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Comment: Re:Errors versus public debate (Score 1) 116

by mbone (#49479159) Attached to: Hubble and the VLT Uncover Evidence For Self-Interacting Dark Matter

You should look into MOND.

"Dark matter" as an effect is very well established. It is a sign of a failure in our models of physics. That failure could be in the microphysics (thus, various particle models, such as WIMPs), or in the macrophysics (i.e., in general relativity, the model for gravity, which is modified by theories such as MOND).

Now, as it happens, these sorts of galaxy cluster collision observations are probably the strongest test of MOND type theories - it is hard to see how a failure of gravity would get separated from the matter causing the gravity. MOND is not yet firmly ruled out, but it does look a lot less plausible.

Comment: Re:Property of Dark Matter (Score 1) 116

by mbone (#49478927) Attached to: Hubble and the VLT Uncover Evidence For Self-Interacting Dark Matter

WIMPs are actually an old explanation of dark matter, probably on the way out unless LHC can pull out a supersymmetric particle in their new run.

In any case, WIMPs only interact through the weak interaction, so it is generally assumed that these "self-interacting" particles are not WIMPs, but some new form of SIDM.

Comment: Re:20 years late (Score 1) 47

by mbone (#49427231) Attached to: Distance of a Microlensing Event Measured For the First Time

I broke the rules and RTFA, this is the first time that they have managed to combine an Earth-based observation and a space-based one separated by far enough from each other to give a reasonably accurate baseline for an accurate measurement of both distance and mass. From the article:

Calculations estimated it to be 10,200 (+/- 1,300) light-years away. . . These observations also allowed the mass of the object to be measured — around 0.23 solar masses

Not quite. If you read further, you see that the key word is that it is first for a "isolated" (i.e., single) star. Dong et al. did this in 2007, but for a binary star.

I must sat that I dislike "firstitis," both in science and on Slashdot. However, these are not easy measurements and this is still quite an accomplishment.

Comment: 20 years late (Score 3, Interesting) 47

by mbone (#49424233) Attached to: Distance of a Microlensing Event Measured For the First Time

This is known as microlensing parallax, and was first done 1995. Parallax breaks lensing degeneracies, enabling the determination of distance,

Now, you may quibble about this particular distance measurement, but it's been done for 20 years now. Routinely. And, yes, its been done from space before too.

My guess is that some needed qualifiers were lost between the astronomer's mouth and the headline writers keyboard, but it ain't first.

Comment: Re:what if... (Score 1) 236

by mbone (#49362193) Attached to: Dark Matter Is Even More of a Mystery Than Expected

There have been several theories built on that assumption, most prominently one called MOND (MOdified Newtonian Dynamics), but more recently one that builds on relativity rather than Newtonian gravity/dynamics.

But none of these theories (hypotheses?) have gained much acceptance from the physics community, as far as I know.

Yes, and one reason is that they find it hard to model these kinds of galaxy cluster observations in MOND / TeVeS without assuming there is also some dark matter or some other non-MOND effect involved. Now, that could be (and MOND proponents will point out that standard CMD also has its problems, e.g., with the core/cusp problem, and we don't throw out CDM every time such a problem is encountered), but it certainly takes some of the shine off of the theory.

Comment: Re:WIMPs (Score 1) 236

by mbone (#49362155) Attached to: Dark Matter Is Even More of a Mystery Than Expected

I don't have the article in the mail yet, but I'm guessing that's new. At the very least, Weakly Interacting is now Really Weakly Interacting.

Here you go.

From my perspective, it hardly changes a thing (it lowers the cross section / mass constraint a little, but not even an order of magnitude). But, then, I'm not a WIMP guy.

Comment: Re:WIMPs (Score 1) 236

by mbone (#49362143) Attached to: Dark Matter Is Even More of a Mystery Than Expected

Math proofs are meaningless without physical observations to back them up.

Fully agree. And, as it happens, General Relativity has a massive amount of physical observation backing it up, and no physical observations contradicting* it.

* If you believe in MOND / TeVeS, then the dark matter observations contradict GR. Let's just say that there is not yet consensus around that view.

Comment: Re:WIMPs (Score 1) 236

by mbone (#49361765) Attached to: Dark Matter Is Even More of a Mystery Than Expected

That the thing about dark matter... it has a perfectly reasonable explanation (WIMPs). It's not that weird of a "thing".

I dunno. Usually when a theory requires more and more unseen entities over time it's a sign that it's time to replace the theory. We know General Relativity is incomplete, both because it doesn't take into account quantum effects and because it has internal contradictions - specifically, it assumes a continuous spacetime geometry but predicts non-continuous points (black hole singularities).

That is not thought to be an internal contradiction of General Relativity, as, even though GR does have singularities, thanks to event horizons and cosmological censorship, there are no known cases where you can use these singularities to derive multiple different estimates of the same observational quantity (which is what having an inconsistent physical model means). I don't believe that there are any mathematical proofs of this, but I suspect you would have to come up with a counter-example if you wanted to convince people GR was self-contradictary.

Comment: Re:WIMPs (Score 1) 236

by mbone (#49361719) Attached to: Dark Matter Is Even More of a Mystery Than Expected

Dark energy is just the latest name for the Cosmological Constant

You know, I'm as happy as anyone else that physicists have been able to do so much with their models, but what kind of navel-gazing mathurbation is this?

Dark energy is an observed physical phenomenon.

The cosmological constant is a term in an equation. It's a very good equation, mind you, but a lot of very good equations have later turned out to be wrong or good for only a special class of phenomena. Equations can predict, but they don't prove anything. It's also worth noting that the cosmological constant was supposed to predict a force that would hold the universe together. Dark energy is a force that is tearing the universe apart. Someone clever pointed out that hey, that works if you just flip the sign of the cosmological constant but I'm not sure I'd call that a win.
 

This is physics. Everything is a term in an equation.

The cosmological constant is the only free parameter in Einstein's equations. The. Only. One. And, it fits exactly all of the available data. Unless and until that changes, there is no good reason to believe to believe that we do not live in a de Sitter space.

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