Final answer:
We have learned that particles comprising warmer and cooler matter differ in their average velocities, with hot and cold dark matter particles moving fast and slow, respectively. The universe's expansion and cooling led to the formation of various particles and elements, with dark matter playing a crucial role in galaxy formation. CMB measurements further help us understand the universe's composition and age.
Step-by-step explanation:
The particles that make up warmer and cooler matter behave differently due to their average velocities. When we discuss 'hot' and 'cold' dark matter in an astronomical context, these terms do not refer to temperature in the traditional sense; instead, they denote the average speed at which these particles move. Hot dark matter consists of particles that move at high velocities, analogous to the faster-moving particles you would find in a heated room as compared to a cooler one. Conversely, cold dark matter particles move more slowly and are compared to the slower-moving particles in a colder environment.
In the context of the Big Bang theory, as the universe cooled and expanded, there was a specific sequence for the formation of particles and elements. Protons and neutrons formed first, followed by electrons and positrons, with fusion reactions then producing nuclei such as deuterium, helium, and lithium. Measurements of deuterium abundance provide evidence that ordinary matter represents only about 5% of the universe's critical density. The remaining mass is speculated to be dark matter, which includes theorized particles like WIMPs (weakly interacting massive particles) yet to be detected in laboratory experiments.
One crucial aspect derived from studying the Cosmic Microwave Background (CMB) is understanding the universe's composition. It has revealed insight into large-scale structures and the age of the universe at 13.8 billion years, while suggesting that dark matter plays a pivotal role in galaxy formation. Cold dark matter, moving slowly, is theorized to have facilitated the creation of gravitational traps aiding the rapid condensation of ordinary matter, leading to the formation of galaxies in the relatively young universe.