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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?"
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Erm, are you SURE about that?
Ignoring the real nearest star, Sol, the next nearest star is Proxima Centauri which is 4.22 light-years away... i.e. its light only takes 4.22 years to get here, not the 25 you claim.
There are 25 known stars within 13 lightyears. Their light won't take 25 years to get to us either.
Seriously. You wanna check your random information before presenting it as a fact!
People should not be afraid of their governments - Governments should be afraid of their people.
A laser is a L.A.S.E.R., which stands for Light Amplification by Stimulated Emission of Radiation. This means that the laser light is an amplification of a smaller light source. Because of the amplification, the laser light waves are synchronous to each other, because they are the amplification of the same light wave. This type of light is called coherent. And because the light waves are synchronous, they can't be diffuse, which would be a contradiction in itself.
:)
If laser light travels, it loses this coherency, so the laser light gets more and more diffuse (the coherency gets slowly down, so the diffuse part increases). Optically this means that the light beam diameter gets wider and wider with the distance from the source. If the starting laser beam is very strongly bundled and has a very small diameter (thus a high energy density), this widening effect gets stronger. Less strong bundled lasers with lower energy density don't widen that much, so most long distance laser experiments (like measuring the distance to the Moon by shooting a laser beam there and take the time until the reflection can be measured) use quite large diameters, which you wouldn't call "laser" at all, because they don't spur the needle fine light
The divergence of a laser beam is, assuming ideal optical components, mostly dependent on the diameter of the beam where it starts. You can take a big telescope and let the light pass through in the opposite direction, so let's say, a diameter of 4 meters. For visible light, that will generate a beam with a divergence of 1e-14 sr. So, to get to 2e29 W/sr, you need a laser with a power of no less than 2e15 watts. (Compare this to a mid-size electrical power plant at 1e9 watt...)
Yes, there exist lasers that can generate ultrashort pulses in the near-infrared, with such a high peak energy, say 100 femtoseconds (100 fs=1e-13 s) and 100 joules per pulse, so there you have our desired fluence.
Unfortunately, such lasers can only fire something like one shot per second. If you really want to appreciate the high peak power, you need a camera with a shutter time of 100 fs. Imagine looking at the sky with such an ultrafast camera. The chance that you actually manage to catch a flash from this laser is virtually zero, unless you have a way to know when the flash is going to come. Someone who is looking at a nearby star and expecting flashes is more likely to have an aperture time of 0,1 seconds or so in order to capture any photons at all. At 0,1 seconds aperture time, the laser is no longer 10,000 times more bright than the nearby star (that is, our sun), but rather 1e8 times weaker.
So, it is unlikely that this is going to word, assuming that someone is looking at us anyway.
Avantslash: low-bandwidth mobile slashdot.
Regarding your final question: this question has been asked and pondered before by Enrico Fermi in 1950. See this Nature article for an extensive discussion on the subject: www.nidsci.org/pdf/nature_v409.pdf. I particularly like the list of canonical answers:
There are no aliens, and there never have been. Humanity is unique in the Universe.
There have been plenty of aliens, but civilizations only moderately more advanced than ours always blow themselves up in nuclear wars.
The lifespan of an alien civilization is only a few million years. They visited us ten million years ago, and will turn up again in ten million years time, but there is nobody around at the moment.
Aliens exist, but interstellar travel is impossible because of relativistic limits on the speed of light, or because living creatures cannot survive it.
Aliens exist, but are not interested in interstellar travel.
Aliens exist and have interstellar travel, but they are not interested in contacting us.
Aliens exist, but galactic law forbids any contact with us because we are too primitive, or violent.
Some aliens see it as their duty to eliminate all other forms of life that come to their attention.
Any technological civilization will develop radio and TV, attract their attention, and be eliminated11. They are on their way now.
They are here already (the preferred answer on the Internet s UFO pages).
Maybe we should consider the possibility that we are part of a device to perform some calculation to find the answer to a certain big question.
Actually, in my opinion, Kurt Vonnegut is the real master of "perhaps humanity only exists for a very stupid reason" stories.
Especially the sub-stories of his sf author character Kilgore Trout often have that theme - humanity exists only to train the hardiest microbes in the universe, because hyperintelligent rays of light want to help organic life travel the universe and only microbes could do that, etc.
In one of KV's books (spoilers for "Sirens of Titan"!), there is an intelligent alien who brings a message from his side of the universe to the only other intelligent species in the whole universe, millions of light years away. Half way, his ship breaks down, the alien manages to land on the moon we know as Titan. He needs a replacement part to fix his ship. His home planet sends the part, but this of course takes a long time; but the thing they can do faster than light is influence the thoughts of the monkeys that live on a planet nearby.
As the millennia pass by, the monkeys evolve under the influence of the far-away aliens, eventually building huge pyramids and the like in patterns that meant "almost there now" to the alien who was watching from some moon, eventually producing an extremely complex story line, including many wars, the stock market, the development of space travel, and fashion, that ends in a human going to Titan with a weirdly shaped piece of metal adorning his neck.
This is of course the replacement part for the alien, who can thus continue his travels. Humanity has served its purpose of producing the spare part, and is left to its own devices.
Eventually the alien reaches the other side of the universe, to deliver the message to the only other intelligent species in the universe. It said "Hello there".
I love Kurt Vonnegut. Adams must have read quite a few of his books.
I believe posters are recognized by their sig. So I made one.
A diffuse source contradicts with LASER
Not necessarilly. A LASER does 3 things:
1. Produces a narrow beam of light
2. Produces monochromatic light
3. Produces coherent light
Monochromatic light is produced by gas-discharge tubes (e.g. sodium lights, etc) - nothing special here.
You can produce a narrow beam of light using a point lightsource and mirrors/lenses.
Now, the special bit - your normal light bulbs produce incoherent light - you get lots of photons emitted but their waves aren't synchronised, so they interfere destructively with eachother. 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.
So if you want to create a omnidirectional optical light beacon, rather than using a normal light bulb and ending up with the photons randomly interfering with eachother destructively, it makes more sense if you can synchronise the wave fronts so they expand away from your light source in neat coherent spheres.
(I have no idea if the technology exists to do this ATM - it seems like a rather complex problem)
http://blog.nexusuk.org