Time dilation Definition and 999 Threads

In physics and relativity, time dilation is the difference in the elapsed time as measured by two clocks. It is either due to a relative velocity between them (special relativistic "kinetic" time dilation) or to a difference in gravitational potential between their locations (general relativistic gravitational time dilation). When unspecified, "time dilation" usually refers to the effect due to velocity.
After compensating for varying signal delays due to the changing distance between an observer and a moving clock (i.e. Doppler effect), the observer will measure the moving clock as ticking slower than a clock that is at rest in the observer's own reference frame. In addition, a clock that is close to a massive body (and which therefore is at lower gravitational potential) will record less elapsed time than a clock situated further from the said massive body (and which is at a higher gravitational potential).
These predictions of the theory of relativity have been repeatedly confirmed by experiment, and they are of practical concern, for instance in the operation of satellite navigation systems such as GPS and Galileo. Time dilation has also been the subject of science fiction works.

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  1. T

    Combining time dilation and length contraction

    So, I am having trouble understanding how time dilation and length contraction in special relativity merge together and describe space-time. I guess the best way to ask this question is to pose a question, which i know how to answer mathematically, but I would like to discuss some thoughts about...
  2. A

    Effect of gravity on time dilation.

    Can anyone tell me What is the relationship between the orbital radius of a satellite and the time gained per second due to its weaker gravity at its altitude? In relation to that how much time does the International Space station lose per-second due to weaker gravity at its altitude? Also...
  3. N

    Time Dilation: Impact on GPS Accuracy

    Hey there guys I just have a question to ask some of you. Given the occurence of time dilation being related to an objects state of motion I have an interesting thought. This is a very general question, my teacher only briefly covered this topic in class as it's not part of our course but it...
  4. D

    Does expanding space affect time dilation etc?

    In special relativity we have the velocity 'u', being the difference in speed between two objects, from which we work out time dilation, length contraction etc. But if those objects are separated by some expanding space, but not moving with respect to that space, is there still the dilation...
  5. G

    Size and Time Dilation: How Perception of Time is Affected by Size | GRB

    Hello all. Not sure if this is the right place for this question, or if it even makes sense. This is my first post since registering a week ago, however I have been lurking and reading on here for a while. Great site! Lots of good information on here. Anyways, I have been thinking about...
  6. A

    Time Dilation and the Flawed World Record Attempt: A Physics Explanation

    An athlete has learned enough physics to know that if he measures from the Earth a time interval on a moving spacecraft , what he finds will be greater than what somebody on the spacecraft would measure. He therefore proposes to set a world record for the 100m dash by having his time taken by...
  7. A

    TIME DILATION. WHY do clocks that are

    moving closer to light speed relative to another clock tick slower? I understand that the waves take longer to reach the stationary observer on the turn around, but that's just appearance. It still seems the clocks would be in sync upon the return. What is making time actually slow down...
  8. L

    Understanding Time Dilation: Explained with an Everyday Example | Help Needed"

    Time Dilation --- Help needed Homework Statement Time dilation says, " Moving clocks run slow". Homework Equations The Attempt at a Solution For example, a stationary clock shows 4 PM and at the same 4 PM a spacecraft moves with a clock inside it showing the same 4 PM. Now after...
  9. U

    Time dilation, mirror question

    I only know time dilation in it's basic form and it was explained to me beautifully using mirrors in a spacecraft . The light would go vertically, taking longer if you were at a stationary frame looking into the spacecraft . This all made sense to me; however, what would happen if the mirrors...
  10. R

    How do I calculate time dilation due to acceleration in SR please?

    2 space stations are separated by a distance of 10 light years and are at rest wrt each other. I set off from A to B at a constant velocity of 0.5c. As I understand it, 20 years would pass for people on the space station but when I arrived at the second station I would have only aged about...
  11. C

    Not Understanding Time Dilation - mk 2.

    Further to the other current thread, I have a different 'don't understand' issue for time dilation. I've thought it over and I might have a slight grasp of 'the answer', but it is still a bit murky for me: Two space ships of the future pass each other in opposite directions, each traveling at...
  12. T

    Not Understanding Time Dilation.

    Hey there, guys. I’m kind of new to the whole physics thing, but I am starting on a quest to try and learn as much about how this universe works as I can. I am currently working on developing a good understanding of special and general relativity. I am not overly math-competent, so I have been...
  13. 3

    Newbie question - Conceptualization of time dilation from matter's perspective

    Newbie question -- Conceptualization of time dilation from matter's perspective I have only a slight familiarity with classical physics, and in trying to conceptualize time dilation in a more intuitive, concrete manner, I attempted to explain time dilation from matter's perspective. What I...
  14. J

    Our 'Background' Speed and How it Fits with Time Dilation

    me: layman's understanding of physics and mathmatics My (very basic) understanding for this question is that: a higher rate of (objective) motion = lower rate of time for anything with mass. Is there a working figure for how much motion we experience per a specific time period from such...
  15. R

    Confusion regarding Time dilation ?

    a situation of twin paradox one twin alice is moving with 99%C another john is at rest on Earth this means 1 second of alice= 100 secs of john (approx) suppose john runs at the speed of 1 km/s for 100 secs then for alice he is at 100 km/sec as she saw the whole what he did in sec and...
  16. B

    Time Dilation Concept Confusion

    Recently I've watched a few videos and read over some explanations of time dilation and am quite confused by several aspects. In the video I watched, the clock tracked time by a beam of light bouncing between two metal plates, incrementing one second per touch of the bottom plate. The path of...
  17. A

    Time Dilation Problem; Find the proper time, ts.

    Homework Statement Alpha Centauri, the closest star to Earth, is 4.3x10^6 m away. How long would it take a spaceship to reach the star if it were traveling at 0.999c? Homework Equations I did get the answer as 0.2a...and the textbook also said it would take about 2 months, I do not...
  18. E

    Need help resolving this paradox with time dilation

    Before I post this, I want to assure everyone that I am not a conspiracy theorist who doubts Einstein or relativity theory in any aspect. I just don't understand special relativity as well as Id like to and I think having this paradox resolved in my mind will help. The paradoxes that I've...
  19. Ryan_m_b

    Exploring Time Dilation: The Case of Alice and Bob

    I understand that the faster one goes the slower time goes but a thought popped into my head recently that I couldn't resolve; Alice and Bob are at rest relative to each other in an otherwise empty universe (i.e no point's of reference). Suddenly Alice observes Bob moving away from her at...
  20. A

    Gravitational Time Dilation - Is my head older than my feet?

    According to general relativity, objects in a strong uniform gravitational field experience time slower that objects in a weak uniform gravitational field. Does this mean that my feet, being closer to the Earth that my head, are younger than my head when I die? If this is correct could someone...
  21. H

    Which Clock Slows Down with Time Dilation?

    If you send an ultra precise clock circling at a huge speed on a train and leave a clock stationary near the rails and then compare them,there would be a small difference in the time they display,right?But if everything is relative,doesn't that mean that from the point of view of the people in...
  22. B

    Question on Time Dilation Experiment

    If time is slowed for an observer circling the Earth and we put an observer on the earth, sun, center of the milky way and finally the center of the universe then would it be correct to say that time would be moving fastest for the observer at the center of the universe? If so is it possible...
  23. J

    Understanding Time Dilation Formula: Exploring the Effects of Speed on Time

    The time dilation formula: \Delta t'=\frac{\Delta t}{\sqrt{1-\frac{v²}{c²}}} says that the closer you come to the speed of light the slower time goes (for the object in movement). That mean if you travel to a distant star in very high speed, there will take shorter time to get there (for the...
  24. Z

    How Does Gravitational Time Dilation Relate to Gravitational Red-Shift?

    Einstein introduced the concept of gravitational time dilation. I get the impression that it was determined to be a consequence of gravitational red-shift. Can anybody tell me the logical reason why gravitational time dilation follows on from gravitational red-shift? Or was the existence of...
  25. S

    Wrong Time Dilation: Why Observers Disagree

    Hello ! Can you tell me what's wrong? I suppose two observers. They measure speed of light. One observer is in rocket of length L. Observer in rocket measured speed C'=\frac{L}{t'} and t' is time from observer's view. Second observer is outside. He measured C=\frac{L+vt}{t} where v is...
  26. D

    Time dilation/ light speed-thought experiments

    There are a few things bothering me about time dilation, its derivation, and special relativity. Einstein started with the assumptions that light travels at a constant speed no matter the observer or their frame of reference. He then details the light box experiment in which two observers are...
  27. R

    A problem with time dilation help?

    A problem with time dilation help!? when we move with light our time is slower and when we move against it then it's slower but what if we move at 99%C in a direction and a light ray is move with us and another light ray moves opposite from our direction simultaneously?
  28. D

    Basic questions on time dilation (probably already answered, sorry)

    New to PF, and while I don't know much about the science behind these things, I do come in peace. I have more a philosophical understanding of special relativity, never having worked out a formula, and can't even understand the language of those physics equations. I do, however, grasp the...
  29. M

    Scenario where time dilation seems to be paradoxal

    Imagine the following scenario: There is a train, that crosses the entire planet, and has the length of the Earth diameter (has no start or no end, it's like a "ring"). This train has in the floor a treadmill that runs in the opposite direction of the train. Also, the treadmill has the length...
  30. G

    Time dilation plus constancy of light implies space is dilated?

    Dear all, I've read the following argumentation for curved spacetime: 1) From the equivalence principle one can derive that time is dilated in gravitational filed.. 2) The velocity of light is constant for all local observers 3) If time dilates, then also space must dilate if one wants the...
  31. B

    Would gravitational time dilation prevent Singularity in a black hole?

    In the current mainstream theory of black holes, there exists a singularity of infinite density. However, it seems to me that matter actually could not compress tightly enough to reach this point. As matter coalesces in a black hole, space-time would increasingly curve. As the density...
  32. A

    Time Dilation and Death: Understanding the Effects of Gravity on Aging

    lets say that there is a triplet at the age of exactly 60 years old.one of them A is in space far away from any gravitational field and not moving , B is on planet earth,and C is near a black hole. C looks at A and see that for every 10 min passes according to his clock(hand and biological) A...
  33. P

    Gravitational time dilation on cylinderical objects

    I am simply looking for the formula to work out the time dilation on cylinders with uniform density. Also, any links to arbitrary precision calculators would be appreciated.
  34. V

    Time dilation and twins paradox

    "The confusion that arises in problems like Example 26.1 lies in the fact that movement is relative: from the point of view of someone in the pendulum’s rest frame, the pendulum is standing still (except, of course, for the swinging motion), whereas to someone in a frame that is moving with...
  35. B

    Time Dilation - Is this a paradox?

    [PLAIN]http://www.science27.com/forum/rocketL2.jpg Above the head of observer “A” a mother-ship is moving east 100,000 km/s. and right above the Earth it is launching a small spacecraft moving west with the same speed (100,000 km/s). REFERENCE FRAME A Observer “A” would now (from...
  36. J

    Gravitational time dilation implies energy change?

    According to Einstein's Gravitational Time Dilation, if an oscillating physical system is elevated to a height H above the Earth then it oscillates at a higher frequency than the same system at ground level. According to Planck's relation between energy and frequency this surely means that...
  37. A

    Exploring Time Dilation and Mass

    Hello, I don't know if this is the right place to come for my type of question but its the place that made sense to me so here it goes. I know that time stretches out when traveling near c (I am familiar with Einstein's twin paradox), however I remember somewhere I heard that objects with a...
  38. N

    Wikipedia: using the four-velocity to understand time dilation (?)

    Hello, I was wondering if the following quote by Wikipedia (http://en.wikipedia.org/wiki/Four-velocity section "Interpretation") makes sense: Cause I would think it doesn't make sense: in this reasoning they're acting as if the norm is something like a^2+b^2+c^2+d^2, so that if...
  39. K

    Exploring Time Dilation Symmetry: A Case Study of a Rocket Traveling at 0.8c

    Homework Statement Hi, I have a problem connected with time dilation symmetry, which is supposed to be explained in a following example: A rocket traveling at 0.8c starts from station P and is directed to station Q 864 million km away. Time taken to travel as measured by space station clocks...
  40. C

    Lenght contraction of a charged wire and time dilation?

    In my class we were doing examples with a current carrying wire and if we moved with a speed v we would see length contraction. And because of this the moving line charge would go up in value and we would see an Electric field. And then we did the same for a solenoid but he said we need to...
  41. B

    Why does time dilation create a velocity barrier but not a density barrier?

    Please explain to me what I'm missing: You can't go faster than the speed of light, because of time dilation. The faster you go, the slower time moves for you as compared to objects at rest, and time would stop for you if you ever went the speed of light. That's what makes C the universal...
  42. V

    Length Contraction and Time Dilation

    Length Contraction and Time Dilation Gamma= 1/sqrt(1-v^2/c^2) = 2 (Assumed) We have L=L’/Gamma…………………………………….1 And dT= dT’ * Gamma ………………………………2 Let primed frame is that of Bob and unprimed that of Dave. Let us define identity as an equation in which values on both...
  43. D

    Ambiguity in time dilation due to relative velocity

    I would like to see some comments on this observation that appears to lead to an ambiguity re: time dilation: The usual definition for time dilation is the expression: t =t'/(1-V^2/c^2)^1/2 where an individual in the unprimed coordinate system "at rest" in empty space, sees a clock in the...
  44. R

    How Much Longer Does an Atomic Clock Run on the Moon Compared to Earth?

    Hi All I whish to know how much longer an atomic clock will run on the moon than it does on the earth. Considering time on Earth for 1 second, I know it will be very slightly longer on the moon. How much longer is my question, or maybe an equation. Don't consider the travel there, start...
  45. C

    Why is the Speed of Light Constant in Time Dilation?

    So when we derive time dilation, and when we have a train moving and we shoot a light beam from the bottom to the top, to an outside observer not on the train he will see the light leave at an angle. So my question is why don't we factor the horizontal speed of the train in order have the...
  46. R

    Time dilation & length contraction

    Hi guys and girls. Need some assistance with these problems, not the hardest examples, but I need some help on the way. Homework Statement 1. An astronaut travels at 0.9c across our galaxy, which is 100 000 light years in diameter. How long time will it take (according to the...
  47. A

    [Special Relativity] - Time Dilation

    Homework Statement If a cosmic ray proton has 15J of energy how long, according to the proton's proper time would it take to travel from the galaxy M31 to our Galaxy, a distance that we mesure as 2.5x106 light-years? Homework Equations K.E = m_{o}c^2 (\gamma -1)The Attempt at a Solution I...
  48. R

    Do Twins Age Differently in Space Depending on Their Travel Path?

    I was wondering, imagine if I had twin brothers who each set off in their space ships at the same time, at a speed of 0.5c. One traveled 20 light years in a straight line, then turned around and traveled 20 light years back to me, the other traveled along a complete circular path, with a...
  49. J

    Time Dilation Puts Two Observers at different Times?

    Okay. A man in a spaceship travels at \beta=\frac{\sqrt{3}}{2} giving him a Lorentz Factor of \gamma=2 and a time dilation of t'=2t Another man sits "stationary" in space. After traveling for one of the stationary observer's seconds the moving observer passes by the stationary...
  50. Z

    Question about time dilation in the schwarzchild metric?

    My first question is the following. Does the radial component of the schwarzchild metric account for just the radius of the body in study or is it the distance between the body and the observer, where the body is treated as a singularity (Point mass particle)? My second question is about how...
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