3 ms·

Doing the math with some quick Google searches... A single red photon has the energy 2.810-19 J. This sensor is for a telescope with the primary mirror size of

Doing the math with some quick Google searches... A single red photon has the energy 2.810-19 J. This sensor is for a telescope with the primary mirror size of 8.4 meters. So area ~ pi8.4m^2 = 221.7 m^2 (square meters) The distance to the closest galaxy, Andromeda, is 2.537 million light years = 2.4×10^22 meters If we assume it's a broadcast message (a poor guess for Andromeda, but reasonable for further galaxies), with energy projected in all directions, we can use the surface area of a sphere given a distance to get an idea for how much energy would need to be broadcasted to detect a single red photon: A=4πr^2 A = 4π * (2.4×10^22 meters)^2 = 7.238×10^45 m^2 (square meters) 7.238×10^45 m^2 / 221.7 m^2 * 2.8*10-19 J = 9.14136×10^24 J (joules) Wolfram alpha helpfully says that is "≈ ( 0.024 ≈ 1/42 ) × energy output of the sun in one second ( 1 s L_ )" Which is better than I expected, honestly. So, even for detecting life in the closest galaxy, an intelligent species would need to be working on the energy level of output of stars to have a hope of light reaching earth. Not even counting getting above the noise of the rest of the stars, and then sending something identifiable as intelligent.

jiggawatts 6y ago
Makes you wonder though... would it be possible to modulate the light from the star using a shutter-like mechanism in the direction you want to communicate? Imagine something like a DLP chip, but super thin: a reflective foil with tiny baffles that can be opened and closed using something like a simple electrostatic system. Make these into an enormous light-sail like sheet the same radius as the star. Place it between the star and the target system, and you have something akin to a signal lamp using the star as the light source. You don't need to generate power on the order of a star, you just need to modulate the light field of one. That's a much lower requirement. Bit of back-of-the-envelope maths is that this is 4*10^12 kg, assuming a sail the radius of our sun, 1 nm thick, and made of aluminium. That's a huge amount of mass, but conceptually manufacturable if using automated asteroid mining or somesuch. I feel like I'm making a mistake in my calculations for the energy requirements to toggle the shutters, but it's certainly low enough that embedded solar cells can trivially provide the energy required even if they're tiny and far apart.
- Kye 6y ago
  Maybe all these light dips we detect as planets transiting their stars are an elaborate "Hello!" in the form of retired Dyson spheres repurposed as shutters.
thamer 6y ago
> The distance to the closest galaxy, Andromeda, is 2.537 million light years There are many (smaller) galaxies much closer than Andromeda: https://en.wikipedia.org/wiki/List_of_nearest_galaxies https://en.wikipedia.org/wiki/List_of_nearest_galaxies There's no reason life would only emerge in large galaxies.

jiggawatts 6y ago

Makes you wonder though... would it be possible to modulate the light from the star using a shutter-like mechanism in the direction you want to communicate? Imagine something like a DLP chip, but super thin: a reflective foil with tiny baffles that can be opened and closed using something like a simple electrostatic system. Make these into an enormous light-sail like sheet the same radius as the star. Place it between the star and the target system, and you have something akin to a signal lamp using the star as the light source. You don't need to generate power on the order of a star, you just need to modulate the light field of one. That's a much lower requirement. Bit of back-of-the-envelope maths is that this is 4*10^12 kg, assuming a sail the radius of our sun, 1 nm thick, and made of aluminium. That's a huge amount of mass, but conceptually manufacturable if using automated asteroid mining or somesuch. I feel like I'm making a mistake in my calculations for the energy requirements to toggle the shutters, but it's certainly low enough that embedded solar cells can trivially provide the energy required even if they're tiny and far apart.

Kye 6y ago
Maybe all these light dips we detect as planets transiting their stars are an elaborate "Hello!" in the form of retired Dyson spheres repurposed as shutters.

thamer 6y ago

> The distance to the closest galaxy, Andromeda, is 2.537 million light years There are many (smaller) galaxies much closer than Andromeda: https://en.wikipedia.org/wiki/List_of_nearest_galaxies https://en.wikipedia.org/wiki/List_of_nearest_galaxies There's no reason life would only emerge in large galaxies.