# B Photon-Wave Duality: Why can't they be separated?

1. Nov 3, 2016

### MittyWalter

Hi!

So the whole Photon-Wave Duality phenomenon really bothers me. I found this little video earlier today:

I'm far more comfortable with reality *being* reality. You're either here or there. Every instant contains a single reality. You cannot be in two places at once, nor can you follow two paths at the same time. If you wind up in California, it's because you either drove or flew there. Not both.

And the observation that you are in Cali is totally separate from how you got there.

I don't question the observations behind photon-wave duality, but I wonder if the *interpretation* of the observations could be wrong?

Instead of saying photons are both particles ~and~ waves, wouldn't it make more sense to say photons are particles that ~emit~ waves?

Maybe "emit" is too specific, so let me rephrase:
Wouldn't it be more logical if Photons were surrounded by and/or traveling with light waves?

If you separate cause (photons as particles) from effect (waves associated with that photon) and say that photons are surrounded by lightwaves, you can observe both without also having to believe in unicorns (multiple realities).

While I watched the video, stopped it at each observation point to ask:
If the photo *itself* was surrounded by waves, could that explain the observation?

At 0:55:
Particle detectors prove that a photon does exist and will only go thru one door or the other (cause). But as soon as you catch it, the interference (effect) goes away. This doesn't make sense to me, unless the two are separated.

If that photon is traveling with it's own waves and you catch it all by itself, of course there would be no other photon (+waves) to interfere with the first one. And if you could truly isolate a single photo and catch it, the interference pattern would be limited by the location of the photon at the exact moment you caught it.

At 2:00:
If you set the device to look for a particle, a particle appears and it goes thru one door or the other (not both). If you set the device to look for waves, then waves are observed and they go thru both doors. Makes no sense again, to me anyway.

Unless you consider that the photon is surrounded by a globe of light waves. And those waves extend out from the center, wide enough to go thru both doors. If the photon is headed toward that back wall, so too is the wavy globe that surrounds it. Waves off to the east and west will still travel thru both doors, regardless of which door the particle goes thru.

Please can someone explain why a photon must be BOTH a particle and a wave? Vs simply a particle that travels with waves?

Thanks,
Mitty Walters

2. Nov 3, 2016

### PeroK

Unfortunately, the video is misleading, to say the least. If you fly to San Francisco, you fly to San Francisco. You don't find out later that you went by car: unless you've been hallucinating.

It does last an hour, but it may be an hour well spent.

You may be suprised to learn that most Quantum Mechanics textbooks don't mention the wave-particle duality at all. One of the most popular books by Griffiths only mentions it in the Afterword, as a historical footnote.

Your own personal theorising is, sadly, is just a guess based on nothing of any mathematical or experimental substance. This thread will probably get shut down, as it isn't allowed to this forum.

Try the Feynman lecture is my advice.

Last edited: Nov 3, 2016
3. Nov 3, 2016

### Staff: Mentor

Unless I'm mistaken, in Quantum Electrodynamics, the theory that is actually used to describe fundamental particles like electrons and photons, there is no duality. I don't know the details of why, though.

4. Nov 3, 2016

### Staff: Mentor

Photons, electrons etc. are neither waves nor particles. Both are analogues from the macroscopic world. They make sense because a wave function describes them and their behavior in most experiments. At the same time, the particle model is also suited in some cases. I think the latter is mainly a historic relic from the times of Rutherford and Bohr. The fact, that they are described by wave functions doesn't turn them into waves. A spring pendulum is also described by a wave function and I don't see a wave there.

These models are used to help us understand what otherwise cannot be understood, since we don't see it and it behaves completely different to the objects we are used to. In the end we are left with the mathematical description alone, wave functions and operators. Personally I'd wish we learnt the mathematics rather than being imposed on pictures we later will have to forget again, or even worse, forced to combine via a virtual duality. The easiest way is to accept, that these "particles" are simply something different.

5. Nov 3, 2016

### DrChinese

First, no one knows "why" the universe is the way it is. Physics attempts to describe the universe, not explain "why". It does that with theories. Yes, the theories can explain some "whys" - but not all.

Theories such as what you mention do not accurately describe photons. Theories which contain elements that are commonly referred to as "wave-particle duality" or "path integral" are much more effective. The Heisenberg Uncertainty Principle is a specific mathematical element which can represent wave-particle duality. Feynman's path integral formulation is also a mathematical treatment (in your version, the many ways to get to California).

You can probably imagine that current physical theories are quite good at predicting the results of actual experiments. That outweighs everything else, including your preferences. There are many modern experiments that demonstrate reality does not have the attributes you think it has. I would recommend that you learn more about this fascinating area by reading a few books, as that will help you see the persuasive arguments involved.

6. Nov 3, 2016

### Staff: Mentor

Do you have any recommendations, DrChinese? I might be interested in reading them as well.

7. Nov 3, 2016

### DrChinese

I was afraid of being asked that! My favorites are too old!! (On the other hand, the laws of physics haven't changed much recently...)

Steven Weinberg's "The First Three Minutes" (1977, updated as of 1993)
https://www.amazon.com/First-Three-Minutes-Modern-Universe/dp/0465024378

There are newer ones, but I usually don't recommend ones I haven't personally read. Below is newer (2003); more specialized but covers a lot of relevant material along the way:

https://www.amazon.com/Entanglement-Amir-Aczel/dp/B0035G02GI

Maybe someone else has a few good recommendations too...

8. Nov 3, 2016

9. Nov 3, 2016

### sandy stone

10. Nov 3, 2016

### Naman Jain Kota

Well i really really wanted to sum up what i understood, please point if i interpreted it wrong.

So basically we don't know what electromagnetic radiation is or what matter is.
All we do is make a theory for matter that is described by a wave function,operators and all and we consider it particle (what is a particle?? i mean definition). We get accurate results but this must not mean this is the actual picture. It's just our way to solve and get answers. Moreover we do sometimes mention wave particle duality, though we don't take it's mathematical account into our theory.

For Photons we have path integral formulation related to quantum field theory (i just googled it!). Thats a good way of describing photons. Even for particles i guess. We consider them to be fields (probably i just looked on google now), and that may not even be happening truly in world. But its more accurate that quantum physics.

11. Nov 3, 2016

### houlahound

yes, yes quiet right. very good - and if the answers correctly predict nature what else do you need to know?

12. Nov 3, 2016

### Staff: Mentor

If you know all of its properties and how it behaves, do you not know what it is?

How would you know if a model is the actual picture? If it is accurate enough, there's no way to tell the difference between the model and "actual reality".

13. Nov 3, 2016

### Naman Jain Kota

So we can confidently say everything exist in form of fields (or whatever quantum field theory is about)!!
But the quantum particle model of wave function, are both equivalent? One of those two must be correct right.

14. Nov 4, 2016

### houlahound

What is the quantum particle model?

15. Nov 4, 2016

### Naman Jain Kota

Sorry for lack of clear expression, basically i meant that a particle is described by its wavefunction, probabilities are linked to a wavefunction. I meant the quantum mechanics as given in griffith's book. We dont consider any types of field in that mechanics.
And yeah I dont have any idea of quantum field theory, so i may have been messing it up :P

16. Nov 4, 2016

### houlahound

there is more than one theory with different constraints.

QFT is the broader theory that explains the behaviour of quantum scale objects with less constraints built in.

the simpler theory with more constraints built in would be Schrodinger's wave mechanics.

17. Nov 4, 2016

### Staff: Mentor

My point is that we can certainly do better than say that we don't know what EM radiation and matter is.

18. Nov 4, 2016

### DrChinese

There is a well-known phrase: the map is not the territory. Theories are the map. They are useful descriptions. You will find that every theory leaves something to be desired.

So don't confuse ANY theory with what it describes. You could never say a theory is the "actual picture".

19. Nov 4, 2016

### MittyWalter

Wow, thanks for all the thoughtful responses! And most especially for all the suggested reading. I have a cup of coffee and can spare an hour, so I'll start my journey with PeroK's movie.

My take from what you guys said:
• The topic of Wave–particle duality is antiquated
• The video in my OP is misleading because it fails to acknowledge other more modern takes
• There are plenty of other theories that can mathematically predict the behaviors (w/o conflict?)

Einstein put it this way:
"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do."

PeroK, you said that my suggestion was "just a guess based on nothing of any mathematical or experimental substance." The first part is true, but the second is not. Granted I did not perform the experiments that underlay Einsteins comments above, but my guess was based some pretty solid work done by Planck, Bohr, and many others.

As a reminder, my guess was that photons are particles surrounded by a globe of waves. The circumference of that globe becomes larger or smaller depending on the excitation of the particle.

I realize I need to dig deeper, read and learn. And, ultimately, fresh_42's take is where I may end up: "The easiest way is to accept, that these "particles" are simply something different."

But I'd still like to know of any theory that accounts for both? Houlahound points to QTF

20. Nov 4, 2016

### MittyWalter

Excellent. I get that, I really do. I was just taking a shot drawing my own map! :D

21. Nov 4, 2016

### PeroK

"A globe of waves" means nothing to me. You can in fact think about the wave-particle duality another way. What actually is a wave anyway? If you flick a piece of rope you see a wave moving along the rope. But the wave is just each part of the rope in turn moving up and down in response to the previous section of rope. Nothing physical is actually moving along the rope. So what exactly is the wave?

Perhaps a pulse of energy? And maybe that's starting to sound almost particle-like?

22. Nov 4, 2016

### MittyWalter

I picture something like this:
http://diygravity.com/circle_array_wavy.jpg [Broken]

And yes, it would be something like energy pulses spinning off the particle.

Last edited by a moderator: May 8, 2017
23. Nov 4, 2016

### Staff: Mentor

This doesn't look like a useful picture to me.

A good layman's presentation of the basics of quantum electrodynamics, which goes into some detail about how to "visualize" the way photons work in QM, is Feynman's QED: The Strange Theory of Light and Matter.

24. Nov 4, 2016

### Staff: Mentor

The nearest we can come to these days is symmetry. But whether it should be taught that way is the subject of a current thread with various (valid) views. Overall, and this is not my view, most are not fans of the idea - at least of the book that attempted to do it.

Thankaks
Bill

25. Nov 8, 2016