Re: Download a new book on quantum mechanics and relativity.

From: tadchem (tadchemNOSPAM_at_comcast.net)
Date: 10/24/04 

Date: Sun, 24 Oct 2004 18:31:33 -0400

"bernard.chaverondier" <bernard.chaverondier@wanadoo.fr> wrote in message
news:417be7b4$0$28586$8fcfb975@news.wanadoo.fr...

<snip>

> I use the coincidence of events z1 and z2 to cause a light flash
> I want to know if observers that will never see this light flash are
> considered to belong to the same universe than those that see it ?

Simultaneity is relative.

Objects have duration and therefore exist over an extended interval in
space-time. Their space-time loci are line segments.

Events have *no* duration and therefore exist only at points in space-time.
Their space-time loci are points.

Events z1 and z2 must occur at different space-time coordinates; otherwise
they would be the same event.

"Coincidence" implies two objects/events at the same location in space AND
time.

"Simultaneous" implies two objects/events at different locations at the same
time.

An observer/detector capable of detecting two non-coincidental events must
exist at a different space-time from at least one of the events. One must
realize that the observer/detector is not detecting the events directly but
rather receiving information that indicates the occurrence of the event.
The information identifying the occurrence of at least one of the events
must therefore be transferred across space-time to the observer/detector.
Because the speed of transfer of information is finite (no greater than c)
this transfer must take some time.

Which event is registered as the "first" event is determined by the timing
at which the information about the events is received at the detector, NOT
by which event actually occurs first. The order in which the
events-identifying information is received at the detector it turn depends
on the position and motion of the detector relative to the events.

One can extrapolate back in time from the position and motion of the
detector relative to the events to obtain a "calculated" space-time locus
for each event, but this is NOT the same as determining that the events were
simultaneous.

In fact, an array of identical detectors scattered throughout the space-time
vicinity of the events will come to different conclusions about which event
was first or whether both occurred simultaneously (to within the precision
available for the measurement). This will depend solely on the relative
position and motion of the detectors with respect to the events.

I wrote the following last year as an exposition of the relativity of
simultaneity:

+++++ The Cosmo-Logical Clock +++++

?See Alice. Alice has a clock. It is a fine clock. Alice’s clock tells
her what time it is. Run, clock, run.

See Bob. Bob has a clock. It is also a fine clock. Bob’s clock tells him
what time it is. Run, clock, run.

Alice and Bob want to synchronize their clocks. Bob lives 100 meters away
from Alice. Bob goes over to Alice and set his clock to match hers exactly.
Bob then takes his clock back home.

Alice gets out her telescope and looks at Bob’s clock. Bob’s clock is
showing a time that is 333
nanoseconds behind Alice’s clock.

Alice gets her phone and calls Bob.

“Bob! There is something wrong with your clock! You synchronized it with
mine, and now 333
nanoseconds slow.”

Bob looks back at Alice’s clock. Bob tells Alice, “No, Alice. It is *your*
clock that is 333 nanoseconds slow!”

Alice tells Bob, “This is too confusing. Lets go talk to Cosmo. He has a
clock just like ours, and he knows about physics.”

Alice and Bob take their clocks over to Cosmo’s House. Cosmo lives 100
meters away from Bob and
100 meters away from Alice.

“Help Us, Cosmo!”, they plead. “There is something wrong with our clocks,
or with the fabric of space and time!”

Cosmo makes sure all three clocks read exactly the same time. Run, clocks,
run.

Cosmo then sends Alice and Bob straight home, but he tells Alice to run and
Bob to go slowly.

Alice takes 30 seconds to run home. Bob takes 5 minutes to get home.

Cosmo then sets up a conference call with Alice and Bob.

“Alice, what do you see when you look at our clocks?” Cosmo asks.

Alice replies, “Why, BOTH of you have clocks that are 333 nanoseconds behind
mine. Does that mean
that both of you have slow clocks, or that my clock is fast?”

“Bob, what do you see when you look at our clocks?” Cosmo asks.

Bob replies, “I see that you and Alice have clocks that are running 333
nanoseconds behind my clock! It looks to me like my clock is the fast one.
But Alice and I can’t each have a clock that is faster than the other
 clock!”

Cosmo explains, “No. You can’t. I see that both your clock and Alice’s
clock show exactly the same time, and that time is 333 nanoseconds behind
the time my clock shows.”

“Now, my clock didn’t go anywhere, and nothing happened to it. We can call
it the ‘Cosmo-logical’ clock. Alice, you moved your clock 100 meters in a
very short time, and it looks to me like it 333 nanoseconds against the
Cosmo-logical clock. Bob, you moved your clock 100 meters in a much longer
time, and it looks to me like it also lost 333 nanoseconds the Cosmo-logical
clock. “

“How FAST you moved your clock has no effect on the result. Alice, your
clock lost 333 nanoseconds in 30 seconds while you were moving away from me.
It seemed to me it was only running 99.99999889 percent as fast as it
should, but when you stopped moving away from me it appeared to resume
running at normal speed.”

“Bob, your clock lost 333 nanoseconds in 300 seconds while you were moving
away from me. It seemed to me it was only running 99.999999889 percent as
fast as it should, but when you stopped moving away from me your clock also
appeared to resume running at normal speed.”

“I’ll bet neither of you noticed a thing.”

Alice answers “No, Cosmo, we didn’t notice.”

Bob adds “What *should* we have noticed, Cosmo?”

Cosmo tell them “If you had been watching my clock instead of watching where
you were going, you both would have seen my clock seem to slow down by as
much as I noticed your clocks slowing down. That would have been dangerous,
however.”

Alice says, “But I see that your Cosmological clock and Bob’s clock show
exactly the same time. How can that be?”

Cosmo answers, “How fast you were moving away from me determined how fast
your clocks seemed to
be losing time. How much time your clocks seemed to lose was determined by
how far you went away
from me. Since you both went the same distance, you both seemed to lose the
same amount of time.”

Bob says, “Cosmo, I hear you using the word “seem” a lot. What are you
trying to say, or to not say?”

“That is very observant of you, Bob,” Cosmo nods. “I say ‘seem’ because
what is really going on is not always what seems to be going on, and *how*
we see the world is limited by the *way* we see the world.”

“First, let me say that the laws of physics are exactly the same for me and
for each of you, whether you are moving or not. Everything in the universe
has to follow the same laws. In physics that is called the ‘Principle of
Relativity.’ It amounts to saying that everything that you see and know
about the universe is relative to your personal point of view. Somebody
else, watching from somewhere else, may see things that you do a little
differently from the way you see them, but you will never see a change in
the laws of physics.”

“We are using light to see each other’s clocks. Light travels at a constant
speed called ‘the speed of light.’ That speed is finite. Light travels at
about 300,000 kilometers per second. It takes 333 nanoseconds for light to
get from me to either of you. It also takes that long for light to get from
either of you to the other.”

“What I see on your clocks is not what is actually there at the instant I’m
looking at it, but only what WAS there at the instant the light left your
clocks. That light then takes its own sweet 333 nanoseconds to get to me
and let me know what *was* going on with you. That is why your clocks seem
to me to be running 333 nanoseconds behind. That is why each of us sees
everyone else’s clocks as being 333 nanoseconds behind.”

“Rest assured our clocks all are functioning normally.”

Tom Davidson
Richmond, VA

Relevant Pages

  • Re: Download a new book on quantum mechanics and relativity.
    ... Alice has a clock. ... It is a fine clock. ... Bob has a clock. ... Lets go talk to Cosmo. ...
    (sci.physics)
  • Re: Download a new book on quantum mechanics and relativity.
    ... Alice has a clock. ... It is a fine clock. ... Bob has a clock. ... Lets go talk to Cosmo. ...
    (sci.physics.particle)
  • Re: Proper Time
    ... >> that observing your own clock alone you can't tell ... > Alice stays at home, and Bob takes off at the high speed of .96c. ... Bob looks at Alice's clock and his own. ...
    (sci.physics)
  • Re: Frequent time reset messages
    ... Bob, the system clock may be broken for SMP, or your hardware may be ... > Symmetricon XLI-GPS stratum-1 NTP server on an isolated network. ...
    (comp.protocols.time.ntp)
  • Re: 24Hr/7 Day Timer
    ... Bob wrote: ... > I have a project that requires turning a plastic disc (about the same size ... need the clock movement -- the clock face itself isn't necessary. ... wire up a "D"-sized battery to replace the AA. ...
    (sci.electronics.basics)
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