The observable universe spans 46.5 billion light-years in radius despite being 13.8 billion years old because space itself has expanded. This article explains the cosmic epochs, the role of inflation, and the evidence from the cosmic microwave background.
Dark matter provided the gravitational scaffolding for the first stars, gathering gas into halos where molecular hydrogen cooling could trigger collapse. Without dark matter, the first stars could not have formed so early in cosmic history, and their properties would be drastically different.
The Laser Interferometer Space Antenna (LISA) is poised to detect gravitational waves from the first generation of black holes—seeds of supermassive black holes formed in the early universe. This article explains how LISA will probe cosmic epochs from the Planck era to reionization, and why these observations will transform our understanding of structure formation.
Molecular hydrogen (H₂) is the essential coolant that allowed the first stars and galaxies to form from primordial gas. It shaped the galaxy formation threshold, influenced the epoch of reionization, and remains a key focus of cosmological simulations and observations.
The cosmic microwave background (CMB) has a redshift of about z ≈ 1100, meaning the universe was roughly 1100 times smaller when the radiation was emitted. This relic radiation, now observed at 2.7255 K, provides a direct window into the early universe and underpins the standard Big Bang model.
The hadron epoch was the brief period in the early universe, roughly from 10 microseconds to 1 second after the Big Bang, when quarks and gluons condensed into hadrons such as protons and neutrons. This epoch set the stage for nucleosynthesis and the formation of matter as we know it.
CMB polarization, first detected in 2002, offers a unique window into the earliest moments of the universe. By analyzing the patterns of polarized light from the cosmic microwave background, cosmologists can test theories of inflation, probe the physics of the primordial plasma, and trace the evolution of cosmic structure.
Explore the evolution of the universe from the Planck epoch to the present day. This guide covers cosmic inflation, the cosmic microwave background, the first atoms, the dark ages, reionization, and the formation of stars and galaxies within the standard Lambda-CDM model.
Recombination is the epoch when the universe cooled enough for electrons and protons to form neutral hydrogen, releasing the cosmic microwave background. This article explores the timeline of the cosmos from the Planck epoch to structure formation, the role of recombination, and the evidence from missions like COBE, WMAP, and Planck.
The Copernican principle states that Earth is not a privileged observer, while the cosmological principle extends this to say the universe is homogeneous and isotropic on large scales. Together they underpin modern cosmology, from the Big Bang to the cosmic microwave background.
