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!

Square Kilometer Array

Jill Tarter was on the May 10th episode Science Friday to discuss SETI. Sadly, but not surprisingly, she took an ignorance-first approach to describing the challenge of SETI. No sooner had I finished writing a post about it, then I heard her say something blatantly false. She claimed this about our ability to detect another civilization using radio astronomy:
"If they're younger and less capable than we are, then we can't detect them over interstellar distances."
But on the Square Kilometer Array website I read:
The SKA will be so sensitive that it will be able to detect an airport radar on a planet 50 light years away.
Which isn't built yet, but Jill does need to get with the times.

Tuesday, May 14, 2013

Zeta Rays

I'm going to complain about talk radio for a bit. On the May 10th episode of the NPR show Science Friday, host Ira Flatow offered a hypothetical blank check to Jill Tarter, and this was her reply:
... I'll take your check, but I wouldn't spend huge amounts on [SETI], because we couldn't guarantee success. It might be Zeta Rays that we should be looking for. I don't know what Zeta Rays are. It's a technology we haven't yet invented.
She is grossly overstating scientific ignorance in an attempt to create an interest in the mysterious nature of SETI. Selling science with ignorance defeats the purpose. Why would any alien use Zeta Rays, when Light Rays are already the perfect tool for communicating over interstellar distances?

No other particle can ever be discovered which travels farther on less fuel. No other particle can be discovered which travels faster. No other particle can ever be discovered that is easier to create (if it were easier, we'd have found it by now). Now, let that last parenthetical sink in a while.

Obviously, any message intended for us will, be light. The questions remain:

  • Which frequencies of light?
  • How might information be encoded?
  • Which direction should we look?
  • How long might the signal last?
  • How strong might the signal be?

All of these questions are interesting, unlike Zeta Rays, and have answers that fit into Ira's question.

  • More money means more frequencies. Build new telescopes that are sensitive on a wider range of the electromagnetic spectrum!
  • More money means more processors. It takes lots of computer time to check for different kinds of signals in telescope data. I'm sure SETI could find use for a few dozen petaFLOPS!
  • Why not look at every star? There are techniques for obtaining spectra for multiple stars at a time. The technique is expensive, but it could enable continuous monitoring of tens of thousands of stars. Also, space-based radio telescopes; how come the Russians have one but we don't?
  • With a blank check, we could setup a trust fund to keep SETI going forever. If SETI technology was improved to the point where we could closely examine a thousand star systems per second, it would take a decade to look through them all. SETI is going to take a long time!
  • With a bit of cash, SETI can detect even very faint signals. The Ooty Radio Telescope can detect 1 watt radio station located 10 million km away in space, and it was built in 1970!

Forget about distinguishing sufficiently advanced technology from magic. Communication isn't about magic. It's about common sense. In this case, we're talking about sense common to every responsible member of the galaxy.

It isn't rocket science. It's just optics, at low frequency.

Thursday, May 9, 2013

Bending Space and Time

Someone asked me if I know how to bend space and/or time. It was asked as a joke, but I happen to know the answer. Space actually does bend, in the vicinity of matter, according to General Relativity. Light beams will appear to bend as they pass through the warped region. This phenomena is called gravitational lensing.

The resulting deflected is equal to the angle θ = 4GM/rc2, where G is the gravitational constant, M is the mass of your object, c is the speed of light, and r is the distance from the light beam to the point source of the gravity.

Let's say, for example, that I want to bend your laser pointer with my body mass. You shine the laser 1 foot from my center of mass. I want to bend the light by just one degree. This small deflection should be observable if you bring your eye towards the laser pointer and look strait down the beam. In this hypothetical, how much do I weigh?

1° = 4GM/rc2
4GM = 1°rc2
M = 1°rc2/4G
M = 1.79 * 1024kg
M = 30% mass of the Earth

Time to go on a diet.

What if you're shining a laser pointer at the mirror left on the Moon by the Apollo astronauts? I walk up and stand one foot from the beam, weighing 100kg. How far does my mass cause your laser beam to drift off target?

First, we have to find the angle of deflection caused by my mass.

θ = 4GM/rc2
θ = 5.58 * 10-23°

Now, we do a little trigonometry to find drift off target, x. Let d represent the distance from the Earth to the Moon.

tan(θ) = x / d
x = d * tan(θ)
x = 3.91 * 10-16 meters
x = 0.391 femtometers

A miniscule effect.