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https://news.ycombinator.com/item?id=21078068 https://news.ycombinator.com/item?id=21078068 - 4 years ago, 346 comments https://news.ycombinator.com/item?id=23

• sigmoid10 3y ago
  And it's still grasping at straws. The idea of a PBH as planet 9 itself is somewhat sound, but this particular paper assumes not just a significant population of MACHO dark matter, but also an additional WIMP-like particle DM that would produce a detectable signal. Is it theoretically possible? Yes. Would it be amazing to find evidence for it? Of course. Is it likely to happen? No. And we probably won't get a conclusive answer to this either way until we can easily send probes outside the solar system or at least have enormous telescopes on the moon's surface. Until then this topic is mostly an easy path to publishing papers to get tenure.
  • ToDougie 3y ago
    Question for you -- how do we protect enormous telescopes on the moon's surface?
    • andrewflnr 3y ago
      Probably pretty similar to how JWST is protected, which is to say not at all, but with enough redundancy to take a couple hits.
      • PaulHoule 3y ago
        Why do you mess around on the surface of the moon when something free floating can be much larger with light construction?
        • huthuthike 3y ago
          You can't just make something free floating bigger and bigger without introducing new issues. In particular, as objects get larger in zero gravity, it becomes harder to dampen oscillations. The lighter the object is the more problematic these oscillations become. You also run into issues with thermal expansion.
          • giantrobot 3y ago
            And torsion effects when trying to move structures or reorient the whole structure.
          • pyinstallwoes 3y ago
            Can you expand the oscillations part? I find that interesting.
            • chaps 3y ago
              Objects have a resonant frequency and will jiggle in strange ways. The larger the object, the larger the possible jiggles. The larger the jiggles the larger the destruction.
              • pyinstallwoes 3y ago
                Are you saying any object in space will naturally be resonating with itself at some frequency or that by proximity and interaction to another object it may cause resonance on another and therefore cause it to jiggle in strange ways. Thanks!
                • chaps 3y ago
                  The latter. Basically [1] but not as exaggerated. Think of things like screws shaking loose over time which leads to structural failure. Plus, no easy means to release that energy like you would when you're attached to a planet. [1] https://www.youtube.com/watch?v=XggxeuFDaDU https://www.youtube.com/watch?v=XggxeuFDaDU
    • dividedbyzero 3y ago
      Make it very modular and have little robots scurry over with a replacement module if one gets hit by a micrometeorite or otherwise fails.
      • LASR 3y ago
        Do you play Factorio? I’m not sure how much of that is actually feasible.
    • caymanjim 3y ago
      Protect them from what? We have enormous telescopes in space already. The moon is safer than where Hubble and JWST are now.
      • dwaltrip 3y ago
        Wouldn’t the moon’s gravity pull in more material, putting a telescope at higher risk?
        • DrBazza 3y ago
          Correct. A large hill/small mountain's worth of debris hits the Earth every year. That includes micrometeorites that without an atmosphere, would pepper the Earth's surface. It's also the reason why any Moon base would be buried under layers of regolith to protect it. Glass domes on the moon are sci-fi fantasy.
          • OkayPhysicist 3y ago
            Since the moon is tidally locked, the side facing Earth and its far more massive gravity well would experience vastly less debris. It'd be a boring place to build your glass domed moon base, but I don't think it would be completely infeasible. Especially if it was built in a depression in the landscape, the approach angles would be greatly limited.
          • ceejayoz 3y ago
            The ISS gets hit with micrometeorites pretty regularly, without any regolith to protect it. Micrometeorites make correspondingly micro holes, which in said glass dome are patchable. A 2mm hole in a Soyuz docked to the station was fixed with a bit of Kapton tape and some epoxy, and was detected by a very small pressure drop in the crew spaces. Larger rocks are more of a problem, but quite rare. Your dome is much more likely to get smashed by someone mixing up the pedals in a rover. https://www.livescience.com/how-many-moon-meteorites https://www.livescience.com/how-many-moon-meteorites > "if you pick a square kilometer patch of ground, it will be hit by one of those pingpong-sized meteoroids once every thousand years or so" We've landed in visibly quite smooth areas; for example: https://www.flickr.com/photos/nasa2explore/48299974871 https://www.flickr.com/photos/nasa2explore/48299974871
  • PaulHoule 3y ago
    It’s the state of physics today. Einstein was able to predict how light was bent around the Sun and Eddington confirmed it right away, it was like Babe Ruth pointing to the stands and hitting a home run. The lag between a phenomenon being predicted or model sped by theoreticians and actually observed is getting longer and longer in fundamental physics, I mean neutrino oscillations were hypothesized in 1957. The fact that you can’t get a Nobel prize posthumously means a theoretician might never get a Nobel in fundamental physics ever again. So they’ve got to do something speculative like this to have a possibility of a legacy unless you are Ed Witten and can convince people you are a genius without any appeal to experiment whatsoever. It does point to a programme of observations to try to catch P9 in a gravitational snare and look really hard in that area with all kinds of telescopes and has the double prize of possibly finding non gravitational evidence for DM. Personally I think interstellar travelers would use FFPs as a resource but the question of how a civilization that lives on an FFP (imagine something like Pluto cut up into small (5000km) ringworlds) finds the next one seems pretty tough to me.
    • irrational 3y ago
      Except, I've never heard of Ed Witten and I'm pretty sure people had heard of Einstein during his lifetime.
      • nonameiguess 3y ago
        I didn't recognize the name but figured he was the guy who came up with M-theory, and sure enough, that's him. I believe the point here is achieving a legacy within the academy, not being known in pop culture. I think there's a lot of ambivalence about his influence, but it's definitely been large. His papers revealing how the whole superstring thing can be constructed in a way that doesn't blatantly contradict observed reality diverted at least a generation of theorists into the search for the holy grail of a theory of everything, but because we have no means of experiementally probing anything at the scales involved, it has also turned a generation of physicists into algebraic topologists largely divorced from experimental practice. You can think of him maybe like the Velvet Underground of physicists. They never achieved much popularity themselves, but virtually every rock band of the past 40 years that has gotten popular cites them as an influence, and many artists would rather have that as a legacy than popularity. Similarity, I think a lot of physicists would rather be well known and influential to other physicists rather than becoming the next Michio Kaku or someone else who shows up on television a lot.
• swader999 3y ago
  And yet we can't escape debating this. Each time this is posted we get sucked in.
  • pyinstallwoes 3y ago
    Do thoughts/ideas have inertia?
    • swader999 3y ago
      They create reality.
      • pyinstallwoes 3y ago
        That contemplation definitely has layers to it.