Henri Poincaré, Why space with three dimensions – Analysis Situs (Topology)
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Geometers usually distinguish two kinds of geometries, which they call the first of metric and the second of projective; metric geometry is based on the notion of distance; two figures are regarded as equivalent when they are “equal” in the … Read More

Henri Poincaré, Space and time (2) – Physical and psychological relativity
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The psychological time, the Bergsonian duration, from which the scientist’s time has come out, serves to classify the phenomena that occur in the same consciousness; it is powerless to classify two psychological phenomena which have for their theater two different … Read More

Henri Poincaré, Space and time (1)
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One of the reasons that led me to return to one of the questions I have most often dealt with, is the recent revolution in our ideas on mechanics. Will the principle of relativity, as conceived by Lorentz, not impose … Read More

Space, time, and time travel
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Newton supported the idea of absolute time, unlike Leibniz, for which time is only a relation between events and cannot be expressed independently, a statement in concordance with the relativity of space-time. (Crisp 2007) Eternalism claims that the past and … Read More

Astronomy live with Microsoft: WorldWide Telescope
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Microsoft researchers has been developing an interesting astronomy application, now as a public beta, allowing you to see pictures from several observatories. The service is free of charge and uses high-resolution images from the world’s best land- and space-based telescopes. … Read More

How much do you pay for an US spy satellite?
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An US spy satellite is out of control and it will plunge to Earth in about a month. As of right now it is not possible to predict the place where the satellite is going to hit the Earth. It … Read More