functionally faster than light.

[md65536]

No, I am not suggesting he physically traveled faster than a photon in any time frame but from his point of view he has made a 7 ly journey in less than one year.

Sure, his proper velocity (http://en.wikipedia.org/wiki/Proper_velocity) is greater than c, but that's not faster than light (whose proper velocity is infinite).

 

He's traveled 7 LY but his destination has aged 7 years. Functionally it is equivalent to slowing his own time (eg. being in stasis in sci-fi). You can travel great distances with little aging, but you can't do it faster than light.

[MigL]

You guys need to look up the definition of an inertial frame.

A frame where you speed up to near c and then decelerate to 'sync-up' with earth's frame is not only NOT an inertial frame, but is also a different frame.

 

Rule #1 of relativity: Do not mix frames ( as Swansont has pointed out several times now ).

[ACG52]

he has traveled 7 ly in one year of his life... correct?

No. What is not being taken into consideration is length contraction. The distance is 7 ly as measured by the stationary (earth) frame. But from the frame of the ship moving at .99c (relative to the earth) the distance traveled is .988 ly. From the ship's frame, just over a year has passed, but as measured on earth, 7.088 years have passed.

Edited March 10, 2013 by ACG52

[Moontanman]

No. What is not being taken into consideration is length contraction. The distance is 7 ly as measured by the stationary (earth) frame. But from the frame of the ship moving at .99c (relative to the earth) the distance traveled is .988 ly. From the ship's frame, just over a year has passed, but as measured on earth, 7.088 years have passed.

 

 

Normally I take your assertions quite seriously but this seems to be nit picking, the man will have traveled 7 ly in one year of his perceived time. This can be obfuscated any way you want but the facts of his travel is quite clear... If he traveled to a star 7 ly years away at .99 c he would experience 1 year of travel time, from his point of view effectively traveling at 7xc... stationary observers would of course disagree with him but his time frame is effectively ftl from his point of view... possibly i am not getting this but to say he would say he had traveled 1 ly due to his experienced time of one year would disagree with both stationary observers and his own observations once he got there...

[swansont]

Normally I take your assertions quite seriously but this seems to be nit picking, the man will have traveled 7 ly in one year of his perceived time. This can be obfuscated any way you want but the facts of his travel is quite clear... If he traveled to a star 7 ly years away at .99 c he would experience 1 year of travel time, from his point of view effectively traveling at 7xc... stationary observers would of course disagree with him but his time frame is effectively ftl from his point of view... possibly i am not getting this but to say he would say he had traveled 1 ly due to his experienced time of one year would disagree with both stationary observers and his own observations once he got there...

 

Definitions in physics can seem nit-picky, but they exist for a reason. Measurements of time, distance and speed have to take place in a single frame of reference. If there is some other useful terms to define then you can define them, but you don't get to call them the same thing that's already been defined.

 

Some of this stems from how Einstein defined clock synchronization and simultaneity in his 1905 paper. If you start mixing definitions up, then you can't properly use the equations of the theory.

[Moontanman]

Definitions in physics can seem nit-picky, but they exist for a reason. Measurements of time, distance and speed have to take place in a single frame of reference. If there is some other useful terms to define then you can define them, but you don't get to call them the same thing that's already been defined.

 

Some of this stems from how Einstein defined clock synchronization and simultaneity in his 1905 paper. If you start mixing definitions up, then you can't properly use the equations of the theory.

 

 

I think i understand that part of it and I understand that frames of reference cannot be mixed but I still don't see why it's not effectively ftl for the guy on the ship.

 

BTW I'm not getting notices of threads I'm following today, I checked my preferences and they seem to be ok, is something wrong with the site today?

[ACG52]

Normally I take your assertions quite seriously but this seems to be nit picking, the man will have traveled 7 ly in one year of his perceived time. This can be obfuscated any way you want but the facts of his travel is quite clear... If he traveled to a star 7 ly years away at .99 c he would experience 1 year of travel time, from his point of view effectively traveling at 7xc... stationary observers would of course disagree with him but his time frame is effectively ftl from his point of view... possibly i am not getting this but to say he would say he had traveled 1 ly due to his experienced time of one year would disagree with both stationary observers and his own observations once he got there...

 

No, he traveled .988 lys in one year of his time (that's what he actually measured). The traveller's measurement of the distance is just as valid as the stationary measurement. If he then immediately turned around and retraced his journey, he will have measured 1.97 lys and just over two years of time.. While this will disagree with what the earth measured, they are both equally valid measurements.

 

There is no preferred frame of reference.

[Moontanman]

 

 

 

 

 

No, he traveled .988 lys in one year of his time (that's what he actually measured). The traveller's measurement of the distance is just as valid as the stationary measurement. If he then immediately turned around and retraced his journey, he will have measured 1.97 lys and just over two years of time.. While this will disagree with what the earth measured, they are both equally valid measurements.

 

There is no preferred frame of reference.

 

So even though he traveled to a point he knows is 7 ly from his starting point he will only measure the distance he traveled as 1 ly when he gets there? He will look back at his starting point and it will only be 1 ly away when he stops?

[ACG52]

So even though he traveled to a point he knows is 7 ly from his starting point he will only measure the distance he traveled as 1 ly when he gets there? He will look back at his starting point and it will only be 1 ly away when he stops?

He knows it's 7 lys, because that's what was measured from the stationary frame. From his own measurements, he knows it is just .998 lys. If he stops, relative to his starting point, he is no longer in the same frame of reference as when he was in motion. If, as he whizzes past his destination without slowing down, he looks behind, he will see the earth as being .988 lys away.

Edited March 11, 2013 by ACG52

[Moontanman]

He knows it's 7 lys, because that's what was measured from the stationary frame. From his own measurements, he knows it is just .998 lys. If he stops, relative to his starting point, he is no longer in the same frame of reference as when he was in motion. If, as he whizzes past his destination without slowing down, he looks behind, he will see the earth as being .988 lys away.

 

 

Ok, now I have it... thanks.

 

i think my main hangup on this was me swamping frames of reference and not realizing it. i thought you were saying one thing and i was saying something else. once i realized the time frame swap it became evident...

[swansont]

I think i understand that part of it and I understand that frames of reference cannot be mixed but I still don't see why it's not effectively ftl for the guy on the ship.

 

Because that's not how we define speed. You can only have one definition for it; you need the math to be self-consistent.

[Moontanman]

just for shits and giggles... I bet his biological brain... would after traveling the 7 ly at .99 c would still logically think of it as effectively traveling at 7c or forwards in time at at rate of 1/7 everyone else

Edited March 11, 2013 by Moontanman

[ACG52]

just for shits and giggles... I bet his biological brain... would after traveling the 7 ly at .99 c would still logically think of it as effectively traveling at 7c

His biological brain (as opposed to...?) is certain it traveled for just less than a year and covered .988 lys. Because that's what it experienced.

[Moontanman]

His biological brain (as opposed to...?) is certain it traveled for just less than a year and covered .988 lys. Because that's what it experienced.

 

It was more of a label of how our minds tend to think but i meant as opposed to counter intuitive mathematics ... yeah works for me...

 

His biological brain (as opposed to...?) is certain it traveled for just less than a year and covered .988 lys. Because that's what it experienced.

 

yes and when he does the same thing back to his starting point gets out and sees his friends aged 14 years and he has only aged two? He is going to assert that he only traveled 2 ly? once he goes back to his original frame of reference he has to see something is out of kilter... in other words he has a preferred frame of reference even if the universe doesn't

Edited March 11, 2013 by Moontanman

[ACG52]

It was more of a label of how our minds tend to think but i meant as opposed to counter intuitive mathematics ... yeah works for me...

 

 

yes and when he does the same thing back to his starting point gets out and sees his friends aged 14 years and he has only aged two? He is going to assert that he only traveled 2 ly? once he goes back to his original frame of reference he has to see something is out of kilter... in other words he has a preferred frame of reference even if the universe doesn't

 

That's correct. He has only aged two years. Once he's back in the original, stationary frame of reference, he will measure the distance as 7 lys. But his on-board odometer will still read just over two lys. That's the distance he travelled, as measured in his own frame. And he will see that the time and distance in his moving frame did not match the time and distance of the earth's frame.

[Moontanman]

we're on the same page

[Didymus]

You guys need to look up the definition of an inertial frame.

A frame where you speed up to near c and then decelerate to 'sync-up' with earth's frame is not only NOT an inertial frame, but is also a different frame.

 

Rule #1 of relativity: Do not mix frames ( as Swansont has pointed out several times now ).

 

Cool. Now apply rule #1 to Hafele-Keating. The entire experiment that "proves" SR is entirely based on the premise you're now saying is faulty. The planes went from a frame stationary to the ground clock, to an inertial frame (back and forth quite a few times for each leg of their journey)... and then when they stopped, they'd actually traveled the entire distance and actually experienced less time. If you are to put your faith into this experiment, it would then extend that a person traveling at .99C for 1 year and then stop would actually have traveled about 7 lightyears in 1 year. If mixing frames in this way is invalid, then the Hafele-Keating experiment is equally invalid.

[Delta1212]

Cool. Now apply rule #1 to Hafele-Keating. The entire experiment that "proves" SR is entirely based on the premise you're now saying is faulty. The planes went from a frame stationary to the ground clock, to an inertial frame (back and forth quite a few times for each leg of their journey)... and then when they stopped, they'd actually traveled the entire distance and actually experienced less time. If you are to put your faith into this experiment, it would then extend that a person traveling at .99C for 1 year and then stop would actually have traveled about 7 lightyears in 1 year. If mixing frames in this way is invalid, then the Hafele-Keating experiment is equally invalid.

I don't think you are quite grasping what mixing frames means.

 

Frame #1: The distance between point A and point B is 7 ly.

Frame #2: The distance between point A and point B is 1 ly.

 

Observer X starts in Frame #1 at point A, enters frame #2, travels to point B, turns around, travels back to point A, re-enters frame #1. Observer Y remains in Frame #1 at point A for the duration.

 

Valid statements according to relativity: While traveling, Observer X measured itself moving 2 ly total over the course of approximately 2 years, therefore traveling at just under c, at the end of which Observer Y is found to have aged approximately 14 years. Observer Y observes X moving a total distance of 14 ly over the course of approximately 14 years, therefore traveling at just under c, during which time X experienced time dilation and aged 2 years.

 

Invalid mixing of frames: Observer X aged 2 years and Observer Y measured 14 ly, therefore Observer X traveled at 7c.

Edited March 11, 2013 by Delta1212

[michel123456]

 

Cool. Now apply rule #1 to Hafele-Keating. The entire experiment that "proves" SR is entirely based on the premise you're now saying is faulty. The planes went from a frame stationary to the ground clock, to an inertial frame (back and forth quite a few times for each leg of their journey)... and then when they stopped, they'd actually traveled the entire distance and actually experienced less time. If you are to put your faith into this experiment, it would then extend that a person traveling at .99C for 1 year and then stop would actually have traveled about 7 lightyears in 1 year. If mixing frames in this way is invalid, then the Hafele-Keating experiment is equally invalid.

I have to admit that the Hafele-Keating experiment baffles my mind.

-----------------------------

 

There are 2 ways to think about it:

1. the traveler comes back and has aged 2 years instead of 14 for the observer at rest.

 

2. the observer at rest enters a spaceship and follows exactly the same trip. When he arrives and meet with his predecessor, there is no gap, no difference in age.

 

The difference between 1 & 2 is introducing a dissymmetry I cannot swallow.

[Delta1212]

I have to admit that the Hafele-Keating experiment baffles my mind.

-----------------------------

 

There are 2 ways to think about it:

1. the traveler comes back and has aged 2 years instead of 14 for the observer at rest.

 

2. the observer at rest enters a spaceship and follows exactly the same trip. When he arrives and meet with his predecessor, there is no gap, no difference in age.

 

The difference between 1 & 2 is introducing a dissymmetry I cannot swallow.

In 1, they different amounts of time in different inertial frames. In 2, they spent exactly the same amount of time in each inertial frame. It would be like me traveling 14 miles in a car but winding up back in my house versus me traveling to my friend's house and my sister than coming to my friend's house later on. In the first case, both me and my sister are at my house, but I've traveled 14 miles and she hasn't. In the latter case, we've both traveled the exact same distance, albeit at different times.

 

If you want it to be more symmetrical, you have the second case where the traveling observer never slows down, but the observer at rest enters a spaceship and catches up with the traveler. The observer who was previously at rest will now be the one who has aged less.

[Didymus]

If we agree on units of length from the frame of reference of the earth. Total distance traveled (the circumference of the earth)/(7 LY) at a speed relative to that frame of reference of (the speed of the plane)/(.99c). This trip was accomplished in (51 nanoseconds less than "ground time")/(6 years less than "ground time").

If the H&K trip actually covered the same journey in 51 nanoseconds less than would be measured from an outside observer... it doesn't matter that this is because "space seems to have shrank" ... it legitimately made the trip in less time. For this to be true, the corresponding example would hold equally true. If the idea that the space craft only perceived 1 year should be discounted... then so should the idea that the plane experienced 51 fewer nanoseconds.

If the spaceship didn't "really" travel 7 lightyears in 1 year because the earth's frame of time is preferred... then neither did the H&K experiment. If it is legitimate to mix the spacial frame at rest and the temporal frame in motion... it must be in all cases. That's the whole "repeatable and falsifiable" part. The math is self-defeating because it imposes limitations, then breaks it's own limitations unless we change the definition of everything in physics to accommodate this one theory.

If I say that I am the tallest man in the world, and provide a formula which proves that anything which SEEMS taller than me is actually just an inch shorter, but existing in expanded space correlating to the amount that they appear taller. Every time someone points out an inconsistency I could easily claim that this simply appears to be inconsistent because of the expansion of space around objects that appear taller than me... and that I can not be directly compared to people because of false simultaneity. I can then test this formula by finding a person or object that appears taller than me, adjusting it per this formula and proving conclusively that the results are exactly as the formula predicts!

 

Think this will catch on?

Of course not. But, this is simply time dilation with a few details swapped out.

Edited March 11, 2013 by Didymus

[swansont]

 

If the H&K trip actually covered the same journey in 51 nanoseconds less than would be measured from an outside observer... it doesn't matter that this is because "space seems to have shrank" ... it legitimately made the trip in less time. For this to be true, the corresponding example would hold equally true. If the idea that the space craft only perceived 1 year should be discounted... then so should the idea that the plane experienced 51 fewer nanoseconds.

 

The idea that the space craft only measured one year is not discounted. It is just that we insist you use the distance as measured from that frame of reference as well when calculating the speed, because that's the definition of speed. It's not really all that complicated. The laws of physics are the same, i.e. the equations work, in any inertial reference frame. Not the combination of two reference frames. Not a non-inertial frame. IOW, if an acceleration is involved, all bets are off.

 

It is for that reason that the Hafele-Keating analysis has to be (and is) done from an inertial frame.

 

 

 

 

If the spaceship didn't "really" travel 7 lightyears in 1 year because the earth's frame of time is preferred... then neither did the H&K experiment. If it is legitimate to mix the spacial frame at rest and the temporal frame in motion... it must be in all cases. That's the whole "repeatable and falsifiable" part. The math is self-defeating because it imposes limitations, then breaks it's own limitations unless we change the definition of everything in physics to accommodate this one theory.

 

It's not because the earth's frame is preferred. The H-K analysis was done in a frame in which the earth was at rest (which is not the frame of the earth) because that was the easiest way to do the calculation. You don't get bonus points for making the calculations tougher when they can be simple.

 

Similarly, you can do the rocket analysis from the moving rocket's frame or the earth's frame. Both are inertial for the purposes of the discussion. What you can't do is mix the frames, taking one value from each.

 

 

If I say that I am the tallest man in the world, and provide a formula which proves that anything which SEEMS taller than me is actually just an inch shorter, but existing in expanded space correlating to the amount that they appear taller. Every time someone points out an inconsistency I could easily claim that this simply appears to be inconsistent because of the expansion of space around objects that appear taller than me... and that I can not be directly compared to people because of false simultaneity. I can then test this formula by finding a person or object that appears taller than me, adjusting it per this formula and proving conclusively that the results are exactly as the formula predicts!

 

Think this will catch on?

 

Perhaps among the gullible, but otherwise no, because it's a BS straw man.

[Didymus]

No point beating that horse anymore. Your faith is quite strong, so, next problem:

 

time dilation supposedly happens due to relative speed, agreed? And neither frame of reference is preferred over the other.

 

Do you agree with both points?

 

I.e. you don't assert that time dilation is some inertial aspect of the acceleration process?

[Delta1212]

Didymus, out of curiosity, do you accept the constancy of the speed of light, or do you believe that to be false?

[ACG52]

Your faith is quite strong, so, next problem:

 

 

 

Using the word faith is a red flag that you don't understand relativity.The predictions of relativity match what is observed in the real universe.

 

time dilation supposedly happens due to relative speed, agreed? And neither frame of reference is preferred over the other.

 

Do you agree with both points?

 

 

 

As long as both frames are intertial, yes. But in order to compare the measurements from the two frames, they must be brought together in the same frame of reference. This means at least one of the inertial frames must undergo non-inertial movement, and it is that movement which differentiates one frame's measurements from the other.

Edited March 11, 2013 by ACG52