Re: Dark matter/energy - is it real?

Shawn Wilson wrote:

All that tells us is that our theories of how fast they should spin are wrong, it does *not* tell us why. Dark matter is a shim to make existing theories work, nothing more. There are theories that explain the variation without dark matter.

We have a discrepancy that indicates that the amount of visible matter that we see in galaxies (including our own) does not explain the motions of the galaxies according to our theories of gravity.

As I pointed out, the dark matter hypothesis is really no different from Fermi concluding that neutrinos existed. Were neutrinos fantasy too?

That is not what dark matter is.

Dark matter is not just matter that doesn't glow, it's entirely different.

Dark matter is non-baryonic. Which is to say it isn't made of baryons. Since protons and neutrons are baryons, dark matter isn't made up of protons and neutrons.

That _is_ all that dark matter is. It's simply matter that is not glowing that we assume is there because our gravitational theories are very good.

There are reasons from the Big Bang model for thinking that this dark matter is not baryonic, as you've pointed out above (and which I pointed out in detail in the message you're responding to). But that is further analysis, not based on a direct observation of the properties of dark matter.

We know it's non baryonic because we know approximately how many baryons the big bang made. For baryonic matter to be the missing mass there would have to be about ten times as many as the theory predicts.

I think it's interesting that you have absolute faith in our understanding of particle physics, baryogenesis, and nucleosynthesis, but apparently absolutely no faith in our theories of gravity. Since you seem to think the nail in the coffin is that dark matter must be non-baryonic, why not conclude that perhaps it's our understanding baryogenesis that's wrong and maybe it's baryonic after all?

You can't have it both ways.

That leaves another form of matter. But there's a huge hole in the theory of dark matter- if the universe is mostly made up of it, where is it? Why don't we see any on Earth? Why do no known physical processes create it? It's not that it's undetectible- we would notice that energy was missing from reactions (which is how we found the neutrino).

There is a perfectly good hypothesis to explain this; namely, that it is composed of weakly-interacting particles. Neutrinos, for instance, behave exactly as you describe, and although they're quite weird compared to normal matter, do not present any great difficulty to our theories of particle physics.

That doesn't mean that dark matter is composed of WIMPs, but the case you're making for them being too bizarre to be real is defeated easily enough by existing members in the particle zoo.

Dark matter, if it exists and judging by the ways galaxies rotate, isn't distributed right either. It would have to itself be unaffected by gravity while affecting non-dark matter, but organize itself into halos around galaxies for some unknown reason.

Dark matter is _obviously_ affected by gravity; why else would it be in halos around galaxies if it weren't affected by gravity? If it weren't affected by gravity, then there would be a uniform distribution of this dark matter throughout the Universe without respect to where the galaxies are, which is not what we observe.

Unless, of course, you're suggesting that it's not gravity but _something else_ that attracts dark matter to galaxies, in which case you're the one who's multiplying entities unnecessarily. At any rate, that is not what dark matter theories predict so it's immaterial.

Once again, collecting halos of particles is precisely how you'd expect weakly-interacting particles to behave. Dark matter theories _do_ predict that dark matter interacts via gravity but very weakly through the other forces. That's why we don't see it. Again, like neutrinos.

It isn't a discovery because it hasn't been discovered. It's just a theory to explain anomalous observations.

Are you playing semantic games now? Is _dark energy_ the name for the phenomenon, or the name for what we expect to be causing it (which we don't know what it is yet)? Does it make a difference?

According to our theories of cosmology, the Universe's expansion should not be accelerating. But it is. "Dark energy" is just a name for that phenomenon. At this point we're very, very sure the phenomenon exists. So arguing that we can't name it yet because we don't have a coherent theory for explaining it seems to be neither here nor there.

Newton works but is wrong too. All we really know is that our theories work on a planetary scale, but not on a galactic scale.

I think it's ironic that you say this (and as much in another response of yours to Tue). If you don't think dark matter exists and is a sham, then no, you _don't_ think Newton works.

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Perfect situations must go wrong
-- Florence, _Chess_
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