In a two-dimensional fluid disorder-causing mechanisms are exceptionally strong and so an absolute order cannot be achieved. Nevertheless, there is an enormous difference between systems of lesser and of greater order (for example between an ordinary fluid such as water and a superfluid such as liquid helium). Liquid helium can flow without any friction and even escape up and over its container walls, which ordinary fluid will not do. The transition between superfluid (say at low temperature) and normal behavior (at high temperature) in two dimensions, is particularly dramatic: It is caused by the appearance of a large number of topological defects in the form of vortices—tiny tornadoes—that destroy the more ordered state. This is the celebrated Berezinskii–Kosterlitz–Thouless (BKT) phase transition for which a Nobel prize in Physics was awarded in 2016. It has been shown to occur in seemingly remote physical systems ranging from liquid helium, ultracold atoms and superconducting thin films to ensembles of spins.
Published: Jan 11, 2018 9:41:02 AM
Scientists on the Dark Energy Survey (DES), which includes UCL researchers, announce their first three years of data including information on about 400 million astronomical objects such as distant galaxies billions of light years away as well as stars in our own galaxy.
Published: Jan 11, 2018 9:24:07 AM
“Is gravitation mediated by a classical channel or by a quantum one?”. It is increasingly acknowledged that such a question should be unambiguously answered well before attempting any investigation on “how” gravity is quantized.
Published: Dec 18, 2017 11:55:20 AM
Two giant galaxies seen when the universe was only 780 million years old, or about 5% of its current age, have been identified by an international team involving UCL scientists using the Atacama Large Millimeter/submillimeter Array (ALMA).
Published: Dec 18, 2017 11:36:31 AM