Gravity and the Theory of Relativity

According to the Theory of Relativity, gravity does not exist in the same way as Sir Isaac Newton believed it did. Newton believed that gravity was a force between two objects that attracted them together whereas Albert Einstein and his Theory of Relativity says that gravity is just a matter of curved space-time (I write “space-time” because the Theory of Relativity now blends space with time to give four dimensions). That is, an object bends and “curves” space around the object itself with the more massive the object, the greater the bend in space-time. This would mean that the Moon orbiting our Earth is following a curved path in space that is invisible to our eyes.

This also means that “gravity” bends our three dimensional space into a two dimensional invisible “curve” in space.

Since both the Moon and the Earth are quite massive, under the Theory of Relativity they must each “curve” space-time around each object but since the Earth is more massive, the Moon orbits it. At least, that is how I understand it. The more massive object wins and its “curve” in space-time is the one that is used. This raises a lot of questions.

If a massive object curves space-time then why don’t all of the planets orbiting the Sun orbit in the same path? According to the Theory of Relativity an object can create one curved path as its mass doesn’t change, so how do multiple objects in different sized orbits occur? Why don’t the moons of Jupiter, for example, break away from their orbit of Jupiter and follow the Sun’s orbit instead? Why does Jupiter’s “curve” override the Sun’s when it comes to its moons? What curve in space-time are humans following when they obey the laws of gravity by walking across the Earth?

If you think about gravity as “curved space-time” and only think very simplistically of one object’s gravity and its effect on another object (for example, the Earth’s gravity effect on the Moon), then it is very easy to see how the Theory of Relativity can apply. However, life is not that simplistic and there are many more objects in the universe than that and many different combinations that Relativity cannot seem to address.

Also, what allows objects to breakout of that curve? Are you punching a hole in the curve or riding over the curve? That would indicate a two dimensional curve and changing three dimensional space into a two dimensional curve is not possible. You can’t throw one of our three dimensions away because it is more mathematically pleasing.

I have seen a lot of people try and explain this phenomenon of gravity being “curved space-time” by having four people hold a flat bed sheet at the corners. A fifth person takes a heavy ball like a shot-put and drops it on the bed sheet. If the people at the corners of the bed sheet keep pulling on the edges to keep the bed sheet near as flat as they can, the ball rolls to the middle of the sheet where it has made a dent or curve in the bed sheet. This is how, the presenter would say, that an object “curves” space. Then they would take another ball, this time a much smaller, lighter one and drop it on the bed sheet only to see the second ball make its way to the first. The presenter would say that this is how gravity works. The second ball is just following the “curve” and doesn’t need to be attracted to the large ball in the centre of the bed sheet.

There are two major problems with this presentation. One is that you need gravity to pull on the shot-put to cause the curve in th efirst place and also to cause the second ball to move towards the first. If you tried this presentation in space, there would be no gravity to aid you, causing the balls to do not much of anything. The second is that you are trying to show three dimensional space as a two dimensional field (the bed sheet is the representation of two dimensional space). Again, there are three dimensions, so you can’t get around that one. Plus the ball is in three dimensions, so how can can you have a three dimensional object and a two dimensional object interact? You can't!   

If you believe that the bed sheet presentation is a true representation of how gravity works under the Theory of Relativity, then how do objects circling another object like a satellite circling the Earth, fall from its orbit? In the presentation the bed sheet has a downward plane caused by the first ball and this downward plane is what causes the second ball to move towards the first. In the presentation, Earth’s gravity is actually working on the second ball and forcing it down the plane of the bed sheet. If this was reality, there is no gravity to force an object down the plane of the “curved space-time” because “curved space-time” is gravity, so how does the curve force a satellite towards Earth? It doesn’t.

The simple truth is that the Theory of Relativity does not explain gravity but Newton’s theory of gravity does.