Dark Energy, Life Searches Make Strange Bedfellows

eldavojohn writes "Both the EU and US are using a strategy to merge what used to be two separate searches: the search for exoplanets that may harbor life and the search for dark energy. In an effort to develop 'robust, low-risk missions that maximize the scientific return,' the article analyzes how, without any changes, a space-based dark energy telescope could also check for microlensing events indicating an exoplanet."

Comments

So can any astronomers explain ...

[Daniel Dvorkin]

... why this isn't obvious, and being done already?

From my layman's POV, it seems like we have telescopes all over the spectrum, from X-rays to long radio waves, constantly gathering enormous amounts of data which could easily be mined for dark energy detection, SETI, and just about anything else conceivable. So while I think it's very cool that two such different applications can share data and techniques, I'd like to know what the reasons are that this doesn't just happen all the time. Is it a reluctance to share data, differences in the type of data needed, or something else entirely?

Re:So can any astronomers explain ...

[dlevitan]

I'd like to know what the reasons are that this doesn't just happen all the time. Is it a reluctance to share data, differences in the type of data needed, or something else entirely?

Actually, it's primarily lack of funding to build archives and, therefore, lack of access to the data. I think most astronomers have no problem sharing data, as long as they're properly credited and the data is used for something other than the original use (i.e. detecting exoplanets instead of dark energy). There are, of course, differences in the optimum observing strategy and obviously you can't figure everything out from the same instrument/observation, but additional observations are always good and there are usually ways to use the data.

What most people probably don't know is that the majority of data from ground telescopes (except for a few roboticized telescopes) is kept only by the observer. Observations often yield something "weird", in which case the "standard" procedure is to ask colleagues if they know what the "weird" thing is. If no one has any clue, the data is often put aside for later analysis, and typically forgotten about. Everyone is guilty of it, but it is entirely possible that what is one person's trash is another's gold mine.

Amusingly enough, at the last AAS (American Astronomical Society) meeting, there was a grad student discussion session with some of the higher ups in AAS. One of the things we grad students were very much in favor of was an observation archive with exclusivity for the PI for 12-18 months (this is the standard for NASA space missions). The reason we were given that this would never happen is funding.

Re:So can any astronomers explain ...

[boristhespider]

Well, I've got a couple of comments on that. Firstly, the article isn't talking about dark matter which is an entirely separate issue to dark energy -- effectively, dark matter is gravitationally attractive and appears on scales ranging from galactic to cosmological, while dark energy is gravitationally repulsive and appears on cosmological scales. Secondly, the search for dark matter cannot (yet) be compared to the search for the aether and any such comment, without being qualified and backed-up with reasonable arguments, is uneducated. The evidence for "dark matter" (meaning an apparent weakness of gravity on galactic and supergalactic scales) is extremely strong -- the problem is there. The next question is simply whether something is wrong with the theory of gravity, which is certainly possible, or whether there is actually missing matter of some form out there.

Taking the second view first, which is more or less the current view, there are plenty of ways that we can get "dark matter". The simplest is simply matter that is difficult to see -- but there are problems with this and it is unlikely that it makes up a significant amount of the problem. Then you get more interesting models. The immediate particle candidate is a neutrino. Neutrinos exist, of this we can be sure, and they appear to have a small but non-vanishing mass -- of this we can be very confident. (This immediately tells us, by the way, that the standard model of particle physics in its simplest form is flawed since it predicts neutrinos of vanishing mass.) Since neutrinos interact only very weakly with matter, they are an immediate dark matter candidate. The problem is that if you make all teh dark matter in the universe the result of massive neutrinos you wash out cosmic structure -- it just doesn't fit observations. So it can't be (entirely) neutrinos. The most common candidate at hte minute would be neutralino, which is the supersymmetric partner of a neutrino. If you believe supersymmetry (which personally I don't, quite, but plenty of people do and there are very good reasons to believe that there's something in it) then you believe in supersymmetric partners; and you also must believe in a *lightest* supersymmetric partner. This particle will be stable, since it can't easily decay into non-supersymmetric particles. In most models, this particle is the neutralino. The hope is that its mass may be such that we can detect it at the LHC. If we do, much of the dark matter problem will be immediately solved -- there would be neutralinos in enough numbers to fit the observations.

The first view, that of modifying gravity itself, is an old one -- and a current one too. It is entirely wrong of you to suggest that people aren't "developing" the theory, since they are and have been ever since Einstein proposed general relativity in the first place. The main ways of modifying relativity come from adding an extra (scalar) degree of freedom into the theory; this can either be done by literally adding in a scalar degree of freedom (which ultimately makes Newton's "constant" time-dependent) or by modifying the "action", the function that generates the equations of motion, such that the Einstein action linearly dependent on the Ricci scalar becomes instead an arbitrary function of the Ricci scalar.

You can struggle to get dark *matter* out of such theories, but if you go one step further and also add in additional vector degrees of freedom, then you have dark matter along with dark energy. (And a really ugly theory.) The other advantage is that you can tune the theory such that in the non-relativistic limit it matches the predictions of "MOND" (MOdified Newtonian Dynamics), which is a purely phenomenological "theory" that aims to predict galactic rotation curves without recourse to dark matter. Effectively, in MOND there is a minimum acceleration below which the nature of gravity changes. With this simple idea, you get startlingly good agreements with many observations (and truly rubbish ones with others, it must be said). The benefit of the

Re:Not the EU, but Europe's Space Program!

[jandersen]

What kind of question is that? Don't you know that America was that close to get a vice-president that wouldn't be able to find the US on a map of Nort America? I think you need to adjust your expectations a bit.