In theoretical physics, top-down cosmology is a proposal to regard the many possible past histories of a given event as having real existence.
[ This idea of multiple histories has been applied to ]cosmology
Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...
, in a theoretical interpretation in which the universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
has multiple possible cosmologies, and in which reasoning ''backwards'' from the current state of the universe to a quantum superposition of possible cosmic histories makes sense. Stephen Hawking has argued that the principles of quantum mechanics forbid a single cosmic history,boundary condition
In mathematics, in the field of differential equations, a boundary value problem is a differential equation together with a set of additional constraints, called the boundary conditions. A solution to a boundary value problem is a solution to th ...
naturally leads to multiple histories, called the 'no-boundary proposal', the proposed Hartle–Hawking state
The Hartle–Hawking state is a proposal in theoretical physics concerning the state of the Universe prior to the Planck epoch. It is named after James Hartle and Stephen Hawking.
Hartle and Hawking suggest that if we could travel backwards in t ...
.
According to Hawking and Thomas Hertog
Thomas Hertog is a Belgian cosmologist at KU Leuven university and a key collaborator of Professor Stephen Hawking.
Early life
Thomas Hertog was born on 27 May 1975. He graduated Summa cum laude from KU Leuven in 1997 with an MSc degree in phys ...
, "The top-down approach we have described leads to a profoundly different view of cosmology, and the relation between cause and effect. Top down cosmology is a framework in which one essentially traces the histories backwards, from a spacelike surface at the present time. The noboundary histories of the universe thus depend on what is being observed, contrary to the usual idea that the universe has a unique, observer independent history."
See also
* Consistent histories
In quantum mechanics, the consistent histories (also referred to as decoherent histories) approach is intended to give a modern interpretation of quantum mechanics, generalising the conventional Copenhagen interpretation and providing a natural i ...
* Multiverse
The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The di ...
* Quantum cosmology
Quantum cosmology is the attempt in theoretical physics to develop a quantum theory of the universe. This approach attempts to answer open questions of classical physical cosmology, particularly those related to the first phases of the universe.
...
* Hartle–Hawking state
The Hartle–Hawking state is a proposal in theoretical physics concerning the state of the Universe prior to the Planck epoch. It is named after James Hartle and Stephen Hawking.
Hartle and Hawking suggest that if we could travel backwards in t ...
References
{{reflist
Physical cosmology
Quantum measurement