0 Members and 1 Guest are viewing this topic.

This would actually be much easier to do with radio waves, given their longer wavelength.

Would it be possible to run a version of the double-slit experiment ...sorry, you cannot view external links. To see them, please REGISTER or LOGINhttp://www.thenakedscientists.com/HTML/content/kitchenscience/exp/measuring-the-speed-of-light/

Interference and diffraction effects happen for all electromagnetic radiations at all frequencies. However if you are talking about observing the non intuitive quantum effects these are only observable for frequencies at which individual quanta can be detected which requires at least infra red frequencies although the quantum effects would still occur at low frequencies.

SSYou seem well versed in this subject. Perhaps you would comment on something that has always perplexed me. Do photons have dimensions? This perplexes me because photons vary in wave length by orders of magnitude.My GUESS is that photons do not have dimension, but leave a variety of measurable wave lengths in the electomagnetic field as they pass.

I do not think that you are being very sensible light arrow.How do you define the size of an object?The only way I can understand it is that it is the volume in which other objects can interact with it.

(HUP)----Quote from it--"Another effect that the wave theory of radiation cannot explain is the transmission of the Sun’s rays through what is virtually a perfect vacuum between the star and the Earth in which there is nothing in which waves can form and carry the transmitted energy, unlike that which occurs in the oceans."

Light arrow the "size" of a photon is approximately the wavelength multiplied by the reciprocal of the fractional bandwidth of the frequency of the photon over which the observation is made. Say for example I was observing radio signals at 100Mhz, this is around the frequency of FM radio, the wavelength is around 3 metres and, if I observed the signal with a receiver with a bandwidth of 10MHz, that is one tenth of the frequency. The receiver therefore needs about ten waves to respond. So the "size" of the photons being observed is about ten wavelengths, that is, around thirty metres.

All this stuff about wave lengths is fascinating, and brings up memories of tuning or 'trimming' antennae for enhanced reception for specific wave lengths. As I recall, you could have full wave length antennae, 1/2 wave, 1/4 wave etc.In the context we are now discussing this is very weird. Specifically, either the antenna could absorb a single photon or it could not. If it required more then one photon to complete 'the wave length' how were they stored up?I have a guess. My guess is that individual radio frequency photons can be absorbed entirely by antennae of various lengths, but the output of the antenna is largely a function of the RESONANT effect between the frequency of the photon and the natural frequency of the antenna.Any thoughts on this.......

Lightarrow and Soul Surfer,I think you're both right, from different points of view. What we classically consider frequency is the number of oscillations per second of a classical monochromatic electromagnetic wave that pass a given point.A photon has a frequency that determines its energy from E=hf, where E is energy, h is Planck's constant, and f is frequency. In addition to determining the energy, this frequency appears in the description of the photon according to quantum electrodynamics. The mathematics of a photon look similar to the mathematics of a quantum harmonic oscillator, where the photon has a frequency just like a harmonic oscillator has a frequency. However, the photon is not modeled by a nice classical wave that oscillates a certain of number of times per second.

The two types of frequency are related to each other, however. If you add up photons of a given frequency in the right way (called a coherent state) they should sum up to give what looks like a classical wave with that frequency, although this wave will have quantum noise present. A classical wave has high enough amplitude that the quantum noise is negligible and the classical model holds.Read this for an overview: ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN The first figure on the right demonstrates how a collection of photons can form a classical wave.

Exactly, infact it's modeled by *nothing*.

Quote from: lightarrow on 11/01/2010 22:44:28Exactly, infact it's modeled by *nothing*.Lightarrow - are you saying there is no model of a photon? I'm not sure I understood your point. Thanks, G

Quote from: Geezer on 12/01/2010 04:19:30Quote from: lightarrow on 11/01/2010 22:44:28Exactly, infact it's modeled by *nothing*.Lightarrow - are you saying there is no model of a photon? I'm not sure I understood your point. Thanks, GExactly.

Lightarrow, I think I see what you're getting at, but I don't really agree with your statement that a photon is modeled by "nothing." There is a perfectly good model for photons via quantum electrodynamics (as a Fock state containing 1 photon). They certainly aren't simple particles zipping between sources and detectors, and the position representation of the photon isn't clear to me (I've browsed over some books that do define it, or make approximations so that a photon can be treated over space, but I'm not well-versed in these techniques). However, photons can be modeled and the models appear to be extremely accurate.

Well, if you go by both waves and photons interactions you have one, as I see it, clear difference. Photons do their work 'instantly' (less than 10-9 s) as far as I now, waves don't. When it comes to how we model them outside a interaction we can't say we observe them.

Although. Thinking of it ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

The full quantum theory, when applied, also explains why classical waves work so well for so many things. It also explains why they don't work well for quantum effects, such as the photoelectric effect.