Henri Poincaré, Why space with three dimensions – Analysis Situs and intuition

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I would like to add a remark which relates only indirectly to the foregoing; we have seen above the importance of the Analysis Situs and I explained that this is the real domain of geometric intuition. Does this intuition exist? … Read More

Henri Poincaré, Why space with three dimensions – Space and Nature

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But the question can be asked from a completely different point of view. We have so far placed ourselves in a purely subjective, purely psychological or, if you will, physiological point of view; we have only considered the relations of … Read More

Henri Poincaré, Why space with three dimensions – Space and movements

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It seems, therefore, that space cannot be constructed by considering sets of simultaneous sensations, which must be considered as sequences of sensations. Always go back to what I said before. Why do certain changes appear to us as changes of … Read More

Henri Poincaré, Why space with three dimensions – Space and senses

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The question seems resolved; we seem to have only to apply this rule, either to the physical continuum, which is the coarse image of space, or to the corresponding mathematical continuum which is its refined image and which is the … Read More

Henri Poincaré, Why space with three dimensions – Continuum and cuts

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But what is a continuum with n dimensions; how does it differ from a continuum whose number of dimensions is larger or smaller? First, let us recall some results recently obtained by the students of Cantor. It is possible to … Read More

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