Question

All the following statements provide evidence supporting the Big Bang theory EXCEPT (A) the discovery of cosmic microwave background radiation. (B) the Doppler effect showing that starlight is red-shifted. (C) spectral analysis of starlight showing a relative abundance of hydrogen and helium. (D) sound waves left over from the Big Bang.

Short answer

The statement that does NOT provide evidence supporting the Big Bang theory is (D) sound waves left over from the Big Bang. This is because while the early universe had pressure waves that are mathematically analogous to sound waves, there are no "sound waves" that we can detect from the Big Bang.

Step-by-step solution

Understand the Big Bang theory

The Big Bang theory is the cosmological model that describes the origin and evolution of the universe. According to this theory, the universe began as a hot and dense state and has since expanded and cooled over time. The theory is supported by various lines of evidence, including the observed redshift of starlight, cosmic microwave background radiation, and the relative abundance of hydrogen and helium in the universe.

Evaluate each statement

Now let's examine each statement: (A) The discovery of cosmic microwave background radiation: This is indeed evidence for the Big Bang theory, as this radiation was predicted by the theory and provides strong support for the initial conditions of the universe. (B) The Doppler effect showing that starlight is red-shifted: This is also true evidence for the Big Bang theory. The Doppler effect explains why the observed wavelengths of light from distant galaxies are shifted towards the red end of the spectrum, which indicates that they are moving away from us. This observation suggests that the universe is expanding, which is consistent with the Big Bang theory. (C) Spectral analysis of starlight showing a relative abundance of hydrogen and helium: This is another valid piece of evidence supporting the Big Bang theory. The universe is observed to contain roughly 75% hydrogen and 25% helium by mass. This abundance ratio is consistent with the primordial nucleosynthesis that occurred shortly after the Big Bang, supporting the theory. (D) Sound waves left over from the Big Bang: This statement is incorrect. While the early universe had pressure waves that are mathematically analogous to sound waves, there are no "sound waves" that we can detect from the Big Bang. Therefore, this statement does not provide evidence for the Big Bang theory.

Identify the incorrect statement

Based on the evaluation of each statement, the only statement that does not provide evidence supporting the Big Bang theory is (D) sound waves left over from the Big Bang.

Key concepts

Cosmic Microwave Background Radiation

The cosmic microwave background radiation (CMB) is a faint glow of light that fills the universe, providing a snapshot of the universe when it was just 380,000 years old. This relic radiation is critical evidence of the Big Bang theory, as it is consistent with predictions made by the theory.
It represents the thermal remnants of the primeval fireball that existed at the time of the Big Bang. The uniformity and slight fluctuations of the CMB help scientists understand the early universe's composition and conditions.
The CMB was first detected in 1965 by Arno Penzias and Robert Wilson, leading to a broad acceptance of the Big Bang model. Its nearly uniform temperature of about 2.7 Kelvin (-270.45 degrees Celsius) across the sky supports the idea that the universe started from a hot, dense state and continuously expanded and cooled over billions of years.

Doppler Effect

The Doppler effect is a change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the waves. When applied to light from galaxies, it results in a redshift where the light's wavelength stretches, shifting towards the red end of the spectrum.
This redshift is observed in the starlight coming from distant galaxies, indicating that they are moving away from us. It's a key piece of evidence for the Big Bang theory as it suggests that the universe is expanding. This observation of an expanding universe was first made by Edwin Hubble in 1929.
The more distant a galaxy is, the faster it appears to be receding, a relationship known as Hubble's Law. This expansion supports the Big Bang theory's core premise that the universe started from a singular point and has been expanding ever since.

Spectral Analysis of Starlight

Spectral analysis of starlight involves examining the light spectrum emitted by stars to determine their composition. When scientists analyze the spectra of various stars and galaxies, they can identify elements based on the characteristic lines each element emits.
One crucial discovery from this analysis is the relative abundance of hydrogen and helium in the universe. Most of the visible universe's mass comprised about 75% hydrogen and 25% helium. This ratio matches predictions from Big Bang nucleosynthesis models, which describe how the first light elements were formed in the few minutes after the Big Bang.
The supporting evidence from spectral analysis aligns with the Big Bang theory, suggesting that these elements were formed in the early universe when conditions were dense and hot enough to allow nuclear fusion to occur.

Abundance of Hydrogen and Helium

The abundance of hydrogen and helium in the universe is one of the major pieces of evidence supporting the Big Bang theory. The high percentage of hydrogen (around 75%) and helium (about 25%) originated from the first few moments after the Big Bang, in a process known as Big Bang nucleosynthesis.
During this time, the universe was hot enough to fuse protons and neutrons to form hydrogen and helium nuclei, but cooled before heavier elements could form. This primordial prevalence of hydrogen and helium not only affirms the Big Bang theory but also explains the lack of heavier elements at that time.
Over time, stars and galaxies formed, and through stellar nucleosynthesis processes, heavier elements were created. But the initial predominance of hydrogen and helium is a cornerstone in cosmological models and serves as crucial evidence for the Big Bang scenario.