In the OG Drake equation this would be the fraction of civs in our entire galaxy that emit signals strong enough for us to detect them. That’s easily sub 5%

@JonathanRay Strongest radio transmitter on earth is 2MW which at a distance of 1 LY would be like 1E26 times weaker than the CMB?

@JonathanRay Another angle of attack: the dimmest object ever observed by Hubble is circa apparent magnitude 31.5 which is around 10^24 times dimmer than the sun’s 1000W/m2 so our detection threshold is like 10^-21W/m^2 but our strongest omnidirectional transmitter at a distance of 1LY would be attenuated to 2E-24 W/m2. So unless we were deliberately aiming a signal at ourselves we’re like 4 OOMs short of being able to detect our own transmissions at the distance of Alpha Centauri.

Define broadcast. We couldn’t detect ourselves a dozen light years away

@JonathanRay I’m using Wikipedia defs here, so the actual statement is “detectable signs of their existence into space” and so includes things like visible Dyson Spheres and other stuff detectable that might not necessarily be a transmission.

@Noit detectable by whom?

@Noit Imagine I'm moving around on the surface of earth, reflecting light into space. What is "detectable"?

think about visual light, the scale would go from

• I am very large wearing pink flourescent clothing, moving really fast and unnaturally, in the daytime, the observer in low earth orbit and can definitely see me with only relatively advanced telescopes

• I am not moving

• I make myself smaller

• I wear black clothing

• I wear camouflage

• I hide behind a tree

• I hide in a cave so only my eye is visible

• It is night now

• The observer moves into a farther orbit

• The observer moves beyond the moon's orbit

• The observer moves 1AU away, etc

At what point do we say I am "broadcasting my existence into space" and when do I stop? You get the point - generically, EVERY action we take broadcasts our existence into space to some extent, since it's not just visual light we're sending, but we're also changing the universal gravity field, obstructing weird particles differently, radiating energy from our bodies and heat and energy producing objects, etc including lots of things we may not know about at all yet.

So I think the word "broadcast" needs some kind of definition, i.e. limit it to EM radiation emissions which are clearly nonnatural, and then quantify it with some kind of strength or minimum level, so we can say "if EM emissions are >=X amount at distance D for at least timespan T, we consider that broadcasting"

Why would it even be possible to hide your existence? Human existence on earth is already detectable for any civilization with telescopes even slightly stronger than ours, not only through radio signals but also through biosignatures and industrial signatures in the atmosphere. Would advanced civilizations have technology that allows them to cloak entire planets? Even if they could stop the EM emmissions from a planet across the entire spectrum, you could still find their planet using its gravitational effect on its host star, and then notice that all other emmissions from the planet are missing.

@Shump at what distance? Changing that can make anything trivial or impossible

Hiding means moving along that axis, for a set telescope size. Full blast em IS different than drastically cut em emissoons. It's always possible to hide less or more. IE make more or less of whatever the other guy is seeing, which decays with distance.

@Ernie Good point. It also depends on the capabilities of the observer. Btw this has been a major gripe of mine with Dark Forest theory. If you are an advanced civilization who is genuinely afraid that unknown civilizations might destroy them, wouldn't you do whatever you can to detect them? Wouldn't it be rather easy for an advanced civilization to send probes to literally every star in the galaxy?

@Shump yeah I think the book contains elements of that. But I think without knowing if you're ahead or behind, it's really hard to tell if your proves are anonymous or not.

If you're ahead all good, but then, it won't matter much. If you're only slightly ahead or behind though, it's risky since info would matter a lot, if it were one-sided. And as much as you try to anonymize a probe, how could you be sure?

So this is if they ever, even a single time, emit something that could be considered a broadcast? That seems like a very low bar

How should we answer if we think civilizations will be very likely to broadcast, but only for a small fraction of their existence?

@robm This is purely probability of broadcasting, duration of broadcast is covered in this market

Results of this market will be used here at first closure:

https://manifold.markets/Noit/how-many-aliens-does-manifold-think?r=Tm9pdA

How Many Aliens Does Manifold Think Might We Talk To? Manifold Solves the Drake Equation

This market resolves based on the output of the Manifold Solves the Drake Equation prediction markets for each variable in the Drake Equation, linked below, as priced at time of this market closure. You can read more about the Drake Equation [here](https://en.wikipedia.org/wiki/Drake_equation). For questions with a percentage output, the YES percentage will be used for the calculation. For questions with a category output, the midpoint of the highest-YES-valued category will be used (e.g. if the category lists 1-10, then the output used will be 5). [markets]