📚 Cosmology Key Points for IB WJEC Physics | 宇宙学考点精讲
Cosmology is the study of the origin, evolution, and eventual fate of the universe. It combines Einstein’s general relativity with particle physics to understand the universe on the largest scales. This guide covers the essential concepts and exam-relevant points for IB and WJEC Physics students, including expansion, redshift, the Big Bang, cosmic microwave background, dark matter and dark energy.
宇宙学是研究宇宙起源、演化和最终命运的科学。它结合爱因斯坦的广义相对论与粒子物理学来理解最大尺度上的宇宙。本指南涵盖IB和WJEC物理学生必须掌握的核心概念与考点，包括宇宙膨胀、红移、大爆炸、宇宙微波背景辐射、暗物质与暗能量。
1. Introduction to Cosmology | 宇宙学简介
Cosmology deals with the large-scale structure and dynamics of the universe. The cosmological principle states that on sufficiently large scales (greater than about 100 Mpc), the universe is homogeneous (same density everywhere) and isotropic (looks the same in all directions). This assumption simplifies the mathematical models and implies that there is no preferred centre to the universe.
宇宙学研究宇宙的大尺度结构和动力学。宇宙学原理指出，在足够大的尺度上（大于约100 Mpc），宇宙是均匀的（各处密度相同）和各向同性的（各个方向看起来一样）。这一假定简化了数学模型，并意味着宇宙没有特别中心。
The scale factor a(t) describes how distances in the universe change with time. By convention a = 1 today, and a was smaller in the past. This is crucial for understanding redshift and the expansion history.
尺度因子a(t)描述宇宙中的距离如何随时间变化。通常规定今天的a = 1，过去的a更小。这对于理解红移和膨胀历史至关重要。
2. The Expanding Universe and Hubble’s Law | 宇宙膨胀
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