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Radio Signal From Direction of Proxima Centauri
When it comes to exoplanet atmospheres and anomalous chemistry or colors, our limits are actually very poor. The only exoplanets we've been able to study in that kind of detail are Hot Jupiters and a few Hot Neptunes. We really don't know anything yet about how common or rare life limited to Earth-like planets is.

When it comes to radio signals, some scientists, such as Jason Wright, argue that we've also searched very little of the "search space":

If alien civilizations engage in interstellar settlement and/or build Dyson spheres, that does sharpen the Fermi paradox considerably, yes. If those things are possible, then civilizations must be quite far apart and also rather slow-growing to have evaded detection so far. Realistically, though, we don't know if those things are feasible in the real world. Perhaps for engineering or economic reasons, they don't occur. So I think that, scientifically, we have to remain open to all possibilities for how technosignatures present themselves. Of course, the researchers here are doing the right thing by keeping their priors heavily weighted to it being human RFI, even while they continue investigating.
There is a possibility that this beam, coming from Proxima the nearest star, could be just the last link in a carefully-designed but sparse network. If each star is only linked to two or three other nearby stars, then the number of links could be minimised but a signal should be able to percolate through the galaxy at a very slow rate. This sort of communication network would work after a fashion, but it would take a long time to send a message to any star that was outside our immediate neighbourhood, and it would take even longer to get a reply back. To send a message to Betelgeuse, or Rigel, or Deneb would require hundreds of steps in the relay system, unless the network is designed quite neatly.
IIRC a fully developed Matrioshka brain would radiate at just barely above CBR temp and so might be very hard to detect. Dysons might be seen as a primitive solution to the idea of a fully developed solar system. Similar issues might apply to things like interstellar comm and travel. Very tight beams might be used or maybe such systems use gravitational solar foci to reduce their transmission power to a tiny fraction of what it might otherwise be. Interstellar travel might be done in some analogous way that maximizes efficiency and is minimally detectable to our tech as a side effect.

On the flip side, something as simple as highly effective birth control might slow down a civilizations growth to the point where it could take a very long time for it to need to develop the universe to the point where we would notice. Or such projects might take place only every few thousand years - so we just aren't seeing one in action atm.

Taking a page from Greg Egan's Diaspora setting - even a civ that can build dysons or similar structures may choose not to and see such efforts as primitive or environmentally destructive.

Basically there are more options than just 'lots of aliens doing what we might currently expect' and 'no aliens'.

Just some thoughts,

I can buy any of those arguments w/r/t a particular civilization, but I can't get behind the idea that any of them might apply to all civilizations.

So the civilization at Denebola considers it wasteful and barbaric to build out a Dyson Swarm. Fine. But we don't seriously believe, do we, that every possible civilization everywhere feels the same way? Or runs into the same limitations or problems?

Even if 99% of all civilizations don't build big obvious things we could spot from another galaxy, the fact that we see a million galaxies without such things would strongly imply that civilizations don't exist at all in 99.99% of all galaxies.

The only reason I'd consider this particular signal to be a possibility is that the Milky Way is a special case, because we're here.

The possibility of panspermia - the idea that we and some other life may have a common origin - means our own existence implies that the odds of finding other life in the Milky Way is considerably higher than elsewhere. And for the same reason the chance of finding it in our own neighborhood considerably higher than in the rest of the Milky Way. So, Proxima is among the highest possible probabilities of the stars we can see.

But that's kind of like being the tallest earthworm. As burrowing creatures their height is usually negative.

(12-23-2020, 04:12 AM)Drashner1 Wrote: IIRC a fully developed Matrioshka brain would radiate at just barely above CBR temp and so might be very hard to detect.

The same is true of any fully developed Dyson swarm, whether it happens to be a Matrioshka brain or not.  So, yes, granted, once fully developed they could be hard to see. 

Ultimately the size of a Dyson swarm is limited by the Hill Sphere of its star.  So one would have to be fairly dense and fairly warm inside any kind of tight grouping like a cluster, but could be absolutely enormous around a medium-large star in uncrowded intergalactic space.  

I haven't done the calculations before but... hmm.  The sun's Hill Sphere is considered to be about a light year.  That means about twelve and a half square light years of surface area.  The sun produces around 4e26 joules of energy, making 3.2e25 joules per square light year.  A light year is 9.5e12 kilometers making 90.25e24 square kilometers per square light year, so the biggest possible swarm here would have a radiant energy density of 0.35 joules or thereabouts per square kilometer of "surface area".  0r 3.5e-7 joules per square meter.  Or, 3.5e-7 watts per second per square meter. 

So this hypothetical Dyson would be taking in radiation from the local stars and CMB etc, and then re-radiating that same amount of energy plus 3.5e-7 watts per second per square meter.  Which would, in fact, be pretty damn hard to detect.

That ignores the possibility that anyone is running nuclear power plants somewhere inside it, which would raise its heat density considerably.  But if someone wanted to be stealthy, yeah it looks like they could.
(12-23-2020, 07:30 AM)Bear Wrote: I can buy any of those arguments w/r/t a particular civilization, but I can't get behind the idea that any of them might apply to all civilizations.  

Yes - but what if it's not a 'simple' matter of either xeno civs are readily detectable, either due to deliberate effort or a side effect of going about their business or it's not because they all build dysons or engage in birth control or whatever? What if instead it's a case of a civ being detectable (by us at our present level of capability) or all of the other options?

Some civs may limit their populations such that they never build sufficiently large megastructures (dysons or whatever).

Some may build them but make them so efficient that we can't readily detect them.

Some may destroy themselves.

Some may decide not to contact aliens.

Some may employ comm tech that we can't detect - not necessarily 'magical' tech based on physics we don't know about either. If they're using really tight beams and/or using their star's gravitational focus as a lens, and/or being really efficient about encrypting or data compressing their signals...would we be able to detect them even if they were talking their heads off all around us (assuming for sake of argument they have heads Tongue)?

And so on and so forth. I don't claim to be up on current thinking in this area, but in past years the list of suggested reasons why we might not be receiving any signals from aliens ran to about a dozen or two possibilities. What if it's not a case of just one of those options having to apply to everybody, but rather a case of Option 1 applies to X percent of civs and Option 2 applies to Y % and on and on until we are left with just a tiny percentage of civs that are either actively attempting to communicate with a civ like ours and/or are engaged in activities that our tech can detect across interstellar distances?

For an added complication, I would suggest there is also the issue of time. In a nutshell:

What if xeno civs don't spend all of their history only doing one thing - instead they go thru different periods doing different things, of which 'attempting to communicate with civs like our human civ at its present level' or 'engaging in activities we humans can detect' are only two out of many activities they might spend their time on over the lifetime of their civ, even if it is a very long-lived one. And for a sufficiently long lived civ, the periods where they aren't doing stuff we can detect (on purpose or not) might be measured in thousands of years or more - and we've only been looking for others for less than a century.

Putting this all together, we may be in the position of trying to find that subset of civs that are choosing to engage in activities that make them detectable to our current technology at the time we are looking for them - and one or more of those conditions may not be being met right now.

Maybe there was a really talky/noisy civ broadcasting all over local space a million years ago, but then they stopped for whatever reason. And maybe the next talky/noisy civ won't start doing its thing for another 100,000 years. Of course if they're located in the Virgo Cluster and everyone closer is currently occupied doing stuff we can't detect - that isn't going to do us much good in the immediate term.

Just some thoughts,

Okay, I thought of one thing that's probably meaningless but at least it's an interesting question to ask.

The proxima signal was detected in October 2020. Proxima's 4.2 light years away. Did we do anything particularly visible in the radio spectrum or particularly technologically new in a high-energy way that could be detected from a long way off, in April or May 2012?

I mean, if this is a dial tone, what did we do that would convince someone we picked up on our end?
The signal was found in the archived data in October, but it was actually received on April 29, 2019:

Interesting idea if something from us would have caught their attention that amount of time before. If they have a Square Kilometer Array equivalent, however, they would have been able to detect our everyday radio leakage for many years, and thus know a technological civilization is here.

If (which is of course a huge if) this were an alien signal, I'd suspect it's one they re-send occasionally to get our attention. I'm sure Breakthrough Listen is scouring every dataset they can find to see if there is a repeat of this somewhere so it can be studied further. Note though that human RFI may also repeat for whatever reason.
Yeah, human RFI is my bet.  I don't think I've ever really seen a full accounting of all the weird delayed echo effects human RFI has already shown us.

Soooo, we should be looking at november or december 2011?

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