When I was a little kid, I knew I wanted to be a cosmologist, like Stephen Hawking. I would tell people that my dream was to have a little office somewhere with a giant blackboard, and I would fill it with equations and solve the mysteries of the Universe. Sometimes I imagined that instead of working in my office, maybe for a change of scene I would sit under an apple tree staring off into the sky, contemplating the nature of reality.Read More
You've probably been hearing a lot about dark matter detection lately. In the past couple of months, there have been announcements of announcements, delays of announcements, press conferences, ambitious claims, cautious optimism, not-so-cautious optimism, and various "hints," "signs" and "clues." But what does it all mean? Have we actually detected dark matter?
Short answer: Um, maybe. Also: It's complicated. Really complicated.Read More
As you might know, the pre-faculty academic life can involve a lot of moving around. For me, I went from an undergraduate institution in California, to grad school in New Jersey, to a postdoctoral fellowship in England. And just a month an a half ago I moved to a second postdoctoral fellowship in Melbourne, Australia.Read More
There have been a few truly transitional moments in the history of the Universe in which something fundamental about the cosmic environment changed. Some of these -- the beginning and end of cosmic inflation, reheating, big bang nucleosynthesis -- altered the very nature of spacetime or the kinds of particles that populated it, and all happened within the first few minutes. The first atoms formed a few hundred thousand years later, marking another milestone. For the 13 billion or so years since then, though, you could argue that it's all been a bit samey. Except for cosmic reionization.Read More
|That's not supposed to happen.|
[Source: Norwalk Citizen Online, Christian Abraham / Connecticut Post. ]
In general relativity, pressure is a form of energy, and energy has a gravitational effect -- your pressure adds to your gravitational field. (So, gravitationally, pressure pulls.) Negative pressure, therefore, subtracts from a gravitational field, and counteracts gravity -- it pushes. For a cosmological constant, the pressure is exactly -1 times the density: p=-ρ. (I'm using units where the speed of light is 1. You could also write this as p=-ρc2.) For other forms of dark energy, there could be a different relationship.
|Fraction of the Universe made of matter (Ωm) plotted against the dark energy equation of state parameter (w). Values in the orange region have a good fit to the data. [Source: Caldwell, Kamionkowski & Weinberg 2003 (PRL, 91, 071301)]|
How often do you get to invent an ultimate cosmic doomsday in the course of your professional life? This is the kind of work I got into theoretical physics to do. It's awesome.