Universal wavefunction

Last updated

The universal wavefunction or the wavefunction of the universe is the wavefunction or quantum state of the entire universe. [1] It is regarded as the basic physical entity [2] in the many-worlds interpretation of quantum mechanics, [3] [4] [5] [6] and finds applications in quantum cosmology. It evolves deterministically according to a wave equation. [7]

Contents

The concept of universal wavefunction was introduced by Hugh Everett in his 1956 PhD thesis draft The Theory of the Universal Wave Function. [8] It later received investigation from James Hartle and Stephen Hawking [9] who derived the Hartle–Hawking solution to the Wheeler–deWitt equation to explain the initial conditions of the Big Bang cosmology.

Role of observers

Hugh Everett's universal wavefunction supports the idea that observed and observer are all mixed together:

If we try to limit the applicability so as to exclude the measuring apparatus, or in general systems of macroscopic size, we are faced with the difficulty of sharply defining the region of validity. For what n might a group of n particles be construed as forming a measuring device so that the quantum description fails? And to draw the line at human or animal observers, i.e., to assume that all mechanical apparata obey the usual laws, but that they are not valid for living observers, does violence to the so-called principle of psycho-physical parallelism. [10]

Eugene Wigner and John Archibald Wheeler take issue with this stance. Wigner wrote:

The state vector of my mind, even if it were completely known, would not give its impressions. A translation from state vector to impressions would be necessary; without such a translation the state vector would be meaningless. [11]

Wheeler wrote:

One is led to recognize that a wave function 'encompassing the whole universe' is an idealization, formalistically perhaps a convenient idealization, but an idealization so strained that it can be used only in part in any forecast of correlations that makes physical sense. For making sense it seems essential most of all to 'leave the observer out of the wave function'. [12]

See also

Related Research Articles

The Copenhagen interpretation is a collection of views about the meaning of quantum mechanics, stemming from the work of Niels Bohr, Werner Heisenberg, Max Born, and others. While "Copenhagen" refers to the Danish city, the use as an "interpretation" was apparently coined by Heisenberg during the 1950s to refer to ideas developed in the 1925–1927 period, glossing over his disagreements with Bohr. Consequently, there is no definitive historical statement of what the interpretation entails.

<span class="mw-page-title-main">Many-worlds interpretation</span> Interpretation of quantum mechanics

The many-worlds interpretation (MWI) is a philosophical position about how the mathematics used in quantum mechanics relates to physical reality. It asserts that the universal wavefunction is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations of quantum mechanics, the evolution of reality as a whole in MWI is rigidly deterministic and local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s.

<span class="mw-page-title-main">Schrödinger's cat</span> Thought experiment in quantum mechanics

In quantum mechanics, Schrödinger's cat is a thought experiment concerning quantum superposition. In the thought experiment, a hypothetical cat may be considered simultaneously both alive and dead, while it is unobserved in a closed box, as a result of its fate being linked to a random subatomic event that may or may not occur. This experiment viewed this way is described as a paradox. This thought experiment was devised by physicist Erwin Schrödinger in 1935 in a discussion with Albert Einstein to illustrate what Schrödinger saw as the problems of the Copenhagen interpretation of quantum mechanics.

The de Broglie–Bohm theory, also known as the pilot wave theory, Bohmian mechanics, Bohm's interpretation, and the causal interpretation, is an interpretation of quantum mechanics. It postulates that in addition to the wavefunction, an actual configuration of particles exists, even when unobserved. The evolution over time of the configuration of all particles is defined by a guiding equation. The evolution of the wave function over time is given by the Schrödinger equation. The theory is named after Louis de Broglie (1892–1987) and David Bohm (1917–1992).

An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments. However, there exist a number of contending schools of thought over their interpretation. These views on interpretation differ on such fundamental questions as whether quantum mechanics is deterministic or stochastic, local or non-local, which elements of quantum mechanics can be considered real, and what the nature of measurement is, among other matters.

<span class="mw-page-title-main">Wigner's friend</span> Thought experiment in theoretical quantum physics

Wigner's friend is a thought experiment in theoretical quantum physics, first published by the Hungarian-American physicist Eugene Wigner in 1961, and further developed by David Deutsch in 1985. The scenario involves an indirect observation of a quantum measurement: An observer observes another observer who performs a quantum measurement on a physical system. The two observers then formulate a statement about the physical system's state after the measurement according to the laws of quantum theory. In the Copenhagen interpretation, the resulting statements of the two observers contradict each other. This reflects a seeming incompatibility of two laws in the Copenhagen interpretation: the deterministic and continuous time evolution of the state of a closed system and the nondeterministic, discontinuous collapse of the state of a system upon measurement. Wigner's friend is therefore directly linked to the measurement problem in quantum mechanics with its famous Schrödinger's cat paradox.

In quantum mechanics, wave function collapse, also called reduction of the state vector, occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an observation, and is the essence of a measurement in quantum mechanics, which connects the wave function with classical observables such as position and momentum. Collapse is one of the two processes by which quantum systems evolve in time; the other is the continuous evolution governed by the Schrödinger equation.

The many-minds interpretation of quantum mechanics extends the many-worlds interpretation by proposing that the distinction between worlds should be made at the level of the mind of an individual observer. The concept was first introduced in 1970 by H. Dieter Zeh as a variant of the Hugh Everett interpretation in connection with quantum decoherence, and later explicitly called a many or multi-consciousness interpretation. The name many-minds interpretation was first used by David Albert and Barry Loewer in 1988.

<span class="mw-page-title-main">John Archibald Wheeler</span> American theoretical physicist (1911–2008)

John Archibald Wheeler was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr to explain the basic principles of nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for popularizing the term "black hole" for objects with gravitational collapse already predicted during the early 20th century, for inventing the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Stephen Hawking called Wheeler the "hero of the black hole story".

The transactional interpretation of quantum mechanics (TIQM) takes the wave function of the standard quantum formalism, and its complex conjugate, to be retarded and advanced waves that form a quantum interaction as a Wheeler–Feynman handshake or transaction. It was first proposed in 1986 by John G. Cramer, who argues that it helps in developing intuition for quantum processes. He also suggests that it avoids the philosophical problems with the Copenhagen interpretation and the role of the observer, and also resolves various quantum paradoxes. TIQM formed a minor plot point in his science fiction novel Einstein's Bridge.

<span class="mw-page-title-main">Hugh Everett III</span> American scientist (1930–1982)

Hugh Everett III was an American physicist who, in his 1957 PhD thesis, proposed what is now known as the many-worlds interpretation (MWI) of quantum mechanics.

In theoretical physics, Euclidean quantum gravity is a version of quantum gravity. It seeks to use the Wick rotation to describe the force of gravity according to the principles of quantum mechanics.

<span class="mw-page-title-main">James Hartle</span> American physicist (1939–2023)

James Burkett Hartle was an American theoretical physicist. He joined the faculty of the University of California, Santa Barbara in 1966, and was a member of the external faculty of the Santa Fe Institute. Hartle is known for his work in general relativity, astrophysics, and interpretation of quantum mechanics.

<span class="mw-page-title-main">Bryce DeWitt</span> American theoretical physicist (1923–2004)

Bryce Seligman DeWitt was an American theoretical physicist noted for his work in gravitation and quantum field theory.

<span class="mw-page-title-main">Hartle–Hawking state</span> Proposal concerning the state of the universe prior to the Planck epoch

The Hartle–Hawking state, also known as the no-boundary wave function 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.

<span class="mw-page-title-main">Wheeler–DeWitt equation</span> Field equation, part of a theory that attempts to combine quantum mechanics and general relativity

The Wheeler–DeWitt equation for theoretical physics and applied mathematics, is a field equation attributed to John Archibald Wheeler and Bryce DeWitt. The equation attempts to mathematically combine the ideas of quantum mechanics and general relativity, a step towards a theory of quantum gravity.

The Mott problem is an iconic challenge to quantum mechanics theory: how can the prediction of spherically symmetric wave function result in linear tracks seen in a cloud chamber. The problem was first formulated in 1927 by Albert Einstein and Max Born and solved in 1929 by Nevill Francis Mott. Mott's solution notably only uses the wave equation, not wavefunction collapse, and it is considered the earliest example of what is now called decoherence theory.

Relational quantum mechanics (RQM) is an interpretation of quantum mechanics which treats the state of a quantum system as being relational, that is, the state is the relation between the observer and the system. This interpretation was first delineated by Carlo Rovelli in a 1994 preprint, and has since been expanded upon by a number of theorists. It is inspired by the key idea behind special relativity, that the details of an observation depend on the reference frame of the observer, and uses some ideas from Wheeler on quantum information.

The von Neumann–Wigner interpretation, also described as "consciousness causes collapse", is an interpretation of quantum mechanics in which consciousness is postulated to be necessary for the completion of the process of quantum measurement.

References

  1. ↑ Everett [1956]1973, "Theory of the Universal Wavefunction", introduction, pg 8–9
  2. ↑ Everett 1957, section 3, 2nd paragraph, 1st sentence.
  3. ↑ Hugh Everett, Relative State Formulation of Quantum Mechanics, Reviews of Modern Physics vol 29, (1957) pp 454–462. An abridged summary of The Theory of the Universal Wavefunction
  4. ↑ John Archibald Wheeler, Assessment of Everett's "Relative State Formulation of Quantum Theory", Reviews of Modern Physics, vol 29, (1957) pp 463–465
  5. ↑ Bryce Seligman DeWitt, Quantum Mechanics and Reality, Physics Today,23(9) pp 30–40 (1970) also April 1971 letters followup
  6. ↑ Bryce Seligman DeWitt, The Many-Universes Interpretation of Quantum Mechanics, Proceedings of the International School of Physics "Enrico Fermi" Coursu IL: Foundations of Quantum Mechanics, Academic Press (1972)
  7. ↑ Everett [1956]1973, "Theory of the Universal Wavefunction", chapter 6 (e)
  8. ↑ Bryce Seligman DeWitt, R. Neill Graham, eds, The Many-Worlds Interpretation of Quantum Mechanics, Princeton Series in Physics, Princeton University Press (1973), ISBN   0-691-08131-X Contains the reprint of Everett's thesis: The Theory of the Universal Wave Function, pp 3–140.
  9. ↑ Stephen W Hawking, James B Hartle "The Wave Function of the Universe," Physical Review D, vol 28, (1983) pp 2960–2975
  10. ↑ Everett [1956]1973, "Theory of the Universal Wavefunction", introduction, pg 6
  11. ↑ Wigner, E. P. (1973). "Epistemological Perspective on Quantum Theory". Philosophical Reflections and Syntheses. Berlin, Heidelberg: Springer Berlin Heidelberg. p. 55–71. doi:10.1007/978-3-642-78374-6_5. ISBN   978-3-540-63372-3.
  12. ↑ Wheeler, John Archibald (1977). "Include the Observer in the Wave Function?". Quantum Mechanics, A Half Century Later. Dordrecht: Springer Netherlands. p. 1–18. doi:10.1007/978-94-010-1196-9_1. ISBN   978-94-010-1198-3.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.