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In the spirit of bringing life into the thread, I thought I’d share something a little different.
https://archive.ph/96KCm
A summary won’t do it justice, and I encourage anyone interested to read the linked article; it’s not long. In short, though, researchers checked out approximately 5 million stars (in our galaxy—close enough to look well at and potentially one day visit) for anomalous ratios of infrared heat to light. The idea here is that if a star is giving off a lot of light that is being captured, it will heat whatever is doing the capturing up significantly. This is suggested to be possibly due to either unusual debris fields around these stars, which would be unexpected due to their age (most planetary collisions happening early on in a solar system’s lifetime, and these stars being older)… Or due to large amounts of sun-orbiting satellites soaking up solar power, a Dyson swarm. Our exoplanet imaging is still very much in its infancy, and we have already discovered planets that seem to bear biosignatures. The latter explanation is plausible, at least.
This is pretty far from standard culture-war fare, but I suspect that there are enough rationalists and futurists here to find it interesting. There are also a few potential links:
This implies that there is either a way through the theorized AI apocalypse, or perhaps that silicon-based life continues growing after taking over from carbon-based life (the “biological boot loader” thesis). While I’m rather attached to my carbon-based existence, it’s at least heartening that in this scenario something is still happening after AI takes over; the spark of life hasn’t left the universe. Unless all that power is going to making paperclips, I suppose.
Does it make sense to enforce population control on a cosmic scale, discouraging humans from expanding to other stars to avoid conflict? Could the “dark forest” hypothesis make sense, where offense is favored over defense and civilizations hide as much as possible?
Mods, I apologize in advance if this is insufficiently culture-war adjacent to deserve posting here. I didn’t think it worthy of its own thread, and feel like it’s perhaps healthy for the Motte to have some fresh topics as well. I’m a devoted lurker and thought I should do my part.
Edit- My list got butchered. Trying to fix it, but it seems the method I chose of writing multiple paragraphs after a question is disfavored.
Propellantless propulsion flies in the face of the conservation of momentum. This is a law which is baked in the current Physics theories, including the standard model and general relativity.
From a theoretical perspective, it follows from the Lagrange function being independent under certain coordinate transformations with Noether's theorem.
The steelman version of this propellantless propulsion would be the claim that of course momentum is conserved, there are just previously undetected particles or fields which carry momentum. Just like a plane can accelerate while staying at the same height without violating the conservation of momentum by transferring some momentum to the air with a propeller, a spacecraft might do the same. Of course, the particles could not be reacting with anything else (like satellites or these fancy detectors we use for dark matter search), otherwise they would have been found long ago. A fundamental part of the universe being discovered by chance through an commercially interesting engineering application seems unlikely -- it would be like if Edison had created the light bulb and physicists had only discovered electricity afterwards to figure out how it works. (By contrast, my priors for observing complex systems exhibiting unexpected behaviors which will surprise physicists are much more relaxed, high temperature (that is, liquid nitrogen) superconductors were a total surprise, and the early experiments with heavier-than-air flight probably took place before we had any idea how a plane is generating lift.)
The priors for that would at least be slightly higher than "Archangel Uriel personally pushes the spacecraft forward", but still lower than for room temperature superconductors or even room temperature fusion.
The best way to convince the world that the "emdrive" works would be to put one in LEO in a cubesat. Even if you can only generate a very moderate thrust from solar power, the ability to create that thrust continuously will integrate to a tremendous delta v. A year at a thousandths of Earth surface acceleration would work out to 309km/s delta-v. Within three years, your spacecraft would pass Voyager 1 in distance. Humans have some capabilities to track satellites, so we could check easily enough.
Photons have momentum. If you're collecting light that's hitting your craft always at the same angle this momentum has to be transferred somewhere, and your craft is this somewhere as there is nowhere else for it to go.
Yes they do. Wikipedia points out that the force is (1/c) times the power, and helpfully converts 1/c to 3.34 Newtons per Gigawatt. The article also helpfully does the calculation for the solar radiation near 1 AU (i.e. Earth) and comes to a value of ten Micronewtons per square meter.
If one wants to use this force, the best thing one can do is have a very large and very light mirror, which is better than first taking the momentum of the suns photons on your solar collectors and then sending a small fraction of that momentum out in the direction you actually want to accelerate in. This is not completely hopeless: metallized Mylar foil might weight some 50 micrograms per square meter, so a space craft where most of the mass is in the foil might accelerate at 40 centimeters per second squared (though there are some constraints on the direction, similarly to sailing). Of course, having a spacecraft with two hectares of foil per kilogram of payload might be difficult from an engineering point, and micrometeorites might become a problem. I would probably play a Kerbal mod which adds Kerbol radiation pressure and giant sails, though.
Or you could actively shine an Earth- or Moonbound laser on your spacecraft.
In general, there is a tradeoff between getting the most momentum out of your propellant mass, which benefits from higher exhaust velocities on the one side (with photons being the optimal choice, and ultrarelativistic ions only slightly worse) and getting the most momentum per energy invested, which favors throwing out a huge mass at minimal velocity. For propulsions where the energy source is decoupled from the reaction mass, such as ion drives, the sweet spot seems to be at a mere 20-50km/s -- which is far away from the 300,000km/s you would get with photons.
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