Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Alternative way to calculate the special relativistic time dilation factor

  1. Oct 24, 2011 #1
    I propose an explanation of the special relativistic time dilation and calculation of its factor in terms of the difference in observational times for incoming and receding objects, based on the following thought experiment:

    Imagine a spaceship coming from planet X to Earth with velocity V. The time during which the spaceship can be observed from Earth equals t – tc, where t is the travel time of the spaceship (the time it takes for the spaceship to come to Earth from planet X), and tc is the time it takes light to come to Earth from planet X; this expression of the observational time is explained by the fact that the spaceship is following behind its own light.

    Alternatively, imagine a spaceship going from Earth to planet X with the same velocity. In this case, the time during which the spaceship can be observed from Earth equals t + tc, as it takes t for the spaceship to go to planet X, plus it takes tc for the light to convey the image of its landing at that planet to observer on Earth.

    So, we have two different observational times for incoming and receding objects travelling the same distance with the same velocity. In order to reconcile the difference between these two observational times, we determine the mean observational time (tm) as the geometric mean of them:

    tm = √ (t – tc)(t + tc) = √ t2 – tc2

    To find out the factor for time dilation, we divide the mean observational time by travel time:

    tm/t = √ 1 – tc2/t2 = √ 1 – V2/C2

    Therefore, in result we have the same factor for the time dilation as the factor used in the special theory of relativity, i.e. the reciprocal of the Lorentz factor (√ 1 – V2/C2).
     
  2. jcsd
  3. Oct 24, 2011 #2

    DaveC426913

    User Avatar
    Gold Member

    You seem to be confusing two things here. Maybe it's just your terminology.

    The approach and recession of an object at relativistic speeds has nothing to do with time dilation.

    You would see the same effect if you examined your craft's flight using classical Newtonian mechanics.
     
  4. Oct 24, 2011 #3
    Thank you for the tip! It looks like I have to reformulate it.
     
  5. Oct 24, 2011 #4
    I thought about it, and I can not agree. The notions of approach and recession are relativistic in their nature, as there is no special direction in space, and we talk about approach and recession as they relate to the observer. There is no notion of "observer" in classical Newtonian mechanics, so why should we have the same effect?
     
  6. Oct 24, 2011 #5

    DaveC426913

    User Avatar
    Gold Member

    :shrug:

    Perhaps I just don't understand what problem you're trying to solve. You've stated the solution, but you haven't stated the problem.
     
  7. Oct 24, 2011 #6
    The problem is rather conceptual: I am trying to show that time dilation can arise not only from the relative motion between two observers, but also from the difference in direction of motion relative to the observer (approaching versus receding), as every motion is either approaching or receding, except the expansion of the Universe: it's only receding because there is no observer outside it. I think that in observational terms there must be some fundamental difference in approaching and receding motion, because light always approaches the observer and never recedes him, as the observer as such does not emit light, he just perceives it. I know, it's overly speculative, so I'd better keep it quiet...
     
  8. Oct 24, 2011 #7

    DrGreg

    User Avatar
    Science Advisor
    Gold Member

    You get time dilation when one observer circles around another; that's neither approach nor recession.
     
  9. Oct 24, 2011 #8
    In reality, such a perfect circling is not possible thanks to gravitation, and the planets periodically approach their stars and recede from them on elliptical orbits.
     
  10. Oct 24, 2011 #9

    DaveC426913

    User Avatar
    Gold Member

    But it doesn't matter if the phenomenon is uncommon, or if it doesn't occur in circumstances of your choice. The fact that it does happen. That invalidates your claim that every movement requires an advancement or recession.

    Heck, we could look down upon a star system from above its pole, and watch a planet rotate around it. Regardless of how eccentric its orbit, the planet is neither advancing nor receding from us, yet it will experience time dilation.


    The point is simply that time dilation indeed occurs independent of direction of motion wrt the observer. That should tell you you're barking up the wrong tree.
     
  11. Oct 24, 2011 #10
    Every observation, in principle, needs time, as you can not do it faster than the speed of light. By the time you get the result of your observation, the circling object would move away from the point of your observation. That means, it's receding.
     
  12. Oct 25, 2011 #11

    DaveC426913

    User Avatar
    Gold Member

    No it doesn't. Look up the definition of receding. It means 'distance increases'.

    An object has quite a bit of freedom of movement without ever having to change its distance from the observer.
     
  13. Oct 25, 2011 #12

    Dale

    Staff: Mentor

    Hi Dave, the part in bold is not correct. Although your overall point is.

    Alexroma, please pay attention to Daves statement here, it is very important. This is a key prediction of SR called transverse Doppler shift. It is considered one of the most important predictions of SR because is is not just quantitatively different from Newtonian mechanics, but qualitatively different.

    Transverse Doppler has been experimentally confirmed, if your formula cannot replicate it then your formula is contradicted by experiment.
     
  14. Oct 25, 2011 #13
    Would someone mind explaining this to me? I recognize that I may be a bit out of my league here but, If the observer sees the spaceship land c * tc after it actually did land, how does that affect time dilation?

    My understanding of time dilation is that one relativistic second is longer than one classical second. So how would the time it takes the information (the light) to get to the observer change anything about the information?
     
  15. Oct 25, 2011 #14

    DaveC426913

    User Avatar
    Gold Member

    Yeah, you're right. With an eccentric orbit you'd see a tiny bit of distance change.

    But he's totally barking up the wrong tree. Imagine observing a planet 5 light years away with an eccentric orbit. We're looking down on the system from above so its orbital planet is normal to us. He thinks he's going to see recessional motion that will cause time dilation?
     
  16. Oct 25, 2011 #15
    Thank you for pointing it out. That's a serious argument. I'll look at it closer.
     
  17. Oct 25, 2011 #16
    It really doesn't affect it in terms of the special theory of relativity. So, Dave was right in his first reply: I chose a wrong terminology for the title of my post. To call it "Alternative way to calculate the special relativistic time dilation factor" is indeed confusing. I should have called it just "Alternative way to calculate the time dilation factor".

    Information and light are not the same. In a sense, information is the message, and light is the medium.
     
  18. Oct 25, 2011 #17
    I got your point. I don't have the ready answers at this stage, because my idea is only three days old, and it's still an idea, it's not even a concept. I really appreciate your comments. Still, I believe they don't kill my idea, because gravitation, which makes planets go in circles, causes time dilation too. I am looking forward to save my idea with gravitation, as it makes the objects to approach each other, but it's a long way to figure it out in details.

    I know, it looks like it does not make sense "to reinvent the bicycle" as soon as we already have STR and GTR, but I still like to approach things differently. That's just my nature.
     
  19. Oct 25, 2011 #18

    Dale

    Staff: Mentor

  20. Nov 3, 2011 #19
    I finally figured out the application of my method of calculation of time dilation to the objects moving in circles and all other non-rectilinear trajectories. First of all, I did not properly present my method. Starting from the title, instead of calling it “Alternative way to calculate the special relativistic time dilation factor”, I should have called it “Non-relativistic explanation and calculation of the time dilation”, as I don’t employ the frames of reference for my calculation.

    As my method is non-relativistic, an observer can be located at any point in space, so for the purposes of calculation of the time dilation of a moving object, we substitute the trajectory of its movement, no matter how complex it is, for a straight line (in a physical sense, it’s possible because time dilation does not depend on the trajectory) and place the observer in the middle of the distance L = Vt, where V is velocity of the object and t is time during which the observer would observe the object going distance L if he saw it immediately, without delay caused by the finite speed of light.

    The effect of time dilation results from the difference of times of observation of an object approaching the observer who is centrally located on the straightened trajectory of the object's movement and receding from him:

    ε = tm/tar = √ (tar – tc/2)(tar + tc/2)/tar2

    In this formula:

    ε is time dilation factor

    tm is geometric mean of times of observation of an object approaching the centrally located observer and receding from him; tm = √ (tar – tc/2)(tar + tc/2)

    tar is time during which the centrally located observer would observe an object either approaching him or receding from him (going distance L/2), if he saw it immediately, without delay caused by the finite speed of light; tar = L/2V

    tc is time that takes light to cover distance L; tc = L/C

    Although the present formula is equivalent to the formula of time dilation factor used in the special theory of relativity, i.e. the reciprocal of the Lorentz factor (√ 1 – V2/C2), it shows that time dilation of a moving object may be explained by an observational effect, rather than by the actual velocity of the object.
     
  21. Nov 3, 2011 #20

    Dale

    Staff: Mentor

    Except that once you straighten the trajectory it has nothing to do with any actual observational effect.
     
    Last edited: Nov 3, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Alternative way to calculate the special relativistic time dilation factor
Loading...