‘What is light?’ Grandy’s The Speed of Light: Constancy and Cosmos

“Perhaps you desire to know the manner in which God’s light is ascribed to the heavens and the earth—or, rather, the manner in which God is the light of the heavens and the earth in His own essence. It is not appropriate to keep this knowledge hidden from you, since you already know that God is light, that there is no light other than He, and that He is the totality of lights and the Universal Light.” Al-Ghazali, The Niche of Lights

We live in light. Before me now, the satiny white curtains of my living room have been transformed into a patchwork of bright silver where the morning sun strikes certain places in the fabric’s undulations. Darker areas (still colored white), are created in places where some of the vertical furrows of the drapes shy away from the radiance enjoyed by the alternating sunlit folds. These create striations and dappling that catch my eye and which I experience directly. I notice it more so this morning because I’ve been thinking about light. I want to write about light and I can’t help notice that I am surrounded by it. It fuses within me and although it is scattered around me, I cannot see it until it strikes my eye here in the center of my universe—I am an observer, a participant with light that creates my visual field and informs my consciousness. I experience light as it combines with my mind, integrating my world at a quantum level and then bubbling up into something that can be acted upon at macro scales.

Light. What is it?

I owe these contemplations to a new book by David Grandy, The Speed of Light: Constancy and Cosmos. Grandy is a philosophy professor at Brigham Young University where he teaches classes in the philosophy of science. This book, published by Indiana Press, is not written for Mormons per se, but one cannot read the book without recognizing that it has something profound to say to a people who have scriptures (D&C 88) that read:

6 He that ascended up on high, as also he descended below all things, in that he comprehended all things, that he might be in all and through all things, the light of truth;

7 Which truth shineth. This is the light of Christ. As also he is in the sun, and the light of the sun, and the power thereof by which it was made.


49 The light shineth in darkness, and the darkness comprehendeth it not; nevertheless, the day shall come when you shall comprehend even God, being quickened in him and by him.

50 Then shall ye know that ye have seen me, that I am, and that I am the true light that is in you, and that you are in me; otherwise ye could not abound.

Grandy begins by showing how, unlike the way we typically take the world such that light, in some sense, is moving through a fixed space and time, it is light that grounds the universe. It is the one constant, the framing structure to which space and time conform and to which they shape their warp and weave.

In this book, Grandy carefully unpacks the implications of the constancy of the speed of light by examining Einstein’s theory of relativity (the clearest explanation I’ve seen)*. But he does more than just catalogue light’s strangeness, he explores the stunning implications of that weirdness. He looks at the physics of light, its effect on space-time; he explores the uniqueness of light and the perplexing way it interacts with observers by affecting and being affected by them; he imagines how time passes for light, or more accurately put, how it is not affected by time’s passage; Grandy looks at ambient light in ways I’ve never thought of and explores the strange connectedness and disconnectedness of light as it moves beyond being both particle and wave; and lays out the case that light is fundamental in ways that we have just begun to discover. “Let there be light!” prior to all particular things (like suns), really is the right description of how our universe has unfolded. Or as Grandy puts it:

“ . . . light speed constancy is inclusive of, even, indistinguishable from, the first moment of creation, the originary event when spacetime bounds were set to what could and could not occur thereafter. I say “indistinguishable from” because, as noted earlier, time does not figure into light’s intrinsic nature.” p. 9.

However, for me the best parts of the book are the latter chapters where he explores the philosophies of Merleau-Ponty and Heidegger on the relationship between consciousness and light. These chapters, despite drawing from rather sophisticated ideas from Continental philosophy, are accessible and well explained. Consciousness and light seem to be part of a unified reality that for LDS readers will seem very familiar. This book was not written exclusively for Mormons, but members of our faith will find much to draw their interest in this book.

I typically read three or four books at the same time, but this one pushed everything to the side. I literally could not put it down. Grandy writes like an angel. My advice is not to start this book on a weekend in which you have things to do—because you will not get them done. Talk someone into putting this into your stocking.

I am sitting on a bench outside the church thinking about this book. The wind is blowing though the trees. Wind produced by the action of light from the sun on the atmosphere; trees fashioned by the action of light on photosynthetic cells drawing carbon out of the air and making trunk, branches, and the few remaining leaves clinging to the terminal sprigs; I close my eyes and listen to the sound of the wind rattling the leaves—a symphony produced by light in the form of wind and birch. I open my eyes to let this dancing light in. There, in the center of everything I experience the glissade of a light infused universe.


Al-Ghazali, The Niche of Lights: A parallel English-Arabic Text Translated, introduced and annotated by David Buchman, 1998. Islamic Translation Series. Brigham Young University Press. Provo, UT.

*If you are riding on an airplane going 600 miles an hour and you walk 5 miles an hour toward the cabin. Someone on the ground would measure your speed at 605 mph. Right? But if you measure the speed of light in that same airplane it doesn’t matter whether it’s going toward the cabin or away. It always measures the same: 670,616,629 mph.

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  1. Beautiful, Steve. I’ll be looking for this book.

    Yesterday I met with the TAs I supervise for tutorial sections accompanying the third of a sequence of calculus-based introductory physics courses (~ BYU’s Physics 123), and we worked through a tutorial worksheet on simultaneity. It rather elegantly shows that by simply assuming the speed of light to be constant in all reference frames (to which you refer in your footnote), one has to choose between two apparent absurdities: either (1) two events that are simultaneous in one frame are not simultaneous in the other, or (2) something can happen in one frame and not happen in another.

    Einstein’s special theory of relativity selects option (1).

    Of course there is also the choice to dismiss the constancy of the speed of light in all frames, but there is much evidence in support of this notion.

  2. Thank you for telling us about this book — and describing your experience with it so beautifully.

    I had occasion to make the acquaintance of David Grandy a few months ago, and have had a handful of conversations with him, but I did not know about this book–he was too gracious to even mention it.

    Moving it to the top of my Christmas list.

  3. But can God go faster than the speed of light? Can He make light go faster or slower? Would the universe be destroyed?

    One minor correction: it is the speed of light in a vacuum that is a constant cosmic speed limit. Moving through air or water, light slows down. In fact, there is an amazing phenomenon, Cherenkov radiation, where an observer can actually overtake the speed of light. The result is a shock wave (like a sonic boom, except with transverse EM waves instead of pressure waves). In some recent Scientific American, scientists had slowed down light in some medium to several centimeters per second!

  4. Dan – cool reference. “Slowing” of the speed of light in materials is actually due to absorption and reemission. Special relativity is beautiful, though, and the experiments you are talking about are pretty interesting.

    I fondly remember many wonderful debates with David Grandy in my undergrad years when he used to attend a history and philosophy of science club I organized. I usually disagreed with him, but always found him stimulating.

  5. Fascinating, Steve, and beautifully written. Thank you for giving us this glimpse of the book and your experience with it.

  6. Great post, Steve. Light is such a fascinating thing, and they way you were able to describe it, and how it seems the book talks about it is incredible. I am excited to pick it up and read it.

  7. Rob Osborn says:

    Ah, the speed of light and relativity, I love it. I used to stay up at night and draw up various scenerios. My favorite was the one about the “shooter”. Here it is-

    Suppose two men were standing facing each other and they both had very accurate time pieces. The one has a special gun able to shoot bullets at exactly half the velocity of light. The shooter looking through his scope starts his timer the exact second he pulls the trigger and stops it when he sees the guy fall down. The other guy being shot at is looking through his eyepiece starts his timer when he sees the shooter pull the trigger and stops it when he is hit. What do both see? And, how long does it take the event to happen from each persons perspective?

    Even though it takes only a certain amount of time it’s truly all relative to where you are standing. This is where the question of light velocity and time really play on the mind. The shooter records a longer elapsed time than the guy being shot. Th etricky part is- what does the guy being shot at see? His elapsed time is shorter, so does the velocity of the bullet appear faster? By the time the guy being shot starts his timer, the bullet is already half way to him.

  8. Interesting, Rob, though I would be hesitant to call it a relativity problem since both observers are in the same reference frame (i.e., they are not moving relative to each other). The only reason they observe different elapsed times between firing and hitting the target is because the second shooter is not accounting for the delay caused by the finite speed of light.

    Another fun thing to consider is that what the guy being shot at would actually observe is the shooter being suddenly vaporized by the recoil of a gun that shoots bullets at half the speed of light, since conservation of momentum would cause the shooter to be thrown suddenly backward at a speed of about 80,000 miles per hour. Awesome!

  9. The last sentence in the first paragraph should read “…because the second observer is not accounting…”

  10. David Grandy’s work deserves a wide audience among Latter-day Saints. Always self-effacing, he’s also one of the smartest thinkers we have and an excellent writer.

  11. This is just lovely. I adore thinking about Big things like this, an do so so seldom these days. I’m glad I waited until my kids were asleep to check in today. You’re fantastic SteveP.

  12. Thanks. I have to tell someone what I want for a gift in a gift exchange. You’ve solved my problem for me, thank you.

  13. BTW my favorite was the really fast pole vaulter. He has a twenty foot pole. He moves so fast that it is only ten feet long to an observer and he is running towards a ten foot long shed. So the observer sees him fit within the shed.

    Of course from the pole vaulter’s view, the shed has compressed to only five feet, so he just got a twenty foot pole in a five foot shed. ;)