Chapter 1.5: Our Expanding Universe - Space and Time!

Apparently, even an infinite static universe cannot prevent Newton's newly discovered gravity to collapse all celestial object into a single point. This question bothered physicists from seventeenth to eighteenth century. Some attempted to explain the situation by making gravity being able to repel at a very large distance so that an equilibrium can be reached. However it also failed at explaining why random motion of stars would change the amount of repulsive or attractive forces between them, which still leads to the collapse of the universe. Another argument is that, if the universe is static without any changes, the night sky would be very bright since other stars can heat up "intervening" matters in space causing them to shine brightly. This suggests that there is a beginning and end of stars, i.e. some stars has died while new ones are born. It is not until in the late 1800s, Hubble (with his famous telescope) discovered the fact that the universe is expanding very rapidly. This proved that the universe is not static.

All of this universe talk created an interesting question: How did the universe actually start? While since beginning of human civilization, people has used their deepest imagination to form creation stories. Often these creation involves one or a few supernatural beings. All of these hypothesis can be right and it is possible that humans may never know. But according to Hubble's discovery, the universe was created from the Big Band, where an intense, dense point (the universe) exploded.

A good scientific theory is some thing that is 1. accurately describes a large quantities of observations with few arbitrary elements in the observations and 2. make definite predictions on result of potential experiments. The diagram on the left shows the general process of how a theory is devised.

Currently, physicists use two partial theories to explain the universe. The first one is quantum mechanics and the second on is the theory of general and special relativity. In next post, I will explore in to the depth of space time and attempt to explain the relativity theories and E=mc2 by Einstein.