• Around?14 billion years ago,?the Universe began from a?very small region?that was?extremely hot?and?dense
• Then there was a?giant?explosion, which is known as the?Big Bang
• This caused the universe to?expand?from a single point, cooling as it does so, to form the universe today
• Each point?expands away?from the others
  • This is seen from?galaxies?moving away from each other, and the further away they are the faster they move

   

• As a result of the initial explosion, the Universe?continues to expand

All galaxies are?moving away from each other, indicating that the universe is expanding

• An analogy of this is points drawn on a balloon where the balloon represents space and the points as galaxies
• When the balloon is deflated, all the points are close together and an equal distance apart
• As the balloon expands, all the points become further apart?by the same amount
• This is because the?space itself?has expanded between the galaxies
  • Therefore, the?density?of galaxies?falls?as the Universe expands

   

A balloon inflating is similar to the stretching of the space between galaxies

• Since there is more evidence supporting the Big Bang theory than the Steady State theory, it is the currently?accepted model?for the origin of the Universe
• The main pieces of evidence for the Big Bang are
  • Galactic red-shift
  • Cosmic Microwave Background (CMB) radiation

   

Evidence from Galactic Red-Shift

• By observing the?light spectrums?from?supernovae?in other galaxies there is evidence to suggest that distant galaxies are?receding?(moving further apart) even faster than nearby galaxies
  • These observations were first made in 1998

   

• The light spectrums show that light from distant galaxies is?redshifted, which is evidence that the?universe is expanding
• As a result, astronomers have concluded that:
  • All galaxies are moving away from the Earth
  • Galaxies are moving away from each other

   

• This is what is expected after an?explosion
  • Matter is first?densely packed?and as it explodes it, it moves out in?all?directions getting further and further from the source of the explosion
  • Some matter will be?lighter?and travel at a?greater?speed,?further?from the source of the explosion
  • Some matter will be?heavier?and travel at a?slower?speed,?closer?to the source of the explosion

   

• If someone were to?travel back in time?and compare the separation distance of the galaxies:
  • It would be seen that galaxies would become?closer and closer together?until the entire universe was a?single point

   

• If the?galaxies?were originally all grouped together at a single point and were then exploded a similar effect would be observed
  • The galaxies that are the?furthest?are moving the?fastest?- their distance is proportional to their speed
  • The galaxies that are?closer?are moving?slower

   

Tracing the expansion of the universe back to the beginning of time leads to the idea the universe began with a “big bang”

Evidence from CMB Radiation

• The discovery of the CMB (Cosmic Microwave Background) led to the Big Bang theory becoming the currently accepted model
  • The CMB is a type of electromagnetic radiation which is a remnant from the early stages of the Universe
  • It has a wavelength of around 1 mm making it a microwave, hence the name Cosmic?Microwave?Background

   

• In 1964, Astronomers discovered radiation in the microwave region of the electromagnetic spectrum coming from?all directions?and at a generally?uniform temperature?of 2.73 K
  • They were unable to do this any earlier since microwaves are?absorbed?by the atmosphere
  • Around this time, space flight was developed which enabled astronomers to send telescopes into orbit above the atmosphere

   

• According to the Big Bang theory, the early Universe was an extremely?hot?and?dense?environment
  • As a result of this, it must have emitted?thermal radiation

   

• The radiation is in the?microwave?region
  • This is because over the past 14 billion years or so, the radiation initially from the Big Bang has become redshifted as the Universe has expanded
  • Initially, this would have been?high energy?radiation, towards the gamma end of the spectrum
  • As the Universe expanded, the wavelength of the radiation?increased
  • Over time, it has increased so much that it is now in the?microwave?region of the spectrum

   

The CMB is a result of high energy radiation being redshifted over billions of years

• The CMB radiation is very?uniform?and has the exact profile expected to be emitted from a?hot body?that has cooled down over a very long time
  • This phenomenon is something that other theories (such as the Steady State Theory)?cannot?explain

   

• The CMB is represented by the following map:

The CMB map with areas of higher and lower temperature. Places with higher temperature have a higher concentration of galaxies, Suns and planets

• This is the closest image to a map of the Universe
• The different colours represent different temperatures
  • The?red?/ orange / brown regions represent?warmer?temperature indicating a?higher density?of galaxies
  • The?blue?regions represents?cooler?temperature indicating a?lower density?of galaxies

   

• The temperature of the CMB is mostly uniform, however, there are minuscule temperature fluctuations (on the order of 0.00001?K)
  • This implies that all objects in the Universe are more or less?uniformly spread out

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