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Ning Hu
science forum beginner
Joined: 29 Jun 2006
Posts: 1
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 Posted: Thu Jun 29, 2006 5:57 am Post subject:
beginner thought experiments
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Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
Thanks,
Ning |
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snapdragon31
science forum addict
Joined: 01 Jul 2005
Posts: 99
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| Posted: Thu Jun 29, 2006 6:25 am Post subject:
Re: beginner thought experiments
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Ning Hu wrote:
| Quote: | Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
|
To the stationary observer the beam travels at the speed of light minus
the speed of the space ship. Assuming that the space ship is
travelling at 0.9 c.
According to Newton 1.0 c - 0.9 c = 0.1 c
According to Einstein 1.0 c - 0.9 c = 1.0 c
What the people on the space ship will see depends on who is on the
ship.
| Quote: | Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
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Let A be Newton and C be Einstein. Both of them agrees that they have
aged the same amount.
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koobee.wublee@gmail.com
science forum Guru Wannabe
Joined: 01 Feb 2006
Posts: 141
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| Posted: Thu Jun 29, 2006 6:39 am Post subject:
Re: beginner thought experiments
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"snapdragon31" <snapdragon31@gmail.com> wrote in message
news:1151562301.775788.227990@p79g2000cwp.googlegroups.com...
| Quote: |
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
To the stationary observer the beam travels at the speed of light minus
the speed of the space ship. Assuming that the space ship is
travelling at 0.9 c.
According to Newton 1.0 c - 0.9 c = 0.1 c
According to Einstein 1.0 c - 0.9 c = 1.0 c
What the people on the space ship will see depends on who is on the
ship.
|
Let's say if you are one of the passengers. What would you see?
| Quote: | Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
Let A be Newton and C be Einstein. Both of them agrees that they have
aged the same amount.
|
You have given an answer that is logical and sound. However,
Larmor/Lorentz/Poincare/Einstein's Lorentz Transform will disagree with
you. In order to stand by that answer, you have to turn your back on
Lorentz Transform. Thus, SR. Are you ready to do so? |
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Dirk Van de moortel
science forum Guru
Joined: 01 May 2005
Posts: 3019
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| Posted: Thu Jun 29, 2006 9:09 am Post subject:
Re: beginner thought experiments
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"Ning Hu" <savagepanda@gmail.com> wrote in message news:1151560665.521927.228380@j72g2000cwa.googlegroups.com...
| Quote: | Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?.
|
speed of light.
| Quote: | What does the people on the space ship see?
|
They can't see light that moves away from them. They can only
see it when it hits their eyes.
But they could measure the speed and they would of course
find the speed of light.
| Quote: |
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
|
Hint:
http://users.telenet.be/vdmoortel/dirk/Physics/TwinsEvents.html
Replace S with B and (S',S") with the friend travelling to A and back
with velocity (v,-v).
Now, replace a modified (S',S") with velocities (-v,v) with the friend
travelling to C and back.
Conclusion: at the return event
- the clock of B shows an elapsed time t = 2T
- the clock of the A-traveller shows an elapsed time of t"A = 2T/g
and of course, since g is independent of the sign of v:
- the clock of the C-traveller shows an elapsed time of t"B = 2T/g
So yes, they have aged the same amount when they finally unite.
Dirk Vdm |
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Dirk Van de moortel
science forum Guru
Joined: 01 May 2005
Posts: 3019
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| Posted: Thu Jun 29, 2006 9:15 am Post subject:
Re: beginner thought experiments
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"Koobee Wublee" <koobee.wublee@gmail.com> wrote in message news:1151563166.495998.59130@m73g2000cwd.googlegroups.com...
| Quote: | "snapdragon31" <snapdragon31@gmail.com> wrote in message
news:1151562301.775788.227990@p79g2000cwp.googlegroups.com...
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
To the stationary observer the beam travels at the speed of light minus
the speed of the space ship. Assuming that the space ship is
travelling at 0.9 c.
According to Newton 1.0 c - 0.9 c = 0.1 c
According to Einstein 1.0 c - 0.9 c = 1.0 c
What the people on the space ship will see depends on who is on the
ship.
Let's say if you are one of the passengers. What would you see?
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
Let A be Newton and C be Einstein. Both of them agrees that they have
aged the same amount.
You have given an answer that is logical and sound. However,
Larmor/Lorentz/Poincare/Einstein's Lorentz Transform will disagree with
you. In order to stand by that answer, you have to turn your back on
Lorentz Transform. Thus, SR. Are you ready to do so?
|
In order to stand by that answer, you have to understand the
transformation, which is exactly what a retard like you does not:
http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/LorentzTale.html
http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/SRBogus.html
How does it feel to be so stupid?
Dirk Vdm |
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PD
science forum Guru
Joined: 03 May 2005
Posts: 4363
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| Posted: Thu Jun 29, 2006 11:13 am Post subject:
Re: beginner thought experiments
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Ning Hu wrote:
| Quote: | Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
|
I assume that both sets of people have some way of measuring the speed
of the light, whether it is traveling towards them or away from them.
They will both measure the speed to be c.
Now you may say, "But that's impossible! The speeds should add or
subtract." They do, but not in the way you think. Speeds u and v (along
the same line) add the following way:
(u + v) / (1 + u*v/c^2).
It probably seems intuitive to you that it should be just (u + v), but
nature doesn't particularly care what you think *should* be, based on
your intuition. Nature might be slightly amused by the fact that (u +
v) works as an effective *approximation* when u and v are both small
compared to c, but that doesn't make it correct, even if Chapter 2 in
your introductory physics text says so.
Now, in the case at hand, let's call the spaceship's speed u and the
light's speed be v = -c (going rearwards), and see what this addition
rule provides...
| Quote: |
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
|
They would age the same amount when they return. The difference in ages
in the traditional Twin Puzzle is *not* due to the motion of one of the
twins. It is due to the difference in the path length through
spacetime. In spacetime, the *longest* interval between two events is
along the straight line. (*Longest*, not shortest, due to that minus
sign in the metric.)
PD |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
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| Posted: Thu Jun 29, 2006 12:13 pm Post subject:
Re: beginner thought experiments
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Ning Hu wrote:
| Quote: | Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
|
Space ships melt long before they achieve relativistic speeds.
| Quote: |
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
|
They will share birthday cake equally.
A 'thought experiment, in physics should represent something
that is physically possible. For example:
"Retarded potential"
http://farside.ph.utexas.edu/teaching/em/lectures/node50.html
Abstract
Einstein addressed the twin paradox in special relativity
in a relatively unknown, unusual and rarely cited paper
written in 1918, in the form of a dialogue between a
critic and a relativist. Contrary to most textbook versions
of the resolution, Einstein admitted that the special
relativistic time dilation was symmetric for the twins,
and he had to invoke, asymmetrically, the general relativistic
gravitational time dilation during the brief periods
of acceleration to justify the asymmetrical aging.
Notably, Einstein did not use any argument related to
simultaneity or Doppler shift in his analysis. I discuss
Einstein's resolution and several conceptual issues
that arise. It is concluded that Einstein's resolution using
gravitational time dilation suffers from logical and
physical flaws, and gives incorrect answers in a general
setting. The counter examples imply the need to reconsider
many issues related to the comparison of transported
clocks. The failure of the accepted views and
resolutions is traced to the fact that the special relativity
principle formulated originally for physics in empty
space is not valid in the matter-filled universe.
C. S. Unnikrishnan
Gravitation Group,
Tata Institute of Fundamental Research,
Homi Bhabha Road, Mumbai 400 005, India
http://www.iisc.ernet.in/currsci/dec252005/2009.pdf
-----
Sue... |
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Dirk Van de moortel
science forum Guru
Joined: 01 May 2005
Posts: 3019
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| Posted: Thu Jun 29, 2006 12:19 pm Post subject:
Re: beginner thought experiments
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"Sue..." <suzysewnshow@yahoo.com.au> wrote in message news:1151583232.146093.180970@y41g2000cwy.googlegroups.com...
| Quote: |
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
|
Don't forget your retarded potential, Dennis
| Quote: |
Experiment 2:
point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?
They will share birthday cake equally.
Thanks,
Ning
A 'thought experiment, in physics should represent something
that is physically possible. For example:
"Retarded potential"
http://farside.ph.utexas.edu/teaching/em/lectures/node50.html
|
Indeed.
McCarthy and his retarded potentials.
Dirk Vdm |
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PD
science forum Guru
Joined: 03 May 2005
Posts: 4363
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| Posted: Thu Jun 29, 2006 12:31 pm Post subject:
Re: beginner thought experiments
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Sue... wrote:
| Quote: | Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
|
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
PD |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
|
| Posted: Thu Jun 29, 2006 12:34 pm Post subject:
Re: beginner thought experiments
|
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|
PD wrote:
| Quote: | Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
|
What does a luge pilot use as a point of reference and why?
Sue...
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PD
science forum Guru
Joined: 03 May 2005
Posts: 4363
|
| Posted: Thu Jun 29, 2006 12:46 pm Post subject:
Re: beginner thought experiments
|
|
|
Sue... wrote:
| Quote: | PD wrote:
Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
What does a luge pilot use as a point of reference and why?
|
The ground.
Why? Convention.
Not for any physical reason.
Why do you ask?
PD |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
|
| Posted: Thu Jun 29, 2006 1:10 pm Post subject:
Re: beginner thought experiments
|
|
|
PD wrote:
| Quote: | Sue... wrote:
PD wrote:
Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
What does a luge pilot use as a point of reference and why?
The ground.
Why? Convention.
Not for any physical reason.
Why do you ask?
|
The luge pilot is concered about what he might interact with
physically (ouch) so the relative speed of ice schards below
his ear lobe tend to be of far greater concen than the ice shards
on Mars, even tho those on Mars are moving much faster.
"Coulomb's Law"
http://farside.ph.utexas.edu/teaching/em/lectures/node28.html
"Railway vacuums" 
http://www-ssg.sr.unh.edu/ism/what1.html
We don't measure light. We measure the motion of a charge.
What a charge is interacting with, can't be ignored by
choosing a distant point of reference any more than the
luge pilot can minimise his injuries by measuring his speed
relative to his sled.
Sue...
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PD
science forum Guru
Joined: 03 May 2005
Posts: 4363
|
| Posted: Thu Jun 29, 2006 1:49 pm Post subject:
Re: beginner thought experiments
|
|
|
Sue... wrote:
| Quote: | PD wrote:
Sue... wrote:
PD wrote:
Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
What does a luge pilot use as a point of reference and why?
The ground.
Why? Convention.
Not for any physical reason.
Why do you ask?
The luge pilot is concered about what he might interact with
physically (ouch) so the relative speed of ice schards below
his ear lobe tend to be of far greater concen than the ice shards
on Mars, even tho those on Mars are moving much faster.
"Coulomb's Law"
http://farside.ph.utexas.edu/teaching/em/lectures/node28.html
"Railway vacuums"
http://www-ssg.sr.unh.edu/ism/what1.html
We don't measure light. We measure the motion of a charge.
What a charge is interacting with, can't be ignored by
choosing a distant point of reference any more than the
luge pilot can minimise his injuries by measuring his speed
relative to his sled.
Sue...
|
And what do spaceships interact with to melt long before they reach c
(measured relative to what?)? |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
|
| Posted: Thu Jun 29, 2006 2:52 pm Post subject:
Re: beginner thought experiments
|
|
|
PD wrote:
| Quote: | Sue... wrote:
PD wrote:
Sue... wrote:
PD wrote:
Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
What does a luge pilot use as a point of reference and why?
The ground.
Why? Convention.
Not for any physical reason.
Why do you ask?
The luge pilot is concered about what he might interact with
physically (ouch) so the relative speed of ice schards below
his ear lobe tend to be of far greater concen than the ice shards
on Mars, even tho those on Mars are moving much faster.
"Coulomb's Law"
http://farside.ph.utexas.edu/teaching/em/lectures/node28.html
"Railway vacuums"
http://www-ssg.sr.unh.edu/ism/what1.html
We don't measure light. We measure the motion of a charge.
What a charge is interacting with, can't be ignored by
choosing a distant point of reference any more than the
luge pilot can minimise his injuries by measuring his speed
relative to his sled.
Sue...
And what do spaceships interact with to melt long before they reach c
(measured relative to what?)?
|
If there is any truth to this business about Coulomb force
objects tend to interact with the nearest matter.
http://www-ssg.sr.unh.edu/ism/what1.html
Luge logic dictatates that is the matter we should
be concerned with.
Why do you keep asking 'measured relative to what'?
Are you under some delusion that physical phenomena
cares a flip for where you measure from? If Sally doesn't
see the cat when it dies, can that alter Jimmy's need
to bury the the cat.
Sue... |
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| Back to top |
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PD
science forum Guru
Joined: 03 May 2005
Posts: 4363
|
| Posted: Thu Jun 29, 2006 10:00 pm Post subject:
Re: beginner thought experiments
|
|
|
Sue... wrote:
| Quote: | PD wrote:
Sue... wrote:
PD wrote:
Sue... wrote:
PD wrote:
Sue... wrote:
Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,
Experiment 1:
A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?
Space ships melt long before they achieve relativistic speeds.
Nonsense. Your chair is traveling at a relativistic speed right now.
Oh, I suppose you haven't considered the frame of reference this is
measured in....
What does a luge pilot use as a point of reference and why?
The ground.
Why? Convention.
Not for any physical reason.
Why do you ask?
The luge pilot is concered about what he might interact with
physically (ouch) so the relative speed of ice schards below
his ear lobe tend to be of far greater concen than the ice shards
on Mars, even tho those on Mars are moving much faster.
"Coulomb's Law"
http://farside.ph.utexas.edu/teaching/em/lectures/node28.html
"Railway vacuums"
http://www-ssg.sr.unh.edu/ism/what1.html
We don't measure light. We measure the motion of a charge.
What a charge is interacting with, can't be ignored by
choosing a distant point of reference any more than the
luge pilot can minimise his injuries by measuring his speed
relative to his sled.
Sue...
And what do spaceships interact with to melt long before they reach c
(measured relative to what?)?
If there is any truth to this business about Coulomb force
objects tend to interact with the nearest matter.
http://www-ssg.sr.unh.edu/ism/what1.html
Luge logic dictatates that is the matter we should
be concerned with.
|
You didn't answer the question Dennis. If a spaceship is 6 light years
from the Sun and 7 light years from the nearest other star, and the
spaceship's speed is 0.4c with respect to the Sun and 0.55c with
respect to the other star, where is the nearest matter that will make
the spaceship melt?
| Quote: |
Why do you keep asking 'measured relative to what'?
Are you under some delusion that physical phenomena
cares a flip for where you measure from? If Sally doesn't
see the cat when it dies, can that alter Jimmy's need
to bury the the cat.
Sue... |
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