Uncovering Signs of Extraterrestrial Civilizations

[SMJB]

Firstly, people, we're already at the point of parsing individual photons, according to the thread about sensors in the library. That's a very convincing argument that sensor technology ain't getting any more sensitive.

Hello, everyone:

I am wondering what are a few possible ways of detecting the cosmic footprints of extraterrestrial civilizations. Specifically, let us suppose for a moment there are four civilizations out there.

A. One of them is a civilization at almost type I, close to our level of technological prowess. This civilization is located, for example's sake, 10000 lighyears away from us.

B. The second is a type II civilization and has technological parity with a fictional universe such as the United Federation of Planets. Let's say that this civilization is situated on the other side of our Milky Way 25000 lighyears beyond Sagittarius A.

C. The third is a type III civilization which has a technological base equivalent to the Galactic Empire from Star Wars. Let us say that this civilization governs almost the whole of our Milky Way Galaxy, or governs a nearby galaxy such as Andromeda or one of the Magellenic Clouds.

D. The fourth is a civilization which spans multiple galaxies like the Xeelee from Stephan Baxter's novels, and whose technology is advanced enough to the point where unbelievable feats of astro-engineering with whole galaxies are conceivable.

So, what I am actually curious about are the following questions. Is our technology and knowledge of science at a sufficient level right now to detect any of these civilizations at the aforementioned specified distances? Which kind of astronomical techniques could we employ so that we could detect the presence of these civilizations? What standards should we set for ourselves in order to refine our search parameters to make our search easier?

A and B are right out--I don't think we can detect individual G-type stars at that range, and B happens to be hidden from our view by the galactic core. With C and D, it depends on what they do. If they're into stellar mining or Dyson swarms, we're going to see stars blink out of existence--a hard-to-miss sign that something unnatural is going on. Assuming of course that they were doing it long enough ago to account for the lightspeed lag, that is. Which is highly probable, as a few thousand years would "realistically" be chump change in the life of a galactic empire.

[Sky Captain]

I guess engine burns of heavy vessels would stand out not because of visible light, but because most of the energy would be in the form of relativistic particles. That is assuming their engines operate like normal rockets by throwing stuff very fast out of the back. So in the end they may show up as a brief fluxes of high energy particles from a star that naturally should not emit anything like that.

We are already observing anomalously powerful particles - sadly, space is kinda big and dispersion between from whatever they came from and here obscured all traces of their origin or starting position. These might even come from ISD engine for all we know, doesn't make us any closer to detecting any alien civilizations, though.

Well, it depends on how far those vessels would be. If they are in another galaxy then exhaust particles most likely would be dispersed into background noise, but if a multi billion ton ship would burn engines to accelerate at hundreds of G near a star few dozen light years from Earth and the engines happened to be pointed at Earth then it should be detectable as a short lived very bright source of relativistic particles from a star that shouldn't be emitting that much energy in the form of particle flux.
I'm not sure how to calculate rocket engine power output when exhaust speed is highly relativistic because normal rocket engine equations don't work anymore then, but I think power requirements for multi billion ton vessel would be in the range of quite significant fraction of a sunlike star.

[Irbis]

The thing is, a few dozen light years is a cute word, short and obscuring its true scale. Imagine you want to try to hit Earth sized target from 36 LY (3 dozens) - 1 light-year is equal to 9,460,730,472,580.8 km, or 1,484,967,897.124596 times Earth's radius. Times 36 it's 53,458,844,296.5 times more. 53.5 billion - to put it in more human terms, it's like trying to hit a target 1 cm across from about twice the distance to the Moon.

What would keep that hypothetical engine exhaust coherent? Even if starship emitting UHERs came into our direct neighbourhood, chances more than one particle at a time would hit Earth are infinitely small. Hell, chances that it would even point at Earth are infinitely small, think about it, how big portion of night sky would be covered by a coin seen from the Moon?

[Napoleon the Clown]

The odds of the engines being pointed at use aren't that tremendously bad. Gamma-ray bursts are extremely rare yet we pick them up all the time. There's a huge difference in energy release, but it doesn't need to be pointed exactly at us to pick up.

Of course, there is a gargantuan difference in energy being released.

[Simon_Jester]

I'd be more interested in the light from the engine wash, not so much the charged particle stream. Charged particles don't actually travel in straight lines over interstellar distances, because of ambient magnetic fields. Light does.

[Borgholio]

The light emitted by an engine wash would have to be astoundingly bright to outshine the local star. Perhaps it'd be easier to see if it were in the outer solar system or in interstellar space. I imagine an infrared heat bloom from the engines would be not too difficult to pick up if the engine bells were of some titanic size. But we'd be talking way larger than a Star Destroyer.

[Sky Captain]

It wouldn't have to outshine the star, just be bright enough to cause detectable changes in brightness. A Kepler telescope can detect Earth sized planets that transit over the star by measuring how much the light output of a star decrease when planet is transiting the star. So if our hypothetical spaceship can cause comparable changes in brightness it would be detectable if instrument like Kepler happened to look at that star.

[Irbis]

The odds of the engines being pointed at use aren't that tremendously bad. Gamma-ray bursts are extremely rare yet we pick them up all the time. There's a huge difference in energy release, but it doesn't need to be pointed exactly at us to pick up.

ISD engine is what, about 100 meter in width? Gamma Ray Burst is, IIRC, explosion of a star - for comparison, Sun is about 1.5 million kilometre wide, 7 orders of magnitude more, and GRB stars are much larger than that. Seeing such explosion produces far more energy than star simply shining, and how little of it reaches us over interstellar distances, I'd say it's actually perfect proof such starship would be undetectable.

Also, another factor no one here considered. Let's assume such ship points its extremely powerful engine at Earth - except, oops, it turns out Earth moves, as does Sun, at multiple km/s speeds. How long such signal would be detectable until we move out of the way?

I'd be more interested in the light from the engine wash, not so much the charged particle stream. Charged particles don't actually travel in straight lines over interstellar distances, because of ambient magnetic fields. Light does.

Except, um, it totally doesn't. For one, because of gravity That's how we detect quite a lot of stuff that would be normally obscured from us.

Another factor that distorts light streams is the fact that space isn't totally empty. Even something so tightly focused as lasers has problems over short (in astronomical terms) distances:

"Laser beams are used because they remain tightly focused for large distances. Nevertheless, there is enough dispersion of the beam that it is about 7 kilometers in diameter when it reaches the Moon and 20 kilometers in diameter when it returns to Earth. Because of this very weak signal, observations are made for several hours at a time. By averaging the signal for this period, the distance to the Moon can be measured to an accuracy of about 3 centimeters (the average distance from the Earth to the Moon is about 385,000 kilometers)."

[Napoleon the Clown]

I did point out the difference in energy release, you know. My only point was that us being in the right place to pick something up, were it to actually be strong enough upon arrival, wasn't as bad as was being said.

[Simon_Jester]

The light emitted by an engine wash would have to be astoundingly bright to outshine the local star. Perhaps it'd be easier to see if it were in the outer solar system or in interstellar space. I imagine an infrared heat bloom from the engines would be not too difficult to pick up if the engine bells were of some titanic size. But we'd be talking way larger than a Star Destroyer.

It wouldn't have to outshine the star, it just creates a momentary uptick in the star's output. But it won't have the same frequency profile as the star, so for anything like modern hardware it's quite easy to sort out from background clutter: "Hm, that's funny, there's a blackbody radiating in the far ultraviolet at 100000 degrees Kelvin somewhere over there, no way did THAT come from the photosphere of a K-class sun."

I'd be more interested in the light from the engine wash, not so much the charged particle stream. Charged particles don't actually travel in straight lines over interstellar distances, because of ambient magnetic fields. Light does.

Except, um, it totally doesn't. For one, because of gravity That's how we detect quite a lot of stuff that would be normally obscured from us.

Irbis, you're acting innumerate. If you don't recognize the difference between light traveling in a "straight line" between stars across interstellar space for a thousand light years, and light failing to travel in a "straight line" because it's grazing past an entire galaxy on its way to us and being slightly deflected along a multimillion light year path... you're really not worth talking to.

Seriously, ask someone who does cosmic ray physics; I'll look up some names for you if you don't believe me. Ask them "do cosmic ray particle trajectories show meaningful curvature when traveling between stars in our galaxy, compared to photons?"

Because seriously, charged particles fly in deranged corkscrews and we have literally no clue where they end up once injected into the interstellar medium, because we have about one space probe that has even begun to chart even the tiniest part of the ambient fields of that medium.

[krakonfour]

Because seriously, charged particles fly in deranged corkscrews and we have literally no clue where they end up once injected into the interstellar medium, because we have about one space probe that has even begun to chart even the tiniest part of the ambient fields of that medium.

Sad, sad story. True explaining the usefulness of such probes to the general public.

[Borgholio]

It wouldn't have to outshine the star, it just creates a momentary uptick in the star's output. But it won't have the same frequency profile as the star, so for anything like modern hardware it's quite easy to sort out from background clutter: "Hm, that's funny, there's a blackbody radiating in the far ultraviolet at 100000 degrees Kelvin somewhere over there, no way did THAT come from the photosphere of a K-class sun."

Would it actually produce enough of an uptick to be detected though? When I think of an Imperial Stardestroyer...it's a big ship to be sure, but the ion engine bells really aren't all THAT big when it comes down to it. How much power would one of those ion drives need to put out to be detected from a reasonable distance? If we're talking something larger than an ISD, how much larger?

[krakonfour]

It wouldn't have to outshine the star, it just creates a momentary uptick in the star's output. But it won't have the same frequency profile as the star, so for anything like modern hardware it's quite easy to sort out from background clutter: "Hm, that's funny, there's a blackbody radiating in the far ultraviolet at 100000 degrees Kelvin somewhere over there, no way did THAT come from the photosphere of a K-class sun."

Would it actually produce enough of an uptick to be detected though? When I think of an Imperial Stardestroyer...it's a big ship to be sure, but the ion engine bells really aren't all THAT big when it comes down to it. How much power would one of those ion drives need to put out to be detected from a reasonable distance? If we're talking something larger than an ISD, how much larger?

Mass x Acceleration x Efficiency: Amount of wattage you're pumping out for everyone to see.

[Borgholio]

Mass x Acceleration x Efficiency: Amount of wattage you're pumping out for everyone to see.

Anybody happen to know the power output in watts of an ISD engine? I can find the output of it's reactor but I doubt it'd be able to channel that full amount into the engines.