1. Banned
Join Date
Mar 2012
Posts
211
Originally Posted by grav
And what is the problem?
You take the geodesic equation and integrate along it.

Even without calculating easy to see that the difference is a few meters compared to a straight line.

Originally Posted by grav
The time that light takes to travel through the curved space-time of the sun should not depend upon the speed of the planets, only upon the point of emission of the light and the point at which it is received. (with a correction for the time dilation at the point within the field that is received and measured)
Let gravity work in physical space rather than Minkowski.

We accept ellipsoidal wave front of a moving source, and then the result is correct.

2. Originally Posted by Hetman
And what is the problem?
You take the geodesic equation and integrate along it.

Even without calculating easy to see that the difference is a few meters compared to a straight line.
Yes, I believe you may be right about that. I tried running some estimations for the extra time along an angled path, but it only gives a few extra nanoseconds. I even wrote a computer simulation to account for the different speed of light in respect to the different angles to the body involved with an angled path, but it made no difference. I started to try to write one for a hyperbolic path, slightly curved at the point of closest approach, but couldn't determine the focus so didn't finish, but I doubt that would add much either, the angle being just too small to allow it to vary enough I think.

Let gravity work in physical space rather than Minkowski.
If the space isn't curved, if that's what you are saying, then either there would be no time delay at all if light travels at the same speed c along the entire path, or it would speed up if we use Newtonian/Galilean gravity and we would receive it quicker, so I'm not sure what you mean by this.

We accept ellipsoidal wave front of a moving source, and then the result is correct.
The shape of a wave doesn't matter, only the infinitesimal part of the wave that reaches us along the direct path between source and receiver each way and according to the speed of the light along that part only, as with a laser or with a single photon, so I'm not sure what you mean by this either.

3. I found something interesting. I'm not sure if this discussion belongs here though, so I'll post it in the other thread.

4. Originally Posted by Jeff Root
I didn't. It was korjik's idea. I was just replying.

I was primarily trying to dismiss korjik's example of
Apollo, because of its low relevance. However, it isn't
completely irrelevant. Apollo needed to be compact
because it was accelerated to high speed. Similar with
our interstellar traveler's spacecraft. As far as I know,
any technique for measuring the distance to a distant
star requires a huge baseline. Huge baseline means
long communication times and simultaneity problems.
I was depending on korjik to specify the technique so
that we could determine what the actual requirement
would be. I was specifically trying to avoid making
a strawman argument.

The fact that the distance to the Moon could not be
measured from the Apollo spacecraft does not support
the idea that the distance to a distant star could not
be measured from a speeding interstellar spacecraft,
but it does rufute korjik's implied assertion that it
supports the idea that such a distance *could* be
measured.

-- Jeff, in Minneapolis
How? You've admitted that your basically hand waving here and don't know if you are raising a stawman and you are. Unless you want to answer my question in #96 I'll have to assume you're just going on some gut feel. This idea is supported by your statement that a traveller
Originally Posted by Jeff Root
I question
whether, under the condition of such an enormous relative
speed, the traveller would be capable of measuring thedistance precisely enough to distinguish between a distance
of 1 ly and 22.3 ly
What makes you think that a traveller can't distinguish between ageing 1 year and 16 days?

5. Originally Posted by Jeff Root
More than preference but less than physics. I am asserting
my interpretation of the physics. We agree on what the
equations of special relativity say. I disagree with what
*some* people say those equations mean. When someone
says that the Universe gets squashed, I disagree. My
interpretation of the physics is that the geometric spacetime
relationship between the observer and the observed changes
when they are in relative motion. A change in that relation
is not a change in either entity.

When korjik says the traveller will think the distance to the
distant star becomes one light-year, I disagree. The traveller
might measure a distance of one light-year (that is yet to be
determined, IMO), but is smart enough to know that the
actual distance, the proper distance, is still 22.3 light-years.
He knows that the geometric spacetime relation between him
and the distant star suddenly changes when he changes speed,
but the distance does not suddenly change.

That's what I think relativity says. It is my interpretation.

-- Jeff, in Minneapolis
No one is saying that the proper distance isn't 22.3ly. Since proper distance is defined as the distance between 2 objects as measured in an inertial frame of reference and you can't be in an inertial frame of reference if your accelerated relative to the other object.

I think everyone here agrees that the accelerated observer can calculate the proper distance if they wanted to. What we are saying is that the accelerated observer will measure the distance to be 1ly. They'll time their trip at just over 1 year in their frame of reference. Yes everything along the direction of their travel is squashed. What I have a problem with is you saying the accelerated observer wouldn't be able to make the measurements to tell the distance, speed or time of the trip during the trip and you've yet to show any proof of this beyond "I think they wouldn't be able to measure it"

6. Originally Posted by Jeff Root
I know you meant what you meant. No question about that!

Apparently you aren't visualizing the contraction correctly.
I said I'm curious how you think the major axis is aligned.
If you tried to explain that I think you would see what is
wrong with the idea that a squashed sphere is a prolate
spheroid. It would actually be an oblate sphereoid, aligned
as you said.

It may be that you read somewhere that spheres (such as
stars) would appear to be prolate spheroids to a relativistic
traveller. I don't entirely understand the geometry of it,
but that seems to be the case, due to light travel time
delays, not length contraction. And they would be prolate
with the major axis parallel to the direction of motion!
They would appear elongated, not contracted!

I added arrows to the diagrams below to show the direction
of relative motion of the observer. Your prolate spheroid on
the left, my oblate spheroid on the right.

-- Jeff, in Minneapolis

.

7. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Originally Posted by WayneFrancis
Originally Posted by Jeff Root
The fact that the distance to the Moon could not be
measured from the Apollo spacecraft does not support
the idea that the distance to a distant star could not
be measured from a speeding interstellar spacecraft,
but it does rufute korjik's implied assertion that it
supports the idea that such a distance *could* be
measured.
How?
There isn't anything to explain, except maybe that my
paragraph-long sentence with three "nots" in it is too
convoluted to interpret reliably.

Korjik suggested that Apollo astronauts could measure
the distance to the Moon, and implied that the ability
supported the idea that a relativistic traveller could
measure interstellar distances similarly. Since Apollo
astronauts could not measure the distance to the Moon,
his implied assertion is refuted. It says nothing about
whether a relativistic traveller could measure interstellar
distances. That is still to be determined.

Originally Posted by WayneFrancis
You've admitted that you're basically hand waving here ...
I assume that you are no longer talking about the
Apollo thing, but about my assertion that a relativistic
traveller couldn't measure interstellar distances.

I'll make that explicit: I am taking the stance that it
would be so difficult to measure interstellar distances
from a spacecraft moving at .999 c relative to the
nearby stars as to be practically impossible. I don't
actually know that. It is a guess, based on everything
I know about the situation at this time. I'm not aware
of any information that supports the claim that it
would be possible.

Originally Posted by WayneFrancis
... and don't know if you are raising a stawman and
you are.
What I said may be wrong, but I don't think it is a
strawman argument.

The basic disagreement is this:

Korjik said in post #3 that the traveller would think
the distance to the distant star was about 1 light-year.
I disagree. I say the traveller would think the distance
was about 22.3 light-years, which is what we measure.

That's it.

Originally Posted by WayneFrancis
Unless you want to answer my question in #96 I'll
have to assume you're just going on some gut feel.
Suggest a method for making the measurement and
specify a bit more about the nature of the object,
and I'll see what I can do.

Originally Posted by WayneFrancis
This idea is supported by your statement that a traveller
Originally Posted by Jeff Root
I question whether, under the condition of such an
enormous relative speed, the traveller would be capable
of measuring the distance precisely enough to distinguish
between a distance of 1 ly and 22.3 ly
What makes you think that a traveller can't distinguish
between ageing 1 year and 16 days?
I didn't say, suggest, or imply that he couldn't.
On the contrary, I see no problem there at all.

-- Jeff, in Minneapolis

8. Order of Kilopi
Join Date
Sep 2004
Posts
5,613
There is one thing that seems to be getting lost in this discussion.

The observer is not accelerated

The observer is moving not accelerated. The traveller does not start at rest, and does not stop at the end of the journey. They are just moving at .999c.

9. Order of Kilopi
Join Date
Sep 2004
Posts
5,613
Originally Posted by Jeff Root
There isn't anything to explain, except maybe that my
paragraph-long sentence with three "nots" in it is too
convoluted to interpret reliably.

Korjik suggested that Apollo astronauts could measure
the distance to the Moon, and implied that the ability
supported the idea that a relativistic traveller could
measure interstellar distances similarly. Since Apollo
astronauts could not measure the distance to the Moon,
his implied assertion is refuted. It says nothing about
whether a relativistic traveller could measure interstellar
distances. That is still to be determined.
You are willfully missing the point here. That is not what I said. What I was trying to she is that moving does not mean you cannot measure a distance. The Apollo astronauts could measure the distance to the moon. That they did not does not mean they could not.

I assume that you are no longer talking about the
Apollo thing, but about my assertion that a relativistic
traveller couldn't measure interstellar distances.

I'll make that explicit: I am taking the stance that it
would be so difficult to measure interstellar distances
from a spacecraft moving at .999 c relative to the
nearby stars as to be practically impossible. I don't
actually know that. It is a guess, based on everything
I know about the situation at this time. I'm not aware
of any information that supports the claim that it
would be possible.
You make an assertion with no proof or evidence. You make an assertion that dosent even make sense. You make an assertion which goes against the very underpinnings of physics.

If you think it is so impossible, then pick a method of measuring the distance and show that it would not work. If you want to overturn the understanding of mainstream physics, YOU have to show it dosent work, not just have a 'stance'.

All you have is a feeling. That is not science, or understanding

What I said may be wrong, but I don't think it is a
strawman argument.

The basic disagreement is this:

Korjik said in post #3 that the traveller would think
the distance to the distant star was about 1 light-year.
I disagree. I say the traveller would think the distance
was about 22.3 light-years, which is what we measure.

That's it.
Never mind the fact that length contraction and time dilation have both been shown

Suggest a method for making the measurement and
specify a bit more about the nature of the object,
and I'll see what I can do.
Fine

You have a 10 light year long meterstick and a stopwatch. The stopwatch is accurate to the femtosecond and you have zero reaction time.

I didn't say, suggest, or imply that he couldn't.
On the contrary, I see no problem there at all.

-- Jeff, in Minneapolis
Now show why you could not measure the distance

10. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Originally Posted by korjik
Originally Posted by Jeff Root
Korjik suggested that Apollo astronauts could measure
the distance to the Moon, and implied that the ability
supported the idea that a relativistic traveller could
measure interstellar distances similarly. Since Apollo
astronauts could not measure the distance to the Moon,
his implied assertion is refuted. It says nothing about
whether a relativistic traveller could measure interstellar
distances. That is still to be determined.
You are willfully missing the point here. That is not
what I said. What I was trying to she is that moving
does not mean you cannot measure a distance.
If that were all you were trying to show, it would
have been a terribly weak and irrelevant comment.
You were trying to show exactly as I said, that the
relativistic traveller of the original post would be
able to measure the distance from here to a star
22.3 light-years away.

For low speeds and short distances, such as that of
astronauts on the Apollo spacecraft near Earth trying
to measure the distance to the Moon, the simultaneity
problem is negligible unless you are trying to get
precision on the order of centimeters or better.

Originally Posted by korjik
The Apollo astronauts could measure the distance
to the moon. That they did not does not mean they
could not.
They had no means to measure the distance to the
Moon which did not depend on knowing the size of the
Moon or the size of features on the Moon. People on
Earth could measure the distance, but the astronauts
in Space could not.

Originally Posted by korjik
Originally Posted by Jeff Root
I'll make that explicit: I am taking the stance that it
would be so difficult to measure interstellar distances
from a spacecraft moving at .999 c relative to the
nearby stars as to be practically impossible. I don't
actually know that. It is a guess, based on everything
I know about the situation at this time. I'm not aware
of any information that supports the claim that it
would be possible.
You make an assertion with no proof or evidence.
As do you. The distance to the star is, as you calculated,
22.3 light-years If you're going to assert that the traveller
would think the distance is only about one light-year, then
you need to support that assertion.

Originally Posted by korjik
You make an assertion that dosent even make sense.
You make an assertion which goes against the very
underpinnings of physics
.
My assertion is that the traveller would think the
distance from here to the star is the distance that has
been measured.

Originally Posted by korjik
If you think it is so impossible, then pick a method of
measuring the distance and show that it would not work.
Should I pick a method that you think would work?

If you want to overturn the understanding of mainstream
physics, YOU have to show it dosent work, not just have
a 'stance'
.[/quote]
How about if I don't want to overturn the understanding
of mainstream physics?

Originally Posted by korjik
All you have is a feeling. That is not science, or
understanding
No, it isn't "a feeling". It is understanding. Feelings
can result from thoughts and thoughts can result from
feelings, but they're different things. My expectation
is based on science just as much as yours is. Your
assertion is the astonishing one here, and was made
before mine, so it is the one needing support first.

Originally Posted by korjik
Never mind the fact that length contraction and time
dilation have both been shown
Certainly they've been shown. I've said so several
times. Have you forgotten? Did you somehow not
notice? Or is that just the only thing you can think
of to say in rebuttal without having to actually

Originally Posted by korjik
Originally Posted by Jeff Root
Suggest a method for making the measurement and
specify a bit more about the nature of the object,
and I'll see what I can do.
Fine

You have a 10 light year long meterstick and a
stopwatch. The stopwatch is accurate to the
femtosecond and you have zero reaction time.

Now show why you could not measure the distance
You've left out a lot of essential details. If it were
a more realistic scenario I'd allow that and try to
provide them myself, but what you gave me is so
ludicrous that I'll respond to that aspect.

The "meterstick" would require several centuries to
construct, at a minimum. The infrastructure required
would compare with the entire current world economy.

Because of its fantabulous length, the "meterstick"
would require a system of sensors to measure stresses
in its material, and a system of actuators which could
prevent it from being bent, stretched, or physically
compressed, even during acceleration to .999 c,
without inducing distortions of its own.

All that means it would never be built.

Try again.

-- Jeff, in Minneapolis

11. Originally Posted by Jeff Root
I disagree. How does the traveller measure the distance
he has moved? That is, what specific measurements does
the traveller make to determine the distance? Stars and
planets are not moving at relativistic speeds relative to
each other. Anyone who travels at relativistic speed gets
a measurement of the proper distance to the destination
before leaving, then accelerates, goes to the destination,
and decelerates. He doesn't measure the distance along
the way because he has no means to do so. The proper
distance is the only distance actually used.

Other measurements are used to determine, for example,
when to begin decelerating, not a measurement of the
distance remaining.

(if we imagine relativistic travel to be practical), it has
no application.

-- Jeff, in Minneapolis
Here we go again. Jeff, we all understand the proper distance would be 22.3ly. The fact doesn't change that distances measured while travelling will be contracted. Just because you think people should only use proper distances doesn't matter. Because if they say they travelled 22.3ly but in only 16 days 8 hours 49 min 30.4seconds then they'd claim they travelled faster then light. So they don't say that. They don't use proper distance and they don't use coordinate time of the departure location. It does have application you just don't like it. Get over it the mainstream science community doesn't have a problem with it.

12. Originally Posted by Jeff Root
...
How does the traveller measure the distance he has
moved? That is, what specific measurements does the
traveller make to determine the distance?

Until you answer that question, you can't claim my point
is wrong, because the answer is my point.
...

-- Jeff, in Minneapolis
And I gave 2 ways of measuring it in another thread and you just hand waved it away claiming the uncertainty principal would prevent it.

So say the destination has a corner reflector. They record their speed via the amount of Doppler shift of the returning laser pulse. They record their distance by a factor of how long it took. And get this just because they are moving with respect to the object doesn't mean they can't calculate where they where at, relative to the object, when the signal was sent out and where they where at when the signal came back. The distance they record will be the distance in the accelerated frame.

ship.png

Now it doesn't matter that the ship will be almost at Object b when it receives the signal back it transmitted when it passed A. The only draw back to this is that you can only measure your distance in the last ~4.5% of your journey.

If you have equipment that is sensitive enough then you can use parallax and that can be used the whole trip.

13. Originally Posted by Jeff Root
No you haven't. You have not answered my question
at all, and you know you haven't. You aren't required
to answer it, of course, but I see no reason why you
shouldn't answer it if you can. The fact that you have
been unable to answer it after four requests suggests
that you don't know how to answer it.

...

-- Jeff, in Minneapolis
Parallax measurement. Works just fine in any frame. You've tried to claim that there would be issues of processing the signal from the 2 end points at relativistic speeds but this is false.

ship2.png

Ship is travelling at .999c
Sensor 1 & 2 record the angle to the destination. They are basically in the same frame as the ship.
If the base line between 1&2 significantly is short, IE this image isn't to scale, then you don't even have to factor in SR with regard to the angle.

For example we do just fine using parallax measurements that are over 20 million times larger then the base line used.

So for our object 1ly away using equipment only as precise as today's equipment you can have a base line of about 475,000,000m or just a bit further then from The Earth to the moon. Your distance measurements would be about 1 second .75 seconds behind where you are but that can be compensated for.

14. Order of Kilopi
Join Date
Sep 2004
Posts
5,613
Originally Posted by Jeff Root
If that were all you were trying to show, it would
have been a terribly weak and irrelevant comment.
You were trying to show exactly as I said, that the
relativistic traveller of the original post would be
able to measure the distance from here to a star
22.3 light-years away.

For low speeds and short distances, such as that of
astronauts on the Apollo spacecraft near Earth trying
to measure the distance to the Moon, the simultaneity
problem is negligible unless you are trying to get
precision on the order of centimeters or better.

They had no means to measure the distance to the
Moon which did not depend on knowing the size of the
Moon or the size of features on the Moon. People on
Earth could measure the distance, but the astronauts
in Space could not.

As do you. The distance to the star is, as you calculated,
22.3 light-years If you're going to assert that the traveller
would think the distance is only about one light-year, then
you need to support that assertion.

My assertion is that the traveller would think the
distance from here to the star is the distance that has
been measured.

Should I pick a method that you think would work?

If you want to overturn the understanding of mainstream
physics, YOU have to show it dosent work, not just have
a 'stance'
.
How about if I don't want to overturn the understanding
of mainstream physics?

No, it isn't "a feeling". It is understanding. Feelings
can result from thoughts and thoughts can result from
feelings, but they're different things. My expectation
is based on science just as much as yours is. Your
assertion is the astonishing one here, and was made
before mine, so it is the one needing support first.

Certainly they've been shown. I've said so several
times. Have you forgotten? Did you somehow not
notice? Or is that just the only thing you can think
of to say in rebuttal without having to actually

You've left out a lot of essential details. If it were
a more realistic scenario I'd allow that and try to
provide them myself, but what you gave me is so
ludicrous that I'll respond to that aspect.

The "meterstick" would require several centuries to
construct, at a minimum. The infrastructure required
would compare with the entire current world economy.

Because of its fantabulous length, the "meterstick"
would require a system of sensors to measure stresses
in its material, and a system of actuators which could
prevent it from being bent, stretched, or physically
compressed, even during acceleration to .999 c,
without inducing distortions of its own.

All that means it would never be built.

Try again.

-- Jeff, in Minneapolis[/QUOTE]

You have obviously put me in my place..

You are wrong Jeff, and completely unwilling to learn why or how. You fit the url quite well.

15. Originally Posted by Jeff Root
The question is not how I do it but how someone
travelling away from the Sun at nearly the speed
of light could do it. You still don't say. However,
you do eventually give a half-baked answer nearly
at the end of your post.
Hand waving

Originally Posted by Jeff Root
It is complicated and difficult, even without time
dilation and length contraction.
Hand waving

Originally Posted by Jeff Root
Until the LM got within a few miles of the surface,
so that the landing radar could be used, the only
way to determine the distance onboard without
assistance from the ground depended on knowing
the size of the Moon or of features on its surface.
That sort of info is presumeably not available to
our speedy interstellar traveller.
straw man. Just because they didn't include the equipment on the capsule doesn't mean they couldn't have. The engineering trade off was the equipment wasn't needed not the equipment wouldn't work.

Originally Posted by Jeff Root
Not impossible, but complicated and difficult even
from Earth.
Hand waving again.

Originally Posted by Jeff Root
Do I? How about you? How do you measure the
distance to a star when you are moving toward it
at nearly the speed of light?
As it has been said. Using the same methods you would on Earth.

Originally Posted by Jeff Root
There are differences. At the speed we're talking
about here, it may be accurate to call them "magic".
Show, with maths, why parallax wouldn't work? Show why radar would not work?

Just because the returning radar image will be shifted by 22x doesn't mean it will not work. If you think it will significantly change "the error bars" then show your maths.

Originally Posted by Jeff Root
Okay.

How?

You need to specify how. It's your claim, not mine.
It has been specified in this and another thread multiple times. Parallax or Radar. Your only reply "Until the LM got within a few miles of the surface,so that the landing radar could be used"
Since the LM landing radar had the following constrains put on it

• 42lb
• Antenna no larger then 20in wide, 24.6in width 6.5in height.
• Power consumption 132W max
• 2 way gain 50.4dB
• altimeter frequency 9.58GHz
• altimeter beam power 87.5mW
• low altitude frequency deviations ±4MHz
• high altitude frequency deviation ±20Mhz

I could go on but the last 2 are the issues as I understand them. It was designed to work close to the moon. Not that the physics broke down the further out it got.

Originally Posted by Jeff Root

I'd like to see some evidence of that before I
accept it as fact.
Yet you hand wave away evidence that without length contraction muons would not reach the surface of the Earth.
Convenient that you get to hand wave away evidence because you think muons have to be sentient and talk to us before we can use them as evidence.
Perhaps you want the hadrons to write an essay on how they feel when they are slammed together in the LHC before you'll believe the data there?

Originally Posted by Jeff Root

Yes.

As yet I haven't seen any evidence that the traveller
would be capable of making such a measurement.
Whether he can do it or not depends on the method
he tries to use.
Because you ignore or hand wave away anything that is posted for you.
You brought up the uncertainty principal but didn't show how it applies in the scenarios presented.
When told you misunderstand the concept you disagree and reiterate that you think you are right
and don't want to spend the time needed to prove it.

Originally Posted by Jeff Root

What method do you have in mind?
How would it be applied in this scenario?
That you won't hand wave away?

Originally Posted by Jeff Root

Yes.

Why would he say that?
Because if it isn't then GR and SR are WRONG and you have to come up with other reasons why we see the speed of light as constant, why GPS works, why muons reach the ground, etc. etc.

Originally Posted by Jeff Root

I very much doubt that I would say it if I were the
traveller. Why would anyone say it?
That is because you have stated over and over that you only think distance measurements are valid in a proper frame between the 2 objects and some how have extended this beyond and think that you can't even make the measurements if you wanted to in an accelerated frame.

Originally Posted by Jeff Root

Of course, that time is calculated, not measured
directly.
Tell that to the people on the ship that have watches. Or in your reality are watches not allowed on board the ship....might make the trip hard without any computers.

Originally Posted by Jeff Root

I agree. I've been familiar with both for over four
Yet here you are claiming that length contraction doesn't happen and even if it did you wouldn't be able to measure it for some reason.

Originally Posted by Jeff Root

I'm familiar with the subject. What I don't understand
and can't look up is what method you propose for the
traveller to use.
RADAR, PARALLAX. There are two ... take your pick. Oh wait that is right you've already hand waved both of those away multiple times.

Originally Posted by Jeff Root

question. You still don't say how he measures the
distance to the star, though, which is the central
question.

Okay. You slipped up and finally answered as I
expected, although you still didn't specify a method.

I do the same as you. I measure the distance to the
destination before starting out. That is your first and
so far only explicit statement of how you measure the
distance. If you measure the distance to the star
before you start out, then you can use the parallax
of Earth's orbit around the Sun. The destination is
close enough that parallax will give a pretty accurate
measurement. So you, and I, or any traveller would
say that the distance is about 22.3 light-years.

-- Jeff, in Minneapolis
Ok so .. you speed up to .999c. You use equipment available in the late 20th century. Your base line is 475,000,000m using 2 out riggers.
They compute a distance of 1ly.

16. Originally Posted by Selfsim
Surely all this wrangling by Jeff isn't merely to make the point that observations made by the moving observer are distorted by relativistic Aberration and relativistic Doppler Shift, and thus would be extremely difficult observations ???
Surely we could assume that the moving observer might have 'plotted' out what observations would be expected (prior to the journey), and so then would have a comparative baseline model against which journey progress could be measured ?

Some disclosure by Jeff at this point might help ...

Regards
But with parallax the base line can be 40 million times shorter then the distance being measured. Using equipment available today this is less then 0.01 arc seconds. Even at relativistic speeds that isn't enough to throw off your measurements. Increasing the base line doesn't cause any more of a problem then increasing the amount of time it takes to get the signal to the centre of the ship.

17. Originally Posted by Jeff Root
There isn't anything to explain, except maybe that my
paragraph-long sentence with three "nots" in it is too
convoluted to interpret reliably.

Korjik suggested that Apollo astronauts could measure
the distance to the Moon, and implied that the ability
supported the idea that a relativistic traveller could
measure interstellar distances similarly. Since Apollo
astronauts could not measure the distance to the Moon,
his implied assertion is refuted. It says nothing about
whether a relativistic traveller could measure interstellar
distances. That is still to be determined.
It doesn't refute his assertion. If it did it would be like this
Korjik: A man in a canoe can see that it is 1 o'clock
Jeff Root: The man couldn't tell it was 1 o'clock because he didn't have a watch.
Wayne: There was nothing physically stopping the man from wearing a watch if he wanted to so that he could tell the time.
Jeff Root: Korjik's assertion is refuted because in this specific case the man didn't have a watch.
The point isn't that the man didn't wear a watch. The point there no physical law preventing him from wearing one or any physical law that would mess up the way his watch works if he did.

Originally Posted by Jeff Root
I assume that you are no longer talking about the
Apollo thing, but about my assertion that a relativistic
traveller couldn't measure interstellar distances.

I'll make that explicit: I am taking the stance that it
would be so difficult to measure interstellar distances
from a spacecraft moving at .999 c relative to the
nearby stars as to be practically impossible. I don't
actually know that. It is a guess, based on everything
I know about the situation at this time. I'm not aware
of any information that supports the claim that it
would be possible.
Argument from ignorance. "My gut says [x] thus [y] is practically impossible."

When it is pointed out to you that it would break both SR and GR if you where right you ignore it and stick with your gut feel.

Originally Posted by Jeff Root
What I said may be wrong, but I don't think it is a
strawman argument.
Glad to see your gut feel may be wrong and you are right it isn't a strawman argument. It is an argument from ignorance and by repeatedly ignoring others a wilful ignorance.

Originally Posted by Jeff Root
The basic disagreement is this:

Korjik said in post #3 that the traveller would think
the distance to the distant star was about 1 light-year.
I disagree. I say the traveller would think the distance
was about 22.3 light-years, which is what we measure.
and you ignore everything that shows that during the trip it the traveller measures it differently.

Originally Posted by Jeff Root
That's it.

Suggest a method for making the measurement and
specify a bit more about the nature of the object,
and I'll see what I can do.

Originally Posted by Jeff Root
Originally Posted by WayneFrancis
This idea is supported by your statement that a traveller
Originally Posted by Jeff Root
I question
whether, under the condition of such an enormous relative
speed, the traveller would be capable of measuring the
distance precisely enough to distinguish between a distance
of 1 ly and 22.3 ly.
What makes you think that a traveller can't distinguish between ageing 1 year and 16 days?
I didn't say, suggest, or imply that he couldn't.
On the contrary, I see no problem there at all.

-- Jeff, in Minneapolis
So you think the traveller could measure that their trip took 16 days, that they accelerated to .999c, but that they can only say that they travelled 22.3ly

Let me see. 16x86,400=1,382,400 seconds @299492665.542m/s = 414018660845260.8m or 0.0437ly. Note this is a 1ly in the proper frame of the source and destination.
Tell me how they can do a calulation of vt and get an answer 22.3x shorter then what they should have if length contraction doesn't occur?

Pick a star that is 22.3ly away in the proper frame of the star and Earth. Guess what ... it only increases the number of seconds by ~22.3times and instead of the crew seeing the distance as .0437ly it is 1ly.

18. Originally Posted by Jeff Root

They had no means to measure the distance to the
Moon which did not depend on knowing the size of the
Moon or the size of features on the Moon. People on
Earth could measure the distance, but the astronauts
in Space could not.
Because they didn't have the appropriate equipment on board. It was a design constraints on the capsule not a physical limitation of not being able to measure if they had the equipment on board.

Originally Posted by Jeff Root
As do you. The distance to the star is, as you calculated,
22.3 light-years If you're going to assert that the traveller
would think the distance is only about one light-year, then
you need to support that assertion.
OK. Special relativity. Seeing you ignore everything else...you can ignore that too.

Originally Posted by Jeff Root
My assertion is that the traveller would think the
distance from here to the star is the distance that has
been measured.
Ship passes Earth at .999c towards Star X
Ship see Earth pass by at .999c
Earthling sees the calendar read Jan 1, 2020
Alien looks at their clock and sees that it reads Day 10,000 at 00:00am of their journey
People measure the distance to Star X as 22.3ly
People watch the ship travel toward Star X.
People see that the ship passed the star ~44.6 years on July 6, 2064 later but know since it took 22.3 years for the light to get back to us that they really passed on March 4th, 2042
Alien passes star X and looks at their clock and sees it reads Day 10,365 08:46
Alien, even if they can't measure distances says Hmmm .999c * 365day 8 hours 46 min = 1 light year. Wow we've travelled 1 light year.

19. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Wayne,

Thank you for going back and replying to my first
post in the thread. Even though you're doing it
because you disagree with what I said, I very much
appreciate your extra effort to get the facts straight.

Originally Posted by WayneFrancis
Here we go again. Jeff, we all understand the
proper distance would be 22.3ly. The fact doesn't
change that distances measured while travelling will
be contracted.
I still haven't seen any evidence that interstellar
distances can be accurately measured by someone
going at relativistic speed between the stars being
measured.

Have you?

That question was the second and third sentences
of the post (post #6) you are replying to:

Originally Posted by Jeff Root
How does the traveller measure the distance he has
moved? That is, what specific measurements does
the traveller make to determine the distance?

Originally Posted by WayneFrancis
Just because you think people should only use proper
distances doesn't matter.
Rather than "because it is what Jeff thinks", how
about "because it is what works"? I prefer the latter.
People should use proper distances because they
work, not because some guy posting on the Internet
thinks they should.

Originally Posted by WayneFrancis
Because if they say they travelled 22.3ly but in only
16 days 8 hours 49 min 30.4seconds ...
You used this figure before, but please remind me
where it came from. The original poster's scenario
specified one year. I see no good reason not to
stick with that figure.

Originally Posted by WayneFrancis
... then they'd claim they travelled faster then light.
Yes. Is that a problem? They would know, of course,
that they weren't travelling faster than light, but almost
everyone making such a trip would joke that they were.
And almost everyone listening to the already-very-lame
joke would know that they weren't.

Originally Posted by WayneFrancis
So they don't say that.
They don't?

Originally Posted by WayneFrancis
They don't use proper distance
They don't?

Have you been on one of these trips? Have you
spoken with people who have been on such a trip?

Originally Posted by WayneFrancis
and they don't use coordinate time of the departure
location.
I'm sure they will refer to the coordinate time of the
departure location frequently. They will have clocks
aboard showing it, right beside the clocks showing
their own proper time. And they will continue to do
so even after they reach their destination.

Originally Posted by WayneFrancis
It does have application, you just don't like it. Get
over it the mainstream science community doesn't
have a problem with it.
Where in the mainstream science community can I
find good evidence that a relativistic traveller would
be able to measure interstellar distances?

-- Jeff, in Minneapolis

20. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Originally Posted by WayneFrancis
Originally Posted by Jeff Root
How does the traveller measure the distance he has
moved? That is, what specific measurements does
the traveller make to determine the distance?

Until you answer that question, you can't claim my
point is wrong, because the answer is my point.
And I gave 2 ways of measuring it in another thread
and you just hand waved it away claiming the
uncertainty principal would prevent it.
That was the other thread? I was thinking it was

As I said somewhere, it isn't the uncertainty
principle (of quantum mechanics) which raises the
problem here, but the uncertainty inherent in the
simultaneity of events (in special relativity).

But my objection to proposals so far is that they have
not been specific enough. You (or somebody) need to
specify a technique. I'll specify that the thing being
measured is the distance between the Sun and a star
which is 22.3 light-years away in the frame of both
the Sun and the distant star, and that the people
doing the measuring are moving at .999 c relative to
the Sun and the distant star. They are somewhere in
the vicinity of the Sun at the time of measurement.
Your choice as to the exact location, and I'll give you
a lot of lattitude. Longitude, too. What technique
can they use that will give a useful measure?

Originally Posted by WayneFrancis
So say the destination has a corner reflector.
Interesting. The destination has to have already
been visited. A corner reflector which works over a
distance of 20-some light-years. And the signal to
the reflector must be be sent more than 40 years
before the trip begins in order to be used near the
trip's beginning.

Originally Posted by WayneFrancis
They record their speed via the amount of Doppler
shift of the returning laser pulse. They record their
distance by a factor of how long it took.
How long what took? The signal to go from the source
to the reflector to the ship? (The signal is encoded
so that the local time of transmission can easily be

Where is the signal sent from? The Sun? The ship?

Originally Posted by WayneFrancis
And get this: just because they are moving with
respect to the object doesn't mean they can't
calculate where they where at, relative to the
object, when the signal was sent out and where
they where at when the signal came back.
That is the question to be answered: Because they
are moving at nearly the speed of light relative to
what they are trying to measure the distance to,
will they still be able to measure that distance
accurately?

Originally Posted by WayneFrancis
The distance they record will be the distance in the
accelerated frame.
That depends on the calculations as well as the
measurements.

ship.png

Nice diagram.

Originally Posted by WayneFrancis
Now it doesn't matter that the ship will be almost at
Object b when it receives the signal back it transmitted
when it passed A.
It doesn't??? You are defining the problem in such a
way that the answer becomes almost useless.

Originally Posted by WayneFrancis
The only draw back to this is that you can only measure
That is an enormous drawback. I'm not inclined to
give you that much longitude.

But you could start sending the signal 40 years before
the trip begins.

for the whole trip? It would save a heckofa lot on energy
useage onboard the ship. Less energy use means less
mass that needs to be accelerated at the start and end
of the trip.

Originally Posted by WayneFrancis
If you have equipment that is sensitive enough then you
can use parallax and that can be used the whole trip.
You're talking about an alternative technique, now?

What do you mean by "sensitive enough"? Magic?

the dramatic difference between theoretical physics and
experimental physics! Spherical cows and unobtanium
everywhere!

-- Jeff, in Minneapolis

21. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Wayne,

While skimming through your next posts after the two
I just replied to, one exchange in the middle of a post
jumped out at me. It says something particularly
essential about the physics question we are trying to
resolve, as well as about our communication problems.
I'm responding to it by itself, right now.

Originally Posted by WayneFrancis
Originally Posted by korjik
The guy on Earth says he went slightly less than
22.3 ly and took 22.3 years.
Originally Posted by Jeff Root
Of course, that time is calculated, not measured
directly.
Tell that to the people on the ship that have watches.
Or in your reality are watches not allowed on board the
ship....might make the trip hard without any computers.
What do the people on board the ship, or their watches,
have to do with what "the guy on Earth" says?

The guy on Earth sees the spacecraft leave the
Solar System and head for the star 22.3 light-years
away. More than 44.6 years later he finally sees the
spacecraft (through the Superduper Ultrahyperdyper
Telescope) arrive at the star. The guy on Earth can
calculate that the trip took 22.3 years, but he does
not and cannot measure that time directly.

I don't know how you made this error, but you do
agree that it was an error, don't you?

The obvious impossibility of the stay-at-home directly
measuring the trip time is closely tied to the perhaps
less obvious difficulty or impossibility of the traveller
measuring the distance.

-- Jeff, in Minneapolis

22. Originally Posted by Jeff Root
Wayne,

Thank you for going back and replying to my first
post in the thread. Even though you're doing it
because you disagree with what I said, I very much
appreciate your extra effort to get the facts straight.

...

Where in the mainstream science community can I
find good evidence that a relativistic traveller would
be able to measure interstellar distances?

-- Jeff, in Minneapolis
Your whole post boils down to. "Wayne, I haven't experienced this myself have you?" and is about a good as a creationist saying "You weren't there to see life over 6 thousand years ago so you can't prove it"

Every bit of evidence that is put forward to you ignore, hand wave away or try to move the goal post.

Originally Posted by Jeff Root
That was the other thread? I was thinking it was
I've got other things going on that I'm having to deal with. At work this post some how reset my last position back to the start thus I replied to your early posts again and didn't realise until I finished posting and ran into one of my own posts.

Originally Posted by Jeff Root
As I said somewhere, it isn't the uncertainty
principle (of quantum mechanics) which raises the
problem here, but the uncertainty inherent in the
simultaneity of events (in special relativity).
Yet you fail in any way to point out how "uncertainty inherent in the
simultaneity of events" would effect any of these. It is my understanding while simultaneity is altered if you know the speeds involved you can still reconcile the events between frames. Please show me how in my parallax thought experiment "uncertainty inherent in the simultaneity of events" would effect the distance measurements?

Originally Posted by Jeff Root
But my objection to proposals so far is that they have
not been specific enough. You (or somebody) need to
specify a technique. I'll specify that the thing being
measured is the distance between the Sun and a star
which is 22.3 light-years away in the frame of both
the Sun and the distant star, and that the people
doing the measuring are moving at .999 c relative to
the Sun and the distant star. They are somewhere in
the vicinity of the Sun at the time of measurement.
Your choice as to the exact location, and I'll give you
a lot of lattitude. Longitude, too. What technique
can they use that will give a useful measure?
This is crazy. But here I go again.

ship4.png

Ship passes Earth towards the object
Earth measures that object as 22.3ly away
The clocks on the ship use "24 hour days"
The clock on the ship reads Day 10,000 at 00:00 when it passes the Earth (LCD Clock) (for both Earthlings and LGMs)
The time on Earth is Jan 1, 2020 00:00 when the ship passes the Earth. (for both Earthlings and LGMs) happy coincidence that their clocks both read 00:00 at the time of passing and their calendars are similar
The ship is travelling towards the object in a straight line past the Earth.
The ship is travelling at .999c
When the ship passes the object they look at their clock and it reads 10,365 08:46
When Earth sees the ship pass the object the date is July 6, 2064 but they know because the light took 22.3 years to get back that the ship actually passed the object on about March 4th, 2042
The ship does a simple calculation when it passed the object (d=vt) v= .999c t = 365day 8hour 46 minutes and calculates d as 1 light year.
The ship using parallax measurements from 2 outrigger devices and measure 3.26163626 arc seconds parallax at the time it passed the Earth. They divide 1 by this number and get the distance of 0.30659458023072137418536057113861 but this is in parsecs so you need to multiply by 3.26163626

If you have any problem with any of this say where you disagree. I know you'll argue that they can't measure the parallax but you've yet to state why besides your gut feel.

Originally Posted by Jeff Root

Interesting. The destination has to have already
been visited. A corner reflector which works over a
distance of 20-some light-years. And the signal to
the reflector must be be sent more than 40 years
before the trip begins in order to be used near the
trip's beginning.
Now you are being ridiculous. The principle is sound and you're complaining because it doesn't agree with your fantasy.

Originally Posted by Jeff Root

How long what took? The signal to go from the source
to the reflector to the ship? (The signal is encoded
so that the local time of transmission can easily be

Where is the signal sent from? The Sun? The ship?
The signal is sent from the ship. Yes you can encode a time stamp within the signal or you could in theory just shoot 1 pulse out and wait for it to return.

Originally Posted by Jeff Root

That is the question to be answered: Because they
are moving at nearly the speed of light relative to
what they are trying to measure the distance to,
will they still be able to measure that distance
accurately?
Yes and unless you actually show us why they can't besides "I don't think they could" then you've got no leg to stand on.
22.3x dilation isn't beyond our equipment to receive. We don't have problems timing things at .999c for that matter we can time things with a much higher speeds. The LHC's 0.999999991c speed limit isn't a problem of our detectors working out the speed but the power and engineering precision to speed the particles up faster. Before you say anything about knowing those particles true speed if we didn't know the speed to a high degree of accuracy then the experiments wouldn't be worth a cent. You might as well as an ant how fast a jet plane is going and wait for a verbal responce.

Originally Posted by Jeff Root

That depends on the calculations as well as the
measurements.

ship.png

Nice diagram.

It doesn't??? You are defining the problem in such a
way that the answer becomes almost useless.
Useless because it won't be in agreement with you. For Radar say the ship started out 140 light years away. It would still be able to tell its distance accurately from before it reached Earth to the point at which it passed the object 1 year later in its own frame of reference.

Originally Posted by Jeff Root

That is an enormous drawback. I'm not inclined to
give you that much longitude.
Hand waving. Just because the radar method is only workable n% of the trip based on the dilation amount is not a problem for that n% of the trip. And it will work a hell of a lot better then them waiting for their home planet to tell them where they are when it is 6ly behind them in their frame and 140ly away in their home planets frame.

Originally Posted by Jeff Root
But you could start sending the signal 40 years before
the trip begins.
But you aren't travelling at .999c so when you did accelerate to .999c you'd be dealing with a signal and time stamp from the proper frame not your own frame but you are right you still could use that signal and just pump it through another formula that took into account how long after the signal pulse was sent did you start your acceleration, how long did it take you to accelerate. I tried to keep it simple and remove as many variables as possible.

Originally Posted by Jeff Root
for the whole trip? It would save a heckofa lot on energy
useage onboard the ship. Less energy use means less
mass that needs to be accelerated at the start and end
of the trip.
Now you are complaining about engineering constraints aboard our ship that can travel at .999c?

Originally Posted by Jeff Root

You're talking about an alternative technique, now?

What do you mean by "sensitive enough"? Magic?
Sensitive enough as in using equipment we have available today. Not equipment from the early 1800s. You are just being obtuse and I'll probably get some infraction points for saying that so feel free to report this line.

Originally Posted by Jeff Root
the dramatic difference between theoretical physics and
experimental physics! Spherical cows and unobtanium
everywhere!

-- Jeff, in Minneapolis
No this thread has a lot of useful information in it and you hand waving, making arguments from ignorance, goal post moving, cherry picking to try to claim that the proper distance is the only valid distance and that distances can't be measured while at relativistic speeds with absolutely NOTHING to back up your claims.

23. Originally Posted by Jeff Root
Wayne,

While skimming through your next posts after the two
I just replied to, one exchange in the middle of a post
jumped out at me. It says something particularly
essential about the physics question we are trying to
resolve, as well as about our communication problems.
I'm responding to it by itself, right now.

What do the people on board the ship, or their watches,
have to do with what "the guy on Earth" says?

The guy on Earth sees the spacecraft leave the
Solar System and head for the star 22.3 light-years
away. More than 44.6 years later he finally sees the
spacecraft (through the Superduper Ultrahyperdyper
Telescope) arrive at the star. The guy on Earth can
calculate that the trip took 22.3 years, but he does
not and cannot measure that time directly.

I don't know how you made this error, but you do
agree that it was an error, don't you?

The obvious impossibility of the stay-at-home directly
measuring the trip time is closely tied to the perhaps
less obvious difficulty or impossibility of the traveller
measuring the distance.

-- Jeff, in Minneapolis
No it isn't an error
1) The rest of us are talking about what the person on the ship sees not the person on the Earth
2) The person on the ship will see their watch say 365 day 8 hours 46 minutes.
3) There is no impossibility!!

They pass the Earth and transmit, to the Earth, that they've zeroed their clock at 0 days 0 hours 0 mins just as they passed the Earth.
The Earth notices that the time progresses on the ship 22.3 times slower when they factor extra time for the distance the ship travels since the last message.
The ship passes the distant object and transmits to Earth their clock reads 365 day 8 hour 46 minutes (Yes we just passed the object)
The Earth receives that message July 6, 2064 but knows the message has been in transit for 22.3 years so was sent on about March 4th 2042

Now you are having a problem because what ... you think the LGMs in this thought experiment are going to lie and fudge the numbers to match SR predictions just to try to foil your warped sense of reality?

24. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Originally Posted by WayneFrancis
No it isn't an error
Obviously it is. You need to look more carefuly at
what people are saying. In this case, you need to
look more carefully at what korjik said in post #29:

Originally Posted by korjik
Pick a method of determinine distance to a star.
Do it from the Earth, then do it from the moving
spaceship right next to the Earth. They will measure
different distances. The stationary observer will
measure 22.3 ly the mover 1 ly. The mover travels
for a year and passes the star. He says traveled for
1 year and went slightly less then 1 ly. The guy on
Earth says he went slightly less then 22.3 ly and
took 22.3 years.
I replied to the last sentence:
Originally Posted by Jeff Root
Of course, that time is calculated, not measured
directly.
Very surprisingly, you disagreed with that. Even
more surprisingly, you still disagree, claiming that
Originally Posted by WayneFrancis
1) The rest of us are talking about what the person
on the ship sees not the person on the Earth
as though the statement I was responding to isn't
relevant to what I said in reply.

There are some grammatical errors in the quote of
korjik's post that may make it harder to understand.
Sometimes I fix such errors when I see them, and
sometimes I don't, depending on the error and on
the context. The quote above is unmodified.

In any case, it is an important fact that observers
in the Solar System cannot measure the travel time
of the spacecraft directly. They calculate it from the
measurements they can and do make. They are able
to calculate an unambiguous travel time because the
destination star is motionless relative to the Solar
System.

I'll try my best to reply to everything else. I see that
you are trying to specify the conditions for measuring
the distance. Thank you. I do appreciate the effort.

-- Jeff, in Minneapolis

25. Originally Posted by Jeff Root
Obviously it is. You need to look more carefuly at
what people are saying. In this case, you need to
look more carefully at what korjik said in post #29:
What korjik is saying there is that you measure distances the same way regardless of the frame you are in. Meaning if you accelerate to .999c you can do distance measurements using the same techniques as you did before you accelerated. You are the one that claims that you can't do distance measurements while accelerated.

Originally Posted by Jeff Root
I replied to the last sentence:

Very surprisingly, you disagreed with that. Even
more surprisingly, you still disagree, claiming that

as though the statement I was responding to isn't
relevant to what I said in reply.

There are some grammatical errors in the quote of
korjik's post that may make it harder to understand.
Sometimes I fix such errors when I see them, and
sometimes I don't, depending on the error and on
the context. The quote above is unmodified.

In any case, it is an important fact that observers
in the Solar System cannot measure the travel time
of the spacecraft directly. They calculate it from the
measurements they can and do make. They are able
to calculate an unambiguous travel time because the
destination star is motionless relative to the Solar
System.

I'll try my best to reply to everything else. I see that
you are trying to specify the conditions for measuring
the distance. Thank you. I do appreciate the effort.

-- Jeff, in Minneapolis
Jeff we, those that have been answering webbo's questions, ALL understand what the proper frame will measure the distance as. We all understand what a proper frame is. We all, besides you, say that the accelerated observer will measure a different amount of time and distance during the trip. You keep claiming that the observer on the ship has some barrier preventing them from doing measurements. No one cares that you prefer using the proper frame. We do care that you try to claim the non-inertial reference frame can't perform measurements and some how has to wait until they return to the inertial reference frame before they know anything or have to be told by someone in the inertial frame.

26. Originally Posted by Jeff Root
Obviously it is. You need to look more carefuly at
what people are saying. In this case, you need to
look more carefully at what korjik said in post #29:
What korjik is saying there is that you measure distances the same way regardless of the frame you are in. Meaning if you accelerate to .999c you can do distance measurements using the same techniques as you did before you accelerated. You are the one that claims that you can't do distance measurements while accelerated.

Originally Posted by Jeff Root
I replied to the last sentence:

Very surprisingly, you disagreed with that. Even
more surprisingly, you still disagree, claiming that

as though the statement I was responding to isn't
relevant to what I said in reply.

There are some grammatical errors in the quote of
korjik's post that may make it harder to understand.
Sometimes I fix such errors when I see them, and
sometimes I don't, depending on the error and on
the context. The quote above is unmodified.

In any case, it is an important fact that observers
in the Solar System cannot measure the travel time
of the spacecraft directly. They calculate it from the
measurements they can and do make. They are able
to calculate an unambiguous travel time because the
destination star is motionless relative to the Solar
System.

I'll try my best to reply to everything else. I see that
you are trying to specify the conditions for measuring
the distance. Thank you. I do appreciate the effort.

-- Jeff, in Minneapolis
Jeff we, those that have been answering webbo's questions, ALL understand what the proper frame will measure the distance as. We all understand what a proper frame is. We all, besides you, say that the accelerated observer will measure a different amount of time and distance during the trip then an observer in the inertial frame of the 2 points in question. You keep claiming that the observer on the ship has some barrier preventing them from doing measurements. No one cares that you prefer using the proper frame. We do care that you try to claim the non-inertial reference frame can't perform measurements and some how has to wait until they return to the inertial reference frame before they know anything or have to be told by someone in the inertial frame.

27. Order of Kilopi
Join Date
Dec 2004
Posts
11,826
Originally Posted by WayneFrancis
Originally Posted by Jeff Root
Obviously it is. You need to look more carefuly at
what people are saying. In this case, you need to
look more carefully at what korjik said in post #29:
Originally Posted by korjik
Pick a method of determinine distance to a star.
Do it from the Earth, then do it from the moving
spaceship right next to the Earth. They will measure
different distances. The stationary observer will
measure 22.3 ly the mover 1 ly. The mover travels
for a year and passes the star. He says traveled for
1 year and went slightly less then 1 ly. The guy on
Earth says he went slightly less then 22.3 ly and
took 22.3 years.
What korjik is saying there is that you measure
distances the same way regardless of the frame you
are in. Meaning if you accelerate to .999c you can do
distance measurements using the same techniques
as you did before you accelerated.
Yes, that is what korjik was saying.

I replied to the last sentence in that quote from korjik:
Originally Posted by Jeff Root
Of course, that time is calculated, not measured
directly.
You, surprisingly, disagreed with that in post #135.
I then carefully explained the exchange and asked if
more surprisingly, you repeated the disagreement in
post #143.

After pointing out to you that what korjak said is
essential to understanding my reply, you now provide
your understanding of what he said. Fine. You have
shown that you understand what he said. That wasn't
in question.

I want to know whether you now agree that I was
right when I said that the travel time determined by
"the guy on Earth" is calculated, not measured.

time around?

I don't want to be hard on you, but if you are going
to try to act strict with me, I'm going to hold you

-- Jeff, in Minneapolis

28. Originally Posted by Jeff Root
Yes, that is what korjik was saying.

I replied to the last sentence in that quote from korjik:

You, surprisingly, disagreed with that in post #135.
I then carefully explained the exchange and asked if
more surprisingly, you repeated the disagreement in
post #143.

After pointing out to you that what korjak said is
essential to understanding my reply, you now provide
your understanding of what he said. Fine. You have
shown that you understand what he said. That wasn't
in question.

I want to know whether you now agree that I was
right when I said that the travel time determined by
"the guy on Earth" is calculated, not measured.

time around?

I don't want to be hard on you, but if you are going
to try to act strict with me, I'm going to hold you

-- Jeff, in Minneapolis
I think it appears that you are hand waving to try to confuse the issue

I'm an observer on Earth that watches a ship pass Earth at .999c
I start my stop watch as it passes.
When it passes the 2nd object it sends a signal back.
When I receive that signal I stop my stop watch.
I have MEASURED how long it has been since the ship passed the Earth in my frame.
I should and do use that measurement and subtract 22.3 years for the time it took for the signal come back and then have the travel time in my frame.
My example clearly stated that both observers where measuring time using their own clocks.

I'm not saying they can not calculate the time. I'm saying they measure the time.

So I do not agree that "the guy on Earth" can only calculate the travel time. Sure he has to minus off the time the signal took to come back but I don't consider that the same as a pure calculation of (dv = t)
My example indicates that "the guy on Earth" measured the time [m] then calculated the trip time by doing m-22.3=t

Again this really doesn't matter. What most of us have a problem with is that you say an accelerated observer can't measure distances during the trip or that some how their distances would = the proper frame's distance or there is some problem with measuring distances while at a speed of .999c without giving any maths to back up your claim.

I'm fully ready to be shown wrong by you but your actions don't indicate you want to show how you are right and you don't want to admit you are wrong. And let me be perfectly clear that we don't agree that an accelerated observer can't measure distances while being accelerated.

29. Established Member
Join Date
Jan 2010
Posts
1,203
I think Wayne Francis is right. Just my opinion. But you both are awesomely smart. Wish we had millions more like you.

30. Thanks Copernicus, don't know if I'm awesomely smart but I certainly have learnt a lot from this board including corrections to my understanding just in this thread. I'm ready for Jeff to show me why he's correct. He's opened my eyes to things I haven't thought of in the past. Just this time I'm seeing no real explanation from him why he thinks we are wrong.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•