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Monday, August 1, 2011



The Nature of Gravity

 Have you ever been to carnival where there is a ride that is a revolving cylinder? It holds about 20 people, who walk in to it and arrange themselves around the perimeter.

 Then when the carnie throws the switch the cylinder begins to rotate and as it picks up speed the riders  feel themselves being pressed against the wall of the cylinder. Then the carnie lowers the platform they were standing on, and there they are suspended with nothing to hold them but the centrifugal force of the turning cylinder. Demonstrating Newton’s 1st law of motion, objects at rest tend to stay at rest and objects in motion tend to stay in motion until an outside force acts to change its speed or direction. In this case it is the friction of the rider’s feet with the floor that starts them moving, and it is the wall of the cylinder that forces them to change direction.

It is the same force at work in the centrifuge in chemistry class.

 Often times, in science we make models to help understand and explain difficult ideas. We make models of DNA, Atoms, Crystals, etc. we also make models of large things like the solar system, globes of the earth and so on.

 Understanding gravity involves understanding our 4 dimensional universe. Since we live in a 3 dimensional world, a concept of the 4th dimension is difficult because we have no perception of it. So it helps to make a model that is scaled down by one dimension, and our model becomes a 2dimensional world in a 3 dimensional universe.

 The 2 dimensional world might be the surface of a trampoline with 2D people that look like coins. And the massive object representing the world might be a large lead sphere. When we place the sphere on the trampoline, it caused the surface of the trampoline to bend down into the 3rd dimension. The people (coins) being 2dimensional, have no perception of the 3rd dimension, but they feel themselves being drawn to the sphere. They conclude that the sphere has a mysterious force called gravity that draws them to it.

 But we, being 3dimensional, can see that the sphere has no mysterious force, but rather, the coins are sliding down the slope of their 2 dimensional space ( the curved surface of the trampoline). Of course the problem with this model is that it requires the earth’s gravity to make it work. If we take our model up to the International Space Station (ISS), setup the trampoline, put the coins on it, and put the massive sphere on it, nothing happens, because there is no gravity.

Remembering the carnival ride, we can cause the ISS to rotate by attaching a couple of small jet engines. The resulting centripetal force causes the objects inside to be drawn to the sides of the ISS. And now we find that our model is working just like it did down on earth.    

So now we scale everything back up by one dimension, and we have a rotating 4 dimensional universe causing massive objects to warp the 3 dimensional space into the 4th dimension, which in turn causes smaller massive objects, like people and rocks, to be drawn towards the large massive objects.

The link below shows a rotating 4D cube.

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