Chapter 1: The Mystery of the Universe's Composition

What remains hidden in the vast 95% of the universe that scientists struggle to observe?

Recent calculations reveal that the mass of all detectable matter in the universe constitutes a mere 5%. This raises an intriguing question: what occupies the remaining 95%? The visible universe encompasses everything from our planet Earth to the sun, stars, and galaxies, which are made up of protons, neutrons, and electrons. Collectively, this ordinary matter accounts for just 5% of the universe's total mass. Scientists propose that the leftover mass is divided into dark matter, making up about 25%, and dark energy, which comprises roughly 70%. But what exactly are these enigmatic substances?

Section 1.1: Exploring Dark Matter

Dark matter remains a profound enigma for researchers. It evades detection by current technology, as it does not emit light or interact with electromagnetic radiation. Despite its invisibility, scientists are confident in its existence, as the gravitational effects of dark matter can be observed in the movements of galaxies and galaxy clusters.

Researchers are actively studying the composition of dark matter. Since the observable universe is predominantly made of baryonic matter, it’s theorized that dark matter consists of non-baryonic particles. Several candidates have emerged in the search for dark matter's true nature.

Subsection 1.1.1: Candidates for Dark Matter

Weakly Interacting Massive Particles (WIMPs) are among the leading contenders for dark matter. These particles possess a mass 10 to 100 times that of a proton but remain elusive due to their weak interactions with baryonic matter.

Another possibility is sterile neutrinos, which do not contribute to baryonic matter. Among the various types of neutrinos, sterile neutrinos are theorized to interact with baryonic matter solely through gravity.

Neutralinos are another potential component of dark matter. They are heavier and move slower than neutrinos, yet they have yet to be detected.

Some scientists propose that dark matter may be characterized by these exotic particles, while others suggest that revising our understanding of gravity might explain its behavior—an abstract concept suggesting multiple forms of gravity might operate differently across the universe.

Chapter 2: Unraveling Dark Energy

The first video titled "The Astronomers: Where is the Rest of the Universe?" delves into the elusive components of the cosmos, highlighting the dark matter and dark energy that dominate the universe.

Dark energy, an even more puzzling phenomenon than dark matter, was only identified in the 1990s. This discovery significantly altered our understanding of cosmic dynamics. Prior to its identification, scientists believed gravity was slowing the universe's expansion. However, measurements revealed that this expansion is, in fact, accelerating.

What is particularly fascinating is that the universe's expansion was indeed decelerating for approximately seven to eight billion years post-Big Bang. At an unknown point, a force identified as dark energy overcame gravity's influence, resulting in the current acceleration.

Researchers attribute this acceleration to dark energy, which appears to be increasing in strength as the universe expands. Nevertheless, our understanding of dark energy is considerably less robust than that of dark matter. One theory posits that dark energy could be a fundamental force known as quintessence, which permeates the universe much like water fills a container.

Cosmologists remain uncertain about whether dark energy will continue to accelerate the universe's expansion, which might lead to a scenario known as the Big Rip, where all cosmic forces could eventually tear the universe apart.

What we currently know about dark matter and dark energy underscores the vast unknowns of our universe. While we grasp the processes that have shaped its evolution, the future of the cosmos remains a mystery. The hypotheses surrounding dark matter and dark energy offer promising avenues for research, yet the journey to fully comprehend the universe's true nature is just beginning.

The second video titled "A Journey to the End of the Universe" takes viewers on an exploration of cosmic mysteries, emphasizing the significant role dark matter and dark energy play in shaping the universe.