Cosmology and the History of the Universe

Last Updated May 28, 2026

Cosmology and the history of the universe examine the largest physical system available to science: the universe itself as an evolving, measurable, structured whole. Modern cosmology is not merely philosophical speculation about origins. It is a quantitative physical science grounded in general relativity, thermodynamics, nuclear physics, particle physics, radiation physics, structure formation, statistical inference, instrumentation, and increasingly precise astronomical observation. It asks how the universe began in its hot early state, expanded, cooled, formed nuclei and atoms, released relic radiation, grew structure, formed stars and galaxies, entered its present era of accelerated expansion, and arrived at the cosmic web observed today.

This matters because the universe is not static. It has a thermal history, an expansion history, a matter-radiation history, a structure-formation history, and an observational history written into light that has traveled across cosmic time. The early universe was hot, dense, and nearly uniform, but not perfectly so. Over time, expansion cooled the cosmos, allowed light nuclei to form, permitted neutral atoms to emerge, released the cosmic microwave background, and allowed small density fluctuations to grow into stars, galaxies, clusters, filaments, voids, and the large-scale cosmic web. Cosmology is therefore one of the clearest examples of physics as historical science: the present universe preserves evidence of earlier physical conditions.

This article develops Cosmology and the History of the Universe as a foundational topic within the Physics knowledge series. It explains expansion, the early-universe timeline, recombination, the cosmic microwave background, structure formation, dark matter, dark energy, and the observational tools that make cosmic history measurable. It also follows the mathematics-first and computation-aware structure used throughout the series while keeping the article body readable. Selected Python and R workflows appear here, while the full GitHub repository contains expanded research-grade computational workflows for Hubble-law modeling, redshift-scale-factor relations, ΛCDM-style expansion calculations, cosmic-era metadata, SQL schemas, numerical integration, and reproducible cosmology workflows.

Why Cosmology Matters

Cosmology matters because it asks how the universe behaves as a whole rather than only in local fragments. Physics can describe stars, atoms, nuclei, fields, radiation, and materials individually, but cosmology asks how all these domains fit into a single evolving universe. It treats the universe not as a fixed container in which physics happens, but as a dynamical physical system whose geometry, temperature, matter content, radiation content, and large-scale structure have changed over time.

This is one of the most important expansions in scientific thought. The universe itself becomes an object of physical inquiry: not merely a backdrop, but a system with a history. Its earliest observable traces are preserved in relic radiation. Its matter distribution records gravitational growth. Its expansion history constrains spacetime geometry and dark energy. Its light-element abundances preserve information about the first minutes. Its galaxies reveal the long transformation from nearly uniform initial conditions into richly organized structure.

Cosmology also matters because it connects the largest scales to some of the smallest-scale physics. The early universe depends on particle interactions, nuclear reactions, quantum fluctuations, and radiation physics. Later epochs depend on gravitation, dark matter, baryonic gas dynamics, star formation, feedback, and structure growth. Present-day expansion measurements constrain dark energy, the Hubble constant, spatial curvature, neutrino masses, and the validity of the standard cosmological model. Cosmology is therefore one of the great integrative sciences: it joins relativity, particle physics, astrophysics, computation, statistics, and observation into one account of cosmic history.

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The Big Picture: From Hot Early Universe to Cosmic Structure

The modern cosmological picture is often described as the history of a hot, dense early universe that expanded, cooled, and formed structure over time. The universe began in an extremely hot and dense state, underwent rapid early expansion, cooled enough for particles and radiation to change behavior, formed light nuclei, remained opaque while matter and radiation were tightly coupled, became transparent when neutral atoms formed, and later allowed gravitational structure to grow.

In the early universe, matter and radiation existed in a dense plasma. Photons interacted continually with free electrons, preventing light from traveling freely over long distances. As the universe expanded, it cooled. In the first minutes, light nuclei formed through Big Bang nucleosynthesis. Much later, when the universe cooled enough for electrons and protons to combine into neutral hydrogen, photons decoupled from matter and began to travel freely. That relic radiation is now observed as the cosmic microwave background.

Still later, matter collapsed under gravity to form stars, galaxies, clusters, and large-scale filaments. Dark matter played a central role in this process because it contributed gravitational structure without interacting with light in the same way as ordinary matter. The broad framework is powerful because it organizes cosmic history into physically intelligible transitions: expansion, cooling, nucleosynthesis, recombination, relic radiation, structure growth, galaxy formation, and late-time accelerated expansion.

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Expansion and the Modern Cosmological Framework

Modern cosmology is built on the idea that the universe expands on large scales. This does not mean galaxies are simply moving through static space in the everyday sense. It means that the large-scale geometry of the universe evolves, increasing typical separations between distant systems. Redshift becomes a measurable clue to that expansion, and distance-redshift relations become one of the main empirical routes through which cosmological models are constrained.

The standard cosmological framework is often called ΛCDM, where Λ represents dark energy in its simplest cosmological-constant form and CDM represents cold dark matter. This model has been remarkably successful in explaining many observations: the cosmic microwave background, large-scale structure, baryon acoustic oscillations, galaxy clustering, and broad features of cosmic expansion. Yet it also leaves major questions unresolved, including the nature of dark matter, the nature of dark energy, tensions among some measurements of the Hubble constant, and the physics of the earliest universe.

This is one reason cosmology depends so heavily on both geometry and observation. General relativity supplies the dynamical framework. Surveys, supernovae, baryon acoustic oscillations, weak lensing, cosmic microwave background maps, gravitational waves, and galaxy catalogs supply the evidence. Cosmology is not simply theory applied to the universe. It is theory constantly disciplined by increasingly precise measurement.

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The Early Universe: Radiation, Particles, and Cooling

The early universe was dominated by high temperature, high density, radiation, and rapidly changing particle interactions. In its earliest accessible phases, the universe was so hot that stable atoms could not exist. Protons, neutrons, electrons, photons, neutrinos, and other particle species interacted in a changing thermal environment. As expansion continued, the universe cooled, and the kinds of structures that could remain stable changed.

Cooling is therefore one of the organizing ideas of cosmic history. At very early times, physics was governed by energies far beyond those of ordinary matter. As the universe expanded and cooled, different processes froze out, decoupled, or became dynamically important. The formation of light nuclei occurred during Big Bang nucleosynthesis. The formation of neutral atoms came much later. The first stars and galaxies appeared after gravitational collapse amplified earlier density fluctuations.

This sequence matters because the universe’s earliest observable stages are not directly visible in ordinary light until recombination. Before recombination, matter and radiation were tightly coupled and the universe was opaque. Cosmology therefore reconstructs early history indirectly through relic radiation, elemental abundances, structure formation, and the predictions of physical theory.

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Recombination and the Cosmic Microwave Background

One of the decisive moments in cosmic history was recombination, when free electrons and protons combined to form neutral atoms and photons were finally able to travel freely over long distances. This is the moment when the universe became transparent to light. The radiation released from that epoch is now observed as the cosmic microwave background, or CMB.

The CMB is one of the most important observational anchors in all of cosmology. It is not merely old radiation. It is a thermal relic of the young universe and a map of tiny temperature variations that encode early density differences. Those small differences later grew into the large-scale structures observed today. The CMB is therefore both a snapshot of the early universe and a record of the initial conditions for cosmic structure.

The importance of the CMB cannot be overstated. It provides evidence for the hot early universe, constrains the geometry and matter-energy content of the cosmos, supports the ΛCDM framework, and places limits on possible extensions of standard cosmology. It is one of the clearest examples of how radiation can become historical evidence.

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Dark Matter and the Growth of Structure

Dark matter plays a central role in modern cosmology because it contributes gravitating mass without coupling to light in the ordinary way. It does not shine, absorb, or scatter photons like baryonic matter, yet its gravitational effects are visible in galaxy rotation curves, galaxy clusters, gravitational lensing, cosmic microwave background patterns, and the growth of large-scale structure.

In cosmic history, dark matter provides much of the workflow architecture for structure formation. Small fluctuations in matter density grow under gravity. Dark matter can begin forming gravitational wells before ordinary matter fully decouples from radiation pressure. Later, baryonic matter falls into those wells, cools, forms stars, and builds galaxies. Without dark matter, the observed large-scale structure of the universe would be difficult to explain within the standard framework.

The result is that cosmic structure formation is not driven by luminous matter alone. The large-scale universe is shaped by an unseen mass component whose microscopic identity remains unresolved. This makes cosmology inseparable from physics beyond the Standard Model: dark matter is essential to the standard cosmological model, but its particle or field nature remains unknown.

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Galaxies, Clusters, and the Cosmic Web

As the universe aged, matter organized into galaxies, galaxy groups, clusters, superclusters, and the web-like large-scale structure seen in modern surveys. The cosmic web is one of the most striking results of modern cosmology. It reveals that matter is not distributed as isolated islands but as a network of dense knots, filaments, sheets, and voids.

This structure reflects the gravitational amplification of early density fluctuations. The tiny anisotropies visible in the CMB were not random visual texture; they were the seeds of later structure. Over billions of years, gravity amplified small differences into galaxies and clusters. Dark matter shaped the gravitational framework, while ordinary matter cooled, formed stars, and produced luminous galaxies.

Large-scale surveys such as DESI make this history measurable. By mapping millions of galaxies and quasars across enormous volumes, cosmologists can reconstruct the distribution of matter, measure baryon acoustic oscillations, and infer how the universe expanded at different times. The present cosmic web is therefore not merely a map of where galaxies are. It is a fossil record of cosmic growth.

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Dark Energy and the Late-Time Universe

The late-time universe appears to be undergoing accelerated expansion, and dark energy is the standard label for whatever drives that acceleration in current cosmological models. In the simplest ΛCDM framework, dark energy behaves like a cosmological constant: a constant energy density associated with spacetime itself. But the fundamental nature of dark energy remains unknown.

This is why recent precision surveys matter so much. DESI has measured the expansion history of the universe across billions of years using baryon acoustic oscillations and large-scale structure. Recent analyses have strengthened hints that dark energy may evolve over time when DESI data are combined with other datasets, though the evidence has not reached the standard discovery threshold. That distinction matters. The possibility is significant, but not settled.

Dark energy is therefore one of the main reasons cosmology remains a live frontier rather than a completed story. The broad outline of cosmic history is strongly supported, but the dominant components of the universe—dark matter and dark energy—remain only partially understood in fundamental terms.

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How Cosmology Is Measured

Cosmology is an observational science built from many kinds of measurement: redshifts, brightness, angular scales, standard candles, standard rulers, background-radiation maps, weak gravitational lensing, galaxy clustering, time-domain observations, and large-scale survey statistics. No single observation establishes the full cosmic history. Instead, cosmology advances through the convergence of many measurement systems.

Distance measurement is especially central. Nearby distances can be measured through parallax. Greater distances require standard candles such as Cepheid variables and Type Ia supernovae. Large-scale structure can be measured through baryon acoustic oscillations, which act as a statistical standard ruler. Redshift reveals how light has been stretched, and in cosmology it connects observation to expansion history.

Metrology matters here. Distance, brightness, timing, wavelength, detector response, calibration, and uncertainty are not incidental technicalities. They determine whether cosmology can become precision science. Telescopes, satellites, spectrographs, detectors, calibration systems, and data pipelines are therefore central to the field’s credibility. Cosmology is about the universe, but it is built through instruments.

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The Universe’s History in Major Eras

It is useful to describe cosmic history in major eras, while remembering that the boundaries between them are model-dependent and often approximate. One begins with an extremely early hot and dense phase, followed by inflation in many current models, reheating, particle interactions, Big Bang nucleosynthesis, the plasma epoch, recombination and CMB release, the dark ages, the first stars, reionization, galaxy formation, large-scale structure growth, and the present epoch of accelerated expansion.

This periodization matters because it clarifies that “the Big Bang” is not best understood as a simple explosion in preexisting space. It names an early hot, dense, expanding state and the long physical history that follows from it. Different processes dominate at different temperatures, densities, and cosmic times.

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Mathematical Lens

A mathematics-first treatment of cosmology begins with expansion, redshift, scale factor, temperature history, and structure growth. A simple present-epoch Hubble relation can be written as:

where \(v\) is recessional velocity, \(H_0\) is the Hubble constant, and \(d\) is distance. This is not the full cosmological story at high redshift, but it captures the low-redshift intuition that expansion becomes measurable through distance-redshift relations.

Redshift is commonly written as:

where \(\lambda_{\mathrm{obs}}\) is the observed wavelength and \(\lambda_{\mathrm{emit}}\) is the emitted wavelength. In expanding-universe language, redshift is related to the scale factor:

If the present scale factor is normalized to \(a_0 = 1\), then:

Radiation temperature scales inversely with the scale factor:

where \(T_0\) is the present CMB temperature. The simplified Friedmann equation for a flat ΛCDM universe can be written as:

where \(\Omega_m\), \(\Omega_r\), and \(\Omega_\Lambda\) represent matter, radiation, and dark-energy density parameters. This equation shows why cosmology is not only narrative history. It is quantitative dynamical modeling of how different components shape expansion through time.

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Variables, Units, and Cosmological Interpretation

Cosmology uses variables that connect observation, geometry, and physical interpretation. The table below summarizes several central quantities.

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Worked Example: Hubble Expansion and Redshift Intuition

A simple way to build intuition is to use the Hubble relation in low-redshift approximation. Suppose a galaxy is \(100\) megaparsecs away and one takes a representative Hubble constant near \(70 \, km/s/Mpc\). Then the recessional velocity is approximately:

This example is deliberately simple and not sufficient for precision cosmology at high redshift, where one must use the full expansion history, curvature assumptions, and cosmological parameters. But it captures the basic logic: on large scales and at low redshift, recession correlates with distance because the universe expands.

One can also connect redshift to scale factor. If \(z = 3\), then:

This means that, under the usual normalization \(a_0 = 1\), the universe’s scale factor was one quarter of its present value when that light was emitted. Higher redshift corresponds to earlier cosmic time, smaller scale factor, and typically hotter radiation temperature. This simple relation is one of the most useful conceptual bridges between observation and cosmic history.

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Computational Modeling

Computational modeling helps make cosmology concrete. Redshift can be converted into scale factor. A Hubble relation can be plotted. A simplified ΛCDM expansion rate can be evaluated across redshift. Temperature history can be modeled through \(T(z) = T_0(1+z)\). Approximate lookback-time integrals can be computed numerically. Survey-style data can be organized into tables and compared against model predictions.

The selected examples below focus on introductory expansion and redshift relations because they are foundational and readable. The GitHub repository extends the same ideas into richer computational workflows, including Python expansion models, R visualization workflows, Julia numerical ODE examples, C++ parameter sweeps, Fortran temperature-scaling tables, SQL metadata, Rust command-line utilities, C examples, documentation, and reproducible sample data.

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Python Workflow: Hubble Relation and Scale Factor

The following Python workflow computes a low-redshift Hubble relation, converts redshift into scale factor, and estimates radiation temperature scaling. It is intentionally compact, fully commented, and designed as an educational bridge from equations to reproducible cosmological tables.

"""
Hubble Relation, Scale Factor, and Radiation Temperature

This workflow demonstrates three foundational cosmology relations:

1. Low-redshift Hubble relation:
       v = H0 * d

2. Scale factor from redshift:
       a = 1 / (1 + z)

3. Radiation temperature scaling:
       T(z) = T0 * (1 + z)

Variables:
    H0 = Hubble constant in km/s/Mpc
    d = distance in megaparsecs
    v = recession velocity in km/s
    z = redshift
    a = scale factor, normalized so a0 = 1 today
    T0 = present CMB temperature in kelvin
    Tz = radiation temperature at redshift z in kelvin
"""

import numpy as np
import pandas as pd

H0_KM_PER_S_PER_MPC = 70.0
CMB_TEMPERATURE_K = 2.7255

def hubble_velocity(distance_mpc: np.ndarray) -> np.ndarray:
    """
    Compute low-redshift recessional velocity from distance.

    Parameters
    ----------
    distance_mpc:
        Distance in megaparsecs.

    Returns
    -------
    np.ndarray
        Recessional velocity in kilometers per second.
    """
    return H0_KM_PER_S_PER_MPC * distance_mpc

def scale_factor_from_redshift(redshift: np.ndarray) -> np.ndarray:
    """
    Convert redshift to scale factor using a = 1 / (1 + z).

    Parameters
    ----------
    redshift:
        Cosmological redshift.

    Returns
    -------
    np.ndarray
        Dimensionless scale factor.
    """
    return 1.0 / (1.0 + redshift)

def radiation_temperature(redshift: np.ndarray) -> np.ndarray:
    """
    Estimate radiation temperature at redshift z.

    Parameters
    ----------
    redshift:
        Cosmological redshift.

    Returns
    -------
    np.ndarray
        Radiation temperature in kelvin.
    """
    return CMB_TEMPERATURE_K * (1.0 + redshift)

def main() -> None:
    """
    Generate simple reproducible cosmology tables.
    """
    distance_mpc = np.array([10, 50, 100, 250, 500], dtype=float)
    redshift = np.array([0, 1, 3, 10, 100, 1100], dtype=float)

    hubble_table = pd.DataFrame(
        {
            "distance_mpc": distance_mpc,
            "recessional_velocity_km_s": hubble_velocity(distance_mpc),
        }
    )

    redshift_table = pd.DataFrame(
        {
            "redshift": redshift,
            "scale_factor": scale_factor_from_redshift(redshift),
            "radiation_temperature_k": radiation_temperature(redshift),
        }
    )

    print("Low-redshift Hubble relation:")
    print(hubble_table.round(5).to_string(index=False))

    print("\nRedshift, scale factor, and radiation temperature:")
    print(redshift_table.round(8).to_string(index=False))

if __name__ == "__main__":
    main()

This workflow shows how a few compact equations can create physically interpretable cosmological tables. The values are simplified and pedagogical, but they make clear that redshift, scale factor, temperature, and expansion are mathematically linked.

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R Workflow: Redshift, Scale Factor, and Hubble Expansion

R is especially useful for cosmological datasets, redshift comparisons, and uncertainty-rich visualization. The following workflow builds small tables for the Hubble relation and redshift-scale-factor conversion, then summarizes the ranges.

# Redshift, Scale Factor, and Hubble Expansion
#
# This workflow demonstrates two introductory cosmology relations:
#
#   v = H0 * d
#   a = 1 / (1 + z)
#
# Variables:
#   H0 = Hubble constant in km/s/Mpc
#   d = distance in megaparsecs
#   v = recessional velocity in km/s
#   z = redshift
#   a = scale factor, normalized to 1 today

library(tibble)
library(dplyr)

h0_km_s_mpc <- 70

hubble_table <- tibble(
  distance_mpc = c(10, 50, 100, 250, 500)
) %>%
  mutate(
    recessional_velocity_km_s = h0_km_s_mpc * distance_mpc
  )

redshift_table <- tibble(
  redshift = c(0, 0.5, 1, 3, 10, 100, 1100)
) %>%
  mutate(
    scale_factor = 1 / (1 + redshift)
  )

summary_table <- tibble(
  maximum_distance_mpc = max(hubble_table$distance_mpc),
  maximum_recessional_velocity_km_s = max(hubble_table$recessional_velocity_km_s),
  minimum_scale_factor = min(redshift_table$scale_factor),
  maximum_redshift = max(redshift_table$redshift)
)

print(hubble_table)
print(redshift_table)
print(summary_table)

This workflow is useful because it makes the basic expansion relation explicit before introducing more advanced cosmological modeling. In a research setting, these simple tables would be replaced by calibrated survey data, uncertainty propagation, likelihood models, and cosmological parameter inference.

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GitHub Repository

The article body includes only selected computational examples so the conceptual and historical argument remains readable. The full repository contains the expanded computational infrastructure: Python Hubble and ΛCDM-style expansion workflows, R redshift summaries, Julia scale-factor models, C++ parameter sweeps, Fortran radiation-temperature tables, SQL cosmology metadata, Rust command-line utilities, C examples, documentation, and reproducible sample data.

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From Cosmic History to Open Cosmological Questions

Modern cosmology has established a remarkably coherent broad history of the universe: early hot expansion, nucleosynthesis, recombination and the CMB, structure growth, galaxy formation, and a late-time expansion history constrained by increasingly precise surveys. NASA, ESA, Planck, DESI, NIST, and many observatories and research collaborations contribute to this framework through observation, instrumentation, measurement, and modeling.

But major questions remain unresolved. The fundamental nature of dark matter is still unknown. Dark energy remains only partially characterized. The earliest phases of the universe remain difficult to probe directly. The Hubble tension raises questions about measurement, modeling, or possible new physics. Inflation is powerful but not fully understood. The connection between quantum gravity and the earliest universe remains open.

Cosmology is therefore both mature and unfinished. It is mature because its broad historical framework is supported by multiple independent lines of evidence. It is unfinished because its deepest components—dark matter, dark energy, initial conditions, and quantum gravity—remain open. The universe has become measurable, but not yet fully explained.

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Related Articles

• Physics
• What Is Physics?
• Galaxies, Black Holes, and the Large-Scale Universe
• Astrophysics and the Life of Stars
• Relativity and the Reconstruction of Space and Time
• Light, Waves, and the Physics of Radiation
• Nuclear Physics and the Energetics of the Atomic Nucleus
• Physics Beyond the Standard Model
• Measurement, Mathematics, and the Structure of Physical Inquiry
• Data Systems & Analytics
• Systems Modeling

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Further Reading

• Berkeley Lab / DESI (2024) First Results from DESI Make the Most Precise Measurement of Our Expanding Universe. Available at: https://newscenter.lbl.gov/2024/04/04/desi-first-results-make-most-precise-measurement-of-expanding-universe/ (Accessed: 24 April 2026).
• Berkeley Lab / DESI (2025) New DESI Results Strengthen Hints That Dark Energy May Evolve. Available at: https://newscenter.lbl.gov/2025/03/19/new-desi-results-strengthen-hints-that-dark-energy-may-evolve/ (Accessed: 24 April 2026).
• ESA (n.d.) Cosmic Eras. Available at: https://www.esa.int/Science_Exploration/Space_Science/Cosmic_eras (Accessed: 24 April 2026).
• ESA (n.d.) Planck and the Cosmic Microwave Background. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_and_the_cosmic_microwave_background (Accessed: 24 April 2026).
• ESA (2013) Planck Reveals an Almost Perfect Universe. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_reveals_an_almost_perfect_Universe (Accessed: 24 April 2026).
• ESA (n.d.) History of Cosmic Structure Formation. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/History_of_cosmic_structure_formation (Accessed: 24 April 2026).
• NASA (2026) Cosmic History. Available at: https://science.nasa.gov/universe/overview/ (Accessed: 24 April 2026).
• NASA (2022) History of the Universe. Available at: https://science.nasa.gov/resource/history-of-the-universe/ (Accessed: 24 April 2026).
• NIST (2025) How Do You Measure the Distance to the Moon, Planets, Stars and Beyond? Available at: https://www.nist.gov/how-do-you-measure-it/how-do-you-measure-distance-moon-planets-stars-and-beyond (Accessed: 24 April 2026).

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References

• Berkeley Lab / DESI (2024) First Results from DESI Make the Most Precise Measurement of Our Expanding Universe. Available at: https://newscenter.lbl.gov/2024/04/04/desi-first-results-make-most-precise-measurement-of-expanding-universe/ (Accessed: 24 April 2026).
• Berkeley Lab / DESI (2025) New DESI Results Strengthen Hints That Dark Energy May Evolve. Available at: https://newscenter.lbl.gov/2025/03/19/new-desi-results-strengthen-hints-that-dark-energy-may-evolve/ (Accessed: 24 April 2026).
• ESA (n.d.) Cosmic Eras. Available at: https://www.esa.int/Science_Exploration/Space_Science/Cosmic_eras (Accessed: 24 April 2026).
• ESA (n.d.) Planck and the Cosmic Microwave Background. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_and_the_cosmic_microwave_background (Accessed: 24 April 2026).
• ESA (2013) Planck Reveals an Almost Perfect Universe. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_reveals_an_almost_perfect_Universe (Accessed: 24 April 2026).
• ESA (n.d.) History of Cosmic Structure Formation. Available at: https://www.esa.int/Science_Exploration/Space_Science/Planck/History_of_cosmic_structure_formation (Accessed: 24 April 2026).
• NASA (2026) Cosmic History. Available at: https://science.nasa.gov/universe/overview/ (Accessed: 24 April 2026).
• NASA (2022) History of the Universe. Available at: https://science.nasa.gov/resource/history-of-the-universe/ (Accessed: 24 April 2026).
• NIST (2025) How Do You Measure the Distance to the Moon, Planets, Stars and Beyond? Available at: https://www.nist.gov/how-do-you-measure-it/how-do-you-measure-distance-moon-planets-stars-and-beyond (Accessed: 24 April 2026).
• Planck Collaboration (2020) ‘Planck 2018 results. VI. Cosmological parameters’, Astronomy & Astrophysics, 641, A6. Available at: https://www.aanda.org/articles/aa/full_html/2020/09/aa33910-18/aa33910-18.html (Accessed: 24 April 2026).

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