So, the paper doesn't mention this, but if -- and only if -- they're looking for pyramids, we're visible to about 0.1% of the galaxy.
Is such a telescope (resolving power etc.) actually possible? At the level of basic physics, could anyone build it, hypothetically?
I don't know, because I am an idiot who has spent 30 years building websites of various complexity and pretending that is advanced knowledge.
It's hard to imagine, but the baseline mentioned is being able to utilize all the energy of their star.
It always felt like the whole thing was made by someone who didn't really have a good grasp of scale. Maybe it's a failure of imagination on my part, but I tend to think that projects on scales like that are just too impractical for real life. It's like if you decided to make up a scale for land speed records, and made type 1 100,000 kph, level 2 100,000,000 kph, and level 3 100,000,000,000 kph.
Tbf web has an unmatched pay to work ratio for the avg. developer, I wouldn't call that idiotic by any stretch.
We wouldn't be able to see pyramid sized objects on alien planets that way because the Sun is only about 1.4 million km diameter, and from other comments it would take a few million km. But for aliens with a bigger star? No problem.
Here's a PBS Space Time episode that talks about the proposals for building a Sun based gravity lens telescope [1].
Likewise, couldn't they detect changes in the mixture of gases on Earth and deduce that these changes would most likely occur in the presence of evolving life? If we posit that evolution typically leads to intelligence and intelligence leads to civilization, then extraterrestrial intelligence would have deduced that we were going to be coming along at some point. Maybe they could even deduce when that civilization-building life was going to spring up, perhaps within about a ~1M-year window, depending on what information they have and what they can reliably deduce from that information.
So in a way we are already "known." The new information that you can glean from the pyramids is that we've just now hit the inflection point of civilization. Maybe now they're watching to see if we manage to make it past the Great Filter. Or they've already launched their relativistic missiles to snuff us out before we can possibly launch our relativistic missiles at them -- if you're inclined to presume the cosmic prisoner's dilemma motivates being the first to launch.
Maybe the great filter is the great promotion, acquiring a knowledge/technology powerful enough to not need to go to other solar systems or expand a lot. But as we are not yet there, we expect invasion fleets.
One of my favorite sci-fi themes about that is that we've already been hit once, about 66 million years ago.
I see two big issues with this:
1) "evolution typically leads to intelligence" is only plausible after the evolution of multicellular life. I don't think there's any reason to suppose "evolution typically leads to multicellular life." Perhaps these aliens are used to a galaxy where 95% of habitable planets are full of primordial soup, where primitive multicellular forms struggle to find a niche. In particular, if most planets are less geologically active than earth, and most solar systems have less asteroids than ours, then perhaps most habitable planets have less extinction events, so there wouldn't be any ecological disruption to spur evolution.
2) "intelligence leads to civilization" is almost certainly false. Orcas have near-human intelligence, including culture and symbolic communication - in fact they might be "smarter" than humans, we don't really know enough about intelligence to answer that. But it will take a bizarre fluke of evolution for them to develop technological civilization, for the simple reason that they don't have hands and there's no selective pressure for them to evolve "proto-hands" - they need the flippers to be good flippers. This is in contrast to primates: we didn't evolve hands to build tools, we evolved hands to climb trees and grab fruits/nuts. It seems far more likely to me that intelligence tends towards super smart crows and dolphins: the physiological capability of building highly advanced tools is orthogonal to intelligence and does not seem inevitable.
I'm not saying you're wrong. But my understanding of the almost-science is that the aliens would be wasting a lot of tachyon missiles if they fired at every planet with evidence of photosynthesis / fermentation / etc.
Surely it’s 4? .5? The great pyramids are from 2500 BC.
Apparent FTL is at least theoretically possible under our current understanding (though a unification of quantum and general physics may change this).
That's news to me. Source?