IGCSE Physics（0625&0972） 已从2023年开始将启用新大纲（2023-2025）。
新增的天体部分，内容比较广泛，涉及了有关地月系、太阳系、恒星及宇宙的各个方面。
今天带大家复习支持Big Bang Theory（宇宙大爆炸）的两大证据（Evidence）。这个知识点的考察考法可以很灵活，可以是选择题，也可以是简短简答题，或者是3分或3分以上的简答题。
先来看新考纲对这两个知识点的要求：
4 Know that redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory
6 Explain that the CMBR was produced shortly after the Universe was formed and that this radiation has been expanded into the microwave region of the electromagnetic spectrum as the Universe expanded
①Red shift 红移
如何解释为什么红移可以作为宇宙大爆炸的证据？
来看样题中的例题：
问题：State and explain what can be deduced from the ‘redshift’ observed by astronomers in the light from all distant galaxies.[3]
答案：
any three from:
- wavelength from distant galaxy is measured/compared with wavelength (of line spectrum) on Earth
- wavelength from distant galaxy is shifted to(wards) red end of spectrum
- distant galaxy is receding OR moving away from the Earth
- evidence that the Universe is expanding
这题共3分，答案从四条中任选3条即可。
Red shift是Doppler effect的其中一种，观察到的wavelength向红光移动，也就是波长增加了。
Red shift意味着distant galaxy在远离地球，并且距离越远的galaxy，远离地球的速度（receding speed）越快。
并且galaxies相互之间也是互相远离的。
这也就说明了宇宙是从一个点（singularity）开始膨胀的，也就是我们说的Big Bang Theory大爆炸理论。
我们再补充两条帮助大家理解这个evidence。
- the further away, the faster the galaxy moves away
- galaxies moving apart from each other implies expansion from a single point or since the Big Bang
②CMBR 宇宙微波背景辐射
如何解释宇宙微波背景辐射可以作为宇宙大爆炸的证据？
来看样题中的例题：
问题：Describe and explain what can be deduced from cosmic microwave background radiation (CMBR).[3]
答案：
any three from:
- microwave radiation is observed at all points in space around the Earth o.w.t.t.e.
- radiation was produced when the Universe was formed
- this radiation has expanded into the microwave region of the electromagnetic spectrum
- this is evidence that the Universe expanded
这题共3分，答案从四条中任选3条即可。
宇宙微波背景辐射在地球周围各个方向、各个点都存在，因此我们叫背景辐射（background radiation）。
这也意味着这些辐射来源于一个点。
在宇宙膨胀的初期，温度较高，因此辐射波长比较短。随着膨胀，宇宙在降温，辐射波长增加。直到膨胀至今，辐射处于微波波段。这也恰恰说明宇宙以前温度很高。
我们补充以下几点来帮助大家理解这个问题。
- CMBR implies all parts of the Universe were in contact a long time ago; or coming from single point or singularity
- wavelength has increased as the universe has expanded; universe was (significantly) hotter long ago
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