The future is commonly unerstood to contain all events that have yet to occur. It is the opposite of the past, and is the time subsequent to the present. Organized efforts to predict or forecast the future may have derived from observations by early man of heavenly objects. In physics, which uses a linear conception of time, the future is the portion of the projected time line that is anticipated to occur. In special relativity the future is considered as absolute future or the future light cone. In physics, time is considered to be a fourth dimension.