A person or piece of equipment that measures something in physics. Frequently, we speak of an observer measuring time or a distance in a particular place.

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A particular point with respect to which positions are measured.  For example, positions on the Earth are frequently measured relative to the point on the Equator which is due South of Greenwich, England.  In GPS coordinates, that point is given as 0,0 (its latitude is 0, and its longitude is 0).  Or we might say something like “10 miles southeast of town hall.”  In that case, town hall would be the origin.

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Four Areas of Science


No amount of experimentation can ever prove me right; a single experiment can prove me wrong.

Albert Einstein

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About SXS

The SXS project is a collaborative research effort involving multiple institutions. Our goal is the simulation of black holes and other extreme spacetimes to gain a better understanding of Relativity, and the physics of exotic objects in the distant cosmos.

The SXS project is supported by Canada Research Chairs, CFI, CIfAR, Compute Canada, Max Planck Society, NASA, NSERC, the NSF, Ontario MEDI, the Sherman Fairchild Foundation, and XSEDE.

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RT @KeefeMitman: Nearly 50 years ago, my advisor, Saul Teukolsky, showed how a perturbed black hole rings down to a state of equilibrium. T…

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