Particle or wave question

Simon Bridge

You mean "does light have gravity?" or, "do we know how a photon got from A (source) to B (detector)?"

I think the speed that light travels at is understood as a property of space.

http://www.physicsforums.com/showthread.php?t=224574
... light has gravity.

(Off the Feynman lectures prev.)
... we consider the exact path of a particular photon to be uncertain. The classical trajectories are what you get on average.

There is a relativistic formulation of quantum mechanics - usually covered at post-grad level.

Does that help?

CLourensS

Both. How does it move from A to B; There must be a form of conductance to carry the information.
If light (a photon (I struggle to say a photon because in my mind it is counter intuitive)) is/has energy and a mass, (to my understanding e and m is almost interchangeable but not quite) it must affect space and have a gravity of sorts.

Now I wonder how this gravity or affected space around a photon could affect what we would observe at the two slits. For example what if the two slits were further apart?

I suspect (probably in ignorance) that the way light travels and gravity could tell us a lot about the structure of space.

Simon Bridge

Well then - both questions have already been answered for you :)
I have provided a "tldr" version in my previous post with a link for a more detailed version. You should read/view those links in order to better frame further questions.

Meantime:In the EM-wave model for light, the electric and magnetic fields sustain each other through space with no need for a conductor or a medium.
In the standard (particle) model, photons get from A to B the same way as any particle. Do you have any trouble with the idea that an electron can travel through a vacuum without having a conductor there? The details of how light, or any particle, gets from A to B, is covered in the Feynman lectures linked to earlier.Light does not have mass.Mass and energy are interchageable through the mass-energy relation.We know how the 2-slit experiment is affected - you can look and see!You know that - just move the slits further apart and see.The way light travels does tell us a lot about the structure of space ;)

You need to check out those links before you reply again.
;)

CLourensS

Space is the medium, the way I see. Vacuum for the least interference. Anything not vacuum would affect the structure of space as medium. To our current model, everything inside our expanding universe is space. And as we know, it is affected by energy and mass. And through which light travels. How it is conducted or transferred is a different question. Light could for example, since it has no mass, be a ripple in space caused by an energy source. (Just an example)

I'm working away from home and office for a bit and have only a Blackberry for internet access, which is challenging for research. Pardon though, and I will read up as soon as I'm back.

Simon Bridge

When we say that something is a medium for a wave - we mean that the wave is composed of the substance of the medium. eg. water waves are composed of water molecules, sound waves air, and so on.

To say that vacuum is the medium for EM waves is to say that EM waves are composed of bits of vacuum somehow - bits of nothingness. Fundamental particles are often described as being ripples in a field associated with that particle ... but not ripples in space.

What education level are you approaching this at?

CLourensS

Space is the medium, the way I see. Vacuum for the least interference. Anything not vacuum would affect the structure of space as medium. To our current model, everything inside our expanding universe is space. And as we know, it is affected by energy and mass. And through which light travels. How it is conducted or transferred is a different question. Light could for example, since it has no mass, be a ripple in space caused by an energy source. (Just an example)

I'm working away from home and office for a bit and have only a Blackberry for internet access, which is challenging for research. Pardon though, and I will read up as soon as I'm back.

HomogenousCow

Light, in classical electrodyanmics is simply the electromagnetic field, when you accelerate a charged particle a part of the field detaches and goes off to infinity (Physicists linguo for "goes off to wherever it might go off to")

CLourensS

Sorry for the duplicate; not only do I have to use a Blackberry, but I also have to content with intermittent reception. The last one appeared to have not gone through.

CLourensS

I would argue that space isn't nothing. It has structure and behavior and affects everything.
The ripple in space was more of an analogy for visualization of an abstract concept.
If matter and energy cause gravity and if gravity is space behaving in a particular way; be it bend or curve, and if it affects the path light travels in. It can be said that light travels through space and is affected by the structure of space. It still doesn't mean space is the medium, although... What limits the speed of light to what it is in a vacuum?

My education? In this field, nothing much more than interest and self study.

harrylin

Agreed. However:
To say that space has properties implies that it is not nothingness.

Simon Bridge

Argue all you like. Can you substantiate these arguments?... this would be a metaphorical structure and behavior?Analogies are not physics. Space does not behave remotely analogously to a medium for EM waves though ... so I don't think it is a useful analogy.Well - it sort-of is and isn't. eg. a uniform gravitational field does not curve space-time.Quite.Why do you think that light needs something external to itself to limit it?
Apart from that - it looks like a "why" question in disguise. "Why does c have that particular value and not, say, some other particular value?" We don't do "why" questions ;)

Light as able to go so fast because it does not have any mass... so it is not actually being "limited". A much more interesting question to ask what is limiting all the massive particles - a question subject to a lot of expensive study.

The reason I ask is so I know where to pitch my replies ... you seemed to be drawing ideas from all over the place and generally mixing models up.

Let us know when you gone through the references I gave you.

CLourensS

The speed of light a property of space, kind of allows for it to ba a medium?
Sound, for example, although not QM, can travel through various substances. Wouldn't those be mediums? And those also limit it's seed. I know it's not like that but..

CLourensS

I will be home tonight late; at airport now. I shall look at the references soonest in the morrow.
Out of ignorance: isn't a uniform gravitational field already curved space?
Thanks for the patience. I'll be switching my phone off for flight. Apparently they make planes drop out of the sky. I think it is because of the uncertainty principle: They are uncertain why we may not have our phones on. And that is why mine shall be in my pocket, merely on silent. As a silent protest for reason.

Dali

To touch on your original question:
I think the best example when light really behaves like particles is the Compton effect, see http://en.wikipedia.org/wiki/Compton_scattering . This experiment can easily be done as an undergraduate lab on a tabletop setup today. To demonstrate the effect one uses an x-ray source that shines x-rays directly on one scintillating crystal detector. Every now and then, a photon hits an electron in the crystal, and the energy of that electron can be measured. At the same time (well, after the photon traveled to your next detector!) you can measure the deflected photon at a specific angle from its original line of propagation. The deflected photon has lost the precise amount of energy that was transfered to the electron it collided with. I.e. the deflected photon has a longer wavelength than it originally had.

This effect it really impossible to explain with light being any kind of classical wave. Firstly, a wave would never kick just one electron like that. And a wave loosing energy should decrease its amplitude, not change its wavelength. Secondly, one can calculate the wavelength-shift as a function of the deflection angle using a simple billiard-ball collision model. This show that light (or x-rays) - in this particular case - really is behaving very similar to a classical particle, and not at all like a wave.

(The two-slit experiment is the other extreme example where light - in that particular case - displays its wave-like properties!)

Simon Bridge

No.... but it is a compelling analogy? Analogies are all very well - but physics has to have a better connection to reality than that. You keep making analogies that lead you in unhelpful directions.

Sound waves are composed of the substance they move through ... if air, then they are the motion of air molecules, if a solid, then the atoms of the solid are shifted from their equilibrium positions.

Sound waves travel faster through a solid than through air because the component parts are more tightly bound to each other - so a displacement of parts in one place strongly affects the other parts nearby.

Light is usually thought of as a disturbance in an electromagnetic field ... the exact kind of disturbance depends on the model being used. None of the models propose light waves composed of

I think all your questions so far have been answered accurately, if not to your satisfaction, and you have a lot of reading to do. You have yet to show that you have started any of that reading. Get back to us when you have.

Cheers and happy learning :)

harrylin

It's not a stupid question at all. There is a joke that light is particles during the week but waves during the weekend. Particles can be modelled with waves; however common waves are modelled as consisting of vibrating particles. Consequently you quickly face the philosophy of those who happen to be reply your question. It may be more constructive to ask how successful the existing models handle the cases that you bring up in your questions.

CLourensS

Ah. This is good news. I have this concept or idea but need to learn more. My knowledge is woefully lacking, especially the math. I have some leads to follow now and material to study. This forum is the bees knees. Hopefully I can do a bit more than ask irritating questions.