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Basic Question about space-time

  1. Mar 11, 2010 #1
    I just joined this forum, so forgive me if this is an inappropriate question for this section.

    Also, I have not studied physics to any meaningful degree; I am just a curious person who likes to think about the universe. So, on to my question...

    The premise:
    I was watching a documentary about Einstein in which the commentary described the force of gravity being a manipulation of space-time. Following this was a graphical representation of the Sun distorting the space-time around it, causing the Earth to orbit around the Sun as if it were a marble spiraling down a funnel-shaped surface.

    My Question:
    Given that the space-time is warped around the Sun, which is the force (gravity) keeping Earth revolving around it. How is it that the Earth does not eventually get pulled into the Sun rather than stay in its stable, consistent orbit? There seems to be nothing keeping the Earth from stopping at the current distance from the Sun. If gravity is he force that keeps us humans on the ground, and if we were to fall through a hole that goes through the entire
    Earth, wouldn't we end up stopping at the center of the Earth? So, if gravity is the same force that is pushing the Earth toward the Sun, it would seem as though the earth should keep heading toward the Sun until something stops it. I'm guessing this has something to do with how the solar system was originally formed and how it got to its current state. I'm just curious to know what exactly is keeping or stopping the Earth from being drawn further toward the Sun since the Sun's gravitational pull (or space-time distortion) is the only thing keep it in orbit in the first place.

    Anyway, sorry about the lengthy post. I just had all these thoughts come rushing to my head when I saw the documentary's description of how space-time gets distorted. :)

    Thanks in advance for your help.
     
  2. jcsd
  3. Mar 12, 2010 #2

    Matterwave

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    Gold Member

    There's no need to invoke Einstein's General relativity to answer this question. The answer is initial velocity. We ARE falling towards the Sun in fact. Every second, we accelerate towards the Sun; however, we also have sufficient initial velocity that we are in a stable orbit. It's like if you shot a cannon ball really fast. The faster you shoot the cannonball, the farther it travels before it hits the Earth. If you shoot the cannonball fast enough, it will drop towards the Earth at the same rate that the Earth is curving, so it never hits the surface.

    Here's an illustration:
    http://upload.wikimedia.org/wikipedia/commons/7/73/Newton_Cannon.svg
     
  4. Mar 12, 2010 #3
    Thanks Matterwave. I actually thought of a similar solution this morning and this makes perfect sense. I really appreciate the response!
     
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