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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cosmic inflation | 1/9 | https://en.wikipedia.org/wiki/Cosmic_inflation | reference | science, encyclopedia | 2026-05-05T13:32:28.848172+00:00 | kb-cron |
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. This enormous expansion supercooled the universe and ended when the energy content of the field driving inflation condensed into hot, dense particles, a process called reheating. Following the inflationary period, the universe continued to expand, but at a slower rate. Inflation theory was developed in the late 1970s and early 1980s, with notable contributions by several theoretical physicists, including Alexei Starobinsky at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. Starobinsky, Guth, and Linde won the 2014 Kavli Prize "for pioneering the theory of cosmic inflation". It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe (see galaxy formation and evolution and structure formation). Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed. The detailed particle physics mechanism responsible for inflation is unknown. A number of inflation model predictions have been confirmed by observation; for example temperature anisotropies observed by the COBE satellite in 1992 exhibit nearly scale-invariant spectra as predicted by the inflationary paradigm and WMAP results also show strong evidence for inflation. However, some scientists dissent from this position. The hypothetical field thought to be responsible for inflation is called the inflaton. In 2002, three of the original architects of the theory were recognized for their major contributions; physicists Alan Guth of M.I.T., Andrei Linde of Stanford, and Paul Steinhardt of Princeton shared the Dirac Prize "for development of the concept of inflation in cosmology". In 2012, Guth and Linde were awarded the Breakthrough Prize in Fundamental Physics for their invention and development of inflationary cosmology.
== Concept ==
Cosmic inflation is the hypothesis that the very early universe expanded exponentially fast. Distances between points doubled every 10−37 seconds; the expansion lasted at least 10−35 seconds, but its full duration is not certain. All of the mass-energy in all of the galaxies currently visible started in a sphere with a radius around 4 × 10−29 m then grew to a sphere with a radius around 0.9 m by the end of inflation. At the end of inflation the driving field converts to particles, leading to a quark-soup phase of the universe, a phase that retains small density variations due to quantum fluctuations in the original small smooth patch of the universe.
== Motivations == Inflation resolves several problems in Big Bang cosmology that were discovered in the 1970s. The Big Bang model successfully explained the cosmic microwave background and synthesis of primordial elements. However these successes relied on assuming initial conditions that were difficult to justify. For example, the model has no mechanism to create density fluctuation which could explain the formation of galaxies. When particle physicists took up the problem of the very early universe they immediately found additional problems. Inflation was first proposed by particle physicist Alan Guth in 1979 while investigating the problem of why no magnetic monopoles are seen today; he found that a positive-energy false vacuum would, according to general relativity, generate an exponential expansion of space. The expansion also resolves other long-standing problems including the flatness problem and the horizon problem as discussed below.
=== Structure formation ===
The Big Bang theory postulates an initial very hot uniform plasma that expands according to the equations of general relativity and ultimately produces all of the stars and galaxies. The production of stars assumes that gravity causes mass to clump, but this requires density contrast: a completely uniform mass density has no force to drive clumping. Statistical variations in density would provide the force, but expansion of the universe works faster, pulling the mass apart before it can concentrate into a star. Without an additional source of variation, Big Bang models could not produce stars.
=== Magnetic-monopole problem ===
Stable magnetic monopoles are a problem for Grand Unified Theories, which propose that at high temperatures (such as in the early universe), the electromagnetic force, strong, and weak nuclear forces are not actually fundamental forces but arise due to spontaneous symmetry breaking from a single gauge theory. These theories predict a number of heavy, stable particles that have not been observed in nature. The most notorious is the magnetic monopole, a kind of stable, heavy "charge" of magnetic field. Monopoles are predicted to be copiously produced following Grand Unified Theories at high temperature, and they should have persisted to the present day, to such an extent that they would become the primary constituent of the Universe. Not only is that not the case, but all searches for them have failed, placing stringent limits on the density of relic magnetic monopoles in the Universe. A period of inflation that occurs below the temperature where magnetic monopoles can be produced would offer a possible resolution of this problem: Monopoles would be separated from each other as the Universe around them expands, lowering their observed density by many orders of magnitude. While solving the monopole problem motivated the original hypothesis, not every cosmologist was impressed. Martin Rees has written,
"Skeptics about exotic physics might not be hugely impressed by a theoretical argument to explain the absence of particles that are themselves only hypothetical. Preventive medicine can readily seem 100 percent effective against a disease that doesn't exist!" However, the flatness and especially the horizon problem are also solved by inflation theory.
=== Flatness problem ===