How Do You Take a Picture of a Black Hole?(www.quantamagazine.org)
23 pointsby dverlaeckt802 hours ago5 comments
  • rustyhancock2 hours ago
    One of the most remarkable aspects of physics is that Newtonian gravity calculations are quite spot on for all the parts of black holes layfolk consider important.

    1. Both predict the same critical radius, now called the Schwarzschild radius.

    2. Both predict a central singularity with formally infinite density in idealised collapse.

    3. Both predict exactly the same finite time to fall into the singularity under equivalent idealised conditions.

    4. Both give the same equation for radial free fall, using different definitions of time.

    What GR added was meaning to these things (and of course precise calculations outside of very idealised scenarios and symmetric conditions).

    • ant6nan hour ago
      Newtonian gravity gives infinite time to fall into black hole?

      I thought you need at least special relativity for time dilution.

      • rustyhancock28 minutes ago
        Both have finite time falling in to the singularity. If you use a point test particle Newton and GR agree on that finite time.

        That's proper time I.e. the infalling particles wristwatch time.

        In GR, external observers would never see the infalling particle cross the event horizon but that's a coordinate artifact. If using our wrist watch time for that particle.

    • ziiinqan hour ago
      [dead]
  • myrmidonan hour ago
    What I find really interesting is that black holes don't really "require" infinite density; the mass density inside the event horizon never exceeds neutron star levels, and becomes in fact lower the heavier the black hole gets (=> event horizon enclosed volume grows faster than mass).
    • Borg317 minutes ago
      For large blackholes of course. And this actually makes other interesting property. Our universe is in fact giant blackhole with our own event horizon outside it. This also support cyclic big bang theory. Once entire universe will collapse to singularity, the smallest possible particles shatters, leaving pure energy. Pure energy doesnt have "static" mass so no gravity => kaboom, we have new iteration. Theory of multiverse (multiple black holes aka universes) is out of scope here because we will never be able to escape ours.
  • monster_truckan hour ago
    I'd use a camera, personally
    • jareklupinskian hour ago
      make sure you set the exposure to a negative value
  • spottedmarleyan hour ago
    First you'll need a camera that can detect mathematical equations.
  • JohnKemenyan hour ago
    Is it just me, or could they have added a, say, picture of a black hole?