A quantum head scratcher / Electromagnetic Radiation / Forums

Forums

4hv.org :: Forums :: Electromagnetic Radiation

« Previous topic | Next topic »

A quantum head scratcher

previous 1 2 3 4 next last

Move Thread

LAN_403

Proud Mary

Thu Feb 16 2012, 09:32PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Surely, a photon is, at one and the same time, both a wave and a particle, and it is only the means we choose to measure it that determines whether we 'see' either a wave or a particle.

Ash Small

Thu Feb 16 2012, 09:48PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'll try to adress both the above posts at the same time.

I'm suggesting that we should forget about the particle side of things, for the 'single atom' mentioned above, as well as for the photon.

I'm suggesting that the 'particle nature' of all matter is an 'illusion' created by the Higgs field. and that we should just be thinking in terms of waves and 'fields'.

Matter and mass were taken for granted in the days of Newtonian physics, but quantum physics has great difficulty in actually explaining them (hence all the Higgs research).

I've been puzzling over this for a few years now, and have suggested on other forums that everything can be explained in terms of waves. It's 'matter' and 'mass' (particle theory) that we are having difficulty in comprehending, understanding and explaining.

Steve Conner

Thu Feb 16 2012, 10:13PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

So, you're saying that an atom can be a foot across, or several light years across, as necessary? But also be microscopic when that is required of it?

Seems radical, but there is a parallel in the classical world, where you can design a radio antenna that has an "aperture" (effective size) much bigger than its actual size, but at the cost of bandwidth.

Or are you trying to get even more meta, suggesting that the concept of "size" itself is invalid?

plazmatron

Fri Feb 17 2012, 02:34AM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Just lifted this explanation from Wikipaedia:

"experiments confirm that the photon is not a short pulse of electromagnetic radiation; it does not spread out as it propagates, nor does it divide when it encounters a beam splitter.[49] Rather, the photon seems to be a point-like particle since it is absorbed or emitted as a whole by arbitrarily small systems, systems much smaller than its wavelength, such as an atomic nucleus (â‰ˆ10âˆ’15 m across) or even the point-like electron. Nevertheless, the photon is not a point-like particle whose trajectory is shaped probabilistically by the electromagnetic field, as conceived by Einstein and others; that hypothesis was also refuted by the photon-correlation experiments cited above. According to our present understanding, the electromagnetic field itself is produced by photons, which in turn result from a local gauge symmetry and the laws of quantum field theory"

Les

Proud Mary

Fri Feb 17 2012, 10:07AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

So far as I understand it... this paper seems to address most of the questions raised in the thread thus far:

Robert J. Buenker, Quantum Mechanical Relations for the Energy, Momentum and Velocity of Single Photons in Dispersive Media

Ash Small

Fri Feb 17 2012, 10:40AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

So, you're saying that an atom can be a foot across, or several light years across, as necessary? But also be microscopic when that is required of it?

Seems radical, but there is a parallel in the classical world, where you can design a radio antenna that has an "aperture" (effective size) much bigger than its actual size, but at the cost of bandwidth.

Or are you trying to get even more meta, suggesting that the concept of "size" itself is invalid?

I'm 'suggesting' that the photon is produced at the 'emitter', takes time, 't', to be 'absorbed' by the 'receptor', at distance 'x' from the emitter (speed of light).

Photons travel in straight lines (subject to no other 'forces'). They can travel in 'any' direction, and be 'detected' anywhere.

During time, 't', they are effectively 'everywhere'.

It's effectively a 'transfer of energy' from the emitter to the receptor, the time taken being dependant on distance.

I'm suggesting that the act of absorbtion is much like the act of emission, photons can be recieved from any direction, just as they can be emitted in any direction, and that between the time of emission and the time of reception they are effectively 'at all possible places at the same time' (Heisenberg?).

(Or, to put it another way, until they are absorbed, they are on all possible trajectories.)

Fulmen

Fri Feb 17 2012, 10:55AM

Registered Member #3883 Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87

Proud Mary wrote ...

Surely, a photon is, at one and the same time, both a wave and a particle

No, it's neither. It's something completely different, but depending on how you measure it it can behave similar to a particle or wave.

Terms like particle and wave are macroscopic phenomenas that just doesn't make sense in any absolute terms when you enter the quantum world. We can use them as metaphors with limited validity to help us understand quantum physics, but it's not real particles or real waves.

Meatball

Wed Mar 14 2012, 10:04PM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
Location:
Posts: 74

Perhaps it is better to say that waves and particles alike, sometime behave like photons. :/

hboy007

Thu Mar 15 2012, 12:36AM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

Sulaiman wrote ...

...how do you generate single photons?

quantum dots exhibit a 2nd order autocorrelation function typical for antibunching (= "just one emission at a time from a single quantum level"). At room temperature, NV- defects in diamond crystallites could be used, see

In practice, a strongly attenuated laser source with poisson statistics will do.

Sulaiman

Thu Mar 15 2012, 01:23PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

From the above posts I see that we know nothing !
(but I'm not sure ;)

and I've seen nothing in any of the above that enables me to make a setup where a single photon can be produced
(definitely NOT using a laser ... where Light is Amplified by Stimulated Emission of Radiation .... 'bunches' of photons surely)

and how does a diffraction grating work .... n-times more spread-out for single photons.

previous 1 2 3 4 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob