TrickyDicky said:
I actually don't think cosmology is so special (even if it has some particular features), I rather refer to the way cosmology is treated by some cosmologists.
Name some names. Off hand, I can't think of any working cosmologists that approach the field in the way that you think that they do.
Why is cosmology different than botany? Hmm, in botany nobody proposes the existence of plants nobody has ever seen to explain some botanic observation, made up of something not known to exist, and that either contradicts know laws of nature or belongs to a realm where the known laws of nature don't work anymore. This doesn't happen in oceanography or meteorology either
For number one, one thing that botanists do do nowadays is that map the evolutionary history of plants and that often involves assuming the existence of plants that haven't been observed.
For number two, cosmologists just don't do this unless they are in a situation where the known laws of physics are known not to work (i.e. Planck's length), and that realm is irrelevant for pretty much all of the situations we are talking about. Anything post-inflation we are working with very well known laws of physics, which poses a problem in explaining stuff, because if you create a model using *only* what is definitely known then it doesn't work. At this point, you look at gaps in what is known, and see what explanations work.
There is precedent for this. The discovery of Neptune and the mapping of the Kupier belt. For that matter our information about the shape and gravitational structure of the Earth comes largely from fitting in satellite orbits.
The major predictions of LCDM involve gas dynamics, and we know that pretty well.
In cosmology this happens, but it is even worst, this speculative entities are pillars of the model, so that without them the model collapses. For instance DM, what happens if you take away this parameter from the LCDM model?
It doesn't fit observations. If you assume that Neptune doesn't exist, then your predictions of planetary motion doesn't work. If I assume the sun doesn't exist, then it's hard to explain why I'm hot at noon.
I'm not sure why you think this is a problem. If you assume that something doesn't exist, things don't make sense. That's evidence that something exists. You then look for that something and see if you can find it. It helps if you have different independent pieces of evidence that something exists. For example, let's forget about LCDM. If you don't have dark matter, then you have a difficult time explaining galaxy rotation curves or why galaxies are bound even without cosmology. Also, we are at the point that we can *map* the existence of dark matter using graviational lensing.
Now if you can make observations work without dark matter, then that's wonderful. People have tried with alternative gravity theories, but you have to do something. The reason that people like LCDM is that right now, it's the model with the fewest "crazy assumptions." You have to invoke the tooth fairy twice, but you have to wave the magic wand only twice and everything works out. Alternative gravity solutions require you to wave the magic wand many different t times in different ways.
Note, that this is just the way things turned out. It's possible to imagine an alternative universe in which alternative gravity models work better than dark matter. It's also possible to imagine an alternative universe in which you don't have to assume anything out of the ordinary to explain what we see. It's just that we don't live in that universe.
And let's remember this parameter was only added in the 80's. The conclusion for some is that DM has got to exist, it must.
Name names. The conclusion that *something* has exist or else galaxy rotation curves don't work.
*No one* that I know professionally things that dark matter has to exist just because. Based on known laws of physics, there are only two explanations that people have come up with, and one of those two has to be correct.
Well, other think that's not the only possibility, these others must be the crackpots of course.
There are two classes of theories. Dark matter and alternative gravity. Dark matter is winning right now because of things like gravitational lensing of the Bullet cluster, and because no one has come up with an alternative gravity theory that doesn't have to be tuned for every situation. Alternative gravity isn't quite dead yet, but it's lost a lot of blood.
Unless we've missed something basic then either you must have dark matter *or* some sort of alternative gravity. The calculation that *something* is weird with galaxy rotation curves is a very simple calculation that a first year physics freshman can do.
Also people that work on MOND and f(R) models aren't considered crackpots. Now if the evidence continues to go in the direction it's been going then in about ten years someone that stubbornly insists on modified gravity might be considered a crackpot. But then again, it's possible that someone will come up with new data, and the MOND and f(R) might turn out to be right after all.
And then there is some interesting work from Whitshire that says that we've got our GR calculations wrong and there is no dark energy.
It's possible that we have missed something, but it's not for lack of looking.
Judging by how the "experts" have wrecked the world economy and trashed the planet, they must have got those very wrong.
Well yes. That's why it's important to get your models right. The worst that Arp can do is to annoy some cosmologists. Robert Lucas and the economics professors of the University of Chicago are showing some crackpotness that are seriously cause major economic problems now.
I see you are very comfortable with your guesses about my getting ideas from pop science books and Stephen Hawking, which lead you to totally irrelevant rants.
OK. Where do you get your ideas from, since they don't make any sense to me. You are assuming that cosmologists view the world in a way that they don't view the world, so I'm wondering where you get your ideas on how cosmologists think from. You are talking to one active cosmologist in this thread and one former astrophysicist. There are also about a dozen other professional scientists that aren't shy about saying what they think, and no one has come to your defense.
I have see some documentary and generally found them horrendous caricatures of science.
So where do you get your information on cosmology and astrophysics from? If it's not from Hawking or popular science books, then where? The reason I'm wondering is that whoever taught you cosmology has done a bad job of it, and you are under some serious misconceptions about what cosmologists believe and why they believe it. I'm wondering where those misconceptions come from.
istory of time), as for pop science books I confess I never got beyond Asimov, and I don't remember reading any in the last 15 years except one by Wilczek that wasn't directly related to cosmology. I have see some documentary and generally found them horrendous caricatures of science.
derived a logic pattern from a sentence you wrote, not exactly from what I believe cosmologists think. You assure me that is not a pattern followed by the majority of cosmologists, ok, that is your informed opinion, and it might be so. OTOH it might be an unconsciously followed pattern. But this is more sociology or psychology and therefore likely to be outside the scope of a physics forum.
