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. Petr Matas

    I Does time dilation prevent event horizon formation?

    I read that time dilation near a black hole's event horizon causes the infalling matter to "freeze" just above the event horizon and never cross it (in a distant observer's frame of reference). Doesn't the same phenomenon prevent the event horizon and singularity from being formed in the first...
  2. Stephanus

    B Exploring What Happens Inside Event Horizon

    Dear PF Forum, What happens inside Event Horizon? 1. Will clock stop inside EH? An object crosses the EH of a black hole around 1 billions solar mass which its Schwarzschild Radius is 3 billions km. It takes light to cross that distance (in 'normal' space) 30 thousands seconds. The time for an...
  3. P

    B Does time dilation work this way?

    Suppose, a ball is thrown upwards. The proper time interval between the throw and the instant at which it attains max height is t. And, the dilated time interval between the same events for a different moving observer is 2t. Now, my question is: Both observers see the same instants happening...
  4. F

    B Examining Time Dilation and the Effects of Velocity on Perception of Time

    In explaining time dilation we usually say, if velocity of A is greater than velocity of B, then time is slower for A as compared to B. However, if vA> vB, using the equation for time dilation, tA>tB. So if 60 seconds passed for B, 100 seconds passed for A. How does that imply that time slowed...
  5. Klairence Leitch

    Time Dilation in the same frame of referance?

    Homework Statement A rocket ship is accelerating through space. Clocks P and Q are at opposite ends of the ship. An astronaut inside the rocket ship is beside clock P and can also observe clock Q. What does the astronaut observe about the passage of time for these clocks? Justify your answer...
  6. victorhugo

    B Mutual time dilation seems to be self-contradictory?

    The first thing I want to say: time dilation doesn't make any logical sense. If one's time is going slower than the other, how could they both see each other's time going slow? if not, then there's a way to tell who's moving as one would see the other in fast motion.
  7. J

    I Time dilation (something seemingly paradoxical)

    Hello. Consider the following case: Two observers, A and B, moving relative to each other with velocity v. For B, it's A that moves (with v) and so DTb=g*DTa (where DT denotes finite time difference and g is/the Lorentz factor gamma). So, (following the same logic as in Morin's Classical...
  8. P

    I Is there any way to derive the time dilation formula?

    I've already read the derivation in which we use the light pulse clock kept in a spacecraft such that the light pulse follows a zig-zag motion due to motion of the spacecraft being perpendicular to motion of the light pulse. Then, we apply Pythagoras theorem to derive the formula. BUT this...
  9. P

    B How can time dilation be the same for both observers?

    Here, I'm not talking about the twin paradox in which one of the observer's frame gets accelerated. I'm talking about the case in which they just move relative to each other without accelerating. I'm having some confusion. Please tell me where I'm wrong: 1.There are two people, Dick and Jane on...
  10. K

    Lorentz Transformation, Time Dilation, Length Contraction

    Homework Statement [/B] A spaceship is approaching Earth from the far side of the sun. The Earth and sun are 8 light minutes apart and the ship is traveling at .8c. Two events are indisputable. 1) the ship is at the sun 2) the ship is at the earth. Assume that the Earth and sun are at rest...
  11. V

    A Time dilation for the clock in the orbit

    Suppose that we want to compute the total time dilation for a clock located in an orbiting satellite relative to the clock in our cell phone on the ground. Consider two different approaches below. 1. Use special relativity and compute time contraction due to velocity. Use approximation of...
  12. adamaero

    Light hours special relativity time dilation

    Homework Statement http://phy240.ahepl.org/Chp1-Relativity-Serway.pdf#page=39 #32 Planet R is 25 lighthours away from Earth. It takes 25 h (according to an Earth observer) for a spacecraft to reach this planet. The clocks are synchronized at the beginning. What is the spacecraft 's time...
  13. K

    I Time Dilation Between Astronaut A and Person B

    Definitions: Astronaut is A Person on Earth is B A travels to a star far away at near light speed, A would see B's time dilate. B would also see A's time dilate Twin paradox revived: What would happen if A returns to B at a very slow speed? Then both frames of reference would see each others'...
  14. hsdrop

    B Time Dilation: Effects on Spinning & Vibrating

    I know that time dilation effects everything that moves in relation to everything else that's around the thing that moving. Does that also include vibrating and spinning thing and if it does how so?
  15. M

    Length contraction and time dilation from Lorentz S

    I'm trying to understand special relativity well enough to explain it to others, ANY others, including myself. I am trying to use Robert Resnick's Introduction to Special Relativity to inform my thinking. In introducing length contraction, he introduces L' as the length measured by an observer...
  16. Punit D

    I Time Dilation Observation: What Does Earth Observe?

    I'm wondering if anyone can answer this question for me. Suppose we send a spaceship to the moon at 299,792,457 m/s (1m/s less than c). That's 99.9999997% of the speed of light. Plugging the numbers into the time dilation formula, we get that the 1.2822 seconds that it takes for the spaceship...
  17. Tazerfish

    B Derivation of time dilation without light clocks

    In the way I was taught about special relativity, time dilation is like the fundamental building block from which you derive things like relativistic mass and length contraction. So it has always struck me as quite odd, that the derivation of time dilation (in some sense the basis of special...
  18. Grayman

    B Problem with the atomic clock and time dilation

    The atomic clock is used as evidence of time dilation and to provide more evidence that light speed is invariant. The problem I have with this is that the clock uses frequency and light. It has a feedback loop that is supposed to correct for inaccuracies but the entire loop will obviously be...
  19. Looeelooee1

    B Solving Weird Time Dilation Question w/ Spaceships

    I put the prefix as intermediate because I wasn't really sure how complicated of a question this is, I am currently a junior in high school... So basically if you were to have two spaceships with people the exact same age in them traveling at 99% the speed of light and they were traveling...
  20. AlgoJerViA

    Time loops, black hole and time dilation.

    Hi I hope this is the right place for this questions, I started to think about this several years ago but had has a hard time finding anyone that's been interested in discussing this. As far as I understand time travel is not ruled out by modern physics at least if you limit yourself to go into...
  21. G

    B Does gravitational time dilation cause gravity's attraction?

    Physics Videos by Eugene Khutoryansky (a widely respected channel) recently posted a video on YouTube suggesting this. I know that gravitational fields cause time dilation (with time passing more slowly the closer an object is to the centre of gravity, relative to more distant observers), but...
  22. S

    B Help Understanding special relativity

    I'm trying to understand something about relativity that doesn't seem to add up. I will extend Einstein's carriage example to incorporate 4 clocks. At the beginning all these clocks are running at the same time when they are together. I put two of the clocks far away from each other (100 km...
  23. G

    I Exploring Time Dilation: The Effects of Temperature on Clocks

    Hi. Temperature is movement on a microscopic scale, and movement leads to time dilation. So what happens if we heat up a clock? Let's for example assume a pendulum with negligible thermal expansion, such that all other thermal effects on the period can be neglected. Will it run slower? What...
  24. D

    I Relative Velocity Time Dilation: Experiments Disproving Theory?

    I have a question regarding time dilation due to relative velocity. (It's just about time dilation due to velocity not about gravitational effects.) I have seen a theory where time dilation is not relative, but always considered against an absolute frame of reference. The absolute frame of...
  25. T

    B Gravitational time dilation depth charge

    Hi. A student wishes to test gravitational time dilation near a black hole within her lifetime, so she travels to a location where a black hole is said to reside and parks her ship at distance where she is not affected by the hole's time dilation effects. She then fires a tethered capsule...
  26. C

    B Light follows Geodesics-Spacetime-Big Bang-Time dilation

    I have these questions: 1) Why must light always move along a geodesic line? What is the principle behind that? 2) A second question about spacetime: We mostly depict or imagine spacetime as a net of flexible fiber that extends everywhere as a plane as we see it.. As we are looking it, what...
  27. robphy

    Insights Relativity on Rotated Graph Paper - Comments

    robphy submitted a new PF Insights post Relativity on Rotated Graph Paper Continue reading the Original PF Insights Post.
  28. steveJOBS

    B Is there an opposite phenomenon for time dilation ?

    Can there be a phenomenon that has the opposite effect as that of time dilation ?
  29. S

    B Observeving Black Hole and Time Dilation Question

    Hello all, Thank you for taking time to read my question. I am curious, what happens if following criteria is met; 1. Place a indestructable stopwatch inside the black hole set it to 5 second 2. Place another stop watch outside of black hole and set it to 5 second 3. Place a...
  30. S

    I Exterior Schwarzschild Solution & Gravitational Time Dilation

    I've been looking in depth into the exterior Schwarzschild solution of the Einstein field equations. I decided to play with the line element by creating some example scenarios for myself and calculating the space-time interval between two events in these scenarios. Here is the line element: ds2...
  31. KiltedNinja

    Time dilation/difference between 2 planets

    Hi folks, I'm writing a story which involves civilisations across multiple planets, and I've been trying to work out the impact of time dilation between them. I'm hoping someone can help me out here (thanks in advance!). (I'm not sure if this exact question may be applicable to one of the...
  32. G

    I Minkowski diagrams without scales on axes

    Hi. I have seen quite a lot of demonstrations of time dilation and length contraction that used standard Minkowski diagrams WITHOUT any scales on the axes at all. If I understand them correctly they seem to directly compare lengths, which would imply (I think) that the scaling on the ##ct/x##...
  33. Quandry

    I Time Dilation Explained: Muon Decay & Reaching Earth

    As I understand it muons have a half life of 2.2 microseconds, thus, at the speed of light cannot get to the earth. But based on exponential decay, of every billion muons which head or way, about 70 will actually get here. Using time dilation the full billion will get here. Do we need a billion...
  34. E

    I Time Dilation & Differential Aging: Defined

    I’ve been told that “differential aging” and “time dilation” are two different things. I had thought that one was the integral of the other. Can anyone give a PRECISE (mathematical!) definition of each, what the distinctions are between them? Thanks. (How the heck am I supposed to know what...
  35. E

    B Time Dilation Model & Wave Interference: Newbie Questions Answered

    I have some newbie kind of confusion The model in question is taken from wikipedia: and If, in the first model, the light ray is reflected back to its source, could there be some kind of detectable interference at the midpoint (where the blue arrows are)? If the answer is yes, would this...
  36. M

    B Calculating Mass for Gravitational Time Dilation

    Hello all. I'm trying to determine the mass of an object required to make it so that a traveler on a massive planet experiences 1 day but on earth, or some infinitely distance away from the planet, 1000 years passes by. I'm using the following equation: t0 = tf*root(1-(2GM/rc^2)) Found here...
  37. philipp

    I Time dilation in special vs. general relativity

    Hi all, I was trying to understand the time dilation in special and general relativity and after much time of "overthinking" I am pretty much stuck now. My problem is, that what seems to me to be the same premises apparently imply opposite things. In special relativity, for two inertial...
  38. N

    I Why does time dilation affect all clocks equally?

    Hello. There is a question that I've been trying to understand for about a year. Why is it that the time dilation effect applies equally to all clocks as it does with "light clocks". For example, if John is moving on a spaceship with respect to Alex who is on earth, and both are sitting next to...
  39. K

    Time Dilation particle lifetime

    Homework Statement An unstable particle with a mean lifetime of 4 microsecond is formed by a high-energy accelerator and projected through a laboratory with a speed of 0.6c a. What is the mean lifetime of the particle as determined by an observer in the labratory b. What is the average...
  40. G

    I 2D Time dilation simulation with several clocks?

    Hi, I'm looking for some kind of simulation for time dilation where you can add several clocks to a 2D plane, synchronize them, give them velocities and accelerate them. For example to simulate the twin paradoxon including the acceleration necessary to (at least) one clock to reunite them. I...
  41. D

    I Time dilation in relativistic Doppler effect

    Hello, It kind of bothers me that the derivation for the Lorentz transformation relies on two dimensions of space. (Here I am referring to the standard derivation where one person is using a vertical light clock in a trolley traveling horizontally at speed v, and an observer outside is...
  42. E

    I How does gravity affect time on different planets?

    If a planet has gravity that is 3,000 m/s^2 instead of 9.8 m/s^2, would time passage be significantly different, or what would one second on Earth be compared to one second on that planet?
  43. F

    B Time Dilation & Relativity: Going Back

    I've read many explanations of time dilation and relativity, that describe things from the point of an observer, and then some other object moves away from it at some fraction of light speed. i.e. say a spacecraft moves away from an observer at 0.1c for 1 year ship time. Then presumably, to an...
  44. G

    B Magnitude of gravitational time dilation

    Hello, I am wondering how is the magnitude of the time dilation in a gravity field related to the time dilation we know from special relativity. How does the dilation caused by just being in the field compare to the dilation you'd have from your velocity if you fell into the gravity field from...
  45. Dyatlov

    I Time Dilation: Lorentz Transf. & Proper Time Equations

    Hello! Got a bit of an issue with thew two above mentioned equations about time. From the Lorentz transformation t' = [t - (vx)/c^2]/lorentz factor, we get that the time read by a moving observer for an event in the stationary observer's frame of reference will always be slower (longer) because...
  46. J

    I Time Dilation in Hypothetical Faster-than-Light Travel

    This sounds like a homework question, but I promise you it's not (I'm not even a student). To be honest, the question is simply for my own personal curiosity, to test a theory about a video game. My question is this: If an astronaut traveled for 15 years (their time) at twice the speed of...
  47. Jonathan Densil

    B Using Lorentz Transformations vs Time Dilation/Length Contraction

    Hey guys, In what circumstance or scenario would you use Lorentz transformations as a opposed to time dilation or length contraction? The reason that I ask this is because in all of the problems that I have worked with, the observer is always stationary relative to the event. For example, if...
  48. Josh_H

    B Where is the slowest point in terms of time?

    If moving inside the event horizon of a super-massive black hole and theoretically surviving we could see the universe pass by at millions of years per second relative to someone on earth, where could we go where time passes at a much faster rate than someone on earth? For example where 2...
  49. Jefffff

    Special Relativity and Space-Time Diagrams

    Homework Statement [/B] S' is moving at 0.5c relative to S. Two events, stationary with respect to S, occur at a distance of 4 light years from the origin at time 3 years and 6.5 years. Estimate the time between the events as measured by an observer in S'. Check your solution with the time...
  50. Benoit

    I Why is B's clock in advance instead of A's?

    Are you good with Lorentz' tranformations ? I tought I was, until I tried to do this exercice (it is really classical): Two planets, A and B, are at rest with respect to each other, a distance L apart, with synchronized clocks. A spaceship flies at speed v past planet A toward planet B and...
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