There are many, many sites on the web with information about special and general relativity. Unfortunately this is an area which attracts the crazies, and you have to be very careful about whether you can trust the information you read. This is particularly true because the syllabus asks teacher and students to speculate on topics which are not, as yet, mainstream physics, which takes you well into the realms of science fiction, and it becomes harder and harder to recognize the dividing line. It is best to stick with sites from the larger universities, or maintained by authors whose credentials you recognize.
The historical and theoretical background to special relativity
There are many accounts of aether theories in the literature. Most books on Special Relativity, including popular accounts and encyclopaedia entries, have information on the topic. It is common for these accounts to imply that aether theories were relatively new at the time of the Michelson-Morley experiment, but this is not so. Aether theories of various kinds can be traced to the Greek philosophers, and Newton expressed some of his views in terms of an aether theory, see pages 19-21 of E. Whittaker, A History of the Theories of the Aether and Electricity, 1951.
The brilliant biography of Einstein, written by Abraham Pais, Subtle is the Lord to cover the topic of the role of the Michelson-Morley experiment in the development of Einstein's views, see pages 111-119. I hope this reading gives some insight into the complexity and difficulty of discovering and interpreting the history of the development of ideas! (L.E.C.)
The physics of this topic can take a very long time to teach, depending how carefully you go into it. Standard approaches can be found in most any mainstream textbook, for example, HRW, chapter 38. A gentler approach is taken in Marion, chapter 9.
A gentle illustrated introduction to the basic concepts of special and general relativity, which is aimed nonetheless at first year university students is the course SpaceTime 101, by a lecturer at Cal Tech, USA: http://www.theory.caltech.edu/people/patricia/st101.html.
A not-too-long, but quite complete article on the history of Special Relativity appears on a site maintained by St. Andrew's University, Edinburgh: http://www-history.mcs.st-and.ac.uk/history/HistTopics/Special_relativity.html.
Some of the consequences of special relativity
Einstein's Theory of Special Relativity - from The Physics Classroom, includes animations
http://www.physicsclassroom.com/mmedia/specrel/specrelTOC.htmlA reasonable looking site Relativity on the World Wide Web that might prove useful is: http://ma th.ucr.edu/home/baez/relativity.html, covering Frequently Asked Questions in this area.
A discussion of the relativity of simultaneity can be found in Chapter, IX of Einstein's Relativity: The Special and the General Theory, a Popular Exposition. This volume is still widely available in public and school libraries. The clarity of Einstein's explanations is unparalleled.
The implications of relativity for space travel
Implications of relativity on ordinary, real life space travel are negligible, so the syllabus is asking for extrapolations into science fiction territory here. It means you will need to be careful about the reliability of sites you look at.
A safe site is one of the NASA "Ask a High Energy Astronomer" pages: http://imagine.gsfc.nasa.gov/docs/ask_astro/relativity.html. It's got answers to most of the obvious questions students are likely to come up with.
To help understand some of the weirder effects that are genuine consequences of relativity, there are some very good computer simulations around, e.g. Relativistic flight simulator: http://casa.colorado.edu/~ajsh/sr/srfs.html.
A site with information about relativistic effects on space travel as well as beautiful computer simulations is by a John Walker, Fourmilab, Switzerland, entitled: C-ship: Relativistic ray traced images: http://www.fourmilab.ch/cship/cship.html#refs.
Once you get into questions like: can spaceships go faster than light? you really have to be careful. An apparently comprehensive site with links to various places discussing relativity and space travel is: http://asia.yahoo.com/science/physics/relativity/relativistic_travel/superluminal_travel/. Some of the sites referred to look OK on a cursory glance, but caution is urged.
Student investigations and experiments
A description of the Michaelson-Morely experiment can be found in most of the many textbooks at an introductory university level, devoted specifically to Special Relativity. See for example pages 18-26 of R. Resnick, Introduction to Special Relativity (1968).
To model the Michelson-Morley experiment, it would be worth considering the analogy of rowing a boat across a stream, versus rowing up and down the river. It would be quite possible for students to discover that the time for the up-down journey is always longer than the across journey, for the same distance travelled. (L.E.C.)
There is a quite technical exposition of Einstein's views on waves in the wonderful biography Subtle is the Lord by Abraham Pais, (1982). I suspect that the "mirror" item mentioned in the Syllabus has been somewhat embellished as an aspect of the history of relativity. (L.E.C.)
Regarding the items referring to Einstein's predictions, the following considerations might be relevant:
- Predictions of the Special Theory include time dilation, length contraction and the equivalence of matter and energy. So far as I know, none of these things was the subject of experimental research before the theory was developed.
- Time dilation was confirmed in many ways following Einstein's prediction. The arrival on the ground of short-lived particles (mesons) produced high in the atmosphere by cosmic rays is often cited as an example. Students should be able to calculate the time dilation for cosmic ray products from data in texts.
- I am not aware of an experiment that demonstrates length contraction, although the interpretation of super-luminal motion in quasars relies in part on the effect.
- Modern navigation systems (such as the Global Positioning System) must make relativistic corrections routinely. Students could calculate the rate of slowing of clocks in satellites or aircraft compared with terrestrial observers, and from this calculate the positional error in long journeys.
- The equivalence of matter and energy is of course illustrated in atomic fission and fusion, as well as in the binding energy of atomic systems.
- Although it is generally overlooked as the consequence of special relativistic effects, the magnetic field around a current-carrying conductor is in fact a strictly relativistic effect arising from the drift of electric charges in the conductor, as viewed by the external observer. (L.E.C.)
Three well-known predictions of General Relativity are:
- The anomalous precession of the perihelion of Mercury, which was known before Einstein's theory was developed, but unexplained.
- The redshift of light in a gravitational field. It was claimed that this was confirmed by observations of the wavelength of spectral lines emitted by the Sun, but the experiment is rendered ambiguous because there are several other phenomena that lead to net line shifts in solar spectral lines. The shift of the spectral lines in compact companions (e.g. white dwarfs) of stars provide a more reliable test.
- The deflection of starlight by the Sun, detected during a total eclipse. This was a difficult experiment and there is now some doubt about the reliability of the reduction of the data that were claimed to support the prediction. (L.E.C.)
Time Dilation http://www.glenbrook.k12.il.us/gbssci/phys/shwave/tdilate.html
Science fiction ideas
The effects of time dilation on the lives of space travellers is well imagined in The Forever War (1975) by Joe Haldeman, and Beloved Son (1978) by George Turner (an Australian sf writer).
The limitations that relativity puts on space travel has been a continual irritation to sf writers. Concepts of "hyperspace" have been around for a long time, with little theoretical justification. But Contact (1985, the book; 1997, the movie) by Carl Sagan introduced the wormhole to sf readers (and to many scientists). It is now standard in modern space opera - see for example, the TV series Babylon 5 (1995) or Galaxy Quest (1999).
Additional related sites
Michelson-Morley Experiment
http://www.treasure-troves.com/physics/Michelson-MorleyExperiment.html
If any one comes across another web site, or chapter in a book, or other material, which they consider useful to them in teaching this module, please email us at: PhySciCH@mail.usyd.edu.au, and we will add that information to the site.
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