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absael
2013-Mar-13, 09:43 PM
I thought that I would find some threads about SETI@home (http://setiathome.berkeley.edu/) here, but the only threads that I could find were 5+ years old, and there weren't many of those. I found the site's SETI team (BAUT (http://setiathome.berkeley.edu/team_display.php?teamid=117834)), but according to the SETI website, there are only 11 active members.

I joined SETI@home in 2002, but I was inactive for a long time. I recently started running it again, along with some other BOINC projects that work on problems related to medical research.

Do you run it? If not, do you think that there is a reasonable chance that it will ever detect a signal from an alien civilization? Do you think that the newer, broader band search (Astropulse (http://setiathome.berkeley.edu/ap_faq.php)) has a better chance of being successful than the narrowband search?

earthstation
2013-Mar-15, 01:26 AM
I did it for a while, but mainly just to get forum access IIRC. The problem I have with it is my electric bills are high enough already. I am leaving my computer on 24/7 at the moment, but my CPU is underclocked and undervolted (1.2 Ghz, 0.94V) to save energy.

I think the chances of any form of traditional SETI actually finding anything interesting are astronomically miniscule. The whole water hole idea is silly. They aren't even listening at the most likely frequencies which are going to be at at least 10 Ghz and may be over 100 Ghz. As a rule higher frequencies are better if you know precisely what you are aiming at and are very good at making precise parabolic dishes. I would expect civilizations thousands or even millions of years more advanced to be transmitting at over 100 Ghz. Our atmosphere severely attenuates transmissions at those frequencies, but SETI on the moon could listen for them. There is a slight atmospheric window at around 74 - 79 Ghz, again at around 33 Ghz, and then not again really until you get to the 10 - 13 Ghz region. The clearest window is 1 -10 Ghz and we have mostly only been listening at the 1.42 Ghz hydrogen line. Water vapor and oxygen lines are mostly responsible for the attenuation. Since the aliens cannot be sure of what kind of atmosphere we are likely to have they cannot anticipate all of that. Although an atmosphere with water vapor is probably a good bet. They may just assume that we will have orbiting or lunar based radio telescopes and not worry about such things at all. In which case all bets are off. They might be transmitting at 330 Ghz or something.

Another problem is that the aliens that may be out there almost certainly don't know that we are here. Any efficient form of signalling is going to be highly directional. They actually have to target at least our system specifically, and maybe they have in the past and got no reply because we only just recently started listening or because we weren't listening at the right frequency or didn't point our own dish in exactly the right direction or because they were transmitting at such a high frequency that their tight beam missed Earth and maybe hit the Jovian planets or something.

In order to know that there is a planet in this system that supports life they'd probably have to be able to detect the gases in our atmosphere. Methane is a good clue. It's hard to say what kind of range even very advanced technology would have to do that. We can do a little bit of that ourselves in limited ways, but there may be a range limit. And if they are somewhat distant form us, like say 250 ly, there really isn't any reason for them to single us out. There would be so many other stars within a 250 ly radius from them. Also, even if they are able to detect the methane and water vapor in our atmosphere from a long way off they have no way to know that there is intelligent life here of the kind that might aim a radio telescope in their direction and listen on the right frequency. Intelligent life doesn't necessarily equal radio telescopes. Think of a highly intelligent, sentient species of octopus.

I think passive SETI is a waste of time. I think the only kind of SETI that makes sense is Active SETI. We could systematically start transmitting messages to Alpha Centauri, Barnards Star, Wolf 359, Lalande 21185, Sirius etc? Or skip the systems we don't think have much chance of life bearing planets. And you don't just ping them. We wouldn't hear a ping. Why should we expect them to hear such a brief transmission? We'd have to transmit to each star for months. Or maybe transmit for 1 period between the star rising and setting times and then rotate back again once you've covered the rest of the stars out to 100 ly or something. After the minimum time for a reply has elapsed you start listening. First for messages from Alpha Centauri 9 years after transmitting, then Barnard's 12 years after and so on.

Wideband, short pulse SETI is a good idea, but if they are still only listening at the hydrogen line it's almost useless. the Benford brothers wrote a great paper (http://arxiv.org/abs/0810.3964) on the fact that wideband ultra-short pulses are a more efficient means of creating a powerful beacon than continuous wave narrow band. I am hoping to do some transmitting myself, and I wouldn't even consider CW transmission. It uses way too much energy for the range you get. The problem with ultrawideband is that you need a huge amount of power, a gigawatt would be the absolute smallest power level you could really consider. That's no problem if you are James Benford and can just build a magnetron that can do that, but nothing like that is commercially available on this planet. If you have such a device your average energy usage will be lower despite the huge peak powers. You just have to avoid looking too much like a pulsar.

absael
2013-Mar-17, 12:41 AM
Great reply, thanks. Sometimes I think that I was born too early... I believe that "Are we alone?" is one of the most important questions that we can ask, but I suspect that we might not have the technology during my lifetime to answer it. I guess I take a bit of comfort in thinking that I'm at least trying to do something to expand our knowledge in this area, but I often feel that I'm wasting time and electricity.

earthstation
2013-Mar-17, 08:58 AM
Might not have the technology during your lifetime? Boy, are you an optimist. I also feel like I was born too early. If only we could hop on a spaceship that could get to a reasonable percentage of c and time dilate our way a few millenia into the future. I actually don't believe the problem is with technology. The problem is that the galaxy is very, very big and stars are very far apart and intelligent life of the dish building variety who also want to search for other life in the galaxy is probably relatively rare.

Even if the average distance between planets with intelligent life is only 1000 light years, meaning that our galaxy is teeming with life, there's little chance of us finding that needle in the haystack or they finding us. Even only 100 light year distances are enough that there is basically no chance of discovering that planet within your lifetime, even if governments decided that Active SETI was the most important thing our species could do and were unafraid of SciFi alien invasion scenarios. With the 'safer' passive SETI the whole thing is just absurdly optimistic and a human lifetime is nothing. It's like waiting for a thousand monkeys and a thousand typewriters to produce a great work of literature. The lesson is, "don't hold your breath". Even with Active SETI, where you are making a real effort at communication and not just praying for a miracle, light is just too slow, and the distances too great for a human lifetime.

Bill Thompson
2013-Mar-20, 12:24 AM
SETI@HOME is gone, right? I mean the project is dead, isn't it?

absael
2013-Mar-20, 01:15 AM
SETI@HOME is gone, right? I mean the project is dead, isn't it?

No, it's quite active. I think it did shut down for a while a few years ago for a reorganization.

Thanatos
2013-Mar-21, 08:04 AM
SETI@HOME remains active, as well as EINSTEIN@HOME.