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I am an astrophysicist who loves GR and Cosmology, with an additional amateur interest in Particle Physics.


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comment Intuitively, how can the work done on an object be equal to zero?
@annav, Thanks (+1) Yes, I know it is cold. It is supposed to have decoupled from the other components when the temperature of the universe was in the order of MeV and after that, it has no means of loosing energy by interacting with anything, it is only affected by the increase of volume due to the expansion (you surely know the details way much better than me). I erased the question because I was a bit ashamed, I realized it was very stupid. I even had assisted to a whole winter school about LCDM cosmology a few years ago. I don't know, I am tired, and mindlessly posed a stupid question.
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comment Classical EM neglects electron recoil?
I'm sorry I use this unorthodox way to communicate with you. I erased my question about dark matter, because your comment made me remember and I realize how stupid the question was. But I wanted to tell you thanks for that comment. In fact, you are right about your guess. I even assisted to a whole winter school a few years ago about cdm. I have written that question in a weird moment of confusion, being tired.
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comment Intuitively, how can the work done on an object be equal to zero?
@MikeDunlavey and probably -1 for my horrible english, ha ha ha
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comment Intuitively, how can the work done on an object be equal to zero?
@MikeDunlavey I think a heavy object leant against the wall is a better example. When you are pushing, there is chemical work inside your muscles. In fact you can exercise and become stronger by means of isometric exercises, with no movement at all (I think Qmechanic was thinking about something in that sense). That is why, if you push hard against a wall, you become tired. There is (another kind of) work involved.
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comment Dark Energy Explanation Found
The source of gravitational forces is the mass in Newtonian gravity. It is somehow "natural" for you to think that after a particle is annihilated, gravity abruptly "disappears". But in General Relativity (where the words "curved spacetime" make sense) the source of gravity is not only mass, but a more complex entity called the energy-momentum tensor that takes into account not only mass, but also flux of energy from one place to another. Thus, the energy released when a mass "disappears" produces no abrupt "vanishing" of gravity.
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answered Intuitively, how can the work done on an object be equal to zero?
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