What causes "Time must be non-negative" in TheAlgorithms/Java?

Pass a non-negative time in seconds; reorder event subtraction as t2 - t1 only when t2 >= t1, or use Math.abs if magnitude is what matters.

TheAlgorithms/Java · error · IllegalArgumentException

Time must be non-negative

Error message

Time must be non-negative

What it means

Thrown by Relativity.timeDilation when time < 0. Time dilation t = t0 * gamma multiplies a proper time by the Lorentz factor; a negative proper time is physically meaningless (proper time is a non-negative interval along a worldline). The velocity v is validated separately when timeDilation delegates to gamma(v).

Source

Thrown at src/main/java/com/thealgorithms/physics/Relativity.java:60

     * @return The length of an object in the laboratory frame (m).
     */
    public static double lengthContraction(double length, double v) {
        if (length < 0) {
            throw new IllegalArgumentException("Length must be non-negative");
        }
        return length / gamma(v);
    }

    /**
     * Calculates the time that has passed in the moving frame.
     *
     * @param length The time that has passed in the object's own frame (s).
     * @param v The velocity of the object (m/s).
     * @return The time that has passed in the laboratory frame (s).
     */
    public static double timeDilation(double time, double v) {
        if (time < 0) {
            throw new IllegalArgumentException("Time must be non-negative");
        }
        return time * gamma(v);
    }

    /**
     * Calculates the velocity with respect to the moving frame.
     *
     * @param v1 The velocity of the object with respect to laboratory frame (m/s).
     * @param v The velocity of the moving frame (m/s).
     * @return The velocity with respect to the moving frame (m/s).
     */
    public static double velocityAddition(double v1, double v) {
        if (Math.abs(v1) > SPEED_OF_LIGHT) {
            throw new IllegalArgumentException("Speed must not exceed the speed of light");
        }
        if (Math.abs(v) >= SPEED_OF_LIGHT) {
            throw new IllegalArgumentException("Frame speed must be lower than the speed of light");
        }

View on GitHub (pinned to fdfb9a395b)

Solutions

Pass a non-negative time in seconds; reorder event subtraction as t2 - t1 only when t2 >= t1, or use Math.abs if magnitude is what matters.
Validate proper-time inputs at the boundary and reject negative values before the call.
Ensure the velocity is subluminal, because gamma(v) will throw separately otherwise.

Example fix

// before
double t = Relativity.timeDilation(t1 - t2, v);
// after
double t0 = Math.max(0, t2 - t1);
double t = Relativity.timeDilation(t0, v);

Defensive patterns

Strategy: validation

Validate before calling

double t0 = Math.max(0, time);
double t = Relativity.timeDilation(t0, v);

Prevention

Order time differences so the result is non-negative, or take the magnitude.
Reject sentinel -1 values from optional fields before they reach physics calls.
Validate the velocity separately since gamma will throw its own message.

When it happens

Trigger: Calling timeDilation(time, v) with a negative time value. A time of exactly 0 is allowed and returns 0.

Common situations: A clock-reading subtraction that produced a negative delta due to event ordering, a timestamp parsed with a sign error, or a default sentinel value of -1 leaking into the call.

Related errors

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/228c484257a8bdac. Report an issue: GitHub.