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Q & A: gravity basics

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Most recent answer: 08/17/2009
Q:
Why do physicists say that space is warped in with the presence of mass? Wasn't the whole concept of spacial coordinates supposed to make measuring distance easier? I think it would be easier to say that matter expands outwards in the presence of space. Also, because of the second law of thermodynamics, and since matter IS energy, would it not be logical to say that matter must continue to expand outwards until it touches other matter? Is this what we call gravity? BTW this isn't my idea, but I think it's an awesome idea but I need someone to verify the thinking is correct.
- Luke S. (age 15)
Wauwatosa, Wisconsin, United States
A:
We say that spacetime is warped by the presence of mass and momentum because the actual measured geometrical features don't match the properties of Euclidean space with location-independent clocks. That's more complicated than our intuition would suggest, but the results still fit a precise coherent picture, General Relativity.

It might be easy to say that matter expands outwards, but it's frequently false. Gravity pulls things together. So the tendency for non-interacting things to expand, implied by the Second Law of Thermodynamics, is definitely not what accounts for gravity, in fact it has the opposite effect. Gravity+the 2nd law actually is what accounts for the clumpiness of things, since the energy released as things clump makes more entropy than is lost in the clumping.

Mike W.

(published on 08/17/2009)

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