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I have a question

  1. Jun 13, 2007 #1
    hey... I have a question... All velocity is relative right... and light has the same velocity irrespective of what velocity I travel in and therefore time slows down whenever I speed up right?

    So does this not mean that I can never attain any sort of velocity and can only slow down time?

    So if this is the case, then my velocity is always a constant 0 right? and if thats the case how the hell do I get from point A to point B?

    I am not studying physics professionally and I am not trying to disprove Einstein or any such thing. Im just curious... :smile:
  2. jcsd
  3. Jun 13, 2007 #2


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    I think you need to do a bit more studying to understand Special Relativity, because reading what you wrote here, you made a very common mistake.

    Your time never slows down even as you are travelling at a high velocity. Your time as viewed in another inertial frame is the one that is slowed down. You experience no time dilation in your own frame. Think about it. We are all moving at some very high velocity with respect to some alien out there in another galaxy. Can you detect how your time has slowed down?


  4. Jun 14, 2007 #3
    The fact that SR asserts it is impossible to detect absolute motion does not mean you cannot get from place to place. Velocity can always be measured relative to an object, but not wrt a featureless void. So even though you cannot make a measurement in your spaceship to determine how fast you are traveling wrt to space - you can still determine that you have a relative speed v between any two objects as you appear to travel from one to the other. You cannot, however, know whether you are moving or whether the two objects are moving. That is why its called relativity
  5. Jun 14, 2007 #4
    From your words "We are all moving...with respect to... aliens..." I gethered you meant that we are able to detect the aliens' time slowed down, time dilation. That is, for instance on earth we are able to detect the time of Martians slowed. Martians are able to detect the time of us earthlings slowed down. I believe my understanding of your words is correct.

    Then in the writings of Einstein's theory, there is a comparison process. That is, authors said two clocks would come together to compare which one slowed down by how much. In your alien case, how could we compare the alien clock with our earth clock?

    If we do compare our clock with the alien's clock, what an outcome will we find? Would you elaborate?
  6. Jun 14, 2007 #5


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    Why can't you compare it as it is? The alien's clock is slower than yours, and your clock is slower from the point of view of the alien. Isn't this a valid comparison?

    What you INTENDED here probably is to compare them in the SAME inertial reference frame. If that is what you want to do, then you have to tell me via what process do you propose for two of them to meet up in this inertial frame. Do you want the alien to slow down as it approaches you so that the alien undergoes a deceleration? Or do you wish that both of you slow down until you both reach a common inertial frame? Each one of these processes (and a whole lot more) can dictate what happens to the clocks by the time you two are together.

  7. Jun 14, 2007 #6


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    The outcome will depend on which one changed velocity so that they could come together.
  8. Jun 14, 2007 #7

    Doc Al

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    In order to compare the readings of the two clocks side by side at least one of the clocks must accelerate. The readings of the two clocks depend on the path they take through spacetime. Look up the "twin paradox". Here's a good start: http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html" [Broken]
    Last edited by a moderator: May 2, 2017
  9. Jun 14, 2007 #8
    Janus, you quoted from Bertand Russell, saying "
    The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.

    It seemed to me Bertrand Russell's words correctly desbribed you guys supporting Einstein's theory because
    you are so certain of yourselves, fanatically certain.

    Let me quote a Britsish scientist Dr. Herbert Dingle, the late president of the Royal Astraunamical Scociety. He said in 1972 in his book "Science At Crossroads" that the Relativity theory was like a stupid story told to a foolish audience. That is, he referred you guys as fools and fanatics who were so certain of Einstein while other wise people who were not so certain, full of doubts of the Relativity.

    Your reply to my question "The outcome will depend on which one changed velocity so that they could come together" shows such airs of you guys, highly certain.
    Were the fools in Russell's saying refferring to you guys?

    No where in Einstein's original writings we could find time dilation happens due to acceleration or deceleration. He always used uniform velocity, the train moved at a uniform volocity v, etc. Especially the light, uniformly and constantly at c. But this uniform velocity c caused the most servere time dilation, stop. Does it or doesn't it?

    So, why the outcome need be dependent upon changed velocity? Will uniform velocity do the trick?
  10. Jun 14, 2007 #9
    Hello Longshinewoole.

    As a fool who knows he is a fool I cannot speak for other members of the Forum but I would be grateful if a wise man such as yourself would point out to me the error of my ways in accepting the word of others who accept until proved to be wrong, the postulates of Einstein and who follow the rigorous logic of mathematics to draw conclusions from them and propose experimentally testable predictions.

  11. Jun 14, 2007 #10


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    It appears that the quotations you are using apply to you as well.

    Have you no clue on General Relativity? It is WHY I asked how you wish to do such comparison in the first place! You never bothered to answer. Instead, you come up with insults like this that is completely irrelevant to the physics content.

    IF you wish to have them meet up in a common frame of reference, THEN this problem has gone BEYOND the strict, naive confines of Special Relativity alone, and General Relativity must be invoked. It seems that you don't have any comprehension beyond that limit other than to belittle those who had spent time explaining to you this.

    If you do not wish to actually LEARN about this, let me know now so that we can end this with as little pain and aggravation as possible.

    BTW, if you do not buy relativity, then I suggest you do NOT fly in air plane or use anything with a GPS. Do NOT turn this into a "bash-relativity" thread.

    Last edited: Jun 14, 2007
  12. Jun 15, 2007 #11
    From post 9: "No where in Einstein's original writings we could find time dilation happens due to acceleration or deceleration. He always used uniform velocity, the train moved at a uniform volocity v, etc. Especially the light, uniformly and constantly at c. But this uniform velocity c caused the most servere time dilation, stop. Does it or doesn't it?"

    Not true - read his original 1905 paper. Einstein starts with two separated clocks that are synchronized in the same frame - then one clock is put in motion moving toward the other. Upon arrival the clock put in motion is found to lag the clock which remained at rest - in order to put something in motion - it must be accelerated - all real age differences involve an acceleration at some point in the experiment - Einstein embellished upon this in his 1918 paper. Two clocks in relative inertial motion will always be judged as running slow if measured by an observer in the other frame - but this in and of itself does not involve a substantive age difference - to get a measureable age difference one clock must undergo at least one acceleration somewhere in the experiment, and usually they will undergo 3 as in the case of the twin paradox... in order that they can be brought together at rest in the same frame for comparison
  13. Jun 15, 2007 #12
    If my language was insulting, I apologize to everyone who felt insulted. But how about Janus Bertrand Russell quote? Was it insulting?

    I did not answer you because I need not answer everybody. To do so would keep me too busy. Let me answer you now. You said: "The alien's clock is slower than yours, and your clock is slower from the point of view of the alien."

    Your language is meanlingless to me. To make it meanglingful, would you say " The alien's clock is slower than yours, and your clock is slower than the alien's?" If you would say so, then it follows that no body's clock is slower than the other.

    I believe Einstein and company have a language problem. When you involve acceleration to justify clock's slowing down, we dessidents thought, deceleration will likewise justify clock's speed-up. That is, if motion would affect the clock's ticking, acceleration and deceleration must work out equal affects.

    By language problem I meant you equallized mathematical time to clock working. Your math produced a shorter time, you said oh the clock worked slower. We dissident believe this equallizing was Einstein's childish dream go craze.

    Would you answer my question: will the uniform speed of light cause time dilation? Or, cause our clocks to stop?

    By thinking over this question of mine, it is easy to understand the language problem...equalizing math time to clocks working. By math, light speed produced the most severe time dilation, zero. It is obvious that this zero time dilation does not cause our clocks stop ticking. Don't you agree?
  14. Jun 15, 2007 #13
    Hello Yogi.

    Not from post 9.

    Please don't confuse me with Longshinewoole.

  15. Jun 15, 2007 #14


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    No, I disagree. This has NOTHING to do with the clock in your own inertial frame. It has everything to do with the clock that you observe in ANOTHER inertial frame. For some odd reason, you can't seem to get that. This effect has been successfully used to account for the presense of muons at sea level that should have decayed way before it got that far. Any SR text would have described this. Did you not come across it in your study of this subject? I would ask for my money back if they left this out.

    What is meaningless is to ask on how to compare 2 clocks without describing the CIRCUMSTANCES of the comparison. This is exactly what Relativity forces us to do, to re-examine various concepts that we took for granted, especially on how we determine and define distance and length.

    I will, right off the bat, question your sincerity in trying to understand this, especially considering that SEVERAL people have essentially explained to you the same thing. The fact that you clearly have the desire to bash the validity of SR support my conclusion in this case.

    Now clearly show me the exact mathematical derivation of time dilation that somehow support what you are claiming, or produce a verified experimental observation that is consistent to what you just said. Failing that, your question has been answered as clearly as anyone can, and the Hyperphysics link that I've given amply illustrates this. If you somehow do not wish to try and understand what you have been given, then that is your problem. But you should not continue to spread what you refuse to understand on here.

  16. Jun 15, 2007 #15
    oops - sorry matheinste, I meant post 8

    To amplify upon what I was refuting in post 8 directed to Longshinewoole:

    Rindler (Special Relativity at pages 30 and 31) gives a good description of the relationship between the time lost between two clocks in relative inertial motion, and why a short initial burst of acceleration has the effect of modifying the time consequences on the reminder of the journey.

    In doing so, Rindler treats it as a Special Relativity problem - the brief acceleration phase does not affect the rate of clocks, nor does the clock which has been accelerated run thereafter at a different rate. In the new frame of the traveler, by his own observation, he has less spatial distance to travel to reach the target - the spacetime interval for both observers is the same, but the interval for the observer that has accelerated will be composed of both space and time, whereas from the perspective of the non accelerated observer, his interval consists only of the proper time measured in the frame which has remained at rest.
  17. Jun 15, 2007 #16
    I am glad you seemed to have accepted my apology. Thank you.

    You said "It has everything to do with the clock that you observe in ANOTHER inertial frame." My understanding of your ANOTHER inertial frame was: remote observation. But, the clock I observed in another inertial frame must come together to compare in order to know how much it has slowed down, such as the Heafle-Keating flight experiment, such as your muon decay. Only upon close examination we are able to find out the other clock has lost some time. In the thought experment that established time dilation equation, it was the observer on the moving train (his own inertial frame) who found out his clock has lost some time when compared with the other clock at the end of the journey. I therefore believe you were contradicting your own people if you meant remote observation.

    If you meant close examination, then, if an alien (or a muon) comes at the speed of light to the earth, we on the earth should find his clock stopped ticking according to relativity.

    By the way my belief has nothing to do with remote observation or close examination. My belief has to do with your language. You people equated mathematical time to clock working. When your math (d/v=t or the time dilation equation) produced a shorter time, your language said it was the clock working slower. Please check into this. Did you people do this equalization? Does it (the equalization) make sense?
  18. Jun 15, 2007 #17


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    What "remote observation"? On that "train" thing, how is this comparison done? By whom? Did the train came to a STOP, meaning it SLOWED down to meet up another inertial frame?

    No, the language problem here has been entirely from you. You talked about "comparing" two clocks, yet you made zero description how you wish to compare such a thing.

    Only if that object continues to be at c. If it came to a stop in your frame, it isn't stopped. You make no explanation how you are comparing this. I'd like to first see an alien or a muon that is travelling at c exactly, thank you.


    Look at the DERIVATION of time dilation. Starting from the postulates of Special Relativity, the derivation is MATHEMATICALLY SOUND. It didn't come out of thin air. If you think it does not make sense, please pull out the standard derivation, and show me exactly where it mathematically failed from the starting point.

    You also seem to have lost the point entirely. The "clock" being illustrated is an example of the actual TIME that we have defined. Relativity has shown that THIS is how we have accepted to be what we have taken to be "time" all along! It has nothing to do with what's ticking on the wall or what you are wearing on your wrist. A muon has no such thing, yet it STILL behave in the same fashion. If you think this is only restricted to some mechanical device, then I would DEFINITELY ask for my money back for the missing part of my education if I were you.

  19. Jun 15, 2007 #18

    Doc Al

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    Not sure what "thought experiment" you are referring to, but realize that an accelerating observer (and his clock) does not remain in a single inertial frame.

    The difference between an experiment with a traveling clock (or twin, a biological clock) that gets reunited with its mate is that the convergence of both clocks at the same spacetime point allows them to be directly compared. Any observer in any frame is capable of viewing this comparison of side-by-side clocks; they all will agree. But the analysis of this comparison is more involved than that of the muon decay experiment.

    The decaying muon is born and dies at different locations--so it's not a simple matter of comparing reunited clocks side-by-side. But the experiment is simpler to analyze, since both earth and muon remain in their respective single inertial frames throughout the trip.
    Whatever do you mean? In physics, quantities are defined operationally as much as possible. Time is what clocks measure. Give an example where a (correctly applied) equation for time does not represent something measured by a clock (at least theoretically). Such an equation would be considered WRONG. Realize that for events taking place at different positions (like the birth and death of that muon) different observers will measure different times between them. (Time and space measurements are frame dependent.)
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