Some physicists have tried to avoid the initial conditions problem by proposing models for an eternally inflating universe with no origin. [48] This resolved the cosmology problems and led to specific predictions for the corrections to the microwave background radiation, corrections that were then calculated in detail. All models of eternal inflation produce an infinite, hypothetical multiverse, typically a fractal. Cosmic inflation is a faster-than-light expansion of the universe that spawned many others. : New Theory on the Universe's Birth", "Gravity causes homogeneity of the universe", "An interpretation of cosmological model with variable light velocity", "Cosmological model with variable light velocity: the interpretation of red shifts", "Gauge cosmological model with variable light velocity. Except in contrived models, this is true regardless of how inflation is realized in particle physics. Some have claimed that this is a signature of non-Gaussianity and thus contradicts the simplest models of inflation. [117], Another problem that has occasionally been mentioned is the trans-Planckian problem or trans-Planckian effects. In such a universe the horizon will slowly grow with time as the vacuum energy density gradually decreases. [74][72] As a physical model, however, inflation is most valuable in that it robustly predicts the initial conditions of the Universe based on only two adjustable parameters: the spectral index (that can only change in a small range) and the amplitude of the perturbations. The discrepancy between how fast the universe seems to be expanding and how fast we expect it to expand is one of cosmology’s most stubbornly persistent anomalies.. Cosmologists base their expectation of the expansion rate — a rate known as the Hubble constant — on measurements of radiation emitted shortly after the Big Bang. {\displaystyle r} This scale is suggested to be around 1016 GeV or 10−3 times the Planck energy. Inflation theory largely resolves these problems as well, thus making a universe like ours much more likely in the context of Big Bang theory. Gravity will cause the more dense regions to start contracting, leading to the formation of galaxies. These models solve the horizon problem through an expanding epoch well before the Big Bang, and then generate the required spectrum of primordial density perturbations during a contracting phase leading to a Big Crunch. In such models, most of the volume of the Universe is continuously inflating at any given time. In the early days of General Relativity, Albert Einstein introduced the cosmological constant to allow a static solution, which was a three-dimensional sphere with a uniform density of matter. It is now believed by some that the inflaton cannot be the Higgs field although the recent discovery of the Higgs boson has increased the number of works considering the Higgs field as inflaton. The "no-hair" theorem works essentially because the cosmological horizon is no different from a black-hole horizon, except for philosophical disagreements about what is on the other side. In the approximation that the expansion is exactly exponential, the horizon is static and remains a fixed physical distance away. In trying to understand the universe, two major problems remained: the flatness problem and the horizon problem. For a general rise in the price level, see. At the end of inflation, although the universe was still smaller than a car, the outer edge had traveled many times faster than the speed of light. In eternal inflation, regions with inflation have an exponentially growing volume, while regions that are not inflating don't. In hybrid inflation, one scalar field is responsible for most of the energy density (thus determining the rate of expansion), while another is responsible for the slow roll (thus determining the period of inflation and its termination). In Guth's early proposal, it was thought that the inflaton was the Higgs field, the field that explains the mass of the elementary particles. [135][136][137][138][139][140] Instead of superluminal expansion the speed of light was 60 orders of magnitude faster than its current value solving the horizon and homogeneity problems in the early universe. In 1978, Zeldovich noted the monopole problem, which was an unambiguous quantitative version of the horizon problem, this time in a subfield of particle physics, which led to several speculative attempts to resolve it. Second, in that context our local universe vacuum energy emerged after inflation stopped locally, before that the frustrated vacuum of inflation … Research published in 2020 indicates that gravity alone may be sufficient to explain the homogeneity of the universe.[126]. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. One of the most severe challenges for inflation arises from the need for fine tuning. Since Guth's early work, each of these observations has received further confirmation, most impressively by the detailed observations of the cosmic microwave background made by the Planck spacecraft. WMAP Bolsters Case for Cosmic Inflation, March 2006,, Articles with dead external links from December 2018, Articles with permanently dead external links, Articles with dead external links from January 2018, Articles with dead external links from June 2020, Wikipedia indefinitely semi-protected pages, Short description is different from Wikidata, Wikipedia articles needing clarification from November 2012, Articles with unsourced statements from May 2014, Wikipedia articles needing clarification from June 2014, Articles needing additional references from November 2016, All articles needing additional references, Creative Commons Attribution-ShareAlike License, This page was last edited on 28 November 2020, at 12:12. [70] This analysis shows that the Universe is flat to within 0.5 percent, and that it is homogeneous and isotropic to one part in 100,000. Like a metastable phase in statistical mechanics—water below the freezing temperature or above the boiling point—a quantum field would need to nucleate a large enough bubble of the new vacuum, the new phase, in order to make a transition. [29][33], The flatness problem is sometimes called one of the Dicke coincidences (along with the cosmological constant problem). Later that same year, Alexander Vilenkin showed that eternal inflation is generic.[100]. Many other observations agree, and also lead to the same conclusion. It also predicts that the total curvature of a space-slice at constant global time is zero. Starobinsky used the action, in the Einstein frame. At present, while inflation is understood principally by its detailed predictions of the initial conditions for the hot early universe, the particle physics is largely ad hoc modelling. Inflation also dilutes exotic heavy particles, such as the magnetic monopoles predicted by many extensions to the Standard Model of particle physics. Inflation is one of the most popular methods known for generating an isotropic and homogeneous universe. Inflating the balloon will make the message readable for you. Even if the universe had curvature when it started, that much expansion would cause it to appear flat today. How does a period of extremely fast inflation very early in the history of the universe explain the observation that the geometry of the universe looks flat (not curved) to us? = When it comes to the expansion rate of the universe, physicists have apparently agreed to disagree. s Inflation predicts that the structures visible in the Universe today formed through the gravitational collapse of perturbations that were formed as quantum mechanical fluctuations in the inflationary epoch. The discrepancy between how fast the universe seems to be expanding and how fast we expect it to expand is one of cosmology’s most stubbornly persistent anomalies.. Cosmologists base their expectation of the expansion rate — a rate known as the Hubble constant — on measurements of radiation emitted shortly after the Big Bang. ... Kazanas (1980) called this phase of the early Universe "de Sitter's phase." One of these problems is the horizon problem. Therefore, he proposed that the early universe went through an inflationary de Sitter era. One of these problems is thehorizon problem. Based on a huge amount of experimental observation and theoretical work, it is now believed that the reason for the observation is that space itself is expanding, and that it expanded very rapidly within the first fraction of a second after the Big Bang. [147], "Inflation model" and "Inflation theory" redirect here. [123] Brane inflation suggests that inflation arises from the motion of D-branes[124] in the compactified geometry, usually towards a stack of anti-D-branes. Others believe that there is no resolution to the paradox and that the multiverse is a critical flaw in the inflationary paradigm. I know, I know. The detailed particle physics mechanism responsible for inflation is unknown. "[6], In order to work, and as pointed out by Roger Penrose from 1986 on, inflation requires extremely specific initial conditions of its own, so that the problem (or pseudo-problem) of initial conditions is not solved: "There is something fundamentally misconceived about trying to explain the uniformity of the early universe as resulting from a thermalization process. , [clarification needed][93] New inflation requires the Universe to have a scalar field with an especially flat potential and special initial conditions. Alternatively, there could have been so much matt… The spectral index, ns is one for a scale-invariant Harrison–Zel'dovich spectrum. At a conference in 2015, Penrose said that "inflation isn't falsifiable, it's falsified. [62][63][64] In the context of inflation, they were worked out independently of the work of Mukhanov and Chibisov at the three-week 1982 Nuffield Workshop on the Very Early Universe at Cambridge University. If this field did not exist, scientists would have to propose a different explanation for all the observations that strongly suggest a metric expansion of space has occurred, and is still occurring (much more slowly) today. Much of the historical context is explained in chapters 15–17 of Peebles (1993). The multiverse theory has created significant dissension in the scientific community about the viability of the inflationary model. In an expanding universe, energy densities generally fall, or get diluted, as the volume of the Universe increases. Hawking and Page later found ambiguous results when they attempted to compute the probability of inflation in the Hartle-Hawking initial state. − [47] It was discovered that Einstein's universe is unstable, and that small fluctuations cause it to collapse or turn into a de Sitter universe. For example, classically scale invariant field theories, where scale invariance is broken by quantum effects, provide an explanation of the flatness of inflationary potentials, as long as the theory can be studied through perturbation theory.[94]. The simplest inflation models predict that ns is between 0.92 and 0.98. There are a number of characteristics of the universe that can only be explained by considering further what might have happened before the emission of the CMB. Later, Willem de Sitter found a highly symmetric inflating universe, which described a universe with a cosmological constant that is otherwise empty. 12 But during inflation, this rapid-and-relentless expansion will increase the size of the Universe many, many times over: by the same amount that it would push any other particle away. This structure for the perturbations has been confirmed by the Planck spacecraft, WMAP spacecraft and other cosmic microwave background (CMB) experiments, and galaxy surveys, especially the ongoing Sloan Digital Sky Survey. Inflation resolves several problems in Big Bang cosmology that were discovered in the 1970s. String theory requires that, in addition to the three observable spatial dimensions, additional dimensions exist that are curled up or compactified (see also Kaluza–Klein theory). Though, as cosmologist 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. Things are constantly moving beyond the cosmological horizon, which is a fixed distance away, and everything becomes homogeneous. The bubble collision problem was solved by Linde[59] and independently by Andreas Albrecht and Paul Steinhardt[60] in a model named new inflation or slow-roll inflation (Guth's model then became known as old inflation). But if inflation lasted long enough to solve the initial conditions problems, collisions between bubbles became exceedingly rare. A person at any point on the balloon might consider themselves to be at the centre of the expansion, as all neighbouring points are getting further away. Each string is a one-dimensional object, and the largest number of dimensions in which two strings will generically intersect (and, presumably, annihilate) is three. [...] BICEP did a wonderful service by bringing all the Inflation-ists out of their shell, and giving them a black eye. [5][6][7] The hypothetical field thought to be responsible for inflation is called the inflaton. It introduces additional scalar fields, so that while one of the scalar fields is responsible for normal slow roll inflation, another triggers the end of inflation: when inflation has continued for sufficiently long, it becomes favorable to the second field to decay into a much lower energy state.[120]. The figure below shows how the image of quantum noise may appear imprinted on the cosmic microwave background. Some physicists believe this paradox can be resolved by weighting observers by their pre-inflationary volume. However, unlike de Sitter space, fluctuations in a contracting inflationary space collapse to form a gravitational singularity, a point where densities become infinite. After about 10-35 seconds, there began a brief period of exponentially fast expansion, known as inflation, that ironed out any curves or warps in space and made the universe flat (because it becomes so large).