2 Particles as Building Blocks of Matter
17
in 1887 at what is now the Case Western Reserve University in Cleveland. They
conducted an experiment which looked at two light beams, one traveling along
the direction of Earth’s motion, and the other perpendicular to it. They wanted
to observe if light in the former case traveled with a different speed due to
the moving Earth, compared to the other. The thinking at that time was that
light travels in a medium, called ether, and the ether will be dragged along the
Earth’s motion like any fluid through which a rigid body is moving. Michelson
and Morley thought that this effect should change the speed of light along the
direction of Earth’s motion, compared to the one perpendicular to it. But they
found no difference between the two light beam speeds, which meant that
regardless of the motion of the medium, light speed always remains the same.
That was an astounding result which established light as having remarkably
different property from all other moving objects like the train.
Einstein took the bold step to postulate that the speed of light remains the
same no matter how fast a frame from which you are measuring the speed
moves. No matter how fast the train moves next to a beam of light, the
light wave never slows down and always moves at the same speed. Einstein’s
genius connected this amazing and unique property of light to the peculiar
property of time and proposed the theory of relativity. The theory of relativity
revolutionized the thinking in physics prior to 1905 about time and space.
It posited that nature of time in a moving train is different from that in a
train standing still. Things that look simultaneous in a moving train will not
look the same if viewed from the ground at rest. At the basis of the theory
of relativity was the result that light speed is independent of the speed of
the object where the source of light is located. It is claimed that this theory
was so revolutionary, that at one point only a few people other than Einstein
understood it. The story goes that the well known British physicist Arthur
Eddington, when asked in 1919 whether it was true that only three people in
the world understood the theory of general relativity, [Eddington] allegedly
replied: “Who is the third?”
Slowly the theory of relativity became part of the physics discussion and its
incredible impact on how things behave started to emerge. One important
consequence among many of the theory of relativity is that the relation
between energy and speed of objects gets fundamentally altered. For example,
prior to the theory of relativity, mass and energy were considered separate,
whereas theory of relativity implied that mass can be converted to energy and
vice versa. Instead of E =
mv
2
2
as the relation between energy, mass, and speed
for slowly moving particles, the relation in the theory of relativity became
E
2
= p
2 c
2
+ m
2 c
4 . Here the variable p is the momentum of the particle
17
in 1887 at what is now the Case Western Reserve University in Cleveland. They
conducted an experiment which looked at two light beams, one traveling along
the direction of Earth’s motion, and the other perpendicular to it. They wanted
to observe if light in the former case traveled with a different speed due to
the moving Earth, compared to the other. The thinking at that time was that
light travels in a medium, called ether, and the ether will be dragged along the
Earth’s motion like any fluid through which a rigid body is moving. Michelson
and Morley thought that this effect should change the speed of light along the
direction of Earth’s motion, compared to the one perpendicular to it. But they
found no difference between the two light beam speeds, which meant that
regardless of the motion of the medium, light speed always remains the same.
That was an astounding result which established light as having remarkably
different property from all other moving objects like the train.
Einstein took the bold step to postulate that the speed of light remains the
same no matter how fast a frame from which you are measuring the speed
moves. No matter how fast the train moves next to a beam of light, the
light wave never slows down and always moves at the same speed. Einstein’s
genius connected this amazing and unique property of light to the peculiar
property of time and proposed the theory of relativity. The theory of relativity
revolutionized the thinking in physics prior to 1905 about time and space.
It posited that nature of time in a moving train is different from that in a
train standing still. Things that look simultaneous in a moving train will not
look the same if viewed from the ground at rest. At the basis of the theory
of relativity was the result that light speed is independent of the speed of
the object where the source of light is located. It is claimed that this theory
was so revolutionary, that at one point only a few people other than Einstein
understood it. The story goes that the well known British physicist Arthur
Eddington, when asked in 1919 whether it was true that only three people in
the world understood the theory of general relativity, [Eddington] allegedly
replied: “Who is the third?”
Slowly the theory of relativity became part of the physics discussion and its
incredible impact on how things behave started to emerge. One important
consequence among many of the theory of relativity is that the relation
between energy and speed of objects gets fundamentally altered. For example,
prior to the theory of relativity, mass and energy were considered separate,
whereas theory of relativity implied that mass can be converted to energy and
vice versa. Instead of E =
mv
2
2
as the relation between energy, mass, and speed
for slowly moving particles, the relation in the theory of relativity became
E
2
= p
2 c
2
+ m
2 c
4 . Here the variable p is the momentum of the particle