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Science Study Notes- Term 4
The ‘Big Bang’
* Scientists believe that the universe originated in an enormous explosion called ‘The Big Bang’ * This was believed to have occurred approximately 15 billion years ago * The idea of this phenomenon is that at zero-time (before time and space existed), the universe was contained in a tiny ‘cosmic egg’ or ‘super atom’- singularity * Much smaller than a proton

* Contained an enormous & incredibly concentrated amount of energy * Matter did not yet exist at this time, as temperatures were so extreme that the Laws of Physics did not apply * Forces of gravity within this cosmic egg drew its contents in closer and closer, into a tinier and tinier volume, creating higher and higher temperatures * When the tiniest possible volume was reached, the extremely high temperature caused an enormous explosion- The Big Bang * At that very instant- universe was so incredibly hot (one trillion trillion °C) * This set off a chain of events in which matter was created and the universe was gradually formed The First Second of the Big Bang

* Initially, universe expanded quite slowly
* Then, within a fraction of a second- became 100 million billion billion times bigger * Particles of matter collided with particles of antimatter, destroying each other releasing a burst of light called a photon * After all these collisions finished, relatively small amount excess matter left * This matter formed universe as it is known today

* After 1 second- universe had cooled to 10 billion degrees Celsius * After 3 minutes-1 billion degrees
* At this point... particles called quarks clumped together in groups of 3 to form protons and neutrons * These protons and neutrons formed hydrogen and helium
EVIDENCE OF THE BIG BANG:
The Doppler Effect
* The Doppler Effect suggests that sound waves in front of a moving source get crowded together, shortening their wavelength & raising the pitch of the sound heard by an observer in front of the source * As the source passes the observer & moves away from them, the waves behind get stretched apart, lengthening their wavelength and therefore decreasing the pitch of the sound * This theory also applies to any moving source of waves i.e. light * Only noticeable for extremely fast-moving light sources e.g. stars and galaxies * White light is composed of several wavelengths, seen as a spectrum of seven colours: red, orange, yellow, green, blue, indigo & violet * Violet has the shortest wavelength and red has the longest * If light wave gets scrunched up or stretched-wavelength changes & this changes the colour * if light source is coming towards you- see a higher proportion of violet light * if light source is moving away- see a higher proportion of red light * ‘red shift’- when light from some of the brighter stars in our galaxy ‘shifted’ towards the red end of the spectrum (had a higher proportion of red light than normal) * This suggested that their waves were being ‘stretched out’ into longer wavelengths- must be moving away from us * Astronomers concluded that this meant that the universe was expanding Hubble’s law

* American astronomer, Edwin Hubble discovered from red shift of distant stars & galaxies: - they are moving away from us
- the further away they are, the faster they are going
- the further away the star is from us, the greater the red shift * This breakthrough centred on the Doppler Effect
* Just because everything is moving away from Earth, doesn’t mean we are centre of universe

Microwave Radiation
* Radio waves emitted from the Sun were interfering with radio signals * Scientists tried to eliminate solar interference, but to their surprise they discovered radiation was coming from stars and galaxies as well * Radio waves travel further than light- stars and galaxies could be detected by observing their radio signals...
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