Two things came up on another forum that I need help with. Number one deals with dark matter.
A poster on the other forum claims that Dark Matter theory is no more valid than religious or mythological solutions to a problem. He says:
So ho true is this? Are scientists talking about Dark Matter leaping to illogical conclusions not based on emprical data? What data is there to support this theory?
Second statement made by the same poster:
This took me by surprise! Is there any truth to this?
Hmm, ok the poster hinted that he was making a point about relativity on that second comment.
I understand the basics of Relativity. And it does say that no inertial frame is absolute. You are always moving relative to something else. Therefore in one inertial frame one can say that a passer by is moving and be correct, whie the passrby can claim that the observer is moving and also be correct.
So is it really possible to claim, relativisticly that the universe moves around the earth?
Dark matter is nothing more or less than mass we cannot see. We don’t know if it is simply ordinary cold matter which does not radiate, or it it is something more exotic. It’s not likely to be simply interstellar gas and dust, since we can detect those indirectly by the absorption of light from stars. Beyond that, we know little about it, except for the approximate amount of mass it represents. Maybe the universe is filled with microscopic black holes. Ok, probably not.
Of course it’s true. Then again, you can take any object in the universe and say it’s the center of said universe. All motion is relative, and you can pick out any point in space and describe the motion of every object relative to that point. We tend to use the Sun as the reference point for our solar system, not because it’s more “valid” to do so than for any other body, but because the resulting equations that describe the motion of the planets and other orbiting bodies are simpler this way. Or something.
Uh, the law of gravity is pretty well supported by empirical evidence, and the amount of matter we can see is, well, what we can see. There is more gravity running around than we can account for, so there must be some matter we can’t see. That’s the definition of “dark matter” – matter we can’t see. If we get better instruments, we may see it. There’s nothing mystical or mysterious about it.
The only thing I can imagine that might have provoked the second statement is the fact that the observable universe is retreating from us uniformly in all directions. Because distant objects are retreating faster, we believe that the entire universe is expanding uniformly, so that it would look the same from every point in the universe, but I suppose that if you ASSUME that the earth is the center of the universe, you may come to a different conclusion from the data.
Sounds like an anti-science rant to me by the poster on this other forum. Could you give us a link please?
One of the most basic principles of science is that it’s conclusions are not definite or final. Dark matter is just a theory, it isn’t the last word on the subject. It may later be proven or disproved. This is what differentiates science from religion. However, the dark matter theory is based on the best empirical data we have at the moment.
In the sea serpent analogy, a definite cause is offered for an unexplained phenomenon. Dark matter, on the other hand, is an indefinite cause for an unexplained phenomenon.
It would be a more valid analogy if the people who didn’t know what caused the tides were to say, “Some force seems to be causing the sea to rise twice a day, and we’re not sure what it is. However, it is predictable, based on these mathematical formulae. We still don’t know what it is, but we know some of its properties, and for now, until we come up with a better term, let’s call it ‘the Sea Serpent Effect.’”
The thread is here: Start at page 8.
http://nwn.bioware.com/forums/viewtopic.html?topic=326677&forum=42&sp=105
This board has a policy against dealings with other forum boards, though, so keep that in mind 
Thanx for the help guys. I’m going to post Nametag’s post there. And I already conceded on the relativity point
Saltire Brilliant! I hope you don’t mind me quoting you
Oh, sure. Pick the second post. 
Q.E.D. basically has it right here. Which frame of reference we choose is primarily a matter of which frame of reference gives us the simplest math. If you’re planning a trip from Rochester to Boston it’s easiest to figure a stationary Earth; if you’re planning a trip from Cape Caneveral to Valle Marineris you might want to consider a stationary Sun with Earth and Mars in orbit around it.
That thread makes baby Jesus cry. 
For some background about the theory, background and evidence for dark matter:
Scientific American search page for articles on dark matter:
http://www.sciam.com/search/index.cfm?QT=Q&SC=Q&Q=dark+matter
New Scientist search page for articles on dark matter:
http://www.newscientist.com/news/search/dosearch.jsp;jsessionid=AEGELALHFNMD?advsearch=dark+matter&searchtype=all&x=15&y=10
As for question #2, the universe will appear to be uniform and equally expansive from any point in it, including the earth. This is not at all the same thing as saying that the universe revolves around the earth, which is not true. I can’t think of any scientist making this claim in any kind of theory, no matter how wild.
Not that the truth will make any difference.
Actually, no. This statement is false.
You can say the the Earth appears to be the “center” of the observable universe – that’s true for any point in space.
You cannot, however, say that the universe “revolves” around the Earth. The universe is not gravitationally bound to the Earth or the galaxy or even the local cluster. Nor, or course, is the Earth the center of mass of the Universe. In fact, the very mechanism that makes the Earth the “center” of the universe absolutely precludes the Universe from having a center of mass. Therefore, it does not and cannot “revolve” around the earth, or anything else, for that matter.
Not only is the Earth revolving around the sun, the sun is revolving around the center of the Milky Way. I don’t know, off the top of my head, if the local group of galaxies is rotating, though I suspect not.
About the dark matter question, as Saltire said, we don’t know what it is, but it apparently has gravity, and we can’t see it, so we’re using the placeholder term “dark matter.” However, said dark matter causes 90% of the large-scale gravitational effects, not just 10%. If this guy is saying that “science” has declared there to be a definite something called “dark matter” out there, end of story, then he has severely misunderstood the problem. If you were to figure out what this stuff is, you could go ahead and book your tickets to Stockholm.
For the question about the Earth at the center of the universe, is that still valid, even though it’s in orbit around the sun? All inertial reference frames are equivalent, but is our path around the sun in one of those? Is it considered inertial in relativistic space-time or something?
Of course, it’s ridiculous to say the universe revolves around the Earth. The point is that you can look at it as though it did and everything could still make sense. I was even told by an astronomy professor that you could explain the equitorial bulge with a stationary Earth and a revovling universe. The problem is the math gets terribly complex. It was the complexity of the math that convinced us that the Ptolemaic model wasn’t a good one and that the Copernican model made more sense, allowing us to formulate a good theory of gravitation. In my earlier example of driving from Rochester to Boston you can pretty much ignore the rest of the universe. And if going from Cape Canaveral to Valle Marineris you’ll need to consider the whole solar system (or at least the Sun and inner planets) but you can ignore the rest of the galaxy and things beyond.
‘Funny you should ask’
Here’s a Washington Post article, reprinted in my local paper this past Saturday, 2/22/04
I was kicked off the Bad Astronomy Bulliten Board recently for fighting with the ignorant, but back in the day I used to spar with geocentrists. You talk to enough geocentrists and you begin to see where they’re coming from.
Basically, geocentrists are wrong. However, there is something in relativity that says you can create a reference frame anywhere. Putting the Earth at the center of a universe that revolves once a day is a highly “non-inertial” reference frame, but in principle you can make the transformation according to general relativity. Unfortunately, the math is a bit out-of-control.
What you can say is that, according to one formulation of the equivalence principle it doesn’t matter what reference frame you choose to do your calculations in. We prefer to talk about inertial reference frames which would exclude the Earth, but as long as you don’t worry about that, said reference frames are equivalent.
There were a number of papers written over the years about formulating a “geocentric” reference frame. This is NOT the same thing as saying that the universe “revolves” around the Earth. It is the same thing as saying that you can create a non-inertial frame where you are stationary and the universe revolves around you. No problem.
Just don’t expect the physics of those situations to be easily done.
By the way: dark matter has two distinct observations that determine its presence in the universe: 1) the rotation curves of galaxies and 2) the things that caused cosmic microwave background radiation anisotropies leading to large-scale structure formation.
Sounds to me like he’s making the unfortunate but sadly common leap from “I don’t get it” to “I don’t believe it.”
I would ask him if he can actually explain the theories he’s dismissing in order to put into context his reasons for dismissing them, or if he’s just dumping on them for some other reason.
there is a grain of truth in the OP first question. All scientific theories presuppose that the universe makes sense and that what happens yesterday holds today. Now both these suppositions are in one sense an act of faith, just as religion is. But given that, I still prefer science to the mumbo-jumbo of religion any day as at least science can make predictions.
Dont forget that many scientific discoveries were “predicted” because of some strange experimental observation. E.g. Neptune and Pluto were predicted and found because of a discrepancy in the orbit of Uranus.
Another way of putting dark matter into perspective is - either our model of the universe and gravitation is wrong, or there is something out there (lets call it dark matter) that is causing it. Both a very exciting possibilities - I await with interest the results
That’s not true. It is our first-pass assumption that this is the case, but it’s been checked. For example, we can look at the emission spectrum coming from far away galaxies, light which was emitted billions of years ago, and we see that it indicates the underlying physics were the exact same way back then.
To get to the heart of this, you need to understand how scientific thought works at it’s most basic level. For a scientific theory to be “true”, it doesn’t have to neccesarily correspond to whatever objective reality that may or may not be out there. It merely has to exhibit the same outwards behaviours that we can observe. For all we know, there might really be tiny gremlins pushing all the individual particles around or the universe might happen to be one of an infinite number of parralel universe for which things make sense. However, to science, all this is irrelevant, as long as a theory is both more accurate and simpler than another, it is “truer”.
Thus, the very fact that dark matter makes theory stick closer to reality means that science regards it as “true”, at least until a better explanation comes along.