# Wave/particle duality

1. Dec 13, 2004

### primal schemer

Hi all,

Just wanted to clarify something in my head about the wave/particle duality of light.

The fact that light is transmitted by photons, means that it can be described as a particle. While the wave nature comes out of the fact that the photons are distributed in a wave like manner. i.e. when you do the double slit experiment, at the final stage, the photon can appear anywhere, but is most likely to appear at the peak of the wave and least likely to appear at the bottom of the wave.

So, presumably when using red light the peaks and troughs of the waves will be further apart than if you used blue light (as red has a lower frequency)??

Also, I guess the same would happen if you used X-Rays, UV rays etc. (of course you need a surface that these cannot penetrate)

Thanks,

PS

2. Dec 13, 2004

### cronxeh

wave phenomenon comes from double slit experiment and it's difraction pattern. particle phenomenon comes from photoelectric effect and it's cutoff frequency

3. Dec 13, 2004

### ZapperZ

Staff Emeritus
This is more appropriate to be in the QM section.

Take note also that the "photon" picture CAN be used to describe ALL the so-called wave effects of light, even the 2-slit experiment! (I've made frequent reference to the Marcella paper). Now it is EASIER to simply use the wave description when light is showing the familiar properties of light. That's a different matter entirely. But we shouldn't confuse "convenience" with "duality".

Also please keep in mind that in QM, there isn't two seperate descriptions of light - just ONE, and only ONE.

Zz.

4. Dec 13, 2004

### dextercioby

Yeah,Zapper,but he made no reference to either of the theories describing light behavior.He didn't say whether he was speaking in the Classical Field Theory/QM/QED context.

5. Dec 13, 2004

### ZapperZ

Staff Emeritus
I think as soon as one make any inference to "wave-particle duality", that's the realm of QM, because no such thing is even considered in classical light description.

Zz.

6. Dec 13, 2004

### dextercioby

You mean QED ,as in QM,electromagnetic radiation is seen classically.A bunch of waves and nothing else.The interaction electron-photon exists only in classical (original) treatment of Sir Arthur Holly Compton (1923) (and here i mean the usual treatment given in highschool:2 relativistic particles scattering one on an another,usually with the relativistic electron assumed fixed) or in the treatment by QED,in either of its two quantum descriptionsriginal (operator) or path-integral.
Quantum mechanics discusses only the scattering of (usually nonrelativistic) electrons on a potential,meaning classical electromagnetic (actually electrostatic) potential.

Daniel.

7. Dec 14, 2004

### primal schemer

Thanks for the answers, but still a bit confused. I didnt realise there was so many different interpretations of light.

When you say that the photon picture can be used to describe all the wave effects of light, does that mean that the individual photons tend to spread their placement into wavelike positions, thus explaining the wavelike nature??

What is the Marcella paper?? I had a quick look on google, but didnt see anything.

PS

8. Dec 14, 2004

### ZapperZ

Staff Emeritus

What you need to understand is that it isn't the photon that the "cause" of the wavelike effects - it is the superposition of all the available PATHS that the photon can take. So when you have a length scale where you can't tell which slit the photon takes, then the superposition of its path causes the wavelike property.

Then this means that the photon isn't unique in exhibiting such behavior. If you can device a similar setup for electrons, protons, neutrons, buckyballs, etc... you can also get the similar wavelike properties. It isn't just the object in question that's causing the weird stuff - it is the whole setup!

Zz.

9. Dec 14, 2004

### yanniru

Particle-only theories like Feymann used in deriving QED can explain double slit experiments by having anti-particles returning from the future to interfere with the particle going forward in time. In this approach there is no wave/particle duality.

The more common sense perspective is to assume that basically only waves exist and they become quanta or particles when they interact with other particles, like at the detector screen behind the double slit. I prefer this perspective. But then you have to explain how a smeared out wave function or EM wave can instantly collapse into a point.

And there are several more equally bizarre explanations of QM. We know how to calculate QED very accurately. But we have no idea what it means to have particles coming back from the future. Even Feymann said no one knows what QKM means, or something like that. My thinking suffers from uncertainty.

10. Dec 14, 2004

### Wave's_Hand_Particle

What this means is that Electron's are travelling faster than light, according to SR?..the MWI also means that Electrons are positioning themselves at specific locations in order to meet 'present-time' photons, they are in a sense blocking the paths of photons, and thus a photon travelling between two Atoms is being manipulated, [determined] by the 'same' single Electron?..what comes to mind here is Bat and Ball! Electron=Bat..Photon = Ball...conforms to the reality of Bat/Particle..Ball/Wave and thus Bat/Wave..Particle/Ball !

Back to the Wave-Particle, the 'Cat-in-Box-event' interpretation of duality, can mean that the geometric structure of a 3+1 spacetime event, is reliant upon, Electrons that confine Atoms to a specific Location, determine events of Observation, present-times.

Photons appear 'anywhere', because Electrons orbit around specific locations, the 'Screen' contains Atoms, Atoms have Electrons..photons need Electrons, a Bat hits Ball, Ball moves form one location to another Undetected if there are NO electron structure between locations.

You cannot make a '3-Dimensional' detector that contains no Electrons?..this is why 3-Dimensional structures cannot be observed outside of Spacetimes, they appear in Spacetime locations and photons 'Vanish'..dimensionally, across the vast Electro-Magnetic-Fields.

A good example of Diffraction-Grating is to think of the Grating as a Geometric 'Shadow' CAUSED by the location of Electrons contained within the Screen. Construct the screen out of differing structured materials, and hey presto this will determine the 'observed' pattern will be altered accordingly., for instance a screen composed of a specific geometric Solid will differ from a screen comopsed of Gas molocules.

LCD 'screens' are a good way to observe and understand dimensional constraints.

A single photon detector cannot exist?..it needs at least TWO electron locations!

Last edited: Dec 14, 2004
11. Dec 15, 2004

### marlon

I an very sorry but what you say here is just wrong wrong wrong...The concept of wave-function (thus also particle-wave-duality) is extensively used in both QED as QCD (basically all QM-field theories).

??? This is against the definition of DUALITY...Both views are valid at all times, just not simultaneously

True story...but you know, this is a typical statement that is true in nature, yet it is useless. Why ? Well, because you are assigning the wrong value and false interpretation to some "physical" concept. Look, particles moving backwards in time are just like anti-particles moving forward in time...These things are extensively used in QED-calculations that on themselves yield real physical and correct results...so what's the problem...who says you need to get this...

This is just the same with virtual particles... Are they real or not ? Are they physical are not ?

Well, THEY ARE NOT REAL ON THEMSELVES YET THEY ARE PHYSICAL...let me explain. Virtual particles are again used in the correct adequate description of physical phenomena. So they definitely have their PROVEN use. Yet these particles are not real because the can only exist as an intermediate step between two stages in an interaction. During this step one could argue that they are "real"...But that is not the point...Point is that virtual particles are used in calculations (somewhat of a mathematical instrument, if you will) and they arise from the unification of special relativity and QM. Virtual particles exist as an intermediate step in interactions between real particles. They exist as a consequence of the fact that there is an interaction going on...Ofcourse the total interaction is real, yet virtual particles are just a way of describing things...thus they are "semi-real" but certainly physical...

regards
marlon

12. Dec 16, 2004

### Louis Cypher

Re: let there be light?

I like to use the analogy of the bird and the cage when looking at light, we see a caged bird. In QM there isn't one description of anything there are plethora of descriptons, that's the whole point, yes I know a rose by any other name and all that, a photon is still a photon regardless of how you chose to percieve it, but if we accept the quantum we must accept that what we're looking at has many possibilities, so we must also challenge what it is we're seeing, is it real or a fantasy, I'm not in a position to answer that question I wish I was, but if QM teaches us nothing - it is to assume nothing :-)

Just a thought?

13. Dec 16, 2004

### ZapperZ

Staff Emeritus
Er... HUH?!

Show me exactly this "plethora of descriptions".

Zz.

14. Dec 16, 2004

### dextercioby

I found only 3:Schroedinger,Heisenberg,interaction picture (sometimes called Dirac-Tomonaga-Schwinger).I assumed that by "desciption" he meant "pictures". And they are unitary equivalent.

Daniel.

PS.He might have meant "interpretations",though,which is something totally different.And they are a "plethora". :yuck: For what's worth,i've said it and i'll say it again."PHOTON" is a completely strange notion to QM.It pertains to QED.

15. Dec 16, 2004

### ZapperZ

Staff Emeritus
Let's not confuse the issue here. You and I know that just via a simple transformation, you are NOT getting a new "description". That's like saying a system described in cartesian coordinate is a different "description" than the same system described in spherical coordinates. There's nothing fundamentally, conceptually, and even mathematically different here.

Zz.

16. Dec 16, 2004

### dextercioby

To me,there was no confusion whatsoever.These things are very clear.Or at least ought to be.He said "description".The english word which translates the word "descriere" (romanian) is "description".I don't know why physicists chose the word "picture",i guess it's an enigma. I don't follow your concept:"simple transformation".It's surely as hell it ain't "unitary transformation".By a unitary transfomation of a model in one "description" (okay,let's call it "picture") you end up in another picture and so on.The three pictures are unitary equivalent.You and i know these things mighty well.
Let's wait to see what re really meat by the word "descriptions".If he's native (American) English speaker,he definitely wasn't referring to "pictures".

Daniel.

17. Dec 12, 2005

### inFinie

Spiral photon path(s)?

Are there any disproven or not yet proven theories about photons going in spiral paths (as in DNA helix). I once heard something like this and a search on this forum did not turned up any results? Any recommendations to look else than google and hakia?