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Old June 4 2013, 05:49 AM   #73
Crazy Eddie
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Re: Strange Dark Matter Theory

iguana_tonante wrote: View Post
And of course, weighting a box of water is exactly the same thing of measuring the gravitational mass of astrophysical objects thousands of light years away from us.

Again, you are seriously underestimating the universe.
On the contrary, I'm saying that our estimates for the mass of those distant objects is far from certain and difficult to determine for sure, as is the behavior of gravity at galactic/intergalactic distances. Thus the "invisible box" assumption is NOT the one that needs to be investigated and ruled out. To complete the analogy, we're talking about a "box" whose composition and basic properties are not fully understood in the first place, for which existing estimates of its mass and the distribution thereof have a huge degree of error, and for which any solid answer to those questions will be monumentally difficult to obtain in and of themselves. My feeling is that scientists are attacking the more fanciful and exotic theory but never sufficiently ruled out the simpler ones.

We did, and guess what? It was in agreement with a cold dark matter scenario.
Not exactly. What they found -- in various studies in the early 2000s -- was there was no direct evidence for the alternate explanations, which in a way came down to special pleading for dark matter. Not that I agreed with this particular explanation, but back in 2002 I read a paper in an astronomy journal that sought to debunk the theory that the higher-than-expected angular velocity of distant galaxies could be better explained by a higher-than-predicted population of large brown dwarfs and/or black holes and neutron stars that do not produce strong x-ray signals. The author called that theory "spurious" and concluded -- I kid you not -- that the lack of confirmed brown dwarfs in the Milky Way disproved this theory, and simply ignored the point about black holes/neutron stars.

I remember it now only because it was the first time a scientific journal ever made my jaw drop in disbelief. Mind you, it's not that I actually agree with the theory that brown dwarf populations or non-luminous massive stars by themselves work as an explanation. It's the counter-arguments AGAINST it are and have been deeply fallacious.

At the moment of writing this, there is no alternative theory that can adequately explain the behaviour of cosmological structures better than dark matter...
Actually there are dozens of theories, many of which are in the process of being tested as we speak. Dark matter isn't the most plausible one, it's merely the most popular.

And we are talking of a large interval of behaviours, from galaxy rotation curves to gravitational lensing of galaxy clusters.
And little else, it turns out. And even gravitational lensing models are based overwhelmingly on the assumption about the mass distribution of dark matter between galaxies whereas alternate models that assume only slightly different than expected mass distributions still managed to replicate the results.

In such cases, the support for the dark matter hypothesis has been based less on the evidence FOR dark matter than by the reseacher's skepticism for the alternate explanations.

It's also worth pointing out that modified gravity is consistent with virtually ALL of those observations. The only reason scientists question modified gravity is because they're uncomfortable with the idea that general relativity may be at least partially incorrect and/or inapplicable. Relativity itself has become a kind of academic sacred cow that scientists and engineers are reluctant to give the appearance of questioning, even when the theory itself is legitimately inapplicable.

Crazy Eddie wrote: View Post
The simplest explanation is that they have either under-estimated the mass or under-estimated the effects of gravity at those distances.
Since we are fond of educated quotes: "Everything should be made as simple as possible, but not simpler".
At the risk of inviting a subjective value judgement: when you a discover a contradiction between the model and reality, which solution is simpler?
- Theorizing that reality contains an undetected and fundamentally undetectable factor that is causing the variation
- Theorizing that your model is in some way flawed

"Dark matter" proceeds from the former assumption: the model WOULD work if the universe was heavier, therefore assume the universe is inexplicably heavier and search for the reason why. I'm proposing the alternate hypothesis: the model DOESN'T work and should be replaced with a better one.
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Last edited by Crazy Eddie; June 4 2013 at 06:19 AM.
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