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I know the idea behind SETI is great, but I have great doubt about the execution. Here is why: From: http://www.damninteresting.com/space-radio-more-static-les

by bh42222 15y ago

I know the idea behind SETI is great, but I have great doubt about the execution. Here is why: From: http://www.damninteresting.com/space-radio-more-static-less-talk/ http://www.damninteresting.com/space-radio-more-static-less-... When any non-focused electromagnetic signal is generated– such as a television broadcast or a cell phone conversation– the energy propagates as a spherical wavefront at the speed of light. When a sphere is doubled in diameter, its surface area increases by a factor of four; but in a spherical wave the “surface area” is the energy itself. This means the signal’s energy is spread over four times more area at twice the distance, resulting in a 75% loss in intensity. To put it another way, in order for a broadcasting tower to double its effective range for a given receiver, it must quadruple its transmitting power. To demonstrate the degrading effect of distance on an everyday omnidirectional signal, one might imagine a spacecraft equipped with an Arecibo-style radio receiver directed towards the Earth. If this hypothetical spacecraft were to set out for the interstellar medium, its massive 305-meter wide dish would lose its tenuous grip on AM radio before reaching Mars. Somewhere en route to Jupiter, the UHF television receivers would spew nothing but static. Before passing Saturn, the last of the FM radio stations would fade away, leaving all of Earth’s electromagnetic chatter behind well before leaving our own solar system. And: http://blog.jackadam.net/2011/the-tiny-humanity-bubble/ http://blog.jackadam.net/2011/the-tiny-humanity-bubble/

hammock 15y ago
You seem to be talking about aliens picking up earth transmissions, while he's talking about receiving alien signals.
- fendrak 15y ago
  Right, but he's saying that if Earth's own signals fail to propagate even outside our solar system, alien signals will have to be exponentially more powerful than ours to even stand a chance of being received. The distance from Earth to Saturn is tiny in comparison to the distance between planetary systems.
  - cma 15y ago
    Polynomially. Not exponentially. The surface area of a sphere doesn't grow exponentially with radius.
    - jjtheblunt 15y ago
      I'm so glad to see you wrote that, seriously. It is absurd how it has become pop-cultural to use "exponentially".
sp332 15y ago
This isn't a "non-focused" signal. This is being directed by an antenna in one dimension. A perfect antenna transmitting through empty space would send a signal that does not diminish at all with distance. The only attenuation would be due to imperfections in the antenna causing a gradual widening of the beam, and obstacles in the path of the signal.
- bh42222 15y ago
  Imperfections in the antenna, obstacles in the path of the signal, etc. From the The Hitchhiker's Guide to the Galaxy: Space... is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is... My point is space is HUGE, and it would take a stupendous amount of effort and energy to create and send a signal which Earth can correctly receive. And that's even if you specifically focus it at us. But why would anyone specifically focus it at us, if our own signals are not focused and quickly (quickly in term of universe distances) become indistinguishable from background radiation, how would they know we are here? What I am ultimately claiming is that even if we have intelligent radio using alien life "near by" we still would never find each other. Because even if we both have a SETI equivalent, neither one of us would initiate the huge effort necessary to send a focused "Hello" signal which the other can receive.
  - oscilloscope 15y ago
    Well, to start we could just send signals to nearby stars with planets. Obviously planets within 20 light years are the low hanging fruit. Since we know there's life on Earth, nearby stars might have a greater than average chance of harboring life as well. http://en.wikipedia.org/wiki/List_of_nearest_stars http://en.wikipedia.org/wiki/List_of_nearest_stars
    - sesqu 15y ago
      There is at least one astronomer who's doing exactly that. I didn't find his name with a quick googling, but I think it was a Russian fellow. Naturally, not everyone agrees on the step from listening to sending focused, targeted bursts.
InclinedPlane 15y ago
You mistake the purpose of SETI. The idea is not to attempt to pick up stray EM transmissions from extra terrestrial civilizations, almost certainly that idea is a non-starter for a wide variety of reasons. Instead, the goal is to pick up signals which are intentionally beamed at Earth. There are a lot of caveats on whether or not that makes sense, but assuming that an ET civilization has detected our planet (which they could do from across the galaxy) and they want to send us a message then it's not too crazy to imagine they might use radio to do so. Also, looking for such signals is pretty cheap, and the potential impact of such a detection would be enormous, so why not spend a little effort looking?
- andreasvc 15y ago
  > assuming that an ET civilization has detected our planet (which they could do from across the galaxy) The closest galaxy to ours is about 25,000 lightyears away, according to wolframalpha. In other words, we'll have to wait that number of years before an ET civilization from there might pick up on us. I think this makes the whole endeavor completely pointless.
  - Dylan16807 15y ago
    Did you read 'across' as 'outside' or something?
    - andreasvc 15y ago
      I did, but the milky way has a diameter of 100,000 lightyears, so it doesn't affect my argument.
      - Dylan16807 15y ago
        But a lot if it is really close too.
  - InclinedPlane 15y ago
    I said detect our planet not detect our civilization. For all we know there is some civilization out there which periodically cycles through all the known possibly habitable planets they've detected and beams radio messages at them.
tocomment 15y ago
So how do you explain that we're receiving our radio signals bounced back to is from 20+ light years away? http://www.rimmell.com/bbc/news.htm http://www.rimmell.com/bbc/news.htm
- michaelf 15y ago
  That story was posted on April 1st in 2009, and isn't hosted on BBC's website. There isn't even a first name given for the researcher (only "Radio astronomer Dr. Venn"). Looks sketchy to me. I can't find any other information about it, so I'm guessing its a hoax / April Fools joke.
  - tocomment 15y ago
    I was actually wondering that too but couldn't find anything definitive saying its a hoax. I have to think it would have been a huge deal if it were real, no?

by bh42222 15y ago

hammock 15y ago

You seem to be talking about aliens picking up earth transmissions, while he's talking about receiving alien signals.

fendrak 15y ago
Right, but he's saying that if Earth's own signals fail to propagate even outside our solar system, alien signals will have to be exponentially more powerful than ours to even stand a chance of being received. The distance from Earth to Saturn is tiny in comparison to the distance between planetary systems.
- cma 15y ago
  Polynomially. Not exponentially. The surface area of a sphere doesn't grow exponentially with radius.
  - jjtheblunt 15y ago
    I'm so glad to see you wrote that, seriously. It is absurd how it has become pop-cultural to use "exponentially".

sp332 15y ago

This isn't a "non-focused" signal. This is being directed by an antenna in one dimension. A perfect antenna transmitting through empty space would send a signal that does not diminish at all with distance. The only attenuation would be due to imperfections in the antenna causing a gradual widening of the beam, and obstacles in the path of the signal.

bh42222 15y ago
Imperfections in the antenna, obstacles in the path of the signal, etc. From the The Hitchhiker's Guide to the Galaxy: Space... is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is... My point is space is HUGE, and it would take a stupendous amount of effort and energy to create and send a signal which Earth can correctly receive. And that's even if you specifically focus it at us. But why would anyone specifically focus it at us, if our own signals are not focused and quickly (quickly in term of universe distances) become indistinguishable from background radiation, how would they know we are here? What I am ultimately claiming is that even if we have intelligent radio using alien life "near by" we still would never find each other. Because even if we both have a SETI equivalent, neither one of us would initiate the huge effort necessary to send a focused "Hello" signal which the other can receive.
- oscilloscope 15y ago
  Well, to start we could just send signals to nearby stars with planets. Obviously planets within 20 light years are the low hanging fruit. Since we know there's life on Earth, nearby stars might have a greater than average chance of harboring life as well. http://en.wikipedia.org/wiki/List_of_nearest_stars http://en.wikipedia.org/wiki/List_of_nearest_stars
  - sesqu 15y ago
    There is at least one astronomer who's doing exactly that. I didn't find his name with a quick googling, but I think it was a Russian fellow. Naturally, not everyone agrees on the step from listening to sending focused, targeted bursts.

InclinedPlane 15y ago

You mistake the purpose of SETI. The idea is not to attempt to pick up stray EM transmissions from extra terrestrial civilizations, almost certainly that idea is a non-starter for a wide variety of reasons. Instead, the goal is to pick up signals which are intentionally beamed at Earth. There are a lot of caveats on whether or not that makes sense, but assuming that an ET civilization has detected our planet (which they could do from across the galaxy) and they want to send us a message then it's not too crazy to imagine they might use radio to do so. Also, looking for such signals is pretty cheap, and the potential impact of such a detection would be enormous, so why not spend a little effort looking?

andreasvc 15y ago
> assuming that an ET civilization has detected our planet (which they could do from across the galaxy) The closest galaxy to ours is about 25,000 lightyears away, according to wolframalpha. In other words, we'll have to wait that number of years before an ET civilization from there might pick up on us. I think this makes the whole endeavor completely pointless.
- Dylan16807 15y ago
  Did you read 'across' as 'outside' or something?
  - andreasvc 15y ago
    I did, but the milky way has a diameter of 100,000 lightyears, so it doesn't affect my argument.
    - Dylan16807 15y ago
      But a lot if it is really close too.
- InclinedPlane 15y ago
  I said detect our planet not detect our civilization. For all we know there is some civilization out there which periodically cycles through all the known possibly habitable planets they've detected and beams radio messages at them.

tocomment 15y ago

So how do you explain that we're receiving our radio signals bounced back to is from 20+ light years away? http://www.rimmell.com/bbc/news.htm http://www.rimmell.com/bbc/news.htm

michaelf 15y ago
That story was posted on April 1st in 2009, and isn't hosted on BBC's website. There isn't even a first name given for the researcher (only "Radio astronomer Dr. Venn"). Looks sketchy to me. I can't find any other information about it, so I'm guessing its a hoax / April Fools joke.
- tocomment 15y ago
  I was actually wondering that too but couldn't find anything definitive saying its a hoax. I have to think it would have been a huge deal if it were real, no?