The Big Bang
Scientists have gathered a lot of evidence and information about the universe. They have used their observations to develop a theory called the Big Bang, which is a concept of I/GCSE physics exam. The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion, and it is still expanding today. This explosion is called the Big Bang, and happened about 13.6 billion years ago
Evidence of the Big Bang
There are two key pieces of evidence for Big Bang theory. These are red shift and the Cosmic Microwave Background radiation.
Red shift
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect. It happens with any wave source that moves relative to an observer.
This happens with light too. Our sun contains helium. We know this because there are black lines in the spectrum of the light from the sun, where helium has absorbed light. These lines form the absorption spectrum for helium.
Spectrum of the sun
When we look at the spectrum of a distant star, the absorption spectrum is there, but the pattern of lines has moved towards the red end of the spectrum, as you can see below.
Spectrum of a distant star
This is called red shift. It is a change in frequency of the position of the lines.
Astronomers have found that the further from us a star is the more its light is red shifted. This tells us that distant galaxies are moving away from us, and that the further a galaxy is the faster it is moving away. Since we cannot assume that we have a special place in the universe this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else. The Big Bang theory says that this expansion started billions of years ago with an explosion.
Telescopes
Optical telescopes
Optical telescopes observe visible light from space. Small ones allow amateurs to view the night sky relatively cheaply but there are very large optical telescopes sited around the world for professional astronomers to use.
Optical telescopes on the ground have some disadvantages:
- they can only be used at night
- they cannot be used if the weather is poor or cloudy
Other telescopes
Radio telescopes detect radio waves coming from space. Although they are usually very large and expensive, these telescopes have an advantage over optical telescopes. They can be used in bad weather because the radio waves are not blocked by clouds as they pass through the atmosphere. Radio telescopes can also be used in the daytime as well as at night.
X-rays are partly blocked by the Earth's atmosphere and so X-ray telescopes need to be at high altitude or flown in balloons.
Objects in the universe emit other electromagnetic radiation such as infrared, X-rays and gamma rays. These are all blocked by the Earth's atmosphere, but can be detected by telescopes placed in orbit round the Earth.
Telescopes in space can observe the whole sky and they can operate both night and day. However, they are difficult and expensive to launch and maintain. If anything goes wrong, only astronauts can fix them.
References:
- https://images-na.ssl-images-amazon.com/images/I/41ViEgmMrOL._SY355_.jpg
And we're all done for today!
Drafted by Kin (Physics)