BB84

@BB84@mander.xyz

• ⁨Comment⁩ on ⁨Call me SKEPT1KAL⁩ ⁨⁨1⁩ ⁨day⁩ ago⁩:

  Unfortunately cosmic string and string theory are completely different things.

  en.m.wikipedia.org/wiki/Cosmic_string says

  Not to be confused with String, the subject of String Theory.

• ⁨Comment⁩ on ⁨Can't install app because it isn't "certified" by the government⁩ ⁨⁨5⁩ ⁨weeks⁩ ago⁩:

  Since when do they have those rules? A year ago I unlocked my Xiaomi phone. Outside China. Did not have a Chinese phone number. It took less than an hour.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  even light can stop following null geodesics because the curvature can be too big compared to the wavelength

  Very interesting! How do you study something like this? Is it classical E&M in a curved space time, or do you need to do QED in curved space time?

  Also, are there phenomena where this effect is significant? I’m assuming something like lensing is already captured very well by treating light as point particles?

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  So if I have a spherically symmetric object in GR I can write the Schwarzschild metric that does not depend on the radial mass distribution. But once I add a second spherically symmetric object, the metric now depends on the mass distribution of both objects?

  Your point about linearity is that if GR was linear, I could’ve instead add two Schwarzschild metrics together to get a new metric that depends only on each object’s total mass?

  But even in a situation with one source, does the shell theorem work in GR? Say I put a infinitely light spherical shell around a black hole. Would it follow the same geodesic as a point particle?

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  For the bowling ball, Newton’s shell theorem applies, right?

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Earth is in this case not an inertial reference frame. If you want to apply Newton’s second law you must go to an inertial reference frame. The 9.81m/s/s is relative to that frame, not to earth.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  That is one very impressive feather.

  Restricting ourselves to feathers made by non-human animals

  🤔🤔🤔

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  the original title was “your mom false significantly faster than g”

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Re your first point: I was imagining doing the two experiments separately. But even if you do them at the same time, as long as you don’t put the two objects right on top of each other, the earth’s acceleration would still be slanted toward the ball, making the ball hit the ground very very slightly sooner.

  Re your second point: The object would be accelerating in the direction of earth. The 9.81m/s/s is with respect to an reference frame (say the center of mass frame). The earth is also accelerating in the direction of the object at some acceleration with respect to the inertial reference frame.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Nope. The argument only works if you conjured the bowling ball and feather out of thin air vacuum. lemmy.world/comment/13237315 discusses what happens when the objects were lifted off earth.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  I didn’t think about that! If the object was taken from earth then indeed the total acceleration between it and earth would be G M_total / r^2, regardless of the mass of the object.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Okay how about now

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  @WolfLink@sh.itjust.works and @theturtlemoves@hexbear.net are correct

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  fixed it sorry

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  I meant cross-section area, not surface area. Sorry. Edited my comment above.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  If your bowling ball is twice as massive, the force between it and earth will be twice as strong. But the ball’s mass will also be twice as large, so the ball’s acceleration will remain the same. This is why g=9.81m/s^2 for every object.

  But the earth’s acceleration would not remain the same. The force doubles, but the mass of earth remains constant, so the acceleration of earth doubles.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Here’s a problem for y’all: how heavy does someone’s mom have to be to fall 10% faster than g? Just give an approximate.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Even in a perfect vacuum the bowling ball still falls faster. See my comment sibling to yours.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Yes, the earth accelerates toward the ball faster than it does toward the feather.

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  A feather has smaller surface area than a bowling ball. But drag acceleration is proportional to the surface area divided by the mass (and this quantity is indeed smaller for the bowling ball).

• ⁨Comment⁩ on ⁨your mom falls significantly faster than g⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  When the earth pulls on an object with some F newtons of force, the object is also pulling on the earth with the same force. It’s just that the earth is so massive that its acceleration F/m will be tiny. Tiny is not zero though, so the earth is still accelerating toward the object. The heavier the object, the faster earth accelerates toward it.

  Both the bowling ball and the feather accelerates toward earth at the same g=9.81m/s^2, but the earth accelerates toward the bowling ball faster than it does toward the feather.

• your mom falls significantly faster than gmander.xyz ↗
  Submitted ⁨⁨1⁩ ⁨month⁩ ago⁩ to ⁨science_memes@mander.xyz⁩ | ⁨122⁩ ⁨comments⁩
• they tricked usmander.xyz ↗
  Submitted ⁨⁨3⁩ ⁨months⁩ ago⁩ to ⁨science_memes@mander.xyz⁩ | ⁨4⁩ ⁨comments⁩
• ⁨Comment⁩ on ⁨👁️ 🌹 💨 💨⁩ ⁨⁨3⁩ ⁨months⁩ ago⁩:

  While it is true that space time dilation can cause red/blueshift, that is a distinct from the doppler effect which is the primary effect here.

  (dilation plays only a small role: without time dilation our answer going from 700nm to 350nm would be 0.5c instead of the 0.6c calculated below)

• ⁨Comment⁩ on ⁨👁️ 🌹 💨 💨⁩ ⁨⁨3⁩ ⁨months⁩ ago⁩:

  One ton of TNT is 1E9 calories which is 4 gigajoules. So 0.2 petajoules should be only 50 kilotons of TNT?

• ⁨Comment⁩ on ⁨👁️ 🌹 💨 💨⁩ ⁨⁨3⁩ ⁨months⁩ ago⁩:

  chonk rose 😳

• ⁨Comment⁩ on ⁨👁️ 🌹 💨 💨⁩ ⁨⁨3⁩ ⁨months⁩ ago⁩:

  Kinetic energy or total energy? Assuming the rose weight 10 grams I get that much total energy, but only 0.225PJ is kinetic.

• 👁️ 🌹 💨 💨lemmy.ml ↗
  Submitted ⁨⁨3⁩ ⁨months⁩ ago⁩ to ⁨science_memes@mander.xyz⁩ | ⁨32⁩ ⁨comments⁩
• ⁨Comment⁩ on ⁨Lots of 429s and broken images from mander.xyz⁩ ⁨⁨4⁩ ⁨months⁩ ago⁩:

  Image upload fails often as well.

• ⁨Comment⁩ on ⁨vibe check⁩ ⁨⁨4⁩ ⁨months⁩ ago⁩:

  Phonon Spectroscopy