PASAG

Report of the HEPAP Particle Astrophysics Scientific Assessment Group (PASAG)

Recently the separation between Astronomy and High Energy Physics (HEP) has been blurred. After years of dedicated experimental work on accelerators, all we found out was around 4% of what there is. Little bang for our bucks!

On the other hand in 1998 two teams of astronomers found startling results in this realm.

Most of what is; is Dark Energy, over 70%. And we are more or less clueless on what this stuff is.

Now the Department of Energy, which has supported accelerator work, joins forces with NASA to study the stuff. A lot of money for the study of nothing. I hope my readers don't include members of the House or Senate. If by any chance, one happens to read this, please read more. I am writing a first impression from reading the PASAG report. Don't base your funding decisions on this only.

Just to calm down any trigger happy republican representative who may want to kill the study of Dark Energy, I can say that it is plausible that a better understanding of vacuum energy, which is a strong candidate for Dark Energy, may in the future have applications. Casimir effect comes to mind.

From the Report:

"Astrophysical observations strongly imply that most of the matter in the Universe is of a type that is very different from what composes us and everything we see in daily life. At the same time, well-motivated extensions to the Standard Model of particle physics, invented to solve very different sets of problems, also tend to predict the existence of relic particles from the early Universe that are excellent candidates for the mysterious Dark matter. If true, the dark matter isn’t just “out there” but is also passing through us. The opportunity to detect dark matter interactions is both compelling and challenging. Investments from the previous decades have paid off: the capability is now within reach to detect directly the feeble signals of the passage of cosmic dark matter particles in ultra-low-noise underground laboratories, as well as the possibility to isolate for the first time the high-energy particle signals in the cosmos, particularly in gamma rays, that should occur when dark matter particles collide with each other in astronomical systems. In the coming decade, the same type of dark matter particles may be produced anew in the Large Hadron Collider (LHC), while relic copies are detected both underground at low energy and from outer space at high energy. Each of these will provide a needed piece of the puzzle. This is a particularly exciting time of convergence of theory and experiment, particle physics and astrophysics."

About Dark Energy, the Report has this to say:

"Astrophysical observations provided another stunning surprise: the expansion rate of the Universe, rather than slowing down due to gravitational attraction, is apparently speeding up. Either three quarters of the energy density of the Universe is of a completely unknown form – dubbed dark energy – or General Relativity breaks down on cosmological scales and must be replaced with a new theory of gravity. Either way, there are profound implications for fundamental physics. The dark energy could be the energy of the vacuum, which is predicted to arise from quantum fluctuations but at a strength that is wrong by more than one hundred orders of magnitude, demanding new particle physics, or something else entirely. By studying the expansion rate history of the Universe with much better precision with several techniques, key questions can be addressed: Is the dark energy density constant over cosmic time, or has it evolved? Are the different manifestations of dark energy consistently described in the framework of General Relativity, or is there something wrong with the framework itself?"

Humbly I can confess that I was wrong when at the young age of 21 I decided to become a Theoretical Particle Physicist. In my mind Astrophysics was not going to get off the ground. It didn't help that my only B in graduate school was in Dr. Morganstern Astrophysics course. Now I know better, I should've been putting more attention on Ralph E. Morganstern's lectures. Professor Morganstern found exact solutions to the Brans-Dicke Theory of Gravity. I wish I had interacted more with Ralph, scalars are back in fashion.

One conclusion of this report is to put money on the study of Dark Energy. I want some of that money.