Planck) scales then the above measurement.

Edited December 24, 2013 by DParlevliet

[sb635]

 

That is because photons has both particle and wave properties. The particle goes one path, but the wave goes both paths and the wave determines the propability of detection of the particle, even with a single photon.

 

That is because you look to it as classical particles, while a photon has particle (and wave) properties

 

Reflection is not absorption/emission, but reflection on electrons, without making the photon non-coherent.

Look to cystal diffraction, based on reflection and interference.

Mirrors give interference pattern, like http://en.wikipedia.org/wiki/Lloyd's_mirror

Read Feynman and you see mirrors and interference.

The above measurement is an interference example I used from Brain Green's "The fabric of the cosmos"

 

That is on much smaller (Planck) scales then the above measurement.

The scaling in the UP is indeed sometimes small, but not that small for understanding the two slit experiment, which is really the interesting setup, not the interferometer. If I understand the two slit experiment, the impacting of a photon in a pixel of the observatory screen also stops a clock. The clock was started (t = 0) when the photon was generated on the other side of the plate with the two slits. Position and time are measured at the observatory screen. If the observed time is used to tell which slit the photon went through, then the ideal situation is wide apart slits with large path length differences, with path times which are much larger than the error in the clock. But a wide apart slit configuration shrinks the distance between the interference fringes, which is like using a gigantic lens which makes really small diffraction patterns of star images. The slits can get far enough apart, where time gets "real good" at telling which pathway was taken. The delta-time differences can get very large, with well separated slits, but the interference fringe separation gets very small, where eventually, photons from two separate fringes get inside one pixel with high probability. At this point, accurate measurement of position has broken down.

 

Let's say the clock error is gross, and can only time the pathways within 1 sec. In any lab experiment that also produces an interference pattern, with that level of a "sloppy" clock, you essentially have no path length information, and the interference pattern appears. Now start using a more a more accurate and precise clock. Eventually, according to the math of the UP, the timing error can get so small, the "error" in position at the observatory screen (and hence which slit was traversed) gets gigantic, which means the interference fringes overlap, and the pattern is "destroyed."

 

The UP math goes something like this. In the UP, the "error" in position is called delta-x. The error in time is called delta-t. QM is confusing in that it does not matter what is the actual source of any of these observable errors, be they measurement errors or something that nature itself (in a manner) "jitters." The product of the errors in your experiment is

 

[math]\Delta x\Delta t[/math]

 

The energy time variant of the UP shows that approximately

 

[math]\Delta x = {v_G}\Delta t[/math]

 

where [math]{v_G}[/math] is the "group velocity" of the wave(s) that is (are) interfering at the observatory screen (see p. 252 of the Cohen-Tannoudji text). The position-momentum variant of the UP states that errors in these "observables" in QM must adhere to

 

[math]\Delta x\Delta p \ge \hbar [/math]

 

The UP does not state that you can't concurrently measure both position and momentum (or energy and time), but rather there is a mind-blowing lower limit of the product of the errors in these observables. And equally mind-blowing, all changes in the product of these deltas must come in integer quantized steps of [math]\hbar [/math], regardless of scale, macroscopic or microscopic, all the way down to Planck scale, where things get really strange.

 

From these equations, the following inequality can be formed

 

[math]\Delta t\Delta p{v_G} \ge \hbar [/math]

 

The above inequality drives the logic of what happens in an experiment. The factor

 

[math]\Delta p{v_G}[/math]

 

is equal to

 

[math]\Delta E[/math]

 

(see the C-T text), and hence

 

[math]\Delta E\Delta t \ge \hbar [/math]

 

This is the energy time variant of the UP, and the mathematical path way shows how measuring time is effectively the same as measuring energy in QM's UP (go backwards in the math). Measuring energy is "the same" as measuring the momentum of the plate, which links your time measuring experiment back to the plate-on-springs momentum experiment in the C-T text. They are effectively the same. The energy time variant of the UP says as "error" in time gets smaller, the increasing "error" in the energy and momentum of the plate translates to "error" in position at the observatory screen itself, which must increase as the "error" in time decreases. The increasing "error" in position eventually destroys the interference pattern at the observatory screen, as the timing "error" gets smaller.

Edited December 27, 2013 by sb635

[DParlevliet]

The measurement discussed (post #32) is principally the same as the double slit (post #20). Both are a "double path" measurement, which is the base of an interference pattern.

 

You let a bad counter go over into a bad detector, but that are technical items. There are fast clocks and small pixels so can you prove with practical values that there is no area between the extremes you describe which shows both time and interference?

 

The math I leave to others to comment, but I suppose this only involves the Planck level world. Double slits are much larger then that.

[Delbert]

That is because photons has both particle and wave properties. The particle goes one path, but the wave goes both paths and the wave determines the propability of detection of the particle, even with a single photon.

Sorry, it can't be both. It can't be a distributed field of whatever name and a definable object at the same time. We might say it appears to have both, but it doesn't. We doubtless say that because of history, whereby there's been scientific argument about what it is. But I don't think at any time the scientific community has said is actually both.

 

I understand the billiard ball model of subatomic particles was a Rutherford conclusion following his experiments. Previous to that I further understand it was the plum pudding model. Little billiard balls are just a model, a convenience for our understanding. But in reality they can't be little ball bearings - little ball bearings (no matter how small) have all sorts of properties like volume, surface area, a nice spherical shape, even surface imperfections, not to mention made of something. And then there's the fact they don't exist until an electron moves from one orbit to another (again, that's how we explain or visualise its appearance).

 

There's an event at the source, followed by an event at the destination. What happens in between is not a photon (as what we would call an identifiable object) moving from source to destination. These events are what call a photon, what happens in between is something different. And the first event followed by the second (landing) event we conclude as a photon moving from one place to another. But if we try to catch it (because we think it's a little billiard ball in flight), or detect it by whatever means during transit we create or cause an event which we construed at a photon hitting, landing or whatever.

 

I previously offered an analogy of hitting a steel rod in reply #29 (perhaps not a very good analogy, but all I could thing of at the time). The hit was a photon and the force of the hit at the other end of the rod was a analogy of a photon at the destination. Perhaps the rod should be a large block to be more realistic.

 

Anyway, back to the two slit job. Detection (as we would describe it) at any point in between creates two sets of events joined together. Consequently the original field is apprehended just before the two slits rendering the result of the experiment being completely different - no interference pattern. Which is what'll happen in your timing diagram - no interference pattern. Rendering your diagram irrelevant to monitoring what happens whilst forming such a pattern. But I outlined all this previously.

[DParlevliet]

But I don't think at any time the scientific community has said is actually both.

 

Every authoritative book tells that a photon has parts of both.

[Endercreeper01]

1. It is only in several states at once if it is not observed. In fact, if a particle is not observed (not interacting with other quantum systems) it has a probability of being in any position.
There is something called the wave function, represented by [latex]\psi (x)[/latex]. The wave function is a function such that [latex]\int_a^b \psi (x) \psi^* (x) dx [/latex] is the probability of observing the particle between position a and b, where [latex]\psi^* (x)[/latex] is the complex conjugate of [latex]\psi (x)[/latex]. When a particle is observed, the wave function collapses and you observe the particle as being in a certain position. The wave function is basically a function describing the quantum system and how it behaves. The wave function can be a function of space, time, or both. There is also a momentum wave function represented by [latex]\phi (p, t)[/latex]. The two wave functions are related by [latex]\psi(x, t) = 1/h^{1/2} \int_{-\infty}^\infty e^{2\pi ipx/h} \phi (p, t) dp[/latex] and [latex]\phi (p, t) = 1/h^{1/2} \int_{-\infty}^\infty e^{-2\pi ipx/h} \psi (x, t) dx[/latex], where h is plank's constant.

2. We don't know

Edited December 27, 2013 by Endercreeper01

[Delbert]

 

Every authoritative book tells that a photon has parts of both.

Well, without the actual quote in the context of which it is mentioned, I'd suggest they're not necessarily saying it actually has both. But rather, it depending on the experiment. And I don't think that therefore means it has both. Indeed, if it has both as you suggest, are there any equations showing how the energy is shared out between the wave function and particle momentum? Although my mathematics is pretty useless, but nonetheless I would be extremely surprised if there were.

 

 

1. It is only in several states at once if it is not observed. In fact, if a particle is not observed (not interacting with other quantum systems) it has a probability of being in any position.

There is something called the wave function, represented by [latex]\psi (x)[/latex]. The wave function is a function such that [latex]\int_a^b \psi (x) \psi^* (x) dx [/latex] is the probability of observing the particle between position a and b, where [latex]\psi^* (x)[/latex] is the complex conjugate of [latex]\psi (x)[/latex]. When a particle is observed, the wave function collapses and you observe the particle as being in a certain position. The wave function is basically a function describing the quantum system and how it behaves. The wave function can be a function of space, time, or both. There is also a momentum wave function represented by [latex]\phi (p, t)[/latex]. The two wave functions are related by [latex]\psi(x, t) = 1/h^{1/2} \int_{-\infty}^\infty e^{2\pi ipx/h} \phi (p, t) dp[/latex] and [latex]\phi (p, t) = 1/h^{1/2} \int_{-\infty}^\infty e^{-2\pi ipx/h} \psi (x, t) dx[/latex], where h is plank's constant.

2. We don't know

I'm going to have to find time to improve my mathematics!

 

But nonetheless, it is clear to me that a photon isn't a little ball (billiard or otherwise), which means it doesn't go about acting like a billiard ball moving and bouncing off cushions. And any attempt to analyse it as such will fail. In fact I'd suggest if it were a tiny billiard ball then we'd really have a difficult time trying to explain it! The ball or particle model is just that, simply a model to help us to understand it. But not actually being a little billiard ball, our analysis of it being so beaks down at the fundamental level.

 

As I've said, for me it's noting more than an event. An event at the source (like my 'hit' analogy above), the energy of that event or hit is transferred through umpteen other events and reactions which eventually manifests at the source as another event. And we get this crazy idea that these two events are evidence of a thing (photon in this case) having moved from one place to another.

[mattcz450]

hi im 13 and I'm pretty sure i find great interest and understanding to the topic

[Enthalpy]

Hi mattcz450, welcome here!

 

QM is interesting indeed; but the present topic isn't the best introduction you can find about it, as it's in some places more philosophy and rhetoric than physics, so a standard text about QM would be a better read.

[mousser69]

Im hoping to gain interest in a theory I have that pertains to exactly what you are talking about. I just need someone to do the math. If its plausible, I only want mention. But at each step, when its not plausible, I need someone inteterested in exploring further my hypothesys. Not, " it just doesn't work that way". Thank you

[swansont]

!

Moderator Note

 

mousser69, please bring up discussion of personal theories in their own thread in speculations.

 

You might consider contemplating why someone would be interested in further investigation past a step where they are convinced it doesn't work.

 

[spocktorwho]

1. To my understanding, only if it is a quantum particle, like an electron or a quark.

 

2. We don't know.

[noxid]

.1 as I understand, one particle can be in two places at the same time. for instance tha particle that is building the table can be in the table and in the same time sumewere els. my question is are we talking about two particles or about one. if we are talking about one particle, what makes the table exist at the time the particle is sumewere els?

 

 

. 2what makes the string vibrate according to the string theory?

 

)I'm apologizing for my poor English(

 

simon

as far as i know the table exist only in one place becuZ it is being oberved (see young's double slit experiment using electrons), when not oberved the particles behave as waves (essentially, the particle is at every possible postion the particle can be), obervation causes a disturbance that materialize and shows where the particle is at that instant