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. L Drago

    B Time Dilation in Black holes

    If I have any misconceptions or misunderstanding kindly point it out and explain it to me.
  2. DaveC426913

    B How far away can a World So Newly Born Be at relativistic velocities?

    The premise (bear with me): In the year of '39 assembled here, the volunteers In the days when lands were few Here the ship sailed out into the blue and sunny morn Sweetest sight ever seen And the night followed day, and the storytellers say That the score brave souls inside For many a lonely...
  3. M

    Pendulum on moving train

    The problem and solution are, However, I don't understand why the answer is correct. I think that time should be dilated since ##\Delta t = γ \Delta t_0 = 2γ## where ##γ \geq 1## for ##v \geq 0##. Does anybody please know what I'm doing wrong here? Thanks!
  4. cianfa72

    I Is time dilation a real effect?

    In the context of SR we know time dilation is basically the rate of change of moving clock's proper time w.r.t. the inertial frame coordinate time. It does mean that in principle the "tick events" of moving clock are compared against the time measurement of clocks Einstein's synchronizated in...
  5. Somoth Ergai

    B Entering a black hole -- I know I must be wrong (Help me understand why)

    From what I understand about time dilation and the relativity of simultaneity; if we imagine two people near a black hole and one of them begins to approach the black hole on a trajectory that crosses the event horizon. The stationary observer will never see the moving observer enter the black...
  6. R

    I A question about Relativity of Time using Time dilation experiment

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  7. MatinSAR

    Question about time dilation

    My try which was failed : Observer at rest measures time ##\Delta {t'}= 2.2 \mu s## In the frame of reference of the Earth observer measures time ##\Delta t=\dfrac {\Delta {t'}}{\sqrt {1-u^2/c^2}}## I have two unknowns ##u## and ##\Delta t## so I cannot find ##u##. Is there another equation...
  8. F

    B Question about "odometer" analogy and time dilation

    Hey again physics forums! I'm just a lug who likes watching science videos and appreciates the occasional answer to questions that pop up as I watch them. This morning I came across a video that explained time dilation really well by using an odometer analogy, that a clock is like an odometer...
  9. H

    I What causes time dilation and length contraction

    This Video [Moderator's note: Unacceptable Reference removed] right here is describing a way of understanding SRs time dilation and length contraction. He tries to explain the phenomena with aether theory and argues that light does not have/is in a preferred frame of reference. So some context...
  10. M

    B Would We See the Same Light After Traveling Back to Earth Faster Than Light?

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  11. S

    Calculating Time Dilation for Space Travelers

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  12. G

    Time slows down at lower gravitational potential

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  13. I

    I What Happens When an Object Accelerating Away from a Black Hole Stops?

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  14. C

    B Question about choice of reference frame

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  15. C

    B Help understanding the Relativity of Simultaneity

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  16. C

    B What does symmetry of time dilation really mean?

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  17. C

    I Question about time dilation symmetry

    Hello everyone, Suppose there is an airplane that is taking off from an airport but before it takes off it synchronizes it's clock to zero with the clock at the airport. In the rest frame of the plane the airport is moving, so you could argue ##T_{plane} = \gamma*T_{airport}## In the rest...
  18. C

    B Question about Morin's time dilation explanation

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  19. M

    B Intuition for time dilation in a cesium clock

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  20. M

    B A well defined thought experiment

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  21. patdolan

    I What about the Big Ben Paradox?

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  22. C

    I Question about the reciprocity of time dilation

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  23. C

    I Question about length contraction

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  24. Hak

    B Does Time Move Slower for Travelers in Special Relativity Experiments?

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  25. BadgerBadger92

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  26. M

    B Is velocity the reason for the time dilation effect?

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  27. J

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  28. L

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  29. Josh S

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  30. D

    Measuring Time Dilation from 25Kg Lead Brick w/3 Cesium Oscillators

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  31. T

    I Is anything not spinning in the Universe?

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  32. D

    B Time dilation in a planet-moon system

    In Wikipedia time dilation is considered: As far as I know, in a planet-moon system, the difference in elapsed time between a clock on the planet and a clock on its moon is calculated using GR/proper time, so it's not very obvious if/how the movement/velocity of the moon around the planet...
  33. jaketodd

    B Transfer speeds of forces affected by time dilation?

    Are forces subject to the Lorentz transformation? Not force carriers; I already got that question answered, thanks to @PeterDonis. But forces. The different forms of them, such as the contact forces etc.: https://en.wikipedia.org/wiki/Contact_force With time dilation, does the rate of force...
  34. joshuadeepak

    B Time Dilation in Non-Stationary Reference Frame: A, B, C

    Let's consider three observers A, B and C. The experiment starts at t = 0. A is 'absolutely' stationary. B immediately (please imagine it) starts moving at speed v1 with respect to A. C immediately starts moving at speed v2 with respect to A in the same direction as B. Let's say A measures a...
  35. S

    B Understanding Time Dilation: How Passing Photons Affect Time Measurement

    Now if two different time durations are measured for one and the same event by two different observers, for example T+1 and T-1 seconds. Is the speed of passage then (T x c)/(T+1) and (T x c)/(T-1) respectively? So not c? You may be wondering…, and yes, there is an example of it!
  36. V

    B Triplets Paradox: Is There a Solution?

    One person (A) stays on Earth, while another (B) goes on a long journey and returns later. We can calculate the time interval for A and the proper time interval for B. Let's say we get Δt=100y and Δτ'=50y. We then consider a second traveler (C) going on a different journey, departing and...
  37. V

    Does Time Dilation Differ Between Earth's Day Side and Night Side?

    I’m physics curious and a middle school science teacher. I was wondering about time dilation on day side of Earth vs. night side. Pervect gave an interesting response on the subject in 2005, complete with link. The link doesn’t work and I cannot find the paper on OpenSky. I’m hoping someone can...
  38. E

    I Sabine Hossenfelder says time dilation is due to acceleration

    Sabine Hossenfelder says time dilation is due to acceleration in the twin's paradox. Is this true? At 12 minutes into this video , Hossenfelder states, "This is the real time dilation. It comes from acceleration." Looking at the equations for time dilation, time dilation comes from...
  39. G

    B Time Dilation: Is This a Reasonable Explanation?

    I thought of this description recently and I think it's pretty intuitive, but I've gotten some side eye telling it to friends and family (maybe because relativity is screwy, maybe because I'm confused, maybe both?) so I want to get some confirmation that it's reasonable. Here goes: If you're in...
  40. G

    Time dilation for a clock thrown vertically

    The non-moving clock will see the other one move upwards and land as predicted by Newton's laws, so using the equation ##z=v_0t-\frac{1}{2}gt^2##, and assuming the moving clock starts at ##t=0##, it will land at ##t=\frac{2v_0}{g}##. Now, using SR only, and the Minkowski metric (with signature...
  41. doudou

    B Explaining Distant Time Dilation & Enhanced Gravitation

    When we observe distant time dilation effects, usually indicated by redshift, there are three possible explanations: 1) The speed of light, is slower there and then; 2) Space, is contracted for light there and then; 3) The frequency, of specific light is slower there and then. However, it is...
  42. T

    B Is Time Dilation About Particle Motion Rather Than Time Itself?

    Hi, i am not a physicist but i have the intuition that time dilation is just slow in the movement of particle's and causality instead of slow in time itself and that this does not affect photons. I understand that there is no way to distinguish between a slow in time and a slow in movement and...
  43. AtoMick-u235

    B Mick's Spooky Time Dilation Puzzle

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  44. I

    Effect of time dilation on Earth/space communication?

    Let's say there is an audio oscillator on earth sending a 440 Hz audio tone over radio to a spacecraft. There is also an audio oscillator on the spacecraft sending a 440 Hz audio tone over radio to earth. Time is slower in the high gravity of earth than the weak gravity in space. Is the 440...
  45. I

    I Time Dilation Paradox: Geosynchronous Satellites

    Time moves faster when higher above the earth. Time move slower the faster you are moving. A geosynchronous satellite has to be very high to be geosynchronous so it's time should be fast, but it also has to be orbiting the earth extremely fast to keep up with a geosynchronous position, so it's...
  46. R

    I Muon Decay Example from Morin's Book: Issues Explained

    From the Lorentz transformation equations we know that $$t = \gamma(t^{'} - x^{'} v/c^2)$$ but for the Muon decay example where the setup is as follows : "Assume for simplicity that a certain muon is created at a height of 50 km, moves straight downward, has a speed v = .99998 c, decays in...
  47. C

    I Effects of time dilation for near-speed-of-light travel

    Hello everyone, I've been learning about special relativity, and so far I believe based on what I read that if you are traveling at a velocity of .6c, you will experience time 20 percent slower than people on earth. Each second in the spaceship will be 1.25 earth seconds. Each second on earth...
  48. marcosdb

    I Time dilation from galactic gravitational mass

    I've been thinking about how rotational speeds don't fall off high distances from galactic centers, for which dark matter is generally an explanation for the increase in acceleration Speed = distance / time But time is relative What "time" is used in these calculations? Wouldn't time be...
  49. Lotto

    B Time dilation - what is the time on the Earth?

    If I understand it well, 10 s did really passed in the rocket, it is according to the observer on the Earth, but if the man in the rocket measured the time, he would measure 10 s. But when we say that the man in the rocket is in an inertial frame of reference as well, he can claim that because...
  50. T

    I Time Dilation & Length Contraction: Graphically Explained

    The thread "twin paradox without math" inspired me try to find fully graphical solution of length contraction. Here is the result: Graph is 3D as I think that is ilustrative to make all in one graph, but I am sure that it is possible to do it in 2 or 3 2D slices. X and Y are spatial axes, T is...
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