I understand the arguments pro/con of BEPAC. I am not saying I disagree with BEPAC’s choice, I am just calling out Tod’s statement that JDEM is a small portion of the pie, which is of course, not true.

Eugene

How thick on the ground are super novae? Would it be possible to use the space telescope in question to do one kind of ‘boring’ observation most of the time, and then just turn it around whenever the fireworks go off?

Of course, I’m ignorant and have my biases – I’m not really fond of Kepler, even if it does what it does very well. To be fair I probably should look up how much that cost. (And I’m being unfair since I lurrrrrrve the dedicated missions of WMAP and Planck.)

Actually, we have no compelling reason to believe either way: see for example

http://arxiv.org/abs/0910.0252

There are degeneracies all over the place, and breaking them is all-important.

Thanks for making my oblique implications more explicit.

I can’t imagine how any space-based mission would be worth the cost without enabling lots of ancillary science besides DE. Thousands of square degrees of Hubble-like imaging? Yes, please.

JDEM emerged from BEPAC because LISA et al were untested (and in many cases yet to be developed) technologies which would cost well in excess of JDEM. As BEPAC was tasked with deciding which of the Beyond Einstein probes should be the first to be built in a budget situation where you could only build one in the next x years (I think 5, I forget the actual number), they concluded (wisely imo) that the one that uses known technology is probably the best bet.

Any multi-satellite mission is unproven technology, so would likely require a pre-LISA mission to develop that technology before starting the LISA design. If JDEM were to be funded, you’d be draining a portion of LISA’s development budget, nowhere close to the full budget. Really the only argument worth having (among the BE designs) for a near term mission is a JDEM vs a descoped SIM vs a descoped con-X (or whatever the current name for it is, as it can’t be a multi-satellite constellation mission).

As I understand it, BigBOSS is a smallish team of scientists, not all from DOE, claiming that a particular observational strategy for JDEM (acoustic oscillations with photometry, and nothing else), which had been gaining traction, can be done around 10x more cheaply from the ground than from space. To drive home the point, they then proposed to do the ground-based survey.

But this isn’t the same as DOE “giving up” on a satellite, it’s just some scientists arguing, correctly, that the science needs to justify the cost: if you’re going to to to space, the science return had better be waaay better than what you can get from the ground. If the BigBOSS claims are correct (and I’m not in a position to say), then JDEM will only be worth it with a more comprehensive approach in terms of the number of DE probes it considers. (The fact that DOE folks had such a strategy in mind is possibly relevant here, though.)

First, there’s an underlying difference of philosophy here of what to do given that one model for DE (Lambda) stands out as the “simplest”. Some people would argue that this means it should be de-prioritized because the “probability” of alternatives to Lambda is small. An alternative viewpoint is that having one theoretically favored model that makes a definite prediction (i.e. where the theory says you shouldn’t need additional fudge parameters) warrants increased priority.

I also think we may have different notions of what “nearly constant in time” means. Exactly constant in time means rho[DE]~a^0 (where a is scale factor). A 0.07 (1 sigma) error in w means that we know the exponent of a to an uncertainty of 0.2 (1 sigma) or 0.4 (2 sigma). The Nature article repeats the common oversimplification (sometimes made by me too!) that this means DE “is constant with a precision of 7%”. Well, not quite. In particular, I disagree with the notion that Lambda is already well enough tested to “check the box”.

As for how we go after DE: if you really do want an ulcer, “my cosmological probe is better than your cosmological probe” is a great argument to have

Cheers,
Chris