Almost 14 billion years ago, our Universe burst into existence in the form of an unimaginably tiny soup of densely packed, searing-hot particles, commonly referred to as “the fireball”. Spacetime has been expanding–and cooling off–from this original brilliant, fiery, glaring state ever since. But what is our Universe made of, and has its composition evolved over time? It is often said that most of our Universe is “missing”, composed as it mostly is of a mysterious substance that we call dark energy. The elusive dark energy is causing our Universe to accelerate in its relentless expansion, and it is generally believed to be a property of Space itself. In August 2017, scientists announced that they now have a new window from which they can study our Universe’s mysterious properties, thanks to an international collaboration of more than 400 scientists called the Dark Energy Survey (DES), that is helping to shed new light on the secretive structure of our mostly 海外升學 missing Cosmos.
On large scales, the entire Universe appears the same wherever we look–displaying a foamy, bubbly appearance, with extremely heavy filaments that braid themselves around each other, weaving a web-like structure that is appropriately called the Cosmic Web. The filaments of the Cosmic Web shine with the fierce fires of a myriad of stars that outline enormous sheets and intertwining braids that host the starlit galaxies of the visible Universe. Immense dark, empty–or almost empty–Voids interrupt this weird, twisting, transparent web-like structure. The Voids contain 海外升學 few galaxies, and this makes them appear to be almost entirely empty. In dramatic contrast, the heavy starry filaments, that compose the Cosmic Web, weave themselves around these dark caverns creating what looks like a convoluted, twisted knot.
We live in a mysterious Universe–most of which we are unable to see. The galaxies, galaxy clusters and superclusters are all imprisoned in halos composed of invisible non-atomic dark matter. This unidentified material knits the heavy filaments of the great Cosmic Web into a remarkable tapestry that extends throughout all of Spacetime. Scientists are almost certain that the dark matter really exists because of its observable gravitational influence on those objects and structures that can be seen–such as stars, galaxies, and clusters and superclusters of galaxies.
The most recent measurements suggest that our Universe is composed of approximately 70% dark energy and 25% dark matter. As of today, the origin and nature of the mysterious dark matter and dark energy remain elusive. A much smaller percentage of our Universe is composed of the badly misnamed “ordinary” atomic matter–the familiar material that composes all of the elements listed in the Periodic Table. “Ordinary matter”–which is really extraordinary stuff–is comparatively scarce in the Cosmos. However, this runt of the Cosmic litter of three is what makes up the stars, planets, moons, people, and all of the rest of the Universe that human beings perceive as familiar. It is also the precious material that allowed life to emerge and evolve in our Universe.
However, the Cosmos may be even more bizarre than we are capable of imagining it to be. Modern scientific cosmology began with Albert Einstein who, in the early decades of the 20th century, applied his theories of Relatively—Special (1905) and General (1915)–to our “Cosmic habitat”. At the start of the 20th century, our Milky Way was believed to be the entire Universe, and it was also thought that the Universe was both static and eternal. However, we now know otherwise.
Our Universe does evolve in Time, and there is much, much more of the vast Cosmos than our own home Galaxy. It is generally thought that the Universe was born about 13.8 billion years ago, when Space itself ripped apart, in an event scientists call the Inflationary Big Bang. At the moment of its mysterious birth, in the smallest fraction of a second, the Universe expanded exponentially to balloon to macroscopic size–beginning as an incredibly tiny Patch that was smaller than a proton. Spacetime has been expanding from this initial brilliant state, and cooling off, ever since. All of the galaxies are drifting away from one another, and our Universe has no center. Indeed, everything is floating away from everything else, as a result of the expansion of Spacetime. The expansion of the Universe is frequently likened to a loaf of leavening raisin bread. The dough expands, taking the raisins along for the ride. The raisins become progressively more widely separated from one another because the dough is expanding.
Georges Henri Joseph Edouard Lemaitre (1894-1966) was a Belgian astronomer, priest, and professor of physics at the Catholic University of Louvain. Lemaitre was one of the first to suggest that our Universe is not static–that it is expanding. He also formulated the theory that would eventually be termed the Big Bang Universe. Lemaitre once commented that “The evolution of the world may be compared to a display of fireworks that has just ended: some few wisps, ashes, and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanished brilliance of the origins of the worlds.”