Your roommate is writing a science-fiction novel set very far in the future, 60 Gy after the Big Bang. One of the characters is a cosmologist, and your roommate wants to know what the cosmologist will measure for the Hubble constant. What's your answer, assuming a steady expansion rate?

Cosmology is the scientific study of the origin, evolution, and eventual fate of the universe. It delves into theories and observations related to the universe's large-scale properties and its dynamic behavior over time. One of the key roles cosmology plays is in the understanding of heavenly bodies and their movements, the cosmic microwave background, and the large-scale structure of the universe.

The study of cosmology has been revolutionized by modern scientific approaches, including both observational and theoretical physics. For instance, through the use of powerful telescopes and satellites, astronomers have mapped out the intricate fabric of the cosmos on scales well beyond our Milky Way galaxy.

As students explore cosmology, they encounter complex phenomena such as dark matter, dark energy, and the Hubble constant—all fundamental in grasping the vastness and the mechanics of the cosmos. Incorporating the latest findings in cosmology into educational content helps students stay informed about the most up-to-date understanding of our universe's grand narrative.

The expansion of the universe is a monumental concept in which the fabric of spacetime itself is stretching, causing galaxies and other celestial bodies to move away from each other. This notion is directly tied to the Hubble constant, which describes the rate at which the universe is expanding.

When the Hubble constant is determined at any point in time, it gives us a rate: typically expressed in kilometers per second per megaparsec (km/s/Mpc). This means that for each megaparsec (approximately 3.26 million light-years) of distance between two objects, the apparent velocity with which one is receding from the other increases by a certain number of kilometers per second.

For educational clarity, imagine marking two dots on the surface of an uninflated balloon—these represent galaxies. As the balloon inflates (expands), the dots move apart even though they are not moving of their own accord—the space between them is what's expanding. This analogy helps students conceptualize how the universe's expansion works on a vastly larger scale, with the Hubble constant serving as a key parameter quantifying this expansion rate.

The Big Bang theory presents the widely accepted explanation for the beginning of the universe, positing that it all started with a singular dense and hot point approximately 13.8 billion years ago. This initial explosion set forth the expansion of the universe that continues to this day.

Following the Big Bang, the universe was a hot, dense soup of particles. As it expanded, it cooled, allowing for the formation of subatomic particles, and later, simple atoms. Massive clouds of these primordial elements later coalesced under gravity, forming stars and galaxies. The Big Bang is also responsible for the cosmic microwave background radiation, which is the afterglow of the initial explosion and a key piece of evidence supporting the model.

Educators strive to simplify this concept by breaking down the sequence of events into more digestible steps and reinforcing the observational evidence that backs the theory, such as the cosmic microwave background radiation, the abundance of light elements, and the large-scale structure of the universe we observe today. By understanding the Big Bang theory, students gain a critical perspective on the early universe's conditions and the events that led to its current state.