## News from the world of maths: How does gravity work?

Tuesday, September 29, 2009

In our fourth online poll to find out what Plus readers would most like to know about the Universe you told us that you'd like to find out how gravity works. We took the question to Professor Bangalore Sathyaprakash of the School of Physics and Astronomy at Cardiff University, and here is his answer. This interview is also available as a podcast.

If you'd like to put another Universe question to experts, vote in the current poll, or leave a comment on this blog.

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posted by Plus @ 9:55 AM

At 11:56 AM,  Jan said...

Thanks for this interesting article - but I do find the paragraph below confusing. My first problem is the sentence: "But according to Newton's gravity, the effect of the Sun's vanishing would be felt immediately, as the Earth would fly away in an tangential direction to its original path." Does this vanishing refer to sight? If so, this has nothing to do with gravity.

"According to Newton's theory, gravitational interaction is instantaneous. Suppose the Sun were to vanish from the horizon today. We would not notice its disappearance immediately just by looking at the Sun, because light takes some time to travel. But according to Newton's gravity, the effect of the Sun's vanishing would be felt immediately, as the Earth would fly away in an tangential direction to its original path." Einstein's special theory of relativity, however, states that nothing, not even information, can travel faster than the speed of light. "It's possible to use the vanishing Sun analogy to construct [theoretical] gravitational telegraphs which would transmit information instantaneously — and that, according to Einstein, is impossible. That's the reason why Einstein had to reformulate the theory of gravity." Einstein published his reformulation in 1916, under the name of general relativity.

Jan

At 2:35 PM,  The Plus Team said...

To clarify: no, here "vanishing" doesn't refer to sight. It refers to the Sun being actually removed, and with it its gravitational pull.