Chapter 3.5: The Models of Universe

There are 3 models of the universe that follows Friedmann's principles of the universe looking like the same.

In this model of the universe, the universe is finite as it will start with the big bang. Eventually, after the outward force of all matters in the universe (due to kinetic energy or pressure) is all used up, gravity will take over and cause a big crunch where the expanded universe will collapse again.

In this model of the universe, it is also infinite, where it is just expanding faster enough that it is above the critical value. This property will cause this universe to look rather flat.







In this model of the universe, it is invite as gravity will never be strong enough to force all the matters in space to collapse to a singularity.

The first model is very interesting since although the fact that the universe is infinite there are no boundaries of space. This is because gravity is actually super strong that it bends space so that it cannot have boundaries. It is similar to if you continue walk in one direction on earth, although it is finite space, the curvature of space on earth allows you to walk infinitely. Note this is practically impossible since you have to travel faster than light to get ahead of the collapsing universe in order to make it around before the universe becomes zero sized. In the third model, it is rather the opposite as space is bent not like a sphere but like a saddle. The second on is just flat...

All three model involve a big bang which is proven mathematically and with some observations (comics radio background) using the general theory of relativity. This shows that the beginning of time involved a dense singularity. 

But, in deciding which of the model is true, one must look at the density of the observable universe and find the amount of gravity needed to halt the expansion of the universe. However, by adding the mass of all the stars, galaxies that are observable, it is find that it is only a small fraction of gravitation force that is needed to stop universe expansion. This caused scientists to rely on the possibility of dark matter and dark energy which increased the gravitation force in our universe. 

More work was done on how stars end their life. To explain, I have this diagram: 

So basically depending on the mass, a star will end up differently.

A black hole is also proven with general relativity and with complex math. This proved the singularity does exist.

Chapter 3: The Expanding Universe!

If you didn't know before...The universe is actually expanding. I can't really blame you for not knowing this though. In fact our "accurate" view of the universe only surfaced after Edwin Hubble observed our solar system, milky way galaxy and a variety of other galaxies through his very good telescope. The Sun is just a normal yellow star and the solar system is slowing rotating around the centre of the galaxy. 

Since the universe is so big with many other galaxies and systems just like our solar system. A problem arises as astronomers need a way to distinguish between billions of different stars in space. The technique of analyzing the light spectrum of each individual star. Since different elements have a different spectrum of light that they release(due to the election orbitals releasing specific amount of energy when collide). By focusing on the spectrum of a single star we can learn the composition of this star. 

When analyzing the different stars, astronomers also notices another pattern and trend. They discovered the fact that most stars seem to be red-shifted and moving away from us (thus the universe is expanding). In order to understand this, we must first learn the Doppler effect. Imagine a stationary radio sending out music. It sends its sound wave (the music) in a concentric pattern (in circles radiates outward). Therefore, everyone will hear the sound wave at the same frequency (same pitch). However, imagine the sound of an alarm on a fire trunk moving towards you. Although the frequency of the alarm (the source) is constant, as the fire trunk moves towards you, the speed of the fire trunk causes the (perceived) frequency of the alarm sound to increase (the alarm's frequency is not changed) this way, you perceive the alarm to be in high frequency or high pitch. But, as the fire trunk moves away from you, the (perceived) frequency of the alarm sound to decrease, this way, you perceive the alarm to be in low pitch. This works with sound but also applies to light (since it belongs to the electromagnetic spectrum). The term red-shift means that the star is moving away since the red colour is lower on the electromagnetic spectrum, and the term blue-shift means that the star is moving close since the blue colour is higher on the electromagnetic spectrum. 

How to know the shift of star

The doppler effect

The expanding universe made it no longer static and allowed general relativity to work better. Also anything is the universe that gives off light, the light will eventually reach us, but it will be an "old light" and not the current light produced by the source. (This is because light is only fast enough to travel through space) Interestingly, the sun we see is not the sun currently it is the sun 8 minutes ago. 

(although Hubble discovered the expanding universe, Alexander Freidmann, a Russian physicist, tried to explain the expanding universe years before Hubble). His two assumption of universe are: the universe looks identical in whichever direction we look, and that this would also be true if we were observing the universe from anywhere else. This is unexpectedly very accurate.

Freedman's hypothesis is proven by other physicists working on microwaves in the Bell Telephone research labs and other scholars working in Preston University. They observed microwaves in every direction and believed that these microwaves must have come from space. Every direction only has very slight change in the microwave amount. Therefore, theory is proven. 

Also the expanding universe suggested the beginning of universe as a big band, an intensely dense sphere explode. 

The big bang theory is full of energy and explosion, even today we can still see it as the cosmic background radiation. These are electromagnetic spectrums left behind from big bangs that travelled to us. But since they are so far away from where we are (and a long period of time has passed), they become the low frequency and long wavelength waves.
Another question is that what will the universe end up - the future of the universe. And this answer will be told tomorrow...

Chapter 2.5: Einstein's thoughts about the universe...

First, we will begin by explaining the theory of special relativity, which states that

• The Principle of Relativity – The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems in uniform translatory motion relative to each other.^[1]
• The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body" (from the preface).^[1]That is, light in vacuum propagates with the speed c (a fixed constant, independent of direction) in at least one system of inertial coordinates (the "stationary system"), regardless of the state of motion of the light source. - Wikipedia 

This basically that all laws of physics are the same although that the relative perceived information for accelerating observers might be different, and the speed of light is constant. What is happening is that since speed of light is constant, if a person is already traveling at a speed of xm/s, time has to slow down for that person in order for the speed of light to remain the same. Also if a clock is at bottom of a tower and another clock is at the top of that tower, since light loses energy as it travels up the earth's atmosphere, the clock on the top of tower will have a slower clock. (This is because the loss in energy result in decrease in the frequency of lightwave) This also cause time dilation, allowing a person to be hanged near a high gravity field therefore making time pass slow for that individual allowing him to travel to future.

There is also an invention by special relativity which is know as a spacetime graph. As we can see there is a time axis and a space axis. When an object is at rest, it only moves straight up the time axis while not moving on the space axis. While if an object has motion, it moves on a slope on the spacetime graph.

Here is a light cone. If we just ignore gravity for a moment, every event (an action or about anything) cause a light cone just like this one. Basically anything in the future light cone will be affected or influenced by the event that cause the light cone, and anything in the past light cone will affect or influence the event. Anything out side of either cone will neither influence or be influenced by the event.

For Einestine's general relativity, massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.

Chapter 2: Space and Time are really confusing...

Throughout history, it was thought that time was fixed. It is assumed if A and B are on opposite sides of the universe while A is stationary and B is moving, as long as they have a synchronized clock at the beginning, their clock will always spin at a consistent rate. This was the basis for Newton's law of motion. As he also assumed everyone's clock would be turing at the same rate (as long as they are really good clocks...) First we must understand Newton's first law of motion, which is that an object's velocity will only change if external force in enacting upon it and that inertia is directly proportional to its mass. For example, an object at rest (zero velocity) will remain at rest unless someone pushes it (giving it a force). Newton's second law says that force is equal to mass of object times the acceleration. Newton's explanation of gravity also states that the amount of gravitational force in directly proportional to the mass of two objects and inversely proportional to the distance in-between the two objects.

As a result of this, all objects should have the same accelerate rate (same change in speed) and therefore when dropped from the same height, they should hit the ground at the same time. (Obviously when dropping a hammer vs a feather the hammer will hit ground first due to the high air resistance on earth) But the feather vs hammer drop experiment was confirmed during the Apollo mission. This theory also explained the elliptical motion of planetary rotation.

Although Newton's model of the universe is able to predict the motion and explain the motion on earth and in the solar system. But another problem arises... People don't understand rest any more. How can objects achieve a state of absolute rest? You may think that a brick siting on a table achieve absolute rest, but since it is on earth and earth is constantly self rotating and orbiting the sun that the brick is also moving with it. (It is only at rest because you being moved with earth, perceives the object as at rest). This fact bothered Newton very much as he believed in an absolute God. But objects can only have perceived rest and under no condition is an object in absolute rest (unless it is in an empty vacuum). 

Everyone believed in absolute time. Obviously time would pass the same for everyone as everyone ages at the same time. This was true for normal objects. i.e. As a train is travelling, the ball's velocity to people on the train is zero but for people on the ground it is the ball's velocity is the velocity of the train. But a problem soon rise as when researchers start studying electromagnetic forces, they discovered that light (part of the electromagnetic waves) seem to have a constant velocity to all observers. (i.e. a light is shined on a travelling train but both the person on the train and the person off the ground see the light as traveling at the same velocity) 

HOW IS THAT POSSIBLE? Turns out, time is not really absolute. and next post, I will explain the Einstein's discovery of theory of relativity!

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.

Chapter 1 My View of The Universe

In the first chapter of "A Brief History of Time", Hawking (this sounds weird to me...) explores in the different historical thoughts about the universe from a variety of different cultures. However, he quickly dives in to the scientific explanations of the universe beginning with Newton. Apparently, Aristotle has already find evidences that prove earth as a spherical body instead of a flat sheet of rock.   The first evidence is that during a lunar eclipse (when the earth is in-between the sun and the moon), earth actually impose a circular shadow on moon. This could only be true if earth is a spherical object or else the shadow should be a stretched elliptical shape. Other evidences include: the position of the North Star and the ability to see a ship's sail before its body. The greeks were fans to circular motion (they sought them to be perfect) so they believed that earth is stationary while other celestial objects (sun, moon, other objects) circulated around it.

Here is the Greek model of the solar system (also the geocentric model of the universe). As they believed the fact that Earth has its stationary rotation (true), and every other planets (not known as planets then, but only objects in the sky) have a self circulation and some have rotation around the earth in orbits. Notice some anomalies exist in this diagram: Why does the Sun have no self circulation on its orbit? Why does Venus and Mercury have no orbit and do not rotate around Earth?





This view of the universe has not changed until recently near 1500 A.D. When Nicolaus Copernicus suggested that celestial objects actually orbited the Sun (the heliocentric model of universe). However, unfortunately for him, his correct hypothesis was prohibited by the Pope and his great mind was decapitated. This new thought only started to surface a century after death of Copernicus. Finally as Galileo invented the telescope and observed satellites orbiting Jupiter, it showed that not every celestial object is orbiting around earth. Also it is also suggested that planetary motion is actually not circular and eclipse, which made this theory more align with observations. Hello centric theory proved that the universe is not fixed in one place, everything is unique and has different properties.

The heliocentric model















The retrograde motion of other planets and starts in the heliocentric system. (How we observe the other planets in our solar system).
For example, as Jupiter moves, Earth moves faster than Jupiter, thus we observe as Jupiter is moving fast. We also observe fixed starts (such as our Sun) as moving because we are moving.





The book now moves on taking about Newton. Newton (and Galileo possibly), in my opinion, is the first real physicist in history. He developed theories, calculations to explain observations. Newton proposed the law of universal gravitation in his Naturalis Pricilla Mathematica. In this book, Newton explained gravity as a force of attraction between every bodies (with mass) of the universe. This force is directly proportional related to their distance and mass. Gravity between Earth and objects makes them fall down. The book also contains complex mathematical explanation of motion of planets.  Newton's law showed that gravity cause moon to orbit earth in elliptical motion and etc.

But, just like every other type of theories, it triggers some other questions. The most important one being that why do stars not collapse into each other into a single point? Newton attempts to explain this by proposing an infinite universe. In an infinite universe, there is not a definite point for stars to fall into However this would not work as the opposite argument can be made as gravity is always attractive and you can pick any point in the infinite universe and the stars on both side is equal, therefore they should still collapse in. What is the actual answer to this question of infinite static universe? What is the missing link to our understanding of universe?
Tune in tomorrow for more!