Mr Palmer's AQA GCSE Physics Notes
Origin of the Universe
The Incomprehensible Scale of it All
Planets orbit stars. There may be none to dozens of planets orbiting one star. The entirety of human civilisation lives on one planet, Earth. It is also the only planet we know of that definitely has life.
Stars, like our sun, are hundreds to thousands of times larger than planets. Stars orbit the centre of their galaxy.
All stars (except our sun) are many light years away. A light year is the distance light travels in one year. This is about 9,500,000,000,000,000 meters.
A galaxy will contain several million stars within it. Each star may have many planets orbiting it. However, the stars in a galaxy are so far from each other that galaxies can pass through each other without a single star or planet crashing into another one. Our galaxy is called the Milky Way and is about 100,000 light years in size.
The observable universe
The Universe has at least one billion galaxies within it. Each galaxy has millions of stars and each star may have many planets orbiting it. The galaxies are many many times further from each other than the stars within them are from each other. The universe is at least 78,000,000,000 light years in size, but probably much larger.
Telescopes
Optical telescopes use lenses much larger than the lens in the human eye. As such, they are able to collect much more light and make the stars appear brighter. The correct combination of lenses is also able to magnify the size of the image.
Visible light is only a small part of the electromagnetic spectrum and the other parts can be used to make observations as well.
Earth's atmosphere interferes with scientists on the ground trying to make observations of space. Weather and clouds can block the view. But even on a clear night the atmosphere still scatters the light from distant objects and makes them appear blurry. Because of this, scientists prefer to put telescopes, such as the Hubble, in space when possible.
X-rays and infra red light are absorbed by Earth's atmosphere so telescopes that wish to view this portion of the electromagnetic spectrum must be placed outside of the Earth.
Radio telescopes collect radio waves from objects to form an image. Radio waves have the advantage that they are unaffected by Earth's atmosphere so the telescopes can be ground based. Radio wave telescopes are also used to search for intelligent life elsewhere in the Universe, such as in the S.E.T.I. project.
The Big Bang
When an object is moving at extremely high speeds (near the speed of light) the colour that the object appears to be changes. If the object is moving at high speeds toward you then its colours will become more blue; this is called blue shift. If the object is moving at high speeds away from you then its colours will become more red; this is called red shift.
This shift in colour happens because when the object emitting the light is travelling toward you, the lights wavelength becomes shorter and the frequency increases. When the object is travelling away from you, the light's wavelength becomes longer and the frequency slower.
When scientists observe galaxies, they see that the light given off is more red than expected. The light is red shifted so the galaxies are moving away from us. More strangely, the further away a galaxy is the more red shifted its light, meaning that it is moving away faster. The conclusion drawn from this observation is that we live in an expanding universe.
This leads scientists to their current model of the formation of the Universe: the big bang. If the Universe is expanding and the galaxies are getting further apart, then in the past they must have been closer together. Therefore, at the beginning of time, the entire Universe must have existed in a single point and expanded since then to its current size.
There are two ways the Universe may end:
- If there isn't enough matter in the Universe the force of gravity is too weak to hold the Universe together and it will keep expanding forever. The galaxies and stars will get further apart and eventually all the useful energy will turn into useless heat. This is called the heat death of the Universe.
- If there is enough matter, the force of gravity will start to pull the Universe back on itself and it will shrink back to a point. This is called the big crunch.
Physics P1 Topics
Physics P2 Topics
- Motion
- Forces
- Energy
- Static Electricity
- Current Electricity
- Mains Electricity
- Momentum
- Nuclear Physics
Other