A constant speed of light in all reference frames? Surely you can't be serious. [Physics]

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From: G. L. Bradford on 11 Mar 2010 05:29

Planet A and planet B are similar planets one light year apart. A ship
leaves planet A for planet B and the length of the voyage is set for one
year, usual for this commuter ship. The month of departure planet A is Mar
2010. The month of scheduled arrival planet B is Mar 2011. The ship leaves
planet A on time (Mar 2010) and arrives planet B on time (Mar 2011).

If an observer from planet A could observe the ship's arrival at planet B,
what date would the observation of arrival planet B, Mar 2011, take place?
As far as planet A is concerned, as far as the observer observes and clocks
the arrival, the arrival at planet B takes place, Mar 2012, two years from
the date of the ship's departure....and thus, observed from planet A, two
years from the date of departure of his twin brother.

The ship goes, and light comes (c). The ship goes farther out, and light
comes from farther out (c). The ship goes even farther out, and light comes
from even farther out (c). The ship goes one light year out in one year and
it takes light one year from the instant of arrival to communicate the
arrival of the ship and brother to the observer (c).....who notices from the
light speed communication that his brother appears to have aged only one
year between Mar 2010 (when he departed planet A) and Mar 2012 (when he
arrived planet B [[per the observation of that arrival at planet A!]]). His
brother APPARENTLY ages only one year while he definitely ages two during
the time period, Mar 2010-Mar 2012.

Of course he is smart enough to realize that his brother's apparent
stretching out in space-time observed during the voyage out was nothing more
than an illusion. Particularly when he arrives home apparently in precisely
the same month (Mar 2012) he is observed to have left planet B (planet B
observed, Mar 2011, from planet A, Mar 2012). He is smart enough to realize
that the planet B observed from planet A is the one that is one year behind
the times of the real-time planets A and B, and that any arrival, and any
departure, observed to be happening there from planet A happened one year
ago, making his age one year ago, and his brother's unobserved age one year
ago upon his actual arrival and departure planet B, the same age.

The twin brother gets to planet B a year before he is observed to get to
planet B from planet A. The observation of the duration of the voyage from
planet A is a year longer than the actual voyage takes. Yet it is the actual
length of the outbound space voyage, one year, that is communicated to the
observer on planet A in a two year long span of time where everything
concerning the ship, and thus the brother, seems to slow down (seems to
stretch) in the observer's view. The ship, the brother, and the ship's
clock, outran by a full year the ship, the brother, and the ship's clock,
the observer observed.

Now someone will say that the time observed from planet A, and thus the
stretching that is observed, is the literal physical reality of the
traveler. They have no concept that the traveler's space-time reality on the
spot might be one thing and his space-time relativity to an ever more
distant observer quite another.

GLB

=======================

From: Inertial on 11 Mar 2010 05:34

"G. L. Bradford" <glbrad01(a)insightbb.com> wrote in message
news:WaidncSioueeWwXWnZ2dnUVZ_sudnZ2d(a)insightbb.com...
> Planet A and planet B are similar planets one light year apart. A ship
> leaves planet A for planet B and the length of the voyage is set for one
> year, usual for this commuter ship. The month of departure planet A is Mar
> 2010. The month of scheduled arrival planet B is Mar 2011. The ship leaves
> planet A on time (Mar 2010) and arrives planet B on time (Mar 2011).

So you have a spaceship travelling at the speed of light. Just a tad
unrealistic.

> If an observer from planet A could observe the ship's arrival at planet
> B, what date would the observation of arrival planet B, Mar 2011, take
> place? As far as planet A is concerned, as far as the observer observes
> and clocks the arrival, the arrival at planet B takes place, Mar 2012, two
> years from the date of the ship's departure....and thus, observed from
> planet A, two years from the date of departure of his twin brother.
>
> The ship goes, and light comes (c). The ship goes farther out, and light
> comes from farther out (c). The ship goes even farther out, and light
> comes from even farther out (c). The ship goes one light year out in one
> year and it takes light one year from the instant of arrival to
> communicate the arrival of the ship and brother to the observer
> (c).....who notices from the light speed communication that his brother
> appears to have aged only one year between Mar 2010 (when he departed
> planet A) and Mar 2012 (when he arrived planet B [[per the observation of
> that arrival at planet A!]]). His brother APPARENTLY ages only one year
> while he definitely ages two during the time period, Mar 2010-Mar 2012.
>
> Of course he is smart enough to realize that his brother's apparent
> stretching out in space-time observed during the voyage out was nothing
> more than an illusion. Particularly when he arrives home apparently in
> precisely the same month (Mar 2012) he is observed to have left planet B
> (planet B observed, Mar 2011, from planet A, Mar 2012). He is smart enough
> to realize that the planet B observed from planet A is the one that is one
> year behind the times of the real-time planets A and B, and that any
> arrival, and any departure, observed to be happening there from planet A
> happened one year ago, making his age one year ago, and his brother's
> unobserved age one year ago upon his actual arrival and departure planet
> B, the same age.
>
> The twin brother gets to planet B a year before he is observed to get to
> planet B from planet A. The observation of the duration of the voyage from
> planet A is a year longer than the actual voyage takes. Yet it is the
> actual length of the outbound space voyage, one year, that is communicated
> to the observer on planet A in a two year long span of time where
> everything concerning the ship, and thus the brother, seems to slow down
> (seems to stretch) in the observer's view. The ship, the brother, and the
> ship's clock, outran by a full year the ship, the brother, and the ship's
> clock, the observer observed.
>
> Now someone will say that the time observed from planet A, and thus the
> stretching that is observed, is the literal physical reality of the
> traveler. They have no concept that the traveler's space-time reality on
> the spot might be one thing and his space-time relativity to an ever more
> distant observer quite another.

Of course, you've ignored relativistic effects completely in that (apart
from having a spaceship travel at the speed of light) .. so I'm not sure
what the point of your post was.

From: Androcles on 11 Mar 2010 05:41

From: Peter Webb on 11 Mar 2010 05:50

"Inertial" <relatively(a)rest.com> wrote in message
news:4b98c72d$0$8803$c3e8da3(a)news.astraweb.com...
>
> "G. L. Bradford" <glbrad01(a)insightbb.com> wrote in message
> news:WaidncSioueeWwXWnZ2dnUVZ_sudnZ2d(a)insightbb.com...
>> Planet A and planet B are similar planets one light year apart. A ship
>> leaves planet A for planet B and the length of the voyage is set for one
>> year, usual for this commuter ship. The month of departure planet A is
>> Mar 2010. The month of scheduled arrival planet B is Mar 2011. The ship
>> leaves planet A on time (Mar 2010) and arrives planet B on time (Mar
>> 2011).
>
> So you have a spaceship travelling at the speed of light. Just a tad
> unrealistic.
>

I think you should lighten up a bit. Photons travel at c, and this is really
just a special case of a more general question.

The real problem is that looking at what happens at exactly c doesn't really
show the general principle, which is why real world hypothetical spacecraft
travel at 0.99c. But Mr Bradford maybe doesn't know that.

I do agree however that his post seemed pointless.

BTW, is you alias Inertial because of SR ?

From: Inertial on 11 Mar 2010 05:59

"Peter Webb" <webbfamily(a)DIESPAMDIEoptusnet.com.au> wrote in message
news:4b98cae0$0$11705$afc38c87(a)news.optusnet.com.au...
>
> "Inertial" <relatively(a)rest.com> wrote in message
> news:4b98c72d$0$8803$c3e8da3(a)news.astraweb.com...
>>
>> "G. L. Bradford" <glbrad01(a)insightbb.com> wrote in message
>> news:WaidncSioueeWwXWnZ2dnUVZ_sudnZ2d(a)insightbb.com...
>>> Planet A and planet B are similar planets one light year apart. A ship
>>> leaves planet A for planet B and the length of the voyage is set for one
>>> year, usual for this commuter ship. The month of departure planet A is
>>> Mar 2010. The month of scheduled arrival planet B is Mar 2011. The ship
>>> leaves planet A on time (Mar 2010) and arrives planet B on time (Mar
>>> 2011).
>>
>> So you have a spaceship travelling at the speed of light. Just a tad
>> unrealistic.
>>
>
> I think you should lighten up a bit. Photons travel at c, and this is
> really just a special case of a more general question.
>
> The real problem is that looking at what happens at exactly c doesn't
> really show the general principle, which is why real world hypothetical
> spacecraft travel at 0.99c. But Mr Bradford maybe doesn't know that.
>
> I do agree however that his post seemed pointless.

Indeed .. I'm not sure if he had a point, or question.

> BTW, is you alias Inertial because of SR ?

I just liked 'inertial(a)rest' .. it seemed an appropriate name for
sci.physics.relativity