Detection of Earth-like Civilizations in Space Now Possible 345
Mr. McGibby writes "Astronomers have come up with an improved method of looking for extraterrestrial life with an Earth-like civilization. Theorist Avi Loeb proposes to use instruments like the Low Frequency Demonstrator (LFD) of the Mileura Wide-Field Array (MWA), an Australian facility for radio astronomy currently under construction. The array could (theoretically) detect civilizations broadcasting in the same frequencies as our own society. From the article: 'Loeb and Zaldarriaga calculate that by staring at the sky for a month, the MWA-LFD could detect Earth-like radio signals from a distance of up to 30 light-years, which would encompass approximately 1,000 stars. More powerful broadcasts could be detected to even greater distances. Future observatories like the Square Kilometer Array could detect Earth-like broadcasts from 10 times farther away, which would encompass 100 million stars. ' The original paper describes the details."
Re:any physicists out there? (Score:3, Informative)
Re:any physicists out there? (Score:5, Informative)
You are thinking of quantum entanglement, aka "spooky action at a distance".
It cannot be used to transmit information. Think of it this way:
Notice that you cannot send actual information by this route. The uncertainty of "which slip of paper is in my envelope?" collapses instantaneously, but it collapses into a random choice. Neither of you could know in advance which color you would find in your envelope.
This illustration changes slightly when executed at the quantum level: while the envelopes were in transit, both slips of paper were actually grey... though some might insist that they were both all possible colors, until they were finally observed.
Re:any physicists out there? (Score:2, Informative)
Re:Knowing Your Neighbours (Score:4, Informative)
TV and communication media are not the only sources of radio waves. It would stand to reason that most civilizations that develop flight will eventually develop radar. Radar is very simple and reliable. Yeah, I know that there are stealth technologies, but commercial jetliners aren't using them. We'll probably be using radar for a very long time. Plus, radio is our current means of communicating with our spacecraft(isn't it? I may be wrong). If the society is space faring, and they have a well-developed space program, that may be a large source of radio waves that won't even have to escape an atmosphere.
Technology trends from our own planet (Score:3, Informative)
Maybe I'm wrong but I would think that as a civilization becomes more advanced that the power of their broadcasts would decrees and the signals would become more focused. Would it be easier to detect a signal from 20 years ago from a few light years away than what it would be to detect today's signals? If so I think we'd be looking at a small window of opportunity to detect another civilization.
This isn't to say that widening the spectrum of the search is a bad thing but I'm just trying to get my head around how useful this might really be.
Re:Knowing Your Neighbours (Score:3, Informative)
Re:Knowing Your Neighbours (Score:3, Informative)
Re:any physicists out there? (Score:3, Informative)
Einstein, Podolski, and Rosen proposed this as a thought-experiment to show that the hocus-pocus in quantum mechanics was silly, and that really the envelope always "knew" what color paper was inside it. They used this setup, together with the understanding that nothing could travel faster than light, to show that the envelopes always had definite papers inside just like you'd imagine, which also means that quantum mechanics is an incomplete theory.
But (much later, in the 60's) Bell thought about extending this thought-experiment a little bit, and proved a theorem relating to it: Bell's inequality. This actually proved that the envelope's contents were in fact indeterminate before being inspected, and that quantum mechanics is a complete theory -- you can't do better. Bell's inequality was experimentally tested, decisively in the 70's. The results agreed with Bell's inequality, and therefore confirmed quantum non-locality. It seems now that Einstein's original idea was turned around and used to prove him wrong (or nearly so)!
Although proving and understanding Bell's inequality is just a little bit challenging (but no problem for a physics undergrad), David Mermin came up with a specific, clever example of this inequality that is easy for anyone to understand.
Wikipedia has a pretty good section on Mermin's exemplary experiment:
http://en.wikipedia.org/wiki/Bell's_Theorem#Examp
I probably can't explain this idea any better Wikipedia. There's an even more lucid description of this in Brian Greene's "The Fabric of the Cosmos", around page 107.
So the original idea of sending off two letters, one with a black paper and one with a white one, is not meant to illustrate quantum entanglement. But it does serve to illustrate how information in this case cannot be transmitted. Even if one envelope seems to know instantaneously when the other one was opened and how, that still doesn't really require the transmission of information. I guess it's because the order in which the envelopes are opened doesn't matter.
Hope that helps.