Six Characteristics of Dark Energy

Sometimes when I write a blog post, I think of this line spoken by Jeff Goldblum’s character in “The Big Chill”, referring to how he writes for People Magazine:

“Where I work, we only have one rule: we can’t write anything longer than the average person can read during the average crap.”

Many people who read blogs, and that includes myself, just don’t have time to read several hundred-word posts; we skim and we glance to get to the interesting stuff.  In fact, it’s about the only way I read content on the web, for better or worse.

While I’ve already written a few, I wanted to write a series of long-ish posts about dark energy.   Being realistic about my time (and yours), I’ve decided that I’ll be a little less ambitous and break them down to some smaller bite-sized chunks (I’ll probably write the same ideas a bunch of different ways before it’s all over in order to help you make sense of this stuff, it’s pretty hard to visualize).

Whether you read them during an average crap is up to you.

Let me start by characterizing what we think we already know about dark energy (ooh look he’s using semi-colons):

1. It makes up 70% of the universe.  You’ve read this a million times by now.  The inventory of the universe goes like this:  5% normal matter (that’s you, me, people magazine, atoms, molecules, etc); 25% dark matter (that’s the stuff that has mass but doesn’t interact with the universe in any meaningful way, except with gravity); 70% something else (astronomers started calling it dark energy, they may regret that one day).
2. Causes the universe to be flat.  If the universe only had normal matter and dark matter, it wouldn’t be flat because there isn’t enough of it.  Since the universe IS flat, there must be something there to cause it to be that way.  They’re naming that thing dark energy.
3. It is an impulsive force that pushes against spacetime.  As the universe expands, the fabric of space is filled with this stuff, and when it appears, it provides an impulse – further pushing spacetime.  It’s not negative gravity, but can be visualized that way if it makes you more comfortable, it’s actually more of a negative pressure.
4. Is causing the acceleration of the universe.  Add up all these little impulses throughout the fabric of spacetime and you get a substantial push, and the push becomes stronger as there is more of it.  Spacetime expands, dark energy appears providing an impulse pushing things apart causing more expansion, etc…  What you’re left with is a universe that may just fly apart and slowly evaporate.
5. It is smooth and persistent throughout the universe.  Whatever dark energy is, it is everywhere (more or less homogeneous) and once it’s there, it stays there in roughly the same density as the universe expands.
6. It’s probably not a particle.  Umm, I should probably say more here, huh? If it is a particle, it’s probably more like the as-yet undiscovered graviton.  Let’s leave it there for now…

Who else but a blogger would think he can summarize something as complex as the nature of the universe in a six-point ordered list?

And yet, I do it anyway.  At least I wasn’t on the crapper when I wrote it.  You may feel otherwise.

Above photo credit:  Lawrence Whittemore