# Is this representation of a photon correct

1. Mar 23, 2014

### shreder

2. Mar 23, 2014

### Drakkith

Staff Emeritus
No, no not at all. It's 100% wrong.

3. Mar 23, 2014

### Cosmobrain

There is no such thing as a correct representation of a photon. No one knows what it really looks like. However, a more accurate representation would be a wave drawn inside a circle (which is the quantum of light).

cb

4. Mar 23, 2014

Staff Emeritus
Drakkith is right. Cosmobrain is not.

5. Mar 23, 2014

### Drakkith

Staff Emeritus
To elaborate, a photon is the quanta of interaction between an EM wave and matter. What that means is this:

An EM wave is a wave that propagates through the electromagnetic field. What's waving? The electric and magnetic field vectors. The field vectors are what we use to show how an electric or magnetic field will interact with charged particles, and can be imagined as arrows that point one way. For example, if the electric field vectors are pointing up, then a negatively charged particle will feel a force that pulls it down. In an EM wave, these vectors are oscillating in magnitude and direction, repeatedly moving between pointing "up" and then "down" (or whatever direction the EM wave is polarized).This is how an antenna works. The EM wave causes the electrons to oscillate in one direction and then the other.

But what about photons? Well, first we must realize that when an EM wave interacts with matter, such as the electrons in an antenna, it gives up energy to them to make them move. This giving up energy is the entire crux of the issue. In classical physics, an EM wave gives up energy in a smooth, continuous manner and the amount of energy it can give up at one instant can be any value. But this is wrong.

The development of Quantum Mechanics showed that an EM wave does NOT give up its energy in a smooth, continuous manner. Instead, it gives it up in little "jerks" or in "packets" of energy. How big each jerk or packet of energy happens to be depends entirely on the frequency of the EM wave. Higher frequency EM waves have more energy in each packet than lower frequency EM waves. This is how an X-Ray or Gamma Ray can ionize atoms and molecules; the amount of energy in its packets is high enough to completely eject electrons from the material.

These packets are what we call "photons".

In addition to energy they also carry some other quantum properties which are beyond the scope of this thread. But they are not physical objects in the usual meaning, nor are they purely waves. And they are most definitely not moving up and down as an EM wave propagates. Those are the field vectors, not the photons. They are, quite simply, the very odd way that light interacts with matter.

6. Mar 23, 2014

### Cosmobrain

I don't get it. He is right simply because he said OP is wrong, is that it? Also, when you say someone is not right, you should at least say why (who am I to say such thing to a mod. Oh well). I believe that what I said is pretty much correct. I've read the latest Drakkith post and it doesn't contradict my post.

cb

7. Mar 23, 2014

### Drakkith

Staff Emeritus
Can you explain how a wave within a circle represents a photon more accurately than the OP's link? What does this wave and circle represent?

8. Mar 23, 2014

### Cosmobrain

The circle is the packet of energy and the wave inside represents the frequency. I think this representation is helpful enough and has been used in several videos, like

this: http://youtu.be/i1TVZIBj7UA?t=3m

or this: http://youtu.be/a8FTr2qMutA?t=1m57s

cb

9. Mar 24, 2014

### f95toli

But that description is also incorrect. There is no way to corectly visualize the frequency of a single photon; it is most definitly not a wave in in some sorft of energy packet.

10. Mar 24, 2014

### Cosmobrain

Sure. As i said in my first post in this thread, there is no way to correctly representate a photon. We don't know what it actually looks like.

cb

11. Mar 24, 2014

### sophiecentaur

There is little point in posting links to YouTube videos unless they represent accepted models. (Have you read PF rules and guidelines?) It just adds confusion. There are no 'cuddly' models of the photon because it is not that sort of entity. It doesn't (and shouldn't have to ) 'look like' anything. You cannot 'dumb down' Quantum Models in a satisfactory way.
Waves are a much more reliable way to describe Electromagnetic energy flow. They are still a metaphor for something very abstract but, at least there are other examples of waves that follow many of the same rules as EM 'waves' so it's a good, valid, way into the subject.

12. Mar 24, 2014

### Cosmobrain

God, why did everybody decide to pick on me. My first post shouldn't even be noticed in the first place. I just suggested a way to represent a photon. Why do you guys always want things to be absolutely perfect. As you said, a photon doesn't (and shouldn't have to) look like anything, then there is no correct way to represent it. That's pretty much what I have said in the previous posts.

cb

13. Mar 24, 2014

### sophiecentaur

No need to take offence; none was intended. If you post something speculative on PF then you really should expect a 'contrary' response.
Yes - things should be as absolutely perfect as you can manage. That's what Science is all about. You presumably would complain if it was suggested that 2 + 2 doesn't always equal 4. It's equally important to avoid nonsense in Physics whenever possible.

14. Mar 24, 2014

### Drakkith

Staff Emeritus
I highly recommend that you don't take critiques of your posts personally. Science is extraordinarily complex and even small things, such as trying to graphically represent a photon, are highly prone to misunderstandings if not done very carefully with a decent understanding of the subject matter.

On top of that, PF values the accuracy of its content very highly, so even small mistakes can and usually will be corrected with varying amounts of tact.

If you're going to post here, you're going to have to learn to deal with this without trying to defend yourself every time someone corrects you.

15. Mar 24, 2014

### Cosmobrain

The thing is I never said I was the owner of the truth or anything.I made myself very clear that there is no accurate way to represent a photon. However, we can use representations that work fine for whatever purpose we have (like the wave in a packet). Topics like this do require some speculation.

cb

16. Mar 24, 2014

### Drakkith

Staff Emeritus
No, topics like this do not require some speculation. Why would you think this? What speculation is required to understand that a photon is not an object with a size and cannot be represented visually unless you clearly state what is being represented? (Such as a cloud of color that gradually fades away to represent the probability of finding the photon at a certain position)

As I just said above, don't take this so personally. Everyone gets corrected here on PF. Peer review is a fundamental part of the modern scientific method after all.

17. Mar 24, 2014

### Cosmobrain

Op asks "Is this representation of a photon correct?"

I say that no, there is no accurate way to represent a photon visually. Then I suggested a way to represent it. It is pretty simple.

Well, we're getting way off topic here. Let's just forget all of this. You'd better reply to me in my profile I guess.

thanks, cb.

18. Mar 24, 2014

### sophiecentaur

That's the problem. Having said it can't be done, you then go ahead and try to do it. I don't think you realise the effect that some of these over simplifications can have on students and 'the uninformed'. Whatever your personal and internal picture of a Scientific concept is, it is pretty important to keep it personal and to stick to the well established ideas in what you write. That is more or less the mission statement of PF and it is there because PF wants to be a reliable source of knowledge and ideas. Hence the emphasis on peer reviewed sources. (Even Wikipedia is referred to with caveats when the subject is anything but classical and mainstream.)

The bottom line for the thread is that the image in the OP is not acceptable and nor is the alternative 'notation'. Even the photon in Feynman diagrams is a dodgy symbol if it is really taken at face value - and that was from the blessed Saint Richard!!