The Scale of the Universe
The universe is vast and complex, with structures ranging from planets to superclusters stretching over millions of light years. It may seem chaotic and random, but it is actually organized and structured, with opposing forces of expansion and gravity shaping the large-scale structure of the universe.
Our Cosmic Address
The Earth is just one planet among many, orbiting a random star. This realization, known as the Copernican principle, marked a larger revelation that we are not special and opened up a world of possibilities for discovery. The cosmic microwave background (CMB) is a fuzzy background static that permeates the sky and is indicative of the relative uniformity of the universe. However, there are also structures such as galaxies, superclusters, and voids that demonstrate the large-scale structure of the universe.
Opposing Forces: Expansion and Gravity
The universe underwent three phases of expansion, with the first phase being extreme and caused by the mysterious inflaton field. The second phase lasted several billion years, during which the universe cooled down and expanded at a more reasonable rate. In the third phase, expansion has accelerated again due to the mysterious energy known as dark energy. Gravity has been battling against the quickening expansion, causing over densities to attract more matter and become more massive.
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The Structure of the Universe
The universe is a vast expanse of matter and energy that has been expanding since the Big Bang. Gravity plays a crucial role in shaping the structure of the universe as matter clumps together to form stars, galaxies, and clusters.
Space telescopes, such as the Cosmic Background Explorer (COBE), Wilkinson Microwave and Isotropy Probe (WMAP), and Planck satellite, have mapped tiny variations in the cosmic microwave background radiation, revealing small fluctuations in the early universe that were stretched out by expansion and clumped by gravity to form the structures we see today.
On Earth, telescopes like the Sloan Digital Sky Survey create maps of the universe by drilling aluminum plates with precise holes for each star or astronomical object in an image, then running fiber optic cables from each hole to spectrographs to determine their distance and motion. These maps reveal vast structures like our local supercluster, the Virgo Supercluster, the Perseus-Pisces Supercluster, and the South Pole Wall, stretching across billions of light years.
A recent discovery, the Giant Ark, challenges our assumptions about the universe on the largest scales, spanning 3.1 billion light years.
Meatballs, Pancakes, and Sponges
Cosmologists have long debated the structure of the universe. American cosmologists like Jim Peebles believe that matter clumps together like meatballs in a low-density soup, while Russian cosmologists like Yakov Zeldevich propose a pancake model where the density in the universe is organized in 2D pancakes, with galaxies forming where the pancakes overlap.
English astronomer Martin Reese acted as a mediator between the two schools and developed a new theory that better matches observations. Richard Gott, Reese's postdoc, developed the sponge theory, which lies conceptually between meatballs and pancakes. In this model, high and low-density regions are connected and complementary, forming a sponge-like structure.
The End of Greatness
As telescopes have seen further and further back in time with increasing detail, a phenomena known as the end of greatness has been observed at around a billion light years, where the universe becomes homogeneous.
