Q_1_06 — Dark Matter and Dark Energy

Approximately 95% of the universe's total mass-energy content is invisible: ~27% dark matter and ~68% dark energy. Dark matter was first inferred by Fritz Zwicky (1933) from galaxy cluster dynamics and confirmed by Vera

Q_1_08 — Observable Universe and Cosmic Web

The observable universe has a diameter of ~93 billion light-years (comoving distance) and contains an estimated 2 trillion galaxies (Conselice et al. 2016), ~10²⁴ stars, and ~10⁸⁰ atoms. But its most striking feature is

Q_1_14 — Vacuum Energy and the Cosmological Constant Problem

The cosmological constant problem is widely regarded as the most severe fine-tuning problem in all of physics. Quantum field theory predicts that the vacuum of spacetime is not empty but seethes with zero-point fluctuati

Q_1_15 — Dark Energy Models and Quintessence

The accelerating expansion of the universe, discovered in 1998 via Type Ia supernovae, demands an explanation. The simplest model — Einstein's cosmological constant Λ with equation of state $w = p/\rho = -1$ exactly — fi

Q_1_05 — Holographic Principle

The holographic principle proposes that all information contained within a volume of space can be encoded on the boundary surface of that region. First suggested by Gerard 't Hooft (1993) and developed by Leonard Susskin

Q_1_23 — White Holes: Theory and Implications

A white hole is the time-reversed analogue of a black hole — a theoretical spacetime region from which matter and light can emerge but into which nothing can enter, as opposed to a black hole's event horizon from which n

Q_1_24 — Cosmic Microwave Background Deep Analysis

The Cosmic Microwave Background (CMB) is the oldest observable electromagnetic radiation in the universe — thermal radiation released approximately 380,000 years after the Big Bang (redshift z ≈ 1,100) when the universe

Q_1_11 — Cosmological Redshift and the Hubble Law

The discovery that distant galaxies' light is systematically shifted toward longer (redder) wavelengths was the first observational evidence that the universe is expanding. Vesto Slipher's spectroscopic measurements (191

Q_1_16 — History of Cosmology: Ancient to Modern

Cosmology — the study of the universe's origin, structure, and fate — is humanity's oldest intellectual pursuit and its most modern science. From the flat-earth mythologies of ancient Mesopotamia through the geocentric c

Q_1_17 — Modified Gravity Theories (MOND, TeVeS, and Alternatives to Dark Matter)

Modified Newtonian Dynamics (MOND) is a hypothesis proposed by Mordehai Milgrom in 1983 that modifies Newton's second law at very low accelerations (below approximately 1.2 × 10⁻¹⁰ m/s²) to explain galaxy rotation curves

Q_1_00 — Foundations Cosmological Models: Subfolder Summary

Q_1_07 — CMB Anomalies and the Axis of Evil

The Cosmic Microwave Background (CMB) — the afterglow of the Big Bang, emitted ~380,000 years after the universe began — is the most precisely measured radiation in the history of science. It matches the theoretical pred

Q_1_18 — Loop Quantum Gravity: Discrete Spacetime and the Planck Scale

Loop Quantum Gravity (LQG) is one of two major approaches (alongside string theory) to the quantization of general relativity — the long-sought unification of quantum mechanics and Einstein's theory of gravity. LQG's fou

Q_1_19 — Cosmic Inflation Alternatives: Bouncing, Cyclic, and Variable Speed of Light Models

Cosmic inflation — the paradigm that the universe underwent exponential expansion in the first ~10⁻³⁶ to 10⁻³² seconds — has been the standard framework for explaining the horizon problem (why the cosmic microwave backgr

Q_1_03 — Ancient Cosmologies Compared: How Civilizations Understood the Universe

Every civilization on Earth constructed a cosmology — a model of how the universe began, how it is structured, and how it will end. What is remarkable is not the differences but the convergences: primordial waters as the

Q_1_13 — Cosmic Strings and Topological Defects

Cosmic strings are one-dimensional topological defects that may have formed during symmetry-breaking phase transitions in the early universe, analogous to cracks in ice or vortex lines in superfluids. Predicted by Kibble

Q_1_10 — Cosmic Inflation and the First Second

Cosmic inflation — the hypothesis that the universe underwent an exponential expansion in the first 10⁻³⁶ to 10⁻³² seconds after the Big Bang — was proposed by Alan Guth in 1981 to resolve critical problems in standard B

Q_1_12 — Conformal Cyclic Cosmology: Penrose's Vision of Eternal Recurrence

Conformal Cyclic Cosmology (CCC), proposed by Roger Penrose in 2005, envisions the universe as an infinite sequence of "aeons" — each beginning with a Big Bang-like event and ending in an infinitely expanded, cold state

Q_1_09 — Fate of the Universe

How will the universe end? This question has moved from philosophy and eschatology into hard physics, driven by the 1998 discovery that the universe's expansion is ACCELERATING (Riess et al. 1998; Perlmutter et al. 1999

Q_1_01 — The Anthropic Principle & Fine-Tuning of the Universe

The universe appears to be astonishingly fine-tuned for the existence of complex life. Alter the cosmological constant by 1 part in 10¹²⁰, or the strong nuclear force by 0.5%, or the ratio of electromagnetic to gravitati