Want to experience relativity? Try riding a bicycle!

Albert Einstein reportedly said that he thought of relativity while riding his bicycle. According to some, he thought of the concept while riding at night with his bike headlight on. He considered the implications of the fact that the speed of light emanating from that headlight was the same whether he was moving or stationary. This brief video offers an idea of those implications.

But relativity isn’t just restricted to bike headlights or trains. It’s something we all experience at one time or another. As Einstein once said:

Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That’s relativity.

However, if you don’t have a pretty girl to sit with for an hour, and you have no desire to put your hand on a hot stove for even a second, it may be difficult to intentionally create an experience of relativity. But not if you have a bicycle!

I was thinking about this last weekend, while I was riding in a big bicycling fundraiser called the Pan-Mass Challenge. The PMC has many cyclists (5,700 this year) riding long distances to raise a lot of money ($40 million this year) to fight cancer through the Dana-Farber Cancer Institute. Because so many people have been touched one way or the other by cancer, there are many spectators along the route who cheer the riders on.

PMC rider and spectators making a connection

While riding this year I was struck by how different the experience of this ride is for the riders and for the spectators.

For the spectators, their location is constant and they see a steady stream of cyclists coming and going. This is the reality of the event for them. But for the cyclists, who are riding in groups with other riders, the group of riders is constant and they see a steady stream of spectators and scenery coming and going.

The end result is that while spectators and riders are interacting with each other for brief moments, the realities they are experiencing are very different – even though both realities are equally true.

The reason for this is that each group is experiencing only a part of a larger whole. The cyclists experience the fullness of the route they are riding, from the beginning to the end. But they are only experiencing a small fraction of the riders in the event: those that fit into the road immediately around them and going the same speed. Meanwhile, the spectators get a much greater sense of how many riders there are in the event: those that continually stream by over many minutes and even hours. But they have no sense of the route as a whole – only the small part of it in their location.

Usually these realities remain distinct from each other. However, sometimes a rider will stop to fix a tire, visit with friends along the route, or for some other reason. When I have done that in the past I’ve been struck by how different the ride feels when I am still and see the many cyclists passing.

While the PMC offers a dramatic example of this phenomena, you can experience it any time you go for a bike ride – especially with a group of friends. So if you want to experience relativity firsthand, get on your bike – the “relativity machine” – and go!