Einstein’s unfinished thought experiment

Mark Anderson

Mark Anderson

As you know, I am fascinated by many aspects of Albert Einstein, and one of them is his habit of doing thought experiments. We don’t do those enough!

In Einstein’s case, he mused (picture him day dreaming) about things such as elevators falling through space and painters inside of them, about two-dimensional beetles crawling around three-dimensional wires, and so on.

But his most famous thought experiment has always bothered me. So I was delighted that Mark Anderson, a physicist who writes the Strategic News Service, which offers trend-spotting analysis, echoes my frustration in a recent newsletter. Here he goes:

The most famous scientific anecdote of all time remains half-done, unfinished, although countless authors have told the story of Albert Einstein as though it makes sense. Here is how the “thought experiment” goes: when he was 16 or so, Einstein decided that he needed to travel alongside light to understand its nature. (Drum roll.) In this way, he came to understand Special Relativity, a bit later in life. Wow.

There’s only one problem with this apocryphal story: Special (and General) Relativity talk about time and space. They don’t say a word about light, except as it responds to gravitational force.

So, none of us knows what Einstein saw (or did not see) of the light itself, as he (illegally) screamed along at the speed of light, looking sideways…

Well, I have been doing this thought experiment for a while now, without success. (That is not surprising since I opted out of physics as soon as I could in high school.) Here, by the way, is a cool illustration of it.

It always seemed to me that if I were looking sideways at a wave-like quantum of light going at the same speed, it should not even “exist”. Mark seems to think the same thing:

Waves, at their deepest origins, are relative. If you stand at the shore, in they come. But if you fly along with one, like a seagull – say, at the crest of a traveling wave – there is no motion at all; there is no wave.

Having said that, I remind myself, through the haze of my confusion about such matters, that Einstein’s Relativity ended up being about time as much as space.

So perhaps what happens to a light-beam rider is that time … stops. Which is, ironically, exactly what happened when I opened my email inbox this morning.

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