PHYSICS · Stage 9 · Chapter 15: The Earth in Space (Universe and Stars)
Physics 15.1 The origin of the Universe — Galaxy Redshift and the Big Bang Theory
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Lesson summary
Physics 15.1 The origin of the Universe — Galaxy Redshift and the Big Bang Theory — Alhussan International Academy — Physics (Stages 7–9) notes: Give the approximate age of the Universe, describe the Big Bang theory and its evidence and compare the time humans have lived with the…
- Observation
- Not special
- Rapid growth
- First animals
- Comparison
- Why uncertain
Section 1 of 7Galaxies moving apart
- Observation
- an astronomer looking at galaxies in the night sky works out that they are all moving away from the Earth
- Not special
- the Earth is not special and is not the centre of the Universe, because every galaxy is moving away from every other galaxy
- Cause
- the space in between all galaxies is expanding
- Andromeda
- there is nothing special about our galaxy, the Milky Way
- If we lived in the Andromeda galaxy it would still appear that all the other galaxies, including the Milky Way, were moving away from us.
Section 2 of 7Evidence for the Big Bang
- 1920s
- astronomers used telescopes to measure how fast galaxies are moving and how far away they are
- Pattern
- the further away the galaxies were, the faster they were moving
- Theory
- scientists used this evidence to develop an explanation called the Big Bang
- Purpose
- it is an idea that explains observations and predicts what might happen in the future
Section 3 of 7The Big Bang theory
- Age
- the Universe began about 14 billion years ago
- Beginning
- the whole Universe expanded from something smaller than an atom and hotter than anything we can imagine
- Rapid growth
- in a fraction of a second the Universe grew to the size of a galaxy, and it has continued to expand ever since
- Cooling
- as it expanded it cooled, and energy changed into particles, making atoms and molecules of hydrogen and helium
- Structure
- eventually there were stars, planets, moons and galaxies, and the Universe we see today
Section 4 of 7Stages in the history of the Universe
| Age of the Universe | Temperature | Stage |
|---|---|---|
| 0 | 10 billion °C | Big Bang |
| 300 000 years | 6000 °C | Atoms and molecules formed |
| 1 billion years | −250 °C | First galaxies |
| 12–15 billion years | −270 °C | Modern Universe |
Section 5 of 7A timeline for the Universe
| Event | Time ago (years) |
|---|---|
| Big Bang | 13 700 million |
| Solar System formed | 5000 million |
| Earth cooled | 4200 million |
| First life | 3900 million |
| Oldest remaining rock | 3600 million |
| Multicellular organisms | 3000 million |
| Animals with shells | 630 million |
| First land plants | 550 million |
| Dinosaurs exist | 200 million |
| Dinosaurs died out | 66 million |
| Humans exist | 0.5 million |
Section 6 of 7The 24-hour analogy
- Analogy = a comparison that makes a timescale easier to picture
- Earth
- if the Universe started 24 hours ago, the Earth would have formed 9 hours ago
- First animals
- they would have appeared about an hour ago
- Humans
- human beings would have existed for less than the time it takes to blink your eyes
- Comparison
- the Earth has existed for a fraction of the time the Universe has existed, and humans for a tiny fraction of the time the Earth has existed
Section 7 of 7The end of the Universe
- Unknown
- no one knows what will happen to the Universe
- Possibilities
- It may expand forever.
- It may expand, and the expansion could get faster.
- Gravity may pull it back in again.
- It may expand to a certain size and stay that way.
- Why uncertain
- to know what will happen we would need to measure the mass of all the objects in the Universe, which is not possible with current technology
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