Chapter 8

Secrets Hiding in the Light

“Your assumptions are your windows on the world.
Scrub them off every once in a while,
or the light won’t come in.”
~ Isaac Asimov

We Take Light for Granted. That’s a Mistake.

Why am I talking about light in a book about gravity?

The best theory we have for gravity is Einstein’s general relativity. General relativity (GR) is more accurate at describing how the universe acts than Newton’s theory of gravity. GR also makes unique and outrageous predictions that have been extensively tested and have come through with flying colors.

But I’m not here to just force-feed you. I want to give you the “why” behind the theories. And to get mentally prepared for GR you have to start with special relativity. And to see why in the world Einstein or anyone in their right mind would formulate the special theory of relativity you have to come to grips with what the experiments of the 1800s revealed about the nature of light.

In this chapter, we follow only those experiments in the 1800s that led up to the special theory of relativity. We will get back to a other threads of mind-blowing experimental results from the 1800s, when we tackle quantum mechanics (Appendixes A and B).

In the early 1800s, a guy named Michael Faraday created ground-breaking experiments revealing the nature of electricity and magnetism. By the mid-1800s, another guy named James Clerk Maxwell went much further, mapping out theories and formulas that combined electricity, magnetism, and light — to create the framework that has allowed us to master electricity and to understand light and electromagnetism.

But the real kicker was when Albert Michelson and his cohort Edward Morley set up an experiment that was supposed to measure the speed at which the Earth was traveling through the luminiferous æther. This luminiferous æther was presumed to permeate the entire universe and give electromagnetic waves a medium to travel through. The results of that experiment were, well, not what was expected. You’ll have to read the chapter.

The you-can-do-this-at-home activity for this chapter is the most elaborate activity that I’m describing in this book. It also requires more supervision than any of the other activities. It involves short-circuiting a battery. This should only be done briefly. The long-term short-circuiting of a battery can cause it to overheat and even explode or catch fire.

Do not do this activity if you are unable to keep a close eye on the battery.

Activity Video for Chapter 8

Here are the links from the text in Chapter 8:

34. Biography “History – Michael Faraday – BBC.”

35. Deeper Dive “Voltaic pile – Wikipedia.”

36. Great Video “How Do Magnets Work? – Fermilab.”

37. Deeper Dive “Electrons DO NOT Spin – PBS Space Time” …that is – they don’t spin the same way a top spins — or the way a wheel spins.

38. Biography “James Clerk Maxwell | Biography & Facts | Britannica.” 1 Nov. 2020, 

39. Deeper Dive “Measuring the Speed of Light – The Star Garden.”

40. Deeper Dive “Rømer’s determination of the speed of light – Wikipedia.”

41. Biography “James Bradley | English astronomer | Britannica.”

42. Biography “Hippolyte Fizeau – Wikipedia.”

43. Biography “Léon Foucault – Wikipedia.”

44. Deeper Dive “Fizeau–Foucault apparatus – Wikipedia”

45. Biography “Albert A. Michelson – Wikipedia.”


47. Biography “Edward W. Morley – Wikipedia.”

48. Great Video “Neil deGrasse Tyson explains the Michelson-Morley ….” 21 Jun. 2013,

49. Biography “Hendrik Antoon Lorentz | Dutch physicist | Britannica.”

50. Physics-Speak Great Video Lorentz Transformations | minutephysics | YouTube. Warning: Contains ads.

51. Deeper Dive “The formation of rainbows, mirages, and the green flash.”

52. Great Video “Why does light bend when it enters glass? – YouTube.” 1 May.