### Experience from the Cockpit of the Nearby Ship

In this hypothetical universe with 'aether-sonis' as a pervasive medium for sound transmission in the vacuum of space, the crew in the cockpit of the surviving spaceship would both **see** and **hear** the explosion of the other ship. However, these experiences would **not** occur simultaneously. Below, I'll describe what they would perceive and explain the underlying physics step by step, based on the properties of aether-sonis described (massless, invisible, permeates vacuum, perfectly transmits vibrations) and real physical principles from relativity and wave propagation.

#### What They Would See
- **Visual Experience**: The crew would immediately see a bright flash of light from the explosion, followed by visuals of expanding debris, fireballs (if the explosion involves combustible materials), and any structural breakup of the enemy ship. This would be similar to explosion visuals in science fiction movies, but grounded in the fact that light (electromagnetic waves) travels through the vacuum unaffected by aether-sonis.
- **Timing**: The visuals arrive "instantly" (or nearly so, depending on distance), as light propagates at the speed of light, \(c \approx 3 \times 10^8\) m/s.

#### What They Would Hear
- **Auditory Experience**: The crew would hear a loud "boom" or rumbling explosion sound, including any secondary noises like screeching metal or venting gases from the exploding ship. Since aether-sonis "perfectly transmits vibrations," this sound would be clear and undistorted, without the muffling or fading you'd get over long distances in a lossy medium like air. The sound would feel immersive, as if the explosion were happening in a dense atmosphere nearby.
- **How They Hear It**: Aether-sonis permeates the vacuum of space, but the cockpit is inside a pressurized ship with air. For the crew to hear the sound with their ears, the vibrations in aether-sonis would need to couple with the ship's hull or internal atmosphere. Since aether-sonis is massless and invisible, it could plausibly permeate matter (similar to how gravitational waves or neutrinos pass through objects). This would cause the hull to vibrate or directly excite pressure waves in the cockpit's air, transmitting the sound to the crew's eardrums. If the ship has external sensors tuned to aether-sonis vibrations, it could amplify and play the sound internally via speakers—but assuming a direct physical transmission, the crew would hear it naturally.

- **Timing**: The sound arrives **after** the visuals, with a noticeable delay depending on the distance to the exploding ship.

#### Would They Experience Seeing and Hearing Simultaneously?
**No, they would not**. The crew would see the explosion first, then hear it after a short delay. This is analogous to seeing lightning before hearing thunder on Earth, where light travels much faster than sound.

- **Example with Distances**:
  - If the ships are 1 km apart (a close-range space battle), light takes ~3.3 microseconds to arrive—effectively instantaneous. Sound (as explained below) takes ~5.8 microseconds, for a delay of ~2.5 microseconds (imperceptible to humans).
  - If the ships are 300 km apart (a more typical "nearby" space battle distance), light takes ~1 millisecond. Sound takes ~1.73 milliseconds, for a delay of ~0.73 milliseconds (still too short to notice).
  - If the ships are 30,000 km apart (longer-range engagement), light takes ~0.1 seconds. Sound takes ~0.173 seconds, for a delay of ~0.073 seconds (potentially noticeable as a slight "echo" effect).
  - At extreme distances (e.g., 300,000 km), light takes 1 second. Sound takes ~1.73 seconds, for a delay of ~0.73 seconds—clearly not simultaneous, like a delayed thunderclap.

The exact delay is \(\Delta t = d \left( \frac{1}{v_s} - \frac{1}{c} \right)\), where \(d\) is the distance, \(c\) is the speed of light, and \(v_s\) is the speed of sound in aether-sonis (derived below). For close ranges, the delay might be imperceptible, but in principle (and at larger distances), seeing and hearing are not simultaneous.

#### Explanation of the Physics
I'll break this down based on wave propagation, relativity, and the properties of aether-sonis.

1. **Light Propagation (Seeing the Explosion)**:
   - Explosions produce light via electromagnetic radiation (e.g., from heated materials or plasma).
   - Light travels through vacuum at speed \(c\), unchanged by aether-sonis (which is specified for vibrations, not EM waves). This is consistent with real physics: vacuum is transparent to light, and no medium is needed for its propagation (post-Einstein, we discarded the luminiferous aether for light).
   - Travel time: \(t_\text{light} = d / c\).

2. **Sound Propagation (Hearing the Explosion)**:
   - Sound is mechanical vibrations (longitudinal pressure waves) requiring a medium to travel. In our universe, vacuum has no medium, so no sound. Here, aether-sonis provides that medium, allowing the explosion's vibrations (from rapid expansion, collisions, etc.) to propagate as waves.
   - "Perfectly transmits vibrations" likely means no energy loss, distortion, or attenuation—waves maintain amplitude and frequency over distance.
   - **Key Property: Massless Medium**: Aether-sonis is massless, invisible, and permeates vacuum. In physics, "massless" implies no rest mass (like photons or gravitons), but it can have energy density (e.g., from relativistic effects or quantum fields). This makes it analogous to a relativistic fluid or "gas" of massless particles, such as the photon gas in the early universe or radiation-dominated plasmas.

3. **Speed of Sound in Aether-Sonis**:
   - In standard physics, speed of sound \(v_s = \sqrt{K / \rho}\), where \(K\) is the medium's stiffness (bulk modulus) and \(\rho\) is density. For a massive medium (e.g., air), \(v_s \ll c\) (e.g., 340 m/s in air).
   - But aether-sonis is **massless** (\(\rho = 0\) rest mass density), so the non-relativistic formula breaks down—it would imply infinite speed, which violates relativity (no information can travel faster than \(c\)).
   - Instead, we use relativistic physics for massless "matter." In cosmology and particle physics, massless fluids (e.g., radiation with equation of state \(p = \epsilon / 3\), where \(p\) is pressure and \(\epsilon\) is energy density) have a speed of sound:
     \[
     v_s = c \sqrt{\frac{dp}{d\epsilon}} = c \sqrt{\frac{1}{3}} \approx 0.577c
     \]
     This is derived from relativistic hydrodynamics for ultra-relativistic gases (e.g., photons or gluons). Waves in such a medium propagate at \(c / \sqrt{3}\), not \(c\), because the "particles" move at \(c\) but collective disturbances (sound waves) average slower due to random motions.
   - Why not exactly \(c\)? Massless particles individually move at \(c\), but sound is a collective density perturbation. In a photon gas, perturbations propagate at \(c / \sqrt{3}\) to satisfy causality and relativity (no superluminal speeds).
   - Aether-sonis fits this: it's a "new form of matter" that's massless and permeates space, behaving like a relativistic medium for vibrations. If it were to propagate at exactly \(c\), it would be more like gravitational waves or light, not "sound" (which implies slower, mechanical waves). The \(c / \sqrt{3}\) value is a physically motivated choice for massless matter.

4. **Why Not Simultaneous?**
   - Light speed: \(c\).
   - Sound speed: \( \approx 0.577c \).
   - Since \(v_s < c\), sound takes longer to travel distance \(d\): \(t_\text{sound} = d / v_s > d / c = t_\text{light}\).
   - The explosion produces both light and vibrations at the same instant, but the signals arrive at different times.
   - Relativity ensures no simultaneity violation: both speeds are ≤ \(c\), preserving causality.

5. **Other Considerations**:
   - **Coupling to the Cockpit**: As a massless, permeating medium, aether-sonis could pass through the ship's hull (like gravitational waves do). "Perfect" transmission implies efficient energy transfer to the internal air, creating audible sound waves (20 Hz–20 kHz) for human ears.
   - **Realism Caveats**: In a real explosion in space (even with aether-sonis), the sound might be muffled if there's no atmosphere to generate typical "boom" noises, but the problem assumes movie-like explosions. Aether-sonis doesn't affect gravity, radiation, or other physics unless specified.
   - **If Aether-Sonis Were Different**: If it propagated vibrations at exactly \(c\) (e.g., like a massless scalar field), seeing and hearing would be simultaneous. But this would make it less like "sound" and more like light, contradicting the trope's intent. The relativistic fluid model provides a more sound-like physics.

This setup justifies the sci-fi trope of hearing explosions in space while introducing realistic delays, highlighting how even a "perfect" vacuum medium doesn't make sound as fast as light.