From: "Vladimir Galogaza" 
To: "ATM shore" 
Reply-To: "Vladimir Galogaza" 


Original question was what happened when  incoming beam of light and light
deflected by secondary (in Newtonian) are crossing each other.

>As others have mentioned, if you put a detector in the area where beams
cross,
>you would detect interference.


I know of no such detector that will be able to detect interference in this case.

Incoming light is not coherent. Quick and dirty calculation is that act of emission
of light by electron jumping from one energy level to lower one last 10^-8 sec.
In that time light travels 300000000 m/sec*10^-8 sec=3 m. Next 3 m long light wave
will not be necessarily in phase  with this one. So light from stars is bunch of
incoherent waves coming in all phases. When they interfere with light waves
crossing their path the interference will last  maximum 10^-8 sec for two
3m long trains passing each other. If this interference was destructive at
certain point
next waves will be not necessarily destructive. So in order to see interference
we should have very fast detector and the resulting field changes  at each point will
have all possible values in time ranging from zero to double amplitude for
each two waves.
And there are milliards of 3 m long wave trains with random phases.

We can observe interference with eyes or some detectors only if interference is
sufficiently stationary so that response time of detector can register it.
This happens in interferometric tests when we are able to produce light of
sufficient
coherence in long time. Than we have sort of standing waves and film
emulsion or other
method can detect such electric fields. (This must be way off topic, Thanks
Michael for patience.) Vladimir.

--- BBBS/NT v4.00 MP