Well Steve, I was right with you, up until 'Colin'.

jamesg1213
Well Steve, I was right with you, up until 'Colin'.

He he
 
I thought I had it licked myself until he asked those extra questions

The speed of light of all wavelengths in a vacuum is the same. Changing the perceived wavelength via the doppler effect does not change the speed of the light, any more than varying the wavelength at the source would make the light arrive earlier or later. The photon is arriving on schedule, but is "vibrating" at a different frequency when it arrives.
 
Another way of looking at the problem is that a light wave propagating from a retreating object should have less energy than one arriving from a stationary object like a baseball thrown backward along the track from the caboose. The baseball will have less velocity relative to a batter standing on the track because the forward velocity of the train will be subtracted. The baseball will arrive at his bat with less energy than if it had been thrown from a stationary object. But in an Einsteinian universe the light can not pick up or lose velocity like the baseball. So when it arrives it must have the same velocity but less energy than if it had come from a relatively stationary object. The lower frequency in the electromagnetic domain like the reduced velocity in the Newtonian world accounts for the loss of energy, as the energy of a light wave is proportional to its frequency.
 
Confusing the properties of a fluid wave with an electromagnetic wave leads to a failure in the thought experiment.

Doesn't recent discoveries with "Dark Matter" nullifies "Empty Space"

I enjoyed reading this thread. It also caught me by surprise that it would be discussed here in the CH.😊

SteveStrummerUK
 
A while back, my good friend Colin asked me to explain the red shift to him.
 
First off, I used the standard analogy of a speeding ambulance and how the pitch of the siren drops as it passes the observer.
 

 
Something along the lines of: The perceived pitch of the note is lower when the ambulance is moving away as the wave-fronts are reaching our ears less often, so as the frequency decreases, so does the wavelength (from λ = v/f). The opposite is true when the ambulance is approaching - the frequency of the wave reaching our ears is increased, hence the perceived wavelength increases too.
 

I’ve read some of your other science-y conversation starters in the past and I just figured you confused the long and short of it when discussing wavelength and frequency.
 
In general chemistry when we get to the section on quantum mechanics and we start discussing the wave equation and electromagnetic radiation I put up diagrams showing waves and the relationship between wavelength and frequency, the relevant wave equation, a linear scale with the colors of the rainbow on it and the equation for the energy of a photon (in terms of either wavelength or frequency).  The kids usually don’t have any trouble with the algebra part and the fact that wavelength and frequency are inversely proportional … BUT … when it comes to the verbiage of wavelength and frequency and their relationship to each other and their correspondence to energy (i.e., the photon part) the kids have a meltdown.
 
I usually put something like this up on the board (next to all the diagrams and equations) so the kids get a feel for the words we use and the descriptions they will be seeing in their word problems when we characterize light in terms of wavelength, frequency (wave model) and energy (particle model) and compare different colors of light and/or energies of the corresponding photons.
 
Red Light                                            vs                                 Blue Light
low energy (photon)                                                                high energy (photon)
low frequency                                                                         high frequency
long wavelength                                                                      short wavelength
small frequency                                                                       large frequency
large wavelength                                                                     small wavelength
decreasing frequency (relative to blue)                                   increasing frequency(relative to red)
increasing wavelength (relative to blue)                                 decreasing wavelength (relative to red)
 
I’ve seen all of these expressions used and more.  The point is it can be confusing (large and small are very confusing but again, I’ve seen them used) when describing two characteristics of something when they are inversely related to each other.

A bad example of the Doppler Effect?

The above photograph illustrates the point that the longer wavelength is associated with lower energy. Note the progression from the relatively energetic pectoralis region to the midsection, a phenomenon that has been lableled relativistic panniculus spatial distortion.

Where I come from it's called Dunlop's disease. And, dern, I miss out on all the fun threads. But many thanks to some above...especially ol quantumeffect for stating it plainly. Kudos.