The Big Bang Theory, Dark Energy & Dark Matter | Physics for Grade 10 PDF Download

The Big Bang Theory

• Around 14 billion years ago, the universe began from a very small region that was extremely hot and dense
• Then there were a series of explosions, which we call the Big Bang
• This caused the universe to expand, cooling as it does so, to form the universe we currently observe
• 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 explosions, the universe continues to expand

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

Evidence for the Big Bang

• By observing the light spectrums from supernovae in other galaxies there is evidence to suggest that distant galaxies are receding (moving further apart) ever faster
• 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 – the galaxies are moving away from us - and, indeed, each other
• This is what happens in 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 you were to travel back in time and compare the separation distance of the galaxies they 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 we would see a similar effect
  • The galaxies that are moving fastest would move the furthest - the distance they move would be proportional to their speed
  • The galaxies that are moving slowest would move the least

Dark Energy & Dark Matter

• Over the past two or three decades, astronomers have gathered plenty of evidence helping us to understand the universe much better
• However, there are still many observations that are still not understood, including:
  • Evidence from the rotation and motion of galaxies suggests that there is much more matter in the Universe than we are able to account for
  • This unseen matter is given the name dark matter and its nature is not currently known
• Measurements of the expansion of the Universe using supernovae suggest that the Universe is starting to expand at a faster rate
  • It has been suggested that this accelerated motion is caused by dark energy pushing everything in the Universe apart
• If gravity is present everywhere in the Universe, it might be expected that everything will one day become closer together, but that is the opposite of what we see
  • This is another reason why dark energy is a possible solution which could be counteracting gravity and expanding the Universe instead