Talk:Starlight problem

From RationalWiki

I've gone faster than the speed of light. I left four years from now and just got back, (President Cheney's making a mess of Iran). CЯacke® 01:32 8 July 2011

[edit] Omphalos

Icewedge, what have you done? I can't even follow the logic of the edits, let alone what is there now... mind if I try to merge what we had with what you've added from AIG? While I copyedit... human^{be in} 21:10, 19 September 2007 (EDT)

[edit] Just a stupid question

But does no one (in the creationists circle, that is) wonder why god would go to the bother to create "Billions and Billions" of stars... if the only exist to provide "us" with pretty lights at night??????????????--WaitingforGodot 17:42, 24 July 2008 (EDT)

YOU QUESTION GODS PLAN. Obviously he wanted Eve to be able to see at night when she was making Adam a sammich. -- Gen. S.T. Shrink ^{I can has rank?} 17:43, 24 July 2008 (EDT)

They also gave her material for questions to pester him with while he was trying to enjoy the game and a few brewskis. ħuman ^random 17:55, 24 July 2008 (EDT)

*insert innapropriate fellatio joke here* -- Gen. S.T. Shrink ^{Mr. President...I lost the WMD's} 17:57, 24 July 2008 (EDT)

[edit] Metric expansion of space

Hello everyone (fabulous wiki you got here... I like it) I believe that the editors of the article may have fallen into a common trap regarding distances, the speed of light and the age of the universe. It doesn't affect the gist of the article so don't worry, you don't have to change your beliefs! (Though as rationalists, you wouldn't mind if you did have to anyway.)

The problem is that one of the furthest objects from earth that can be seen currently is 28 billion light years away. The light that reaches us now from this object (incidentally, a pulsar) has taken 12 billion years to do so. The reason for this seemingly contradictive occurance is that 12 billion years ago, the pulsar was 4 billion light years away from earth, but instead of taking only 4 billion years to reach us, the distance between us and the pulsar (and hence the distance between us and the light on its journey) has increased over time. So the photons have travelled 'against the flow' of the space they are in, if you see my point. For a nice diagram of this, see the ever-wonderful Wikipedia (http://en.wikipedia.org/wiki/Image:Embedded_LambdaCDM_geometry.png#Mathematical_details).

This is called the metric expansion of space, and is the reason for the Doppler effect, and the basis of the Big Bang theory (extrapolating back in time to a point where everything was a lot closer together). So it is helpful to think of the big bang as a stretch rather than an explosion - the galaxies themselves aren't moving relative to eachother (much), instead the space between them just got bigger. 86.153.222.16 11:51, 12 September 2008 (EDT)

I make no great claim to any expertise here, but isn't the speed of light supposed to be invariable between any two points regardless of their velocities? I had understood that what changes was its frequency - the Doppler effect. So, if light from an object 4 billion light years away started out now it would reach us in four billion years time. However if there were a significant difference in the velocities of the star and ourselves it would be red shifted if the star was moving away or blue shifted if it was moving towards us. I accept that the position of the star itself would be vastly different from where it was when the photons started out. Or am I way off? --Bob^{bing up} 12:13, 12 September 2008 (EDT)

I am not an expert either, merely an inquisitive undergraduate student! Yes, all that you say is right, except that "light from an object 4 billion light years away started out now it would reach us in four billion years time" is wrong. Its hard to explain, except to refer to the often-used 'balloon model' of the universe - imagine the earth and the pulsar as points on its surface. Obviously these points get further apart as the balloon expands, but what is a little harder to imagine is what would happen to another point that is moving between these two fixed points. The moving point has to travel a lot further than the original distance between the two fixed points, as the balloon is expanding while the moving point is travelling. But it also has to travel less far than the final distance between the two points, as by the time the balloon has expanded to its final size, the moving point has already travelled most of the way. I'm sorry if I'm not the best explainer - I've seen digging at Wikipedia and found this more rigorous explanation by someone else: http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2008_March_16#Speed_in_space.28not_the_drug.29 . 86.153.222.16 12:36, 12 September 2008 (EDT)

This is a good point. It's easy to confuse Doppler redshift vs. cosmological redshift (which is ultimately what I think this discussion is about), but I don't immediately see a way to work it into this particular article without explaining it to such an extent that it dilutes the main point.--Bayes 15:14, 12 September 2008 (EDT)

The one thing that I was thinking could be done, to ensure accuracy with the minimum of explanation, would be to correct the following sentence, with a reference to provide explanation if people want it: "Because light travels at a finite speed, only stars within 6,000 - 10,000 light years of earth should be visible in the creationist model of history. This is not the case though, since radiation from stars over 13 billion light years away have been detected[1], which would seem to put the lower limit on the age of the universe near 13 billion years."

What I'd suggest is this: "Because light travels at a finite speed, only stars within a few tens of thousands of light years from earth should be visible in the creationist model of history. This is not the case though, since quasars over 28 billion light years away have been detected^[1], which, allowing for the metric expansion of space, puts the lower limit on the age of the universe near 13 billion years." Unfortunately I do not know how to accurately extrapolate the creationist age of the universe to a maximum radius (I don't know anyone that would bother to try), but it would be roughly the same ratio as the 13 billion years/28 billion light years for the universe studied by those of us who have a grip on reality - so 6000-10000 years gives a radius limit of a few tens of thousands of light years. What do you reckon? 86.153.222.16 15:51, 12 September 2008 (EDT)

I think the best solution would be to refer to the issue somewhere within the article and link to a comprehensive explanation from there. (Adding a line along the lines of "in reality it's not quite that simple as is explained here". And if somebody has got the smarts to write a RationalWiki article that would be great, as I find it a bit of a mind twister.--Bob^{bing up} 16:21, 12 September 2008 (EDT)

That's kind of what I suggest as all that's changed is a few words, but the comprehensive explanation is contained in a wikipedia article rather than on RW. I think that's fine, as this wiki is primarily concerned with refuting anti-science, and regularly links to more detailed wikipedia articles. 86.153.222.16 17:47, 12 September 2008 (EDT)

Actually, as a general rule we don't link to WP and prefer to explain things ourselves and go to primary sources. This is in part because our objectives differ to those of WP, and in part because we don't really want to be a WP "add on".--Bob^{bing up} 10:22, 14 September 2008 (EDT)

Really? There are lots of RW articles that link to WP, & it's a shortcut in the wiki coding we use - eg. [[wp:Wikipedia]] rather than having to do a full external link. RationalWiki:Project Whitewash/What is a RationalWiki article says:

"Most of the contributors at RationalWiki enjoy Wikipedia, and we encourage people to use it for research, fun, or anything else that requires more encyclopedic and neutral articles. We cannot and do not want to compete with Wikipedia. We are attempting to create something that is different but hopefully complementary to Wikipedia."

Doesn't that rather contradict what you just said? weaseLOId~ 10:40, 14 September 2008 (EDT)