Should SETI Be Looking For Lasers Instead?

colonist writes "Frank Drake, creator of SETI's famous equation, says the detection of extraterrestrial radio signals won't work, because Earth's own radio signal will only be around for 100 years. More and more of Earth's communications use cable and satellites, with no radio-frequency leakage to space. Instead, we should be looking for intentional signals in the form of high-powered lasers that could 'outshine the sun by a factor of 10,000'. Meanwhile, Paul Davies writes that we should be conducting SETI in our DNA. In turns out that an alien message designed to last millenia should be 'inside a large number of self-replicating, self-repairing microscopic machines programmed to multiply and adapt to changing conditions', otherwise known as living cells. Are we the message?"

Comments

Optical SETI

[Space cowboy]

Optical (ie: laser detection) SETI has been up and running for a while now (see Optical SETI overview for example). Drake ought to declare an interest though, since he's one of the investigators on the project.

It's a reasonable argument, but it's far harder to set up optical "listening" posts than radio ones. It cost me about 1000 uk pounds (WHY is the pound symbol banned from /. ?) to set up a SETI listening post, including all the costs from dish/low-noise-amplifier through receiver and PC. Setting up an optical one is waaay more expensive. Optics in general are far more expensive than radio components, and large-scale ones are extortionate :-(

The counter argument of course is that to detect laser light, the remote civilisation have to be pointing their laser at us, whereas with radio it doesn't matter since it's not a directed beam. Against that you have to offset the time-period over which transmissions of either kind could be made...

The chances of getting a radio contact may be a few orders of magnitude lower than getting an optical contact, but since the chances of me setting up an optical SETI station are precisely 0, the chances of getting 'the' signal with radio is infinitely greater than with optics, at least for me :-)

Simon

Re:Optical SETI

[selderrr]

a very stupid question from a non-engineer : is it not possible to have non-directed optical signals ? Some sort of 'ambiet laser'. I understand that you'd have to go low voltage in order not to burn everything around you, but aren't pulsar stars some sort of ambient light beacon ? ? And how about we set up SETI to search for radioactivity residue slung into space ??

Re:Optical SETI

[Hal-9001]

A LASER does 3 things:

1. Produces a narrow beam of light
2. Produces monochromatic light
3. Produces coherent light

Actually, condition 3 is the only one that is necessarily true of all lasers. There are solid-state lasers with very wide bandwidths, thereby violating condition 2, and it is easy to expand or diffuse a laser beam, thereby violating condition 1.

To be honest, there is little point in creating an omnidirectional laser source, at least for SETI purposes, because that only degrades the signal-to-noise ratio. However, if you want to do so, it's pretty trivial: shine the laser beam into a high numerical-aperture microscope objective, and the wavefronts that emerge beyond the focal point will be an excellent approximation of ideal spherical waves.

Re:Optical SETI

[boicy]

"By contrast the light you get off a LASER is coherent - all the waves are synchronised, so they interfere constructively, making the light appear brighter."

Hmm, not actually sure if this is correct. This is going back a bit but I think:

Laser stands for Light Amplification by the Stimulated Emission of Radiation.

A LASER doesn't produce light because of waves contructively interfering. The light is amplified by the absorbtion and emission of photons at specific wavelengths.

There are two types of photon emission, spontaneous and stimulated.

Spontaneous emission occurs when an electron in an atom "jumps" from a higher quantised state to a lower one giving up energy. This energy is emitted as a photon. This is what happens in street lights, electrons fall back to a lower energy level and that corresponds exactly to the wavelength of the orange light we see. The photon can be emitted in any direction.

Stimulated emission occurs when an atom absorbs a photon causing an electron to move to a "higher" state but in this case the electron can immediately jump back to it's lower state. This causes two photons to be emitted in exactly the same direction as the original photon was travelling.

Essentially a LASER works by putting mirrors round a cavity and multiplying the photons by bouncing them back off the mirrors and into the emitting atoms thereby causing a "chain reaction" to take place where two become four etc.

The reason that you get monochromatic light (normally) is that the wavelength of the photons produced is exactly related to the energy levels in the atom producing them. The reason you get coherent light is because the photons are travelling in the same direction.

IWAPIU (I was a physicist in Uni) and built a Nitrogen LASER for my final year project. That was a good 8 years ago now though.

Are we the message?

[EachLennyAPenny]

Is a message allowed to read itself?

The real alien DNA

[mikeophile]

is in our mitochondria.

Quantum SETI

[essreenim]

With the promise of quantum communication, it is conceivable that (if Quantum communication is indeed feasible) we should be focussing our optical light search on specific photons of light.

Anyone know about beam splitting entangled pairs etc. Many moons ago, Einstein, Podolski, and Rosen carried out there unusual experiment whereby the they observed what is now known as quantun weirdness. A photon in an entangled state could be split using a sophisticated 50:50 beam splitter. Each split photon could travel off in opposite directions and appear to be twins, in the sense that any change in behaviour of one would instantly (exactly synchronized regardless of distance!!!) be felt by the other, its twin.
Evidence that this was no fluke is gathering thanks to continuing experiments, yet it is still not in stone.

My reasoning is that if this phenomenan is genuine, it could be one way extraterrestrials would chose to contact us. Why not. They send a conventional optical signal, only this time encased in a surrounding cylindar of light, thus allowing for the entangled photons charateristic properties to be influenced only by this cylinder of light. Allot can till go wrong so conceivably, the 'ET's' would send a large stream of such light cylinders- the centre of which is a stream of entangled photons. That way any measurement of the entangled photon would cause an immediate change to its twin (The twin photon - of entangled pair)would presumably be archived on the alien world bouncing back and forth in a cavity (not unlike the cavities we use today - only presumably far more advanced.) So, once change is observed, an immeditae alarm bell is triggered. The ET's can know instantly someone/something has comeinto contact with their signal. Just like Earth SETI, the ET SETI would categorise all their findings and have mant false positives. They would probably already have chartered the area of space to which they send a signal. They may know the only objects (meteorites, stars, planets, commets...) that are likely influences over the transmitted light signal. Hence, if we Earthlings intercept the light in a very manufactured manner (i.e fire a encoded light signal of our own into theres, they are likely to get some unusual data back at there end - instantly.

Anyway, lets face you can't have an interest in SETI without being imaginative.

All Im tring to say is.

1) If I were a highly advanced ET, I would use Quantum entaglement (if it is indeed feasible) to transmit photons of light.

2)I believe we should start sending entangled photons of light, encased in our own manufactured cylinders of background light, out into space.

3)I hope SETI read this.