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View Full Version : If there were 10 Kardashev Level 2 civilizations in the Milky Way, would we know it?



Tom Mazanec
2012-Jun-18, 05:01 PM
Could our SETI efforts detect such civilizations?
Assume they are scattered at random, are Dyson Swarms, and radiate as large a fraction of their total energy usage as radio as 2012 Earth does.

Ara Pacis
2012-Jun-18, 06:50 PM
Could they even detect each other? It would depend on distance and distribution. According to research that's been mentioned in BAUT previously, there is reason to believe that our radio emissions are not detectable beyond a fairly short radius.

eburacum45
2012-Jun-18, 08:20 PM
The detection question is actually the real reason Kardashev invented these categories. The different categories represent a thought experiment, designed to determine how far away any particular civilisation might be detected.

These categories were not intended to be realistic goals for any civilisation (they are not) but instead maximum output levels for transmitters at various distances.
See his original article;
http://adsabs.harvard.edu/abs/1964SvA.....8..217K

JustAFriend
2012-Jun-19, 10:53 PM
Until you can actually figure out how to detect one or have detected one, such questions are pointless.

The only answer is "maybe".

mutleyeng
2012-Jun-20, 02:25 PM
Could they even detect each other? It would depend on distance and distribution. According to research that's been mentioned in BAUT previously, there is reason to believe that our radio emissions are not detectable beyond a fairly short radius.

ive often heard seth shostak argue, in responce to those that say we shouldnt advetise our presence, that the horse has already bolted. That any civilisation capable of doing us harm would easily be able to pick up our signals at many light years distance.
Not getting into that issue, i have often wondered if that is actually true... is just better technology and more sensative recievers sufficient? I would have thought, at some point signals would disolve into background noise no matter how sensative your equipment.

neilzero
2012-Aug-08, 04:15 PM
That is my semi educated guess also. If the the signal plus the noise is the same as the noise without the signal, then detection is not possible: And the signal needs to be at least ten percent of the average noise to extract even rare bits of data from the combination. Worse, lots of things are moving so the strongest transmission path shifts significantly by the hour if not the second, which means detection typically lasts seconds and may not repeat for many years even if the source transmits continiously which it may not. Humans produce a wide variety of signals; logically ET produces some signal that we have not even imagined. Spread spectrum modulation is difficult to detect unless you know the algorithm and the time srandard even for strong signals, and many algorithms are possible. Neil

cathal
2012-Aug-13, 12:13 PM
Even if the civilisations aren't making large efforts to be undetectable (as I believe it would be in their interests to do), the developments of communications technology tends toward difficulty to distinguish. Efficient compression and encryption both make a signal resemble noise if not properly analysed. Good EM manipulation allows collimated production of a wide range of wavelengths.

Even then, the emitted EM is potentially useful energy for a hungry swarm element. Without some limiting factor, the energetic incentives seem to push toward the cloud's radiating the power of the parent star at close to uniform black-body radiation. There has to be a very good reason to stick with the parent star and not jump ship long before that, though.

Are the civilisations prevented from sending out even von Neumann probes? They could greatly increase the efficacy of their detection apparatus by increasing the volume enclosed.

Detecting civilisations may have the ability to use their own star's gravitational lensing.

Ara Pacis
2012-Aug-13, 05:52 PM
ive often heard seth shostak argue, in responce to those that say we shouldnt advetise our presence, that the horse has already bolted. That any civilisation capable of doing us harm would easily be able to pick up our signals at many light years distance.
Not getting into that issue, i have often wondered if that is actually true... is just better technology and more sensative recievers sufficient? I would have thought, at some point signals would disolve into background noise no matter how sensative your equipment.

Some people think not really. (http://www.straightdope.com/columns/read/3058/can-alien-beings-listen-in-on-tv-and-radio-broadcasts-from-earth)

Believers contend it can be done. An antenna similar to the 1,000-foot-diameter Arecibo radio telescope in Puerto Rico could probably detect our passive radiation from 30 to 50 light years away. With a giant array of 1,000 100-meter dishes linked together, that distance could be extended to 500 light years.

Just one problem. The aliens would be able to hear us at those enormous distances only if they already knew where we were and could point their telescope at us. If all they had was a hunch that we were out here somewhere, the likelihood they’d find us seems almost nil.

Even under the most favorable circumstances, all alien listeners would be able to detect would be a signal that stood out against the background buzz. The notion that they’d be able to collect and decode enough signal to be able to listen to, say, I Love Lucy reruns is fantasy — the signal would need to be 20,000 times stronger.

potoole
2012-Aug-14, 11:36 PM
ive often heard seth shostak argue, in responce to those that say we shouldnt advetise our presence, that the horse has already bolted. That any civilisation capable of doing us harm would easily be able to pick up our signals at many light years distance.
Not getting into that issue, i have often wondered if that is actually true... is just better technology and more sensative recievers sufficient? I would have thought, at some point signals would disolve into background noise no matter how sensative your equipment.

Since we have been transmitting radio waves from Earth for 75 years, or longer, supposedy those waves will have reached 75 light years distant. Isn't there a point, or time, when those radio waves will have become total meaningless garbage combined with all of the other radiation in space.

(Unlike modern TV radiation, which becomes immediate garbage)

PO'T

Noclevername
2012-Aug-15, 12:08 AM
Since we have been transmitting radio waves from Earth for 75 years, or longer, supposedy those waves will have reached 75 light years distant. Isn't there a point, or time, when those radio waves will have become total meaningless garbage combined with all of the other radiation in space.

(Unlike modern TV radiation, which becomes immediate garbage)

PO'T

I think the figure commonly mentioned is half a light year using our current detection technology.

swampyankee
2012-Aug-15, 01:07 AM
ive often heard seth shostak argue, in responce to those that say we shouldnt advetise our presence, that the horse has already bolted. That any civilisation capable of doing us harm would easily be able to pick up our signals at many light years distance.
Not getting into that issue, i have often wondered if that is actually true... is just better technology and more sensative recievers sufficient? I would have thought, at some point signals would disolve into background noise no matter how sensative your equipment.

I have read that human radio emissions are, in some frequency bands, stronger than those of the Sun, so, presuming this is true, there is a potential method of detection. If our aliens are close enough -- within about 75 light-years -- and perform frequent full-sky radio surveys, they could, at least hypothetically, detect a more or less rapid increase in our star's radio emissions. They may find this interesting enough to start paying constant attention. Depending on the ET's location, they may be able to detect a periodic change in the radio output the Sun, which may lead them to conclude that there is a radio source orbiting that star, which they may consider worth more investigation.

Xibalba
2012-Aug-19, 05:59 PM
Well it depends greatly on the distance, the intensity, and if they use the same ways of communication than us... Since when they are an evolved civilization is also important.

In the end, it might be us that make contact with a less advanced civilization.

ravens_cry
2012-Aug-20, 05:54 AM
I wonder how common efforts like SETI, the Voyager Record and the Arecibo transmissions will be among our potential cosmic neighbours?
Is looking up at the stars and wondering "Who else is home?" a purely human trait, or is it common to most intelligence?
Or are we alone, if not in the universe, but in our quest for Others?

mutleyeng
2012-Aug-26, 12:54 AM
well the one thing going for SETI is that they assume intelligent life to be that which can build radio transmitters.
I think the jump from a species building radio transmitters to a species that is inquisitive about the wider universe is one of the lesser assumptions that have to be made