Einstein’s Theory Of Special Relativity — Explained With Simple Examples

“The most incomprehensible thing about the universe is that it’s comprehensible” — Albert Einstein

Imagine two events taking place in a jet plane. One observed by a person on the plane & one on the ground.

To the observer on the plane there will be zero distance between those two events. But to an observer on the ground, the events will be separated by the distance that the plane has traveled in the time between both events.

This explains that two observers who are moving relative to each other will not agree on the distance between the two events.

Now suppose the two observers observe a beam of light traveling from the tail of the plane to its nose. Again with one observer on the plane and one on the ground.

Just as explored in the above example, they will not agree upon the distance traveled by the beam of light from being emitted at the tail to being received at the nose.

Now we know that Speed (s) = Distance(d) / Time (t)

So if both observers agree upon the speed of the beam, i.e. the speed of light, they will not agree upon the time interval taken for the beam between its emission & reception.

Now, here’s what makes this strange. Although both observers measure different times depending on their ‘frame of reference’ which is basically their relative position to the event, they are observing the same physical process.

Einstein didn’t create any artificial explanation for this, he went in a rather logical fashion, and for this startling discovery, he came to the conclusion that the measurement of the time taken, just like the measurement of the distance covered, depends on the observer doing the measuring based on their frame of reference.

Einstein was 26 when he postulated this theory called “Zur Elektrodynamic bewegter Körper” which translates to “Electrodynamics of Moving Bodies.”

Einstein’s paper demands a revolution in our concepts of space & time.

Applying Einstein’s theory to timekeeping by measuring it with clocks further explores the concept.

If we consider two observers looking at a clock, special relativity holds that the clock runs faster or slower according to the observer’s frame of reference.

For an observer who is at rest, the clock runs faster, while to observers who are not at rest, the clock runs slower.

If we use the same example of a pulse of light traveling from the tail to the nose of a plane to the tick of a clock, we see that for an observer on the ground, the clock runs slower because the beam of light has to travel a greater distance from that frame of reference.

While for an observer on the plane, the clock runs faster.

Einstein’s theory of special relativity shows that time cannot be absolute, as Newton suggested. In other words, it’s simply impossible to assign to every event a time with which every observer will agree.

Instead, all observers have their own measures of time, and the times measured by observers who are moving relative to each other will not agree.

This led to Einstein’s development of special relativity, which corrects mechanics to handle situations involving all motions and especially those at a speed close to that of light (known as relativistic velocities).

This further translates to the motion of planetary bodies, that’s where general relativity comes in & where Einstein theroised that spacetime is curved & not flat & is distorted by the mass & energy in it.

“As an object approaches the speed of light, the object’s mass becomes infinite and so does the energy required to move it. That means it is impossible for any matter to go faster than light travels. This cosmic speed limit inspires new realms of physics and science fiction, as people consider travel across vast distances.” — Space.com

Einstein’s model of special relativity got rid of the earlier theories of absolute time & absolute rest, which were Newtonian models.

Special relativity has a wide range of consequences that have been verfied by experiments. They include the relativity of simultaneity, length contraction, time dilation, the relativistic velocity addition formula, the relativistic Doppler effect, relativistic mass, a universal speed limit, mass–energy equivalence, the speed of causality and the Thomas precession.

To explain a bit more about one of these phenomena like time dilation,

“At speeds approaching the speed of light, the effects of time dilation could be much more apparent. Imagine a 15-year-old leaves her high school traveling at 99.5% of the speed of light for five years (from the teenage astronaut’s perspective). When the 15-year-old got back to Earth, she would have aged those 5 years she spent traveling. Her classmates, however, would be 65 years old — 50 years would have passed on the much slower-moving planet.” — Space.com

This was one of the central themes of the Christopher Nolan science fiction movie ‘Interstellar’.

“Special relativity and quantum mechanics are two of the most widely accepted models of how our universe works. But special relativity mostly pertains to extremely large distances, speeds and objects, uniting them in a “smooth” model of the universe.” — Space.com

But with quantum theory, things start to get a bit spooky.

In another post, I explored another theory of quantum physics: Does The Universe Exist If We Aren’t There To Observe It? — According To Quantum Physics

Einstein would further include gravity into his more widely known general relativity, but this paper on special relativity was the start of his journey in postulating theories that have shaped the very fabric of physics and that have given us a model with which we can explain & observe the universe.

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