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The concept of "light" described by modern physics seems, to me at least, an incomprehensible bundle of properties: a "universal constant," the "maximum speed," a "wave-particle" phenomenon, the invisible source of "visibility," the equivalent of the square root of "energy divided by matter," a limit of causality, an "electro-magnetic field," and the "fastest possible information," etc.

I can read the basic physics and follow the explanations, but really cannot make sense of it or develop an intuitive grasp of what in the world we are talking about. In addition to the basic physics, I have read David Grandy and a bit of Merleau-Ponty for a phenomenological view of light. Also, some of Heisenberg's philosophical essays.

But is there anything in between this and the physics? Are there some interesting modern philosophical works on the nature, properties, and meaning of "light," with a basic grounding the physics of light? I might also welcome "philosophical" or "synoptic" works by physicists without the standard analogies. Something that gets away from flashlights, twins on rocket ships, wave functions, photons, and the usual rigamarole.

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    I see three possible approaches to this. One is a philosophical approach bounded by the physical properties of light. The other is a philosophical approach which bounds the physical properties of light (i.e. explains everything of physical light but also has additional implications). The final approach would be a mixture of the two. I think these naturally lead in different directions, and I'm curious which one is most useful for you. – Cort Ammon Dec 1 '15 at 23:14
  • There is a metaphysics of light, that substitutes light for being - but I don't think it's what you're looking for. – Mozibur Ullah Dec 1 '15 at 23:39
  • @CortAmmon. Not sure how to answer that. Possibly the first. I guess I'm looking for a very reductive, abstract framework, but that's not much help. I am intrigued by alternative spatial perspectives like "shape dynamics," though I do not yet have any grasp of that. – Nelson Alexander Dec 1 '15 at 23:51
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    @MoziburUllah. Not sure what you have in mind, but I might be interested. I find Hegel's descriptions of gravity and other concepts from physics very interesting and helpful, but I was looking for more recent views. – Nelson Alexander Dec 1 '15 at 23:53
  • What is your objective? Are you simply trying to "understand light"? Unfortunately, no one knows what "light" is, so no one can explain it. All that can be done is to measure and describe its effects within theoretical frameworks. But if you have some other objective/goal for your question, other answers might be possible. – user2338816 Dec 2 '15 at 0:52
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Richard Feynman explains Quantum Electrodynamics in a wonderful non-technical series of lectures: QED: Photons -- Corpuscles of Light.

QED is a theory which describes how light and matter interact.

It naturally includes no metaphysics, but it does in my opinion include a lot of philosophy.

At one point in the lectures he offers his interpretation that positrons may be electrons that as result of an interaction did not only change direction in space, but also in time — that is, they are electrons travelling back in time.

There is also a good exposition of special relativity by the philosopher of science Tim Maudlin in his book: Quantum Non-Locality and Relativity: Metaphysical Intimations of Modern Physics. That book is worth its weight in gold for its explanation of Bell's theorem.

And if you can handle a little physics, Feynman's lectures are a mind blowing source, for he could not help but teach physics with a ton of philosophy, intuitions and clarity.

  • I give up! The times I've looked at Feynman I just didn't take to him somehow. But everyone raves, so I suppose you are right, I better buy QED give him a more persevering try. Have a book on time by Maudlin, but haven't looked at the one you mention. – Nelson Alexander Dec 1 '15 at 21:34
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    @Nelson Alexander : I'm a bit of a Feynman fan, but he didn't get everything right. Photons have an E=hf wave nature, so the word "corpuscles" can be misleading. And whilst there is a way in which a positron can be thought of as a "time-reversed electron", it isn't travelling back in time. If you're interested in time you might care to read something I wrote here. – John Duffield Dec 1 '15 at 23:43
  • @John Duffield Concerning ontology I consider a photon according to the corpuscular model, because a photon multiplier registers either the whole photon or nothing, but never a part of a photon. The wave in question is the probability wave of the photon state. - You are right that a positron does not travel backwards in time. But of course Feynman did know this too, and prior to us :-) Possibly Feynman means that the conception of particles and anti-particles traveling in different time directions unifies their representation and interaction by Feynman diagrams. – Jo Wehler Dec 2 '15 at 14:01
  • @Jo Wehler : see Compton scattering where the electron effectively "takes a slice" off the incident photon. The wavelength reduces. IMHO there's no issue saying a photon is a corpuscle provided you remember that each has an E=hf wave nature. The quantum nature of light relates to the way the dimensionality of action can be expressed as momentum x distance. Take a look at some pictures of the electromagnetic spectrum. What's always the same regardless of wave height? – John Duffield Dec 2 '15 at 14:39
  • @John Duffield Compton scattering is generally considered supporting the corpuscle model of a gamma-quant, also in the reference of your link. Where is the notion "takes a slice" taken from? - That the gamma-quant looses some energy does not mean, that afterwards only a fraction of the gamma-quant exists. - Could you please explain the last sentence of your comment, what does "wave height" mean? – Jo Wehler Dec 2 '15 at 15:14
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Hans Reichenbach's "The Philosophy of Space and Time" and "Philosophic Foundations of Quantum Mechanics" are a little bit dated (Pre John Bell) but still relevant. I like the texts because of their "perfect mix" of philosophy and physics (which seems like what you are looking for). Beware though that Reichenbach was part of the Vienna Circle, and take what he says with the occasional grain of salt.

  • Thanks, I've read some Reichenbach and have that, but will dip back into it. You're right, he's very clear but somehow not the "alternative" overview I'm looking for, not that I know what that is. – Nelson Alexander Dec 1 '15 at 21:29
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The speed of light is a physical constant. Hence one needs a textbook on physics to understand it, not a philosophical treatment.

Light is an electromagentic wave like radio waves, infrared radiation, gamma rays. Light is distinguished only by the accidental property, that humans are sensible for light but nor for the other kinds of electromagnetic radiation with different wave lengths.

Classically, the whole theory of light is a special case of Maxwell's theory of electromagnetism. All eletromagnetic waves travel with the same speed as light.

A new aspect entered the subject with Einstein claiming that the speed of light is a universal constant, i.e. that it is always measured the same value, independent from the speed of the observer. That's a singular effect. We do not know why it is the case. But it was an ingenious conclusion Einstein derived from the Michelson-Morley experiment.

A further turn in the investigation of light came with quantum electrodynamics. For me the lectures and books of Feynman are the best introduction, see the answer of @nir.

Feynman has written for any level of physical background. Like @nir I consider The Feynman lectures on Physics a sound base, see http://www.feynmanlectures.caltech.edu/

  • Thanks. Per my response to @nir, I give in. As you say, the "singular effect" is the baffler, and it forces me to think about what is even meant in this context by a "speed" or a "fastest speed," (which Leibniz used as an example of a nonsensical absurdity, not sure why.) I tend to think of it as the "least possible difference," without knowing what that means. – Nelson Alexander Dec 1 '15 at 21:42
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    Speed of light is no mystery: Take the ususal definition of "velocity = covered distance divided by used time". The first measurement of the speed of light was made by Ole Roemer (17th century) by considering a certain moon of Jupiter. - Also fastest speed means just what it literally says: You cannot increase your speed, moving faster and faster until your speed finally excels the speed of light. This is made plausible by the Special Theory of Relativity: When approximating the speed of light, the mass increases such that it would become infinite when reaching the speed of light. – Jo Wehler Dec 1 '15 at 22:01
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    "... an ingenious conclusion Einstein derived from the Michelson-Morley experiment." -- that is true. and he might have even conceived it without the help of M-M. -- "We do not know why it is the case." -- yes we do know why. it is the case because, unlike the wind, we don't know the difference between sitting "stationary" in a vacuum or having the vacuum whiz by our face at a 100 million meters/sec. it's still just a vacuum. that means, no matter who thinks they are moving or who thinks they are stationary, all inertial observers have the very same laws of physics, incl. parameters. – robert bristow-johnson Dec 1 '15 at 23:43
  • @robert bristow-johnson I apologize for not understanding your argumentation concerning the vacuum. Why does it explain the constancy of the speed of light? - Of course, all inertial systems are on equal footing concerning the laws of physics. But that's a conclusion, it does not explain the Special Theory of Relativity. – Jo Wehler Dec 1 '15 at 23:57
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    "all inertial systems are on equal footing concerning the laws of physics. But that's a conclusion,..." no, it's a postulate. and a very sensible one. why should one inertial frame (which seems stationary to the observer in it) have different physics than another inertial frame (which also seems stationary to the observer in that one)? who says which different physics goes to which inertial frame? who is truly "stationary" (while the other frames are "in motion")? then how can these different observers have different variants of Maxwell's equations? (with different \epsilon_0 and \mu_0?) – robert bristow-johnson Dec 2 '15 at 0:08
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You might like Lucas and Hodgson's Spacetime and Electromagnetism". Lucas is a philosopher and Hodgson was a physicist. Their book describes itself as an essay on the special theory of relativity and it covers both the physics of the theory and the philosophical aspects of it.

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Recommended discussions of light and “the speed of light” in modern philosophy?

Have a look at Is The Speed of Light Everywhere the Same? It's by Don Koks the PhysicsFAQ editor, and the answer is no. If the speed of light was the same throughout the room you're in, your pencil wouldn't fall down. Sadly a lot of physicists will tell you the speed of light is absolutely constant. Even though this flatly contradicts Einstein, see this from 1920:

enter image description here

Also see Shapiro's 4th test of General Relativity. There's lots of other examples. The problem is that people confuse the speed of light with the locally measured speed of light. That's a defined constant because we use the local motion of light to define our second and our metre, and then we use them to measure the local motion of light. Duh. See Magueijo and Moffat talking about the tautology here.

The concept of "light" described by modern physics seems, to me at least, an incomprehensible bundle of properties: a "universal constant," the "maximum speed," a "wave-particle" phenomenon, the invisible source of "visibility," the equivalent of the square root of "energy divided by matter," a limit of causality, an "electro-magnetic field," and the "fastest possible information," etc.

Sadly there are issues with some aspects of contemporary physics. I'm an outsider, an IT guy who got involved about ten years back when I came to realise that physics was going to hell in a handcart. I'm trying to do something about it, but it's not easy.

I can read the basic physics and follow the explanations, but really cannot make sense of it or develop an intuitive grasp of what in the world we are talking about. In addition to the basic physics, I have read David Grandy and a bit of Merleau-Ponty for a phenomenological view of light. Also, some of Heisenberg's philosophical essays. But is there anything in between this and the physics? Are there some interesting modern philosophical works on the nature, properties, and meaning of "light," with a basic grounding the physics of light?

If you ask a typical physicist what is light, you won't get a satisfactory answer. But there are physicists out there who do know, and I know them. So, what do you want to know?

I might also welcome "philosophical" or "synoptic" works by physicists without the standard analogies. Something that gets away from flashlights, twins on rocket ships, wave functions, photons, and the usual rigamarole.

You should read The Other Meaning of Special Relativity by Robert Close. The real reason special relativity "works" is because of the wave nature of matter.

  • My pleasure @Nelson Alexander. Don't give in, because IMHO all this stuff is simpler than you think. It's late now, I have to go, but think on LIGO, and Maxwell's transverse undulations, and four-potential, and the dimensionality of action being expressable as momentum x distance. And this: When a seismic wave moves through the ground, the ground waves. When an ocean wave moves through the sea, the sea waves. And when an electromagnetic wave moves through space... – John Duffield Dec 2 '15 at 0:13
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The metaphysics on light is a turn in Islamic peripatetic/Neoplatonic philosophy, which substituted Light for Being; it's associated with Suhrawardi.

There are is also a corresponding development in Kashmir, by the Kashmiri philosopher Abhinavagupta; and which, according to this conventionally scholarly thesis by Kirk Templeton was independent.

This, though is well outside the framework you're exploring - modern, contemporary, and physics based; though there is some correspondance with phenomenology, perhaps - light being that by which we see: some other element or medium that is neccessary to bring the object to the subject; or take the subject to the object.

This may seem exotic, outré and eccentric, but Frank Wilzek (2004 joint Nobel Laureate) points out in his book,The Lightness of Being - which is discursive in the usual manner that:

A central theme of this book is that the ancient dichotomy between celestial light and earthy matter has been transcended. In modern physics, all the stuff out there is unified into one Being more like the traditional idea of light than of matter.

I haven't read the book, so I can't say much more on it; but I expect that the argument will be similar to how visible light is only a small part of the electromagnetic spectrum, and this is generally accepted; the next step is to note that all the modern theories of forces (apart from gravity) are couched in theoretical terms taken from Maxwell, Freeman Dyson quotes him as saying (reprinted in only the second volume of Nature):

Another theory of electricity which I prefer denies action at a distance, and attributes electric action to tensions and stresses in an all-pervading medium, these stresses being the same in kind familiar to engineers and the medium being identical to that in which light is propagated.

The terms highlighted is what Einstein managed to introduce to gravity.

Generally, Maxwells equation are presented as a set of four vector equations; but why four dimensions? Can we generalise for higher - and it turns out we can (using the language of forms), and better the equations simplify to an almost symmetrical pair of equations - so the number of equations have been cut in half (originally Maxwell had twenty equations - so there's been a long process of chipping them down).

But more, in this form it's also true for any curved space - this is also very useful because physically, spacetime is curved; and we need the equations to be valid in just such a context and not the usual boring Euclidean space that we're all used to simply by living, being and perceiving.

The second development is to notice that light has a hidden symmetry - a circle; this can be made a little more explicit if you view light as a travelling wave with transverse components of a magnetic and electric field.

This is most easily seen visually; but in words if you take the vector sum of the field strengths you get exactly what looks like a clock-hand spinning around a circle; and this picture and metaphor is useful as light beats out time.

This is the hidden symmetry of light; Geometrically thought of as a circle; it's also referred to as 'gauge freedom', or 'internal symmetry space'.

The next step was taken by Yang and Mills; when they replaced the circle by higher spheres.

It's in this form that EM and the weak force was unified - electroweak and then the strong force formulated.

Then the obvious thing to think, is that given the origins of this theoretical development in Maxwells EM, to see corresponding features in its concrete generalisations.

Interestingly, gravity itself can be cast into this language (but whereas light can be quantised in this language, gravity still proves resistant).

This is one of the key moves in the last century - geometrisation; not only in physics, but also number theory (ie Grothendiecks theory of schemes) ; they're essentially the same language - fibre- bundles or just bundles: whereas GR just has spacetime, EM for example, attaches (or bundles) a fibre (which looks like a circle or sphere) at every point.

Actually, all this is also interesting from a metaphysics of light perspective; given geometry is something we do by eye - as opposed to algebra which we do by touch ie counting on ones fingers.

But this isn't really what the metaphysics is about; the locus classicus is Socrates in the Republic, where he asks why is a third thing is required to see - the Sun.

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