Notices
Results 1 to 20 of 20

Thread: Time-Dilation

  1. #1 Time-Dilation 
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    Could anyone explain to me how time-dilation actually occurs. If the speed of light is always speed C regardless of the observer how can time-dilation be possible?


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Ph.D. Nevyn's Avatar
    Join Date
    Jan 2007
    Location
    UK
    Posts
    881
    I am not sure as to why, but here is how.

    If you have a photon clock (a photon bouncing between to plates) then this photon will take a certain amount of time to complete one bounce. As you speed up the photon is now bouncing at diagnals so it takes longer to complete one bounce hence time is slowing down.
    When you reach C then as a particle of light it can never complete the bounce or it will miss the plate so time is said to have stopped:


    Come see some of my art work at http://nevyn-pendragon.deviantart.com/
    Reply With Quote  
     

  4. #3  
    Forum Professor
    Join Date
    Apr 2007
    Location
    In the circuitous haze of my mind
    Posts
    1,028
    Is that the limiter of how fast you can go? I mostly here things about the amount of energy that would be necessary to go even the speed of light; but does it also have something to do with time dilation?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    The speed of light is the universal speed limit. Time-dilation has to do with time slowing down as you speed up. The thing I don't understand though is if time slows down then wouldn't that be evidence that the speed of light is not always seen at C relative to the moving object.
    Reply With Quote  
     

  6. #5  
    Forum Professor
    Join Date
    Apr 2007
    Location
    In the circuitous haze of my mind
    Posts
    1,028
    Now I get it; good point. It depends on what point of view the scientists have. You could see it as speed being relative to you as the observer watching the particle slow down, or as if you are the particle itself, in which its speed along with your speed of perception would slow down, allowing for indication of a speed change. I'm actually not sure about how scientists measure the speed of light; also I don't know the change in rate of time change that a particle would incur, like what the slope is, whether its exponential or logarithmic, etc..

    Basically if time dilation was linear starting from a lower velocity, and had a 1/10000 perception of speed loss, as it went faster the loss of speed would exponentially decrease(I think), until the loss led you to .999999999999C, and on and on. Maybe this only applies to us and not photons.

    I need more information.....it could be wikipedia time.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
    Reply With Quote  
     

  7. #6  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    The equation is 1/sqrt(1-(v/c)^2) (someone correct me if I'm wrong), if that helps, but the key thing to realize is that any observer moving at any speed will measure any light to be moving at c.
    Reply With Quote  
     

  8. #7  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,075
    Quote Originally Posted by EV33
    The speed of light is the universal speed limit. Time-dilation has to do with time slowing down as you speed up. The thing I don't understand though is if time slows down then wouldn't that be evidence that the speed of light is not always seen at C relative to the moving object.
    Time dilation has to do with the fact that two observers moving reative to each other will not measure the same time interval as occuring between two events.

    Say you have two observers(A and B), each sits next to and is at rest with respect to a light clock. A and B have a relative motion with respect to each other. For each of them there resepect light clock "ticks"( the light makes one round trip between the mirrors) once every microsecond. For each the light travels at c.

    Both A and B will note that while the light for their light clock travels straight up and down between the mirrors, the light for the other observer's light clock travels along a diagonal and a longer path. Thus each of them determines that the other's light clock ticks slower and that time slows down for the other observer.

    Put simply, time dilation is something that always happens to the "other guy" and never you.

    This brings up the spectre of the "twin paradox"; the idea that if one twin leaves on a spacetrip and then returns, he will will be younger than his brother. The supposed paradox comes in when you consider what I've said above. If it is true then both twins should see the other as aging slower, and both twins should say that the other twin is the younger at the end the trip.

    The solution lay in the fact that there is more to Special Relativity than time dilation, there is also length contraction and the relativity of simultaneity. You have to take all three into consideration to properly determine what happens.
    Reply With Quote  
     

  9. #8  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,232
    The solution lay in the fact that there is more to Special Relativity than time dilation, there is also length contraction and the relativity of simultaneity. You have to take all three into consideration to properly determine what happens.
    Ok, so what happens? With length contracting, does that also affect time in some way? Does that happen only to the guy on the spaceship? No that would mean a absolute frame of reference.....
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  10. #9  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,075
    Quote Originally Posted by KALSTER
    The solution lay in the fact that there is more to Special Relativity than time dilation, there is also length contraction and the relativity of simultaneity. You have to take all three into consideration to properly determine what happens.
    Ok, so what happens? With length contracting, does that also affect time in some way? Does that happen only to the guy on the spaceship? No that would mean a absolute frame of reference.....
    Length contraction works just like time dilation, so it also happens to the "other guy". For example, assume that your twin travels to a star 7 light years distant as measured by you on the Earth. He travels at 0.99c. From your frame, he takes a tad over 7 years to get there, but due to time dilation only ages a tad over 1 year.

    From his frame, you, the Earth the star he is traveling to and the distance between this star and the Earth length contract by a factor of 7, making the distance 1 light year. One light year traversed at .99c takes a tad over 1 year by his clock.

    Relativity of simultaneity comes into play in explaining why, at the end of the trip, he agrees that you have aged 7 years (assuming he stops at this star.)
    Reply With Quote  
     

  11. #10  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,232
    Which of these effects have been experimentally verified? You chose the arbitrary distance of 7 LY, so would 50 LY take the same time from his frame?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  12. #11  
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    I think I can word my question a little better. Why does time stretch as you move faster?
    Reply With Quote  
     

  13. #12  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,075
    Quote Originally Posted by KALSTER
    Which of these effects have been experimentally verified?
    Time dilation has been experimentally verified, but length contraction follows as a natural consequence.
    You chose the arbitrary distance of 7 LY, so would 50 LY take the same time from his frame?
    I chose 7 ly because it was a convenient value to use with 0.99c which has a time dilation/length contraction factor of 7.

    If the distance was 50 ly as measured from Earth, then it would take a little over 7 yrs 2.5 months by "shiptime".
    Reply With Quote  
     

  14. #13  
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    Can anyone here answer the question, why does time stretch as your speed increases.
    Reply With Quote  
     

  15. #14  
    Forum Professor
    Join Date
    Apr 2007
    Location
    In the circuitous haze of my mind
    Posts
    1,028
    I don't think anyone knows actually.

    I could E-mail some guy at MIT and see if he knows....
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
    Reply With Quote  
     

  16. #15  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    All of special relativity follows from saying "the speed of light is a constant in all inertial reference frames." How exactly time dilation/length contraction/etc. follows from this is something I can't explain clearly enough. Maybe someone else can though?
    Reply With Quote  
     

  17. #16  
    Forum Professor leohopkins's Avatar
    Join Date
    Dec 2006
    Location
    Dulwich, London, England
    Posts
    1,417
    Quote Originally Posted by Janus
    Quote Originally Posted by EV33
    The speed of light is the universal speed limit. Time-dilation has to do with time slowing down as you speed up. The thing I don't understand though is if time slows down then wouldn't that be evidence that the speed of light is not always seen at C relative to the moving object.
    Time dilation has to do with the fact that two observers moving reative to each other will not measure the same time interval as occuring between two events.

    Say you have two observers(A and B), each sits next to and is at rest with respect to a light clock. A and B have a relative motion with respect to each other. For each of them there resepect light clock "ticks"( the light makes one round trip between the mirrors) once every microsecond. For each the light travels at c.

    Both A and B will note that while the light for their light clock travels straight up and down between the mirrors, the light for the other observer's light clock travels along a diagonal and a longer path. Thus each of them determines that the other's light clock ticks slower and that time slows down for the other observer.

    Put simply, time dilation is something that always happens to the "other guy" and never you.

    This brings up the spectre of the "twin paradox"; the idea that if one twin leaves on a spacetrip and then returns, he will will be younger than his brother. The supposed paradox comes in when you consider what I've said above. If it is true then both twins should see the other as aging slower, and both twins should say that the other twin is the younger at the end the trip.

    The solution lay in the fact that there is more to Special Relativity than time dilation, there is also length contraction and the relativity of simultaneity. You have to take all three into consideration to properly determine what happens.
    Hi sorry but i think that relativity of simultaneity is a load of old cobblers if you ask me. We KNOW that light takes a certain amount of time to travel from one place to another so therefore we would we stupid to assume that just because we "see" something it means it happening the second we see it; because thats simply not true; EVERYTHING we see and hear happened in the past (even if fractions of femto seconds ago) through to billions of years (depending on far we look)

    A person will look at the sky and see lightning and say "There is a storm"
    A blind person will hear thunder a few seconds later and say "There is a storm" - but it doesnt matter, we MUST take into account the distance and the medium of information travelled in order to work out when these events TRULY occured.

    The only true way to know if the car crashed in both the USA and Australia occured at the same time would be to work out how far the distance is between them and use triangulation to know where to stand so you could see both at the same time, but for an exact quantum measure your position and distance between the two events would need to be EXACTLY equal.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

    www.leohopkins.com
    Reply With Quote  
     

  18. #17  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,075
    Quote Originally Posted by leohopkins
    Quote Originally Posted by Janus
    Quote Originally Posted by EV33
    The speed of light is the universal speed limit. Time-dilation has to do with time slowing down as you speed up. The thing I don't understand though is if time slows down then wouldn't that be evidence that the speed of light is not always seen at C relative to the moving object.
    Time dilation has to do with the fact that two observers moving reative to each other will not measure the same time interval as occuring between two events.

    Say you have two observers(A and B), each sits next to and is at rest with respect to a light clock. A and B have a relative motion with respect to each other. For each of them there resepect light clock "ticks"( the light makes one round trip between the mirrors) once every microsecond. For each the light travels at c.

    Both A and B will note that while the light for their light clock travels straight up and down between the mirrors, the light for the other observer's light clock travels along a diagonal and a longer path. Thus each of them determines that the other's light clock ticks slower and that time slows down for the other observer.

    Put simply, time dilation is something that always happens to the "other guy" and never you.

    This brings up the spectre of the "twin paradox"; the idea that if one twin leaves on a spacetrip and then returns, he will will be younger than his brother. The supposed paradox comes in when you consider what I've said above. If it is true then both twins should see the other as aging slower, and both twins should say that the other twin is the younger at the end the trip.

    The solution lay in the fact that there is more to Special Relativity than time dilation, there is also length contraction and the relativity of simultaneity. You have to take all three into consideration to properly determine what happens.
    Hi sorry but i think that relativity of simultaneity is a load of old cobblers if you ask me. We KNOW that light takes a certain amount of time to travel from one place to another so therefore we would we stupid to assume that just because we "see" something it means it happening the second we see it; because thats simply not true; EVERYTHING we see and hear happened in the past (even if fractions of femto seconds ago) through to billions of years (depending on far we look)

    A person will look at the sky and see lightning and say "There is a storm"
    A blind person will hear thunder a few seconds later and say "There is a storm" - but it doesnt matter, we MUST take into account the distance and the medium of information travelled in order to work out when these events TRULY occured.

    The only true way to know if the car crashed in both the USA and Australia occured at the same time would be to work out how far the distance is between them and use triangulation to know where to stand so you could see both at the same time, but for an exact quantum measure your position and distance between the two events would need to be EXACTLY equal.
    You've missed point of the Relativity of Simultaneity. It isn't what you "see" its what you "determine" taking distance and the speed of light into account.

    For example:

    You have a light source placed exactly between two clocks. The clocks are set to zero and are set to start ticking when hit by a flash of light from the source. A flash of light is emitted from the Light source and reaches the clocks.

    For anyone sitting next to the light source or either clock, Both clocks start simultaneously. A person sitting at the source will "see" the clocks start at the same time. A person sitting at either clock we "see" the other clock start after his, but will "determine" after taking the time delay of light travel into account that the other clock started at the same time as his. This determination by this person does not depend on whether or not we consider this set up is moving or not, as long as this person is at rest relative to the clocks.

    Now consider the same situation from the frame of someone for which the clocks are traveling at velocity "v" in a direction parallel to a line passing through both clocks.

    The flash is emtted and travels at c towards both clocks. The leading clock will be moving away from the point of emission at a speed of v, making the closing speed between the light pulse and the clock is c-v. The trailing clock will be moving towards the point of emission at v, making its closing speed c+v.

    The pulse reaches the trailing clock before it reaches the leading clock and the leading clock starts ticking after the trailing clock. Again this is not what he "sees" but what he determines taking distance and light speed delay into account.

    If he were passing by the leading clock when the light carrying the information that the other clock has started reaches that point, he would "see" the same thing as someone sitting next to and at rest with respect to the clock sees, The other clock starting. But while the person at rest with respect to clock will determine that the other clock actually started at the same time as his, the person passing by the clock will determine that the trailing clock started before the leading clock.

    In a very real way, events that are simultaneous in one frame are not simulanteous in a frame with a realtive velocity to the first.
    Reply With Quote  
     

  19. #18  
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    Honestly I agree with you completely leohopkins that is why I am asking so many questions about this. My high school physics class taught relativity like it was fact, but to me it all seemed like complete crap, whether it is or not I don't know.
    Reply With Quote  
     

  20. #19  
    Forum Freshman
    Join Date
    Nov 2007
    Location
    Washington State
    Posts
    77
    Janus I'm sure you know more about this then me but by saying c+V and c-V wouldn't that be saying that Einsteins Second Postulate is wrong because that would me that the speed of light in all frames it not a constant. No matter the velocity of the thing that makes the light pulse the speed of light is always C.
    Reply With Quote  
     

  21. #20  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,075
    Quote Originally Posted by EV33
    Janus I'm sure you know more about this then me but by saying c+V and c-V wouldn't that be saying that Einsteins Second Postulate is wrong because that would me that the speed of light in all frames it not a constant. No matter the velocity of the thing that makes the light pulse the speed of light is always C.
    Don't confuse "closing velocity" with "relative relative", these are two different things.

    Relative velocity is the velocity difference between two objects as measured by either object.

    Closing velocity is the difference in velocity between two objects that are both moving relative to another frame as measured from that frame.


    For example:

    You have a space ship that passes you at a relative velocity of 0.99c.
    After it gets 1 light second past you, you emit a light pulse after it. The pulse travels at a relative velocity of c.

    The closing velocity is the difference between these two velocities or 0.01c

    Now since the light pulse is "chasing" the ship, from your frame, it will take 100 sec to "catch" the ship. In other words, after 100 sec the light pulse traveling at c will be the same distance from you as the ship with its 1 light second head start and traveling at 0.99c will be. The closing velocity concept comes in handy because 100 sec is the same answer you get if you take the starting distance between the light pulse and the ship and divide it by the difference of the relative speeds of the light and the ship or,

    t = 1 lightsec/(c-0.99c) = 100 sec.

    What the second postulate says is that the relative speed of light is always a constant in any frame. IOW, the speed that light travels in a vacuum is always measured by you as being c relative to you.

    Thus while you measure the closing velocity between the light and the ship as 0.01c, you measure the relative speed of light as c.

    OTOH, in the frame of the ship one would measure the relative of the light c (relative to the ship) and the [i]closing[i] velocity between you and the light as -1.99c (negative because the two are separating.)
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •