Einstein's Relativity and Everyday Life -- Clifford M. Will

Einstein's Relativity and Everyday Life -- Clifford M. Will
http://www.physicscentral.com/writers/writers-00-2.html

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Einstein's Relativity and Everyday Life
Clifford M. Will

What good is fundamental physics to the person on the street?

This is the perennial question posed to physicists by their non-science
friends, by students in the humanities and social sciences, and by
politicians looking to justify spending tax dollars on basic science.
One of the problems is that it is hard to predict definitely what the
payback of basic physics will be, though few dispute that physics is
somehow "good."

Physicists have become adept at finding good examples of the long-term
benefit of basic physics: the quantum theory of solids leading to
semiconductors and computer chips, nuclear magnetic resonance leading
to MRI imaging, particle accelerators leading to beams for cancer
treatment. But what about Einstein's theories of special and general
relativity? One could hardly imagine a branch of fundamental physics
less likely to have practical consequences. But strangely enough,
relativity plays a key role in a multi-billion dollar growth industry
centered around the Global Positioning System (GPS).

When Einstein finalized his theory of gravity and curved spacetime in
November 1915, ending a quest which he began with his 1905 special
relativity, he had little concern for practical or observable
consequences. He was unimpressed when measurements of the bending of
starlight in 1919 confirmed his theory. Even today, general relativity
plays its main role in the astronomical domain, with its black holes,
gravity waves and cosmic big bangs, or in the domain of the
ultra-small, where theorists look to unify general relativity with the
other interactions, using exotic concepts such as strings and branes.

But GPS is an exception. Built at a cost of over $10 billion mainly for
military navigation, GPS has rapidly transformed itself into a thriving
commercial industry. The system is based on an array of 24 satellites
orbiting the earth, each carrying a precise atomic clock. Using a
hand-held GPS receiver which detects radio emissions from any of the
satellites which happen to be overhead, users of even moderately priced
devices can determine latitude, longitude and altitude to an accuracy
which can currently reach 15 meters, and local time to 50 billionths of
a second. Apart from the obvious military uses, GPS is finding
applications in airplane navigation, oil exploration, wilderness
recreation, bridge construction, sailing, and interstate trucking, to
name just a few. Even Hollywood has met GPS, recently pitting James
Bond in "Tomorrow Never Dies" against an evil genius who was inserting
deliberate errors into the GPS system and sending British ships into
harm's way.

But in a relativistic world, things are not simple. The satellite
clocks are moving at 14,000 km/hr in orbits that circle the Earth twice
per day, much faster than clocks on the surface of the Earth, and
Einstein's theory of special relativity says that rapidly moving clocks
tick more slowly, by about seven microseconds (millionths of a second)
per day.

Also, the orbiting clocks are 20,000 km above the Earth, and experience
gravity that is four times weaker than that on the ground. Einstein's
general relativity theory says that gravity curves space and time,
resulting in a tendency for the orbiting clocks to tick slightly
faster, by about 45 microseconds per day. The net result is that time
on a GPS satellite clock advances faster than a clock on the ground by
about 38 microseconds per day.

To determine its location, the GPS receiver uses the time at which each
signal from a satellite was emitted, as determined by the on-board
atomic clock and encoded into the signal, together the with speed of
light, to calculate the distance between itself and the satellites it
communicated with. The orbit of each satellite is known accurately.
Given enough satellites, it is a simple problem in Euclidean geometry
to compute the receiver's precise location, both in space and time. To
achieve a navigation accuracy of 15 meters, time throughout the GPS
system must be known to an accuracy of 50 nanoseconds, which simply
corresponds to the time required for light to travel 15 meters.

But at 38 microseconds per day, the relativistic offset in the rates of
the satellite clocks is so large that, if left uncompensated, it would
cause navigational errors that accumulate faster than 10 km per day!
GPS accounts for relativity by electronically adjusting the rates of
the satellite clocks, and by building mathematical corrections into the
computer chips which solve for the user's location. Without the proper
application of relativity, GPS would fail in its navigational functions
within about 2 minutes.

So the next time your plane approaches an airport in bad weather, and
you just happen to be wondering "what good is basic physics?", think
about Einstein and the GPS tracker in the cockpit, helping the pilots
guide you to a safe landing.

________________________________


Clifford M. Will is Professor and Chair of Physics at Washington
University in St. Louis, and is the author of Was Einstein Right? In
1986 he chaired a study for the Air Force to find out if they were
handling relativity properly in GPS. They were.

 

And apparently a master and skilled BS'er too.

1) GPS corrections do not actually use the relativistic computations,
they just re-synchronize. GR says "you have a mismatch,
re-synchronize",
as would have any another system which would have computed
the time required for light to travel the distance.

2) There is indeed a difference between GR, and any non-GR system
used to compute the time required for light to travel the distance.
But this difference is much smaller than the 38 microseconds,
and cannot be discovered at this scale.

Basically, instead of using GR, one could have divided the
distance by the speed of light to arrive at the time difference.
That works, too.

 

I told you, Mukes Prasad, eating your own shit on a daily basis makes
you mad (in addition to your being born a cretin). See here, how GPS
really works, fuckhead:

http://relativity.livingreviews.org/open?pubNo=lrr-2003-1&page=node5.html

Do your parents know? Are your children retarded? Of course!

 

Ignorance is bliss!

 

No, apparently not. I know Dr. Will personally. He has to be one of the
straightest, least tolerant of any kind of BS man I've ever known. Read
his book. It's an easy read, marvelously written. You can see his dry,
to the point, matter of fact approach to problems from the way he
writes.

 

What planet are you from? Even the steward of a nukular
arseinall isn't choosen on merit. I'ts about *marketing*.

;-)

Sue...

 

What an argument for top posting

 

<yawn>
| What an argument for top posting

 

The 38 microsec per day drift of a standard clock in GPS orbit was
_measured_ during the initial setup of the first satellite. If, as you
claim, this correction was to be applied by simply "re-synchronizing"
the clocks, then in order to meet the accuracy specification of 3
meters, the clocks would need to be "re-synchronized" 3,800 times per
day, or almost 3 times every minute. Needless to say, a system based on
such frequent "re-synchronization" could not possibly work. And indeed,
the actual system uses corrections applied typically daily, and these
corrections are MUCH smaller than 38 microsec (because the basic 38
microsec per day is programmed into the satellites).

That is not the problem. The problem is that standard clocks located in
the satellites drift by ~38 microsec per day relative to standard clocks
on earth.

Hmmm. The "distance' is what one wants to determine, because the GPS is
a _geo-location_ system. Basically the satellites repeatedly broadcast
their position and time, and the receivers use that information from 4
or more satellites to determine their location on earth. You seem to be
singularly ignorant of what the GPS is, why it was built, and how it
works. Perhaps you should actually _LEARN_ something about it before
attem[pting to discuss it.

Besides, what you claim simply does not work when the clocks in orbit do
not remain in synchronization with clocks on the ground.

Neither. The _physical_ correction to tick rate is applied to the
satellite clocks, and that keeps them _approximately_ in synch with
earth clocks and each other. Due to uncontrollable variations, small
corrections are uploaded to the satellites daily; these are typically a
few nanoseconds, or about 0.1% of the GR correction.

Your reading ability as as poor as your understanding of the GPS. Plain
and simple: the GR correction is built into the satellites. <shrug>


Tom Roberts

 

What you are saying COULD be right -- but your post is a basic
repetition of published facts. Since relativity is heavily political
and opposing viewpoints do not get equal press, therefore
it is equally possible that there are facts that have not
been published. In fact, it is highly possible.

Furthermore, all theoretical considerations indicate that
theoretically,
what you are saying should not be right. A theory resulting from
random mathematical manipulation with no insight behind it
just shouldn't describe reality, as it would be the wildest of
coincidences . Therefore, in lack of open debates on the matter,
it is at the very least very doubtful.

 

In addition to "random mathematical manipulation", also
note, theories resulting from failure to understand
how an em wave could propagate in empty space. It is hard
to see how theories built upon a failure to understand
something, and upon random insightless mathematical
manipulation, can describe reality. It is much easier
to see how they can become political snowballs,
and generate false but extremely complicated defenses.

 

You can find the correction factor by trial-and-error in a trivial way.
GPS clocks are corrected just once before lift-off and that is all.

[snip remaining crap]

Is there another application of GR? Even the cats in the streets are
starting getting tired of this apologetic talk about GPS and such.

By the way, INS (inertial navigation system) worked in 747's long
before GPS and did the job as well.

SR/GR - hahahahahahahahahahahaha - Falsified over ten times

Mike

 

I don't think there is anything political about relativity.
Nor is there any lack of published results. NASA, NSF and
other sources still fund basic scientific research including
relativity. Its biggest application, GPS is $30B+ industry,
applying relativity to create a global infrastructure benefiting
people all over the world.

 

Certainly some corrections could have been determined by trial and error,
but relativity theory predicted the degree of correction and explains
it cause! Relativity correction were designed into the engineering,
not added "just once before lift-off",

See: http://edu-observatory.org/gps/gps_books.html

 

No, there is no lack of published research. But
all published research *must* support relativity
in order to get published.

There have been reports that papers were refused publication
because they were seen as implying something against relativity.

That's not open, honest, inquiry. Honest researchers
would get all research widely published and openly
debated, and see where it leads. Prior suppression
and filtering, is nothing but cheating.

So after it's been established clearly that a certain segment of
the researchers routinely cheat in their behavior, you are asking
for a lot of unwarranted trust, in taking it at faith that all the
details have been published honestly where the same segment
of the researchers is concerned.

 

See what you started!

How do you figure the gravitational force is four times weaker at
20,000 km above the surface of the earth?

 

One can but admire this reasoning.

Paul

 

No , cocksucker . The correct statement is : Failure for the cretin
Mukesh Prasad to understand how em propagates in empty space (and
failure to understand everything elese in physics).
What did you graduate in? Cock sucking?

 

Where did you get that , idiot Mukesh Prasad?

Because they were incorrect, refutable by prior experiment, shithead
Mukesh Prasad

Why, some of you cretin "papers" got rejected, Mukesh Prasad?

They don't cheat. You try to and you get exposed every time, asshole!

 

[next time you line your hat, use a little more tinfoil...]