## Description

Special Relativity Poster

First published by Albert Einstein in 1905, special relativity describes the relationship between space and time. While Sir Issac Newton theorized that space and time were independent of each other, Einstein concluded that the two are inextricably linked.

The two main tenets of Einstein’s special theory of relativity are:

- the laws of physics are the same for all non-accelerating observers
- the speed of light in a vacuum is constant regardless of the speed of the observer

Consider a car speeding down the highway, heading north at 55 mph. When it turns northeast to merge onto another highway, it suddenly isn’t traveling north at 55 mph anymore since some of that motion has been shifted east during the merge.

The same principle applies to space and time. For example, a parked car may not be traveling through space – but it is traveling through time with each passing second and minute. If the car is parked and quickly speeds away, some of that motion through time is diverted into travel through space.

It is important to note the second tenet – the speed of light is constant – because it means combined motion of any object through space and its motion through time is always equal to the speed of light. In the analogy, this means that the car cannot accelerate as it moves northeast to maintain a northward velocity of 55 mph. Therefore, the speed of light is essentially a speed limit.

This relationship also means that time slows down for the driver of a moving car relative to time for a stationary observer. This might seem outlandish since a cross-country plane trip doesn’t slow aging, but the idea of time slowing down was proven in 1971, when Joseph Hafele and Richard Keating flew atomic clocks around the world on a commercial jet. After the pilots landed, their clocks were compared to identical clocks left on the ground. It was determined that time had indeed slowed for the flying clocks – by a few hundred billionths of a second.

Therefore, since light has all of its motion being used traveling through space – time has stopped for anything traveling at the speed of light.

Einstein’s special theory of relativity also showed that speed of light squared (c^{2}), which is a very large number, and a small amount of mass (m) – translates into a huge amount of energy (E). Through the equation E=mc^{2}, Einstein could then explain the enormous energy released by massive stars.

At the time Einstein published his theory, he was unsure if there was an accessible physical mechanism by which that reaction can take place on Earth. Unfortunately, those of use living in the nuclear age know that there are several physical processes capable of releasing massive quantities of energy. In fact, when Einstein found out decades later that his work would be used to make a bomb – he wrote a letter to President Franklin Roosevelt, warning about the power of such a device.

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