Question

Which of the following formed latest in the universe? a) quarks b) protons and neutrons c) hydrogen atoms d) helium nuclei e) gluons

Short answer

Answer: c) Hydrogen atoms

Step-by-step solution

Understand the formation sequence in the early universe

The early universe went through several phases, which can be summarized as follows: 1. Planck Epoch (up to ~10^-43 seconds after Big Bang): The universe was incredibly hot and dense, with both time and space not yet well-defined. All four fundamental forces were unified, including gravity. 2. Grand Unification Epoch (~10^-43 to 10^-36 seconds): The strong force separated from the electroweak force, while temperature and density were still very high. 3. Inflationary Epoch (~10^-36 to 10^-32 seconds): The universe underwent rapid expansion and cooled down significantly. During this phase, quantum fluctuations were stretched to cosmic scales, creating the seeds for the formation of large-scale structures. 4. Electroweak Epoch (~10^-32 to 10^-12 seconds): The electroweak force separated into the electromagnetic force and the weak nuclear force. Quarks and gluons formed at this stage, with quark-gluon plasma filling the universe. 5. Quark Epoch (~10^-12 to 10^-6 seconds): Quarks and gluons were still not confined in protons and neutrons due to the high temperature and density. 6. Hadron Epoch (~10^-6 to 1 second): As the universe cooled and expanded, quarks and gluons combined to form hadrons, including protons and neutrons. 7. Lepton Epoch (1 to 10 seconds): Leptons, such as electrons, took center stage in the universe and interacted with the hadrons. 8. Nucleosynthesis Era (10 seconds to 20 minutes): Protons and neutrons combined to form atomic nuclei, such as hydrogen and helium nuclei. 9. Recombination Era (380,000 years): The universe cooled down enough for electrons to combine with atomic nuclei, forming neutral atoms, mainly hydrogen and helium.

Identify which particle or structure formed last among the given options

Based on the sequence of events mentioned in Step 1, we can map the given options to their respective epochs: a) Quarks: Formed during the Electroweak Epoch (~10^-32 seconds) b) Protons and neutrons: Formed during the Hadron Epoch (~10^-6 seconds) c) Hydrogen atoms: Formed during the Recombination Era (380,000 years) d) Helium nuclei: Formed during the Nucleosynthesis Era (20 minutes) e) Gluons: Formed during the Electroweak Epoch (~10^-32 seconds)

Determine which of the given options formed latest in the universe

Comparing the times associated with each option, we can conclude that hydrogen atoms (option c) formed latest in the universe during the Recombination Era, approximately 380,000 years after the Big Bang.