5 research outputs found
The Oort cloud
Views of the large-scale structure of the solar system, consisting of the Sun, the nine planets and their satellites, changed when Oort demonstrated that a gigantic cloud of comets (the Oort cloud) is located on the periphery of the solar system. The following subject areas are covered: (1) the Oort cloud's mass; (2) Hill's cloud mass; (3) angular momentum distribution in the solar system; and (4) the cometary cloud around other stars
Cosmological Acceleration from Virtual Gravitons
Intrinsic properties of the space itself and quantum fluctuations of its
geometry are sufficient to provide a mechanism for the acceleration of
cosmological expansion (dark energy effect). Applying
Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy approach to self-consistent
equations of one-loop quantum gravity, we found exact solutions that yield
acceleration. The permanent creation and annihilation of virtual gravitons is
not in exact balance because of the expansion of the Universe. The excess
energy comes from the spontaneous process of graviton creation and is trapped
by the background. It provides the macroscopic quantum effect of cosmic
acceleration.Comment: 6 pages, REVTeX
Dark energy from instantons
We show that in imaginary time quantum metric fluctuations of empty space
form a self-consistent de Sitter gravitational instanton that can be thought of
as describing tunneling from "nothing" into de Sitter space of real time (no
cosmological constant or scalar fields are needed). For the first time, this
mechanism is activated to give birth to a flat inflationary Universe. For the
second time, it is turned on to complete the cosmological evolution after the
energy density of matter drops below the threshold (the energy density of
instantons). A cosmological expansion with dark energy takes over after the
scale factor exceeds this threshold, which marks the birth of dark energy at a
redshift and provides a possible solution to the "coincidence
problem". The number of gravitons which tunneled into the Universe must be of
the order of to create the observed value of the Hubble constant.
This number has nothing to do with vacuum energy, which is a possible solution
to the "old cosmological constant problem". The emptying Universe should
possibly complete its evolution by tunneling back to "nothing". After that, the
entire scenario is repeated, and it can happen endlessly.Comment: 11 two-column pages, 1 figure, V2 is updated pre-publication version.
The title is changed. Section 4 (Birth of Dark Energy) is extended. Misprints
are fixe