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sorry for this daft question I imagine a very very slow moving rock in space - going at 1 m/s (relative to earth) in a straight line, the earths mass causes sp

sorry for this daft question I imagine a very very slow moving rock in space - going at 1 m/s (relative to earth) in a straight line, the earths mass causes spacetime to bend making the rock head towards earth, but then the rock starts to accelerate the bit I don't understand is why does the rock accelerate towards mass? Why does the bending of spacetime make it not carry on at 1 m/s towards earth and since this rock has increased its speed due to accelation, where has this extra energy come from?

cercatrova 5y ago
> sorry for this daft question No need to feel dumb about asking questions, that's how we all learn :) With regards to your question, looks like someone answered this in another comment chain: https://news.ycombinator.com/item?id=27096279 https://news.ycombinator.com/item?id=27096279
- 123pie123 5y ago
  thanks, so the rock that was heading towards earth at 1 m/s will technically not accelerate - with in its own reference point, but the rock will accelerate to the earth (from the earths reference point) slight change of question, if the rock was heading directly in a straight line towards earth at 1 m/s, as the rock nears the earth it will accelerate (from the earths perpective) where has the extra energy come from? before it was heading at 1 m/s, but as it hits earth it will be travelling much faster
  - drdeca 5y ago
    From the gravitational potential energy, I would think.
ItsMonkk 5y ago
I really have no business answering this, but in the spirit of Cunningham's law I'm going to try to give an answer how I think of it. Would like some feedback and some guidance. This is purely a intuitive answer and not at all an academic one. As we know from relativity and time dilation, as our GPS satellites need to be resynchronized as they move fast and at a lesser mass level. The center of the Earth is very heavy and is therefore going through time slower than the rock or surface objects. Gravity doesn't really exist. Gravity is merely the side-effect of heavy-mass objects going through time slower than lighter objects. This is what is meant when it is said that spacetime is curved. So back to your question, where does the extra energy come from to accelerate the rock towards the Earth? An easy way to think of it, expanding on E=mc^2, Et=mc^2, where t is time. As the ball is now falling further and further into the Earth's gravity well, it is now going through time slower and slower. With t going slower, E must increase to balance the equation, which speeds it up.
- 123pie123 5y ago
  I've always thought that at slow speeds - ie less than 1/10 speed of light, then time can be ignored

cercatrova 5y ago

> sorry for this daft question No need to feel dumb about asking questions, that's how we all learn :) With regards to your question, looks like someone answered this in another comment chain: https://news.ycombinator.com/item?id=27096279 https://news.ycombinator.com/item?id=27096279

123pie123 5y ago
thanks, so the rock that was heading towards earth at 1 m/s will technically not accelerate - with in its own reference point, but the rock will accelerate to the earth (from the earths reference point) slight change of question, if the rock was heading directly in a straight line towards earth at 1 m/s, as the rock nears the earth it will accelerate (from the earths perpective) where has the extra energy come from? before it was heading at 1 m/s, but as it hits earth it will be travelling much faster
- drdeca 5y ago
  From the gravitational potential energy, I would think.

ItsMonkk 5y ago

I really have no business answering this, but in the spirit of Cunningham's law I'm going to try to give an answer how I think of it. Would like some feedback and some guidance. This is purely a intuitive answer and not at all an academic one. As we know from relativity and time dilation, as our GPS satellites need to be resynchronized as they move fast and at a lesser mass level. The center of the Earth is very heavy and is therefore going through time slower than the rock or surface objects. Gravity doesn't really exist. Gravity is merely the side-effect of heavy-mass objects going through time slower than lighter objects. This is what is meant when it is said that spacetime is curved. So back to your question, where does the extra energy come from to accelerate the rock towards the Earth? An easy way to think of it, expanding on E=mc^2, Et=mc^2, where t is time. As the ball is now falling further and further into the Earth's gravity well, it is now going through time slower and slower. With t going slower, E must increase to balance the equation, which speeds it up.

123pie123 5y ago
I've always thought that at slow speeds - ie less than 1/10 speed of light, then time can be ignored