Dark Matter

[SearlesGold]

WHAT IS THAT DARK MATTER IN BACK OF ALL OF EVERYTHING THAT IS LIT AT NIGHT.......A BLACK CURTAIN?:shrug:

[astro_nutt]

Hi Searlesgold!
Nice and warm in sunny California?..
Well the "black curtain" is the dark voids in between the Planets, Stars, and Galaxies, etc..in the vacuum of space where the only things that we can see are those that create or reflect light that is bright enough for us to see!
The "black curtain' is simply empty black space!
Space is so big that the light from the Stars and Galaxies are so far away that we cannot see them unless we use a telescope.
I hope this answers your question

[Dujon]

Don't lead him/her up the garden path with scientific jargon, astro_nut! We all know that The Creator left the building and turned off the light. There is proof that the so called 'red shift' is real and has nothing whatsoever to do with the recession speed of observed objects; it's just the light elements cooling down.

Just wait a million years or so until the Andromeda galaxy starts to redden and then tell me I'm wrong - go on, I dare you.

Mind you, SearlesGold's question does bring to mind the occasion on which I asked my teacher why, if I created a shadow with one hand, the light didn't reappear when I used my other hand to block the shadow. :(

[astro_nutt]

You're right!..Dujon...I was a bit heavy with the scientific jaron..I..er..will exercise a more subtle answer next time...
Wait a million years or so until the Andromeda galaxy starts to redden?..you're on!!..LOL
Kindess regards to you!

[Dujon]

SearlesGold, please excuse my light hearted response.

If, apart from your 'black curtain', you were asking a serious question then you are in the company of many a serious scientific mind. I think it was Olbers (don't hold me to that) who raised the conundrum which was basically the question, "If there is an infinite numbers of stars then why does night exist, as the combined light from them should light up the sky even more than does our sun?". Even if one raised the point that there are dust and gas clouds between us and many of the sky regions the suggestion that they block light doesn't hold. This is because the universe is so old that those objects would have already absorbed so much energy from the stars that they would have been saturated to the point where they emit as much energy as they receive. The assumption in this situation is that the universe and the laws of physics as we know them are the same wherever you might be located and that the universe is static.

Someone once calculated that should this obviously false situation hold then the Earth would probably be hotter than the surface of our Sun. I don't know how that was worked out as logic would say that infinite stars would produce infinite energy. The only reason is probably that, at some point, we would be shielded from most of the more distant radiation by those stars which block light from those 'behind' them from our perspective. So why is it not so?

Well, basically because the universe is not static. In fact it is expanding. Any energy source which is moving away from a measuring point (in this case us on Earth) appears to be less energetic than it would do should it be stationary. That's part one. Part two is simply that, even if the universe is infinite, most of it is and never will be observable from our part of the universe because at a critical point anything that exists beyond that will be retreating faster than the light which is directed towards us is approaching us.

Whew, I hope that encapsulates the basic ideas. Still, astro_nutt's explanation is still correct when it comes to what we see with our eyes, or even our telescopes.

astro_nutt, I'll accept your challenge and bet you AUD1. I'll be waiting to collect. :whistle:

[JimmyH155]

Guess who it was who sussed the answer to why the night sky is black? It was Edgar Allen Poe - that crazy-verse writer. Apparently he was very interested in astronomy, and even the great minds of the time couldn't think why... His answer completely smashed the theory of a static infinite universe, and from then on, the realisation that the univerese is expanding, caught on.;) :lol: :D

[Calin]

Just a quibble, I understand the red shift occurs as a result of expansion and 'things' moving further away from us (relative position) over time - however the Andromeda galaxy is actually moving towards us in our local group and is expected to merge with the 'Milky Way' eventually - 3 billion years or so ... So this galaxy is actually blue shifted (opposite of red shift). A million years from now I am doubting you would notice anything, as this is a very short time frame, though at currently estimated 100-140km per second approach speeds we will be a little closer. :hi:

[Dujon]

Calin, you misinterpret my light hearted (read, "stupid") comment. Sorry about that, I really shouldn't invent such fantasies on a forum such as this.

Your comment regarding the Andromeda galaxy and that in which we live is, as best I know, a pretty good description of where both are at this point in time. Top marks, with honours, to you and an 'F' (for Fool) for me.