Newby question with apologies..

[theendisnigh]

Why is the whole sky not white if light is travelling in all directions from each star and do photons diminish after a certain distance? Ie. Is there a maximum distance light can travel before fading to nothing? Thanks in advance

 

 

[Zermelo]

4 minutes ago, theendisnigh said:

Why is the whole sky not white if light is travelling in all directions from each star and do photons diminish after a certain distance? Ie. Is there a maximum distance light can travel before fading to nothing? Thanks in advance

 

 

Welcome to the forum, and no need for apologies, this one has exercised some very good minds.

It's called "Olbers' Paradox":

https://en.wikipedia.org/wiki/Olbers'_paradox

[theendisnigh]

Thanks very  much for the link.

The mind still boggles.. lol

 

 

 

 

 

 

[saac]

The individual photons don't loose energy as such, unless they are travelling such distances that are influenced by the metrical expansion of the universe which would stretch their wavelength (energy being directly proportional to frequency).  Rather what we see is that the intensity of the light from the star (the energy falling per second per unit area) reduces with distance.  The relationship between distance and intensity follows what is known as an inverse square law so the distance from the star doubles the intensity would be 1/4 of its original value, if the distance increases x 4 the intensity would be 1/16 th and so on.   Think of those photons being radiated out from the star in a sphere, as distance increases the volume of the sphere increases as does its  surface area so the photons are being spread over an rapidly increasing area.  Each photon that arrives at your eye, unless it has been red shifted, has the same energy as it left the star  (E = hf  where E = energy, h = Plank's constant and f = frequency). Without expansion the photon would traverse the universe undiminished, however expansion stretches its wavelength, our high energy photon (X Ray, UV) that left the star being potentially stretched to infrared and microwave - hence the effect seen as the Cosmological Microwave Background Radiation , an echo of the birth of the universe.

As per Olber's paradox the reason we do not see a star at every line of sight in the night sky is that there has not been enough time for star formation to place a star at the end of each line of sight. In other words, the universe is not eternal (steady state theory) rather it had beginning. 

Jim

Edited January 22, 2023 by saac

[theendisnigh]

Thank you for the response.. 

My personal belief is an infinite universe. There cannot be an end, hence it troubles me that photons can travel for infinity..

Much to ponder!!

 

 

 

 

 

 

 

[saac]

12 minutes ago, theendisnigh said:

Thank you for the response.. 

My personal belief is an infinite universe. There cannot be an end, hence it troubles me that photons can travel for infinity..

Much to ponder!!

Indeed, much to ponder   Oh and yes welcome; you have found a great place to do the pondering.

Jim 

[Floater]

Welcome. Hope you have lots of fun and that you enjoy the pondering … 🙂

[SuburbanMak]

Welcome! Strong start, I think you’ll like it here…

[LandyJon]

1 hour ago, theendisnigh said:

Why is the whole sky not white if light is travelling in all directions from each star

 

 

I'm wondering if the first part of your question is asking why does 1 star not fill the sky with light.

Just to clarify the light from each star is travelling in all directions but you can only see the photons that have directed to the tiny pinhole in your eye, or larger bucket of your telescope.  There are still photons hitting people in the other hemisphere and missing earth entirely, but you'll only see/capture the ones coming from that tiny pinpoint in the sky billions of lightyears away that are directly aimed at you.

The rest has been answered pretty well, but to add for almost the entire history of astro study there has been a gulf of a gap between what we've looked at.  Decades ago it was realised we could see in radio waves with telescopes like Jodrell Bank and Arecibo and for centuries we've been studying the visual light spectrum.  So as has been explained about the frequency shift of light over the vast distances, its safe to say we've studied the relatively near and glimpsed the super far, but there is a gulf in between that we're only just starting to see with Webbs infra red imaging sensors.

Welcome to the forum, I hope this adds to the pondering ! since this is why we all look up.

[theendisnigh]

Very good response and I understood. 

 

do seem to spend way too much time pondering and trying to get to grips with infinity.  Keeps me awake at night..

"What a terrifying word!!"

Our known universe could be like a grain of sand in a vast desert!

Thanks once more for your response.