Understanding Photon Propagation: Entity or Quanta?

[zonde]

A calculation using a physical model is part of that model, and obviously so.

Right. But Feynamn's probability amplitudes are not physical but mere calculation tools.So the calculation is part of phenomenological not physical model i.e. there are no quantities in the calculation that are given status of being "physically real".

 

[bhobba]

Right. But Feynamn's probability amplitudes are not physical but mere calculation tools.

Feynman's turning arrows help to calculate probabilities so in that sense its just a calculational aid - and if someone asked that's what I would say - but its a rather meaningless distinction IMHO.

Thanks
Bill

 

[DrClaude]

I like the wording they use in this recent study, they are using "A pulsed 775 nm-wavelength Ti:Sapphire picosecond mode-locked laser", I assume each pulse is a bunch of 775 nanometer wavelength (1.6 eVolt) photons.

The actual text of the paper, as opposed to the figure caption you are citing, is

At the source location a mode-locked Ti:Sapphire laser running at repetition rate of approximately 79.3 MHz produces picosecond pulses centered at a wavelength of 775 nm

Note the important use of the word "centered."

 

[zincshow]

The actual text of the paper, as opposed to the figure caption you are citing, is

The quote is from a different location in the article, but certainly not all of the burst of photons are exactly 775 nm. Some of the photons are probably 775.1, some 774.9 and a variety of values in between. The important aspect to this discussion is that a bunch of 775 (approximately 775nm or 1.6 eV each) nm photons are pulsed in a short period of time. If you add them all up, you will get the total amount of energy in the pulse and it will be a multiple of 1.6 eVolts subject to nothing in an experiment being "exact" to an infinite number of decimal points.

 

[Nugatory]

If you add them all up, you will get the total amount of energy in the pulse it will be a multiple of 1.6 eVolts subject to nothing in an experiment being "exact" to an infinite number of decimal points.

Right, we don't have an infinite number of decimal places. Do we have enough decimal places to make the measurement of the total energy accurate to a fraction of 1.6 eV? If not, it's meaningless to say that it's a multiple of 1.6 eV.

You can't count the number of grains of rice in a five-kilogram sack unless you can weigh the sack with an accuracy better than the weight of a single grain of rice.

 

[bahamagreen]

When you take the Fourier transform of a quantum field you get the momentum representation...
Bill

This is important and maybe a possible way to see somewhat through the about unmeasured attributes.

The way I think of it informally, when a measurement is made, the experimental apparatus is configured to make a particular measurement. When you use Fourier to decompose a wave into a set of component sine waves of various amplitude, phase, and wavelength, you are choosing to use the sine wave as your basis for decomposition... the most simple basis waves correspond to familiar attributes (sine wave basis yields an answer in terms of a momentum attribute).

But, Fourier decomposition may be performed using any arbitrary basis wave (cosine, square, triangle, or more complex ones like a five oscillator synthesizer playing a certain tone of C#...) and different choices of basis wave (different experimental measurement setups) would then be measuring various corresponding attributes, some of them possibly too complex to actually perform or interpret with respect to the simpler attributes with which we are most familiar or that show up as terms in familiar equations...

So, one kind of has a choice as to whether to think of the unmeasured object as having either all possible attributes awaiting potential expression through measurement pending the right corresponding basis, or thinking of the unmeasured object as having no attributes whatsoever before measurement. I think generally most are going to take the second of those for practical thinking once the object's attributes are separated from the unmeasured object and moved into the measurement basis choice itself... that is, prior to choosing a basis, the attributes simply don't exist yet.

The conceptual challenge is to extend this to all attributes, including the simple familiar ones that are hard to let go of - position, momentum, etc.

Of course this suggestion is totally hand wavy and looks like it might not apply to the photon propagation question (it is just a hopeful hint about how to think of unmeasured objects' attribute status prior to being measured). :)