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Cosmology - Albert Einstein

Albert Einstein and Cosmology go hand in hand. Sure there have been some remarkable discoveries by some remarkable men since Albert Einstein released is Special and General Theories of Relativity, but the work by Einstein paved the way.

There are so many websites dedicated to Albert Einstein that I will not go into his biographical data - just do a Google search, and you will see what I mean. Of course, my favorite picture of him is:

He does what he wants and I like that.

A misconception regarding Einstein's work is that while he did win a Nobel Prize, it was not because of his works in Relativity - his Nobel Prize was for the discovery of the Photo-Electric Effect.

Hyperphysics has an excellent section on the photo-electric effect:


(Image Credit)

The photoelectric effect basically proves the duality of light:

When light strikes a piece of metal, like the image above, the photon from the light are of a high enough energy to eject electrons on the surface of the metal.

Its easy to remember that nothing travels faster than light, but there are other things to conceder:

  • Light in a Vacuum travels at 299,792,458 m/s

  • Light travels slower than that depending on the medium - i.e. the refractive nature of the medium

Why is this? Because light is also a particle and like all other particles, they interact. The limit on the speed of light is because light is also a particle. This may not make sense, but Relativity helps to explain this.

The Theory of Relativity:

In 1905, Albert Einstein published his Special Theory of Relativity and in 1916, his General Theory of Relativity was released. While Einstein is best known for his theories, the ideas of Relativity really began with Galileo Galilei. This "Galilean Relativity" was called by Einstein as common sense (and not in the way as an insult, more like a base of understanding). An example of this "common sense" is the train and baby analogy:

A train is moving at 'x' velocity past a train station. On the train, a baby is crawling in the direction of the train. Observers in the train see the baby crawling at 'y' speed. As the train passes the train station, observers standing still see the baby moving at the speed of x + y.

The idea of Relativity is that to any observer, the speed of an object depends on their time frame. I may see my friend throw a football and I can see the ball move at a particular speed. A plane flying overhead either in the direction or against the direction of the moving football will witness a different speed. One is not more correct than another, just another frame of reference. This is the essence of Relativity.

What make Einstein's theory of Relativity special is that it addresses objects that are traveling at high speeds - like the speed of light. Astronomers often use the term "relativistic" when describing or studying a certain phenomenon. This term that can have two meanings:

  • The object or phenomenon is moving near or at the speed of light

  • The speed of the phenomenon will change depending on the frame of reference

Discussing the Theory of Relativity will take far too many pages - and I am by no means an expert. Two very good books for additional reading are:

Einstein, Albert. Relativity. The Special and the General Theory. Crown Trade Paperbacks. New York, 1961.

Sartori, Leo. Understanding Relativity. A Simplified Approach to Einstein's Theories. University of California Press. Berkeley, 1996.

A basic summary of Einstein's works:

  • The laws of physics are the same in any reference frame

  • The speed of light is the same for all observers

  • "A moving clock runs slow" - in other words, time slows down to the outside observer

  • The length of a reference object is shorter to the outside observer

Keep in mind that these changes in time and length are very minute, and any noticeable changes will only occur as that reference frame travels closer to the speed of light.

Our nearest star is Proxima Centauri Alpha (Alpha Centauri) at 4.3 light years away. That means if I had a light powerful enough to reach this star, it will take 4.3 light years to get there. If I were to get on a space ship and fly to Alpha Centauri, I am now in a different reference frame with my own clock - as I reach velocities near the speed of light, I notice that it does not take 4.3 years to reach my target, it is actually less.

The twin paradox is a famous example of Relativity in action:

There are two brothers that are twins. At the age of 30, one of the twins takes a cruise on a rocket that is traveling 99% the speed of light. He does this for a straight year, returning to Earth on his 31st birthday. To his surprise, his brother is 7 years older.

The formula above is the formula to use if you want to determine your own reference frame.

While all of this talk of slowing time sounds fantastic - and hypothesis' abound such as travel beyond the speed of light for time travel - but there are two boundaries to overcome also based on Relativity:

  • Nothing can travel faster than the speed of light

  • The mass of an object increases as the velocity towards the speed of light is reached

The second statement means this: if I were traveling at the speed of light, or pretty close to it (i.e. 98 to 99%), my mass would become infinite. The energy required to move infinite mass would also be infinite.

Some rules of physics still apply regardless of the frame of reference.

To end this section, I will regale a joke/riddle I heard as a child:

If you are traveling in a car at the speed of light, and you turn on your headlights, do they work?

The answer to this question is yes - because the speed of light is the same for ALL observers, including those traveling at the speed of light.

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