# Gravity as a distorion of space-time

1. Aug 2, 2015

### EngWiPy

Hello,

We were taught at school that gravity is a pulling force between two objects related to their masses and the distance between them. Based on this, it seemed reasonable why we can walk on Earth while on space or on the moon we cannot.

But then I came to the Einstein's theory of gravity as masses distort the space-time fabric. How can we explain what I mentioned earlier using this model?

Thanks

2. Aug 2, 2015

3. Aug 2, 2015

### davenn

Hoe did you come to that conclusion ??
have you not see the 100's of photos and videos of men walking and driving on the moon ?

Dave

4. Aug 2, 2015

### tommyxu3

Why cannot people walk on the moon?

5. Aug 3, 2015

### EngWiPy

Walking as on Earth where your next position relative to the current one is one foot away not like 5 or 10 feet. Walking not jumping. Anyway, I appreciate if someone simplifies the answer to me in English because I am not a physicist, and this question has been in my mind for a while now. I watched a YouTube video for Michio Kaku saying that gravity pushing us down not the Earth pulling us down. How is that?

6. Aug 3, 2015

### PWiz

I guess you're trying to understand why astronauts feel 'lighter' on the moon when compared to the Earth, right?

What Einstein's general theory of relativity says is that spacetime (together) becomes (intrinsically) curved (not "distorted) in the presence of energy/mass. You can think of it as someone standing on a trampoline. All other (less massive) objects naturally move along these 'depressions' (the technical word for a free-falling path is a geodesic) or curves until they hit the object that is creating the most curvature (of course, the infalling objects also create cause some curvature, but the motion of the massive body along these "light curves" is negligible). So when you're standing on the Earth, the surface is preventing your body from moving along the curves to the center of the Earth, and so you feel a 'force'. If nothing stopped you, you would feel no force as you move towards the gravitating object. The moon is less massive than the Earth, and hence curves spacetime by a smaller amount. Therefore, the moon's surface exerts a lower force on you when it prevents you from moving toward it's center of mass.

7. Aug 3, 2015

### EngWiPy

Thanks for replying. My problem precisely is the following then: if we assume that space-time is two dimensional and flat, the Earth will curve it downward, right? as in a trampoline. This will make people on the upside earth pulled down because of this curvature, (Please correct me if I am wrong), but how can we explain why people all over the Earth's Surface are pulled toward the center of Earth, and not toward the curved space?

8. Aug 3, 2015