Albert Einstein

It seems that betting against the man, Albert Einstein, is tantamount to setting yourself up to lose. Why someone would undertake such a venture is perplexing to me. First, you have to understand his theories (which I find mind-boggling and stressful to my imagination) then you have to find holes in them after you have appreciated them. If you were from his generation, you would run into more problems concerning the magnitude of his laboratory (the universe) and the speed of his variables (speed of light).

_{^{Pixabay Creative Commons: A Curvature in Space-Time}}

I am not a theoretical physicist. Therefore my problems with Einstein's theories are much more elementary. In making this post, I hope to find kindred spirits who have difficulty understanding what exactly are space-time, time, special relativity and general relativity.

Apart from his equation which says that energy and mass are related by E = mc², the other things for which Albert Einstein is famous for are his special theory of relativity and the general theory of relativity. Unfortunately, these theories are difficult even for some smart people to comprehend because of the underlying concept. One of these concepts is the concept of time and space-time.

The Relativity of Time

The distinction between the past, present and future is only a stubbornly persistent illusion ~ Albert Einstein^[1]

Our view and understanding of time were dramatically changed after Albert Einstein published both theories of relativity in 1905 and 1915. It was from these theories that we realised that time was not absolute. After the special theory of relativity, we went from absolute time to a notion of time which is one dimension in space-time. When general relativity was published, we saw time as one dimension in dynamically curved space-time.

According to Einstein the speed of light is fundamental, invariable, absolute and he realized that if this was true, then it is space and time which must be variable to allow for the invariability of the speed of light.

Space-Time

One aspect of the special theory of relativity is that space and time are inextricably merged in a four-dimensional space-time fabric of the universe. As with most of Einstein's work, to understand what space-time means, we have first to understand another definition: an event.

An event is both a place and a time which can be represented by a point in space at a particular time. The implication of this is that if we can point out an infinite number of events, we would have succeeded in creating the whole space-time. If time and space are merged in this way, then it becomes difficult to imagine time as something that flows from the past to a present and to the future. As space exists interwoven with time, time is also just "there". However, we must admit that space is not as "directional" as time apparently seems to be (the Arrow of Time). In other words, apart from gravitational pull, we do not pass through space as we seem to move through time.

The concept of space-time was further refined in the general relativity with Einstein's realization that gravity is not a force that is acting on space-time but is actually a property of space- time which makes it warped and dynamically curved.

This property is noticed around very massive objects and black holes where space-time is substantially warped that lights passing close to them change directions.

Time Dilation

With the theory of special relativity, it became obvious that time varies depending on the relative speed of the observer. That this means is that if two clocks are synchronised and sent off at different speeds, the time in them would vary at the end. However, this change in time is not observable at low speeds. But as the speed of the object approaches the speed of light, which is called relativistic speeds, the difference becomes more and more noticeable such that to an outside observer, the time in a spaceship travelling at 99% the speed of light would be twice as slow as the time of the stationary observer. Increasing the speed to 99.5% of the speed of light, the observer would see the clock moving about ten times slower than that of the stationary observer. As the speed of travel gets closer to the speed of light, the observed difference increases such that if it is possible to travel at the speed of light itself, time will stand still.^[2]

If this sounds like a thoroughly cock-eyed idea, it is because you have forgotten the other three views:

1. the speed of light is fundamental, invariant and absolute;
2. space and time are interwoven to form the fabric of the universe and;
3. if changes are made in the universe, it is space and time that must adjust to accommodate those changes.

Therefore an intuitive way to view this concept is to realise that since the moving object is moving through space and space and time are woven together, as the speed covers more space, time must slow down. This is similar to a particle somewhere between x and y-axis but destined to the y-axis. You would notice that as the particle moves closer to anywhere near the y-axis, the x component of the co-ordinates of the particle reduces and approaches zero. As soon as the particle reaches the y-axis, the x component of those co-ordinates equals zero. This is analogous to what happens to time as the speed of an object approaches and reaches the speed of light relative to a stationary observer.

Of course, the direct implication of time dilation is that even though it would take a spaceship travelling to the nearest star about 200,000 years round trip, which is about 100,000 light years away, an astronaut in such a ship would hardly have aged a day by the time he returns. This idea makes people think that time travel is possible. Of course, we have been travelling forward in time, but when people talk about time travel, they usually mean the possibility of slowing the speed at which we are travelling forward or even travelling backwards. According to Einstein's theory, it is possible to move back in time.

Einstein's Special and General Theory of Relativity

Having talked quite a lot a lot about time and space-time, we are ready to find out what are the special and general theory of relativity.

Special Theory of Relativity

Special Theory of Relativity is Einstein's determination, in 1905, that the laws of physics

• are the same for all non-accelerating observers, and;
• that the speed of light in a vacuum was independent of the motion of all observers. In other words, the speed of light is invariant.

The above statement is the special theory of relativity which introduced the concept of space-time as a continuum and introduced a new framework for physics. It is called special because it applies to frame of reference in constant motion and does not consider accelerating bodies.

General Theory of Relativity

It was not until 1915 that Einstein was able to include acceleration in his special theory of relativity.

Then, he found that massive objects cause a warp, curvature of distortion in space-time which was the effect described by Newton in 1687 as gravity. He also discovered that such massive objects bend light that come close to it, much like a lens, giving an observer of far-away stars wrong impressions of their locations and multiple images. This is called Gravitational Lensing

While these two theories seem like mere observations, they were accompanied by elegant calculations and have equally profound implications. Some of these effects are:

1. Time is relative and does not pass at the same speed for everyone: a fast moving person would experience the passing of time slower than a stationary observer.
2. Space and time are interwoven to form a continuum
3. The behaviour of both mass and light in distorted space-time led to the famous formula E=mc² which means that mass can be converted to energy.
4. When a body moves at high speed, its kinetic energy increases, and due to E=mc², the mass of that object appears to increase too, depending on the speed. This increase in mass is not apparent in normal speeds. But as the speed of the object approaches the speed of light, the object acquires infinite mass.
5. Due to the number 4 point, Einstein suggested that it would be impossible to build an object that has mass which can travel at the speed of light.

References

1. Brainy Quote | Albert Einstein
2. Exactly What is Time | Relativistic Time
3. Space | General Theory of Relativity
4. Space | Black Holes

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