# About light in the universe [duplicate]

As a light source in the universe (e.g. sun) emits light in different directions, some of the light emitted reaches places like Earth, and some doesn't. So does the light that reaches the Earth disappear or it is reflected in other directions? And for the light that doesn't reach any place, does it keep on going forever? If it does keep on going forever, will the universe become brighter and brighter? Thanks!

## marked as duplicate by Rob Jeffries, Yashas, Jon Custer, David Hammen, JMacJul 17 '17 at 17:04

• Search for the Olbers paradox ! – Cham Jul 17 '17 at 1:13
• @Cham It only tells that the universe is expanding and therefore we don't see a sky full of starlight every night. It didn't tell what I am asking about. – Sharona Mily Jul 17 '17 at 1:17
• Your question isn't clear enough, then. What's the question ? – Cham Jul 17 '17 at 1:18
• If Olber's paradox does not answer the question for you, then either your question is not clear or you do not understand Olber's paradox. The paradox answers the question as I read it. – Cort Ammon Jul 17 '17 at 3:58
• @SharonaMily: That latest comment is pretty much the basis for Olber's paradox, as Cham and Cort both commented. – Kyle Kanos Jul 17 '17 at 10:08

As you probably know, the light that you mention is an electromagnetic radiation, so it is part of a large spectrum in which $\textit{visible light}$ makes only a small part. Even the sun emits tons of radiation, but not all of it is visible light. When you say about the brightness of the Universe (referring only to the visible light which is radiated by the cosmic objects), you need to be careful here: the brightness of the Universe can be calculated actually if you know how much light each cosmic object emits. Of course if you know the brightness of say Andromeda galaxy, then you probably know enough details about its components (i.e. nebulas, stars and so on). Scientists want to measure the brightness of the Universe ( see here). Probably they will obtain a value which of course will be large, but of course, finite. It can also change in value due to normal cosmic events: supernovae, quasars, death of stars (so it can decrease or increase) but I guess the change in value is NOT noticeable in one day :D