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I don't buy this argument. Let's pretend for a moment that there are currently 5-20 intelligent species in our galaxy, and everyone except us developed deep spa
by ohazi 7y ago
I don't buy this argument. Let's pretend for a moment that there are currently 5-20 intelligent species in our galaxy, and everyone except us developed deep space ships and successfully colonized thousands of other planets (make up almost any numbers you want here; the results still hold).
What would our telescopes see? It seems like we would most likely see exactly what we see today.
The probability that one of those ships happened to fly anywhere close to our solar system, while we were looking, is still vanishingly small. Omnidirectional radio transmissions spread so quickly that they fall below the noise floor almost instantly over interstellar distances.
Space is really really really really big. We can see stars. We can just barely see some planets in a few very specific configurations. We can sometimes make coarse estimates of the chemical composition of those planets. And that's about it. We don't really know how to detect life on extrasolar planets. The ones we've already found could be teeming with life and we wouldn't know it.
- phkahler 7y agoFor a simple example, can anyone see Elons Tesla Roadster out near Mars? And that's something we know is there.
- ianai 7y agohttps://www.whereisroadster.com/ https://www.whereisroadster.com/ “A telescope about 51,075 ft (15,568 m) in diameter would be required to resolve the Upper stage from Earth. A smaller one could see him as an unresolved dot, about 98.2 ft (29.9 m) in diameter, in ideal conditions” So I recon that reinforces the hypothesis.
- aruggirello 7y agoNot necessarily, the apparent magnitude is the issue here, not resolving power. Located at a comparable distance, Deimos, the smaller moon of Mars, reaches at most magnitude ~12.5, meaning that any telescopes smaller than 6" to 8" might not even be able to ever detect it's there. And we're talking about a 6.2Km sized moon, not an object with an overall visible area ~40000 times smaller - that would mean an apparent magnitude of ~23-24 as seen from Earth, meaning only the most powerful telescopes on Earth would be barely able to detect that "unresolved dot" - provided it had the same albedo of Deimos. https://en.wikipedia.org/wiki/Deimos_(moon) https://en.wikipedia.org/wiki/Deimos_(moon) https://en.wikipedia.org/wiki/Apparent_magnitude https://en.wikipedia.org/wiki/Apparent_magnitude Edit: corrected
- Balgair 7y agoThe angular resolution of a telescope scales as the size of the diameter of the telescope, essentially [0]. Meaning that if you want to image the roadster in visible light, you need a telescope lens about the size of Washington DC (currently). To just see it at all you need a lens about the size of a McMansion. To image something like the roadster on a Planet orbiting Vega (~26 LY away, furthest star anyone on Earth could visit and then return from in a lifetime) you're looking at lenses greater than the orbit of Pluto, ish. Optics/Physics is a bitch here. To really see/prove there are aliens running about, they have to screaming at the top of their lungs for a very very long time, hoping against hope that anyone will hear. It's just really really hard to build equipment that can passively listen for accidental broadcasts and spy on alien cars. At least under our current understanding of physics. [0] http://hosting.astro.cornell.edu/academics/courses/astro201/diff_limit.htm http://hosting.astro.cornell.edu/academics/courses/astro201/...
- ByThyGrace 7y agoI wish I could save comments so I'm just replying instead. It is so fascinating.
- hnuser123456 7y ago>Vega (~26 LY away, furthest star anyone on Earth could visit and then return from in a lifetime) It is not necessarily true that more time is spent aboard a ship than light would spend taking the same path, as measured by an external observer. If you had a ship capable of accelerating at 1g indefinitely, then as measured by the crew, they could cross the galaxy in only 24 years. https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_using_constant_ac... To an observer who is self-propelled (and has enough energy), the speed of light (as seen by others) is no limit. It's not like you can fire your thrusters and NOT gain momentum and speed; or that, as you accelerate, the stars start passing by at the speed of light, and suddenly your ship jerks, ceasing to accelerate, because you hit an invisible velocity brick wall.
- aetherson 7y agoThe thing is, why "5-20"? That's a super narrow range. The parameters would have to be tuned to a very small degree to produce just a handful of technological species in a galaxy. A much larger range of the parameter-space could produce either thousands+ of technological species (which we have pretty good evidence is not the case) or less than one on average pretty galaxy. So we have the options: Lots of species (contradicted by the evidence) A handful of species (inherently unlikely) Very few species (current best bet)
- ohazi 7y agoI think you could increase the guess to 1,000 or 1,000,000 species and the outcome would still be basically the same. We do not know how to detect life outside of our solar system. The only way our measurements would change is if one of them literally landed on top of us.
- aetherson 7y agoWell, we know how to detect laser and radio transmissions. If there are thousands, tens of thousands, millions of species out there right now, we've looked at several of their stars. And if there are all these technological species, we would expect some of them to be much more advanced than we are. Why haven't some of them noticed us? You can come up with possible answers to these questions, it's just that those answers look less likely than, "those species aren't actually out there."
- lonelappde 7y agoFurther, think about how powerful a transmission has to be in order to not be drowned out by the power of a star. A laser would have a far higher chance (yet still hugely powerful to cross the distance), but only if aliens found us and pointed a laser directly at us.
- sdenton4 7y agoConsider that we have, ourselves, gotten far harder to detect over the last fifty years. Energy spent accidentally sending signals into space is wasted. And we are making much greater use of cryptography and compression schemes, which would make signals look like pure noise. So, question: how strong does an undirected, random signal need to be to be reasonably detected at 10 light years away?
- pfdietz 7y agoWhy would they stop at thousands of colonies? What is it preventing the colonies from themselves creating colonies? Also, realize that a colony in the system of another star will move away from the originating system. In our neck of the galactic woods the rate of separation is typically about 10^-4 c, so in a million years they'd separate by 100 light years.
- ohazi 7y agoI think you could change these guesses to be almost whatever you wanted with similar results. We would not observe anything different unless one of them actually flew to our solar system and tried to contact us. That's how bad we are at detecting distant life.
- lonelappde 7y agoI reckon astronomers would find anything that entered our solar system and stayed in some solar orbit.
- ohazi 7y agoTrue, but without radio transmissions, I bet we would spend decades arguing about whether it was actually an asteroid and a measurement anomaly. We can't really distinguish a rock from a Battlestar at those distances without physically flying over to look.
- close04 7y agoAt this point we're relying almost exclusively on radio waves to detect any traces of intelligent life out there. So whether they're building moon stations in their neighborhood, or sending rockets here and there, we'd still look for their transmissions to identify their existence and to tell them apart from a random natural event. And while intelligent life may exist on a planet for millions of years, their window of actually emitting something into the void in a manner we can detect with our tech today [0] will probably be a lot shorter than that. This gives us a relatively tiny and limited visibility window into the history of life out there. Unless we manage to sync our window perfectly with theirs we'll never know they existed. [0] https://www.xkcd.com/638/ https://www.xkcd.com/638/
- alecco 7y agoWe might be see them already and not be able to single them out. Like the disappearing stars reported recently.
- hoorayimhelping 7y ago>What would our telescopes see? It seems like we would most likely see exactly what we see today. We'd see more red than we do - more heat and less light. Civilization produces heat. Advanced civilizations would presumably convert starlight to energy and produce waste heat.
- pavel_lishin 7y agoWho's to say that the amount of red we're seeing now isn't exactly what you're describing? Maybe if we lived in a barren galaxy, we'd see a lot more _blue_, as stars shone unencumbered by matrioshka brains.
- ncmncm 7y agoAn advanced civilization, by definition, would not be dependent on starlight. Or planetary surfaces.
- hnews_account_1 7y agoWhere else could they possibly get energy from? Planets can be replaced by orbitals, but there's no way to replace the sun.
- ncmncm 7y agoEven extreme primitives have magnetic-confinement fusion.
- hnews_account_1 7y agoAh ok. That makes sense. In that world, they can even use miniature black holes once they can stabilise and capture them in a field, to generate energy.
- JKCalhoun 7y agoWhy would they send themselves? Even we send robots, not humans, out to the distant edges of our solar system. Why send the robot or alien at all if you can instead send the design/machine to make the alien. Perhaps they need send nothing more than RNA/DNA on an incoming space rock....
- tomatotomato37 7y agoOne issue with that is based on current physics, a deep space ship that isn't some millenia generation ship but accelerates to a decent percentage of c will expel a fuckton of energy in some type of fusion/fission/antimatter reaction, which tends toward being very, very visible. The first sign of a torchship-capable civilization wouldn't be random radio emissions, but would instead be some star system suddenly gaining another star that ignores orbital physics and instead ends up leaving said system at some absurd speed, probably with a bowshock measured in AUs from all the interstellar dust going nuclear as it collides with said ship.