Another form of interference can produce what is known as a standing wave. A standing wave pattern is formed when two waves of the same frequency interfere whilst traveling in opposite directions. The diagram below shows how two such waves (green & blue) of the same frequency will interfere to produce a standing wave (red). The blue wave and the green wave interfere according to the principles of superposition. This means that they will add together to form a new (resultant) wave, which in this case is a standing wave.
From this animation we can see that there are fixed points on the wave, at which no displacement occurs. These points are known as nodes, and are evenly spaced along the wave. The nodes are formed by the destructive interference of the two original waves, thus all the motion is canceled. The points along the wave at which there is maximum displacement are known as anti nodes. These are caused by the constructive interference of the original waves. When the standing wave is at maximum displacement it energy is said to be entirely in the 'real'. When the wave is flat, or at minimum displacement the energy is entirely in the imaginary (i). Thus the energy oscillates between the real and the imaginary (i). The term 'imaginary' is used in mathematics to develop equations and is not to be taken as literally meaning imaginary.
Rubens Tube Experiment
This video shows how we can visualise the standing waves produced from sound waves interfering inside a tube. This experiment is known as a Rubens Tube. Thanks to youtube user twinrawk for uploading the video and explaining it well..
The mysterious properties of electromagnetic waves and interference have lead some people to abandon conventional physics. A form of wave known as a scalar wave is said to vibrate entirely between the imaginary realm and some 'higher dimension'. This theory is mainly the work of Tom Bearden, but there are many supporters of this theory. The next section give details of the 'Scalar field theory' and also gives an explanation to why it is not accepted by standard science.