It is possible to at once project love, amazement, and disgust at Virilio’s (1997/2008) Open Sky; Virilio is entertaining enough that he excites the extremes of all the emotions one feels upon reading an engaging text. Take, for example:
“If the interval of time (positive sign) and the interval of space (negative sign) have laid out the geography and history of the world through the geometric design of agrarian areas (fragmentation into lots of land) and urban areas (the cadastral system), the organization of calendars and the measurement of time (clocks) have also presided over a vast chronopolitical regulation of human societies. The very recent of emergence of an interval of the third type thus signals a sudden qualitative leap, a profound mutation in the relationship between man and his surroundings.
Time (duration) and space (extension) are now inconceivable without light (limit-speed), the cosmological constant of the speed of light, an absolute philosophical contingency that supersedes, in Einstein’s wake, the absolute character till then accorde to space and time by Newton and many others before him” (Virilio 1997/2008: 13).
which draws on a body of philosophy dealing with the nature of space and time (it is with this literature that I am deeply enmeshed in preperation for section 3 of my doctoral comps). First, the associations between time-positive and space-negative come directly from Einstein’s general relativity, in that “the equations that define space-time as a four dimensional continuum (for example c²t² – x² – y² – z² = 1), the three spatial co-ordinates x, y and z are subtractive when the temporal co-ordinate t is additive and vice versa” (Murphy 1999: 68). The practical ramifications of this equation are easily explored with the use of a spacetime diagram:

Here, time is represented by the vertical Y axis, and space by the horizontal X-axis. The speed of light (v=c) is denoted by the dotted red line, which proceeds at 45° from both axes. If your velocity is less than the speed of light – v<c – then your movement occurs in the upper 45º of the graph. This is called a timelike path, and is the path that normal matter assumes in the spacetime of relativity. Contra, a velocity greater than the speed of light (v>c) gives rise to a spacelike path, which is the path that timetravelers and tachyons follow. The dotted red line itself is a lightlike path or null path. Ray (1991) explains:
In the spacetimes of the STR [special theory of relativity] and The General Theory of Relativity (GTR), we may connect any two points geometrically by timelike, null, or spacelike paths… When a timelike path connects two points, a signal travelling at less than the speed of light may pass continuously from one point to the other. When a null path connects two points, only a signal travelling at the speed of light may pass between them. The notion of causality in relativity is tied to the idea of light being the fastest possible causal signal between two points. [...] So the ‘light cone’ of an event C may be thought of as the cone of possible causal influence – C may be regarded as a physical cause of any event within or on the lightcone” (Ray 1991: 60).
This is perhaps more easily visualized when space in generalized to two, rather than one, dimensions:

where anything lying outside of the “future light cone” of the observer is thus, by definition, incapable of causually influencing the observer in the future. Put another way, if nothing can move faster than the speed of light, then only objects that lie within the spacetime bounded by the speed of light relative to the observer (i.e., the future light cone which expands as time progresses) can causually influence the observer. Tachyons, or any other object following a spacelike path, violate the law of causality and the vectored 1-dimensionality of normal time, giving rise to the paradoxes of time-travel.
Ray goes on to note that “the laws of STR do not legislate against particles travelling faster than light. The key idea behind STR is the invariance rather than the limiting character of the speed of light” (1991: 61). This, of course, strikes to the heart of Virilio’s second point quoted above, that “the cosmological constant of the speed of light, an absolute philosophical contingency that supersedes, in Einstein’s wake, the absolute character till then accorde to space and time by Newton and many others before him”. The absolute space and absolute time of Newton were transformed by Einstein – not into relative spaces and relative times – but an absolute spacetime denoted by the universal invariance of the speed of light. Speed, after all, is denoted in meters per second or some other such notation – understandable only in the relationship between space and time. Where the speed of light is fixed, so too space and time.
Virilio ties this exposition of spacetime back into modern human existence with the following:
“The exposure time of the photographic plate is thus simply the exposure of time, of the space-time of its photosensitive matter, to the light of speed, that is, ultimately, to the frequency of the photon carrier wave. [...] These days, the screen of real-time televised broadcasts is no longer a monochromatic filter like the one familiar to photographers which lets through a single color only of the spectrum, but a monochronic filter which allows a glimpse only of the present. An intensive present, spawned by the limit-speed of electromagnetic waves and no longer registered in chronological time – past-present-future – but in chronoscopic time: underexposed-exposed-overexposed” (Virilio 1997/2008: 28).
Interesting, no?
Enough meditation on the ontology of spacetime (although I could go on, bringing in Schivelbusch’s The Railway Journey and “the vast chronopolitical regulation of human societies”). What else is interesting in Virilio? What about this gem:
“Historically, we thus find ourselves faced with a sort of great divide in knowing how to be in the world: on the one hand, there is the original nomad for whom the journey, the being’s trajectory, are dominant. On the other, there is the sedentary man for whom subject and object prevail, movement towards the immovable, the inert, characterizing the sedentary urban ‘civilian’ in contrast to the ‘warrior’ nomad.
A movement that is today intensifying due to remote control and long-distance telepresence technologies that will soon land us in the ultimate state of sedentariness where real-time environmental control will take over from the development of the real space of the territory.
Terminal – and final – sedentarization; a practical consequence of the emergence of a third and final horizon of indirect visibility (after the apparent and deep horizon): a transapparent horizon spawned by telecommunications, that opens up the incredible possibility of a ‘civilization of forgetting’, a live (live-coverage) society that has no future and no past, since it has no extension and no duration, a society intensely present here and there at once – in otherwords, telepresent to the whole world” (Virilio 1997/2008: 25)
And another, discussing the same theme:
“Once more we are seeing a reversal in trends: where the motorization of transport and information once caused a general mobilization of populations, swept up into the exodus of work and then of leisure, instantaneous transmission tools cause the reverse: a growing intertia; television and especially remote control action no longer requiring people to be mobile, but merely to be mobile on the spot” (Virilio 1997/2008: 20)
Meditate on that, if you will. As Virilio succintly notes: “Service or servitude, that is the question” (Virilio 1997/2008: 20).