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17 Cards in this Set

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Length contraction hypothesis
Proposed by Lorentz and Fitzgerald. The idea was that all bodies are contracted when in motion relative to the stationary ether, with the contraction taking place only in the direction of relative motion. The light beam moving parallel to the ether current would have a shorter distance to traverse, thus catching up to the beam going across the current. This catching up was a "gift from above".
Ether-drag hypothesis
The assumption that ether was dragged along by all objects so tha tthey had no relative velocity with respect to the ether frame. But light did not drag the ether with it so light had the unique property of motion relative to the ether.

But this hypothesis was rebuked because of the observation of rain and the fact tthat light could bend so it's not like a person can drag rain even though it seems to always follow them when they walk.
Einstein's suggestion
Suggested that Maxwell's electromagnetic theory can be freed from the ether hypothesis and that the motion of absolute motion be rejected.
Einstein's Principle of relativity
All the laws of physics must be so formulated as to be invariant (or the same in mathematical form) to all inertial frames of reference
The Invariance of the Speed of Light
The relative velocity between the ether and any physical frame of reference is zero. Regardless of the relative velocities amongst themsevles, the speed of light in vacuum is the same as the value predicted in Maxwell's theory. The speed of light is a univeral quantity and the concept of the ether frame is superfluous.

Therefore one does not need to specify a frame of reference for the speed of light. It is the same for all observers, and all observers are equivalent insofar as the speed of light is concerned.
The Special Theory of Relativity
1) All inertial frames of reference are equivalent

2) The speed of light is the same to all inertial observers

These are postulates for a physical theory. This special theory of relativity provides a framework upon which the physical models of the universe are to be constructed. Space and time started to not have an absolute character.
Concept of Absolute Time
That there exist a cosmic clock, perhaps deep in outer space, ticking away the moments of true, absolute time.

We take it for granted that ll reliable clocks run at the same rate, as they, in turn, tick in perfect harmony with the cosmic clock.
Concept of Relative Time
The Concept of absolute time didn't match with the postulates of relativity.
Light beam clock
The issue with time in connection to it's relativity is the intervals of time.

A light beam is a device that traps a light pulse between two parallel mirrors so that the pulse bounces off the mirrors at perfectly regular intervals of time.
Observations about Time
Time is viewed by the ground-based observer as running slower in a moving frame of reference. The pilot's heart beat beats slower than that of the ground based observer. All activities in the spaceship proceed at a slower rate.
Theory of relativiity
Time exists in intimate relationship to the observer and thus becomes an entirely relative concept.
Set up observating time
Two similar light-beam clocks are used. One is placedon the ground and another in a spaceship. As long as the spaceship remains stationary on the take off strip both light-beam clocks tick at the same time. A light been has the same speed no matter where it is. But a longer path for light means a longer time of transit. Thus the ground based observer believes that the spaceship clock runs slower than his own.
Time dilation - A quantitative analysis
The spaceship observer finds that his clock advnces by a time interval t' during a complete round trip of a pulse in the light-beam clock. If the length of the ligh-beam is L', the light pulse would be traverse a distance of 2L' during the time interval t'

t' = 2L' / c where c is the speed of the light pulse.
Time dilation equation by Einstein in his special theory of relativity
t = t' / square root of 1 - v2/c2
An example of time dilation
There are two observers, a spaceship observer and an earth bound observer. The spaceship observer finds that the time interval which a flower lives from the bud sprouting to the falling of the withered flower. The earthbound observer measure the speed of the spaceship, which is where the flower is, and found that the speed (v) is 99.2 percent or .992 the speed of light.

So with t' = the time interval of the life of a flower, v= being the speed of the spaceship while the flower is inside it you get the lifespan of the flower on earth to be 7.7 months when it was just a month in space.
The use of muons for experimentation
D.H. Frisch and J.H Smith wwere physicists who studied clocks in high speed motion. They used a radioactive substance called muons. Radioactive substances specify half life which divides the original subatance into two each time.
Experimental confirmation of time dilation
The half life of muons in flight, were going at 99% the speed of light. They counted the number of these particular muons at a certain altitude and counted the surviving ones at sea level. The detector recorded the arrival of 563 muons every hour as they were in flight. If time were absolute only 27 muons per hour if they just decayed on ground level without movement would be recorded.