THE GREATEST PUZZLE OF ALL (1)

If you claimed you have seen light, you must be mistaken. For no man has seen light itself. What you have seen are the effects of light as they are reflected back to our retina from an object.

Plato remarked that light takes on visibility as objects and ideas flash into existence by the grace of light (306-35). He did not mean that light qua light is thereby revealed, for he understood that "rather than being a component of visibility, light has an originality of its own" (Vasseleu 4)

Consider Plato's proposition that light is immuned to visual apprehension. If this were not true, then seeable or opaque light would block our view of things other than light. Since it does not, we instinctively imagine light as an intermediate transparency between perceiver and perceived. Such thinking, however, confers upon light a reality that no experiment or experience, even in principle, can sustain.

To elaborate this point, let us try to locate light in our field of experience. Three possible locations present themselves. Light is (1) striking the retina; (2) striking a perceived object; and (3) traveling from the object to the retina. Given light's uniqueness, none of these possibilities can be defended in conventional language that permits us to assert that thing x is at location y. Possibility (3) is rendered problematic by the aforementioned fact that light cannot be hailed in advance. If indeed we could see it at a distance--see it passing through intermediate space--some light-like agency would have to present it to the retina, and then that agency would be light as we know it and just as immune to delimitation in intermediate space.

Possibilities (1) and (2) may seem more straightforward, but in fact the two collapse into each other. Yes, (1) may be said to occur, but when it does we see (2), even though a space-time interval separates the two events. This collapse, of course, is the very essence of vision, and despite its deep familiarity, can teach us much about light.

Foremost is the recognition that though light is present when it strikes the retina, its presence is non-local; that is, completely given over to distant objects. These objects, in fact, must "keep their distance" from the retina if they are to be seen, for once they make immediate contact with the eye, vision fails. Light, by contrast, strikes the retina and if it is to make any statement at all, must announce the existence--the distant presence--of something other than itself. Thus, the local presence of light implies its absence: it is here striking the eye but affording us visual witness of what lies beyond by absenting itself as a local entity to be seen. If it is to do its work of vision, it cannot register itself as visual fact, for then it would interfere with the seeing process.

Sometimes, of course, light does appear to interfere with seeing, and then it is natural to regard light as distinct from the objects we look at--to suppose that light has an appearance or visual texture of its own. But when this happens, we mistake a seeming excess of reflected, refracted, or scattered light for light per se. Sunlight, for example, is never seen in isolation. It is seen in conjunction with the white snow that reflects it, the atmospheric air molecules that scatter its blue component, the atmospheric haze that scatters its reddish component, and the material, gaseous backdrop of the sun itself. True, the midday sun is hard to look at owing to its abundant light, but we would never be dazzled if light were not interacting with the physical matter that constitutes the sun. It is that interaction that brings the sun into visual being and gives it bright announcement. And while that announcement may be too bright for human eyes, we can no more see brightness or light per se than we can see an abstract, unattached adjectival quality. When we say, therefore, that direct sunlight is too intense for human vision, we are not registering the fact that light somehow shows up by itself as we look at the sun. We are merely acknowledging a physiological threshold of our ability to see bright objects.

If, indeed, we could see light, it would be hard (seemingly impossible) to see stars in the night sky: they would not show up against a backdrop of darkness but would be surrounded by the light they radiate into empty space. This is a variation on the remark that a flashlight beam fails to show up in the night sky unless a material entity (an insect or raindrop, say) intervenes to be given visual announcement. Even laser beams remain unseen without material interaction; they are not self-luminous but borrow their visual texture from illuminated gas particles.

These considerations have prompted some physicists to insist that seeing light merely amounts to seeing "things lighted." What's more, if light does not show up on its own, then the notion of its propagation in empty space is empirically gratuitous. Stephen Toulmin, Ron Harré, Geoffrey Cantor, and Vasco Ronchi have all developed this point by noting that the concept of moving or projectile light is part of the legacy of geometrical optics. After rehearsing the history of optics since the late Middle Ages, Ronchi states that if we are to learn to talk coherently about light, "we must definitely avoid assuming any distribution of the radiant energy during its supposed propagation" (271). Cantor argues that although light's nature is "beyond our ken, " we instinctively find ways to bring it "under the umbrella of matter," albeit generally without realizing that a poetic leap has been made (96-97). As a case in point he singles out "projectile optics," a metaphorical outlook that draws heavily on material particles in motion but which, in his view, is infected with deep tension.

Trying to develop a cognitive model of vision, James J. Gibson arrived at similar conclusions. In his last book, he wrote: "Vision is a strange and wonderful business. I have been puzzling over its perplexities for 50 years. I used to suppose that the way to understand it was to learn what is accepted as true about the physics of light and the retinal image, to master the anatomy and physiology of the eye and the brain, and then to put it together into a theory of perception that could be tested by experiments. But the more I learned about physics, optics, anatomy, and visual physiology, the deeper the puzzles got. The experts in these sciences seemed confident that they could clear up the mysteries of vision eventually but only, I decided, because they had no real grasp of the perplexities. (xiii) "

This retreat into non-visibility or unknowing is hardly a new idea. John Locke suggested that the eye's self-blindness enables optical vision (87). Aristotle stated that nous or mind must be a self-emptiness amounting to pure capacity or receptivity: "For if [nous] shows its own identity, it hinders or obstructs what is other than it; hence it can have no nature but that of capacity. What is called nous of the soul, then... is not anything until it knows" (qtd. in Ballew 128).

If Aristotle is right, we apprehend the world by the grace of some agency that does not show up on its own; further, this agency is a kind of open set that freely receives other things and only then registers its own existence. Light, it seems, follows a similar principle: by retreating or failing to dawn as a freestanding entity, it clears or opens space for the appearance of other things. It is, as Hans Blumenberg insisted in his elaboration of light's many aspects, "the 'letting-appear' that does not itself appear, the inaccessible accessibility of things" (31).

Thanks to light, material objects visually present themselves to our senses. For this presentation to be effective or "clear," light also must be clear, but in a different way. To the extent that objects show up with clear, well-defined details that enable apprehension and understanding, light qua light fails to show up at all: it must be clear in the opposite sense of being transparent or invisible. Light is a formless clarity or openness that permits seeing without being threatened by seeing.

Gibson said " Geometrical space is a pure abstraction. Outer space can be visualized but cannot be seen.... The doctrine that we could not perceive the world around us unless we already had the concept of space is nonsense. It is quite the other way around: We could not conceive of empty space unless we could see the ground under our feet and the sky above. Space is a myth, a ghost, a fiction for geometers."

Nor, said Gibson, do we see rays of light streaming to the retina--another geometrical abstraction. Rather, we see illuminated surfaces, the collective, shifting array of which conveys meaning as surfaces interrelate. Hence, meaning inheres in the world, in its ecological inter-linkage, not in a particular part of the world--the brain--that putatively confers meaning on the rest.

Gibson affirmed light's role in seeing but reconfigured that role along the lines of actual experience in such a way as to break the traditional connection between light and space. His concept of ambient light coincides with our sense of vast and immediate visual contact with distant objects. Not only is the visual landscape generally much larger than one's attentive focus, but there is no delay across space: we do not, upon opening our eyes or turning our heads, have to wait for images to arrive or link up with previous images. From these considerations and others, Gibson concluded that though light is transparent, it is not a spatial blank or emptiness, and this because it is immediately informative of objects. He wrote that "information is not transmitted [and] the speed of light is irrelevant to vision. The [optic array] does not consist of light rays but of sight lines... information does not have to be carried by light from place to place" (qtd. in Reed 257). Put differently, information "is simply available in the optical structure of ambient light" (Reed 257).

Gibson's views permit the suggestion that the unexpected properties attributed to light by physicists reside also in the seeing experience. Simply put, light is difficult to locate in conventional terms. We cannot recover it as an intermediate, spatially separate (and therefore separating) entity between perceiver and perceived. That is, it cannot be snatched out of the context of the visual experience and held up for independent scrutiny, for unless light first drops out of sight, no visual experience is forthcoming. That experience, it seems, arises from light's failure to respect, or perhaps even participate in, the space-time gap between here and there. In one stroke, light exchanges or gives up its local presence--its contact with the retina--for the visual presence of distant objects. Physically absent, they become perceptually present, while light, physically present, becomes perceptually absent.

Long ago Anaximander proposed a disparity between the visible, determinate elements of reality and a necessarily more fundamental, indeterminate substance: if the latter fully participated in the former, determinate reality would never emerge because the more fundamental substance would "swamp the other world-constituents and never allow them to develop" (Kirk et al. 113). According to Paul Feyerabend, this implies that "the basic substance, or the basic elements of the universe, cannot obey the same laws as the visible elements" (58). A modern reaffirmation of this principle, he continues, is Werner Heisenberg's uncertainty principle, which posits an interference effect between the material constituents of the world and the light by which we see them.

But why should light be this kind of fundamental substance? Aside from the aforementioned anomalies, what warrants the suggestion that light visually announces the world without announcing itself as a separate entity in the world? Speaking epistemically, there is no other option. If seeing occurs by the agency of light, then no explanatory purpose is served by "seeable" light: seeing is thereby defined in its own terms by light, and we fail to move to a more fundamental level of explanation, light itself.

This rationale applies to all unexplained phenomena, but it would seem to apply with particular force to light. Because light is integral to all visual experience, we should resist the inclination to clothe it with visible properties. Such restraint brings light forward simply as a principle of seeing; that is, something that is communal with and prior to our optical investigation of nature. Before we try to grasp the world, light freely gives us a graspable world. This is an empirical fact--light gives us the event-articulated expanse we call the cosmos--but the tendency is to overlook this giving or pre-giving in favor of distinct, light-illuminated objects and events.

Light, of course, readily permits oversight of itself. By allowing other things to spring forth visually at a cost to its own visuality, light introduces us to another--an other--world. Communal with light but now stretched by light's absence into otherness, we find ourselves in an untoward setting, one provoking restlessness and disquietude. What is missing is light's presence, which is given up to other things.

Better than any other discipline, modern physics affirms physical light's metaphysical depth by problematizing the commonsensical assumption of light's presence in local and intermediate space. This assumption is eroded by the dawning realization that light is missing from the space-time regime in which things other than light make their appearance. One might say it is present elsewhere, but this ambiguous construction is fostered by light, by the way light cedes its own immediate presence to that of distant objects, thereby affording us the epistemic luxury of mentally endowing those objects with presence. Given this movement away from self and towards otherness, we should be wary of restricting light to the space-time setting (the material cosmos) it announces. Physics rewards such caution by indicating that light is absent from that setting, notwithstanding routine discourse to the contrary. Indifferent to the separating modalities of space and time, light is larger than--unconfined by--the objects and set of objects it makes visible.

Classical physics regarded light as one of many elements in the space-time set of things, but modern physics implies that light is not a proper member of that set. Indeed, light is its own, higher (more comprehensive) set, one that gathers up and supersedes space-time. To be sure, this fact is rarely acknowledged in an explicit way in modern physics, but it resides tacitly in its foundational principles. In relativity theory, the speed of light is given as a universal constant that bounds the structure of space-time and thereby limits the velocity of material bodies. As bodies are seen to accelerate by stationary observers, they undergo changes that make further acceleration increasingly difficult. They become more massive (thus requiring greater energy input to maintain acceleration) and their length (or space itself) is contracted in the direction of their motion. Given these effects, reaching the speed of light is a physical and conceptual impossibility, for that would entail skipping from the realm of finite, measurable intervals to one of zeros and infinities. If a body were to achieve light speed, for example, its length would be contracted to zero and its mass would become infinite. Moreover, the body's passage through time would slow to a halt, since moving bodies also undergo the relativistic effect of time dilation.

Although this nether-realm of zeros and infinities is off limits to material objects, it is light's native economy. Since the speed of light is intrinsic to light, light may be said to be beyond space and time, whose aegis ceases at light speed. This claim, however, seems to be contradicted by the fact that light travels at a finite velocity--186,000 miles per second. How can light be a matter of zeros and infinities on the one hand, and, on the other, reducible to a finite numerical value?

Of all the ambiguities associated with light, this one is fundamental. In his first paper on relativity theory, Einstein brought the speed of light forward as a universal constant or unchanging velocity: no motion or maneuver on our part can alter the finite value that we assign to light upon measuring its speed. Having posited this constancy, Einstein wrote that "the velocity of light in our theory plays the role, physically, of an infinitely great velocity" (401). This tension between finiteness and infinitude is central to relativity theory, and it plays itself out in ways that touch on the aforementioned profundities regarding our optical experience of light.

Widely publicized are counterintuitive scenarios like the twin paradox (where two twins undergo asymmetric aging owing to time dilation). Of greater import is the simple fact that light does not move in a conventional way. Any phenomenon whose velocity is an irreducible value cannot be said to move as other things move. Well before Einstein, thinkers realized that a body's velocity is not an objective or absolute fact. It is a function of both the body and the motion of the observing person or instrument. Hence, one object can have as many relative speeds as there are external observers, if each observer is moving differently. This, of course, is hardly abstract scientific fact but the stuff of everyday experience. Light, or the motion of light, does not accommodate itself to such experience, however. Our own motion does not affect the observed motion (speed) of light.

Going further, one may propose that once light is said not to move conventionally, we may say that it does not move at all. We can, of course, infer light's motion. As already noted, however, such inference has no basis in direct experience. Even in relativity theory, light's motion is no more than an inference, and one that is challenged by the theory itself. True, light is said to travel invariably at 186,000 miles per second, but as the theory unfolds, the assertion that light travels unconventionally opens out onto the realization that we lack the resources for imagining how light travels, if in fact it does.

For a body to move in a conventional sense, it must negotiate space and time. But a ray of light whose clock is stopped (whose time dilation is complete) is not in temporal process. Consequently, in Hermann Bondi's words, "light does not age; there is no passage of time for light" (108). Once time falls out of light's nature, so, by implication, does space. What would it mean, after all, to travel through space timelessly? It would mean something like the following:

In the reference frame of light, there is no space and time. If we look up at the Andromeda galaxy in the night sky, we see light that from our point of view took 2 million years to traverse that vast distance of space. But to a beam of light radiating from some star in the Andromeda galaxy, the transmission from its point of origin to our eye was instantaneous. (Haisch 31)

In allowing us to see distant stars, light situates us within a vast expanse of space-time. Classical physics took this expanse as complete and definitive, an absolute and all-encompassing reference frame. In positing the speed of light as a universal constant, however, Einstein subordinated space and time to a new absolute. Light consequently became "its own thing" (Zajonc 260), not part of the space-time regime. So, while the classical image of light moving through space and time may still be invoked in relativity theory, eventually it must be set aside, and this because the theory assigns to light a velocity that cannot be reduced to the familiar terms of motion: space and time. Granted, light shows up in the space-time regime moving at 186,000 miles per second, but it always shows up in conjunction with other (space-time) things, thereby tilting our vision and understanding away from itself and its own uniqueness. Furthermore, that motion is merely inferred, never directly witnessed, as light allows material space-time bodies--otherness--to become the cynosure of all eyes.

Reasoning from relativistic principles, P. W. Bridgman concluded that it is "meaningless or trivial to ascribe physical reality to light in intermediate space, and light as a thing travelling must be recognized to be a pure invention" (153). While this judgment issues up from Einstein's redefinition of light, it has always been implicit in our optical experience of the world. To state the matter in terms made plausible by both modern physics and contemporary philosophy, light admits no spectators. If we experience light, it is because we participate in the space-time drama it offers us. Never do we see it from a distance; never do we get any objective distance from it. In a literal sense, light is always "in your face," striking the retinas and ceding its own local presence to distant bodies. This double-movement--the absenting of immediate light and the presencing of other things across space-time intervals--turns light into an opening without recovery or bounds. Were it bounded or encompassed by space and time, it could hardly play the role of "an infinitely great velocity," and the structure of the world (and our experience thereof) would be very different.

Light, in brief, has no space-time frame; it is an unframed window on the material world, an opening or clearing in which that world is situated. This idea is made explicit by physical experiments that indicate light's indifference to space and time intervals. Two distantly separated parts of light--two photons--interact non-locally; that is, as if they were conjoined (Chiao et al.). When one showed as as postive, the other was instaneously negative. This is a dead-end puzzle for anyone invoking the classical assumption of light's subordination to space-time. Liberation occurs when one realizes that light itself is liberated. Not part of the space-time regime, light does not participate in modes of action that presuppose space-time intervals.

Writing about seeing as a process of enveloping the exterior, Levinas said " Light makes possible... this enveloping of the exterior by the inward, which is the very structure of the cogito and of sense. Thought is always clarity or the dawning of a light. The miracle of light is the essence of thought: due to the light an object, while coming from without, is already ours in the horizon which precedes it; it comes from an exterior already apprehended and comes into being as though it came from us, as though commanded by our freedom. (Existence 48)

Levinas seems to acknowledge light's bi-directionality, its ability to make other things present while absenting itself in the clarity of the moment. Further, light "comes from an exterior already apprehended," so that it seems to arise from within via thought. Already "there" before we make the here/there distinction, light seems "here" as well.

While light's ambiguity erodes the authority of familiar space and time intervals, it also undermines our ability to speak clearly about its nature. David Michael Levin states that Levinas's view of light and vision is "quite complicated" owing to an ambivalent characterization (250). Often Levinas describes light as imperialistic and totalizing: its expansiveness overtakes the world and thereby subjects it to objective knowing. What's more, that kind of knowing engenders a self-satisfaction that keeps one from trying to see beyond the expanse marked out by light:

"To see is always to see on the horizon. The vision that apprehends on the horizon does not encounter a being out of what is beyond all being. Vision is a forgetting of the there is [il y a] because of the essential satisfaction, the agreeableness [agrément] of sensibility, enjoyment, contentment with the finite without concern for the infinite. (qtd. in Levin 249) "

Interpreted thusly, light acts to delimit and finitize human experience. Yet Levinas also recognized that seeing by light involves an immediacy, a closeness without interval, that runs counter to the finite, interval-laden vision that we see: Sight is, to be sure, an openness and a consciousness, and all sensibility, opening as a consciousness, is called vision; but even in its subordination to cognition, sight [still] maintains contact and proximity. The visible caresses the eye. One sees and hears like one touches. (Collected 118)

This characterization calls forth light's generosity, its graciousness in revoking the interval so that visible images may caress the eye. Here light's infinite aspect emerges as the finite intervals that inform the seeing experience are invisibly overcome. At issue is the uncanniness of light as it put us in touch with distant, seeming untouchable entities. That touching bespeaks integrative embrace, welcoming, rather than objective knowing, borne of separating intervals.

Light expands our sight and our interaction with the universe. But Light also limits our sight to only what we want to see. Light defines our finite world, but it is in itself undefined and outside this world. And thats is the mystery. Where is light ?