The Shape of Time ( Cont.)

Part 3 Our Past Light Cone

A past light cone, as pictured above, are the paths in which spacetime of the light rays from distant galaxies reach us during present times. In other words, basically when we look at galaxies millions of miles of away from us within the universe we are looking at a much earlier version of them because light travels at an finite speed. So by the diagram above we can see that if we represent time by the vertical line within the cones, and we represent the two of the three space directions by the horizontal lines, than we can observe that the light reaching us now, at this point, must travel to the vertex, in order for us to see it. As we go down from the vertex to the bottom of the cone we observe earlier and earlier versions of galaxies out there in our universe. Also to all this, since the universe is expanding , and all the galaxies used to be much closer back then, we will only be able to observe the regions of a much higher matter density. From all this information, scientist have concluded that our past light cone must be able to pass through a specific amount of matter as it follows back on the y-axis or vertical line of the cone. This then supports that with this specific amount of matter, we can see that it is enough to curve spacetime, so the light rays from previous sources are bent toward each other.

The Shape of Time (Cont.)

Part 2 Spacetime

With general relativity and the better understanding of time and space now available to scientist, thanks to Einstein,  the theory shows that there is a combination of of time dimensions as well as the three dimensions of space which form to create what is known as spacetime. Basically what the theory just showed was that there are ties that include the effect of gravity over all the distribution of matter and energy in the universe. This energy and matter warps, thus distorting spacetime, which shows that it is actually not so flat after all. Since spacetime itself is curved, the objects trying to move in a straight line will be affected and their paths will be bent. The object moves as if it is being affected by a gravitational field. 

The Shape of Time

Part 8 What is Time?

As with Einstein's Theory of General Relativity rolling out into the world, it is important to see the correlation it has with time and space. As quoted by Charles Lamb, a nineteenth century author, he wrote: "Nothing puzzles me like time and space. And yet nothing troubles me less than time and space, because I never think of them." With that in mind, it is really imperative to grasp an understanding of not only of what we think time is, but also how we came about to the discovery of time. The first scientist to show mathematical models about time was actually none other than Issac Newton himself. He published his book called the Principia Mathematica, in 1687, and according to Newton's understanding, time and space were a background in which events took place but were not affected by them.

As stated within the book, time was separate from space and was considered to be a single line, or to simplify it, a railroad track, that was infinite in both directions. By looking at the picture below, you can observe that one cannot curve space without curving time with it as well. This then means that time itself does have shape, but on the other side of this, it is only a one way direction, as the the locomotives show in the picture.

A Brief History of Relativity (Cont.)

Part 7 Black Holes & The Big Bang

      With the thought of Einstein's faults with the cosmological constant in mind, it is important to realize that even general relativity can predict the that the universe itself was created by the big bang. In all actuality, this proven by the author himself, Stephen Hawking as well as his counterpart Roger Penrose, so this is pretty recent in discovery. This is why Einstein had his worries about his theories. He was aware that the theory implies time to have a beginning, which he was unhappy with from the beginning. Also, he was even more reluctant to recognize that general relativity also predicts the time of death for massive stars, and this when the star reached the end of its life, no longer able to produce or generate enough heat to balance its own gravity, which inevitably made it smaller. The reason Einstein was so displeased by this was because he believed that stars broke down into some final state, but unfortunately for him we now know this is not true because stars have no final state configuration. They simply continue to shrink until they become "black holes", which are regions in space that are so warped within the realm of space time, that not even light can escape it.

    What happens to form such powerful region in space is that when a massive star of any sort, loses its nuclear fuel, it will in turn lose heat and contract. This thus warps space and time so greatly that the black hole will appear which prevents any light from escaping it. As a result of all this, time itself, will come to an end within it. As I mentioned before, Penrose and Hawking proved this, and so this means that time ends for stars. However, this does not help Einstein's theory of relativity because both the beginning and end of time still cannot be defined.  As a result of that, we still cannot predict what emerged as a result of the big bang, besides what we theorize.

A Brief History of Relativity (Cont.)

Part 6 Space & Time 

      Even though Einstein's general theory of relativity was creating some drastic change during his time about space and time, it turns out that there was yet another flaw to his renown idea. This problem is still being questioned today and is one of the most prominent problems within physics. As explained by Einstein the universe is full of matter, and matter warps spacetime which inevitably creates a flux in where bodies of this mass fall together. So Einstein did eventually realize this too that his equation did not contain the solution that describes a static universe, which is unchanging in time. To fix this, Einstein decided to fudge together his equations in which he had to create another mathematical variable into the mix. This variable is known as the cosmological constant and this constant went over the abilities of warped spacetime in which it did so by an opposite effect, and so this resulted with the bodies of mass moving apart. 

    Now this is the problem with adding this cosmological constant to the mix, in which was a missed opportunity for Einstein. If he had just stuck with the original equation he would of have the ability to predict that the universe must be either expanding or contracting and with an observation like that, we could see that the farther away a galaxy is, the faster they are moving away from us.  

A Brief History of Relativity (Cont.)

Part 5 Einstein's Ideas

     As it was known throughout the 20th century, Einstein re-imagined and completely changed some of the most prominent scientific thought of his time. However, he was not done there with his theory of relativity and E=MC2, for once his gears started moving, so did the rest of the scientific world. There was one fault to Einstein's theory of relativity though, and that was even though the theory coincided with the laws of electricity and magnetism, it was not compatible with Newton's law of gravity. As stated in the book, it says that this law explains "that if one changed the distribution of matter in one region of space, the change in the gravitational field would be left instantaneously everywhere else in the universe." With this law, it essentially means that we could send signals faster (which is forbidden by the law of relativity) through out the universe. It also, meant that there had to be a required existence of universal time, which the theory of relativity also abolished. Once Einstein returned to Prague in 1911, this is when he seriously put some thought into deciding what he could do to solve the problem and this is what he deduced.

       There is an actual tight relationship between gravitational fields and acceleration, and so he came up with this example of a man within an elevator. He said to imagine someone inside a closed box, such as the elevator, the individual inside could not tell if that box or elevator in this case  was at rest due to Earth's gravitational field. Also, one could not even accelerate in that matter or free fall at an extreme distance within the elevator due to confinement. As a result of this conclusion Einstein, upon his return to Zurich in 1912, discovered that the there will be an equivalence with acceleration and gravitational fields only if the geometry of space time was curved and not flat.

 To put it in other words, for example, from the book, objects such as an apple or planet would try to move in a very straight and forward line through space time, but due to the gravitational fields, their paths would seem to appear to bent because space time itself is curved. Eventually after this study, Einstein collaborated with Marcel Grossman, to write a joint paper putting out the idea that what is known as a gravitational field to us, is simply a result to due the curvature of space time.

A Brief History of Relativity (Cont.)

Part 4 E=MC^2

As time progresses in Einstein's year, his theory of relativity starts reach some critical acclaim within the world of science which eventually gets him the Nobel Prize in 1921.With the establishment of Einstein's foot now firmly planted, he starts to express his ideas more rampant throughout the world. With the theory of relativity, their was one consequence of the relativity which is due to the relation of mass and energy. As a result, Einstein postulates an idea, or in this case an equation known as E=MC^2, which inevitable leaves its mark not only on the world of physics, but as the world as a whole. This equation explains that since the speed of light appears the same to everyone, then nothing within our known universe can move faster than the speed of light. To break this idea and equation even further down, is that when an object uses energy to accelerate any process, than the mass must increase as well, which in turn makes the object more difficult to accelerate. Now, to accelerate an object to the speed of light then, there must be an infinite amount of energy. What Einstein done with this equation is that it explains that mass and energy are equivalent, and all that is needed to be done is to square the speed of light. His equation showed a very important relationship with mass and energy which ultimately lead to one of the most dangerous weapons known to mankind. As a result of the discovery of nuclear fission, the atomic bomb was created through the Manhattan Project. This led to the creation of two bombs that would not only end World War II, but also completely obliterate the Japanese cities of Nagasaki and Hiroshima. Since Einstein was the man behind the discovery of the relationship between mass and energy, he was heavily blamed for the destruction.  However, as quoted from the book "that is like blaming Newton for causing airplanes to crash because he discovered gravity" and in all actuality, Einstein never participated with the Manhattan Project and he was utterly horrified by the droppings of the atomic bombs over the cites.

This video gives a brief description over the equation and really explains the concept well. Check it out!