More Words, Deeper Hole

Assume

: james_nicoll; January 25th, 13:27

For the moment that there is a civilization much like ours with a suspiciously similar level of technological knowledge as humans, and that it is located conveniently nearby on a world orbiting Alpha Centauri B (a bit over 4 LY away). When's the earliest that communication could begin?

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( 18 comments — Leave a comment )

filkerdave

2013-01-25 06:44 pm (UTC)

A bit over 8 years after we hear from them, or they from us.

Time to notice that they're there
4+ years to send a message
4+ years to get a reply.

Or did you mean "what year could we have started?"

Also, cats.

james_nicoll

2013-01-25 06:54 pm (UTC)

What is the earliest date by which we could have noticed each other?

filkerdave

2013-01-25 07:01 pm (UTC)

Very earliest? If the signals were powerful enough (meaning that they were directed at us and not obviously natural) then the early 1930s. Now, you could say that we didn't notice because of the War and make it mid-1940s, but...yeah, that's about as early as you could go.

fridgepunk

2013-01-25 11:03 pm (UTC)

Only japan was doing ww2 during the 1930s, that's the time when Hitler sent his olympic broadcast to those pi aliens from Contact after all.

However, the first meaningful sky survey of radio sources pops up in the 1950s, but it was done by interferometers in the northern hemisphere, and Alpha Centauri is only visible in the southern hemisphere iirc.

There's also the slight problem that afaik, Alpha Centauri is too dull to be surveyed by radio telescopes.

dsrtao

2013-01-25 06:45 pm (UTC)

Radio technology was advanced enough in the 1940s. Maybe a little earlier. SETI projects started listening in the 1960s; it could easily have happened then.

doc_lemming

2013-01-25 07:39 pm (UTC)

Was SETI looking at the right section of the sky? I vaguely (that is, probably incorrectly) remember that it wasn't, being focussed on likelier stars.

And other projects since might have been looking at the right part of the sky; I don't keep track.

autopope

2013-01-25 07:45 pm (UTC)

Actually, no. You need directional antennae actively looking at that part of the sky if you're going to pick up any signal with an emitter of less than stellar output. We didn't really begin pumping out the megawatts until the big cold war over-the-horizon radars came along in the 1950s. To detect anything unusual from a planet orbiting Alpha Centauri B, I think you'd need something like the Jodrell Bank Transit Telescope (1947) -- however Centauri is in the southern hemisphere, hence outside the Transit Telescope's range. It might even take something of the scale of the Lovell Telescope from 1957 (more on the Jodrell Bank radio telescopes here) to observe -- and even with a big steerable dish you're not going to be able to pull in a useful signal from even a high powered AM or short wave radio station at that range; you're just going to know that there's something not-quite-right about Centauri system (that it's putting out a lot of very mushy radio spam that is quite unlike similar stars).

So basically you're waiting for a big steerable dish to show up in the southern hemisphere.

NB: All bets are off if the Centaurans are deliberately blasting a signal straight at us in the hope that we'll hear it. But how often have we done that?

Edited at 2013-01-25 07:50 pm (UTC)

dsrtao

2013-01-25 08:33 pm (UTC)

In the other direction, if the Centaurans have always had a strong preference for wired communications, fiber optics and line-of-sight laser (let's say that they have signals-intelligence paranoia), we could still be a few years away from noticing their unintentional leakage. Cities lit up at night, that sort of thing.

autopope

2013-01-25 09:33 pm (UTC)

Free oxygen in the planet's atmosphere would be enough of a sit-up-and-pay-attention notice to make us take a hard look, possibly with new purpose-built instruments.

Hmm. Would the absorption spectrum of CFCs in a terrestrial planet's atmosphere be detectable at ~ 1 parsec distance? If so, that'd be a definite turd-in-the-punchbowl moment (AIUI CFCs do not occur in nature).

akawil

2013-01-25 11:12 pm (UTC)

Exoplanet spectra are only about six years old, and spectra of non-transiting planets only about three years old, according to a quick Google. And as far as I can tell no one's managed any spectra of terrestrial planets yet.

So in this case, your answer agrees with

dsrtao's, I think.

neowolf2

2013-01-26 02:11 pm (UTC)

Terrestrial planets in the habitable zones of white dwarf stars (if such exist) might be the first habitable planets to have their atmospheric spectra taken.

http://arxiv.org/abs/1301.4994

ariaflame

2013-01-26 02:05 am (UTC)

So the SKA might pick something up?

keithmm

2013-01-26 05:13 am (UTC)

The Parkes Observatory dish was built in 1961 and fully operational in 1963, so that's probably the earliest.

bedii

2013-01-25 08:02 pm (UTC)

Listen: if they'll promise to make Vox Day's service provider go away, I'll set an Aldis lamp up in the backyard and start flipping the lever.

whl

2013-01-25 10:01 pm (UTC)

Jansky and Reber would probably not have noticed (although there are better experts than I on Reber that I know browse here.)

Project Ozma would seem not to have targeted that area.

Project Ozma II, 1972-1976, would be my guess, although I have not yet found a list of the 674 targets surveyed.

See this list of surveys.

beamjockey

2013-01-26 12:17 am (UTC)

Jansky and Reber would probably not have noticed (although there are better experts than I on Reber that I know browse here.)

Being Northern Hemisphere guys, in New Jersey and Illinois, respectively, neither one had Alpha Centauri in his sky.

whl

2013-01-26 01:28 am (UTC)

What can I say but, Oops!

neowolf2

2013-01-25 11:02 pm (UTC)

I wonder how long it would take for us to have lasers, and sufficiently sensitive detectors, for a narrow-band laser beacon to be visible over that distance (over and above the light from the star.)

("Optical SETI" has looked at this in detail, I'm sure.)

(EDIT: I see at http://seti.harvard.edu/oseti/ that pulsed lasers have become available that could do the trick.)

Edited at 2013-01-25 11:17 pm (UTC)

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