Same question as to Wei Dai: do we notice all type 1A supernovaea that occur, or just some of them? The fact that we’ve only noticed out to 10 billion light years suggests we probably can’t see all of them?
Some more thoughts pertaining to limits of detection:
The Milky Way weighs 5.8e11 times M*, which itself is 2e30kg. Total mass of the galaxy = 1.2e42kg.
If all that mass were converted to energy with perfect efficiency, say via black hole evaporation, or annihilation with antimatter, then that’s a total of 1.0e59 joules.
That many joules over 5 billion years (1.5e17 s) is a power of 7e41 watts. At a radius of 7 billion light years (6.6e25m), that’s an energy flux of 1.3e-11 W/(m*m).
The sun puts out about 1400 W/(m*m)at our distance. So the sun would be about 1e14 times brighter than this distant galaxy trying to get our attention. Move the sun 1e7 x farther away to about 158 light years to match this brightness, and you get a ~8.5 magnitude star, never visible without aid. (Note: If using 1000x as much energy it becomes a clearly visible star and among our top 20 or so.)
So, if a type III civilization were using the entire mass-energy of 1 galaxy with 100% efficiency and used this resource to signal continuously for 5 billion years, they would not be bright enough to see unaided. We would still probably notice the light as a third-rate star if it wasn’t blocked by dust.
How could they make it unusual enough to be noticed as a signal? Perhaps the signal has a complete blackbody spectrum, but they surround the galaxy with an unusual spectral absorption signature. Example: Surrounding the galaxy they could have concentric clouds of He, Li, B, N, Na, Al, etc. The elements with a prime atomic number.
That’s unusual enough to draw attention. Maybe they could even encode a message in the degree of absorption.
Same question as to Wei Dai: do we notice all type 1A supernovaea that occur, or just some of them? The fact that we’ve only noticed out to 10 billion light years suggests we probably can’t see all of them?
I expect we don’t notice most of them. We may notice a lot more the next few decades though. Some would still probably be hidden behind dust.
If we only notice 10% (say), then that seems to increase the cost of being noticed by 10x, so wouldn’t yet be above the bar.
Some more thoughts pertaining to limits of detection:
The Milky Way weighs 5.8e11 times M*, which itself is 2e30kg. Total mass of the galaxy = 1.2e42kg.
If all that mass were converted to energy with perfect efficiency, say via black hole evaporation, or annihilation with antimatter, then that’s a total of 1.0e59 joules.
That many joules over 5 billion years (1.5e17 s) is a power of 7e41 watts. At a radius of 7 billion light years (6.6e25m), that’s an energy flux of 1.3e-11 W/(m*m).
The sun puts out about 1400 W/(m*m)at our distance. So the sun would be about 1e14 times brighter than this distant galaxy trying to get our attention. Move the sun 1e7 x farther away to about 158 light years to match this brightness, and you get a ~8.5 magnitude star, never visible without aid. (Note: If using 1000x as much energy it becomes a clearly visible star and among our top 20 or so.)
So, if a type III civilization were using the entire mass-energy of 1 galaxy with 100% efficiency and used this resource to signal continuously for 5 billion years, they would not be bright enough to see unaided. We would still probably notice the light as a third-rate star if it wasn’t blocked by dust.
How could they make it unusual enough to be noticed as a signal? Perhaps the signal has a complete blackbody spectrum, but they surround the galaxy with an unusual spectral absorption signature. Example: Surrounding the galaxy they could have concentric clouds of He, Li, B, N, Na, Al, etc. The elements with a prime atomic number.
That’s unusual enough to draw attention. Maybe they could even encode a message in the degree of absorption.