Block Universe Explorer

Spacetime diagram Block universe

Time is the horizontal axis, space is vertical. Every dot is an “event” that exists in the 4D block, whether or not your current “now” slice has reached it.

Past

Your “now”

Future

Selected event

space

time →

Click events · drag the slider

Deep space

Orbit

Atmosphere

Earth surface

Lab frame

Observer A (slow)

Observer B (fast)

Choose a "now" slice (coordinate time) 4 Δt

Slide right: more of the block is labeled “past” from your perspective.

Selected event None (click an event)

Frame: Lab frame

Click any glowing node in the grid.

Each dot is a space–time coordinate. Clicking it makes that event your focus without promoting it to “present” in an absolute sense.

Coordinates –

State –

Worldline –

How to read this toy model
The grid is not to scale; it’s just a discrete cartoon spacetime. Time runs left to right, space runs bottom to top. You, as an observer, pick a “now” surface using the slider.

Events with a time-coordinate smaller than your slider setting are tagged as “past”, equal to it as “present”, and greater than it as “future”. The point of the block universe picture is that all those points already exist in the 4D structure; the slider just labels them relative to your chosen notion of “now”.

This is philosophy-friendly, not a full GR simulation. Treat it as a visual metaphor, not a literal physics engine.

Block universe heuristics in this toy:

All events are “there” in the grid whether you’ve slid past them or not.
Changing the slider doesn’t create events; it only relabels them.
Different worldlines (A vs B) cut through the same block with different “angles”, hinting at relativity of simultaneity.
If you want to hack it: the data structure is a small JSON object in the script tag – edit, delete, or add events there.