| Topic: |
Science > Physics |
| User: |
"Email me at CS not Boole" |
| Date: |
10 Aug 2004 01:28:29 AM |
| Object: |
Opinion poll on a version of the twin paradox |
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
--
Don't contact me at pratt@boole.stanford.edu, substitute cs for boole instead.
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| User: "Old Man" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 02:15:43 PM |
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"Email me at CS not Boole" <pratt@boole.Stanford.EDU> wrote in message
news:cf9pud$2mo$1@news.Stanford.EDU...
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
Voting doesn't count in physics. The "Twin Paradox" is
a hoax, generated by idiots, like Pratt, who haven't a clue
about the significance of an inertial reference frame.
In Earth orbit, one has gravitational time dilation folded
in with relativistic time dilation. An orbital altitude exists
wherein the two effects cancel. Through ignorance, and
most probably, stupidity, Pratt has under-specified the
problem. [Old Man]
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| User: "Igor" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 04:58:13 PM |
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(Email me at CS not Boole) wrote in message news:<cf9pud$2mo$1@news.Stanford.EDU>...
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
You can't do science by poll. Nature doesn't care what anyone thinks
about anything. Only with experiment and observation do we arrive at
the truth.
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| User: "Uncle Al" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 10:38:31 AM |
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Email me at CS not Boole wrote:
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
[snip]
http://sheol.org/throopw/sr-twin-01.html
http://fourmilab.to/etexts/einstein/specrel/specrel.pdf
<http://www.geocities.com/physics_world/sr/ae_1905_error.htm>
Don't you even suspect that cumulatively more than 100,000
physics grad students and their teachers have pondered this
primitive point and reached some sort of satisfactory
conclusion? GET YOUR LAZY ***** IN GEAR AND FIND IT. You are
missing the big picture. You haven't even expended the minimal
effort to learn it is called the Twin Paradox.
One twin travels relativistically, one twin stays at home. When
they reunite the traveling twin is seen to have aged much less
than his genetic double.
Acceleration breaks the symmetry of who ages faster. To
accomplish that, the acceleration can occur before the clocks (or
the twins) exist. Only reference frames matter.
Inertial frames with relative *velocities* pursue different paths
through spacetime in Special Relativity. No clock anomaly is
apparent in any of them until clocks are compared (by all being
local when you do it, initial calibration then experiment).
Acceleration is irrelevant in SR to the running of the clocks (as
opposed to Equivalence Principle acceleration in GR).
Acceleration is necessary at some arbitrary time not associated
with the experiment itself for breaking the symmetry of clock
observation. Acceleration defines which reference frame takes
what path through spacetime - even if it occurs when the clocks
are *off* (or not even constructed yet, or destroyed) - so the
situation is NOT symmetric. There is a difference between the
reference frame and any clocks in it.
1) Acceleration is an absolute measurement and it does not
require a clock to make the measurement (e.g, simultaneous
displacement of three independent orthogonally cantilevered
masses). There is no doubt who was accelerated even if a clock
was not running/existing during aceleration. Any past
accelerated reference frame has a different mixture of space and
time from an unaccelerated frame.
2) Past acceleration is irrelevant to the running of present
clocks, but not to the mixture of space and time in the reference
frame that said clocks measure. This is an important subtlety
and the key to the whole thing. You cannot synchronize clocks
except by having them local. That's what Relativity demands. If
they are local at the start, you can tell who was naughty
thereafter without needing a clock to do the acceleration
measurement. Accelerometers are not clocks.
EXAMPLE: We have three identical clocks that are off (a state of
not running, or of not even having been fabricated) and zeroed.
Each clock has/will have a very short toggle jiggger switch
sticking out. We load them (or their parts, or ore and a smelter
and a machine shop) in individual spaceships and set up the
experiment.
CLOCK 1: That's our clock. It sits stationary in our inertial
reference frame with a little jigger sticking out. Touch the
jigger and the "off" state becomes "on" or the "on" state becomes
"off." Clock 1 is "off." Or we can build it from parts just
before we need it, and in the "off" state, zeroed.
CLOCK 2: In a spaceship traveling at 0.999c relative to our
inertial frame of reference. Clock 2 is "off." It was built
after all acceleration ceased, and set to zero. It skims past
Clock 1 (our clock), the jiggers touch, both Clocks 1 and 2 are
now "on" and locally synchronized by touching. Elapsed time
accumulates in each one. The situation is NOT symmetric! We
have an accelerometer and they have an acelerometer. We know who
accelerated to set up the experiment even if there wasn't a clock
present when it happened.
CLOCK 3: In a spaceship traveling at 0.999c relative to our
inertial frame of reference, but 180 degrees counter in direction
to Clock 2. Clock 3 is zeroed and "off." It was built after all
acceleration ceased, and set to zero.
Some arbitrary time after Clocks 1 and 2 synchronize and turn
"on" by touching, Clocks 2 and 3 brush past each other, touching
jiggers. Clock 2 is now "off," Clock 3 is now "on." Write down
the elapsed time in now "off" Clock 2, then smash the clock with
a sledgehammer. Or melt it down, or toss it over the side. The
spaceship with Clock 3 is returning back over the path taken by
the spaceship with Clock 2.
CLOCK 1: That's our clock. It sits stationary in our inertial
reference frame with a little jigger sticking out. Clock 3
rushes past, jiggers touch. Clocks 3 and 1 are now off. All
clocks are off. No clock has accelerated while "on" or even
while existing. Write down elapsed times, smash each clock with
a sledgehammer. Or melt them down, or toss them.
BOTTOM LINE: Get all three slips of paper together...
Accelerate as you need. Or send all the results to all three
folks by radio and never decelerate. All clocks have been
smashed, melted, tossed. Their elapsed times were written down.
The numbers on the papers won't change when you accelerate or
broadcast the data.
Acceleration is arguably General Relativity, as we did setting up
the experiment. It is irrelevant to the clocks. No clock is
running or even exists during acceleration. Numbers written on
slips of paper are unaffected by Special or General Relativity.
One could as easily build the clocks from their component parts
after setting up the experiment. No clock exists during
acceleration up or down. The *reference frame* has accelerated
in the past, and that changes its mix of space and time relative
to an unaccelerated frame. The clocks are passive observers in a
presently unaccelerated setting.
Finally.... compare elapsed times. Elapsed time #2=#3 (straight
line motion for both traveling clocks, no acceleration!), but
elapsed time #2+#3 does not equal #1, the local stationary
reference frame summation. The sum of #2+#3 elasped time is only
about 4.5% that than of #1's accumulated elapsed time. You have
the Twin Paradox (or, Triplets) without any running clock having
been accelerated - or having even existed during acceleration up
or down.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Bjoern Feuerbacher" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 04:25:20 AM |
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Email me at CS not Boole wrote:
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
The answer depends on the height of the orbit, due to the effect by
General Relativity here.
Bye,
Bjoern
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| User: "REMOVE XXX TO REPLY Jim Campbell" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 09:12:54 AM |
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If she were in orbit, wouldn't a constant acceleration play a role in
the calculations? I recall (from a very general, unstudied
understanding of physics) that the deceleration/acceleration in "turning
around" to return to Earth plays a role in determining why the departing
twin is the one who doesn't age.
I do not think this would be matter of opinion - relativity ought to
give you an exact prediction of the temporal consequences.
- Jim
Email me at CS not Boole wrote:
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
.
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| User: "Eric Gisse" |
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| Title: Re: Opinion poll on a version of the twin paradox |
10 Aug 2004 03:34:07 AM |
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On Tue, 10 Aug 2004 06:28:29 +0000 (UTC),
(Email me at CS not Boole) wrote:
I'd be interested in people's opinion as to whether Terence (the twin
in the Physics FAQ on this topic who remains earth-bound) or Stella
(the twin who goes zipping off on a trip of long duration into space
and back) is older when they are eventually reunited, in the scenario
where Stella spends essentially all her time (except for blast-off and
re-entry) in orbit around Earth. For definiteness assume she spends
twenty years in orbit.
In the usual version of the paradox, Stella travels many parsecs at
close to lightspeed. However as a practical matter it is obviously a
lot easier to actually carry out the experiment with a satellite-borne
clock than one with a round-trip ticket to 61 Cygni.
So which in your *opinion* would have aged more, Stella or Terence?
Don't bother actually doing the calculation, I just want to know which
way the voting goes when people have to make a stab at the answer.
Vaughan Pratt
Opinion does not mean ***** in physics.
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