In addition, a striking limitation of the Standard Model has appeared in recent years. Around every galaxy, astronomers observe a large cloud of material that reveals its existence via the gravitational pull that it exerts upon stars and by the way it deflects light. But this great cloud, of which we observe the gravitational effects, cannot be seen directly and we do not know what it is made of. Numerous hypotheses have been proposed, none of which seem to work. It’s clear that there is something there, but we don’t know what. Nowadays it is called “dark matter.” Evidence indicates that it is
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