4 ms·
How sure are we that a galaxy’s worth of heat can’t be radiated in a single direction, calculated to avoid as many observers as possible?
by jl6 4y ago
How sure are we that a galaxy’s worth of heat can’t be radiated in a single direction, calculated to avoid as many observers as possible?
- sbierwagen 4y agoThe universe is isotropic and homogeneous. You could certainly avoid the nearest neighbor but your beam of heat would hit some other galaxy within a few dozen megaparsecs. Given ships that can survive coasting intergalactic distances at high c that would still put your galaxy under threat with current assumptions about the lifespan of the universe.
- jl6 4y agoIt might not be a perfect cloaking device, but if it can reduce visibility to that one galaxy a few dozen megaparsecs away, perhaps it’s enough to evade the survey that the article covers?
- sbierwagen 4y agoThe PDF says they used the data from the WISE all-sky infrared survey to find the 100,000 galaxies, of which a "significant population" had a redshift z of over 2. https://arxiv.org/pdf/1504.03418.pdf https://arxiv.org/pdf/1504.03418.pdf Depending on the Hubble constant, a z of 2 is more than 8000 mpc, 27 billion light years. That's a big search volume, and they didn't find anything obviously artificial.
- Qem 4y agoDue to the finite speed of light, for many of those galaxies the images are a snapshot of several billion years ago. So we have no idea of what is thriving there today.
- sbierwagen 4y agoOkay, but that makes it worse. You can spend a million years beaming your waste heat at an apparently-dead galaxy, only to have one of its indigenous species bootstrap up a technological civilization in a blink of an eye (a mere thousand years) and launch an invasion fleet. If it's the Dark Forest scenario then it's simply not safe to show any technosignatures at all, ruling out megastructures entirely.