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Why do objects fall through curvature of spacetime?

  1. Jul 1, 2013 #1
    Just wondering, if the way to describe the movement of objects through spacetime is to say that they fall through the curves created in 4D spacetime, then is it a stupid question to ask why objects don't rise through spacetime? Or is this the same thing and rising and falling are one of the same in the 4D world?
  2. jcsd
  3. Jul 1, 2013 #2
    Hey Steve....
    Lots of common colloquial terminology has historical origins. Rising and falling are two that tend to relate to the frame origin in use. Gravity acts so as to reduce gravitational potential...make it more negative and has nothing to do with 'up' or 'down', 'rising' or 'falling' except as a traditional references.....analogous to such statements as look at the stars 'up' there.....the sun 'rises' in the morning......all relative to earth....

    In Newton's day, an apple FELL from a tree to earth. People tended to use earth as a reference. Yet nobody tends to mention that earth RISES towards the apple. In that case common terminology is that the earth 'moves' towards the apple if it is mentioned at all.

    In outer space there often is no such common 'up' or 'down' so when dispersed matter coalesces, as does hydrogen gas clumping together to form stars, it's uncommon to use 'falling'.....but one could say particles 'fall towards the center of mass'...yet it is said things 'fall' towards a black hole via gravitational attraction, likely because the BH tends to be the reference point in such discussions.

    I see wikipedia uses 'elevated' and 'height' [as conveniences]:

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