1. Dec 16, 2016

Are photons(when described as a particle) considered objects? You can't see them on an individual level, but they hit you and interact with gravity. Might be a silly question, but was just debating it with a friend.

2. Dec 16, 2016

### Drakkith

Staff Emeritus
That pretty much depends on what you define as an object. I doubt there's a hard answer to your question.

3. Dec 16, 2016

### phinds

Photons are real and I think it's fair to consider them as objects, but they are not the little billiard balls that you sometimes see them represented as and light does not travel as photons. It travels as a wave and it is the wave that "hits" you. A photon is the result of the wave interacting with a particle (of your skin or your retina or a phosphorous screen, etc.)

4. Dec 16, 2016

### Delta²

A photon doesn't have dimensions like an object big or small has(of course then again it depends how you define an object). A photon is a point particle. It does NOT have mass either (though it interacts with gravity but this is due to the curvature of space time due to gravitational field). So a photon doesn't have two of the most (at least according to me) important properties of an object, that is dimensions and mass, so I doubt we can consider a photon to be an object.

5. Dec 16, 2016

### DennisN

It's not a silly question.
That's true. But there are other ways to detect them, see e.g. these links
• Nondestructive Detection of an Optical Photon

6. Dec 23, 2016

What about Gluons?(the other massless particle) do they have dimensions?

7. Dec 24, 2016

### Delta²

No all the elementary particles of the standard model regardless if they are fermions like electron and quark, or bosons like photon and gluon are all considered to be point like particles.

Even if we are to make a modification of the standard model where the elementary particles have dimensions they would be very small for the current technology to see it (dimensions of the order of $10^{-100}$ or even smaller). However the main argument against such modification is that if an elementary particle has dimensions, then it should consist from other smaller particles which have even smaller dimensions and these smaller particles if they have smaller dimensions they should consist from other particles with even smaller dimensions and so on, so we are like forced to accept that if a particle is elementary then it has no dimensions, it is point like.

8. Dec 25, 2016

### electro-physics

Does that mean photon is part of matter to which light hits and not part of light wave itself?

And if it's true that photon is part of matter then does it shows that this photon should always have some tiny mass?

If photon has no mass then can we say it's the discrete property of a shock wave generated when light bounces with matter?

9. Dec 25, 2016

### Drakkith

Staff Emeritus
It does not. It just means that the interaction of the EM wave with matter is quantized, with each interaction transferring a discrete amount of energy instead of a continuous amount.

10. Dec 25, 2016

Photons are particle as well as wave
This phenomenon is known as wave-particle duality
Every thing (including you) behaves as a wave . Very object has a wavelength but bigger objecys like us have very very very small wavelength but as the things goes on decreasing in size there wavelength starts increasing and at a very small level like at photon level they starts behaving like a wave
This phenomenon is known as wave larticle duality

11. Dec 25, 2016

### weirdoguy

No they are not. Wave-particle duality is an outdated concept.

12. Dec 25, 2016

### SleepDeprived

But seriously, if wave-particle duality is an outdated concept, what has replaced it? Could you provide a link?
There is a online video at World Science Festival where Brian Green, Sean Carrol ... and others talk about how they are still struggling trying to explain the wave-particle duality I guess there are still a lot of "we just don't know yet".

[Mentor's note: This post has been edited to remove some off-topic comments]

Last edited by a moderator: Dec 26, 2016
13. Dec 25, 2016

### phinds

Well, "replaced" isn't quite the right concept, it was just dropped since it was not correct. Quantum Mechanics says that EM radiation is not a particle or a wave, it is a quantum object and will exhibit wave characteristics if you measure for wave characteristics and it will exhibit particle characteristics if you measure for particle characteristics but neither of those types of measurements means that the quantum object is a particle or a wave.

14. Dec 26, 2016

So because all of these point like elementary particles don't have dimensions, does this also mean that they have no volume as well?

15. Dec 26, 2016

### Staff: Mentor

The longer answer: They are called "particles" for historical reasons, but they are not anything like what the ordinary English-language word means. That word suggests something like a tiny grain of sand with some tiny but definite volume that's located somewhere in space (although we may not know exactly where); and quantum particles are nothing like that.

16. Dec 26, 2016

### Staff: Mentor

Wave-particle duality is part of the "old quantum theory" which was replaced by the modern theory of quantum mechanics; the key papers of the modern theory were published starting in 1925, and the new theory was largely complete by 1933 or thereabouts. Even then, however, the theory did not allow for the effects of special relativity, so could only be used when the speeds involved were small compared with the speed of light and the energies involved were small compared with the $E=mc^2$ energies of the particles involved. Of course, neither condition applies to photons ($m=0$, and their speed is the speed of light); it took another decade or so of work to hammer out quantum electrodynamics and quantum field theories to arrive at the modern understanding of photons.

That video is not exactly wrong (it's more of a lie to children) but it's also not a serious explanation of what the science really says. Sources like this are not acceptable references under the Physics Forums rules - sometimes there's no substitute for the real thing.

17. Dec 27, 2016

### lychette

There are no outdated concepts.....please qualify by quoting the current concept. All current physics txt books refer to wave-particle duality in their explanation of modern physics. Which ones should we ignore ??

18. Dec 27, 2016

### Staff: Mentor

You will find the modern form of the theory (which isn't that new - about 85 years old new) in many texts - https://www.amazon.com/Quantum-Mechanics-Development-Leslie-Ballentine/dp/9810241054 is a good one. Or, you can just look at the Schrodinger equation - there's no wave-particle duality there, just quantum states with more or less variance in the possible outcomes of a position measurement.

There are certainly modern textbooks that refer to wave-particle duality, but most of them do so only as part of the historical summary that they use to motivate the development of QM.

Last edited by a moderator: May 8, 2017
19. Dec 27, 2016

### lychette

Are you suggesting that wave - particle duality has no place in modern teaching of physics. Should it be transferred to teaching of history?

Last edited by a moderator: May 8, 2017
20. Dec 27, 2016

Exactly.