Recent content by Sagittarius A-Star

  1. Sagittarius A-Star

    Undergrad Small question about constantly accelerating charges

    According to Wolfgang Rindler, the EP cannot be applied to the "paradox" of an accerated charge, because it's field is not local. An electric charge at rest on the surface of the earth does not radiate by energy conservation. A charge, fixed inside an orbiting satellite, does radiate. Source...
  2. Sagittarius A-Star

    Graduate Can a causal or time-like structure emerge without assuming a metric?

    Maybe this helps: https://www.wolframphysics.org/technical-introduction/potential-relation-to-physics/time-and-spacetime/ via: https://www.wolframphysics.org/technical-introduction/
  3. Sagittarius A-Star

    Undergrad Photons & Time: t=0 What?

    For example: If you send a light pulse from Earth to Alpha Centauri, then the spacetime-interval between the emition-event on Earth and the absorbtion-event on Alpha Centauri is zero. But a spacetime-interval along a worldline is called "proper time" only for time-like worldlines, not for...
  4. Sagittarius A-Star

    Undergrad Photons & Time: t=0 What?

    For example: The distance from Earth to Alpha Centauri is 4.367 LY. If you travel with 99.99999999 % light speed (relative to Earth) to there, then the distance is length-contrated in your rest-frame by a factor of ##1/70710.7##. Calculation of gamma-factor...
  5. Sagittarius A-Star

    Graduate Can a causal or time-like structure emerge without assuming a metric?

    Maybe that helps: Source: https://en.wikipedia.org/wiki/CPT_symmetry#Derivation_of_the_CPT_theorem
  6. Sagittarius A-Star

    Graduate Can a causal or time-like structure emerge without assuming a metric?

    In classical physics, the only "asymmetric" law, which contains an arrow of time, is the the second law of thermodynamics.
  7. Sagittarius A-Star

    Is A.I. more than the sum of its parts?

    I have the suspicion, that the following physics videos are also AI fake: https://www.youtube.com/@TheUniverseAccordingtoSusskind https://www.youtube.com/@PhysicswithFeynman-1
  8. Sagittarius A-Star

    Undergrad Why can coefficient "a" between spacetime intervals depend on velocity between systems?

    The absolute value of relative velocities is in both cases not ##4m/s##. If the individual velocities of your 4 frames refer to a certain unnamed inertial reference frame, then you must use the relativistic velocity addition formula. From equation ##(2.6)## in the scan in the OP (posting #1)...
  9. Sagittarius A-Star

    Undergrad Linear vs rotary motion

    Mach described it in the following way: Source (chapter 2 "Nonrelativistic Machian Theories" , page 109): https://www.amazon.com/-/he/Machs-Principle-Newtons-Quantum-Einstein/dp/0817638237?tag=pfamazon01-20 Original German text "Mach, Ernst: Die Geschichte und die Wurzel des Satzes von der...
  10. Sagittarius A-Star

    Undergrad Derive the Lorentz transformation in Minkowski four-dimensional spacetime spacetime

    Derivation of the Lorentz transformation in Minkowski spacetime diagrams:
  11. Sagittarius A-Star

    Undergrad Derive the Lorentz transformation in Minkowski four-dimensional spacetime spacetime

    The ##x'## axis rotates counter-clockwise (hyperbolic rotation of the coordinate system), see https://www.geogebra.org/m/NnrRvA46 Also, the scales of the ##ct'## and ##x'## axes change with velocity. This keeps the speed of light in vacuum (45° world-line) the same in both coordinate systems.
  12. Sagittarius A-Star

    Undergrad Revisiting the Light Clock

    The usual light clock does not contain sources of light located on a flat inclined surface. Both mirrors are oriented horizontally. I calculated an approximation for a small angle in posting #18 of the old thread. You should also use the full Lorentz transformation, to account for the...
  13. Sagittarius A-Star

    Undergrad Revisiting the Light Clock

    This doesn't exist. But you can for example approximate locally a (small) segment of a spherical wave-front by a plane, because the surface of a sphere is locally flat. Garbage in -> garbage out (see above) To understand why the light clock works, you need to understand the following key...
  14. Sagittarius A-Star

    Undergrad Axial angular momentum calculation

    Yes. In this case, the cross product must be replaced by the wedge product. ##\mathbf L = \mathbf r \wedge \mathbf p##
  15. Sagittarius A-Star

    Undergrad Can a Gyroscope in a Satellite Detect Orbit?

    They try to avoid the use of thrusters and use control moment gyroscopes most of the time, to not disturbe micro-gravity experiments. Source: https://www.quora.com/How-does-the-ISS-keep-its-orientation/answer/Robert-Frost-1?ch=99&oid=42053686&share=6bbd3c52&srid=5Gqkk&target_type=answer