A Light Fantastic: Could Aliens Be Sending Us Laser Signals?

March 11, 2009

Over a decade ago SETI pioneer Jill Tarter and I had a dinner discussion about the protocol procedures for announcing to the world the first detection of a signal broadcast from an extraterrestrial civilization.  

I expressed relief that I would never have to worry about publicizing such a discovery from Hubble Space Telescope. “Hold on Ray,” Jill said, “you never know, Hubble might conceivably pick up a signal that other telescopes can’t detect.”

Oh, my worst nightmare! Imagine keeping that information under a news release embargo!

Now, some readers will scratch their heads at this because SETI has been popularized in the 1997 movie Contact where actress Jodie Foster “listens” for radio signals from E.T. with the huge radio telescope array near Socorro, New Mexico.

But another communication strategy that aliens might use instead of radio signals is to send brief and intense bursts of laser light across the galaxy – sort of like a signal lamp between two ships. Some space telescopes would be ideally suited to pluck out such a signal from the sky background.

Why laser beams instead of radio transmitters? A directed beam across interstellar space would be unmistakable from the stellar background and could penetrate thousands of light-years. With each pulse of energy a signal from a big enough laser optics system could appear 1 million times brighter that the transmitting planet’s parent star.  The thought is that an alien society would use an agile laser-transmitter to  “paint” nearby target sunlike stars with a “searchlight beam.”

An advanced alien civilization would not have to bust its annual GNP to construct a super-laser. Ideally, they would build a telescopic mirror the width of 10 football fields. They’d shine a laser into it that is capable of pumping out a blinding 1 quadrillion watts of energy in brief bursts (just such a laser is already in operation at the University of Texas).  

Now, a petawatt is 1,200 times the entire electrical generating capacity of the United States -- but the shots last for less than a trillionth of a second each. The laser could pulse at one blast per second or so.

The pulse sequence might have a mathematical pattern embedded in it. This could yield a complex and lengthy message, or simply repeat a shorter transmission for redundancy (so long as it does not decode into those sappy musical tones from the 1977 film Close Encounters of the Third Kind)

There have been numerous optical SETI (OSETI) searches with ground-based telescopes, going all the way back to the early 1970s. Ironically, the newly launched NASA Kepler space observatory might be capable of stumbling across just such a signal too. It has the light sensitivity, photometric precision, time resolution, and sample size (170,000 stars) to do, serendipitously, an unofficial (and unsanctioned) OSETI experiment from a space platform.

In addition to doing a census of stars with Earthlike worlds, it is not entirely impossible – however remote – that the observatory could stumble upon an artificial laser transmission. In fact SETI researcher Steve Kilston has gone so far as to assert that if Kepler doesn’t get laser-zapped, the result would statistically reduce the estimated number of actively laser-transmitting civilizations in the Milky Way Galaxy to less than one million (and of course it could also be "zero").

A variety of other space telescopes could be similarly adept at coming across an OSETI signal. The European Space Agency’s Gaia observatory (2011 launch) will map the position and velocities of one billion stars in our galaxy. Its onboard multi-color photometer is capable of serendipitous OSETI detections.

A wildly ambitious, spendthrift super-civilization – a million years more technically evolved that us -- might build a moon-sized laser mirror. They would tap a fraction of their star’s energy just to power a godzillion-watt laser capable of transmitting an intergalactic beacon across millions of light-years.  

Perhaps a future space telescope might intercept such a signal. The question is, how long will it take the researchers to shake off their amazement and disbelief, and dare tell their colleagues?

Photo Credit: University of Texas, Adam Contos/Ball Aerospace

 

 

Comments

[Adam]

I'm not altogether sure we'd recognise a signal if we saw one. Perhaps it'd just seem like a highly variable emission line?

[John Davis]

Wow pretty amazing theory, not too far fecthed and certainly doable!

RT
www.online-privacy.pro.tc

[Sam Sweiti]

Not convincing. Why at all would we even assume that any extraterrestrial technologies would be anything like ours why would we even think they'd look anything like us? They've probably evolved in their own world and their own environment and it cannot be identical to our earthly existence. If we were in a smaller planet we could have been much taller... gravity is different.
Laser... Really? Chances are there are existing things in our universe that we haven't even imagined yet, let alone named!

[Dustin Case]

The aliens are most likely bumping the Defyant Alliance album through space in an attempt to make contact with other hardcore underground Hip Hop loving planets. I'm sure every inhabitable planet has Hip Hop! I mean, come on WE do.

[MichaelL]

Back when the first Pulsars observed, didn't astronomers think that they had stumbled upon such a signal? I do find it interesting that we can assume any extraterrestrials would have evolved to become something quite different than us, and yet, we are assuming that they would have developed technology similar to ours.

[shamansun]

Although I strongly support the search for other civilizations, it does seem assumptuous to think other species would have a drive to search other sentient life. Most of all though, I suspect that an advanced intelligent civilization could have better instruments (and easier) than cosmic laser shows. It's a good idea to put a beacon out there, but wouldn't it be easier to believe they have sensitive instruments which can get good, hard looks at planets in other solar systems, similar but way more advanced then Kepler? If so, they might see dozens of worlds with life, and make their way to some of them. They also might leave life alone on other worlds, letting them grow into their own developed state - to be communicated with later. Consider Star Trek's prime directive too.

[ali]

"Not convincing. Why at all would we even assume that any extraterrestrial technologies would be anything like ours why would we even think they'd look anything like us? They've probably evolved in their own world and their own environment and it cannot be identical to our earthly existence. If we were in a smaller planet we could have been much taller... gravity is different.
Laser... Really? Chances are there are existing things in our universe that we haven't even imagined yet, let alone named!"

Everyone(thing) has the same physics to work with... they don't have to look like us either.

From our perspective, lasers are readily available and easy to work with. We would assume that much for another civilization. That's why it makes sense.

[Chris]

Another big advantage of lasers over radio transmissions is their inherent monochromaticity. Interstellar dispersion will have a negligible effect. Radio transmissions having a measurable bandwidth get smeared quite badly by this effect.

[J]

I thought laser is a coherent light in a tight beam. How would you see that beam if it's not focused exactly on you? What are the chances someone will point at your planet and beam you. I'd say infinitely small.

[Doug]

The thing is, that if they aim a laser beam at where our sun (or any star they may wish to communicate with), by the time it travels the distance to that star (even at light speed), the star is no longer there. Stars move within the galactic plane at a fairly fast pace. So unless they track the target star and aim at where its going to be when the beam arrives, this type of communication is not practical for long-distances.

[Harvey Birdman]

All very compelling; however, points deducted for ripping on Close Encounters.

[Chris]

I would agree, lasers are so "tightbeam" that you would have to be aligned with the transmission, don't forget that the universe is rather large.

[B S Murthy]

It needs still further more study on this

[Diginess]

Yeah, but can we even see a burst that is only a trillionth of a second in duration?

[Ray]

I’m delighted at all the interest this posting got.

Here’s my take on some of the comments:

“Why at all would we even assume that any extraterrestrial technologies would be anything like ours”?
-No they probably are not. But (to borrow from Yogi Berra) we can’t imagine what we can’t imagine. So, all we can do is hold out some hope they use primitive technology for backwater civilizations. That makes a big assumption about them being altruistic, which is probably naive too. Anyway, I don’t know how to build a “Z-wave” detector or whatever they commonly use.

Other possibilities:

X-rays lasers
Gamma-rays
Neutrinos
Gravitational waves
Subspace (faster than light) - ala "Star Trek"

“They also might leave life alone on other worlds,”
--They probably leave us alone because there is nothing to learn from us. We have about as much anthropological interest to them as watching a colony of ants. Still there could be civilizations that just love to show off and announce that they are the smartest entities in the galaxy.

“How would you see that beam if it's not focused exactly on you?”
--The beam does diverge to tens of thousand of miles, depending on distance.

“So unless they track the target star and aim at where it’s going to be when the beam arrives, this type of communication is not practical for long-distances.”
Any aliens smart enough to build a super-laser are smart enough to measure our precise distance, and the Sun’s proper motion across the sky from their vantage point.

“Yeah, but can we even see a burst that is only a trillionth of a second in duration?”
--One idea is that we would be “painted” with a string of bursts, lasting say a minute or so before the laser aims for another target star. Several hours may elapse before the beam returns to start a new stellar scan cycle. But now I’m trying to think like an alien!

[شات]

nice
thanks

[GODISMYSHADOW]

What if pulsars are really alien signals? Astrophysicists don't want us believing that, however. They concocted this wild hypothesis about pulsars being spinning neutron stars and try to prove it using mathematics. Then they can publish their papers, write books, teach courses and make money.

[francis lavoie]

I'm new to this and don't have all the technical terms to discuss with all of you but like Ray says, I guess we could live on hope for the receiving of a signal.. I know I hope but don't you all think that the chances of having intelligent life living at the same time as we do is practically impossible? Planets and stars come and go have been around for millions of years and will be around for millions of years... so the reason for us being on earth is so perfect when you think of what it took for us to survive, live and develope ourselfs! Other worlds would need the same perfection to produce intelligent life and to add to this, produce life at the same time as us.

[b9mh]

thank you

[بنت 18]

thaankes

[شات]

rrr