Cosmic Inflation
Cosmic inflation is a theoretical period of exponentially rapid expansion that the universe underwent approximately 10⁻³⁶ to 10⁻³² seconds after the Big Bang, during which it expanded by a factor of at least 10²⁶ in linear size. Proposed by Alan Guth in 1980 and refined by Andrei Linde and others, inflation elegantly resolves three major cosmological problems: the horizon problem (why the CMB is so uniform), the flatness problem (why the universe appears spatially flat), and the magnetic monopole problem. Quantum fluctuations during inflation are thought to be the seeds of all large-scale structure, stretched to cosmological scales.
Key Formula
a(t) ∝ e^(Ht); H = sqrt(V(φ) / (3 M_Pl²))
LaTeX: a(t) \propto e^{Ht}, \quad H = \sqrt{\frac{V(\phi)}{3 M_{\rm Pl}^2}}
| Symbol | Meaning | Unit |
|---|---|---|
| a(t) | Scale factor of the universe | dimensionless |
| H | Hubble parameter during inflation | s⁻¹ |
| V(φ) | Inflaton field potential energy | J/m³ |
| M_Pl | Reduced Planck mass | kg |
Cosmological Problems Solved by Inflation
| Problem | Description | Inflationary Resolution |
|---|---|---|
| Horizon Problem | CMB is uniform despite causally disconnected regions | All regions were in causal contact before inflation |
| Flatness Problem | Universe is spatially flat to 1 part in 10⁶⁰ initially | Inflation drives curvature to zero |
| Monopole Problem | GUT predicts abundant magnetic monopoles | Inflation dilutes relic densities to unobservable levels |
| Structure Origin | Seed density perturbations unexplained | Quantum fluctuations stretched to macroscopic scales |
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Related Terms
Big Bang Theory
The Big Bang Theory is the prevailing cosmological model describing the origin and evolution of the universe, proposing that all matter, energy, space, and time originated from an extremely hot, dense singularity approximately 13.8 billion years ago. The rapid expansion from this primordial state led to cooling, the formation of fundamental particles, and eventually atoms, stars, and galaxies. Evidence supporting this model includes the observed expansion of the universe, the cosmic microwave background radiation, and the abundance of light elements like hydrogen and helium.
Cosmic Microwave Background
The Cosmic Microwave Background (CMB) is the thermal electromagnetic radiation permeating the entire observable universe, representing the afterglow of light released approximately 380,000 years after the Big Bang when the universe cooled enough for protons and electrons to combine into neutral hydrogen atoms. It is observed today as a nearly uniform blackbody radiation at a temperature of approximately 2.725 K, with tiny temperature fluctuations of about 1 part in 100,000 that encode the seeds of large-scale cosmic structure. The CMB is considered one of the strongest pieces of evidence for the Big Bang model and provides precise measurements of cosmological parameters.
Expanding Universe
The expanding universe is the observational discovery that the fabric of space itself is stretching over time, causing galaxies that are not gravitationally bound to each other to recede from one another at velocities proportional to their separating distances. First confirmed observationally by Edwin Hubble in 1929 through measurements of galaxy redshifts, this expansion is described by the Friedmann–Lemaître–Robertson–Walker (FLRW) metric in general relativity. The rate of expansion, parameterised by the Hubble constant H₀ ≈ 67–73 km/s/Mpc, has been measured to be accelerating due to dark energy.
"Cosmic" from Greek "kosmikos" (of the universe). "Inflation" from Latin "inflatio" (a blowing up, from inflare: in- + flare to blow), chosen by Alan Guth in 1980 by analogy with economic inflation (rapid growth). The model was proposed to resolve problems in the standard Big Bang theory.