What is Dilation: Definition and 1000 Discussions

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. S

    Falling Into a Black Hole: Time Dilation & Survival

    So for an outside observer it appears someone falling into is slowing down and then gets redder and redder. But what about for the local observer? From the perspective of the person falling I would imagine that the universe would appear to speed up tremendously. Is it possible you could survive...
  2. Isaac0427

    How does the time dilation equation work?

    Hi all! I've been doing some studying length contraction and time dilation and I came across this link http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html . I completely understand what it did with length contraction but when I got to time dilation I couldn't figure out one thing. They...
  3. S

    Time Dilation for Interplanetary Migration: Can We Go?

    In various documentaries they bring up the argument that we won't be able to visit other stars because even if we would travel with the speed of light, it would take xxx years, since the next habitable planet is xxx lightyears away. BUT: What about time dilation? If an object approaches light...
  4. N

    Special Relativity: Time dilation

    Hello. This is not a concrete problem, rather conceptual question. Homework Statement 2. Homework Equations 3. The Attempt at a Solution [/B] Spaceship with speed v with respect to the Earth is traveling from the Earth to say some distant star, which is distant L apart from the Earth looking...
  5. T

    B Trying to Explain Time Dilation

    Greets everyone. I am having great difficulty trying to explain to a group of friends who do not understand math too well that the unit we know as time does not speed up or slow down since 1 second is no different than marks on a ruler and has an established interval length, in this case...
  6. M

    I Is the relativity of simultaneity the reason for time dilation?

    A yes answer can cause conceptual problems. What is your opinion?
  7. sunrah

    Ratio of time dilation relation in different potentials

    In the weak field limit, we have dt = (1 + 2\phi)^{-\frac{1}{2}}d\tau where the usual meaning of the symbols applies. This means that in GR dτ < dt analogous to SR. Let suppose we measure the period dtS of a photon emitted at the surface of the Sun as well as the same photon, i.e. same atomic...
  8. Warfen

    Gravitational Time Dilation & Orbits of Objects

    For example if there were two objects orbiting each other and one was much heavier than the other, for instance a dwarf star and a neutron star. Would the lighter object have a greater gravitational pull than it's mass would say it should because it's pull was operating longer on the heavier...
  9. N

    Time Dilation at ISCO for Kerr Black Holes

    Hello, I like to calculate the time dilatation at the ISCO of a Kerr black hole: According to general relativity the time dilation is given by following formula: d \tau = \sqrt{g_{\mu \nu} \dot{x^{\mu}} \dot{x^{\nu}}} If I'm interestet in the time dilation at the ISCO I set \Theta =...
  10. I

    Special Relativity - time dilation and length contraction

    Homework Statement The highest energy protons have gamma factors around ##1.0*10^{12}##. (a) Our galaxy has a disk diameter of 30 kpc, which is ##9.3*10^{20}m##. If a photon and one of these high energy protons start traversing the galaxy at the same time, by how long will the arrival of the...
  11. P

    Attempting to understand relativity and time dilation

    Homework Statement t = t0/(1-v2/c2)1/2 Homework Equations t = 10/(1-.95c^2/c^2)1/2 The Attempt at a Solution [/B] The provided solutiojn to the example given above is: t = 10/(1- (.95c)2/c2)1/2 t = 10/(1- .952)1/2 t = 10/ .312 t = 32 Unfortunately, no matter what I do the answer I...
  12. D

    Relativity time dilation and length contraction

    Homework Statement can somebody help my figure out what t0 l0 l and t is? For instance: A girl an her dad are in an airplane, the girl starts running 20m in 8 seconds. There is also a boy standing beneath the plane (lets pretend that the airplanes floor is seethrough. Homework EquationsThe...
  13. E

    Does time dilation occur between comoving galaxies?

    As an astronomer observes a galaxy, which is receding, Does time dilation occur between the two comoving galaxies? If so, which (rf) is (t) longer in, as observed here on Earth (Our local Milkyway galaxy or the remote galaxy)? Thank you.
  14. M

    Explanation of time dilation due to c being the maximum speed

    I have seen a video in which the time dilation due to velocity is explained by saying that light and light interactions inside a moving body must travel a longer distance in space, which reduces the passage of time. Video: This explanation is new to me, and in fact, I recently heard an almost...
  15. D

    What time dilation do muon observers experience?

    Re. time dilation muons, CERN. Given the accelerated muons were observed to have a lifetime increased by approximately x 29, What happens to the observers life span? Thank you.
  16. B

    Time Dilation: Rel. Ref. Frames and Universal Reference Frame

    I understand that if someone is traveling away from Earth at a very high speed, time will slow down for the traveler relative to the people on earth. However, why is it not the other way around? If there is no universal reference frame, could this situation not also be thought of as the traveler...
  17. seb7

    Exploring the Truth Behind Time Dilation: Debunking Common Misconceptions

    The video is pretty popular and being spread by science channels. Is the last bit about the cause of time dilation correct? I used to think like this, but came to the concoction its wrong, but seeing this video makes me wonder once again how could this be correct. If the video is true then -...
  18. D

    Basic Questions on Time Dilation Implications

    I'm relatively new here, and was told that the GP group was a good place to ask some basic questions. If this isn't he right place for the question, please direct me to the proper group. For years I have been fascinated with the implications of the time dilation mental experiment -- the...
  19. writer

    I Time dilation time travel for novel - I need a calculation

    Hi! I've written a novel in which my main character travels through time (into the future) 18 years. While the concept of time travel is necessary to the plot, the details are not. Meaning, the book isn't sci-fi, but contains elements that wouldn't normally exist in a contemporary novel, so...
  20. iForget

    Time Dilation for Slower Objects - Physics Explained

    Good day, I'm a high schooler so my knowledge of physics is futile and still expanding. Please correct me when I'm wrong, I love physics. Now to my question. I'm still a bit fuzzy on this theory of time dilation and the speed of light etc. But if time dilation happens at the speed of light can...
  21. m4r35n357

    I Is it time to "retire" time dilation and length contraction?

    Considering the enormous number of questions posed on this forum and other places, the concepts seem fundamentally flawed (because both are formally and practically unobservable). The calculations themselves (together with the Lorentz Transform) are highly error-prone and the results misleading...
  22. Orodruin

    Insights A Geometrical View of Time Dilation and the Twin Paradox - Comments

    Orodruin submitted a new PF Insights post A Geometrical View of Time Dilation and the Twin Paradox Continue reading the Original PF Insights Post.
  23. SuperfundMatt

    B How does time dilation appear to a third observer?

    Let’s assume it is 5,000,000 years in the future and we have created a quantum synchronization box that can broadcast a signal, used to synchronize two clocks and video feeds, no matter where they are in the universe. The third observer watches a split TV screen, which features the faces of two...
  24. Smattering

    Time dilation at the event horizon of a black hole

    Dear all, As far as I understand, for a distant observer, time stands still at the event horizon of a black hole, right? In particular, nothing will ever pass the EH. Instead, everything that approaches the BH will get stuck at the EH and stay there forever from the perspective of the distant...
  25. K

    Which Quintuplet Returns to Earth Last Based on Time Dilation Ranking?

    Homework Statement Five identical quintuplets leave Earth when they reach the age of 21, in the year 2121. Each quintuplet goes on a spaceship journey that takes T years, as measured by a clock in each spaceship. During the journey they travel at a constant speed v, as measured on earth, except...
  26. D

    Time Dilation and different clock types

    Hello PF. A moving clock is seen by the platform observer to run slow. This applies to all clock constructions. A light clock runs slow because the light path lengthens and the clock takes longer to tick over. Other types of clocks don't have a light path to lengthen. By what mechanism do...
  27. H

    Gravitational Time Dilation: A Layman's Explanation

    I think I have a layman's understanding of time and length contraction. However, I don't really understand gravitational time delay or distance contraction. If we were to put two clocks at the front and end of a rocket, the one on the top would experience time more quickly than would the one on...
  28. S

    Time Dilation by Light Alone? A Software Engineer's Exploration

    Let me first preface this with a couple facts about me. I am not a physicist, nor have I ever taken any classes in my life to warrant any extensive knowledge on the subject. I'm a software engineer by trade but have a great interest in physics (or at the very least, spacetime and how it all...
  29. mileymo

    Gravity, Time Dilation & Black Holes: Q&A

    I'm wondering if a ship orbited a black hole for a year, how large would the black hole be for it to equal 10,000 years on earth?
  30. newjerseyrunner

    Can time dilation be explained by changes in the rate of entropy?

    I was watching a Youtube video and the narrator mentioned that sometimes antimatter can be thought of matter traveling backwards in time and that confused me. I started thinking about what time is and it doesn't make any sense that antimatter acts in any way like it's traveling backwards in...
  31. W

    Time Dilation & Acceleration: Leaving Earth Effects

    Leaving Earth at constant acceleration will make time on board go slower. Acceleration will take the ship closer and closer to c Question is: How long will acceleration act on the ship? The time as measured on Earth or on the ship? The final v will be greatly different. Of course, given enough...
  32. T

    I Black Holes - Spaghetification countered by time dilation?

    Here is an oddball that I am wondering - could the spaghetification be countered by time dilation? Because as you approach a black hole (assuming you go in legs first) not only do your legs experience higher gravity than your torso, but they are also subjected to more time dilation - as they...
  33. E

    B Is time dilation just a problem with our clocks?

    [Mentor's note: This thread was split off from https://www.physicsforums.com/threads/time-dilation-and-redshift-for-a-static-black-hole-comments.835277/ as clarifying misunderstandings about time in general is off-topic in a thread about the specifics of time dilation around a black hole]...
  34. B

    Time dilation - Is the time between events longer or shorter

    So let's say there's a train and according to the passengers on the train the trip takes a time t to go from the station and back. According to an observer at the station, would they measure a time interval of gamma *t or t/gamma? I know they both should see the others clock ticking at a...
  35. stevebd1

    Insights Time Dilation and Redshift for a Static Black Hole - Comments

    stevebd1 submitted a new PF Insights post Time Dilation and Redshift for a Static Black Hole Continue reading the Original PF Insights Post.
  36. H

    I Exploring Time Dilation: The Effects of Destroying an Atomic Clock

    I will not bother saying to much because the post will just get closed if I do not accept the forced discipline. If I shot the aeroplane out of the sky with the Keating experiment on board, destroying the atomic clock in essence stopping the beats per second of the clock, does this mean time...
  37. Keermalec

    Time dilation in an elliptical orbit

    The formula for time dilation in a circular orbit is readily available but the literature seems to indicate it would not be so simple in the case of an elliptical orbit, and no simple formula seems to be available. Given that time dilation in a circular orbit adds the velocity effect (GM/r) to...
  38. A

    Time dilation on the surface of the sun

    Hi, I am wondering. Is it possible to predict the amount of time dilation on the surface of the sun compared to the surface of the earth? Is this a correct question to ask, or have I made a bad assumption? Thanks in advance. Ayjay
  39. Dynamotime

    Time Dilation: Twins Separated by Black Hole's Gravity

    is This example correct? I made it up Twin Z get close to a black hole to observe it (theoretically he is Not in orbit, Not moving but close in off to an black hole to be affect by the gravity of it, and the black is not moving in space or rotating) And Twin X stay behind on the mothership...
  40. Dynamotime

    Time Dilation due to Gravity: Formula Explained

    If possible can someone tell me what is the formula of time dilation for an object Which theoretically is Not in orbit, Not moving but close in off to an black hole to be affect by the gravity of it. It will be greatly appreciated.
  41. Gaz

    Determine Absolute Speed Using Time Dilation

    So if time dilation is what's left after correcting for the optical effect and we want to know our motion through the universe. We can't use light because we have no reference point to what not being in motion is and there's lots of attempts using light which doesn't work. Why don't we just take...
  42. Tomvader1988

    Does time dilation affect only the measurement of time?

    As I understand, 'Einstein's mirrored light clock' shows us that a vessel (containing said clock) traveling at any speed greater than that of a duplicate, at rest will observe a slower passage of time. I understand that this is because of simple Newtonian physics that shows us that in the case...
  43. D

    Time dilation and speed of light

    Hello Physics Forum. Given time runs slow as seen by a moving observer, why doesn't light travel further in the slowed time? Thereby negating the greater distance light has to travel, mirror to mirror in the light clock on the train thought experiment?
  44. Gaz

    Time Dilation & Doppler Effect: Conclusions?

    [Mentor's note - split off from https://www.physicsforums.com/threads/are-time-dilation-experiments-conclusive.826952/ as this is a different question] This makes sense. And fact they appear to slow down is due to red shift of light created between the two frames?
  45. Boro Petrovic

    Are time dilation experiments conclusive?

    Before posting reply, please think about time as a concept that is used to describe a change relative to some other change. For example, a traveler will arrive on a destination after Earth completes x rotations. At the beginning, people used Earth rotation as a reference change and called it a...
  46. P

    B Do Gravitational Time Dilation and Redshift Contradict Each Other?

    Timedilation seems clear when you study special relativity and read about the Hafele-Keating experiment. Gravitational redshift seems logical when you assume that light should lose energy when it is leaving a gravitational field. But the two seem to be contradictory to each other. Question 1...
  47. Raman Choudhary

    How does this proof demonstrate the concept of time dilation?

    Suppose there is person A in a frame S with respect to which a light beam clock is at rest , now time taken by a photon to go from bottom to top is L/c according to A. now the same clock is looked at by a person B traveling with velocity v w.r.t S and according to him time taken by photon to...
  48. G

    What is the cause of time dilation in Special Relativity?

    One of the basic foundation of special relativity is that the speed of light is a constant, hence time is relative to the inertial framework reference. Usually GPS is also mentioned as a modern experimental evidence. My questions: if Maxwell's equations describe EM fields, how can we derive a...
  49. godzenon

    Time Dilation of Fast-Moving Objects: Exploring Forces

    I meant to say fast moving "objects" in the title, my bad... my title kind of sucks https://en.wikipedia.org/wiki/Relativistic_electromagnetism#The_field_of_a_moving_point_charge That section is basically what my questions are about. I want to know generally about the overall forces. Two...
  50. S

    Time Dilation with a Tennis Ball

    So I just finished reading my textbook on special relativity and am a bit confused by the discussion of time dilation. We equip an observer with a light source, a mirror, and a clock and herd him onto a train moving at constant velocity relative to a second observer located at the station. If...
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