# Instructor guide: Light-cone interval and causality atlas

Course: Special relativity without shortcuts

Suggested time: 45–55 minutes

## Learning target

Learners classify event separation from the invariant interval and distinguish coordinates from causal structure.

## Prepare

- Draw axes in ct and x units.
- Prepare one example of each causal class.
- State the metric-sign convention used by the lab.

## Facilitation moves

- Ask whether a light signal can connect the events before naming the class.
- Keep events distinct from objects.
- Return to invariant statements whenever coordinates appear subjective.

## Misconception checks

- **Relativity means every statement is observer-dependent.** Coordinates vary; intervals, causal class, and meetings are invariant.
- **A warp proposal lets a craft locally pass through light speed.** Metric proposals alter global geometry while local timelike motion remains inside the local cone.

## Accessibility and participation

- Narrate inside, on, and outside the cone without relying on the diagram.
- Use shape and labels in addition to color.
- Provide a numeric classification table before graphing.

## Evidence of learning

- Three correct causal classifications
- A boundary-case calculation
- A coordinate-versus-invariant explanation

## Extension

Apply a Lorentz transformation to one event pair and verify the interval numerically.

## Evidence boundary

Assess the learner's reasoning only within the declared model and recorded observations. Do not upgrade a simulation result into a claim about an unmodeled physical system.