Light, Photons, Waves, Particles: Wave-Particle Duality....

[ISamson]

Me and my friend have recently (half a year ago) had a huge debate, between ourselves, about the wave-particle duality.
We took sides in light being a particle or a wave. I was for particle he was for waves. At the end of a hot-filled week of arguing, the debate ended up with the acceptance of light being as both. We just couldn't decide between the Double Slit experiment and the particles known as photons. Double Slit proves the argument for waves, but what are photons then? (This was my main argument for particle light). If light is wave, then what did all the wise physicists "invent" photons for?

However, recent advances with String Theory have led me to confusion, as everything, all particles, end up being waves, or to be more precise, vibrating strings. (What is meant by strings? A form of matter (a new particle) like "String"?) If it is like this, then all matter is waves. Right?
Am I missing some basic information on the field? Am I not up to date with some recent, recent advances in the field?
I value your opinion and help.
Thank you.

 

[mfb]

String theory is a highly speculative approach. Forget it. It leads to more confusion than clarity.

A proper treatment of light needs quantum electrodynamics (and a few years of study to learn that). It is neither wave nor particle. Sometimes light behaves similar to what we would expect from a wave, sometimes it behaves similar to what we would expect from particles. That doesn’t mean it would be either of them.

 

[Orodruin]

It is also worth pointing out that what modern physicists describe as "particles" are not small balls or anything that is remotely close to small balls. It is a nomenclature that has remained and stuck with us. Again, a proper treatment requires years of study of quantum field theory at A level.

 

[ISamson]

It is also worth pointing out that what modern physicists describe as "particles" are not small balls or anything that is remotely close to small balls.

What do physicists describe them as then?

String theory is a highly speculative approach. Forget it. It leads to more confusion than clarity.

Ok, good.

A proper treatment of light needs quantum electrodynamics (and a few years of study to learn that). It is neither wave nor particle. Sometimes light behaves similar to what we would expect from a wave, sometimes it behaves similar to what we would expect from particles. That doesn’t mean it would be either of them.

If light is neither a particle or wave, then what is light?
Is it possible to describe 'light' in a paragraph, or is it necessary to learn physics for years? Can 'light' be described simply?

Thanks for the replies.

 

[Orodruin]

What do physicists describe them as then?

Excitations of quantum fields.

 

[ISamson]

Excitations of quantum fields.

Wikipedia says: "Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum."
, but are we talking about the electromagnetic spectrum?
Where can I find resources for reading about light from a quantum physics' point of view?

 

[Nugatory]

Where can I find resources for reading about light from a quantum physics' point of view?

Googling for "quantum electrodynamics" and "quantum optics" will find a ton of stuff, but I'm not sure how helpful it will be. (And be warned that the article on quantum optics is among wikipedia's weaker ones).

Feynman's book "QED: The strange theory of light and matter" is a good layman-level explanation, and I highly recommend it.

 

[bhobba]

This thread is marked as B level - its can't really be explained at that level - you need at least an I level, and even then an A level thread would be better - but you can to a large extent get a 'feel' for what's going on at the I level.

In that vein, and in the hope the OP and others reading this thread, can glean something from reading it see the following:
http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

Thanks
Bill

 

[Zafa Pi]

"Fifty years of conscious brooding have brought me no closer to answering the question, 'What are photons?'" A. Einstein

 

[bhobba]

"Fifty years of conscious brooding have brought me no closer to answering the question, 'What are photons?'" A. Einstein

That was Einstein.

This is now.

I would say we know exactly what going on as a mathematical model - beyond that - I will leave up to philosophers.

Einstein of course had a particular view of reality, which is why he believed QM incomplete - not incorrect - he thought the form it was bought into by Dirac was correct (in fact he considered Dirac's book his bible on QM - or something like that - and always carried a copy) but not complete. The then very popular Copenhagen interpretation grated at the view of reality he had. Was he correct - who knows - he was certainly correct about it being incomplete as quantum gravity readily attests to - although its issue is not as usually portraid - but that is a whole new thread in itself. These days Copenhagen, while still popular, has a lot of competitors, including the interpretation Einstein came up with called the Ensemble which is the one I hold to. Do I hold to Einsteins view of reality - no - I look on reality as what our models describe. Very unsatisfactory and quite likely circular - but hey - nobody said this stuff was easy.

Added Later:
What was Einsteins exact view of reality - it actually isn't too far from mine, but does differ in crucial areas. Here is an interview he gave that I think sums it up rather well:
https://www.scienceandnonduality.com/wp-content/uploads/2014/09/einstein_tagore.pdf

Just as an aside - and the mods can remove it as they see fit - I think Tagore was basically sprouting mumbo jumbo - but hey - Einstein is way smarter than me and maybe saw more clearly than I what his point was.

Thanks
Bill

 

[Zafa Pi]

That was Einstein.

This is now.

I would say we know exactly what going on as a mathematical model - beyond that - I will leave up to philosophers.

Laplace felt the same way 200 years ago. If history is any indicator, then the current models will be fundamentally revised. Models provide a recipe for predicting, I'm not convinced they necessarily provide knowing, e.g. the correlations from measurements of entangled photons, or the double slit.

Einstein of course had a particular view of reality, which is why he believed QM incomplete - not incorrect - he thought the form it was bought into by Dirac was correct (in fact he considered Dirac's book his bible on QM - or something like that - and always carried a copy) but not complete. The then very popular Copenhagen interpretation grated at the view of reality he had. Was he correct - who knows

In order to make it complete he proposed hidden variables, which now most find incorrect.

I look on reality as what our models describe. Very unsatisfactory and quite likely circular - but hey - nobody said this stuff was easy.

Our models employ the real numbers. Are they part of your reality? In trying to make that case you will become one of those "philosophers".

I think Tagore was basically sprouting mumbo jumbo

I couldn't agree more. I'm surprised Albert deemed it worthwhile to engage with him (actually maybe he didn't, I think he was sarcastic when he said he was more religious than Tagore).

 

[bhobba]

Laplace felt the same way 200 years ago. If history is any indicator, then the current models will be fundamentally revised. Models provide a recipe for predicting, I'm not convinced they necessarily provide knowing, e.g. the correlations from measurements of entangled photons, or the double slit.

I have no doubt about it - but as some kind of limit our current theories will likely survive.

Regarding the other Einstein stuff that's best done in another thread I will start on Einsteins view of QM - its getting rather off-topic for this thread.

The new thread should be there in a couple of minutes and I will link to it, and link back to this one:
https://www.physicsforums.com/threads/einsteins-view-of-qm.934283/

Thanks
Bill

 

[bhobba]

I couldn't agree more. I'm surprised Albert deemed it worthwhile to engage with him (actually maybe he didn't, I think he was sarcastic when he said he was more religious than Tagore).

I have started a new thread but must mention here just in case some don't get it - I am sure Einstein thought he was sprouting 'nonsense' and playing along a bit - the key point Einstein was making is objective reality exists independently of us and science's job is to find out about it. That was his belief. That was the issue he had with his good friend Bohr, Copenhagen and the subjective wave-function completely describing the world. Although I never understood much of what Bohr wrote, especially Complementary, his ideas while subtle, were not, well I won't mince my words, mystical gibberish.

Thanks
Bill

 

[edmund cavendish]

What Einstein described as "spooky action at a distance" i.e quantum entanglement has been shown to be correct. Also cf the measurement problem I am not so sure about the relegation of the oberver in a world of independent objective reality.

 

[phinds]

If light is neither a particle or wave, then what is light?

It is a quantum object, which is a thing which, if measured for wave characteristics, it shows wave characteristics and if measured for particle characteristics, it shows particle characteristic (but NOT classical particles which are little tiny balls and have nothing at all to do with light or photons).

 

[Haborix]

FYI: y'all are resurrecting an old thread.

 

[phinds]

FYI: y'all are resurrecting an old thread.

Nuts. Didn't notice that. Thanks for the head's up.

 

[vanhees71]

What Einstein described as "spooky action at a distance" i.e quantum entanglement has been shown to be correct. Also cf the measurement problem I am not so sure about the relegation of the oberver in a world of independent objective reality.

The only important point is that there are no "spooky actions at a distance" when measuring entangled parts of a quantum system. Entanglement doesn't describe (inter)actions at a distance but correlations between parts of a quantum system, which cannot be described by any "local realistic theory" a la Bell.