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Absolute Maxwellian acceleration?

  1. Apr 8, 2010 #1
    This recent thread:
    leads me to the following thought experiment:

    Your spaceship flies by another spaceship which appears to be highly electrically charged. From measurement of E and B fields on board your craft, you conclude that either you or the other craft is accelerating. Without referencing any other physics besides Maxwell, can you tell which craft is accelerating? That is, you do not use any Newtonian or Einsteinian or galactic far field acceleration measurements. Only EM field measurements.
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Apr 9, 2010 #2
    An accelerated charge will radiate...
  4. Apr 10, 2010 #3
    Accelerating charges only radiate when viewed from differently accelerating frames.
    Two charges side-by-side, accelerating together do not cause radiation fields to appear against one another.

    The way to tell is (for example) to map the electric field of a point charge in your ship. If it deviated from the basic Coulombic shape, then you are accelerating. Put a different way, gravity and acceleration deform electric and magnetic lines of force the same way as they change the trajectory of a moving ball. If your ball doesn't move in a strait line, you ship is accelerating or is in gravity.
  5. Apr 11, 2010 #4
    Ah, thank you. Now I know what I was trying to ask.

    Two thought experiments. In both cases we have two space craft,. One is highly charged with a static electrical charge. The second, uncharged, craft is the observer. The two fly by each other. The observer craft measures ONLY the electromagnetic fields generated by the OTHER craft's passage, even though it obviously could do other measures. The observer measures the exterior E and B over a suitable time period.

    Test 1: The charged craft flies by while accelerating at a constant rate. The observer does not accelerate.

    Test 2: The observer craft flies by while accelerating at a constant rate. The charged craft does not accelerate.

    Question: For identical rates of acceleration, will the the fields measured in Test 1 match the fields in Test 2?
  6. Apr 11, 2010 #5

    Vanadium 50

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    First, you can always tell if you are accelerating. You feel a force.

    Second, it's not possible to build a device that measures the fields from a specific object. One can measure only the total fields.
  7. Apr 12, 2010 #6
    Acceleration is absolute, at least within relativity theory (both special and general) and therefore, electromagnetism. The accelerated charge will lose energy through radiation, the other one will not. @Antiphon: an accelerated dipole radiates too.
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