Create Relativity.java

Created the file that implements relativity formulae.

Author: kvadrik

src/main/java/com/thealgorithms/physics/Relativity.java

@@ -0,0 +1,78 @@
+package com.thealgorithms.physics;
+
+/**
+ * Implements relativity theory formulae.
+ * Provides simple static methods to calculate length contraction and time dilation
+ * in the laboratory frame with respect to the object's own frame, and velocity 
+ * with respect to the moving frame.
+ *
+ * @see 
+ * <a href="https://en.wikipedia.org/wiki/List_of_relativistic_equations">Wikipedia</a>
+ */
+public final class Relativity {
+
+	/* Speed of light in m s^-1 */
+	public static final double SPEED_OF_LIGHT = 299792458.0;
+	
+	/**
+     * Private constructor to prevent instantiation of this utility class.
+     */
+	private Relativity() {
+	}
+	
+	/**
+	 * Calculates the gamma parameter that is of paramount importance in relativity 
+	 * theory. It is a dimensionless parameter that is equal to 1 for zero velocity
+	 * but tends to infinity when velocity approaches the speed of light.
+	 *
+	 * @param v The velocity (m/s).
+	 * @return The value of gamma parameter.
+	 */
+	public static double gamma(double v) {
+		if (Math.abs(v) >= SPEED_OF_LIGHT)
+			throw new IllegalArgumentException("Speed must be lower than the speed of light");
+		return 1.0/Math.sqrt(1-v*v/(SPEED_OF_LIGHT*SPEED_OF_LIGHT));
+	}
+
+	/**
+	 * Calculates the length of an object in the moving frame.
+	 * 
+	 * @param length The length of an object in its own frame (m).
+	 * @param v The velocity of the object (m/s).
+	 * @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");
+		return (v1 - v)/(1 - v1*v/(SPEED_OF_LIGHT*SPEED_OF_LIGHT));
+	}
+}
+