Put your hand on a hot stove for a minute, and it seems like an hour.
· Sit with a pretty girl for an hour, and it seems like a minute.
· THAT's relativity.
A. Einstein

Twenty-six year old German-born Albert Einstein, while holding down a full time job as a patent clerk (third class) in Switzerland in 1905, set the physics world on its ear with the publication of no fewer than five breakthrough papers in physics. While he won the Nobel prize in 1921 for his explanation of the photoelectric effect, perhaps his most famous (and most controversial) work dealt with special relativity. The "special" in special relativity deals exclusively with those cases when objects move with uniform speed in straight lines.
He explained the nature of accelerated objects and gravity in his general theory published in 1915. The ten-year lapse in publication was probably due in part to: 1) the distraction caused by the acclaim he received from his early work; 2) the fact that he moved back to Germany; 3) the outbreak of WWI; and 4) some serious domestic discord which led to estrangement and divorce from Mrs. Einstein.

The interested student will be well-rewarded for reading one of the several biographies available describing the life and thoughts of this scientist-turned-icon.



Consider a trailer truck with a trailer having transparent sides. Our assistant is ridiing in the trailer and holds a ball over an X marked on the trailer floor. On cue, she will drop a ball exactly once from rest. Describe the path of the ball as seen by three different observers.
Observer one is in the trailer with our assistant. He says that the ball has no horizontal velocity so that the path is a straight line ceiling to floor
Observer two is stationary at the roadside watching the trailer proceed past at a constant rate of speed. Observer two reasons that the ball has a forward velocity from the trailer. Hence the path is a parabola arcing forward.
Observer three meanwhile is passing the trailer truck while riding in a convertible as the ball is dropped. Because she ascribes all of the motion to the trailer truck with herself at rest, she reasons that the truck is backing up and has a rearward velocity; hence, the path of the ball is arcing toward the rear of the truck.
Which is the three observers is correct in describing this event?
The answer of course is that all three of them are correct. That each description is different is due to the fact that each observer saw the events from a different point of view. This will be a very compelling argument in special relativity. Observers will differ on events because they are seeing things from a different point of view


The consequences of the special theory alter our concept of space and time by predicting that

The special theory of relativity is predicated on the validity of two postulates. If experimental evidence finds a discrepancy in either of these principles, then the conclusions derived from these principles will have to be changed. Despite all the challenges that have been mounted over the last 100 years, the two postulates stand as published in 1905.









to and in http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

TIME DILATION: an experiment with mu-mesons

this classic film documents an experiment done in 1963 the results of which can only be explained when one accepts the consequence that moving clocks run slow. This phenomenon is known as time dilation. The timekeeping device is the mu-mesona, a subatomic particle with origins away from the Earth moving at relativistic speed. What follows here is an explanation of the experiment described in that film.

Many mu-messons rain down every hour on the Earth from sources outside of the Earth. The mu-messons are radioactive and they decay into other particles. The mu-messons are detected by a scintillation chamber which emits a flash of light whenever a particle enters the chamber or decays in it. Experimenters used photomultiplier tubes to detect light flashes and an oscilloscope measure the time between an entering flash and a decay flash.

Using a 4.5 feet thick pile of iron bars, experimenters are able to stop the mu-mesons in the detection chamber. Mu-mesons travel at .99c which translates to 1000 feet per microsecond. Mt Washington where this experiment takes place, is 6300 feet above sea level. The crux of the experiment is: how many mu-mesons will survive a trip from an altitude of 6300 feet to sea level. Of a sample of 568 mu-mesons arriviing at the top of Mt Washington only 27 live longer than 6.3 µs. That means, if they repeat the experiment at sea level 27 or about 27 mu-mesons should reach a laboratory at sea level.

When this experiment was repeated at sea level, 412 mu-mesonss made it to the chamber. This was many times more than 27 that they expected. The only conclusion that they could draw was that mu0mesons measured time differently because they were moving.

What does this look like to an observer sitting on the mu-meson? This Observer expects a short lifetime of this particle.He sees Mt. Washington, known to be 6300 feet high, pass by at only 700 feet high, still high enough for the particle to travel a short distance in the short amount of time that it has


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