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4. Experiential Light
- Indiana University Press
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Horizonal Light · 39 light is intrinsically indifferent to space and time, the Newtonian constancies for determining speed. In nearly every instance one may say that light moves at c in a vacuum because this statement holds for all slower-than-light reference frames, even those moving at just under the speed of light. But what about light itself? In what sense does it move? Here we are talking of light’s proper motion, its motion within its own frame. By way of introduction we can say that like anything else, light is at rest relative to its own frame. To situate something in a reference frame is to make it motionless therein. Given this, we should not be surprised by the assertion that light does not move; how could it move relative to the frame that, by definition, stays abreast of its motion? But in the case of light the word “frame” can be misleading, for by suggesting spatial and temporal containment, it plays to the classical notions of absolute space and absolute time. It becomes reflexive, then, to imagine light’s frame as something within the space-time regime, and, by implication, light is there as well. Special relativity militates against this inclination to slip back to Newtonian modes of thought, but language can send the mind in wrong directions. Applied to any phenomena but light, “frame” is a perfectly appropriate word. This is because all slower-than-light phenomena are spatially and temporally bounded or framed, even when time dilation and length contraction are ascribed to them. But at the speed of light, those bounds fall away: in the mathematics of special relativity, space (length) and time collapse to zero magnitude . They are no longer there to frame light. Part of my purpose is to propose that there is a sense in which light is unframed and that this feature of light shows up not only in special relativity but also in the unbounded seeing experience. But before moving toward this idea, we need to say more about light’s relation to space and time. Implicit in what we have said already is the notion that light is indifferent to space and time, that it is not reducible to “matter or its motions.”2 Some thinkers have tried to grasp light from within its own economy and have variously concluded that it is ageless or atemporal, or that “[l]ight and influences propagated by light make zero-interval linkages between events near and far.”3 Here is what Sydney Perkowitz says about light: “To the best understanding we can muster . . . the universe is made so that light always travels its own distance of zero, while to us its clock is 40 · The Speed of Light stopped and its speed is absolutely fixed. These sober conclusions read as if they come out of some fevered fantasy. Light, indeed, is different from anything else we know.”4 As counterintuitive as these judgments may be, they follow from special relativity. That theory, far from collapsing the mystery of light, raises it to a new level. Not only do we fail to understand light’s motion (speed), we are hard-pressed to grasp a phenomenon that is intrinsically indifferent to space and time. The two difficulties , of course, go hand in hand. Embedded in space and time, our bodies spatially and temporally configured, we have little capacity to imagine the universe from light’s point of view. Nevertheless, it is worth trying. In noting that the “solid, stable world of matter appears to be sustained at every instant by an underlying sea of quantum light,” Bernhard Haisch remarks: If it is the underlying realm of light that is the fundamental reality propping up our physical universe, let us ask how the universe of space and time would appear from the perspective of a beam of light. The laws of relativity are clear on this point. If you could ride a beam of light as an observer, all of space would shrink to a point, and all of time would collapse to an instant. 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...