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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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seti in dna article : bugmetnot is your friend
very stupid question from a non-engineer : is it not possible to have non-directed optical signals ? Some sort of 'ambiet laser'
Um, yes. Just take a look at your closest lightbulb. There's your omnidirectional light source right there. One might actually consider variable stars as messages from outer space...
In the interests of mentioning something real that actually exists, take a look at 802.11 over IR
Lasers are used for point-to-point links because there is usually an intended recipient. All of the energy goes to that single, intended direction. However, there shouldn't be anything to stop creating ambient monocromatic light source..
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.
WHY is the pound symbol banned from /. ?
:-)
I believe the answer would be because Slashdot only supports the lower 128 bits/characters of ASCII because the upper or extended 128 bits/characters are not standardized. Or rather, there are too many standards - hundreds of them - used by different people and countries to represent various different characters. Perhaps Slashdot should support the most common of them, ISO-8859-1 (Latin-1), in which the code for the UK pound symbol is 163... but Unicode will probably be supported before that happens. In short, Slashdot sucks a bit.
As an AC showed in reply to this thread, you can display the UK pound symbol using its HTML equivalent '£' - producing £.
== Jez ==
Do you miss Firefox? Try Pale Moon.
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.
That's an interesting idea, but what the Einstein, Podolski, and Rosen's experiment showed was "spooky action at a distance", not instant data transmission at a distance. It is true that reading the state of one of the entangled photons coming out of their device uniquely determines some qualities of the other photon (that is, WE now know something about the other photon), but the other observer doesn't get any information from us this way.
EPR were just freaked because it seemed to them that a signal that carried information about the system seemed to travel fater than light. (Not an informative signal that we originated, however)
What it all boils down to is, we don't know of a way (yet) to send information faster than light, even though it seems that some phenomona in the universe are governed by a connection that links/correlates points in space faster than it is possible for light to travel between each.
http://en.wikipedia.org/wiki/EPR_paradox
(insulanus)
The author Iain M. Banks has discussed this issue throughout his "Culture" series of books. He suggests that perhaps there are galazy spanning civilisations out there, but that they are evolved enough to leave us alone until we reach a level as a species where we can be considered for inclusion in the galactic community.
Why would they need to do anything as unsubtle as establishing moonbases when they could have invisible ships 30 kms long able to control every single tv screen on this planet from outside the orbit of Jupitor? :)
In fact, one of his short stories from the collection The State of the Art is about what happens when the Culture use Earth as part of a control group. An excellent read.
Of course this is sci-fi but you get the drift. If anyone is interested I would go as far as saying that for thought provoking Sci-Fi, Iain M. Banks is the man to beat at the moment.
Here he is in an interview at scifi.com talking about his writing. And here is the man with a few introductory notes on the Culture for the unitiated - I just picked this site from the top of google so I hope they don't mind me posting here :P
Switch back to Slashdot's D1 system.
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
Well, besides the lightbulb others already mentioned there actually is a kind of ambient laser - the random laser. It differs from others that you don't have a cavity but a little sphere (or a cloud) of the active medium. On their way out of it the photons get scattered, but also amplified by stimulated emission. This type of laser usually radiates in all directions. Here's some more information about them: random lasers. Look under publications, there are 2 papers on the 2nd page.
:w!q