Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: yor_on on 04/10/2011 00:37:12

Title: If you move away from a lightsource, will photons become 'spaced out'?
Post by: yor_on on 04/10/2011 00:37:12

It has to do with using light as a 'clock' of sorts.
I like to think of it as such.

As waves, we do not define it as (singular) particles, and what we see is a redshift. But thinking of it as photons we should have to assume that they will become 'spaced out' relative us. And those coming to 'meet us' from the direction in where we travel 'compressed'. Now, those two may take themselves out, they should, shouldn't they, so that we will find a 'average' defining us the same as when 'unmoving'.

The other way is to use it as 'c'. That way every 'singular' photon will have the same speed 'locally' relative our direct measurement, from all directions. The difficulty here is how to describe that as a 'clock'.

So, what I'm really wondering. Do we have a experiment confirming that 'photons' will become 'separated' in space, relative me moving away from them? I use 'c' in my definition, which is correct any which way we define it as, waves or 'singular corpuscles' (photons). but 'c' then becomes something slightly different than light itself in my mind. It's not an abstraction but I find it hard to define.

Title: If you move away from a lightsource, will photons become 'spaced out'?
Post by: Geezer on 04/10/2011 00:55:32

The only way they could alter their relative separation would be if they travelled at different speeds (like a train coming apart as it travels along the tracks). We know they have to travel at c, so they can't separate, and the energy difference caused by the speed difference between the source and receiver produces a frequency shift.

Title: If you move away from a lightsource, will photons become 'spaced out'?
Post by: yor_on on 04/10/2011 03:06:56

It's a tricky one in that no matter how fast you move from that light source the photons still will reach you at 'c', the same invariant speed. When it comes to a expansion we use that for defining 'photons' getting spaced out, fewer arriving over any specified time interval.

And you can think of this too as a 'expansion' between two points, 'light source' <-- --> observer.

We might for simplicity assume measuring it in a uniform motion. and so find that there is no difference between this and a expansion, as I see it at least?

The train analogue is nice though, and it's important to me to see where the difference might be.
==

That one became tricky in its own right. That 'acceleration' we see in the expansion is because it 'adds up' as it grows, as I think of it, with the 'expansion' in each point being equal. But you might define it differently, as a acceleration, and if so we need to let those two 'points' above accelerate, both or one of them. But I find it simplest to let them be in a uniform motion myself, as that lets me define both as being still, or neither :)

Title: If you move away from a lightsource, will photons become 'spaced out'?
Post by: yor_on on 04/10/2011 03:50:22

The thing being that in space, assuming a same gravity between those points, the 'photons' shouldn't lose any energy. Their momentum will differ with their speed, relative the detector, as I see it, and their frequency as a wave but as they never 'change energy' intrinsically?

And if they don't get 'spaced out', why do we define them as getting 'spaced out' in a expansion? Where is the difference between having light source and detector separating in a uniform motion and them being on both sides of a expansion? We can in both cases define both light source as well as the detector as being 'absolutely still' or either or both 'moving', and as far as I can figure there is no difference? Distant stars will be seen to 'move' over the expansion, and in a black box scenario there won't be a difference either as I can see?

It's a old enigma for me this one, and I would really like to see what thoughts you guys and gals have.

Title: If you move away from a lightsource, will photons become 'spaced out'?
Post by: jartza on 04/10/2011 06:37:43

Yes photons are spaced out when you are moving away from a light source.


How do photons, that are on their way, become spaced out, when you start to move away from them?

A photon behind a photon slows down more than the photon in front of it, when you are accelerating. When you stop accelerating photons move normally again.


How do photons become spaced out when you start to move before the photons exist?

Well, it's the continuous increase of distance between you and the light source that is the cause.