Understanding Relativity: The Spacetime Interval Explained

I then ran a summary of relativity through Grok with the output from my initial questioning (previous page), and this is Groks reply, a ‘bridging the gap’ analysis.

Explaining Relativity’s Spacetime Interval
In special relativity, spacetime is a four-dimensional setup: three spatial dimensions (X, Y, Z) and one time dimension (T). The “interval” (S) measures the separation between events in this 4D arena, like a distance that accounts for both space and time. Here’s the rundown:
1. Time as a Perpendicular Dimension:
○ Relativity treats time as a coordinate, distinct from X, Y, Z—like a fourth axis at right angles to the spatial trio. You can’t picture it (our brains are 3D-wired), but mathematically, it’s a clean extension. Why perpendicular? It keeps space and time independent yet linked, letting us plot events as points (x, y, z, t).
2. Imaginary Units for Time:
○ The “1 second = 300,000i km” bit comes from an older convention (Minkowski’s early formulation). Space is measured in real units (km), but time’s scaled by the speed of light (c ≈ 300,000 km/s) to match units—seconds become “light-distance” (T = ct). The “i = √(-1)” tags time as imaginary to flip its sign in the math. So, T becomes ict (imaginary distance), distinguishing it from spatial terms.
3. Generalized Pythagorean Theorem:
○ In 3D space, distance is √(X² + Y² + Z²)—the Pythagorean theorem. In spacetime, the interval S adjusts for time: S = √(X² + Y² + Z² – (ct)²). The minus sign (or imaginary i) reflects that time “subtracts” from spatial distance, not adds. Why? Because spacetime isn’t Euclidean—it’s Minkowski spacetime, where time and space mix differently (e.g., moving faster in space slows your time).
○ Modern notation skips the “i” and uses S² = X² + Y² + Z² – (ct)² (or c²t² – X² – Y² – Z², depending on convention). The square root’s optional—S² is often enough. This interval is invariant—same for all observers, unlike raw space or time alone.
4. What It Means:
○ S measures a “distance” that’s physical but not like a ruler—it’s the spacetime gap between events (e.g., a photon’s path has S = 0). Positive S² is spacelike (space dominates), negative is timelike (time dominates), zero is lightlike. It’s how relativity ties frames together despite their differing clocks and rulers.
Rationalizing with Your Framework
Our agreed view: time doesn’t “exist”—change does. Time’s an abstract tool (dimensionally, it calibrates/indexes change; collectively, it’s all change events). Space is relative static position (dimensionally) or all physical stuff (collectively). Spacetime’s either the dimension of relative motion or the totality of changing things. No fabric, just change driven by energy. How does this mesh with S = √(X² + Y² + Z² – T²)?
1. Time as a Dimension of Change:
○ Relativity’s “T” fits your dimensional time—it’s a coordinate tracking change (e.g., clock ticks). The “perpendicular” bit is just math’s way of keeping it separate from X, Y, Z, which mark static positional snapshots. Your “relative motion” spacetime (change in position) aligns here: T calibrates how positions shift, and X, Y, Z index where they start. The imaginary units? A trick to make the math work—time’s not “imaginary” in reality, just signed differently (-T²) to reflect change’s unique role.
2. Change, Not Time, Is Real:
○ You’d say T isn’t a thing—it’s a proxy for change events (e.g., a particle moving X km in T seconds). The interval S doesn’t need time to “exist”—it’s a measure of how change (motion) spans space and ticks. X² + Y² + Z² tracks positional shift; -T² adjusts for the rate of that shift. No fabric bending—just a formula tying observable change across frames, which fits your “quintillion arrows” idea: each event’s change, related by energy.
3. No Fabric, Just Relations:
○ The minus sign (-T²) and “i” don’t imply a physical spacetime substance. They’re abstract tweaks to unify space and change into one metric. Your rejection of “fabric” holds—S isn’t a warped sheet; it’s a relational tool. For example, time dilation (slower clocks in motion) is just change rates varying by frame, not a bent “T.” Energy differentials (e.g., velocity, gravity) drive those rates, per Barbour and your view.
4. Two Spacetimes and the Interval:
○ Dimensional Spacetime: S = √(X² + Y² + Z² – T²) works perfectly here. It’s your “dimension of relative motion”—X, Y, Z as static positions, T as change, S as the net result. It’s abstract, not physical, matching your stance.
○ Collective Spacetime: Trickier. If Spacetime is all changing things, S doesn’t define it—it measures gaps within it. The collective’s too vast for one equation; S applies to specific events, not the whole swarm. Still, each “arrow of change” could have its own S, linking local motions without a universal fabric.
Bridging the Gap
Relativity’s setup doesn’t contradict you—it’s just a different lens. You see T as abstract, change as real; relativity uses T as a stand-in for change, then adjusts it (-T²) to match reality’s quirks (e.g., light’s speed limit). The “imaginary” bit’s a historical artifact—modern physics drops it for simpler c²t² terms—but it’s still about calibrating change, not reifying time. S rationalizes your view by focusing on what’s measurable: positional shifts (X, Y, Z) and their pacing (T), driven by energy, not a cosmic clock.
Your Spin
You could say: “Relativity’s S isn’t spacetime’s fabric—it’s a yardstick for change across frames. T’s not a direction; it’s a tally of ticks, and X, Y, Z snapshot where they happen. No ‘i’ or perpendicularity needed—just math mapping real motion.” That keeps your “change is king” line, ditches the fabric, and nods to physics without buying time as a thing.

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