Astronomers will never directly observe the first few minutes of the universe because a. the universe was opaque at that time. b. the universe is too large now. c. there were no particles or other matter to see. d. there were no photons.

When we talk about the opacity of the early universe, we mean that it wasn't transparent to light. In the initial few minutes after the Big Bang, the universe was extremely hot and dense. This high energy state caused an environment where particles and photons (light particles) were constantly interacting.
This interaction meant that photons couldn't travel far without colliding with particles like electrons. Imagine trying to look through a fog where the water droplets scatter light. Similarly, the dense particles of the early universe scattered photons, making it impossible to see through.
This scattering kept the universe opaque until it cooled enough for these interactions to lessen. Once it cooled, around 380,000 years after the Big Bang, atoms formed from protons and electrons, leading to a transparent universe. This event is known as the decoupling or recombination era. However, the opacity of those very first moments is why astronomers can't directly observe that period.

Photon scattering was a significant process in the early universe. During the first few minutes after the Big Bang, the universe's temperature was so high that particles like protons, neutrons, and electrons couldn't combine to form atoms. Instead, these particles were in a constant state of frenetic motion due to the immense heat.
In this chaotic environment, photons couldn't travel uninterrupted. They continuously scattered off free electrons, similar to how headlights scatter in thick fog. This scattering process was known as Thomson scattering, dominant in the hot plasma of the early universe. As a result, photons were constantly bouncing around, preventing any direct line of sight through the universe.
It wasn't until the universe cooled down, and electrons and protons combined to form neutral hydrogen atoms, that the scattering ceased significantly. This allowed photons to travel freely across the universe, giving rise to the Cosmic Microwave Background Radiation (CMBR) – the afterglow of the Big Bang that we can observe today.

The early universe was a bustling mix of fundamental particles. Right after the Big Bang, the universe was in a state of extreme energy and density. This period saw the presence and creation of elementary particles like quarks, gluons, protons, neutrons, and electrons.
At such high temperatures, quarks and gluons formed a quark-gluon plasma. As the universe expanded and cooled, these particles combined to form heavier particles such as protons and neutrons. Neutrons and protons further combined during nucleosynthesis to create the first light elements, such as hydrogen, helium, and lithium.
These particles were in a constant state of interaction because the temperature was high enough to keep them energetic. Photons, the particles of light, also existed but were forever interacting with free electrons. This state of constant interaction is why the early universe was not transparent.
Once the universe cooled down enough, electrons and protons combined to form neutral atoms, allowing photons to travel freely and the universe to become transparent. This transition marked the beginning of a universe we can observe through various cosmic signals, such as the light from distant stars and galaxies.