# How space time affects apple?

1. Mar 10, 2009

### thinker93

I've been wondering since a long time how does the space time curve affect the apple. If the apple isn't attracted by any force but because of the space time, then help me visualise the correct picture of space time which makes the apple fall on the earth.

2. Mar 10, 2009

### cesiumfrog

The surface of Earth is accelerating upward (due to the pressure in its core), pushing the tree to accelerate upward, pulling the apple stems to accelerate upward. By the inertia of the apples they lag downward and place tension on the stems and branches (and pressure on the roots and everything below). If the stem breaks then the apple stops accelerating and keeps going at the speed it already had, but the tree keeps on accelerating upward and the accelerating ground catches up with the apple. Just like if the apple tree were in a rocket-elevator in outer space.

Where does space-time curvature come into it? It allows the opposite sides of the planet not to be getting any further apart, despite their accelerating in seemingly opposite directions.

Last edited: Mar 10, 2009
3. Mar 11, 2009

### thinker93

To cesiumfrog,
I'm not talking about newton's discovery. If you have ever read about space time, you would surely know that it is the space time curve that creates gravity. Gravity is not a force. It is actually a curve in the space time. I want my answer in this context.

4. Mar 11, 2009

### HallsofIvy

Cesiumfrog's claim that "The surface of Earth is accelerating upward (due to the pressure in its core)" is non-sense anyway.

5. Mar 11, 2009

### Klockan3

No its not, his description was actually exactly what the OP was asking for.

The apple "accelerating" downwards is not actually an acceleration in GR but instead it is its movement along a straight line aka it have no acceleration. When it lies still it don't move according to a straight line any more and thus it must be accelerating, as such if you implement GR every part of the surface is accelerating upwards while if you throw an apple it stops accelerating upwards, while the rest do accelerate upwards making it look like the apple is accelerating downwards when it is actually the other way around.

6. Mar 11, 2009

### Ich

@thinker93: read again, cesiumfrog gave the answer.