# From the Editor: E=mc²

May 31, 2012

It is one of the most recognizable equations in the world, to mathematicians, physicists and layman alike. It is the Theory of Relativity and it is most widely attributed to one of the greatest thinkers of the early twentieth century, Albert Einstein, even though this theory of time and space is not the result of his genius alone.

It is called the Theory of Relativity because it posits that the measure of time and length are not absolutes. A second in time or a kilometer along a road are not necessarily the same throughout the Universe.

Although it is not humanly possible, with all due respect to Doc Brown and H.G. Wells, if I were to travel a kilometer in outer space at close to the speed of light (300,000km/s) and you were to travel a kilometer hear on earth at a “normal” speed and we had the ability to compare the two times and distances, we would find that your watch would be going slower than mine and you would have actually traveled a shorter distance.

One of the easiest ways it has been described is in the twin paradox:

“One 25 year old twin stays on earth while the other, fresh out of astronaut school, sets off on a space voyage travelling at 90% of the speed of light. After 10 years in space, with her mission accomplished, she turns round and heads back to earth. By the time she lands she knows from her on-board clock that 20 years have passed. She is now 45 years old. Fortunately, her study of relativity has prepared her for the shock when she sees her twin sister, who is now 71 years old.”

In essence, traveling through space very fast is not only space travel, but also time travel.

So why am I writing about the space-time continuum in the pages of Quality Magazine? Here on earth, with the technology we currently have, we cannot change space or travel at the speed of light. We are resigned to following the Euclidean model-three dimensions of space and one dimension of time; an x, y, and z-axis plus time.

The x, y, and z-axis will be familiar to everyone who has ever worked with 3-D modeling software. In fact, some of those 3-D models might resemble the graphic here representing the space-time continuum.

For more on 3-D, check out this month’s features, “The Case for 3-D Assembly Verification” and “The Gate to 3-D Quality Control.”

As for space and time, see how we can make the best use of it as it exists and learn how sandwich plates can reduce space needed and increase efficiencies in your measuring room with our measurement article, “Fixture Success.”

As always, enjoy and thanks for reading!