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March 17, 2011 / Anke van Eekelen

Slow motion approach to “the speed of light”

By Anke van Eekelen

Let’s face it, some fundamental concepts in science are just too hard to get your head around. The average person may get a hint of their meaning, but only if the issue is simplified at large.  A good example of such a notion beyond grasp is light and the properties of its motion.

Brian Greene, author of the book entitled “The Elegant Universe”, goes to great length to bring the scaringly complicated physics of the universe closer to the reader.  In his chapter on “The Speed of Light” (pp 31-33), he demystifies the idea of relative motion with a sequel of examples that gradually build up a story of increasing complexity. The feeling that you, as the reader, are the main character in the tale is quite effective as well.

This engaging approach starts with a basic observation of a down to earth experience: a game of throw & catch with a baseball. Greene then wants you to take a next step: imagine now that it is no longer a ball but a grenade that is thrown at you. You would want to run away as quickly as you can and because you do, the perception of its speed will be less than if you would have remained in place and attempted to catch it like a ball. The same message comes across when the reader is placed in the mountains and faces an avalanche of snow.

What the reader has experienced in his or her mind can be explained by the classical theory of motion according to Newton. But what follows reaches the limits of most people’s comprehension. As soon as the grenade is swapped for a light beam or laser in the remainder of examples, running away is as useless as “hitching a ride on spaceship Enterprise and zipping away”.  Why? Because “the speed of light is always the same”, it is always 670 million miles per hour.

Star Trek spaceship Enterprise

Greene softens the blow of this ‘hard to swallow’ climax of his enjoyable lesson on the physics of motion by indicating that only a few bright lights in history, among which Einstein, were able to embrace this fact.

For all ordinary people, it is encouraging to know that common experiences and basic observations compellingly placed in a context that speaks to the imagination, can shine light on complex scientific ideas you otherwise would have wanted to run away from.


Greene, B. (1999). The Speed of Light : Space, time, and the eye of the beholder. In The Elegant Universe (pp 31-33). New York: W.W. Norton & Company.



Leave a Comment
  1. SONG / Mar 24 2011 1:54 pm

    I guess this is a well summarised information of the source, especially, I think you effectively used that example, Throw&Catch, and then moving to another example (StarTrek) for explaining the case of light. (at least, I see it makes more sense than throwing photons.)

    But one thing I’d like to suggest is, you might have some ‘more common’ example for explanation.
    This is another example that I used to here about the relativity and speed of light.
    “If you are flying in speed of light, and holding a mirror in your hand, what would you expect to see from it?”

    What do you think about this question?

    • ankevaneekelen / Mar 30 2011 6:20 am

      Hi Song,

      Thank you for your response and please accept my apology for my late reply and thinking you would be a reader of this blog outside our class. The confusion must have come from the way (use of a non-UWA email address) your comment was submitted.

      With regard to the content of you comment, I would like to argue that Greene’s success in simplifying this difficult concept in physics lies in the initial use of common examples. These then need to become more far-fetched to illustrate the complexity of the concept. Who would feel challenged to come up with other (more down to earth) examples to explain the difficult to grasp fact that the speed of light does not change with our perceptions of movement?

      I don’t think I can even give you an answer to the question posed in your comment. Maybe the best would be to ask an expert in physics and let’s hope that this expert has similar communication skills as Greene to explain to us what we would see in the mirror.


  2. Rosanna Margetts / Mar 26 2011 8:12 am

    Hi Anke, one thing that stood out for me was that your blog flowed very well. I also noticed your sentences were nice and succinct.

    • ankevaneekelen / Mar 29 2011 3:00 am

      Hi Rosanna,

      Thank you very much for your encouraging comment regarding the way I have tried the blog to be appealing to read by others. As you can see from the comment above, it even attracted a comment from a reader outside our class. I am amazed!


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