Echo is a relational phenomenon, always relative to the observer.
If we were to surf the soundwave at the same speed it moves, we wouldn’t hear it (theoretically, at least). There would be no return of the sound — only silence, unless we fell, and the wave would crash over us.
Surfing the soundwave is surfing in complete silence. But surfing the lightwave is even crazier. Because light travels through space at maximum speed, from the point of view of the photon, there is no temporal shift between the moment it is emitted and the moment it arrives at its final destination. Everything it sees on its journey stands in absolute stillness.
If a soundwave had a memory, it might see you as an echo on its journey — passing you by and returning to you a moment later (after reflecting off the wall). But light appears to exist in a completely still, omnitemporal world. It couldn’t have a memory because, from the perspective of the photon, everything from its birth to its death happens at the same time.
This difference between the visual and auditory senses has been noted by philosophers such as Nancy, Husserl, Bergson, and Ihde, among others.
In his book Listening, Jean-Luc Nancy writes: “The visual persists until its disappearance; the sonorous appears and fades away into its permanence.”
And: “Listening takes place at the same time as the sonorous event, an arrangement that is clearly distinct from that of vision […] Visual presence is already there, available, before I see it, whereas sonorous presence arrives.”
It would be easy to overlook this difference by attributing it solely to the biological differences between the eye and the ear, or by assuming it applies universally to all audio-visually sensitive lifeforms. But I believe there is deeper poetry at play here.
The luminous world is capable of stillness because the speed of light allows it; the sonorous constantly fades in and fades out.