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Thread: Twin paradox

  1. #1 Twin paradox 
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    My question is how can the two times read different for the two twins?

    I see that the traveling twin travels a contracted distance which makes his trip shorter but I don't see how that effects only one of their clocks and not both.

    This is the link to the twin paradox that I have been learning from
    http://www.phys.vt.edu/~jhs/faq/twins.html

    I know what relativity of simultaneity is but when the author of this article starts discussing it as the reason for the differences in the clocks he loses me. He discusses this in paragraph 15 and 16.


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    Try checking out the sticky thread at the top of the Physics forum entititled "Special Relativity Primer":

    http://thescienceforum.com/Special-R...mer-19044t.php

    Then come back with any questions you may have.


    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  4. #3  
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    The paragraph under the sub title space twin uses the phrase "the distance is crossed". What do you mean by that?
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  5. #4  
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    Quote Originally Posted by EV33
    The paragraph under the sub title space twin uses the phrase "the distance is crossed". What do you mean by that?
    The Space Twin crosses the distance between the Earth and Endpoint. (Or from the perspective of The Space twin, The Earth, the Endpoint and space between them move past the Space Twin.)
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    Oh I was reading the word cross as meaning intersecting rather than going across.

    I am still pretty confused though. I feel like that last paragraph is explaining what relativity of simultaneity is rather than explaining why ralativity of simultaneity makes for the two clocks having different times upon the arival of the space twin. I am sure I am probably just missing something but I don't know what I am missing here.
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  7. #6 Re: Twin paradox 
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    Quote Originally Posted by EV33
    My question is how can the two times read different for the two twins?

    I see that the traveling twin travels a contracted distance which makes his trip shorter but I don't see how that effects only one of their clocks and not both.

    This is the link to the twin paradox that I have been learning from
    http://www.phys.vt.edu/~jhs/faq/twins.html

    I know what relativity of simultaneity is but when the author of this article starts discussing it as the reason for the differences in the clocks he loses me. He discusses this in paragraph 15 and 16.
    There is no paradox. Special relativity and the equations that describe it are valid in an inertial refrence frame and only in an inertial reference frame. The "traveling" twin in the "twin paradox" must accelerate to start, accelerated to stop or turn around and accelerate at the end of the journey. The reference frame of the traveling twin is not inertial and because of that the two viewpoints are not equivalent. It is only in the reference frame of the stay-at-home twin that it is allowable to apply special relativity.
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  8. #7  
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    I read that it can be explained without acceleration though. Is that not true?

    Also should I be looking more so into general relativity to explain this rather than special relativity then?
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  9. #8  
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    Quote Originally Posted by EV33
    I read that it can be explained without acceleration though. Is that not true?

    Also should I be looking more so into general relativity to explain this rather than special relativity then?
    I have no idea what that is supposed to mean. The traveling twin cannot travel without acceleration. So, without acceleration there is no problem statement.

    The issue can indeed be explained using general relativity. In fact that is the proper way to analyze both world lines. But, be warned, general relativity is much more complicated than special relativity.

    You can understand special relativity using nothing more than basic high-school algebra. General relativity requires knowledge of Riemannian differential geometry. That is several quantum steps beyond high-school algebra.
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  10. #9  
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    The question I was trying to get across in the what is time theory relates to this theory on the twin paradox.

    Logic tells me that if two objects leave the earth and return later and have a difference between the amount of change that has occurred physically between the earth and each of the two objects that something physically has happened to them to produce such results. Dr Rocket doesn't seam to get this basic idea and has advised me to see a witch doctor in order to answer my question.

    The question I have is simply what physical changes would cause two objects (clocks in this case) to deviate when they started out from the same origin and returned to the same origin. Normally when we have this inaccuracy it's caused by mechanical imperfection that causes drift. For our example lets assume we are talking about nuclear clocks that are extremely accurate.

    So given our two nuclear clocks and both leaving the same location and returning back to the same location what would physically cause them to drift apart in their measurements? The easy answer would be to just say time slowed and thus the clocks slowed, but in reality something is causing these clocks to physically change the way they operate compared to clocks back at their origin.

    http://en.wikipedia.org/wiki/Atomic_clock

    Looking at the above link and how a nuclear clock works it seams to me that our two clocks would have to undergo some slowing at an atomic level. One can say time slowed and caused these variations but this really translates in to matter and energy changes. So toss time aside for a second and figure out how one would externally cause the two clocks to drift without physically touching them or altering their electronics. If we know how we would do so without speed we might be one step closer to finding out how speed might be causing it.
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  11. #10  
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    DrRocket of course in the real world there would need to be acceleration but according to the link I gave in the first post it is not necessary to use acceleration to explain the twin paradox.
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    DrRocket now that I have looked at you previous explanation a few times it does make sense to me.


    Thank you all for all of the help.
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  13. #12  
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    Quote Originally Posted by (In)Sanity
    The question I was trying to get across in the what is time theory relates to this theory on the twin paradox.

    Logic tells me that if two objects leave the earth and return later and have a difference between the amount of change that has occurred physically between the earth and each of the two objects that something physically has happened to them to produce such results. Dr Rocket doesn't seam to get this basic idea and has advised me to see a witch doctor in order to answer my question.
    You don't read well and it is not I who does not "get it".

    I told you that science describes HOW nature works. If you want an explanation at to WHY it works that way they you need to go see the witch doctor. HOW and WHY are totally different issues.

    Quote Originally Posted by (In)Sanity
    The question I have is simply what physical changes would cause two objects (clocks in this case) to deviate when they started out from the same origin and returned to the same origin. Normally when we have this inaccuracy it's caused by mechanical imperfection that causes drift. For our example lets assume we are talking about nuclear clocks that are extremely accurate.
    There is NO physical change that causes the clocks to deviate, except for the basic nature of space-time as per the theory of relativity. If you traveled along with the traveling twin you would see NOTHING out of the ordinary occurring in your reference frame.

    Quote Originally Posted by (In)Sanity
    The easy answer would be to just say time slowed and thus the clocks slowed, but in reality something is causing these clocks to physically change the way they operate compared to clocks back at their origin.
    The problem is that your statement here is completely wrong. It is that simple. In realith there is nothing "causing these clocks to physically change the way tey operate compared to clocks back at their origin." In fact, using the general theory of relativity there is no possible means, even in principle to compare the two clocks during the trip. They can only be compared once they are back at a single point in space-time. What you are allowed to compare is the result of integrating the metric over world lines on the space-time manifold. You cannot compare them at distant points in space. There is NO global coordinate system for measuring either time or distance in a general curved space-time.
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    There is NO physical change that causes the clocks to deviate, except for the basic nature of space-time as per the theory of relativity. If you traveled along with the traveling twin you would see NOTHING out of the ordinary occurring in your reference frame.
    No shit, did I ever mention anything about traveling along with them ? No. If their is NO physical change as you claim then how do they end up different once they reach their origin. They go from the same to different upon return. How can one have the same and now different without Physical change ?

    The problem is that your statement here is completely wrong. It is that simple. In realith there is nothing "causing these clocks to physically change the way tey operate compared to clocks back at their origin." In fact, using the general theory of relativity there is no possible means, even in principle to compare the two clocks during the trip. They can only be compared once they are back at a single point in space-time. What you are allowed to compare is the result of integrating the metric over world lines on the space-time manifold. You cannot compare them at distant points in space. There is NO global coordinate system for measuring either time or distance in a general curved space-time.
    Again I made absolutely no mention of distant space, traveling with them or anything outside of their origin point. I simply asked what physical change made them change and thus be different once they returned to their origin point. Learn to read what people type and learn to type. What is "realith" ?
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  15. #14  
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    Quote Originally Posted by (In)Sanity

    Again I made absolutely no mention of distant space, traveling with them or anything outside of their origin point. I simply asked what physical change made them change and thus be different once they returned to their origin point. Learn to read what people type and learn to type. What is "realith" ?
    "Realith" is clearly a typo. I would have thought you could recognize that.

    You have implicitly made mention of a lot of things that don't make sense.

    The physical change that made them different is that one ages less. That is it. That is really all that occurs. You answered your own question and didn't even recognize it.

    In not recognizing that the only difference is aging, once they are reunited at the end point of their different world lines, you implicitly made the assumption in asking "what physical change made them change and thus be different once they returned to their origin point?" that there is some mechanism whereby their age and other quantities are able to compared while they are separated. There is no such mechanism in general relativity.

    This is an important point. In a curved space-time there are NO global coordinates for either space or time and all that can be compared is the difference between observations made along world lines with a common end point. You can't ask questions such as what was going on WHEN the trip was half over, since there is no WHEN that corresponds to that question.

    So, no shit, you don't know what you are asking. You are using words that correspond to everyday experience in a context in which that experience does not apply -- it is meaningless.
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  16. #15  
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    Quote Originally Posted by Janus
    Try checking out the sticky thread at the top of the Physics forum entititled "Special Relativity Primer":

    http://thescienceforum.com/Special-R...mer-19044t.php

    Then come back with any questions you may have.
    This is important. Check out the primer that Janus has started, and look at some of the comments in the associated thread.

    A couple of significant points need to be made.

    1. In physics a theory is not a conjecture. A theory is in fact a term conferring the highest level of acceptance that is placed upon a body of organized knowledge that has two significant attributes. Those attributes are broad predictive capabilities and support by a large body of experimental data of the highest quality and reliability. There are 3 fundamental theories in physics. They are General relativity (the theory of space-time the curvature of which is what we call gravity), Quantum Chromodynamics (the theory of the strong interaction), and the electroweak theory (the quantum field theory that comprises the theory of the electromagnetic interaction and the weak interaction.

    2. Special relativity is the theory of space and time in the absence of gravitational effects. It is an important special case of the general theory of relativity, but must be applied with due consideration for its limitations, including the equivalence principle of general relativity which states that gravity and acceleration are indistinguishable. Special relativity allows the existence of a global set of coordinates for space and time, which is not permitted in a general curved space-time. Special relativity is basically a theory of space and time, and it shows that neither space nor time are absolute concepts. This is a tremendous break from classical Newtonian mechanics. Attempts to explain special relativity, or time, or space in Newtonian terms are doomed to failure and represent a failure to grasp the deep implications of relativity.

    3. The twin paradox is neither a paradox nor a theory. It is simply an example of the confusion that can arise when special relativity is applied improperly. It shows that in special relativity not all viewpoints are equivalent -- special relativity is only applicable in inertial reference frames, and inertial reference frames are an idealization. The twin paradox is resolved by noting that only the reference frame of the twin that does not travel is inertial, and the traveling twin actually does ages less. This has been proved by direct experiment using atomic clocks.

    4. There is no explanation of WHY the traveling twin ages less in any fundamental manner beyond the simple fact that time is dependent on the reference frame, and that the effects are completely consistent with the predictions of relativity. Within relativity there is a complete model that explains HOW clocks behave differently in different reference frames, but WHY they behave that way is not a question for science. Physics formulates and validates mathematical descriptions of nature, but it does not explain why those laws are what they are.
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  17. #16  
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    DrRocket,

    For the questions I'll ask below, let's assume a fixed frame of reference. Let's call it a transparent test chamber in a lab on earth and these events occurring inside that chamber. Let's also assume we have some technology that can achieve the results outlined inside our test chamber. The results of each test to be compared with some precision "time" measuring device outside of the chamber and one inside.

    Let's also always assume we are looking in to this chamber and that time is not altered from our vantage point. Perhaps toss in some biological life forms such as insects inside the chamber for a visual reference along with our precision clock.

    So on to the questions.

    What happens if you stop "time" ? The only answer I can come up with would be that matter and energy also stop. This goes all the way to the sub atomic levels. From what I can tell any other answer would indicate something is still moving and time is still moving forward with it relative to the inside of the test chamber. If anything moves, even down to the sub atomic level we can reference this to our laboratory clock and come up with a "time".

    If you can agree on that then ask what happens when you slow down "time". The answer I come up with is that matter and energy slow in their normal cycles all the way down to the sub atomic levels. Again all of these examples are from the same exact reference frame inside the test chamber and compared with that outside the test chamber.

    What would happen if you speed up time ? From my point of view the energy and matter would speed up in their normal cycles in respect to that outside of the test chamber. The clock inside the test chamber would pull ahead of that inside the laboratory.

    If we can't agree on these concepts then it would explain why we don't understand one another.
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    3. The twin paradox is neither a paradox nor a theory. It is simply an example of the confusion that can arise when special relativity is applied improperly. It shows that in special relativity not all viewpoints are equivalent -- special relativity is only applicable in inertial reference frames, and inertial reference frames are an idealization. The twin paradox is resolved by noting that only the reference frame of the twin that does not travel is inertial, and the traveling twin actually does ages less. This has been proved by direct experiment using atomic clocks.

    4. There is no explanation of WHY the traveling twin ages less in any fundamental manner beyond the simple fact that time is dependent on the reference frame, and that the effects are completely consistent with the predictions of relativity. Within relativity there is a complete model that explains HOW clocks behave differently in different reference frames, but WHY they behave that way is not a question for science. Physics formulates and validates mathematical descriptions of nature, but it does not explain why those laws are what they are.
    This is all very useful information and I appreciate you taking the time to write it. I see the flaw in my logic. I'm trying to get science to answer the why. I can accept how it is achieved, I just am having a hard time dealing with the concept of not knowing why it does this. I assume someone somewhere is trying to answer this question.
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  19. #18  
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    Quote Originally Posted by (In)Sanity
    What happens if you stop "time" ? The only answer I can come up with would be that matter and energy also stop. This goes all the way to the sub atomic levels. From what I can tell any other answer would indicate something is still moving and time is still moving forward with it relative to the inside of the test chamber. If anything moves, even down to the sub atomic level we can reference this to our laboratory clock and come up with a "time".
    ...
    That would be more of a question of philosophy rather than physics but yes I think that this is quite correct from the point of view of those watching from outside. This is, in fact, matches what relativity concludes is observed of something in the limit of that something approaching the speed of light relative to the observer.

    BUT just because the observation matches does not mean that this is what is happening in the case of relativity. And the reason that it is not the same, is that relativity says that there are no abolute measures of space and time. Instead it says that in order to measure space and time in a consistent manner then how you do it has to be relative to the inertial frame you are in.

    In the Twin paradox, while the twins are in different inertial frames their measures of space and time contradict each other (if they insist on their own natural measure of space and time as an absolute measure that is). But later when they meet up they can agree according to the measure of space and time in the inertial frame where they meet.

    They can of course agree ahead of time to stick to the measure of space time according to the inertial frame of the solar system. In that case, then they would see things as you suggest that all the clocks and motion on the ship has indeed slowed down and if we ever do have relativistic travel I have no doubt that this is in fact what they would do (assuming people stay on the earth).

    However the objections of the physicists here to this are based on the fact that this is really just an arbitrary agreement on their part and does NOT mean that motion really is slowing down of the ship any more or less than motion is slowing down on the earth. The physicists know that difference in the measures of time by the twins is really down to the relativity of simultaneity and not any effect of velocity on the motion of molecules.


    Quote Originally Posted by (In)Sanity
    This is all very useful information and I appreciate you taking the time to write it. I see the flaw in my logic. I'm trying to get science to answer the why. I can accept how it is achieved, I just am having a hard time dealing with the concept of not knowing why it does this. I assume someone somewhere is trying to answer this question.
    Well the only scientific answer to that question that I can think of would be that this is the geometry of space time. Space-time is not put together in a Eucleadean geometry but in a locally Minkowsky geometry. Does that help?
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    Well the only scientific answer to that question that I can think of would be that this is the geometry of space time. Space-time is not put together in a Eucleadean geometry but in a locally Minkowsky geometry. Does that help?
    Not really, it would be hard to explain to a family on earth that they are now 6 years older then their love one that has just returned from a 10 year deep space mission because of geometry

    Ohh and I forgot to mention trying to explain to them that even though he didn't age as much nothing physical has happen to him at all. He just didn't age as much. Talk about a paradox of words.
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    Quote Originally Posted by (In)Sanity
    Well the only scientific answer to that question that I can think of would be that this is the geometry of space time. Space-time is not put together in a Eucleadean geometry but in a locally Minkowsky geometry. Does that help?
    Not really, it would be hard to explain to a family on earth that they are now 6 years older then their love one that has just returned from a 10 year deep space mission because of geometry

    Ohh and I forgot to mention trying to explain to them that even though he didn't age as much nothing physical has happen to him at all. He just didn't age as much. Talk about a paradox of words.
    I would not say that nothing physical happened to him. He was accelerated to an extremely high velocity after all. That is not as easy as it sounds. Do you realize how much energy is involved? At a velocity of ony 86.6% of the speed of light, if he were to collide with the earth (without his ship) he would produce the same explosion as a nuclear bomb with 1000 times his mass in plutonium (enough for 5000 nuclear warheads in the case of a 150 pound man).
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  22. #21  
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    Quote Originally Posted by (In)Sanity
    Well the only scientific answer to that question that I can think of would be that this is the geometry of space time. Space-time is not put together in a Eucleadean geometry but in a locally Minkowsky geometry. Does that help?
    Not really, it would be hard to explain to a family on earth that they are now 6 years older then their love one that has just returned from a 10 year deep space mission because of geometry

    Ohh and I forgot to mention trying to explain to them that even though he didn't age as much nothing physical has happen to him at all. He just didn't age as much. Talk about a paradox of words.

    Okay, let's try this:

    You have two playing cards, the King of Spades and the King of Diamonds as in the following image.



    At the bottom of the image you see how the cards sit relative to each other and the top shows how each card "appears" to the other. each card sees the other the same size as itself and the other card appears "normal". There is a one to one ratio.

    This represents two objects at rest with each other and how they compare their separate time rates.

    The next image shows one card contracted along its width. The bottom shows the cards relative to each other and the top how each card appears to the other.



    Note the the Red King looks "squashed" to the Black King. The Red King however doesn't know that he is "squashed", and by his measurement it is the Black King that is "stretched out".

    This is how you are trying to visualize objects moving with respect to each and how time dilation effects the measurement of time rate between them.

    So of course you ask. "What physically act on the Red king to squash it". This requires also for there to be a concept of absolute rest, so that we know which card is really moving.

    But here is how Relativity describes it.



    Here the cards are turned at an angle to each other. Each card measures the others "Width" as compared to its own, as represented by the black and Red dashed lines. And each card sees the other as "squashed". But neither card is physically altered, just its orientation to the other. Also unlike the last example, there is no way to tell which card is "really moving", you get the same results if you consider the Red king moving as you do if you consider the Black King and moving. There is no absolute rest against which to measure movement.

    This "change of orientation" of the cards when they move relative to each other is fundamentally built into the geometry of the universe.

    This "change of orientation" doesn't just effect how we compare time but also distance.

    So for your family at home, they age 16 years because it took their loved one 16 years to travel to a certain distance from Earth and return. They see their loved one aging only 10 years because of how the "Change in Orientation" between relatively moving frames affects the comparison of their measurement of time between them.
    For the loved one, he returns after aging only aging 10 years because of how this "Change of Orientation" affects how he measures distance compared to those left behind.(Length Contraction} The same distance that they measured as X light years, he measures as 10/16 X light years. Since it only takes 10 years to travel 10/16 X light years and back at his relative speed to the Earth, this is how much he aged.

    Nothing physically acts on either family or loved one to cause this difference, they just measure the same time interval from different "perspectives" .
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  23. #22  
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    Quote Originally Posted by mitchellmckain
    Quote Originally Posted by (In)Sanity
    Well the only scientific answer to that question that I can think of would be that this is the geometry of space time. Space-time is not put together in a Eucleadean geometry but in a locally Minkowsky geometry. Does that help?
    Not really, it would be hard to explain to a family on earth that they are now 6 years older then their love one that has just returned from a 10 year deep space mission because of geometry

    Ohh and I forgot to mention trying to explain to them that even though he didn't age as much nothing physical has happen to him at all. He just didn't age as much. Talk about a paradox of words.
    I would not say that nothing physical happened to him. He was accelerated to an extremely high velocity after all. That is not as easy as it sounds. Do you realize how much energy is involved? At a velocity of ony 86.6% of the speed of light, if he were to collide with the earth (without his ship) he would produce the same explosion as a nuclear bomb with 1000 times his mass in plutonium (enough for 5000 nuclear warheads in the case of a 150 pound man).
    I was being a little sarcastic. I think it was DrRocket that said nothing physically happens to the person. I think the answer was that they just aged less. I of course don't accept that aging less is not a physical event. It just seams to me that if you leave and come back and your not as old as your suppose to be then something physically had have happen to you.

    Very cool on the energy, makes it sound pretty much impossible to get a man to that speed.
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    So for your family at home, they age 16 years because it took their loved one 16 years to travel to a certain distance from Earth and return. They see their loved one aging only 10 years because of how the "Change in Orientation" between relatively moving frames affects the comparison of their measurement of time between them.
    For the loved one, he returns after aging only aging 10 years because of how this "Change of Orientation" affects how he measures distance compared to those left behind.(Length Contraction} The same distance that they measured as X light years, he measures as 10/16 X light years. Since it only takes 10 years to travel 10/16 X light years and back at his relative speed to the Earth, this is how much he aged.

    Nothing physically acts on either family or loved one to cause this difference, they just measure the same time interval from different "perspectives" .
    Hang on , perhaps I'm reading something in to this that doesn't actually even exist.

    Using the earth as a frame of reference, if John age 30 leaves his wife age 30 on earth and heads off on a deep space trip at close to the speed of light and returns when his wife is now age 40 is John in a physical sense younger then 40 when he returns back to his wife ? I realize John would have not noticed that he was gone 10 years or that his clocks would not have calculated a 10 year span, I'm just really wondering now if when he returns he would be from a molecular level younger then his wife ? If he is then I have to conclude something physically happened to him to produce this result. I think everyone has to remember that for now everything we do in this physical existence has to reference back to the one and only place we know life. That would be earth. So when discussing the possibilities I like to reference the end results to the time frame of earth. If when two people re-unite and neither has aged any different yet they both swear they were gone a different amount of time then the other I find this a bit easier to swallow. If they both come back and have physically aged different then each other and their families I have to conclude that their travels have had a physical effect on their bodies to cause this slowing of cellular degeneration.

    Hope this makes sense.
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  25. #24  
    Forum Isotope (In)Sanity's Avatar
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    Just thought of another example that I would love to have answered

    Let's take two ships, both start out next to the earth and have as close as we can get no noticeable movement in comparison to the rest of the universe. The earth and everything else is moving away or toward these two ships. Now lets give one of these ships a high powered laser that is pointed at a receiver on the other ship. Let's send a data stream down that laser that is a count of 1 . 2 .3 . 4 ... at an interval of 1000 counts per second. Let's assume both ships agree on the duration of a second and both see the same count. When ship 2 sends a number 234 ship 1 receives a 234 within nanoseconds due to their close proximity.

    Ship #2 starts to accelerate away from ship #1 in a perfectly straight line in order to keep the laser pointing at the receiver. At this point data being transmitted by ship #2 is taking longer to reach ship #1. Ship #2 if they were able to see the actual data floating in space would now see the spacing of these numbers further apart relative to their position. The spacing would widen more and more the faster they went. Looking at the frequency at which the data is being transmitted ship #2 would still see they are sending 1000 number per second. Light being a constant speed I would assume ship #1 would also be receiving these numbers at 1000 per second. Would at any point ship #1 start to see that the numbers being sent by ship #2 slow in their send rate, for example would they start to appear to be sent at a rate of 999 or less per second? Clearly if ship #1 was moving as well in any opposite direction they would in fact see that the numbers were coming from ship #2 at a slower rate. With ship #1 being stationary would this same effect be witnessed ?

    Think of it like this. I assume at this point that the speed of light is absolute in respect to the entire universe (perhaps I'm wrong on that?) Ship #1 (S1) is stationary against the edge of our page.

    Code:
    S1  { 1 2 3 4 5 6 7 8 9 } S2
    S1  { 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18}S2
    S1  { 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25} S2
    Ship #2 I assume if it could see it's data trail would see something like this as it accelerated faster and faster.


    Code:
    S1  { 1 2 3 4 5 6  7  8  9 } S2
    S1  { 4 5 6  7  8  9   10   11   12     13      14       15      16      17      18}S2
    S1  { 7  8  9   10   11   12     13      14       15      16      17      18        19          20          21            22                  23                      24                        25} S2
    So the question is would Ship #1 always see data coming over like it did in the top example, or would it start to see a widening of the data like in example #2? If it does widen would it be caused by the osscilator that is sending the data from ship #2 slowing down and producing less numbers per second relative to the clocks on ship #1, or would it be caused by some other factor such as the speed of light being relative to Ship #2 and not a fixed global constant?
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  26. #25  
    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by Janus
    Here the cards are turned at an angle to each other. Each card measures the others "Width" as compared to its own, as represented by the black and Red dashed lines. And each card sees the other as "squashed". But neither card is physically altered, just its orientation to the other. Also unlike the last example, there is no way to tell which card is "really moving", you get the same results if you consider the Red king moving as you do if you consider the Black King and moving. There is no absolute rest against which to measure movement.

    This "change of orientation" of the cards when they move relative to each other is fundamentally built into the geometry of the universe.

    This "change of orientation" doesn't just effect how we compare time but also distance.

    So for your family at home, they age 16 years because it took their loved one 16 years to travel to a certain distance from Earth and return. They see their loved one aging only 10 years because of how the "Change in Orientation" between relatively moving frames affects the comparison of their measurement of time between them.
    For the loved one, he returns after aging only aging 10 years because of how this "Change of Orientation" affects how he measures distance compared to those left behind.(Length Contraction} The same distance that they measured as X light years, he measures as 10/16 X light years. Since it only takes 10 years to travel 10/16 X light years and back at his relative speed to the Earth, this is how much he aged.

    Nothing physically acts on either family or loved one to cause this difference, they just measure the same time interval from different "perspectives" .
    Now that is an excellent piece of educational composition Janus!

    What (In)Sanity doesn't know is that this orientation explanation is actually suggested by the mathematics itself in terms of hyperbolic trig functions.

    This is a post for relativity educators to take note of and remember.
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  27. #26  
    . DrRocket's Avatar
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    Quote Originally Posted by (In)Sanity
    DrRocket,

    For the questions I'll ask below, let's assume a fixed frame of reference. Let's call it a transparent test chamber in a lab on earth and these events occurring inside that chamber. Let's also assume we have some technology that can achieve the results outlined inside our test chamber. The results of each test to be compared with some precision "time" measuring device outside of the chamber and one inside.

    Let's also always assume we are looking in to this chamber and that time is not altered from our vantage point. Perhaps toss in some biological life forms such as insects inside the chamber for a visual reference along with our precision clock.

    So on to the questions.

    What happens if you stop "time" ? The only answer I can come up with would be that matter and energy also stop. This goes all the way to the sub atomic levels. From what I can tell any other answer would indicate something is still moving and time is still moving forward with it relative to the inside of the test chamber. If anything moves, even down to the sub atomic level we can reference this to our laboratory clock and come up with a "time".

    If you can agree on that then ask what happens when you slow down "time". The answer I come up with is that matter and energy slow in their normal cycles all the way down to the sub atomic levels. Again all of these examples are from the same exact reference frame inside the test chamber and compared with that outside the test chamber.

    What would happen if you speed up time ? From my point of view the energy and matter would speed up in their normal cycles in respect to that outside of the test chamber. The clock inside the test chamber would pull ahead of that inside the laboratory.

    If we can't agree on these concepts then it would explain why we don't understand one another.
    Your questions and answers are all predicated on the assumption that you are an outside observer and that you have a clock that behaves in the manner in which you would expect a clock to behave in your reference frame.

    That is precisely the situation for an observer in an inertial reference frame in special relativity.

    Now, you further posit that inside the box that clocks are "stopped" relative to your reference frame. If you would replace "stopped" with "slowed" then that is precisely the situation that an observer in an inertial reference would see with respect to another inertial reference frame in relative motion to his. So the scenario that you are setting up is essentially that of two inertial reference frames in motion with respect to one another in special relativity.

    Now. neither mass nor energy would "stop" or "slow down". What would "stop" or "slow down" would be things that are measured with respect to time. Let's take kinetic energy for example. Kinetic energy is a quantity that is dependent on the reference frame. Let's call the reference frame of you, as the observer A, and the other reference frame B. If B is in motion with respect to A then objects at rest in B are in motion relative to A and therefore possess kinetic energy in the frame A, but not in B. So what A sees relative to kinetic energy is quite different from what B sees, and in this case those objects in B that have no kinetic energy in their own reference frame would be quite energetic in A. So, no the time dilation in B as perceived by A is not accompanied by a reduction in energy, rather the opposite.

    Mass in and of itself does not imply motion, except at a quantum level. However, the objects in B that are in motion with respect to A would seem to have greater mass-energy than they would in the reference frame of B. So again, the mass effect that accompanies the time dilation is not a reduction in mass but rather an increase in mass-energy. This can also be formulated in terms of momentum for those who prefer to think of mass as only relating to rest mass. But in any case mass does not decrease.

    Now, as far as some other notion of "freezing time" goes, there is simply no context in which that is possible. It is not a question that can be addressed using physics, since it violates all known physical principles.

    Without some notion of different reference frames and effects on clocks the notion of either "speeding up time" or "slowing down time" is completely nonsensical. Speed is simply distance divided by time. Without a notion of time there is no sense to any notion of speed. In particular you cannot "speed up time" since that is a self-referential idea related to time itself and it makes no sense. To talk about speeding up or slowing down time within a single reference frame is just gibberish.

    The problem with describing time by saying that mass and energy speed up their normal cycles is that they don't have normal cycles per se. Now if you want to say something like the rate of decay of unstable nuclei decreases, then that does make sense, and that is precisely what happens in special relativity. The muon for instance, is known to be produced by gamma ray collisions high in the atmosphere and to penetrate further into the atmosphere than would be expected by the normal lifetime of the muon. The explanation for how it does this is that it is moving quite fast, and the lifetime in the reference frame of an earth-bound observer is greater (due to time dilation) than what is seen when the muon is at more modest speeds. Alternately from the reference frame of the muon length contraction results in its penetrating deeper since the distance that it sees is substantially less than the distance seem by an earth-stationary observer.

    If what you are describing is consistent with what I have described, then what you are talking about is the response of mechanical systems to differences in time itself as measured in two difference reference frames. But that is fairly key to understanding special relativity -- the behavior of the mechanical systems is a response to the nature of time. Of course the clocks are themselves "mechanical" in some sense, whether you are talking about pendulum clocks or atomic clocks. Of course things "slow down" as a result of time dilation --that is simply because of the nature of how speed is calculated based on time.

    All of this applies when the approximations of special relativity are sufficient for an accurate description. When you start to deal with highly curved space-time situations that call for the full machinery of general relativity, you suddenly find that neither time nor space are clearly defined and that you cannot compare times at locations that are spatially removed from one another. You cannot even talk very clearly about "distance" in the usual sense. Time and space get mixed together and it is not generally possible to separate the two.

    What you cannot do is set up your scenario in any manner that is inconsistent with the theories of relativity. You cannot set up some sort of box and just "stop time" with nothing else happening. That simply violates too much known physics and you are then talking fan tasty and in fantasy anything can happen.
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  28. #27  
    . DrRocket's Avatar
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    Quote Originally Posted by (In)Sanity
    Just thought of another example that I would love to have answered

    Let's take two ships, both start out next to the earth and have as close as we can get no noticeable movement in comparison to the rest of the universe. The earth and everything else is moving away or toward these two ships. Now lets give one of these ships a high powered laser that is pointed at a receiver on the other ship. Let's send a data stream down that laser that is a count of 1 . 2 .3 . 4 ... at an interval of 1000 counts per second. Let's assume both ships agree on the duration of a second and both see the same count. When ship 2 sends a number 234 ship 1 receives a 234 within nanoseconds due to their close proximity.

    Ship #2 starts to accelerate away from ship #1 in a perfectly straight line in order to keep the laser pointing at the receiver. At this point data being transmitted by ship #2 is taking longer to reach ship #1. Ship #2 if they were able to see the actual data floating in space would now see the spacing of these numbers further apart relative to their position. The spacing would widen more and more the faster they went. Looking at the frequency at which the data is being transmitted ship #2 would still see they are sending 1000 number per second. Light being a constant speed I would assume ship #1 would also be receiving these numbers at 1000 per second. Would at any point ship #1 start to see that the numbers being sent by ship #2 slow in their send rate, for example would they start to appear to be sent at a rate of 999 or less per second? Clearly if ship #1 was moving as well in any opposite direction they would in fact see that the numbers were coming from ship #2 at a slower rate. With ship #1 being stationary would this same effect be witnessed ?

    Think of it like this. I assume at this point that the speed of light is absolute in respect to the entire universe (perhaps I'm wrong on that?) Ship #1 (S1) is stationary against the edge of our page.

    Code:
    S1  { 1 2 3 4 5 6 7 8 9 } S2
    S1  { 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18}S2
    S1  { 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25} S2
    Ship #2 I assume if it could see it's data trail would see something like this as it accelerated faster and faster.


    Code:
    S1  { 1 2 3 4 5 6  7  8  9 } S2
    S1  { 4 5 6  7  8  9   10   11   12     13      14       15      16      17      18}S2
    S1  { 7  8  9   10   11   12     13      14       15      16      17      18        19          20          21            22                  23                      24                        25} S2
    So the question is would Ship #1 always see data coming over like it did in the top example, or would it start to see a widening of the data like in example #2? If it does widen would it be caused by the osscilator that is sending the data from ship #2 slowing down and producing less numbers per second relative to the clocks on ship #1, or would it be caused by some other factor such as the speed of light being relative to Ship #2 and not a fixed global constant?
    You don't get a constant speed of information transmittal. That is because it is not the photons that transmit the information but rather the pulse width (the turning on and off of the beam) that transmits the zeros and ones. And the pulse width does change while the speed of the photons themselves does not.

    In wave terms, the frequency of the light changes, and with it the available bandwidth for information transmittal.
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  29. #28  
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by mitchellmckain

    Now that is an excellent piece of educational composition Janus!

    What (In)Sanity doesn't know is that this orientation explanation is actually suggested by the mathematics itself in terms of hyperbolic trig functions.

    This is a post for relativity educators to take note of and remember.
    Thanks!


    The reason I've tried so hard to find a way to explain this to (In)sanity is that I can remember thinking much along the same lines as he is when I first came across Relativity. I'm hoping to spark an "AHA" moment.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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