The year 1927 in science and technology involved some significant events, listed below.
Astronomy and astrophysics
Edward Emerson Barnard's A Photographic Atlas of Selected Regions of the Milky Way is published posthumously.
Botany
The Cholodny-Went model of tropism in emerging monocotyledon shoots is first proposed by Nikolai Cholodny of the University of Kyiv.
Chemistry
Fritz London and Walter Heitler apply quantum mechanics to explain covalent bonding in the hydrogen molecule, which marks the birth of quantum chemistry.
Environment
Carbon emissions from fossil fuel burning and industry reach one billion tonnes per year.
Genetics
American biologist Raymond Pearl publishes an influential attack on the basic assumptions of eugenics.
Mathematics
Publication of the 2nd edition of Principia Mathematica by Alfred North Whitehead and Bertrand Russell, one of the most important and seminal works in mathematical logic and philosophy.
Medicine
António Egas Moniz develops cerebral angiography.
Microbiology
Ronald Canti's ground-breaking stop-motion cinematic technique vividly illustrated the microscopic behaviour of normal and neoplastic cells; irradiation was shown to cause immobilisation and mitotic arrest in suspensions of cells.
Physics
February 23 – German theoretical physicist Werner Heisenberg writes a letter to fellow physicist Wolfgang Pauli in which he describes his uncertainty principle for the first time. April – Abbé Georges Lemaître publishes in the Annales de la Société Scientifique de Bruxelles "Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques" proposing the theory of the expansion of the Universe, deriving what will become known as Hubble's law, making the first estimation of what will become called the Hubble constant, and proposing what becomes known as the Big Bang theory of the origin of the Universe, which he calls his 'hypothesis of the primeval atom'. October – The fifth Solvay Conference meets in Brussels to discuss the newly formulated quantum mechanics. Albert Einstein attacks the theories of Niels Bohr and Werner Heisenberg.
Technology
August 2 – American electrical engineer Harold Stephen Black invents the negative-feedback amplifier. September 7 – Philo Farnsworth's electronic image dissector television camera tube transmits its first image at his laboratory at 202 Green Street in San Francisco. November 5 – Completion of a bridge by Westinghouse Electric and Manufacturing in Turtle Creek, Pennsylvania, the world's first railroad bridge of wholly welded construction. Date unknown Emil Lerp invents the transportable gasoline chainsaw. Vibraphone developed in its modern form by Henry Schluter of J.C. Deagan, Inc. in the United States.
Zoology
Last known specimens of the Syrian wild ass die.