The Physics Police

The Physics Police

Wednesday, May 15, 2013

Dark Magic

Jill Tarter was on the May 10th episode Science Friday to discuss SETI. I know it seems like I'm ragging on her, having posted twice about this episode already. But she says a lot of interesting things, some of which happen to be untrue or unjustified. So blame her for this third post. Here's what she said:
Let me remind you that Arthur Clarke once said that any sufficiently advanced technology would be indistinguishable from magic. Might it be indistinguishable from Dark Energy? Might [Dark Energy] actually be some manifestation of an extraordinarily advanced technology?
The short answer to her question is a resounding NO. Read no further if you like.

Saul Perlmutter at first deflected the question, then concluded by saying he wouldn't bet on it.

It's actually a fascinating thought, so, as is my style, I will refuse to wallow in ignorance at the feet of the Arthur Clarke's ghost. I will attack the problem at face value.

Here's what we know about Dark Energy:
  • 68.3% of the energy budget of the Universe.
  • Uniformly distributed.
  • Causes acceleration of the expansion of the Universe, as seen in our epoch.

Anything further we wish to say about Dark Energy must come from within a theoretical framework which explains (or may eventually explain) the phenomena. If we don't constrain ourselves to one or another theoretical framework, we aren't doing science. This is where I probably lose the likes of Jill. She has taken off her science hat, and put on her fundraising hat. That's fine. We're not going to do that, here.

There are two popular theories to explain Dark Energy:

  • Cosmological Constant is the cost of having space. Because the quantum vacuum is not empty, but roiling with virtual particles, all that activity has some net energy at any given time. This vacuum energy is not amenable to intelligent control, because it comes strait out of the theory of quantum mechanics. The trouble is, the predicted value is way off from the observed amount of Dark Energy. This theory leaves room for some undiscovered term which nearly cancels the quantum-derived vacuum energy. Maybe aliens have spread out invisibly throughout the universe, and their negative energy density (nearly) cancels the vacuum energy? Not possible because, before the universe gave rise to life forms capable of such technology, the huge cosmological constant would have blown the big bang apart so that no stars could have ever formed. Stars are the engines that produce metals, required for that chemistry which is the stuff of life. No, you can't let the Cosmological Constant rely on sentient technology. It's required for our universe to get started!

  • Quintessence. This theory requires a new field, too, but one which can vary in space and time. In order for it not to clump and form structure like matter, the field must be very light so that it has a large Compton wavelength. Maybe there are aliens who use this field as a medium, to communicate or live and think, but that doesn't make them responsible for its existence. You still need to have a primordial Quintessence field to account for the particulars of inflation. Aliens couldn't have influenced the energy density of a Quintessence field before the formation of stars. If they use it as a place to hang out and smoke dope, that's fine. But it can't be a consequence of this use!

Any other explanation of Dark Energy is going to have a similar problem. Jill puts the card unmistakable before the horse by suggesting alien technology is what explains Dark Energy, because Dark Energy happened before life, and therefore technology, could have arisen!

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