Detection of Earth-like Civilizations in Space Now Possible

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?

[MindStalker]

Only if you redefine c. Theoretically c can be increased in some special situations such as extremely high gravity fields and other things. But in general traveling faster than c reverses cause and effect, which can't happen. Though one may eventually figure out how to jump from one side of the universe it wouldn't be traveling per say.

Re:any physicists out there?

[inviolet]

Isn't there something to do with the spin of an electron, which when you reverse the spin, immediately reverses the spin of some other electron, with no delay? Couldn't you reverse the spin of a bunch of electrons on earth, and have their counterparts match the reversal, 30 light years away. It could be used for exchanging information at faster than light speeds.

You are thinking of quantum entanglement, aka "spooky action at a distance".

It cannot be used to transmit information. Think of it this way:

1. You take two slips of paper, one black and one white, and put them in envelopes.
2. You randomly select an envelope and mail it to your brother in Poughkeepsie. You keep the other envelope for yourself.
3. While the envelopes are in transit, nobody has yet observed their contents (i.e. their spins). Yet you know that their contents (their spins) must be opposite because they are an entangled pair.
4. The envelope travels to Poughkeepsie at the speed of light, or significantly slower in the case of the US Postal Service.
5. Your brother receives and opens his envelope. He observes that his slip of paper is black. The uncertainty collapses: he now instantly knows that your slip of paper is white.

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?

[infinityxi]

I believe you are talking about Quantum Physics but the problem with that would be that you couldn't really send coherent information out. You have 2 particles and once you "know" the spin of one particle you "know" the spin of the other. To alter the spin of a particle would contaminate it, because you would have known what the spin was to reverse it. I could be wrong, and I think actually there is some method using 2 pairs of particles to transmit information but I'd have to look it up it was all theory in Brian Greene's "Fabric of the Cosmos" (Good Read) but using the method you describe there is no way to send a message.

Re:Knowing Your Neighbours

[silentounce]

This argument has come up several times. If you RTFA then you will see this: "On Earth, military radars are the most powerful broadcast sources, followed by television and FM radio. If similar broadcast sources exist on other planets, facilities like MWA-LFD might detect them."

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

[east coast]

More powerful broadcasts could be detected to even greater distances [over 30 LYs].

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

[Reducer2001]

Coelacanth [wikipedia.org]

Re:Knowing Your Neighbours

[cnettel]

Coelacanths. A specific species within a large group was found in 1938. Established science had assumed them to be extinct, simply because the last fossil records were 70 million years old or so. No European had gone out of their way to really look for it, and when a reward was announced and the news of it trickled out, it was discovered that it was known to exist in the seas around the Comoros.

Re:any physicists out there?

[TopherC]

The history of this feature of quantum mechanics is fascinating!

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#Exampl e_for_Bell_Inequalities [wikipedia.org]

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.