The mystery of light

[CSM]

I am probably being totally naive, but I have always wondered why the light coming into a Newtonian reflector doesn't interfere with the light being reflected from the flat, and vice-versa? How do they dodge each other? Do one or the other decide that they are particles in honour of Newton and somehow miss the waves?

[Cath]

When you say 'the flat', do you mean the primary mirror?

[CSM]

No - light coming in, which is then reflected from the primary mirror on to the flat, which is then reflected out to the side of the tube 'across' other light coming in to the scope.

[tenbyfifty]

i'm no expert but i think it may well be the case that light waves from different directions will interfere with each other in a complex way (i think the frequencies have to be the same or similar though to create interference) but the reason you can see an image through a reflecting scope is simply because enough photons get through to your eye to form an image even after absorption, scattering and interference. sorry if this sounds like its stating the obvious.

[Astro Imp]

That is another really interesting question to which I have no answer.

[L8-Nite]

If I recall correctly ? . . . . . When light comes through glass, it comes through as short wave radiation. When it hits an object (mirror) it changes to long wave radiation, so they do not interfere with each other. This effect can be experienced when sunlight travels through car windows, hits the interior, becomes long wave radiation which cannot exit; the effect is heat.

[Kropster]

If you see light as photons , they can stream in, bounce off mirrors etc... but just effectively pass by each other in their travels as they are tiny.

Seen as waves, they can pass through each other... like rain drop rings in a puddle...and go happily on their way.

To get stationery interference patterns you would need coherent light of exactly the same frequency... like a laser produces.

Light from stars is a jumble of frequencies and waves so does not produce this effect.

[ibraidwo]

To demonstrate/prove the effect, switch on two torches and point them across each others light path, one torch's light path won't be affected by the others path.

Unlike two streams of water, which would interfere with each other...

[laser_jock99]

If you see light as photons , they can stream in, bounce off mirrors etc... but just effectively pass by each other in their travels as they are tiny.

Seen as waves, they can pass through each other... like rain drop rings in a puddle...and go happily on their way.

To get stationery interference patterns you would need coherent light of exactly the same frequency... like a laser produces.

Light from stars is a jumble of frequencies and waves so does not produce this effect.

Pretty much correct- to get any kind wave/interference effects you need a coherent (e.g. laser) light source, where all the photons are in phase, the same polarisation and the same wavelength. Looking at a typical night sky scene there will be many wavelengths all at random polarisations.

[trazor]

Imagine a large round table, around which 20 people sit, all seated with their eyes at the same level.

Each of them looks in the eyes of the person sitting directly opposite.

In the centre of the table all 20 observations pass by each other with no interference at all.

Never ceases to amaze me.

[Kropster]

Photons are effectively massless and have no electric charge, so interaction with each other is very unlikely.