Photons & Probability Wave

Don't ya just hate getting ideas right before bed? I want to get this down so I don't forget it.

Quantum physics tells us that we don't know where a particle will appear, but we can guess where they might appear. Doesn't this define the probability wave function?

If so, why is it that we know exactly where photons will appear when we turn on a light? The photons emitted from a lightbulb will always light up a room. I've never heard of anyone seeing a space of darkness where the photons didn't appear when a light is turned on.

If this is worthy of discussion, I'll continue it tomorrow. Have a good night, all.

reply to post by jiggerj

I'm not a scientist by a coons age. But maybe each individual photon has the probibility state and location undecided, but when you turn on a light there are at least dozens of photons flying around (lol), maybe even hundreds on a good day, and not all of those will be jumping out of their expected sequence. If those numbers ever got any higher you couldn't tell that any were even missing. (if I'm anywhere in the vicinity of "Why?" I'd be a little semi-surprised).

Originally posted by jiggerj
If so, why is it that we know exactly where photons will appear when we turn on a light?

Rather like meeting your friend at a huge rock concert, you know where the group of spectators are, but you cant easily find the location of any one specific person.

You dont know where any individual specific photon will go, so all you can say is that ON AVERAGE the photons will head out in all directions to illuminate the room.

Originally posted by jiggerj
I've never heard of anyone seeing a space of darkness where the photons didn't appear when a light is turned on.

Its a probability thing.
It is entirely possible that, randomly, photons will not go in one particular direction for a moment... but its just rather unlikely.

The issue here is that the lightbulb photon emission comes from a tungsten coil (in an old incandescent) or a wavelength shifters/phosphors in a Compact Fluorescent bulb. The tungsten coil acts as a black body emitter, the process of it producing photons to loose some of its energy is purely random, there is zero predictive power when it comes to telling exactly the point emitting the light. Hotter parts will emit more but that is about as accurate a prediction you can get.

In a Fluorescent you are seeing the production of UV in the mercury vapour, absorption and re-emission. Once again, the photons of UV in the mercury are produced randomly, there is no predictive power to say exactly when each photon will come out, what direction it will be travelling and what wavelength it will be...

Furthermore, for these bulbs we are talking millions of photons... if not more

reply to post by alfa1

Rather like meeting your friend at a huge rock concert, you know where the group of spectators are, but you cant easily find the location of any one specific person. You dont know where any individual specific photon will go, so all you can say is that ON AVERAGE the photons will head out in all directions to illuminate the room.

Oh, you're good!

Originally posted by jiggerj
Don't ya just hate getting ideas right before bed? I want to get this down so I don't forget it.

Quantum physics tells us that we don't know where a particle will appear, but we can guess where they might appear. Doesn't this define the probability wave function?

If so, why is it that we know exactly where photons will appear when we turn on a light? The photons emitted from a lightbulb will always light up a room. I've never heard of anyone seeing a space of darkness where the photons didn't appear when a light is turned on.

If this is worthy of discussion, I'll continue it tomorrow. Have a good night, all.

The reason you don't experience the uncertainty of quantum fields in normal human circumstances is that the number of photons being produced by a light is extremely, nearly astronomically, large. The large number of them make it such that if the probability is non-zero the chance of having photons is essentially 1 in that state.

In practice, the intensity will follow the probability distribution extremely well, because the fluctuations are suppressed by the large N count of photons.

By contrast, when optical scientists do tests on individual photons in extremely dark laboratory conditions using extremely sensitive light amplification devices for detection (quantum optics), the uncertainty of the underlying quantum behavior becomes apparent.

In a nutshell: yes, it is probabilistic but you won't ever see it unless you work in a very expensive optical laboratory and have a PhD in physics or engineering.

Originally posted by Aleister
reply to post by jiggerj

 

I'm not a scientist by a coons age. But maybe each individual photon has the probibility state and location undecided, but when you turn on a light there are at least dozens of photons flying around (lol), maybe even hundreds on a good day,

Lightbulb might emit at light with a peak near say 0.65 um.
Individual photon energy is E=hc/lambda

= 6.63 x 10^-34 j s * 3 x 10^8 m/s / 0.65 * 10-6 m = 3.06 * 10^-19 j

A 100 W incandescent bulb might emit about 2.5W of visible optical power so
2.5 j/s / (3 x 10^-19j) is a little under 10^18

about 8 quintillion (8,000,000,000,000,000,000) photons per second in visible frequencies.

Many many more in infrared.

You can do single photon counting with about....£50 worth of kit but yeah you are bang on the numbers there.

My PhD was actually to characterize a single photon counting device for use in an experiment, It is interesting to see how the device behaves compared to the theoretically perfect, and determine all its properties... anyway I digress.

That calculation i think looks good, its similar to one i was doing to characterise a pulsed LED, I think thats where my million came from...

The idea is where many of the major pitfalls come from when trying to look at a system and think of quantum mechanics... in reality there are only one or two large scale examples of quantum effects on matter or on the way we experience things. Quantum mechanics has a habit of being totally explainable in terms of classical mechanics when you go to large numbers or large scales.

reply to post by jiggerj


I have had a similar question for a while now, if a particle behaves differently when observed compared to not being measured, why is is it then, that in the "unobserved state, the particle behaves in a way that has a certain order, albeit different to the "observed" state, which isn't chaotic as you would expect?

The question here is, does Chaos exist in the quantum world?........ even though it lives happily in my home, but that's beside the point