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Time dilation in acceleration or velocity

  1. Jan 26, 2012 #1
    it seems to me that time dilation takes effect in the process of acceleration- similar to the affect of gravity on time- rather than in the kinetic energy of a constant velocity.

    1- consider two ships departing earth in opposite directions at 200,000 km/hr each. an earthling sees the ships' clocks run slower, but the ships don't even see each other at all- since their combined separation speed is faster than the speed of light. are they aging backward relative to one another? that is absurd.

    2- consider galaxies that are moving away from earth at near the speed of light. are their stars aging more slowly than the milky way's stars? that is equally absurd.

    time dilation must occur in the process of acceleration.
  2. jcsd
  3. Jan 26, 2012 #2

    Simon Bridge

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    The twins paradox is resolved when you consider the effect acceleration has on time dilation. However, there is nothing wrong with time dilation wrt to speed.

    Note: the two ships moving apart at 2/3rds c? They don't see each other retreat at 4/3rds c but at (12/13)c. That is a common misconception.
    Otherwise I could travel at 0.9c from the Earth and fire a missile forward at 0.2c and the Earth sees the missile travel at 1.1c
    Last edited: Jan 26, 2012
  4. Jan 26, 2012 #3
    so from a relativistic view: 2/3c + 2/3c = 12/13c


    26/39c + 26/39c = 36/39c but, mechanically, that only makes sense as 18/39c + 18/39c = 36/39c

    so where did the relative 16/39c go? it seems that space must be carrying the objects toward each other at 52/39c! and both objects are then moving toward earth at 44/39c. this only makes sense if space is shrinking everything at "the speed of light"- or faster if photons have mass- and space is carrying everything toward itself at faster than the speed of light.

    but the math still doesn't seem to work- so the photons must be getting crushed by space, too- just at a lesser rate than their source material. certainly that is possible for a space so powerful that it can keep the moon in orbit at such a close distance to earth. it seems photons must have a mass.

    or from the perspectives' of the ships. let's say photons are massless- then the ships are being crushed in place at the "speed of light" so they are naturally receding from each other at a combined rate of 2c, then their velocities are moving them away from each other at an additional combined rate of 4/3c, so the total rate of recession between the ships is 10/3c (130/39c), but they perceive each other as receding at 12/13c (36/39c), so space is carrying the light emitted from one ship to the other ship at a relative (to absolute space) speed of 94/39c (130/39 - 36/39). but actually, when the light is emitted from the source ship, it remains stationary in space so that cuts 2/3c off of the rate of recession (of the observing ship)- so that means space is closing the distance between the light emitted from the source ship and the observing ship itself at a rate of 68/39c (94/39 - 26/39).

    but what if you just measured the rate of closure from a photon emitted by each ship at absolutely the same time. then you'd have to cut another 2/3c off the rate of closure. so the photons would be closing the distance between each other (in absolute space) at a rate of 42/39c (68/39 - 26/39). so the rate of spatial closure at the time the photons meet would be 42/39c, but the spatial closure at the time the observing ship would receive that emitting ship's photon would be at a rate 68/39c. so the rate of spatial closure greatly increases between the time that the two ships' photons meet and the time that the observing ship receives that photon. which seems to indicate that, not only is each individual particle shrinking at an increasing rate, the entire cosmos that we know is collapsing toward itself at an increasing rate. and the body of the cosmos as a whole must be collapsing on itself faster than each particle is shrinking; else how would we stay together?

    if we are shrinking at an increasing rate that must mean that time is slowing down for us as our measuring sticks get smaller. it would seem the wavelengths of photons would get shorter- in an absolute sort of way- as we wiggle our way toward infinitesimally small- receding from our previously emitted light that is fixed in space (if it is massless). so from the eyes of the universe, we are getting really small and really fast, and from our eyes, the universe is getting really big and really slow.

    "space is the substance, and matter is the unsubstantial dream" -albert einstein
    Last edited: Jan 26, 2012
  5. Jan 26, 2012 #4


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    Morningstar, please read the link that Simon Bridge posted which answers the majority of your questions. It is rather rude to not even bother to read answers which have been provided.
  6. Jan 26, 2012 #5


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    Your understanding of relativity is what is absurd--not relativity. Are you interested in learning relativity or just promoting your own senseless notions? If you choose the latter, you'll probably get banned. I suggest that you take Simon Bridge's answer and try to understand it instead of trying to get the rest of us to understand your personal theories. Please take this suggestion as a friendly warning based on prior experience of others who have started down the same path you are traveling.
  7. Jan 26, 2012 #6


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    Additionally, light always has speed c relative to any observer. The light leaves one ship at speed c relative to the other and so, no matter how far away it is, will eventually catch up to it.
  8. Jan 26, 2012 #7
    Wow. If you are correct, you have just made the most astounding and dramatic discovery in physics since Einstein. You have overturned Einstein himself and should immediately publish your results in Phys Rev and submit your findings to the Nobel committee (anyone proving Einstein's relativity wrong will surely get the next Nobel prize in physics).
  9. Jan 26, 2012 #8
    bobc2- if it's right- you can have it.

    dalespam- the real offense is not properly using the faculty of your intellect- don't be so rude- I don't have any disagreement with the functionality of the math in simon bridge's link. but I am interested in the cause behind it.

    simon bridge- thanks!

    "imagination is more important than knowledge" -albert einstein
    Last edited: Jan 26, 2012
  10. Jan 26, 2012 #9
    He was being sarcastic.

    Your post seemed to suggest that you completely ignored his link. It addresses some of your misconceptions and would be worthwhile to read.

    "Cause" is a bad word to use. The logic behind it is presented clearly in Simon's link.

    Maybe, but that doesn't mean knowledge isn't important as well. You need to have a framework of knowledge to build on if you're going to imagine anything useful.
  11. Jan 26, 2012 #10
    what is it about the substance of space that causes energy to behave the way that we observe, in special relativity? if space is the substance, then it seems that space must be the acting body and energy is simply reacting to its interaction with space- according to its nature.
  12. Jan 26, 2012 #11


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    What reason do you have to say that the "substance of space" does "cause energ to behave" in any way? You seem to be saying that in your second sentence but I can't make sense of it. What do you mean by "if space is the substance"? Many of your questions start with assumptions that are not true.
  13. Jan 26, 2012 #12
    einstein said 'space is the substance and matter is the unsubstantial dream'. his definition of substance made space the acting body- the real and tangible thing, and energy the reactive agent- and illusory. it is space itself that causes energy to act the way it does. that is the underlying truth of special relativity and general relativity. all of the equations are simply measuring space's affect on differing forms of energy. you have several observable forces, but they all exist due to space acting on different forms of energy- or different "sizes" of fundamental particles. space itself is the underlying mechanism.
    Last edited: Jan 26, 2012
  14. Jan 26, 2012 #13


    Staff: Mentor

    Then at least attempt to use the math in the link and ask about the cause behind it rather than persisting in using incorrect math to arrive at nonsense conclusions.

    What irritated me about your response is that Simon Bridge had provided a very useful link which you clearly did not even bother to click on, let alone read. If you are too lazy to click on and read useful answers then why even bother posting a question in the first place? You waste everyone's time that way.
  15. Jan 27, 2012 #14
    ok for this

    u -------> A
    -------> B
    C w

    I use this formula that make sense to me

    u + v
    w = ---------
    1 + uv/c2

    now what

    w -u
    v = ---------
    1 - wu/c2

    this formula is used for ? this I guess ?

    u -------> A
    <------- B
    C w

    It's not printing exactly the way I wanted see reference http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html
  16. Jan 27, 2012 #15


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    Put it in a code block.
  17. Jan 27, 2012 #16
    morningstar, I'd really like to know your reference for that quote. I think the circumstance and context associated with that quote would be important. What is meant by "unsubstantial dream.?" Are you sure Einstein said that? (why "dream?"--and what does that mean?)
  18. Jan 27, 2012 #17

    Simon Bridge

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    "The problem with quotes found on the internet is that they're not always accurate."
    -- Abraham Lincoln

    I would like to point out that if I see two objects both approaching me at (2/3)c, then they are approaching each other at (4/3)c > c and that this is quite fine and dandy in SR. Neither of the objects is superliminal, it is the distance between them that is decreasing so fast. It is only when you want to use this information to deduce what speeds each object measures for me and the other object that these formulas have something surprising to say. (Off your last question: you get the second formula off the first because one of u or v has changed sign... it's going the other way.)

    I think I know what you are trying to ask about though - but it will benefit you to attempt to reword your questions so they make better sense in terms of relativity. As you work at this you will come to a closer understanding.

    The intuitive approach to relativity plays us false - the problem is that it does not correctly predict what we see in all situations. Special Relativity has a method that has better predictions and is based on the property of the Universe that absolute velocity does not exist.

    This is the property that informs the speed-of-light limit, (everyone must measure the same speed for light in a vacuum) and that velocity addition formula, and has the beauty of also working for everyday objects. There are lots of ways of describing it - for instance, in terms of symmetry.

    That there may be other possible symmetries for a Universe to have is a highly speculative part of cosmology - we happen to live in this one, which has these symmetries... best we can make out. Like it or lump it - thems the rules. Understanding them is a work in progress.

    My favorite intro to relativity resource is
    ... it covers the basics, the geometric tools to help you understand them, and has a good discussion of the challenges facing any FTL theory in an accessible manner. Thus it covers the stuff most people starting out need to know and are interested in.
    Last edited: Jan 27, 2012
  19. Jan 29, 2012 #18
    Great links by Simon. I'm a newcomer, just interested in the subject. I played a little with the velocity equation presented earlier.

    Speed1 Speed2 Result(km/s) Diff (%)
    050,000 050,000 097,297 02.7
    100,000 100,000 180,000 10.0
    150,000 150,000 240,000 20.0
    100,000 200,000 245,455 18.2
    250,000 250,000 295,082 41.0
    280,000 280,000 299,287 46.6
    300,000 300,000 300,000 50.0

    Diff means the difference between the relativistic resulting speed and as per clasical mechanics (simply both speeds added). At first I found it hard to swallow, that where both speeds add up to the same result classically, the results are different in relativity.
  20. Jan 29, 2012 #19
    I haven't been able to find this quote anywhere. Or anything close to it.
  21. Jan 29, 2012 #20

    Simon Bridge

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    Welcome to PF:

    You are not alone - SR has strong experimental verification so we just have to live with it.

    Actually it's not that bad to use - there are surprising simplicities that come out like "easter eggs" in a video game. Fun to explore.
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