Did our universe expand from a hot dense state?

  • Clarifying the question

    A circle with twelve symmetrical arrows pointing every direction away from it.

    One of the most compelling pieces of evidence supporting the Big Bang theory is the observed expansion of the universe. By tracing this expansion backward in time, we can infer that the universe originated from an extremely hot and dense state. This idea suggests that all of space emerged from a singular point, which then expanded and cooled over time. But does the evidence truly support the notion that the universe expanded from such a primordial state, as Big Bang cosmology predicts?

“Yes, after all…

  • Galaxies are diverging like dots on a balloon

    There are two ovals with galaxies. The first oval is smaller and pushes the galaxies closer. The second oval is larger and the galaxies in it are spread farther apart. Lines connect the two ovals.

    As predicted, Galaxies are diverging like dots on a balloon (i.e. diverging with a velocity proportional to their distance). We know this because…

    • Their spectral light is redshifted, meaning it shifts more towards the red end of the spectrum as the distance from us increases. “In 1929 Edwin Hubble collated about 40 results for the red shift measurements in the spectra of galaxies and published his famous law: the velocity at which a galaxy is moving away is directly proportional to its distance from us”

    This diverence supports the Big bang because, “Of all the great predictions that science has ever made over the centuries, was there ever one greater than this, to predict, and predict correctly, and predict against all expectation [from General Relativity] a phenomenon so fantastic as the expansion of the universe?” [John Wheeler, “Beyond the Black Hole.” In H. Wolf (ed.), Some Strangeness in the Proportion (Addison-Wesley, 1980), 354.]

  • The "Cosmic Microwave Background Radiation" exists

    There exists a precise “Cosmic Microwave Background Radiation” (CMB) with gas-like distribution The CMB is a faint glow of microwave radiation that permeates the entire universe, and it can be detected by radio telescopes as a uniform background noise. This radiation exhibits a distribution remarkably similar to that of a hot gas that has expanded to fill the universe.

    Uniformity and Isotropy: The CMB is remarkably uniform in all directions, with slight fluctuations that represent the seeds of all current structures in the universe. This uniformity suggests that the universe was once in a very hot, dense state that has since expanded and cooled. Blackbody Spectrum: The spectrum of the CMB matches that of a perfect blackbody with a temperature of about 2.7 Kelvin. This indicates that the radiation was emitted from an extremely hot and dense state, which is consistent with predictions from the Big Bang theory The CMB originated : The CMB originated approximately 380,000 years after the Big Bang, during an epoch known as “recombination.” At this time, the universe had cooled enough for protons and electrons to combine into neutral hydrogen atoms, allowing photons to travel freely. These photons constitute the CMB we observe today.

    This supports the expansion of the Universe from a hot-dense state insfoar as these characteristics of the CMB—its uniform distribution, blackbody spectrum, and tiny fluctuations—are precisely what we would expect from an inflationary scenario.

    1. This background radiation was discovered on accident in 1964 by two Nobel prize winning radio astronomers (Arno Penzias and Robert Wilson).

  • Predicted He4, Dt, He3, Ith7

    The Big Bang model makes precise predicts about the this elemental profile of the Universe. Observations show that the universe contains specific amounts of certain light elements that comport with these expectations, particularly helium-4, deuterium, helium-3, and lithium-7. 1

    • Helium-4 corpises about 25% of the mass of ordinary matter in the universe. This high abundance cannot be explained by stellar nucleosynthesis alone, as stars would not have had enough time to produce such a large amount of helium-4 in the early universe.
    • Deuterium is found in trace amounts, about 20 to 30 parts per million by number of hydrogen atoms. Deuterium is a fragile isotope that is easily destroyed in stellar interiors. The observed amount of deuterium is consistent with predictions from the Big Bang nucleosynthesis and provides a crucial constraint on the density of baryons (ordinary matter) in the universe.
    • Helium-3 is much rarer than helium-4, with an abundance of about 10 parts per million by number of hydrogen atoms. The production and destruction processes of helium-3 in stars and during the Big Bang nucleosynthesis are well understood, and the observed abundance fits within the predicted range from the Big Bang model.
    • Lithium-7 is found in trace amounts, about one part per 10 billion by number of hydrogen atoms. While there is a known discrepancy between the predicted and observed abundances of lithium-7 (the “lithium problem”), the overall presence of lithium-7 in the amounts observed still supports the general framework of Big Bang nucleosynthesis.
    1. Alexander Vilenkin: “Calculations show that about 23 percent of all nucleons end up in helium, and almost all the rest in hydrogen. Small amounts of deuterium and lithium are also produced. Modern analysis, using the latest data on nuclear reactions and extensive computer power, give precise element abundances as they come out of the cosmic furnace. These calculations are in very impressive agreement with modern astronomical observations. By studying the spectrum of light emitted by distant objects, astronomers can determine their chemical composition. …less than 23% of helium… deterium… one part in 10,000… lithium… one part in a billion… [Many Worlds in One (Hill and Wang, 2007), 36.] (Also see Quentin Smith, “The Uncaused Beginning of the Universe,” in William Lane Craig & Quentin Smith, Theism, Atheism, and Big Bang Cosmology (Oxford, 1993), 109. n. 1.)