TIME DILATION LAB / VISITOR GUIDE
Your guide to
the journey.
Choose an experiment, know which clock you’re reading, and discover what happens when a ship comes home. Start with the quick tour, or jump to the control you need.
START HERE / ABOUT A MINUTE
Watch messages from home.
- Open the Earth-message experiment. Follow the launch link above. You can begin directly beside the postcards; opening the 3D deck is optional.
- Choose “Launch & watch Earth messages.” The default ship travels at 90% of light speed to a point 5 light-years away, then returns. The mission starts here, without scrolling back up.
- Watch the three readings inside the postcard panel. Earth elapsed time and crew elapsed time describe the clocks. “Earth time / arriving light” is the older Earth timestamp reaching the ship now.
- Select “Watch the return.” This jumps to the turnaround and starts the homeward leg. Messages arrive more often as the ship approaches Earth. Use Pause or the Journey slider to inspect any moment.
- Compare at reunion. Both clocks meet again. For this default journey, Earth has aged about 11.11 years and the crew about 4.84 years.
WORKBENCH / 01 SPEED & SPACEFLIGHT
Send a clock out and bring it home.
In the first workbench, choose 01 / Speed & spaceflight. Velocity sets the fraction of light speed; one-way distance sets how far the ship travels before returning. Distances are measured in Earth’s frame.
- Choose a velocity and distance, or use Half light speed or 99.99% of light speed.
- Choose Reset for a fresh departure, then Play reunion. The Journey slider lets you inspect the outward and return legs.
- Read Earth reference clock, Traveler clock, and Difference below the scene. Choose Compare at reunion to jump to the final comparison.
The small clocks illustrate their relative rates in this comparison. Their hands are accelerated for teaching. The numeric elapsed times are the calculated results; they are not measured from the animation’s wall-clock duration or pixel distances.
The worldline diagram and “What your clocks are saying” panel explain the selected result. Inspect the calculation opens the model notes farther down the lab page.
Go to the workbench ↗WORKBENCH / 02 GRAVITY & CLOCKS
Know where A and B are.
Select 02 / Gravity & clocks, then choose an environment. Use the legend and location markers beside the picture to identify the clocks. The orbit animation and the clock hands are separate teaching illustrations.
| Environment | Clock A / turquoise | Clock B / amber | What to change |
|---|---|---|---|
| GPS satellite / orbiting | Ground station on Earth | Satellite in the modeled circular orbit | Height and comparison interval. The result separates gravity, orbital motion and their net effect. |
| Earth / stationary altitude | Reference clock at sea level | Clock held at the selected height | Height and comparison interval. At zero height, the clocks share the same modeled location and rate. |
| Black hole / static hovering | Far clock, hovering at 20 horizon radii | Near clock, hovering at the selected radius | Near-clock radius and comparison interval. The interval is measured on Clock A. |
Earth-clock hands may look almost identical. The differences are tiny, so use the microsecond readouts. “Magnify tiny Earth-clock drift” exaggerates only the visual rate difference and clearly marks the magnification; the numeric results retain their physical values. Black-hole hovering clocks can have much larger differences.
The satellite can pass behind Earth and become hidden. That is part of the illustration. The black-hole location guide uses a compressed distance scale, and the hovering clocks stay outside the horizon.
INSIDE THE STARSHIP / OPTIONAL 3D
Take the pilot’s seat.
At the panoramic flight deck, choose Click or tap here to enter. A progress bar shows the scene loading. This opens the deck; choose Launch inside it, or Launch mission below, to start traveling. If you already started beside the messages, the deck opens at that same mission position.
Use Choose a mission for a preset, or set cruise speed and one-way distance. Choosing a preset or changing distance starts a fresh journey. Changing speed pauses at the same path position and recalculates the entire comparison at the new constant speed; it does not simulate gradual acceleration.
| Control | What it does |
|---|---|
| Look ahead | Faces the ship’s direction of travel. |
| Side window | Looks sideways relative to the ship’s motion. |
| Find Earth | Looks aft during departure and forward on the homeward leg. Earth has an enlarged locator marker. |
| Drag / direction buttons | Rotates your view. The center button restores the forward view. |
| HUD | Hides or restores the instrument panels for a clearer window view. |
| Compare sky at rest | Shows a zero-velocity optical comparison. The mission clocks and Earth messages keep their selected physics. |
| Show Doppler color & brightness | Toggles the approximate color and brightness effects. Direction changes from aberration remain. |
The sky already previews cruise optics before launch. Clocks remain at zero until the journey starts. At extreme speeds, stars crowd tightly toward the forward direction and side windows can look nearly empty. The wavelength readout describes a 550 nm test light at the center of your current view, not the full spectrum or color of every star.
Native resolution / sharpest is the default. Battery saver reduces rendering resolution. “Close experiment / unload 3D” releases graphics resources and closes this shared mission; reopening starts a fresh journey with the chosen speed and distance. You can then use Earth messages alone without reopening 3D.
Go to the flight deck ↗EARTH MESSAGES / CONTROL THE MISSION HERE
Receive a signal. Read its date.
The Earth elapsed clock, crew elapsed clock and arriving Earth timestamp are grouped inside the postcard panel, so you can compare them with the postcard’s sent date while messages arrive. Each live clock keeps years on the first line and the remaining duration on the second, with fixed-width number and unit positions. Zero years stays visible for shorter durations so the layout remains stable.
You can start and run this experiment beside the messages. Once it is open, the local mission selector, Launch/Pause/Resume button, Reset, Watch the return, Compare at reunion and Journey slider all control the same journey as the deck above. You do not have to scroll back to launch.
| Reading | Question it answers |
|---|---|
| Earth / time elapsed | How much Earth-coordinate time has passed since departure? This is calculated, not an instant live view from the ship. |
| Crew / time elapsed | How much proper time has accumulated on the ship’s own clock? |
| Earth time / arriving light | What Earth timestamp is reaching the ship in light right now? It changes continuously. |
| Postcard / transmitted from Earth | When did the latest numbered message leave Earth? It changes only when another scheduled message arrives. |
Message #00 is the shared departure. Earth continues sending on the printed schedule. The signal map marks packets traveling at light speed and shows how many are sent, received and still in transit. The postcard updates when a numbered packet reaches the ship; its stamp is elapsed time on Earth since launch.
Outbound messages can take a long time to arrive. At 99.99% light speed, you can receive no new numbered postcards during the outward leg even while Earth sends many. This is expected: the messages have to catch a rapidly receding ship. Read the sent/received count, wait for the return, or choose Watch the return to jump to turnaround and play homeward.
Received signal rate measures message cadence relative to crew time. Below 1× means more time between arrivals; above 1× means less. During the return, arriving dates advance faster, while your own clock still ticks normally for you. This arrival rate is different from the final difference in accumulated clock time.
Replay a received message pauses and moves the whole shared mission to that message’s exact arrival. Use Resume mission here to continue. “Try the turnaround” pauses at halfway and keeps keyboard focus beside these message controls. “Watch the return” starts the homeward leg immediately.
Two tables: event times, travel durations and arrival spacing
All clocks start at launch. These are elapsed times, not calendar dates. “Sent 6 months after launch” means Earth transmitted that packet when Earth’s clock had advanced six months. It does not mean the packet has already been traveling for six months. No calendar year such as 2100 is assumed.
Below the receiver and recent-message replay buttons, the tables list every numbered message starting with #01. Message #00 is the shared launch event. Received so far is the default. Choose All scheduled messages / include predictions for the complete planned schedule. Unreceived rows are labeled as predictions.
Table 1 / When each message was sent and received gives the elapsed time after launch for sending on Earth, reaching the ship in Earth’s frame, and the traveler’s age at that arrival. These event counters keep increasing as the mission progresses. The row also shows direction and both speeds. Select a received message number to replay its arrival.
Table 2 / Travel duration and the wait between messages answers two different questions. Time spent traveling is Earth-frame reception time minus Earth send time. Wait since previous message is the gap between receipts on the crew clock. The first wait begins at launch (#00); a gap spanning both legs is marked “Spans turnaround.”
For the default 90%-light-speed journey to a point 5 light-years away, message #01 leaves Earth 6 months after launch and reaches the outbound ship 5 years after launch, in Earth’s frame. Its travel duration is 4 years 6 months. The traveler has aged approximately 2 years 2.2 months at that arrival. Crew age and packet travel duration use different endpoints and must be read separately.
Return-leg messages arrive more frequently. The comparison above Table 2 gives the steady-cruise wait between receipts for each leg. In the default mission, Earth sends every 6 months. The crew receives them about every 2 years 2.2 months while receding and every 1.4 months while returning: 19 times as frequently. A receipt interval crossing turnaround combines the two rates.
At a fixed return speed, that faster arrival cadence is constant. Each later inbound message has less distance to travel before meeting the ship, so its individual travel duration decreases. In the default mission, returning message #02 spends about 4 years 9.5 months in transit, while #22 spends about 19.2 days. The first return message can take longer than the final outbound message if it meets the ship farther from Earth; successive inbound messages then show the shrinking delay.
Every message still moves at 100% c in vacuum, as measured from Earth or in an inertial frame aboard: approximately 186,282 miles/s (299,792 km/s). See Stanford’s explanation of light-speed invariance ↗ and the University of Virginia’s explanation of signal cadence and travelling twins ↗.
Received rows remain fixed during playback. Choosing another speed or distance recalculates both tables for a new whole-mission comparison. Predicted rows remain clearly marked. At the idealized reunion, the ship stops; a message sent exactly then has zero travel time.
The display uses years and months, with days, hours, minutes or seconds for shorter intervals. One modeled year is 365.25 days; a displayed month is one twelfth of that year, approximately 30.44 days. These are rounded duration units, not calendar dates. All calculations retain full precision. On phones, swipe within the tables to see the remaining columns.
The numbered messages are illustrated teaching postcards, decoded by a fictional receiver even when the signal shifts outside visible light. The picture is not a live photograph of a future Earth.
Go straight to Earth messages ↗MISSION CHALLENGE / 100 YEARS AND 10 YEARS
Make a prediction before launch.
- Open either the Earth-message experiment or the 3D deck so the shared mission settings and challenge become available.
- Choose Take the 100 / 10 challenge. Your target is to return after 100 Earth years while aging 10 years aboard.
- Choose cruise speed and one-way distance. The century preset is a useful starting point. Selecting settings clears an earlier prediction.
- Enter the crew time you predict, then choose Lock my prediction before launch. The field locks while the mission is in progress.
- Launch from any of the shared mission controls. At reunion, compare your prediction with the result and the two timeline bars.
The timelines share the same year scale. The challenge accepts a result within 0.5 Earth years and 0.1 crew years of the target. Use Reset for another prediction and flight. You can also fly any preset without taking the challenge.
REFERENCE / WHAT EACH ACTION CHANGES
Keep your place in the experiment.
| Action | Result |
|---|---|
| Launch / Resume / Pause | Starts, continues or pauses the same shared mission. Replay starts again after reunion. |
| Reset mission | Returns to departure and clears a locked prediction, keeping the chosen speed and distance. |
| Journey slider | Pauses and inspects any position: 0% departure, 50% turnaround, 100% reunion. |
| Go to turnaround / Try the turnaround | Pauses at 50%. Resume to continue home. |
| Watch the return | Jumps to 50% and plays homeward. In reduced-motion mode, it advances to reunion. |
| Compare at reunion | Jumps to 100% and shows the final elapsed times. |
| Pause at the turnaround | Optional stop at halfway during playback. Resume when ready. |
| Choose a mission / change distance | Resets the shared journey and any prediction. |
| Change cruise speed | Pauses, keeps the path position, recalculates the whole constant-speed comparison, and clears the prediction. |
| Use the Speed & spaceflight settings above | Copies speed and distance from the original workbench into a fresh starship/message journey. Later changes remain separate until you copy again. |
PHONE / KEYBOARD / MOTION
Use the controls that suit you.
On a phone: the direction buttons and viewing shortcuts stay inside the 3D port. Use them to look around while ordinary vertical swipes scroll the page. The message controls work without a 3D view. On smaller screens, the clock readings and control buttons stack to remain readable.
With a keyboard: Tab moves between controls; Enter or Space activates a focused button. Arrow keys adjust focused sliders. When the 3D canvas itself has focus, arrow keys look around, Home centers the view, and Space toggles mission playback.
Reduced motion: the starship uses stage advances instead of continuous flight. Launch advances to turnaround; Resume advances to reunion. The Journey slider still lets you inspect intermediate states. The original workbench also respects the device’s reduced-motion preference.
Pausing away from the experiment: hiding the browser tab or scrolling the entire starship/message experiment offscreen pauses its mission. Scrolling from the flight deck down to its messages keeps the mission available; the offscreen 3D scene stops drawing. Use Resume beside the messages when needed.
Numeric readouts, control labels and message-arrival announcements provide the essential results without requiring you to interpret the canvases. Help tables can be scrolled horizontally when needed.
IF SOMETHING SEEMS STUCK
Check the mission state.
The stars look different, but the clocks are still at zero.
You are seeing the cruise-optics preview. Choose Launch to begin the journey. Moving the speed slider changes the preview and pauses an existing journey.
The postcard is still #00. Is the receiver broken?
Check the sent and received counts. At high speeds, many messages remain in transit during the outward leg. Choose Watch the return to see arrivals become more frequent. A postcard’s date changes only when a numbered message arrives.
The mission stopped while I was reading or changing settings.
Look for Resume beside the messages or inside the deck. Changing speed, dragging Journey, replaying a message, hiding the tab, and leaving the entire experiment pause the mission. Presets and distance changes reset it.
The side windows are nearly empty at extreme speed.
Strong forward crowding is an aberration effect. The illustrated star sample, colors, exposure compression and dot sizes also affect the picture. Use Compare sky at rest or reduce speed to compare. The renderer is not an exact prediction of everything a human eye would see.
The 3D flight deck will not load.
Read the loading message and try again. You can still use the original workbench and open Earth messages directly. If graphics are interrupted after entry, close the experiment and reopen it. Native resolution is the default; Battery saver is available if your device struggles.
I cannot edit my mission prediction.
Predictions must be made before departure. Reset, choose your settings, then enter and lock a prediction. Changing the settings clears a previous prediction.
READ THE RESULTS WITH THE MODEL IN MIND
Illustrations and calculated quantities.
The ship model uses constant-speed outward and return legs, with instantaneous launch, turn and stopping. It omits fuel, realistic acceleration and gravity. The original Earth modes use simplified weak-field corrections. Black-hole clocks are idealized static hovering clocks outside a nonrotating Schwarzschild black hole, rather than free-falling clocks.
Distances, ship size, halos, orbit playback and clock-hand speeds are illustrative. Sky directions and signal timing follow the equations in the lab’s model notes; star colors and brightness are display approximations. The sky is synthetic, not a measured star catalog or a complete spectral simulation. The black-hole artwork is an illustration, not a photograph or a full ray-traced image.
Read Inside the data / model boundaries and the starship’s expandable model notes for the formulas and linked sources. For a real-world clock example, see NIST’s introduction to precision clock tests ↗.
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