At the end of this section students should be able to:

·       discuss the principle of relativity
·       describe the significance of Einstein’s assumption of the constancy of the speed of light
·       analyse and interpret some of Einstein’s thought experiments involving mirrors and trains and discuss the relationship between thought and reality
·       analyse information to discuss the relationship between theory and the evidence supporting it, using Einstein’s predictions based on relativity that were made many years before evidence was available to support it
·       identify that if c is constant then space and time become relative
·       discuss the concept that length standards are defined in terms of time in contrast to the original metre standard

It is a popular misconception that Einstein was awarded a Noble Prize for his work in relativity.  He actually received his Noble Prize, in 1921, for his work with the photoelectric effect.  His 1905 theory of special relativity was discounted for many years and was seen as merely a good theoretical idea, but not reality. This theory was developed from the outcomes of the Michelson-Morley experiment and the work of Maxwell, from which Einstein asserted that the speed of light was independent to the frame of reference of the observer, that is regardless of where light is seen from it always is travelling at the same speed, and later that the concept of the aether was not necessary to explain the way light travelled.  The following video provides a brief explanation of these ideas.


The assertion of a constant speed of light has consequences for how we come to understand space and time.  Time was considered to be a constant value always moving forward at the same rate regardless of where a person was in the universe.  Einstein postulated that all observers regardless of where they were would always see light travelling at the same speed, namely 3.0 x 10^8 m/s, indicated as 'c'.

The following website provides excellent multimedia clips and background information about the implications of Einstein's theory of relativity and the postulate of the constant speed of light.  Take time to review the resources on this website and watch the variety of clips.  On this website are also a variety of links to background information about the various aspects of the theory.  



Students should make notes and summaries of the information on the above webpage.  From this you should create a brief explanation of time dilation and length contraction as consequences of special relativity.  

Make a brief presentation around these two ideas and try to explain them to someone else using your presentation.