(continued and concluded)
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Originally Posted by Ken G
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Originally Posted by Nereid
"Dark Energy": two teams almost simultaneously discovered a consistent trend in high-z Ia SNe data; a flurry of activity followed, much of it involving strenuous efforts to ensure 'accelerated expansion' (and 'cosmic jerk') was a consistent conclusion.
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Another perfect example of what I'm talking about. The discovery was observational, and grossly disagreed with the current best models. One did not need a gigantic "black box" simulation to tell us that acceleration meant gravity was doing something weird! Even now when we do quantitative simulations, we are forced to use a rough treatment of dark energy, via the simplest possible equations of state we can think of. Again we're having at that third decimal place-- yet do we really think that physics 100 years from now will not have discovered something that significantly changes the entire picture of what dark energy is? Only if we are no students of history! |
I think I'm beginning to see what you're saying; let me play it back as a check:
Conservatively, the best we can do, today, from observation is say that maybe some of the multitude of theories which purport to address "dark energy" are mildly inconsistent (there is "some tension") at the 1 sigma level*, but certain teams are boldly forging ahead, developing dazzling (and dizzying) models that they claim can deliver phenomenological predictions accurate to the third significant figure (or better). That's not such a bad thing; the behaviour you are concerned about has to do with what you see as a possible future acceptance of these models when the observations do, one day, get to that third significant figure.
How far off the mark am I?
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Much of this effort necessarily involved elaborate models, but for me the key take-away is the robustness of the conclusion, and that robustness depends critically on (at least some) of the models being quite elaborate.
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I take a different message-- I claim that if you analyze those elaborate models, you will generally find that something much simpler actually constrains any particular observation you want to understand. It can be different for different scales and different questions, so it's nice to have it "all in one place", i.e., in the kitchen sink somewhere. But that's no reason to ignore that oftentimes physics involves a simple interaction embedded in a much more complex milieu-- and isn't it our job to find that out? We end up with less egg on our face when some new physics means the "kitchen sink" simulation is no longer reliable. (No matter, one nice things about codes is they are as easy to change as a four-day weather forecast...)
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We may be at cross purposes; the 'elaborate models' I was referring to are those used in the various chains that ended up constraining (or taming) the multitude of alternative explanations for the observations (dust, grey dust, cosmological evolution of Ia SNe, Ia SNe as a heterogeneous class, etc, etc). This is, as I'm sure you agree, a very necessary part of doing physics/science, but also tends to be very unglamorous^.
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WMAP and Planck: missions designed explicitly and specifically to study the CMB; compared to COBE the amount of modelling and number-crunching is stupendous; more important however is the combination of robustness and smarts that has gone into the 'how' of digging a cosmological signal out of the raw data (compare, for example, how COBE addressed the zodiacal light component).
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I would view these as observational details. Yes many observations require sophisticated data reduction and analysis-- but that's in an effort to isolate and separate the physics of interest, it is not necessarily part of why you did the observation in the first place-- that's usually done to try and isolate a particular physical effect that is embedded in whatever is the complete simulation you are using. Extraction and isolation is a key element of doing physics, that's basically all I'm saying.
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Indeed.
Yet these 'observational details' may well involve quite elaborate simulations, and the effort leading up to the 'first light' of something as complex as GLAST chock-a-block full of stuff that I think you'd agree is no less a "kitchen sink" model (or simulation). One difference is that the 'existence proof' of the models/simulations nearly always comes quickly and flaws may have fatal consequences (which was the Mars mission that involved a team using MKS and a team using miles/pounds/etc?). I think one thing you're saying is that in much of astronomy there is little, if any, opportunity for this kind of existence proof.
Also, don't you think WMAP and Planck are examples of (future) observations that are "
theory driven" rather than "
technology driven"? After all, no one would invest $$$$ to build a Planck if there were no LCDM models! LSST and Pan-STARRS are good examples of "technology driven", yet both are being fine-tuned to align with capability to test hot theories ...
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Some Galaxy Zoo (GZ) findings: it seems an imbalance of clockwise vs anti-clockwise spirals, reported in some papers, is due to some bias in humans' interpretations of images; NGC3314 has approval for HST time to investigate Hanny's Voorwerp; a paper on 'blue ellipticals' will be coming out soon; 'zooites' (or 'zooties'!) found 'green peas', this is now been investigated; ... to be sure, even a dozen papers from GZ would be a drop in the bucket of astronomy/astrophysics/cosmology papers.
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This is mixing in issues about analysis of complex datasets. I am certainly not suggesting that reality is not complex-- I'm suggesting that our job is become adept at finding ways that allow us to pretend, in some isolated context, that it isn't.
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Cool!
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caveat: I am not attempting to be complete or accurate; this is illustrative
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for every paper tentatively concluding that, say, Ia SNe are heterogeneous (much less the wild exaggerations such a paper elicits in popsci mags, nor the glee with which certain BAUT members seize upon juicy bits quote mined), there are 100 tentatively concluding they are good standard candles; not one of these 100 makes it to any popsci mag article ...