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Gravity has defied quantum (particle) explanation. Theory abounds on the subject of quantum gravity. The best cases for detecting quantum gravity effects are gravity waves. Gravity waves occur when black holes or stars revolve around each other in a binary system. General relativity says that must be true. These waves will travel through space, and if lucky could pass through the earth. Gravity waves will causes contraction in the direction of propagation and expansion in the tranverse direction. This effect is opposite of tidal gravity. Gravity waves travel at the speed of light. Anyway, detecting gravity waves is hard. Gravity wave detection devices rely on detecting minute contractions or differences in perpendicular distances. One such example is a large metal cylinder with piezoelectric sensors on it. If a gravity wave comes along, the sensors will give an electrical signal. Unfortunately, the signal will be tiny for several reasons. One, the source will far away, and the effect will fall off as distance squared. Two, the magnitude of the effect depends on the gravitational constant and Planck's constant. And three, human machines can only be so accurate. Gravity wave detection is at the very limit of our capacity to detect (if it exists). The theoretical particle of gravity is a graviton. For it to be a long ranged force it must be massless like a photon. I believe it should have a spin of 2 (a photon is spin 1) for angular momentum. The strong and weak nuclear forces are understood to be short ranged because the mediating force particle has mass. The bigger the mass, the shorter the range. Gravity or general relativity does not fit well into a quantum mechanical framework. It must for its particle nature to be fully understood. If it did, then a Grand Unifying Theory (GUT) could be established, and we would claim to understand the four forces of the universe (gravity, strong, weak, and electromagnetic). Gravity does seem to go on forever. Much of what you have learned about electromagnetic waves can be applied to gravitation. Things like Gauss' Law have gravity equivalent forms. However, to solve this problem a pleasant marriage between quantum mechanics and general relativity must be forged. And it hasn't been completed yet. Dig a little deeper than this and you will find tons of "easy" literature. Go a lot deeper, and you wake up one day a general relativity grad student. Sincerely, Tom Cull

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