Astronomical hypotheses

theoretical cloud of planetesimals at the far edge of the solar system

The multiverse is the hypothetical set of all universes. Together, these universes are presumed to comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The different universes within the multiverse are called "parallel universes", "flat universes", "other universes", "alternate universes", "multiple universes", "plane universes", "parent and child universes", "many universes", or "many worlds". One common assumption is that the multiverse is a "patchwork quilt of separate universes all bound by the sa

thumb|upright=1.3|A wormhole visualized as a two-dimensional surface. Route (a) is the shortest path through normal space between points 1 and 2; route (b) is a shorter path through a wormhole.

zone around the star with strong possibilities for stable liquid water and evolution of life

probabilistic argument to estimate the number of alien civilizations in our galaxy

radiation with a blackbody spectrum radiated from an event horizon

constant representing stress-energy density of the vacuum in Einstein's equation, which accounts for the rate of expansion of the universe

paradigm that living organisms interact with their surroundings in a self-regulating system

discredited hypothesis about Solar System planets' orbits

philosophical consideration that observations of the Universe must be compatible with the conscious and sapient life that observes it

hypothetical planet between the Sun and Mercury

hypothesis that complex extraterrestrial life is a very improbable phenomenon and likely to be extremely rare

alternative explanation of the non-Newtonian rotation of galaxies

the proposition that the occurrence of life in the universe is very sensitive to the values of certain fundamental physical constants and that the observed values are, for some reason, improbable

location in the extreme Solar System

1597 astronomy book by Johannes Kepler

hypothesis that alien life has not been discovered because alien civilizations are silent and very cautious

several theories in particle physics and cosmology related to superstring theory and M-theory

in the early days of the Solar System, Jupiter moved inward then reversed course ("tacked") to its current orbit

assumption that the chemical processes of hypothetical extraterrestrial life must be constructed primarily from carbon

the idea that something must fall between two extremes

idea that any intelligent life is destroyed by aliens

the hypothesis that the numerical similarity between the proton–electron gravitational force–electrical force ratio and the classical electron radius–age of the universe ratio is not a coincidence

thumb|right|200px|Gamma-ray bursts might have regulated the advent of intelligent life Neocatastrophism is the hypothesis that life-exterminating events such as gamma-ray bursts have acted as a galactic regulation mechanism in the Milky Way upon the emergence of complex life in its habitable zone. It is one of several proposed solutions to the Fermi paradox since it provides a mechanism which would have delayed the advent of intelligent beings in local galaxies near Earth.

deterministic model of the universe

the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System