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Discussion (41 Comments)Read Original on HackerNews

DamnInteresting•2 days ago
I wrote an article about this same general topic way back in 2007[1], wherein I conducted a thought experiment with an Arecibo observatory traveling away from Earth. I calculated that even mighty Arecibo would be unable to detect Earth's omnidirectional FM radio as far out as Saturn, let alone from another star.

Since that writing, we've lost Arecibo observatory, discovered gobs of exoplanets, started scrutinizing those exoplanets with JWST, and increased our radio sphere radius by another 19 lightyears.

[1] https://www.damninteresting.com/space-radio-more-static-less...

socalgal2•2 days ago
I asked a friend at JPL, if there was a civilization at Alpha Centauri and they were sending out the same types of signals as Earth does today, could we detect those signals at Earth with our current tech?

Answer: No (which the article also mentions in so many words)

keithnz•2 days ago
the article seems way too generous, we'd barely be able to detect things like 1980s tv broadcasts, they fall below galactic noise before alpha centauri, let alone 50 light years out.
throw0101a•2 days ago
> 1936: Berlin Olympics first major TV broadcast

Bit of a plot point in Sagan's novel (and the movie adaptation):

* https://en.wikipedia.org/wiki/Contact_(novel)

RF_Enthusiast•2 days ago
WBCQ in Monticello, ME (USA) says it broadcasts to outer space via a modulated laser.

From <http://www.wbcq.com/>: WBCQ’s laser broadcasting service is available to beam your program into outer space via our high-powered, modulated, laser system. So in addition to broadcasting worldwide over shortwave radio, you can transmit into space over our high-powered lasers. It’s a lot of fun. The cost for this service is $50 an hour.

wahern•1 day ago
Lasers obey the inverse square law as perfect collimation isn't possible. But I guess as a practical matter it does make it easier to achieve a particular energy level at a target. You still apparently need megawatt scale lasers just to discern a signal from Alpha Centauri, though: https://academic.oup.com/mnras/article/516/2/2938/6668809 (I dunno how to calculate the other way around--from here to there--as it's partly a function of the origin star's luminosity.)
chasil•2 days ago
I think that an atmosphere with measurable oxygen gas is a far longer lasting, pervasive and interesting signal that by itself could prompt investigation.

The oxygen has been here for far longer than us, sometimes at much higher levels.

3eb7988a1663•2 days ago
In the book Diaspora, ancient aliens replaced the elements with the unusual form - I forget the details, but say N15 instead of the common N14, O15 instead of O16. Gives a big bright signal that something unusual is happening on this planet.
api•2 days ago
Earth has been screaming it has a very likely biosphere for at least 500 million to a billion years. To anyone with huge space based telescopes.

So why no visitors? If there had been, we wouldn’t know. Any probes that dropped into our planet any further back than a few tens of thousands of years (and less if they landed in a hot wet region) might be gone by now. They’d have been eaten by corrosion and mechanical erosion and eventually by plate tectonics.

They also likely would have been small, meaning even if they got fossilized we’d have to get super lucky to find one. The energy required to accelerate something to meaningful fractions of light speed and then decelerate at the other side means a probe is probably an orbiter the size of a basketball and then a little drone the size of a golf ball or something.

We might have had dozens or hundreds of little visitors over the last billion years and we’d never know unless we got real lucky.

Flyby missions are also likely due to the physics. The energy for slowing down might instead be spent just going faster to get results faster. The probe just streaks past at 7% the speed of light and takes a bunch of pictures and measurements.

jerf•1 day ago
I consider this a disproof of the "dark forest" hypothesis. That doesn't affect the Three Body Problem as a work of science fiction at all; science fiction gets to make a few assumptions and then ride from there. But if it were advantageous to pre-emptively nuke anything that looks like a threat Earth should have been toasted hundreds of millions of years ago.

(And no, the dinosaur asteroid was not it. If an alien species is going to destroy Earth, they will destroy it, not slightly inconvenience the biosphere.)

pests•1 day ago
It did take using the sun as an amplification source.
asdff•1 day ago
If I were the leader of an alien civilization and I wanted to probe a potentially hostile life bearing planet, last thing I would do is have the probe look like anything compelling. I'd make it look like a regular old asteroid. And boy do plenty of those buzz past our planet with regularity.
chasil•1 day ago
Well, if there was a "Three Body Problem" civilization looking for a new home, we have not been inconspicuous.

I think we can rule that out.

Teever•1 day ago
If there is intelligent alien life out there it seems very probable to me that the asteroid belt is littered with sentinel probes that have been sent out to observe for particular signs of threatening or otherwise noteworthy activity in star systems.

2001 probably wasn't far off. I envision a small probe sent to each star system that finds a nice little hidey-hole inside an asteroid or moon and it burrows down in there and uses solar energy and local material to build more extensive infrastructure to replicate and send out copies to other bodies in the star system as well as to other local star systems.

DoctorOetker•2 days ago
chemistry has more reactions than just with oxygen, oxygen alone is a poor indicator of life...
jerf•2 days ago
Oxygen is a highly reactive element that on a cosmological time frame instantly disappears by bonding with things. It is very difficult to come up with an explanation other than "life" for why an atmosphere would be full of oxygen; it may well be impossible to come up with an explanation other than "life" for why an atmosphere would be full of oxygen for 500 million years, especially on a ball of iron. Even having a transient explanation would be very difficult.
marcus_holmes•2 days ago
Not all living organisms use oxygen (even on our planet), true.

But you don't get free oxygen on a planet without life to continually produce it.

It's a good indicator of some forms of life.

adrianN•2 days ago
We don’t have a lot of examples of technological life forms that don’t need oxygen.
derbOac•2 days ago
This was portrayed in the film Contact (1997) closely to what's described in this piece (maybe it's in the book too? I haven't read it).
nik282000•1 day ago
Read the novel, or listen to the audiobook. The film was good but totally misses the punchline at the end of the novel.
boznz•2 days ago
Nice article. I had to go down this rabbit-hole researching my first book. Actual likelihood of anyone actually being able to receive these past a few tens of LY is quite low without very sensitive receivers. Also as another commenter pointed out the window for receiving us is closing as more modern wide-band and spread-spectrum signals are more power efficient, directed, and look much closer to noise than data.
api•2 days ago
A lot of people think the “great silence” from SETI means something, unfortunately.

A civilization using only low power radio wouldn’t be detectable in the Centauri system.

rao-v•2 days ago
I’d love for this chart to also capture the loudest signals we’ve sent. Surely somebody must have accidentally broadcasted a non-directional megawatt radio signal at some point right?

Actually humm maybe nukes are our brightest non directional transmission?

analog31•2 days ago
Something that I muse about is that this bubble may indeed be a thin shell. My rationale is that already the bulk of our communications are confined to waveguides -- optical fibers. Our wireless comms continue to be engineered to produce less power and to be almost indistinguishable from noise. Much of our AC power travels along paired wires whose fields cancel one another at the equivalent of an inverse-fourth law or worse. Soon they may all be DC.

The civilizations who are "out there" may only have a narrow time window to pick up our signals. Like we've fashioned a poor man's Dyson sphere.

marcus_holmes•2 days ago
Agreed. Also, the audience and business model for commercial radio and television stations are declining, and it's easy to see a point where nobody listens to radio or watches television any more and they stop broadcasting.
amarant•2 days ago
I'm surprised anyone does either of those things now!

Well except for that one special time of year, but honestly Eurovision ought to be streaming online instead of broadcasting on TV already!

marcus_holmes•1 day ago
Aliens will enjoy the kitsch just as much as we earthlings surely?!
wa2flq•1 day ago
There was a Star Trek book (The Abode of Life?) that had a planet that where the communication was mostly confined to the planet. I think Uhura detected the planet from the background noise.
josuepeq•2 days ago
I was thinking about this a few weeks ago.

Doppler shift would substantially change the wavelength, and frequency too.

Perhaps the number of light years a wave has traveled moving in the same direction that Earth is moving in, would be less distance than the side facing the direction that we are moving away from.

The Earth, and Solar System are always moving in motion; I would imagine doppler shift would also have a significant impact on the success of receiving such transmissions.

diziet•1 day ago
The velocity of the Solar System rounds to 0 when expressed as a fraction of c.
cwmoore•1 day ago
In our orientation with the Sun, I think the bubbles should be cardioid and not spherical. But with the nature of the inverse-square law and background noise, it doesn’t seem to matter.
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sidewndr46•2 days ago
Given that we don't receive signals like this from at least some direction in the universe, I feel like we can be relatively certain that once this signal reaches some specific area humanity will be toast.
carlostkd•1 day ago
Discovery live in another planets can be challenging but the real question is: Are we sure that we want to discover them? What if they are not friendly?
GJim•1 day ago
> What if they are not friendly?

And the purpose of them choosing to attack another civilisation across interstellar space would be.....?

HelloUsername•1 day ago
> And the purpose of them choosing to attack another civilisation across interstellar space would be.....?

They don't like my stupid face

GJim•1 day ago
Harsh. But fair.
meatmanek•2 days ago
> What they first received

Shouldn't every cell in this column be the same?

cosmicSap•about 9 hours ago
why? each star receives a different signal because the bubble has been expanding since 1900 so a star 4.2 LY away received whatever we were broadcasting in 1904, while a star 25 LY away is only now receiving our 1925 broadcasts. The column reflects what signal has actually reached each star so far, not what we're broadcasting today
marcus_holmes•2 days ago
I assumed that it was something to do with signal strength, but re-reading it, you're right, this doesn't make sense.
fuckinpuppers•2 days ago
Makes me think of the intro to Contact, which was a really cool “visualization” of this… with Hitler and the 1938 Olympics being the first tv broadcast of strength, which aligns with reality