
Originally Posted by
kojax

Originally Posted by
TheDr.Spo
I do wonder why you are so afraid of a new concept such as Dark Matter. ..
I would say the reason I am scared of it is because unobservable quantities are difficult to compare with experiment/observation, and I don't want to see cosmology just become a big guessing game. I mean sure: it's fine to guess when forming hypothesis, but after it's formed that's when the guessing should stop. Confirmation should be found in something that can be seen for certain, a concrete reality.
A modified version of gravity would have the benefit of being comparable with observation on a very specific level. One after another, instances can be compared with it and we can see for ourselves whether each one exactly matches the outcomes of the formulas. If the formulas are wrong, then you'd have to be lucky enough to be continually guessing the right number time after time after time in order for a discrepancy not to emerge. DM doesn't give us that. We only know how much DM is present after we've applied the theory. How do you get narrow predictions out of that?
We know what types of properties DM has. From that we know how it should behave under given circumstances, and in what ways this will differ from
any modified version of gravity. Then you look to see if you find instance of this type of behavior.
Example: There is a cluster of galaxies in which tidal forces are strong enough to tear the galaxies apart. Some of the galaxies are being ripped apart, but others aren't. They are subject to the same tidal forces, but something is holding them together. Just modifying gravity won't solve the problem, since it would have to apply to
all the galaxies and not just some. This restriction does not apply to DM, as nothing prohibits one galaxy from having more DM than another. Thus you have a situation where DM provides a solution and modified gravity can't. Just because it would be neater to be able explain things by new gravity theory, doesn't mean that it is possible to.

Originally Posted by
Janus
I find it ironic that someone who believes so strongly in the Ether, something far more intangible, more bizarre and with much less evidence of existence, has such a problem with dark matter. But it just goes to show how irrational some people can be with their beliefs.
I find it ironic that you have a go at me for hand waving, and now your essentially doing the same thing towards the Ether.
1. The Ether is not intangible.
What else do you call something that cannot be perceived by the senses or measured in any way? That pretty much the definition of "intangible".
I think it's kind of funny that you reject unobservable Aether so adamantly, and then turn around and embrace unobservable Dark Matter with open arms. ( .....though..... I guess you could similarly chuckle at me for entertaining a version of the Aether theory and disliking DM. :?)
The difference is that the Aether is the invisible elephant that leaves no traces whatsoever of it existence, and DM is the invisible elephant that leaves footprints. In fact, in the case of the Bullet cluster, it leaves footprints where there is nothing else to do so.
DM doesn't play a different role than Aether used to play. It's a miraculous substance that makes it possible for certain correlations to emerge between observable matter and gravitational behavior.
Except that the Aether is superfluous and DM actually performs a function and explains observations that cannot be explained otherwise. And DM is not "miraculous". Simply put, it has mass and does not interact electromagnetically. It behaves perfectly naturally for something with those properties. And its not as if that combination of properties doesn't have precedent. The neutrino exhibits them. To insist that the neutrino can be the only example seems a little silly.
I really fail to see what gets people's undies into a twist about it.