Mass curves space-time fabric through time dilatation and space contraction, while curved space-time fabric accelerates movement of the mass towards the massive object which in the first place creates curve of space-time, making the other object fall towards the massive object in a circular movement or rotation which becomes faster and faster as it approaches the massive object.
Time and space are physical characteristics or property of the universe. The space between galaxies is empty space but it is space nevertheless. When we think about the idea of the creation of the universe as some initial hot dense place less than the size of an atom, which explodes to become a universe, expanding ever since then, the image that is immediately created in our mind is a scenario where this explosion occurs in an empty space; the space, which we know, and which can be imagined that exists as such between galaxies or between any celestial bodies in the universe. This is not what really happened at the explosion of the universe.
Picture 6.01
The universe was created in a big explosion as the Big Bang theory explains, but this was an explosion of energy and matter as well as of space and time. There was no time and there was no space before the Big Bang happened. The beginning of the universe starts from zero time and zero space. To go into the philosophy as to why there was nothing before the Big Bang and why the universe developed into the way it is today is beyond my capability as an ordinary layman. In Foundations of Modern Cosmology by John F. Hawley and Katherine A. Holcomb it is stated that: Because science must deal with physical entities, the issue of the creation of the universe is necessarily metaphysical.
When fundamental constants of nature are considered such as speed of light, Planck’s constant, charge of the electron and the gravitational constant, to mention just a few, it can be said that they have an exact value needed to be there to create matter in the way it is created which creates conditions to support the creation and existence of life within the universe. One of the ways which can be used to explain why the universe has developed in this way with such particular characteristics is the so-called Anthropic Principle. According to this principle, it is a presence of life which determines the development of the universe in such a way that permits creation and existence of life.
It was Fred Hoyle, British mathematician and astronomer, who used anthropic reasoning, predicting that the intrinsic energy level of a carbon atom has almost equal value as the sum of the energetic value of 3 helium atoms in the core of a star to allow fusion of these atoms of helium into a carbon atom to take place. Such nuclear reaction progresses under these conditions very quickly. It is because it is said to be resonant. There was, therefore, the exact condition created within a star for a carbon atom to develop which will serve later on as a building block of organic compounds leading to the creation of life. Every living organism is composed of chemical compounds and each organic chemical compound has carbon atoms as a core of their structure.
It was found out that the next chain in the nuclear reaction involving the fusion of one more helium atom with a carbon atom to create an oxygen atom failed to be resonant and, as such, prevented carbon atoms burning to oxygen. It was due to the different energy levels of oxygen, carbon and helium that this nuclear process went in such a way within the star that carbon was created and remained safe. Combinations of the value of the fundamental constants of nature determine such energy levels. If the value of constants is slightly different then the outcome of nuclear reaction will be different with no possibility of creating carbon atoms in abundance.
Carbon atoms to be released from a star require the star to die in a supernova explosion. In this process, many elements with higher atomic numbers were made. The average lifespan of a star is billions of years. As the universe expanded through this time, it was necessary for the universe to be very big in a size of billions of light years before conditions were met such that planets were made of dust which was left as a remnant of a supernova explosion. Such cloud contained the elements to build rocky planets and a number of necessary elements for life to be created.
This is one way of looking at the question as to why the universe developed the way it did.
I should go into the nature of space and time as a property of the universe, but before that, I believe it is the right place to mention a few things about the size and shape of the universe.
We are able to observe the edge of the universe, which corresponds to a time around 380 000 light years after the Big Bang when photons decoupled from matter and went away from the matter in every direction. These photons are now reaching us from all directions, not in the spectrum of visible light but in the spectrum of microwave background radiation. These signals of cosmic microwave background (CMB) travelled to us from a distance of around 13.7 billion light years, which is a snapshot of that time of the universe when photons decoupled from matter. That corresponds roughly to the beginning of the universe which is the reason for the statement that the universe is 13.7 billion years old. It also corresponds to the edge of the universe at that time, 13.7 million years ago. This is, however, not the current edge of the universe. (I am referring here to the edge of the universe or size, not the age of the universe or how old the universe is.) The reason it is not the current edge of the universe is that the universe has expanded from the time we received CMB radiation which was the edge of the universe 13.7 billion years ago when these photons left these areas and have now reached us after 13.7 billion years. Meanwhile, the universe has expanded and it is estimated that now its radius is around 46 billion light years or diameter around 92 billion light years. These calculations are made taking into account the Hubble constant that refers to the rate of the expansion of the universe. It is how I am making sense of it.
WMAP, which stands for the Wilkinson Microwave Anisotropy Probe, is a spacecraft (also called Explorer 80) launched by NASA in 2001, which is equipped with technology to measure differences in the temperature within CMB radiation called anisotropy of CMB radiation. The data collected supports the current standard theory or standard model of cosmology called the Lambda-CDM model which is modified Big Bang theory to take into account cosmological constant (lambda) and cold dark matter (CDM). This theory is more precise or reflects more accurately or gives a more plausible explanation of the origin of the universe based on the Big Bang theory.
WMAP confirmed that the universe is flat in shape in 2013 with accuracy with only 0.4% of margin error. (Details taken from NASA website: http://map.gsfc.nasa.gov/universe/uni_shape.html)
It is consistent with the Big Bang theory and the inflationary theory. The reason that the universe is in flat shape is ratio between mass density and critical density which is almost equal to 1.
What does it mean?
We know that gravitation depends on mass density and pressure. There are a minimum amount of particles which need to be per unit of volume for gravitational force to remain and exert or have an effect in this space. This can be called critical density of space. If this space has more mass density than critical density then we can expect that this space can expand to the maximum point but then will start to contract, as mass density is bigger than critical. How far this place will extend before it starts to contract will depend on how much higher mass density is than critical density. If the universe has a very higher mass density than critical density then it would not be able to expand more than is the size of our Milky Way galaxy or less, again depending on mass density over the critical density. If the mass density is less than the critical density, the universe will go on expanding indefinitely.
When mass density is equal to critical density then the universe has a flat shape.
The following analogy to understand it better is not the best I can think of as it can be challenged very easily, but I will use it anyway.
When we pour water into a pan it does not take the shape of a ball but fills the pan to a depth of 1-2 ml (if we pour just a little bit of w
ater). We can say that water lies in a pan and has a flat shape as it does not have enough mass density which will pull molecules water together to make a ball shape. If we now add to this flat-shaped amount of water, flour or chocolate powder, then the density of a mass will increase above the critical density, making the powder and the molecules of water come together. Now we are able to make a ball-shaped mixture of water and chocolates.
In the previous chapter, dark energy is explained as acceleration of expansion of intergalactic space. A galaxy on its own does not expand within itself in the sense of getting increased distances between stars in galaxies. That is because the mass density is bigger than the critical density within the diameter of galaxies (there is stellar dust, for instance), which make them, overcoming the effect of dark energy so it is only that intergalactic space is increasing.
I cannot resist mentioning the importance of the current scientific approach to studying nature, taking into account all needed to arrive at a theory or theories which will give a logical and accurate explanation of phenomena we observe in our universe.
The basic approach is the Copernican principle. It is based on the principle that if a theory requires a special condition around which the theory needs to bend, then this theory cannot be plausible or reflect what is really happening in relation to a particular phenomenon which the theory tried to explain.
An example is the Ptolemaic geocentric system, which puts the Earth at the centre of the universe. In order to keep this theory alive or plausible, Ptolemy created the theory of epicycles, which explained the movement of planets then known. So binding the theory around the presumption that the Earth is the centre of the universe, he created the theory, which looked plausible but could not exist long, as it did not reflect the reality.
We know that Earth is not the centre, but goes around the Sun. We know that the Sun is not the centre of the universe and it goes around the Milky Way, our own galaxy. Our own galaxy is not the centre either and is only one of many galaxies in a local cluster of galaxies.
On a large scale, the universe is isotropic and homogeneous.
Isotropy refers to a situation where there is no special direction wherever you are placed in the universe. The universe would look the same in any direction, regardless of the place we are in the universe. This does not appear to be at small distances for the universe. For example, if we look locally within our solar system then of course directions look different as we have our sun giving us daylight, the Moon that looks bigger than other celestial bodies. Stars within our galaxies have particular positions creating particular shapes in the sky called constellations. However, when the universe is observed on a large scale with distances of millions of light years then it does look the same in any direction. In other words, the universe is isotropic.
Homogeneity means that every place in the universe is the same and not different to the others. The fact that the universe is homogeneous is important as thanks to this we are able to detect the same elements such as helium or hydrogen that exist everywhere in the universe, regardless of the place we pick to observe.
The universe is isotopic and homogeneous which means there is no centre. Because there is no centre then there is not a particular place where the Big Bang occurred. In other words, the Big Bang has occurred everywhere. Every point in the universe is the centre of the universe where the Big Bang occurred.
The best way to explain it is if we imagine a birthday balloon before it is inflated. This balloon has its particular shape and is composed of molecules or atoms, which make its wall. Let’s imagine these atoms or molecules as huge, almost indefinite numbers of dots tightly situated next to each other, making the wall of this balloon. Now we start to inflate this balloon. As the surface of the balloon enlarges, the distance between each dot enlarges as well. If I am at one of these dots (being reduced in my size by some technology) then I will see how all the other dots are moving away from me in all directions. That would be the same experience if I were at any other dot. I would be able to see other dots moving away from me in all directions until they move away from me beyond a distance of 13.7 billion light years. Afterwards, I would not be able to see them any more as it will take time for light from those dots to come to me. 13.7 billion light years is the diameter of the observable universe in all directions and is the same from whatever position we are looking. It would be the same if we look at the universe from our planet or from a planet that is located in the Andromeda galaxy, for example.
Momentum Conservation Principle
In Chapters 1 and 3 I gave an explanation of the conservation of matter and energy in the way I could make sense of it. Einstein’s famous formula, which reflects the possibility of energy change to a matter and vice versa, requires modification of conservation of matter and energy as a separate entity into a more precise statement of conservation of mass-energy within a closed system or the universe.
There is one more very important law of conservation, which is referred to as the conservation of the momentum.
The conservation of the momentum is simply defined as a product of mass and velocity. As it refers to velocity or movement of the mass in any direction of tridimensional space, I found that this chapter is the right place to mention a few things about this law.
Conservation of momentum means that in a closed system where there are no external forces acting on a system, the total momentum of the system does not change.
When I tried to make sense of the conservation of energy or internal energy within the closed system I outlined that the internal energy can change if energy from outside is transferred in the system. This transfer will take place by the help of work or heat. However, if the system is closed and there is no outside from where energy can be inserted to the system, then the internal energy within the system remains conserved, unchanged.
Like internal energy is changed if it is inserted in the system by work or heat, so the momentum is changed if velocity changes, which means that force is exerted from outside.
To understand it better, it is important to keep in mind that momentum is product of mass and velocity:
momentum = mass x velocity
Velocity is a change in the position of the object or its displacement, which takes place over a period of time. It has a vector property as it applies to a particular direction.
Force is, however, described as a product of mass and acceleration:
force = mass x acceleration
Acceleration is a change of velocity over a period of time. So the above equation can be arranged as:
Mass x velocity is momentum so we can replace the right side of the above equation with momentum. However, the velocity changes over a period of time. As momentum is a product of mass and velocity and velocity is changing over a period of time, then product or momentum changes over a period of time as well. Therefore, force is a change of momentum over a period of time:
Ultimately, we have a change of momentum if external force is exerted on the system from outside. If the system is closed with no external forces, then momentum before motion and after motion within the closed system remains the same.
If two objects are on a collision path within the closed system then their total momentum before collision is equal to the total momentum after collision. When we hit a tennis ball with a racket then the ball will fly away but the product of ball mass and velocity of the ball will be equal to the product of velocity by which the ball was hit and the mass of the racket.
racket x velocity = tennis ball x velocity
The ball velocity will be higher than racket one but the mass of the ball will be less than racket one. Therefore, the product of the corresponding masses and their velocity will be the same. In this particular case, the racket will lose its momentum upon collision with the ball while the ball will gain the same momentum.
There are two types of momentum:
Line
ar momentum or translational momentum. This is the product of mass and velocity of an object, which is in motion linearly as explained above.
Angular momentum or rotational momentum is the product of moment of rotational inertia and rotational velocity.
Angular momentum = moment of inertia x rotational velocity
Moment of inertia is rotational analog to mass in linear momentum as rotational velocity is to velocity of linear momentum. Rotational velocity is angular velocity, which can be mathematically described as ratio of velocity and radius.
As with linear momentum, angular momentum is conserved within the closed system as long as it is not affected by applying external forces, which in the case of angular momentum is a torque. Torque is influence, which tends to change the rotational motion of an object. Angular momentum is very important in astronomy.
In the history of Earth, the prevailing theory is that another planet hit our planet at an early stage of her life. The result of this collision was displacement of the Earth’s axis, which tilts at around a 23-degree angle. It is thanks to this that we have seasons. The other thing which happened is that in this collision the Moon was formed from debris and was much closer to the Earth than it is today. Due to conservation of angular momentum, Earth rotated faster when the Moon was closer to Earth. The same applied to moon velocity being faster around the Earth at that time. As the Moon moved away, its orbital velocity as much as rotational velocity of the Earth reduced. A day lasts twenty-four hours in present time but was much less than twenty-four hours in the distant past of Earth’s history when the Moon was closer and Earth consequently rotated faster. This change of rotation with the change of the distance of the Moon from the Earth is due to conservation of angular momentum. To explain this I have to introduce a little bit of mathematics.
Journey Through Time Page 11
