Ask a physicist, biologist or chemist what got them interested in science and chances are they'll talk about a dramatic single moment - some refer to it as a calling. I've written about mine on Sulphur Mountain in Banff. Two young physicists took the time to try and explain their cosmic ray telescope. Much of it was beyond me but the idea that something from outside our solar system slammed into the upper atmosphere and created a shower of other particles stuck. And that these wouldn't live long enough to make it from the upper atmosphere to their telescope unless time was different for them. I had no idea how that worked, but the fact that they could show that universal time - a master clock for the universe - didn't exist ate at me for nearly two years. I didn't know it but I was about to become a physics student.

Somehow I found two correspondence mentors who taught me a little physics and more math. Two years after Sulphur Mountain I finally understood why time ran more slowly for those speeding muons than for me. That and what E =mc^{2} really meant and how Einstein figured it out. Einstein figuring it out was extraordinary, but more extraordinary is Special Relativity is simple and clear - beautiful - even if the results seem odd. A high school student could read his paper and follow everything with just basic algebra and trigonometry.

There are more than a few explanations in print and online. To really learn it you need to puzzle it out for yourself with pencil and paper guided by a good textbook and problems. Instead I'll talk about how he came to that flash of insight.

Around the age of sixteen Einstein had been kicked out of the German school system. He moved to Switzerland and spent a year at a school that put a premium on visualization and individualism. There he learned about electromagnetism - light was just oscillating electric and magnetic fields that traveled at the speed of light. He found himself wondering what it would be like to run alongside a beam of light. Could he visualize what these fields looked like?

Maxwell's equations said that electromagnetic radiation - light - travels at 300,000,000 meters per second in a vacuum. If he was going that fast the fields would vanish. That didn't work. Since Galileo physics was built on the idea of relativity. The laws of physics didn't depend on how fast you are traveling. All you can measure is the velocity of one object relative to another. He had run directly into a wall.

For a decade Einstein kept at the problem. Finally he went with a crazy idea (to be fair he tried a few crazy ideas). What if the speed of light was the same for all observers no matter how fast they were moving? If you were on a train traveling at 80% the speed of light and pointed a flashlight forward, you'd measure the speed of light from the flashlight as 300,000,000 meters per second, as would a stationary observer watching from the ground as your train sped past.

The way out of this paradox was the person on the train and the observer on the ground experienced time differently. Two events can happen simultaneously for one observer and at different times for another and both could be right. Understanding exactly how that works requires learning about special relativity and you can't avoid the math and some sketches.

Einstein offered the following *gedankenexperiment* (thought experiment): An observer near a train track watches a speeding train go by. Exactly as the midpoint of the train goes by two bolts of lighting strike the train - one at the front, the other at the back. The distance from each strike to her is exactly the same and she says the lightning strikes were simultaneous.

A passenger is sitting at the train's exact midpoint. Because the train is moving the light from the pulse at the back has to travel a bit further than the pulse from the front. He says the strike at the front of the train came first. They weren't simultaneous. *The key is it's simultaneity that's relative.* Once you understand that the algebra is simple. The construction you are left with is space and time are intimately connected in a four dimensioned coordinate system called spacetime. Spacetime doesn't change, but objects in the 3d world we perceive and time have different measurements for observers who are moving relative to each other.

I remember the amazing feeling when it came together in my mind. It was early June around sunrise. I got on my ten speed and rode as fast as I could.

## a 33 year old olympian writes a letter to her younger self

Sarah's letter is excellent - even if you're not a sports fan.

It seems like a good exercise in self-reflection and I briefly considered writing one to myself. Of course if I received a letter I'd think: "OMG! time travel exists!" which, of course, it doesn't, but.. I'd probably tell myself not to focus on a goal, but rather pay attention to the path. Next would be to recognize serendipity in the sense it was originally intended - to have the sagacity to recognize and opportunity and act on it. Listen more and finally become more well-rounded - to have more range. In the end my life has played out very differently than I expected and has been much more interesting.

Quarantine or not, many of us will have a bit more time to reflect. Writing a letter to your teenage self might be a good way to spend some of it.

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