Re: Speed of light or refractive index
- From: alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (Alan)
- Date: Fri, 23 Dec 2005 09:29 +0000 (GMT Standard Time)
In article <Xns9734CD68CBCBCzsp@xxxxxxxxxxxx>, azen@xxxxxxxxxx (Al Zenner)
wrote:
> "=?utf-8?B?SmEg4pml?=" <tadapope@xxxxxxx> wrote in
> news:1135302328.667954.304450@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:
>
> > I think he's looking for that data from
> > dimensions beyond the 4th.
>
> He didn't say so. Specificity matters.
Hey Al, I suppose you do understand the concept of space-time?
Time is the fourth dimension.
Time is not completely separate from and independent of space as you would
ordinarily assume. In his Special Relativity theory, Einstein assumed that the
fundamental laws of physics do not depend on your location or motion. Two
people, one in a stationary laboratory and another in a laboratory aboard a
train or rocket moving in a straight line at uniform speed, should get the same
results in any experiment they conduct. In fact, if the laboratory in the train
or rocket is soundproof and has no windows, there is no experiment a person
could conduct that would show he/she is moving.
The laws of physics include the laws of electromagnetism developed by James
Maxwell and Maxwell found that electromagnetic waves should travel at a speed
given by the combination of two universal constants of nature. Since the laws of
physics do not depend on your location or motion, Einstein reasoned that the
speed of light will be measured to be the same by any two observers regardless
of their velocity relative to each other. For example, if one observer is in a
rocket moving toward another person at half the speed of light and both
observers measure the speed of a beam of light emitted by the rocket, the person
at rest will get the same value the person in the rocket ship measures (about
300,000 kilometers/second) instead of 1.5 times the speed of light (=rocket
speed + speed of beam of light). This assumption has now been shown to be
correct in many experiments. To get the same value of the speed (=
distance/time) of light, the two observers moving with respect to each other
would not only disagree on the distance the light travelled as Newton said, they
would also disagree on the time it took.
Einstein found that what you measure for length, time, and mass depends on your
motion relative to a chosen frame of reference. Everything is in motion. As you
sit in your seat, you are actually in motion around the center of the Earth
because of the rapid rotation of the Earth on its axis. The Earth is in motion
around the Sun, the Sun is in orbit around the center of our Galaxy, the Galaxy
is moving toward a large group of galaxies, etc. When you say something has a
velocity, you are measuring its change of position relative to some reference
point which may itself be in motion. All motion is relative to a chosen frame of
reference. That is what the word ``relativity'' means in Einstein's Relativity
theories. The only way observers in motion relative to each other can measure a
single light ray to travel the same distance in the same amount of time relative
to their own reference frames is if their ``meters'' are different and their
``seconds'' are different! Seconds and meters are relative quantities.
Two consequences of Special Relativity are a stationary observer will find (1)
the length of a fast-moving object is less than if the object was at rest, and
(2) the passage of time on the fast-moving object is slower than if the object
was at rest. However, an observer inside the fast-moving object sees everything
inside as their normal length and time passes normally, but all of the lengths
in the world outside are shrunk and the outside world's clocks are running slow.
One example of the slowing of time at high speeds that is observed all of the
time is what happens when cosmic rays (extremely high-energy particles, mostly
protons) strike the Earth's atmosphere. A shower of very fast-moving muon
particles are created very high up in the atmosphere. Muons have very short
lifetimes---only a couple of millionths of a second. Their short lifetime should
allow them to travel at most 600 meters. However they reach the surface after
travelling more than 100 kilometers! Because they are moving close to the speed
of light, the muons' internal clocks are running much slower than stationary
muons. But in their own reference frame, the fast-moving muons's clocks run
forward ``normally'' and the muons live only a couple of millionths of a second.
Time and space are relative to the motion of an observer and they are not
independent of each other. Time and space are connected to make four-dimensional
spacetime (three dimensions for space and one dimension for time). This is not
that strange---we often define distances by the time it takes light to travel
between two points. For example, one light year is the distance light will
travel in a year. To talk about an event, you will usually tell where (in space)
and when (in time) it happened. The event happened in spacetime.
Another consequence of Special Relativity is that nothing can travel faster than
the speed of light. Any object with mass moving near the speed of light would
experience an increase in its mass. That mass would approach infinity as it
reached light speed and would, therefore, require an infinite amount of energy
to accelerate it to light speed. The fastest possible speed any form of
information or force (including gravity) can operate is at the speed of light.
Newton's law of gravity seemed to imply that the force of gravity would
instantly change between two objects if one was moved---Newton's gravity had
infinite speed (a violation of Special Relativity). The three strange effects of
Special Relativity (shrinking lengths, slowing time, increasing mass) are only
noticeable at speeds that are greater than about ten percent of the speed of
light. Numerous experiments using very high-speed objects have shown that
Special Relativity is correct.
Special Relativity also predicts that matter can be converted into energy and
energy in to matter. By applying Newton's second law of motion to the energy of
motion for something moving at high speed (its ``kinetic energy''), you will
find that energy = mass × (speed of light)2. More concisely, this is Einstein's
famous equation, E = mc2. This result also applies to an object at rest in which
case, you will refer to its ``rest mass'' and its ``rest energy'', the energy
equivalent of mass. The amount of rest energy in something as small as your
astronomy textbook, for example, is tremendous. If all of the matter in your
textbook was converted to energy, it would be enough energy to send a million
tons to the Moon!
http://www.astronomynotes.com/relativity/s2.htm
HTH
Alan
http://www.veloceraptor.free-online.co.uk/enigma.html
http://veloceraptor.blogspot.com/
.
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