Our Understanding of The Cosmos [I]

Throughout time, we humans has always wondered how things work. In the end, it always lead to certain discovery and finally, an invention that will change the course of history.

We used to assume the earth was flat. This is because our mobility at the dawn of humanity was really limited. Not until the ancient Greek finally got it right.


The Blue Marble- one of the most public photo ever copied.

With a few arguments that nature offered (through observing the nature) Aristotle finally wrote two observations of the nature that support the earth is round.


Aristotle is the right, Plato is the left (Plato is Aristotle's teacher)

I. The apparent position of North Star (Polaris) in different places. In this case, Greece and Egypt.


The star at the centre is the Polaris.

II. The moon can be eclipsed by the earth is because the earth is round, therefore able to cast a round shadow to the moon that we see as lunar eclipse.

There's even a third evidence that support the earth is indeed round.

The fact that we see the mast of a ship before we see the whole ship when it is "rising" from the horizon.

Inside the purple circle is the mast of a ship. (Click to enlarge.)

For some divine reason, Aristotle also assumed that the earth is the centre of the universe and it is stationary. The planets and the sun circle around it in their perfect circular orbits.

Earth is the centre of the universe.

Ptolemy (Ancient Greek Mathematician) later elaborated the geocentric model, that the earth is stationary, and there's eight "globe" of celestial body encased on top of another. The first shell is the Moon, Mercury, Venus, The Sun, Mars, Jupiter, Saturn and lastly, the globe of "fixed" stars.

Ptolemy

His model was accepted generally but not everyone accepted.

But the model was adopted by the Christian church. Because the model favor the advantage of the model because outside the globe of "fixed" stars, there's place for Heaven and Hell. And the model follows the Scripture.

St. Peters Basilica - The Vatican

No one bothered or dare to challenge the Church. It was until later, at 1514, Nicholas Copernicus proposed a theory, that the sun is in the centre of the system and earth rotates around it (Heliocentric model). At first, he circulated the idea anonymously, afraid to be branded as a heretic and probably burnt alive.

Nicholas Copernicus

It as another 100 years until heliocentric model is taken seriously by another two leading scientist of the day. Their name was Galileo Galilei and Johannes Kepler. Galileo Galilei publicly supported the theory. He showed everything fall on earth with the same rate despite how heavy they are.

Galileo Galilei

The Geocentric model was finally destroyed in 1609 when Galileo observed the night sky using the newly invented telescope and discovered Jupiter's moon, orbiting its mother planet. This proved that not everything have to orbit around the earth and finally the Church put him into house arrest for the rest of his life.

Once the most blasphemous tool ever invented - the telescope.

As for Johannes Kepler, he modified the theory, saying that the planets orbit the sun not in perfect circles but in ellipses (ellipse is an elongated circle, oval). Now the model fit perfectly with the observations. But to him, ellipse is considered to be ugly because it's obviously less perfect than circles.

The symbols are used by alchemists back then.

He does not understand why planets orbit in ellipses.
Until another man arrived who thinks ahead of his time. Sir Isaac Newton.

Sir Isaac Newton

He published his Philosophiae Naturalis Principia Mathematica at 1687, which is one of the single greatest work ever published in all of physics.

A genius's masterpiece!

He states that matter that has mass will attract any other mass via a force called gravitation.
And he formulated the Universal Law of Gravitation.

Where F = The attractive gravitational force
G = Gravitational constant

m = Mass of the object

r = The distance between the object

F1 = F2

Suddenly, the reason why the orbit of the planets are elliptical is revealed.

But in 1691, Isaac Newton received a letter from Richard Bentley. After reading, Newton knew immediately something is wrong. It's the Bentley paradox. And it's crushing Newton's law.

"If gravity is always attractive, why not the entire universe collapse into a spot? (Where all the stars crashed into each other)"

Newton wrote a letter back saying:
There should be infinite stars distributed evenly in the universe in an infinite space. Then, the gravitational force will cancel each other out.

Newton is smart enough to know that the situation is not really stable. Should any single star moved a slightest bit away, then all the matter in the universe will squeeze into a dot. He finally concluded that God will have to adjust the position every now and then so that the universe does not collapse.

But before the 20th century, no one thought of the solution as in the universe is expanding or contracting.

It is thought that the universe has always existed since the beginning of time and will last eternally