The scale of the universe is truly astonishing. Take our familiar Milky Way, for example, with a diameter of about 100,000 light-years, containing billions of stars and countless planets. And within the universe are countless galaxies similar to the Milky Way, each containing hundreds of millions of stars and planets.
As our vision extends, we can witness even larger cosmic structures. Galaxy clusters are colossal structures consisting of hundreds, or even thousands, of galaxies spanning millions of light-years. These superclusters are interconnected through the “large-scale structure” of cosmic filaments, forming a gigantic cosmic web.
In the universe, there are various types of galaxies, stars, and planets. Some galaxies have spiral structures, while others have regular spherical structures. Image: Zhihu
Beyond their immense scale, the mass within the universe is also unimaginable. Stars are the basic building blocks of the universe and combine to form star clusters, nebulae, and galaxies. However, the mass of stars is relatively insignificant. Scientists have discovered massive star explosions, supernovae, releasing more energy than all the stars in an entire galaxy combined.
Furthermore, there exists the mysterious and awe-inspiring presence of black holes in the universe. Black holes are extremely dense and compact celestial objects, often weighing several, or even millions, of times more than a star. Their gravitational pull is so intense that not even light can escape. When any matter comes close to a black hole, it is devoured by the relentless gravitational force.
Yet, even the vastness in size and mass of the universe pales in comparison to the universe’s timescale. The age of the universe is approximately 13.8 billion years, which is almost insignificant compared to the colossal spatial expanse. Galaxies and nebulae in the universe took hundreds of millions of years to evolve into the scenes we observe today.
The universe is a vast and enigmatic existence, filled with countless wonders and mysteries, constantly perplexing humanity’s quest for understanding. With technological advancements and the development of scientific theories, we are beginning to realize that the universe may not only exist in three-dimensional space but could also extend into curved spacetime and parallel universes.
Dark matter and dark energy are currently significant puzzles that scientists are exploring. They do not have direct perception of mass and energy but influence the universe’s evolution through gravitational effects. Image: Zhihu
In traditional geometry, space is often considered flat, but in reality, according to Einstein’s theory of general relativity, space can be curved due to the presence of mass and energy, causing gravitational curvature. We commonly use Einstein’s famous field equations to describe this phenomenon, where the presence of mass and energy affects the properties of spacetime. It suggests that the curvature of spacetime serves as the foundation for the marvels of the universe.
One prevalent form of spacetime curvature is the presence of gravity. Newtonian physics proposed that gravity is caused by mass attracting other objects, but in Einstein’s theory of general relativity, gravity is essentially the curvature of spacetime caused by mass and energy. This existence of spacetime curvature makes objects subject to the force of gravity. For example, the curvature of spacetime around Earth causes objects to be drawn in by Earth’s gravitational pull.
Meanwhile, parallel universes are other universes coexisting alongside our universe. According to the multiverse theory of quantum mechanics, whenever an event occurs, the universe splits and gives rise to numerous parallel universes. These parallel universes may share similar physical laws and atomic particles with our universe but could have subtle or even entirely different laws of physics and entities.
The concept of parallel universes is fascinating. It implies that there could be countless versions of the universe, each with different histories and futures. For instance, in a parallel universe, you might have chosen a different career or pursued a different dream. This idea is not only intriguing but also encourages scientists to delve deeper into its exploration.
The vastness of the universe is beyond imagination, like a sky full of endless stars. From a scientific perspective, we know that the universe is boundless, without borders, and without an endpoint.
Our Earth is just an insignificant point in the universe, or more accurately, just a speck of dust in the universe. The galaxies, stars, and planets within the universe are immensely vast and countless. It’s astonishing how these galaxies and stars are separated by such vast distances, leaving us in awe of the universe’s vastness.