h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This article http://www.bbc.co.uk/h2g2/guide/A644942 is an update on an unfinished article. I have basically tried to finish what Calroth started. Take a look. I think this will be a good addition to the edited guide.

In addition to reviewing the subject matter, I would welcome any corrections to my spelling or capitalization. I am sure there are a few errors there that I am just not seeing.

a small point about matter.

visible matter can only be 5-10%
dark matter (including all baryonic matter) can only take that to about 30%
the rest has to be "dark energy".

Is there no dark matter entry? er... yes there is:
http://www.bbc.co.uk/h2g2/guide/A588224

I could consider a link to that page as well as to A 614558.
the main problem I have with A588224 is that it ignores dark energy and claims the whole ninety percent of stuff in the universe.
some researchers would dispute that figure.

A accelerating universe/dark energy entry is on its way, see http://www.bbc.co.uk/h2g2/guide/A642331 for a preview of sorts. I wish I had mentioned dark energy in a588224 now, but I wanted to keep it simple; as some people take some convincing that dark matter exists, I wanted to stress the immense ammount of evidence that it exists, and I avoided mentioning dark energy as it's still an uncertain area. Most scientists were very sceptical about it until a few years ago, and even now there are many different theories about what it is. I wrote the entry from a traditional point of view which treats dark energy as a dark matter candidate (which I then didn't mention).

Anyway, enough about that entry, it's good to see this one moving again. The guide really should have something on the Big Bang. Wait a moment while I read your new version, Shagbark.

Nice work, Calroth's script was a good outline, but riddled with mistakes. You've cleared up a lot of these. But there's still a lot more to do.

The desciption of Hubble's work is rather muddled. I think you need to rewrite it to explain that Hubble didn't think up the idea of red-shift, he measured the red-shift of distant galaxies and showed that they are all moving away from us, therefore the universe is expanding. Mention that the red shift is a way of measuring the relative speed of objects. I would say the wavelength is stretched rather than expanded to avoid confusion.

Use for powers. Personally I would avoid phrases like 'divine intercession', I think they only make it more complicated than it needs to be; but other researchers like that sort of thing so it's up to you.

I don't like the talk of expansion force (for a similar reason to why Hoovooloo doesn't like centrifugal force), it implies there is some sort of cosmic force driving expansion (there may well be given some dark energy theories). But the dominant contribution is from the momentum given to matter by the pressure of the early universe (when it was really hot and dense)

This isn't very clear:
"If the force of gravity is exactly equal to the force of expansion, then the universe will continue expanding forever. If there's more expansion force, then the universe will more than expand forever. (Best not to think about that too hard.)"
The situation is, if expansion is just balanced by gravity (as the vast majority of theoretical and observational evidence suggests), then the universe will expand at an ever decreasing rate which will fall to zero at an infinite time in the future when the universe approaches an infinite size.
However if the mutual gravitational attraction of the universe is less than the 'critical density' it will continue to expand forever at a finite speed.

I could say some more, but I'll leave it for now. The entry appears to improve every time I look at it, I look forward to the final version.

If this appears a bit hard. It's because I believed edited guide entries on science should be as accurate as possible, to contrast the many unedited accounts. I expect the same treatment for my entries.

Keep up the good work

MP

This is from an October 5 press Release from the Hubble Space Telescope Institute:"A recently discovered 'baby Galaxy' had a redshift of 5.58 corresponding to an age of 13.4 Billion Years.
(prss release STSCI PR01-32) So the universe is older than 12 Billion as stated in some other pages here at h2g2. I am still searching
for ways to simplify some of the language.

someone recently wrote(I think it was in Analog) "It's not what we don't know that causes us the most problems. It's what we know that just ain't so. Some people know that the universe is twelve billion
years old. the true age is uncertain. I was sure I knew that Hubble came up with the term Red Shift. Now I'm not so certain. After reviewing sorces I need to credit Vesta Slipher for his work and connect it to Hubble's.

Liked the article

Some minor points to help you:

A misstype "Hubbell" appears in the second paragraph.

You might want to refer to "Omega", a value of universe density. The theory:
If Omega = 1 then the universe is flat (will continue to approach a maximum size), is "Omega" is greater than one than the universe will collapse again, and if Omega is less than one then the universe will continue expanding for ever.

Thanks for the suggestion but I think I will keep omega out of this.

Sure. it's your article .

I think that this is an improvement on A343856 and Calroth has not
surfaced to object so maybe he is gone for good this time.

A minor point.

you seem to present hoyle's steady state theory as total garbage, but the mechanism he suggested does actually exist, it just doesn't work fast enough.

I did mention elsewhere that stars are still being born, but if the material they are created from was originally in the singularity, that is different from what Hoyle was talking about. He didn't believe that the singularity existed.

the thing that I refer to is the ongoing spontanious creation and destruction of matter and antimatter. this was postulated by hoyle as the mechanism for the steady state universe. he was proved to be right about the existance of this mechanism, but unfortunately for his beliefs, the process was happening much too slowly for his theory to work.

Perhaps you should write an article on it. As it is I think I have gotten off the subject of the Big Bang too much already in talking about him.

Nice little entry Shagbark. This sort of thing is generally incomprehesible to me but I found this fairly easy to follow. I would make just one small suggestion. For the sake of people like myself, who don't really even know the basics, perhaps you could explain briefly, maybe in a footnote, what is meant by a "singularity".

I added the footnote, and in looking for info on singularities
I found a nice BBC page on Massive Black Holes which contain singularities. You can compare my definition with the one in that article. They are not identical but I believe express the same idea.

I like this entry, though I am not a big fan of Big Bang theory.

One suggestion though, A lot of the sentences are very short and choppy. It would make a better read if some of these were combined into compound sentences and such....less staccato you know....

Towards the beginning one Big Bang is left uncapitized.
"As things approach... wavelength" should be plural.
Ther Universe.... should be The

now I'll explain why I don't like Big Bang theory... besides that it is ridiculous... Time and space are quantities, and in this theory we attempt to determine those quantities, a process not unlike trying to determine the highest number...Our theories for Astrological happenings work quite well for our little corner of space, but what no one seems to have pointed out is that in everything outside our solar system, and most particularly outside our galaxy, we are only ASSUMING that everything works the same...All of cosmology is based on that assumption. The distances and sizes involved are merely guessed at, in a sort of academical way, with "astrological yardsticks" and a bunch of other near mysticism.... Asking "what is the universe and how did it begin?" is no different than asking "what is God?" you can make a bunch of theories and look here and there, but at the end of the day you still don't know. Now I'm not saying that all this is a complete waste of time, sure its all interesting stuff...... I'm just saying that it is a pretty big leap to go from "stuff sure looks red" to "all of time and space was compressed into a singularity and then *poof* something happened".... There is one more point to be made, and that comes from Quantum theory, which some will argue doesn't apply here...to them I say "pooh"... It has been "proven" (whatever that means) that subatomic particles exist in all possible states until observed...something in the act of observation forces them to choose a state...now, since everything is made up of subatomic particles it seems that the same would apply on the grand scale. This means if a tre falls in the forrest and no one is around, then the tree is in a state of "limbo" both falling and not falling until someone shows up on the scene...This version of reality is difficult for most people to accept...they want things to be clearly defined...it is This or it is That, end of story....all I'm saying is try not to draw any conclusions at all...just keep an open mind and cleary perceive what is there...there was a time when everyone "knew" the earth was flat...now we laugh at them because we "know" the earth is round...so who will be laughing at us?