Gravity & Energy: Questions on Object Acceleration & Hydrogen Cloud Collapse

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An object moving towards Earth is accelerated by Earth's gravitational field, converting its potential energy into kinetic energy, resulting in no net change in energy. Similarly, a hydrogen cloud in space possesses potential energy due to the separation of its atoms, which is converted during collapse into a star, again showing no net change in mass-energy. The discussion highlights a tension between Newtonian gravity and General Relativity, with some arguing that GR's perspective on energy gain is insufficient. The question of energy source during gravitational interactions remains a complex topic in physics. Overall, both scenarios illustrate the conservation of energy principle in gravitational contexts.
BobiG
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I have a quick question, if an object is moving straight towards say Earth, isn't the gravitational field of Earth going to accelerate that object giving it extra energy? Where does that energy come from? Similar question, you have a hydrogen cloud in space, isn't the mass(energy) of that cloud less than the mass(energy) of that same cloud when it collapses into a star due to gravity? Again where does the extra energy come from? It may be a stupid question but I have to ask!
 
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BobiG said:
I have a quick question, if an object is moving straight towards say Earth, isn't the gravitational field of Earth going to accelerate that object giving it extra energy? Where does that energy come from?
If an object "is moving straight towards say Earth", it must have been above the Earth and so has potential energy. That potential energy converts to kinetic energy.
There is no net change in energy.

Similar question, you have a hydrogen cloud in space, isn't the mass(energy) of that cloud less than the mass(energy) of that same cloud when it collapses into a star due to gravity? Again where does the extra energy come from? It may be a stupid question but I have to ask!
Similar answer- the hydrogen cloud has potential energy due to the fact the hydrogen atoms are separate. There is no net change in "mass-energy".
 
Not a stupid question at all. I suppose everyone just goes back to Newtonian gravity to answer that one, since I don't think General Relativity has an answer to it. GR says that the object isn't gaining energy when viewed from the appropriate free-falling frame. I think that's a cop-out, because in that frame, the ground is accelerating toward you. Where does *that* energy come from?
 

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