Section 1.1 The Birth of Special Relativity

The Michelson-Morley experiment laid the groundwork for Einstein's theory of Special Relativity, which posits that light's speed is the same for all observers, regardless of their motion. This insight led Einstein to construct his renowned Gedankenexperiment, or thought experiment, positing that a stationary observer would record different measurements than a moving observer.

In mathematical terms, this difference can be expressed using the Lorentz factor. When the velocity (v) is small, the formula approximates to 1, meaning there is little difference in measurements between stationary and slowly moving observers. However, as speed increases, the distinction grows more pronounced. For instance, at 0.86 times the speed of light, the Lorentz factor is 1.96. Thus, while we don’t notice relativistic effects in our daily lives, they become significant at speeds approaching that of light.

The Lorentz factor also explains why light speed serves as the universal speed limit. If an object were to reach light speed, the equations would become undefined, indicating that only mass-bearing objects can approach, but never reach, light speed.

After establishing Special Relativity, Einstein expanded his research into General Relativity, which considers acceleration. In this framework, the differences in measurements between two observers are influenced by their relative acceleration, visualized as a distortion of four-dimensional spacetime. Gravity, as an accelerating force, can also be viewed as a curvature of spacetime, suggesting that massive objects warp the surrounding space and create the illusion of gravitational attraction.

Section 1.2 The Expanding Universe

Utilizing General Relativity, Alexander Friedmann demonstrated that the universe is indeed expanding. Edwin Hubble's observations of light from distant galaxies confirmed this, revealing redshift—the stretching of light waves, indicating that galaxies are moving away from us.

Hubble made a groundbreaking discovery that not only were galaxies receding, but they were doing so at accelerating speeds. He concluded that, beyond a certain distance, galaxies would surpass light speed. While light emitted from a galaxy could eventually reach us, any light emitted after that galaxy surpassed light speed would remain forever beyond our reach. This creates a cosmic event horizon beyond which information is irretrievable.

Neil DeGrasse Tyson has expressed concern over this phenomenon, pondering what other structures in the universe might remain unseen due to this cosmic barrier. In an interview with Stephen Colbert, he remarked that future cosmic explorers may only have the stars of the Milky Way to contemplate, leaving many chapters of the universe unreadable.

Big Rip: The Fate of the Universe

While galaxies receding faster than light may seem contradictory to the universal speed limit, they do not violate it. The speed limit pertains to movement through space, not the expansion of space itself. Simply put, the space between us and distant galaxies expands more rapidly than light can travel.

The force driving this expansion is referred to as dark energy, a concept that remains poorly understood. Dark energy compels every point in the universe to expand, causing a cascade effect as more space leads to even more expansion.

Currently, gravity is sufficient to maintain the integrity of matter, allowing galaxies, stars, and planets to exist. However, if this acceleration continues, fundamental forces may eventually be overwhelmed, leading to a scenario where even subatomic particles are torn apart. This scenario is termed the Big Rip, resulting in a universe devoid of any structure, ultimately becoming an infinitely stretched void.

Is this truly how the universe will meet its end? It is uncertain. There is a possibility that dark energy might weaken, slowing the expansion and allowing gravity to reclaim dominance, resulting in a Big Crunch and a potential new Big Bang. However, as it stands, the universe appears to be heading towards a gradual fading rather than a dramatic end.

The first video titled "Will the BIG RIP Destroy the Universe?" explores the implications of dark energy on cosmic expansion and the potential fate of our universe.

The second video "Could the Universe End by Tearing Apart Every Atom?" examines the consequences of the Big Rip and the theoretical limits of cosmic destruction.

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Originally published at http://thehappyneuron.com on December 31, 2020.