Schrödinger's Cormorant

Key Points from Chapter 2:

The speed of light is the same in all inertial frames of reference. This means that movement of the light’s source relative to its observer has no effect on the speed of the light travelling between them.

The knock-on effect of accepting this is that we have to change our understanding of the way in which space and time work. Specifically, we have learned about:

Time dilation: if you watch a moving clock and a stationary one, you will observe that the moving one runs more slowly. In other words, if something takes a time t0 to happen in a stationary frame of reference, it will take a longer time (t1) when observed in a moving frame. This is expressed by the relationship:

Length contraction: if an object is stationary relative to one observer but moving at velocity v relative to a second observer, it will have a length (D1) which is decreased in the direction of movement, when measured by the observer for whom it is moving, compared to the length measured by the stationary observer (D0). This is expressed as:

Because the factor √(1/(1 - u2/c2)) is close to 1 unless u is approaching the speed of light, time dilation and length contraction are negligible in most circumstances. This means that errors introduced by using Galileo's relativity are negligible for practical purposes, unless speeds approaching that of light are involved.

If you are enjoying getting your head around special relativity, you might want to have a look at the Appendix to this Chapter. This gets into the theory in a little bit more depth and looks at some of the issues it raises, including the famous twin paradox.

The appendix is, however, an optional extra: You don’t need it to progress to chapter 3 and beyond: so if you’re in a hurry to find out why E is equal to mc2 or to get stuck into quantum theory, feel free to skip it.

Back

Appendix

Chapter 3

Chapter Guide

Page updated

Google Sites

Report abuse