Should SETI Be Looking For Lasers Instead? 694
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?"
Re:Optical SETI (Score:5, Informative)
user reg bypass (Score:4, Informative)
Re:If they outshine Sol by 10,000x... (Score:2, Informative)
Re:Regarding RF Leakage to Space (Score:3, Informative)
But if we did, we'd really have to pump the power up, and since we're illuminating the sky, we'd have to pump far more energy out into the wild blue yonder than for the equivalent space in low frequency RADAR bands.
--Dan
Re:Optical SETI (Score:5, Informative)
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 [wi-fiplanet.com]
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..
Re:Light takes 25 years from nearest star.. (Score:1, Informative)
The nearest star to ours, Alpha Centauri, is only 4 light years away.
Where did you pull 25 from ?
Re:Light takes 25 years from nearest star.. (Score:5, Informative)
Erm, are you SURE about that?
Ignoring the real nearest star, Sol, the next nearest star is Proxima Centauri [nasa.gov] 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 [nasa.gov]. 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!
Re:We should decode viruses too (Score:2, Informative)
I disagree. [dnafiles.org]
To quote the above linked source
"In reassortment, two separate viral strains, sometimes from different host species, infect the same cell and swap whole segments of one or two genes. This is how the 1957 and 1968 strains may have originated. The 1957 strain, which killed 70,000 in the United States, carries three gene segments from ducks and five from humans. The later version, which took a U.S. toll of 34,000, mixes two duck segments with six human ones."
Human and Duck DNA in one strain of the Flu virus doesn't sound very efficient to me.
LK
DNA messages? Where have I seen this before? (Score:3, Informative)
Re:Optical SETI (Score:5, Informative)
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
10,000 times outshine the sun? Yeah right. (Score:5, Informative)
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.
Re:Optical SETI (Score:5, Informative)
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 £.
Re:This reminds me of a saying... (Score:5, Informative)
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).
The Outer Limits (Score:2, Informative)
That's exactly the idea from The Outer Limits : Double Helix, and sequel, The Origin Of Species.
http://theouterlimits.com/episodes/season3/307.ht
http://theouterlimits.com/episodes/season4/418.ht
Re:message of means? (Score:5, Informative)
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.
Re:Quantum SETI (Score:3, Informative)
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)
Re:This reminds me of a saying... (Score:4, Informative)
The author Iain M. Banks [iainbanks.net] 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 [iainbanks.net] 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 [scifi.com] talking about his writing. And here is the man with a few introductory notes [onetel.net.uk] 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
Re:Optical SETI (Score:5, Informative)
Re:Optical SETI (Score:5, Informative)
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)
Re:YOU FUCKING RETARD!! (Score:2, Informative)
This is based solely the 'linear intelligence' model, which thinks that all civilizations follow the same tree of technology, and if a civilization has a technology that we don't, then it means they've 'passed us up' on this imaginary tree and know everything that we do.
It's basically meaningless. The ability to get from one system to another could simply mean that the civilization, at one point or another, needed a means of space-travel to survive and now happens to be way ahead in transportation. Or they may be a bunch of dunces who stumbled on a way to bend space into wormholes.
And there are a billion ways to exist here unknown to human perception and inventions. Or at least quite a few. Just one look: Many of us are still bent on denying spirits and anything else we're told to believe is 'paranormal' (a funny little scarecrow-word that's kept us away from anything we're not told to acknowledge or figure out). Do you think the government could get funding to detect something they can't see at all? They wouldn't have much success getting funds for something that a politician can just call a ghost chase.
If we can't even detect something as frequent as a spirit, then moving around under our radar would be a snap for someone with the right skills or technology.
But kudos for not sacrificing your credibility and using the fearful old 'tinfoil hat' scarecrow, anyone else would have chickened out and gone 'Eek! Anyone who doesn't believe me has a tinfoil hat!!'
Optical SETI technical issues (Score:2, Informative)
--Andrew Howard
you can't 'detect' entanglement changes (Score:2, Informative)
Re:Quantum SETI (Score:3, Informative)
For the record (Score:3, Informative)
Re:Optical SETI (Score:2, Informative)
If the incident photon would excite an electron, which by falling back into its lower state will emit another photon, you cannot get out 2 photons identical to the incident one. This violates conservation of energy.
With stimulated emission an incident photon interacts with an already excited atom, where the excitation energy must be (more or less) equal to energy of the photon. Then this photon can cause the electron to drop into a lower state, producing another photon, which will be identical to the incident one (and travel in the same direction).
Re:We won't stop using RF (Score:2, Informative)
Re:Optical SETI (Score:3, Informative)
basically an energy issue... (Score:3, Informative)
photon energy is proportional to frequency
So for a given amount of energy you can get either more photons at a lower frequency or fewer photons at a higher frequency.
Since visible light is in the THz range (10^12) and radio waves are in the say MHz range (10^6), that's a factor a million less photons emitted per unit of energy.
Since we are essentially detecting a bunch of photons, this is the gist of the problem.
Of course it follows that the odds of finding one of a million needles in trillions of haystacks is easier than finding 1 needle in a trillion haystacks...
Of course if you are living on a pulsar, then energy (from gravitational collapse) is not a worry (pulsars tend to emit frequencies all over the spectrum from radio up to x-ray), but I don't think "intellegent" civilizations are going to be tossing around that much energy w/o thinking about it.
Note that a signal from a pulsar is very different from an omnidirectional phase-coherent electromagnetic "pulse". A pulsar spews pretty much incoherent EM, but from hotspots on a fast spining object (think about a person with a gardenhose spinning around really fast, you'll see how a stationary observer will see "pulses" of water drenching her when in fact the garden hose is just spraying incoherent water).
However, it is technically possible to generate a reasonably coherent, mostly omnidirectional EM pulse from a process known as superfluorescence.
I suppose it's feasible that this would be able to be repeatable enough to generate a pulse train (imagine a spherical lasing cavity around a superfluoresenct object). For some basic info on this, check this out...
http://ist-socrates.berkeley.edu/~lvov/OSF.html
However, given the "energy" argument above, I doubt any intellegent aliens would have turned on a beacon like that (Did you see the movie independence day? Maybe turning on a beacon isn't such a great idea)...