Editing 1909 in science (section)

==Physics==
* [[Paul Ehrenfest]] presents the [[Ehrenfest paradox]].<ref>{{cite journal|last=Ehrenfest|first=Paul|year=1909|title=Gleichförmige Rotation starrer Körper und Relativitätstheorie|trans-title=[[s:Translation:Uniform Rotation of Rigid Bodies and the Theory of Relativity|Uniform Rotation of Rigid Bodies and the Theory of Relativity]]|journal=[[Physikalische Zeitschrift]]|volume=10|page=918|title-link=s:de:Gleichförmige Rotation starrer Körper und Relativitätstheorie}}</ref>
* [[Albert Einstein]] together with [[Marcel Grossmann]] starts to develop a theory which would bind [[metric tensor]] ''g''<sub>ik</sub>, which defines a [[space]] [[geometry]], with a source of gravity, that is with [[mass]].
* [[Hans Geiger]] and [[Ernest Marsden]] discover large angle deflections of alpha particles by thin metal foils.
* [[Ernest Rutherford]] and [[Thomas Royds]] demonstrate that [[alpha particles]] are doubly [[ionization|ionized]] helium atoms.