He doesn't say that to insult you but...

[Ben the Ignorant]

 

[johninderby]

Tell me something I don’t already know. 🙄

condescending

adjective

having or showing an attitude of patronizing superiority.

 

[andrew s]

If you want to know more Richard Feynman's book QED The StrangeTheory of light and matter is still good read even though published in 1990. Like the video it leaves out the polarisation of light.

Regards Andrew 

 

[vlaiv]

How about time?

That is one of aspects that confuses me - do we add all trajectories that can add up with speed of light being constant for duration of photon "wave-packet"? What about those before / after? Do they add to their own probability sum? (We have different sums depending on total travel time?).

Do we add only straight paths? Some of the graphical explanation that I've seen involves "curved" trajectories for photons. Some on the other hand when saying "we need to sum up all trajectories" mention nebulous things like - even photons going to Andromeda galaxy and back

 

[andrew s]

30 minutes ago, vlaiv said:

How about time?

That is one of aspects that confuses me - do we add all trajectories that can add up with speed of light being constant for duration of photon "wave-packet"? What about those before / after? Do they add to their own probability sum? (We have different sums depending on total travel time?).

Do we add only straight paths? Some of the graphical explanation that I've seen involves "curved" trajectories for photons. Some on the other hand when saying "we need to sum up all trajectories" mention nebulous things like - even photons going to Andromeda galaxy and back

 

The book goes into the details. What is happening is that they are using Feynman's path integral approach to give a picture of what is happening. As with classical variation methods all paths are considered and in this case all are traversed at the speed of light c.

I don't  really like it as an image as people tend to believe it is real rather than a mathematical tool.

Regards Andrew 

[vlaiv]

1 minute ago, andrew s said:

The book goes into the details. What is happening is that they are using Feynman's path integral approach to give a picture of what is happening. As with classical variation methods all paths are considered and in this case all are traversed at the speed of light c.

I don't  really like it as an image as people tend to believe it is real rather than a mathematical tool.

Regards Andrew 

When I think about it - I just imagine a spherical wave bouncing all over the place - it then interferes with itself. This of course means two things:

Each path must be straight (no bent paths or curves) and if we assume that "ripple" is wave packet - meaning it has "length" of certain number of wavelengths - it is also "limited" in time - we can't sum paths that won't converge at point of interest in given time.

[andrew s]

Your image @vlaiv is more akin to the classical wave model. In variation approaches you start by pinning the beginning and end and the do the variation over all simple (no loops, touching) paths between them. 

Regards Andrew 

 

[Paul M]

2 hours ago, andrew s said:

If you want to know more Richard Feynman's book QED The StrangeTheory of light and matter is still good read even though published in 1990. Like the video it leaves out the polarisation of light.

Regards Andrew 

 

I read that back in the day and seem to remember having understood it. Maybe my memory is playing tricks!