Comments on: Dark Energy Task Force Report

By: Dark Energy Fundamentalism: Simon White Lays the Smackdown | Cosmic Variance

Thu, 19 Apr 2007 20:34:52 +0000

[...] I kind of agree, actually. More specifically, this is one of those cases where I disagree with all of the background philosophizing, but am sympathetic to the ultimate conclusions. (In contrast to the framing discussion, where I’m sympathetic to the philosophizing but disagree when it comes down to specific recommendations.) Dark energy is extremely interesting, and any little bit of info we can get about it is useful; on the other hand, there is a fairly narrow set of things that we can do to get info about it, and concentrating on doing those things to the detriment of the rest of astronomy would be a bad thing. Happily, astronomy is one of those nice fields in which it’s hard to learn about one thing without learning about something else; in particular, as the dark energy task force has recognized, the actual things that can be usefully observed in an attempt to get at dark energy will inevitably teach us many interesting things about galaxies, clusters, and large-scale structure. [...]

By: Mark

Mark — Tue, 23 May 2006 15:12:24 +0000

Thanks Mike.

By: Mike

Mike — Mon, 22 May 2006 21:11:35 +0000

Mark, you’re a poo-poo head.

By: Doug

Doug — Sat, 20 May 2006 00:15:40 +0000

Mark,

Remember, the SM is the SM of fundamental interactions of light matter/energy; that is, it is a model of how matter/energy behaves. If we had a comparable SM of fundamental interactions of dark matter/energy, we still would not know what matter/energy is, which is the ultimate answer we seek, if we are to understand the physical structure of the universe.

That’s the point that leads to the question, “where is the LETF?”

By: Aaron Bergman

Aaron Bergman — Fri, 19 May 2006 19:33:01 +0000

Sean, those papers seem to do this weird spatial averaging procedure to get “acceleration”. As far as I understand it, we measure the distances to distant supernovae. I can’t see why that has anything to do with the quantity that Kolb et al define. All that matters is what happens along the geodesic from the supernova to us, so I still think Hirata and Seljak (or arguments along those lines) ought to apply.

By: Dick

Dick — Fri, 19 May 2006 19:29:24 +0000

Dear Physicists,

After you have measured the equation of state of the dark energy, what will you know then? Let’s say it turns out to be w = -1. “Aha!,” you will say, “It is the cosmological constant.” But what will that tell you? What is the cosmological constant? Why is it there? You won’t know the answers as long as you have no idea what spacetime is. You really need to put the abstract mathematics aside for a while and get back to doing physics. Quantum field theory and general relativity are inadequate to the task, being only effective theories. String theory and loop quantum gravity are impressive mathematically, but as physics theories, they aren’t even wrong. Quantum mechanics offers all the tools you need. You will discover that spacetime inflates, expands, and accelerates because that is its nature; it can’t do anything else. But perhaps you prefer stumbling around in a pitch-black room, looking for a pitch-black cat that you aren’t even sure is there. (It is.)

By: Mark

Mark — Fri, 19 May 2006 19:05:13 +0000

It is quite right to say that there are things we don’t understand in the SM. However, it is incorrect to describe it as merely a parameterization of the data, as you seem to be doing, and as we in essence treat dark matter and dark energy as. The SM, once one chooses those few parameters, makes all kind of detailed predictions qwhich have then been spectacularly confirmed by experiments, both laboratory and cosmological. It is just not right to make a comparison between this and the dark components.

By: Doug

Doug — Fri, 19 May 2006 18:35:45 +0000

Mark wrote:

I don’t quite get what you mean Doug. We have an exquisite understanding of “light matter”. QED is one of the best-tested theories in all of science.

Mark, where would QED, or the standard model be, if we couldn’t input mass as a free parameter? The only difference between our knowledge of the dark and light matter/energy is that we can measure the properties of the latter more directly, but we can’t explain why the light side has the properties we measure in its effects, such as mass, charge, spin, etc, any more than we can explain why the dark side has the properties we measure in its effects, or the effects that we are currently attributing to it.

By: Darkness | Cosmic Variance

Darkness | Cosmic Variance — Fri, 19 May 2006 17:19:58 +0000

[...] No time for quality blogging, so here’s a poem in honor of the Dark Energy Task Force report — Darkness, by Lord Byron. (Line spacings added by me to make it easier to read on screen.) I had a dream, which was not all a dream. The bright sun was extinguish’d, and the stars Did wander darkling in the eternal space, Rayless, and pathless, and the icy earth Swung blind and blackening in the moonless air; [...]

By: Sean

Sean — Fri, 19 May 2006 16:26:27 +0000

References in the most recent Kolb papers. The Hirata and Seljak argument refers to the earlier incarnation, which everyone agrees is dead.