" wrote in
:

On Mar 12, 12:20*am, "Dirk Van de moortel" dirkvandemoor...@ThankS-NO-
SperM.hotmail.com wrote:
wrote in message

*

On Mar 11, 9:08 pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a
journey that started at x=4[ly] and ended at x=0, during a time of
one hour
,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Is there anyone interested in answering my question?

Like David said, you divide a distance as measured in the
Earth system (4ly) by the time measured on your lock (1 hour),
but speed is defined as the ratio of distance to time both measured
in the same frame. To you the distance looks shorter and to the
Earth the time looks longer in such a way that both measure the
same value for the speed.

Dirk Vdm

I did not change frames. We are talking about the frame of the
spaceship. The ship was first at rest on earth, and then it
accelerated towards Centauri.
It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

Ram.

Assume that someone in orbit around AC sends a pulse every year toward
earth. You leave earth just as a pulse arrives.

You intercept 8 pulses during your trip to AC.

By your clock, they are 7.5 minutes apart.

You measure their wavelength and frequency and compute the velocity from
wavelength and frequency. You find it to be 'c'.

You conclude that the distance from earth to AC is slightly more than 1/2
light hours.

Nothing went faster than light.
You compute your velocity as ~c/2 so it should take you an hour to travel
the distance.

[it is not important if I got the exact numbers right, the idea is correct
per SR.]

As you were told earlier, you were mixing measurements made in one frame
[stationary frame, distance to AC] with measurements made in another
frame[moving frame, time].

You can not do that and expect to get a correct
answer.

The distance and time need to be measured in the same Frame of Reference





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

On Mar 11, 9:02*pm, "N:dlzc D:aol T:com \(dlzc\)"
wrote:
Dear xxein:

"xxein" wrote in message

...
On Mar 11, 6:44 pm, dlzc wrote:
...

Is there anyone interested in answering my question?

Answered.
xxein: *Who is moving to have a timerate?

All processes have a time rate. *Part of (or requirement of) the
second law of thermodynamics.

What determines a timerate?

The System.

David A. Smith

xxein: Define the system. Why does c exist?

Dear xxein:

"xxein" wrote in message
...
On Mar 11, 9:02 pm, "N:dlzc D:aol T:com \(dlzc\)"
wrote:
Dear xxein:

"xxein" wrote in message

...
On Mar 11, 6:44 pm, dlzc wrote:
...

Is there anyone interested in answering my
question?

Answered.
xxein: Who is moving to have a timerate?

All processes have a time rate. Part of (or
requirement of) the second law of
thermodynamics.

What determines a timerate?

The System.

xxein: Define the system.

Everything you would / could assign coordinates (or mass /
energy) to.

Why does c exist?

Coupling constant between "adjacent" *nows*. We are only ever in
contact with a single point in both space and time, and light is
the only messenger "between" points.

The question is, is the evolution parameter between "decisions"
(or choice and result) time, or is time only that which binds
*now* to an ever evolving "Big Bang"? Do we have no free will,
or do we mutually form the Universe around us?

David A. Smith

In sci.physics.relativity,

wrote
on Tue, 11 Mar 2008 12:08:30 -0700 (PDT)
:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Several problems, but assuming they can be met, the conclusion is
reasonably sound; this is another expostulation of the famous
Twin Paradox. However...

[1] Gamma is about 4 years / 1 hour = 35000. This yields a velocity
of (1 - 4.06 * 10^-10) c and far more energy than one can get from
even an antimatter-based drive.

[2] The acceleration would be phenomenal, squishing one to a rather
flat pancake.

[3] Radiation during transit would fry you. If one assumes 1 proton
per cc of space and a cross-section of 10 m^2 (the size of a good
sized room on Earth), one gets 2.99792458 * 10^15 protons per
light-second or 3.78 * 10^23 protons over the trip. Since the trip
takes 1 hour subjective, that's 1.051 * 10^19 protons per second,
each of them with energy 32.8 TeV. Total power: 5.53 terawatt per
square meter. Smells like...like....victory...

--
#191,
Windows. When it absolutely, positively, has to crash.

--
Posted via a free Usenet account from http://www.teranews.com

On Mar 12, 2:05*am, Randy Poe wrote:
On Mar 11, 6:52*pm, "
wrote:



On Mar 12, 12:20*am, "Dirk Van de moortel" dirkvandemoor...@ThankS-NO-

SperM.hotmail.com wrote:
wrote in message

*

On Mar 11, 9:08 pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Is there anyone interested in answering my question?

Like David said, you divide a distance as measured in the
Earth system (4ly) by the time measured on your lock (1 hour),
but speed is defined as the ratio of distance to time both measured
in the same frame. To you the distance looks shorter and to the
Earth the time looks longer in such a way that both measure the
same value for the speed.

Dirk Vdm

I did not change frames.

You are using numbers from two different frames.

We are talking about the frame of the
spaceship.

The travel distance is not 4 light years in that
frame.

The ship was first at rest on earth, and then it
accelerated towards Centauri.

When it is moving at the very high gamma you
proposed, the distance to Centauri is a small fraction
of 4 light years in that frame.

It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

Huh?

* * * * * * * - Randy

Randy: How is this two frames? How? Imagine a guy sitting in the
spaceship. The ship is resting on earth, not moving. Then the ship
accelerates and AC becomes closer, until eventually coming to the
spaceships. I am talking about the frame of the guy in the spaceship?
It is a non-inertial frame, true, but it's still a frame, isn't it? I
mean, for that guy sitting in the ship, AC seemed to travel faster
than light!

It seems that the core of our argument is that you claim that these
are two separate frames. Why? Is it because by "frame" you mean
"inertial frame"?

Best Wishes,
Ram.

wrote in message
...
On Mar 12, 2:05 am, Randy Poe wrote:
On Mar 11, 6:52 pm, "
wrote:



On Mar 12, 12:20 am, "Dirk Van de moortel" dirkvandemoor...@ThankS-NO-

SperM.hotmail.com wrote:
wrote in message



On Mar 11, 9:08 pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me
to
be one hour. Will it not seem to me that Alpha Centauri made a
journey
that started at x=4[ly] and ended at x=0, during a time of one
hour,
and therefore its speed was much faster than lightspeed? Where is
my
mistake?

Ram.

Is there anyone interested in answering my question?

Like David said, you divide a distance as measured in the
Earth system (4ly) by the time measured on your lock (1 hour),
but speed is defined as the ratio of distance to time both measured
in the same frame. To you the distance looks shorter and to the
Earth the time looks longer in such a way that both measure the
same value for the speed.

Dirk Vdm

I did not change frames.

You are using numbers from two different frames.

We are talking about the frame of the
spaceship.

The travel distance is not 4 light years in that
frame.

The ship was first at rest on earth, and then it
accelerated towards Centauri.

When it is moving at the very high gamma you
proposed, the distance to Centauri is a small fraction
of 4 light years in that frame.

It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

Huh?

- Randy

| Randy: How is this two frames? How? Imagine a guy sitting in the
| spaceship. The ship is resting on earth, not moving. Then the ship
| accelerates

No problem, we'll just add acceleration of AC to the list of things
Poe doesn't believe in.

| and AC becomes closer,

That's frame hopping. AC accelerated, the rocket exhaust gas (fourth frame)
moved away from AC twice as fast as the rocket moved toward AC.
Net mass displacement zero. If you see AC coming toward you then AC
accelerated without any exhaust. Magic.


| until eventually coming to the
| spaceships. I am talking about the frame of the guy in the spaceship?
| It is a non-inertial frame, true, but it's still a frame, isn't it?

Of course. So is the photon. So is the exhaust gas.

| I
| mean, for that guy sitting in the ship, AC seemed to travel faster
| than light!

No problem, we'll just add parallax to the list of things Poe doesn't
believe in.

| It seems that the core of our argument is that you claim that these
| are two separate frames. Why?

Because each has their own origin. Why?

| Is it because by "frame" you mean
| "inertial frame"?

Einstein never once use the term "inertial" and did not mean inertial.

"If we assume that the result proved for a polygonal line is also valid for
a continuously curved line"

Not that he ever proved the result for a polygonal line anyway...

In article ,
says...

On Mar 11, 9:08=A0pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Is there anyone interested in answering my question?

First, note that your spaceship does *not* travel faster than
light: if you sent a light signal towards Alpha Centauri at
the same moment you launched your ship, the light signal
would get there first.

What your example illustrates is that the speed of light
is only 300,000,000 meters per second if measured in an
*inertial* coordinate system (Minkowsky coordinates).
In a noninertial coordinate system, or in a curvilinear
coordinate system, the speed of light can be position-dependent
or time-dependent.

From the accelerated coordinate system of a spaceship
undergoing constant acceleration in the x-direction (as measured
using on-board accelerometers), things seem very different from
any inertial coordinate system:

1. There is an apparent "gravitational field" pushing things
towards the rear of the spaceship. This field is not constant,
but instead is stronger towards the rear of the spaceship and
weaker towards the front of the spaceship.

2. The rate at which clocks advance (and the rate at which
people get older) is position-dependent. Clocks run faster
towards the front of the spaceship, and clocks run slower
towards the rear of the spaceship.

3. The speed of a light signal is not constant; it varies
with position. In the rear of the spaceship, the speed of
light is slower, and in the front of the spaceship, the
speed of light is faster.

From the standpoint of this noninertial coordinate system,
Alpha Centauri is in "freefall" under an enormous gravitational
field (remember point 1: the apparent gravitational field is
stronger the farther you get from the rear of the spaceship).
So Alpha Centauri appears to be accelerating towards your
spaceship at an enormous rate, quickly getting up to a
speed that is much larger than 300,000,000 meters per
second.

If all this seems weird, it's because it's all just
artifacts of using weird noninertial coordinates. That's
why it's important in General Relativity especially to
get clear about which effects are physical and which
effects are artifacts of your coordinate system.

--
Daryl McCullough
Ithaca, NY

On Mar 12, 3:24 am, "
wrote:
On Mar 12, 2:05 am, Randy Poe wrote:



On Mar 11, 6:52 pm, "
wrote:

On Mar 12, 12:20 am, "Dirk Van de moortel" dirkvandemoor...@ThankS-NO-

SperM.hotmail.com wrote:
wrote in message



On Mar 11, 9:08 pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Is there anyone interested in answering my question?

Like David said, you divide a distance as measured in the
Earth system (4ly) by the time measured on your lock (1 hour),
but speed is defined as the ratio of distance to time both measured
in the same frame. To you the distance looks shorter and to the
Earth the time looks longer in such a way that both measure the
same value for the speed.

Dirk Vdm

I did not change frames.

You are using numbers from two different frames.

We are talking about the frame of the
spaceship.

The travel distance is not 4 light years in that
frame.

The ship was first at rest on earth, and then it
accelerated towards Centauri.

When it is moving at the very high gamma you
proposed, the distance to Centauri is a small fraction
of 4 light years in that frame.

It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

Huh?

- Randy

Randy: How is this two frames? How?

1. Earth

2. Spaceship

They have a relative velocity. How is that not
two frames? Do you know what a frame of reference is?

Imagine a guy sitting in the
spaceship. The ship is resting on earth, not moving.

It is at rest in the earth frame.

Then the ship
accelerates and AC becomes closer,

As soon as the spaceship has a nonzero velocity
relative to earth, it is now at rest in a different
frame of reference than earth. Hence Lorentz transforms
apply, as they do to any two frames with a relative
velocity.

until eventually coming to the
spaceships. I am talking about the frame of the guy in the spaceship?
It is a non-inertial frame, true, but it's still a frame, isn't it?

Yes. And the earth is another. That makes two.

I
mean, for that guy sitting in the ship, AC seemed to travel faster
than light!

Wrong. That's where you get it wrong. His perception
of the trip is not that he was moving faster than
c at any point.

It seems that the core of our argument is that you claim that these
are two separate frames. Why? Is it because by "frame" you mean
"inertial frame"?

No, I mean "rest frame of earth" and "rest frame of
spaceship".

Why does it seem strange to you to say that
during the trip, he is not at rest in the rest frame of
the earth? Isn't the earth getting farther away?

- Randy

Martin Hogbin wrote in message

wrote in message ...
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Does anyone know the name of the speed calculated by ram?

Coordinate distance over proper time.
I think it is called "proper velocity", or in this case "proper speed"

Dirk Vdm

wrote in message ...
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Does anyone know the name of the speed calculated by ram?


--
Martin Hogbin