Ancient Greek universe view: Adhering to the idea that the earth is the center of the universe, for example, Aristotle believed that the earth was still and that celestial bodies were moving around it in a circular motion. This concept was influenced by the limitations of observation methods and philosophical thoughts at that time.

Geocentric theory: The Ptolemy system elaborates on constructing a complex round-round-round model to explain the seemingly irregular motion trajectory of celestial bodies. This model was widely accepted at the time and dominated the astronomy community for a long time.

Heliocentric theory: Copernicus proposed to break the long-term rule of the geocentric theory, pointing out that the sun is the center of the universe, and the earth and other planets orbit the sun. This theory triggered an astronomical revolution and embarked on a new journey of scientific exploration of the universe.

Modern cosmology's understanding of the universe: Based on a large number of observations and scientific theories, it believes that the universe is constantly evolving, developing from the early hot and high-density states to the present, and includes many galaxies, stars, planets, as well as mysterious dark matter and dark energy.

Light-year: defined as the distance from which light travels in a vacuum for one year, about 9.46 trillion kilometers. It is an important unit for measuring the distance between celestial bodies in the universe and helping people understand the scale of the vast universe.

The role of telescopes: From the initial simple optical telescopes to today's radio telescopes, space telescopes, etc., it greatly expands the human vision of observing the universe. It can capture light from more distant celestial bodies and analyze information such as chemical composition, temperature, and motion state of celestial bodies.

Classification and distribution of galaxies: Galaxy is divided into spiral galaxies, elliptical galaxies, irregular galaxies, etc. according to their shape. They are not uniformly distributed in the universe, but gather to form galaxy clusters and supergalaxy clusters, presenting complex large-scale structures.

The size and structure of the universe: The diameter of the universe can be observed is about 93 billion light years, and contains hundreds of billions of galaxies. The overall structure of the universe is considered to be flat and infinitely extended, with various levels of material aggregation and hollow areas.

Big Bang Theory: The core point is that the universe originates from a singularity explosion with extremely high temperature and extremely dense density. At the moment of explosion, huge energy and matter were released, and then the universe expanded while cooling, and matter gradually gathered to form celestial bodies such as stars and planets.

The evolution process of the universe: Starting from the Planck period after the Big Bang, it went through the Hadron Age, Lepton Age, Nuclear Synthesis Age, Photon Age, and until neutral atoms were formed, the universe became transparent, and then the gravitational action prompted the accumulation of matter. Galaxy and stars.

Cosmic microwave background radiation: The "afterglow" of the Big Bang is a weak electromagnetic radiation evenly distributed in the universe with a temperature of about 2.725K. Its spectrum has thermal radiation characteristics. This discovery provides key evidence for the Big Bang theory.

The principle of constant speed of light: No matter how the light source moves between the light source and the observer, the speed of light in the vacuum is always constant, about 299792458m/s. This principle subverts the traditional concept of superposition of speed.

Principle of relativity: The laws of physics have the same form in all inertial reference systems, and there is no absolute static reference system, and all motion descriptions are relative to specific reference systems.

Lorentz Transformation: Based on the principle of invariant speed of light and relativity, it describes the transformation relationship between time and spatial coordinates between different inertial reference systems, and corrects the concept of independence of time and space in Newton's classical mechanics.

Relativity between time and space: the time lapse of moving objects slows down (time expansion), and the length shortens along the direction of movement (length contracts), which becomes more significant when the object moves at a speed close to the speed of light.

Space-time chart and light cone: The space-time chart uses time as the vertical axis and space as the horizontal axis to visually display the position and relationship of events in space-time. The light cone represents the trajectory of light propagation in space and time, divides space and time into past, present and future areas, revealing the space and time limitations of causal relationship.

Equivalence principle: locally, the gravitational field is equivalent to the inertial force in the accelerated reference system, that is, a reference system in a free-fall body and an inertial system without a gravitational field cannot be distinguished locally.

Gravity and space-time bending: Einstein believes that gravity is not a force in the traditional sense, but a manifestation of mass and energy bending space-time. Objects move along geodesics in curved space-time, just like being affected by gravity, such as the mass of the sun flexing the surrounding space-time, causing the planet to move along an elliptical orbit.

The formation and characteristics of black holes: When the fuel of a large-scale star is exhausted and collapses to a certain level, the gravity is so strong that even light cannot escape, a black hole is formed. Black holes have an event horizon, and matter and information entering the horizon cannot escape, and their mass is highly concentrated at the central singularity.

Gravitational lens effect: When light passes near a large-scale celestial body, it deflects due to time and space bending, just like passing through a lens. This effect can cause distorted, amplified or multiple images of distant celestial imaging, helping astronomers observe more distant and darker celestial objects.

Characteristics of quantum: There is a minimum indivisible unit of physical quantum, that is, quantum. For example, energy quantization, the energy of microscopic particles can only take a specific discrete value, rather than a continuous change.

Wave-particle duality: Microscopic particles not only show particle characteristics, such as having a certain position and momentum; they also have fluctuations, which can produce fluctuations such as interference and diffraction. For example, electrons will experience interference fringes through double-slit experiments.

The principle of uncertainty: Heisenberg proposed that the position and momentum of a particle cannot be accurately measured at the same time. The more precisely one quantity is measured, the greater the uncertainty of the other quantity, which is the basic limitation of quantum mechanics.

Quantum states and quantum entanglement: Quantum states describe the state of microscopic particles, which can be in superposition states, that is, in multiple states at the same time. Quantum entanglement is the correlation between multiple particles. Even if they are separated from each other from a long distance, the measurement of one of the particles will instantly affect the state of other entangled particles. Einstein called it "ghostly super-distance effect."

Quantum origins of the universe: In the very early days of the universe, quantum effects played a leading role. Some theory believes that the universe may originate from quantum fluctuations, producing slight fluctuations of energy and matter from nothingness, and then rapidly expands through the surge mechanism to form the current universe.

Quantum fluctuations and the formation of cosmic structure: Quantum fluctuations in the early universe were amplified during the expansion of the universe and became seeds with uneven density of matter. Under the action of gravity, these slightly higher density areas gradually attract more matter, forming cosmic structures such as stars, galaxies and galaxy clusters.

Hawking radiation and the evaporation of black holes: Hawking proposed that black holes are not completely "black". Virtual particle pairs will be generated due to quantum fluctuations near its event horizon. One particle falls into the black hole and the other particle escapes, forming Hawking radiation. This causes the black hole to gradually decrease in its mass and may eventually evaporate and disappear.

Directionality of time: In daily life, time shows a clear one-way flow, flowing from the past to the future. People can remember the past rather than the future. Various physical processes are also directed, such as heat transfer from high-temperature objects to low-temperature objects.

The difference between the past and the future: The past events are determined and unchangeable, and the future is uncertain. In physics, the past and future states are distinguished by physical quantities such as entropy, and the system state evolves in a specific direction over time.

The second law of thermodynamics: Clausius said that heat cannot be spontaneously transmitted from low-temperature objects to high-temperature objects; Kelvin said that it is impossible to absorb heat from a single heat source, so that it becomes completely useful without causing other effects. The above shows that the entropy of an isolated system always tends to increase.

Entropy increase principle: Entropy is used to measure the degree of disorder in a system. Over time, the entropy of an isolated system continues to increase, from order to disorder. For example, if the room is not sorted out, it will become more and more messy, which reflects the close connection between the time arrow and the increase in entropy.

The theory of the heat silence of the universe: Based on the principle of entropy increase, if the universe is an isolated system, as time goes by, all energy will be evenly distributed, entropy reaches the maximum value, the universe falls into a state of thermal equilibrium, that is, thermal silence, and all macroscopic movements stop. This is A pessimistic idea of ​​the future of the universe.

The relationship between time arrows and the evolution of the universe: The universe evolved from a low-entropy and highly ordered state in the early stages of the Big Bang. As the distribution of matter gradually became even, the entropy continued to increase, pushing the universe to develop into a more disordered state. This process is related to the direction of time arrows Consistent, the time arrow becomes an inherent manifestation of the evolution of the universe.

Definition of a black hole: A celestial body with huge mass collapses under its own gravity, forming an area with extremely strong gravity. Its boundary is called the event horizon. Any matter, including light, cannot escape once it enters the event horizon.

The horizon of a black hole: The event horizon is the boundary of a black hole. It is a one-way film where light and matter can only enter but not leave. Its radius (Schwarsey radius) is proportional to the mass of the black hole. The larger the mass, the larger the horizon range.

Mass and density of black holes: The mass of a black hole can range from several times the mass of the sun to billions of times the mass of the sun. Because its mass is concentrated at extremely small singularities, the density is extremely high, such as the density of stellar black holes can reach hundreds of millions of tons per cubic centimeter.

The hairless theorem of black holes: No matter how complex the initial state of matter that forms a black hole, the black hole is ultimately completely determined by only the three parameters of mass, charge and angular momentum, just like losing all other "hair" characteristics.

The concept of wormholes: proposed by Einstein and Rosen, also known as the Einstein-Rosen Bridge, is a narrow tunnel connecting two different space-time areas in the universe, which can achieve ultra-long-distance time and space travel.

The space-time structure of wormholes: The wormhole has a special space-time curved structure, with two ends located at different space-time points and narrow channels in the middle. Theoretically, if the wormhole can be maintained stably, the spacecraft can reach a distant destination in an instant through it.

The relationship between wormholes and time travel: Since wormholes connect different time and space, it may provide the possibility of time travel. If you travel through the wormhole to the past, it may trigger a paradox of causality, such as the grandfather’s paradox. There is no conclusion on the feasibility of time travel and how to avoid it.

The rate of expansion of the universe: Through observations of distant galaxies, the universe is expanding continuously, and recent studies have shown that this expansion is accelerating. Astronomers determine the rate of expansion of the universe, namely the Hubble constant, by measuring the relationship between the galaxy's descent speed and distance (Hubble's Law).

The role of dark matter and dark energy: dark matter does not emit light or interact with light, but has gravitational effects, accounting for about 85% of the total amount of cosmic matter. It plays a key role in the formation and stability of galaxies and galaxy clusters. Dark energy has negative pressure, which is believed to be the reason for the accelerated expansion of the universe, accounting for about 68% of the total energy of the universe, but its essence remains one of the biggest mysteries in cosmology.

The ultimate destination of the universe: Based on the current trend of the universe's expansion, there may be several outcomes. If dark energy continues to dominate, the universe will continue to expand at an accelerated pace, galaxies and stars will gradually move away, and eventually enter a state of large tear, and all matter will be torn into elementary particles; if the density of the universe is large enough, gravity may eventually defeat expansion, and the universe will shrink. It triggers a large squeeze and returns to a high-density state similar to that before the big explosion.

Human exploration of the universe: from observing the starry sky with the naked eye in ancient times, to now using various advanced astronomical telescopes and detectors to penetrate the universe. Human beings are constantly breaking through cognitive boundaries and exploring the origin, evolution and the mysteries of life, such as the detection of planets in the solar system and the search for exoplanets.

Possibility of alien life: Considering the huge number of stars and planets in the universe and the existence of a habitable environment similar to the earth, many scientists believe that alien life is likely to exist. From simple microorganisms to intelligent life, humans have been searching for alien civilization signals through radio telescopes, such as the SETI program.

The relationship between the future development of mankind and the universe: The evolution of the universe and the environment profoundly affect the future of mankind. On the one hand, the earth may face threats of cosmic events such as asteroid impacts and solar evolution; on the other hand, humans' ideas on the development and utilization of cosmic resources and interstellar immigration may change the fate of mankind, promote human beings to become interstellar species, and move towards a broader cosmic space. .