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Relativity

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Nezaket Özgirin

on 10 May 2012

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Transcript of Relativity

The Elegant Universe - Einstein's Relativity
Visualization of the thery of relativity
While listening with a task
It’s a little known fact that Albert Einstein’s famous work on special relativity was spurred by a thought experiment he conducted when he was only 16 years old. In his book Autobiographical Notes, Einstein recalls how he once daydreamed about chasing a beam of light as it traveled through space. He reasoned that if he were able to move next to it at the speed of light, he should be able to observe the light frozen in space as “an electromagnetic field at rest though spatially oscillating.” For Einstein, this thought experiment proved that for his imaginary observer “everything would have to happen according to the same laws as for an observer who, relative to the Earth, was at rest.”

What it Means:
In truth, no one really knows for sure. Scientists have long debated how this deceivingly simple thought experiment helped Einstein make the massive theoretical leap required to arrive at special relativity theory. At the time, the ideas in the experiment contradicted the now-debunked belief in the “aether,” an invisible field through which light was believed to travel. It would be years before he could prove he was right, but this thought experiment was somehow the “germ,” as he called it, for Einstein’s theory of special relativity, one of the ideas that first established him as a towering figure in theoretical physics
http://www.youtube.com/watch?v=wteiuxyqtoM&feature=player_embedded
in 5 minutes
2.Complete the text below with the words in italics. You may use the same word more than once.

radius, circumference, circle, diameter, arc, segment

The radius of a circle is the distance from the center point to the edge of the………... It's the same distance anywhere on the circle, because the circle has radial symmetry. So it doesn't matter where you measure the …………. on the circle, and if you know one radius measurement for a circle, then you know all of them. Try it for yourself and see!
One example would be if you were trying to measure a big tree. It would be pretty easy to take a rope and wrap it around the tree, and then measure the length of the rope to find out how big around the tree was (the circumference), but you'd have to cut the tree down to measure the ………….. We don't want to cut this big tree down, so we'll need to use math to figure out the radius instead. Luckily we know that the radius of any circle is always the same as half of the …………………divided by (pi). So the radius of this tree is 30/ = 9.55 centimeters, divided by two is 4.77 centimeters.
A-radius,
B-circumference,
C-segment,
D-arc circle,
E-diameter
Objectives

1. Watch a short video and try to find out what time dilation is.

2. Now try to answer more specific questions

a) Time moves more ………….. for someone who is running at a …………….. speed …………. to someone else.

b) How was it proved that time slowing down is a measurable effect

c) How big is this effect?

d) What does it mean that the slowing down of time is symmetric?
e) How did Einstein rephrase the question below? Why did he do it?
What time does this train leave the station?


f) How does Einstein’s theory of relativity change the Newtonian perception of time?
g) What physical quantity is used to explain time dilation according to the theory of relativity?
1. Explain in basic terms the apparent contradiction which Einstein’s special theory of relativity attempts to explain.

2. Display familiarity with Einstein’s concept of thought experiment.

3. Describe in simple terms the thought experiments which Einstein proposed to illustrate the following phenomena:
• Time dilation
• Lorentz-Fitzgerald contraction
• Non-simultaneity
Vocabulary
DESCRIBING THE PROPERTIES OF A CIRCLE
radius, circumference, diameter, arc, segment

DESCRIBING MOVEMENT AND CHANGE IN MAGNITUDE
to be stable, to be at rest, to dilate, to contract, increase/decrease by a factor of

DESCRIBING THE RELATIONSHIP BETWEEN EVENTS OR MEASUREMENTS
simultaneous, to coincide, frame-dependent, with respect to

CATEGORIES OF KNOWLEDGE
principle, law, assumption

DESCRIBING THE MOVEMENT OF LIGHT
to emit/receive a light signal, beam of light, flash
The radius of a circle is the distance from the center point to the edge of the…
CIRCLE
……... It's the same distance anywhere on the circle, because the circle has radial symmetry. So it doesn't matter where you measure the …
RADIUS
………. on the circle, and if you know one radius measurement for a circle, then you know all of them. Try it for yourself and see!
One example would be if you were trying to measure a big tree. It would be pretty easy to take a rope and wrap it around the tree, and then measure the length of the rope to find out how big around the tree was (the circumference), but you'd have to cut the tree down to measure the ……
RADIUS/DIAMETER
…….. We don't want to cut this big tree down, so we'll need to use math to figure out the radius instead. Luckily we know that the radius of any circle is always the same as half of the ……
CIRCUMFERENCE
…divided by (pi). So the radius of this tree is 30/ = 9.55 centimeters, divided by two is 4.77 centimeters.
POST 2012
A) Newton B) Galileo C) Einstein
1. Who was the first to observe the phenomenon of relativity?
b. Galileo: Free-falling objects.






9. Imagine a cat in a box with a vial of poison and a single radioactive atom which has a 50% chance of decaying and triggering the vial, causing the cat to die. Before the box is opened, the cat is considered to be both alive and dead, because one has no way of knowing what's inside the box. Do you agree?
For more thought experiments go to http://www.toptenz.net/top-10-most-famous-thought-experiments.php

2. According to the theory of relativity, it is impossible to…………………………………………………………………….
3. Explain the Principle of Relativity


4. The lecturer gave a few examples e.g. a beam of light travelling between mirrors, light being observed by different observers? What do we call those?
5. Complete the definition of a thought experiment below
A thought experiment is an ………………………………which is carried out in the realm of the ………………………, rather than in a laboratory. Thought experiments are designed to test ideas, theories, and hypotheses which ……………………..physically be tested, at least with current scientific equipment. In addition to being used in some branches of the theoretical sciences, thought experiments also crop up in fields like philosophy, where people often explore complex topics which cannot be empirically tested or observed. They should be distinguished from thinking about …………………………., from merely imagining any experiments to be conducted outside the imagination, and from psychological experiments with ……………... .
A thought experiment is an experiment which is carried out in the realm of the imagination, rather than in a laboratory. Thought experiments are designed to test ideas, theories, and hypotheses which cannot physically be tested, at least with current scientific equipment. In addition to being used in some branches of the theoretical sciences, thought experiments also crop up in fields like philosophy, where people often explore complex topics which cannot be empirically tested or observed. Thought experiments should be distinguished from thinking about experiments, from merely imagining any experiments to be conducted outside the imagination, and from psychological experiments with thoughts

6. Explain the thought experiment involving one person shining a light at a mirror and another person observing it from a moving vehicle. What did this show? What term did Einstein apply to this phenomenon?
7. What does the following thought experiment show? What term is given to this phenomenon?

8. Explain the thought experiment which illustrates the principle of non-simultaneity.
tell whether an object is at absolute rest or in motion
The laws of physics are the same in all inertial frames of reference.
A thought experiment

A person standing still shines light at mirror
Measures time taken for the light to hit mirror
Another person passing in car also measures time taken for light to hit mirror
Because moving person has velocity the distance perceived is longer, therefore time longer
It showed that something moving and something still do not make the same measurements of time. He called it “Time Dilation”.
A stationary observer sees a stick at rest measuring 50 cm. A moving observer sees the same stick at rest but measuring about 35 cm.

If you are moving distances seem shorter than for someone who is standing still. / Distance depends on the viewer. Lorentz contraction
Stationary person at equal distance to two lights to left and right
Another observer in a car
When lights turned seen as simultaneous by stationary person
Person in vehicle sees the one they are going towards as turned on first
https://www.youtube.com/watch?v=G-R8LGy-OVs#t=19
Relativity
http://www.phys.unsw.edu.au/einsteinlight/
Qestions from December, 2013
6. What does the following thought experiment show? What term is given to this phenomenon?
A particle drops from the atmosphere to earth and passes a pole which is stuck in the ground. From the particle’s perspective, it thinks it is at rest and the pole is shooting past it, and because it has velocity the length of the pole is shorter than it appears to someone standing at the bottom of the pole.

1. Complete the sentence below that describes relativity.
One cannot tell whether they are at1 ………………. or moving with a 2…………………. velocity (3……………………. motion.)
2. Why can’t we feel the earth’s movement?
The lecture gave an example of an observer standing in an equal distance between 2 sources of light. The lights come on and the observer sees them light up at same time/simultaneously. On the other hand, when the observer is moving towards one of the light sources, they will see the closer of the lights come on earlier than the other. This constitutes the concept of non-simultaneity.

An experiment which is not actually performed (but explores the potential consequences of a hypothesis).
1rest, 2constant, 3uniform
The orbit’s curvature is so small that we do not feel it. Moreover, the rotational and orbiting speeds are constant.
3. Explain the notion of non-simultaneity.
5. What is time dilation?
It describes a phenomenon related to the theory of relativity that concerns measuring time at speeds close to the speed of light. Basically the moving clock ticks more slowly than the clock at rest. The faster the clock moves, the measured time passes more slowly.
Or
A person standing still shines light at mirror
Measures time taken for the light to hit mirror
Another person passing in car also measures time taken for light to hit mirror
Because moving person has velocity the distance perceived is longer, therefore time longer
It showed that something moving and something still do not make the same measurements of time. He called it “Time Dilation”.

4. What is a “thought experiment”?
If you are moving distances seem shorter than for someone who is standing still. / Distance depends on the viewer. This example describes Lorentz-Fitzgerald contraction.
Full transcript