Dear all I felt that when YMji writes and I do write and a few well
versed may easily go through; but many feel why these bore? So when i was
going through the book accidentally spotted by YMji , from my shelf a
chapter here covered in a week might easily make everyone understand what
is newton einstein etc Can we learn a little science? K Rajaram IRS 3724
4724
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Is Empty Space Empty? (p40 in FABRIC OF THE COSMOS)
Light was the prime actor in the relativity drama written by Einstein in the
early years of the twentieth century. And it was the
work of James Clerk Maxwell that set the stage for Einstein's dramatic
insights. In the mid-1800s, Maxwell discovered four
powerful equations that, for the first time, set out a rigorous theoretical
framework for understanding electricity magnetism, and their intimate
relationship.' Maxwell developed these equations by carefully studying the
work of the English physicist Michael Faraday, who in the early 1800s had
carried out tens of thousands of experiments that exposed hitherto unknown
features of electricity and magnetism. Faraday's key breakthrough was the
concept of the field. Later expanded on by Maxwell and many others, this
concept has had an enormous influence on the development of physics during
the last two centuries, and underlies many of the little mysteries we
encounter in everyday life. When you go through airport security, how is it
that a machine that doesn't touch you can determine whether you're carrying
metallic objects? When you have an MRI, how is it that a device that
remains outside your body can take a detailed picture of your insides?
When you look at a compass, how is it that the needle swings around
and points north even though nothing seems to nudge it? The familiar answer
to the last question invokes the earth's magnetic field, and the concept of
magnetic fields helps to explain the previous two examples as well. I've
never seen a better Way to get a visceral sense of a magnetic field than
the elementary school demonstration in which iron filings are sprinkled in
the vicinity of a bar magnet. After a little shaking, the iron filings
align themselves in an orderly pattern of arcs that begin at the magnet's
north pole and swing up and around, to end at the magnet's south pole. The
pattern traced by the iron filings is direct evidence that the magnet
creates an invisible something that permeates the space around it-a
something that can, for example, exert a force on shards of metal. The
invisible something is the magnetic field and, to our intuition, it
resembles a mist or essence that can fill a region of space and thereby
exert a force beyond the physical extent of the magnet itself. A magnetic
field provides a magnet what an army provides a dictator and what auditors
provide the IRS: influence beyond their physical boundaries, which allows
force to be exerted out in the "field." That is why a magnetic field is
also called a force field.
Relativity and the Absolute
An airport metal detector's magnetic field seeks through your
clothes and causes metallic objects to give off their own
magnetic fields-fields that then exert an influence back on the
detector, causing
its alarm to sound. ,4n MRI's magnetic field seeps into your body, causing
particular atoms to gyrate in just the right way to generate their own
magnetic fields-fields that the machine can detect and decode into a
picture of internal tissues. The earth's magnetic field seeps through the
compass casing and turns the needle, causing it to point along an arc that,
as a result of eons-long geophysical processes, is aligned in a nearly
south-north direction.
Magnetic fields are one familiar kind of field, but Faraday also
anaiyzed another: the electric field. This is the field that causes your
wool scarf to crackle, zaps your hand in a carpeted room when you touch a
metal doorknob, and makes your skin tingle when you're up in the mountains
during a powerful lightning storm. And if you happened to examine a compass
during such a storm, the way its magnetic needle deflected this way and
that as the bolts of electric lightning flashed nearby would have given you
a hint of a deep interconnection between electric and magnetic
fields-something first discovered by the Danish physicist Hans Oersted and
investigated thoroughly by Faraday through meticulous experimentation.
Just as developments in the stock market can affect the bond market which
can then affect the stock market, and so on, these scientists found that
changes in an electric field can change in a nearby magnetic field, which
can then cause changes in the electric field, and so on.
Maxwell found the mathematical underpinnings of these interrelationships,
and because his equations showed that electric and magnetic fields are as
entwined as the fibres in a Rastafarian's dreadlocks, they were eventually
christened electromagnetic fields, and the influence they exert the
electromagnetic force.
Today, we are constantly immersed in a sea of electromagnetic fields. Your
cellular telephone and car radio Nork over enormous expanses because the
electromagnetic fields broadcast by telephone companies and radio stations
suffuse impressively wide regions of space. The same goes for wireless
Internet connections; computers can pluck the entire World Wide Web from
electromagnetic fields that are vibrating all
around us-in fact, right through us. Of course, in Maxwell's day,
electromagnetic technology was less developed but among scientists his feat
was no less recognized: through the language of fields, Maxwell had shown
that electricity and magnetism, although initially viewed as distinct, are
really just different aspects of a single physical entity.
Later on, we'll encounter other kinds of fields-gravitational
fields, nuclear
fields, Higgs fields, and so on-and it will become increasingly clear that
the field concept is central to our modern formulation of physical law. But
for now the critical next step in our story is also due to Maxwell. Upon
further analysing his equations, he found that changes or disturbances to
electromagnetic fields travel in a wavelike manner at a particular speed:
670 million miles per hour. As this is precisely the value other
experiments had found for the speed of light, Maxwell realized that light
must be nothing other than an electromagnetic wave, one that has the right
properties to interact with chemicals in our retinas and give us the
sensation of sight. This achievement made Maxwell's already towering
discoveries all the more remarkable: he had linked the force produced by
magnets, the influence exerted by electrical charges, and the light we use
to see the universe-but it also raised a deep question.
When we say that the speed of light is 670 million miles per hour, experience,
and our discussion so far, teaches us this is a meaningless statement if we
don't specify relative to what this speed is being measured. The funny
thing was that Maxwell's equations just gave this number, 670 million miles
per hour, without speaking or apparently, relying on any such reference. It
was as if someone gave the location a party as 22 miles north without
specifying the reference location, jinx north of what. Most physicists,
including Maxwell, attempted to explain the speed his equations gave in the
following way: Familiar waves such as ocean waves or sound waves are
carried by a substance, a medium.
Ocean Relativity and the Absolute waves are carried by water. Sound
waves are carried by air. These waves are specified with respect to the
medium. about the speed of sound at room temperature being 767 And the
speeds When we talk miles per hour (also known as Mach 1, after the same
Ernst Mach encountered earlier), we mean that sound waves travel through
otherwise still air at this speed. Naturally, then, physicists surmised
that light waves-electromagnetic waves-must also travel through some
particular medium, one that had never been seen or detected but that must
exist. To give this unseen light carrying stuff due respect, it was given a
name: the luminiferous aether, or the aether for short, the latter being an
ancient term that Aristotle used to describe the magical catchall substance
of which heavenly bodies were imagined to be made. And, to square this
proposal with Maxwell's results, it is, as suggested, that his equations
implicitly took the perspective of someone at rest with respect to the
aether. The 670 million miles per hour his equations came up with, then,
was the speed of light relative to the stationary aether.
As one can see, there is a striking similarity between the luminiferous aether
and Newton's absolute space. They both originated in attempts to provide a
reference for defining motion; accelerated motion led to absolute space,
light's notion led to the luminiferous aether. In fact, many physicists
viewed the aether as a down-to-earth stand-in for the divine spirit that
Hens More, Newton, and others had envisioned permeating absolute space,
(Newton and others in their age had even used the term "aether" in their
descriptions of absolute space.) But what actually is the aether? What is
it made of? Where did it come from? Does it exist everywhere?
These questions about the aether are the same ones that for centuries had
been asked about absolute space. But whereas the full Machian testfor
absolute space involved spinning around in a completely empty universe,
physicists were able to propose doable experiments to determine whether the
aether really existed. For example, if you swim through water toward an
oncoming water wave, the wave approaches you more quickly; if you swim away
from the wave, it approaches you more slowly. Similarly, if you move
through the supposed aether toward or away from an oncoming light wave, the
light wave's approach should, by the same reasoning, be faster or slower
than 670 million miles per hour. But in 1887, when Albert Michelson and
Edvard Morley measured the speed of light, time and time again they found
exactly the same speed of 670 million miles per hour regardless of their
motion or that of the light's source. All sorts of clever arguments are
devised to explain these results. Maybe, some suggested, the experimenters
were unwittingly dragging the aether along with them as they moved. Maybe,
a few ventured, the equipment was being warped as it moved through the
aether, corrupting the measurements.
But it was not until Einstein had his revolution an insight that the
explanation finally became clear.
Relative Space, Relative Time
In June 1905, Einstein wrote a paper with the unassuming title "On the
Electrodynamics
of Moving Bodies," which once and for all spelled the end of the
luminiferous aether. In one stroke, it also changed forever our
understanding of space and time. Einstein formulated the ideas in the paper
over an intense five-week period in April and May 1905, but the issues it
finally laid to rest had been gnawing at him for over a decade. As a
teenager, Einstein struggled with the question of what a light wave would
look like if you were to chase after it at exactly light speed. Since you
and the light wave would be zipping through the aether at exactly the same
speed, you would be keeping perfect pace with the light. And so, Einstein
concluded, from your perspective the light should appear as though it
wasn't moving. You should be able to reach out and grab a handful of
motionless light just as you can scoop up a handful of newly fallen snow.
But here's the problem. It turns out that Maxwell's equations do not allow
light to appear stationary-to look as if it's standing still. and
certainly, there 1s no reliable report of anyone's ever actually catching
hold of a stationary clump of light. So, the teenage Einstein asked, what
are we to make of this apparent paradox?
Ten years later, Einstein gave the world his answer with his special theory
of relativity. There has been much debate regarding the intellectual roots
of Einstein's discovery, but there is no doubt that his unshakable belief
in simplicity played a critical role. Einstein was aware of at least some
experiments that had failed to detect evidence for the existence of the
aether.' So why dance around trying to find fault with the experiments?
Instead, Einstein declared, take the simple approach: *The experiments
were failing to find the aether because there is no aether*. And since
Maxwell's equations describing the motion of light-the motion of
electromagnetic waves-do not invoke any such medium, both experiment
Relativity and the Absolute theory would converge on the same
conclusion: *light,
unlike any other kind of wave ever encountered, does not need a medium to
carry it **along*. Light is a lone traveller. Light can travel through
empty space. But what, then, are we to make of Maxwell's equation giving
light a speed of 670 million miles per hour? If there is no aether to
provide the standard of rest, what is the what with respect to which this
speed is to be interpreted? Again, Einstein bucked convention and answered
with ultimate simplicity. If Maxwell's theory does not invoke any
particular standard of rest, the most direct interpretation is that we
don't need one. The speed *of *light, Einstein declared, is 670 million
miles per hour relative to anything and everything.
Well, this is certainly a simple statement; it fit well a maxim
often attributed
to Einstein: "Make everything as simple as possible, but no simpler." The
problem is that it also seems crazy. If you run after a departing beam of
light, common sense dictates that from your perspective the speed of the
departing light has to be less than 670 million miles per hour.
If you run toward an approaching beam of light, common sense dictates that
from your perspective the speed of the approaching light will be greater
than 670 million miles per hour. Throughout his life, Einstein challenged
common sense, and this time was no exception. He forcefully argued that
regardless of how fast you move toward or away from a beam of light, you
will always measure its speed to be 670 million miles per hour-not a bit
faster, not a bit slower, no matter what. This would certainly solve the
paradox that stumped him as a teenager: Maxwell's theory does not allow for
stationary light because light never is stationary; regardless of your
state of motion, whether you chase a light beam, or run from it, or just
stand still, the light retains its one fixed and never changing speed of
670 million miles per hour. But, we naturally ask, how can light possibly
behave in such a strange manner?
Think about speed for a moment. Speed is measured by how far something goes
divided by how long it takes to get there. It is a measure of space (the
distance travelled) divided by a measure of time (the duration of the
journey). Ever since Newton, space had been thought of as absolute, as
being out there, as existing "without reference to anything external."
Measurements
of space and spatial separations must therefore also be absolute:
regardless of who measures the distance between two things in space, if the
measurements are done with the adequate care, the answers will always
agree, And although we have not yet discussed it directly, Newton declared
the same to be true of time. His description of time in the Prin*cipia *echoes
the language he used for space: "Time exists In and of itself and flows
equably without reference to anything external." In other words, according
to Newton, there is a universal, absolute conception of time that applies
everywhere and everywhen. In a Newtonian universe, regardless of who
measures how much time it takes for something to happen, if the
measurements are done accurately, the answers will always agree.
These assumptions about space and time comport with our daily experiences
and for what reason are the basis of our commonsense conclusion that light
should appear to travel more slowly if we run after it. To see this,
imagine that Bart, who's just received a new nuclear-powered skateboard,
decides to take on the ultimate challenge and race a beam of light.
Although he is a bit disappointed to see that the skateboard's top speed is
only 500 million miles per hour, he 1s determined to give it his best shot.
His sister Lisa stands ready with a laser; she counts down from 11 (her
hero Schopenhauer's favourite number) and when she reaches 0, Bart and the
laser light streak into the distance. What does Lisa see? Well, for every
hour that passes, Lisa sees the light travel 670 million miles while Bart
travels only 500 million miles, so Lisa rightly concludes that the light is
speeding away from Bart at 170 million miles per hour. Now let's bring
Newton into the story). His ideas dictate that Lisa's observations about
space and time are absolute and universal in the sense that anyone else
performing these measurements would get the same answers. To Newton, such
facts about motion through space and time were as objective as two plus two
equalling four. According to Newton, Bart will agree with Lisa and will
report that the light beam was speeding away from him at 170 million miles
per hour.
But when Bart returns, he doesn't agree at all. Instead, he dejectedly claims
that no matter what he did-no matter how much he pushed the skateboard's
limit-he saw the light speed away at 670 million miles per hour, not a bit
less. And if for some reason you don't trust Bart, bear in mind that
thousands of meticulous experiments carried out during the last hundred
years, which have measured the speed of light using moving sources and
receivers, support his observations with precision.
How can this be?
Einstein figured it out, and the answer he found is a logical yet
profound extension
of our discussion so far. It must be that Bart's measurements of distances
and durations, the input that he uses to figure out how fast the light is
receding from hlm, are different from Lisa's measurements.
Think about it. Since speed is nothing but distance divided by
time, there is no other way for Bart to have found a different answer from
Lisa's for how fast the light was outrunning him. *So, Einstein concluded,
Newton's Ideas of absolute space and absolute time were wrong*. Einstein
realised that experimenters who are moving relative to each other, like
Bart and Lisa, will not find Identical values for measurements of distances
and durations. *The puzzling experimental data on the speed of light can be
explained only if their perceptions of space and time are different.*
*KR IRS 3724 4724 Part1*
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