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. Green dwarf

    I Time Dilation in Gravitational Field: Potential vs Field Strength

    I'm wondering is whether it is the gravitational potential (in J/kg) at a point in space that determines the rate of passage of time, or whether it is the gravitational field strength (in m/s2). To clarify, suppose you had a very heavy hollow spherical shell. The gravitational potential would...
  2. N

    I Time Dilation for Photons: Explained

    So, I have a question. The time dilation formula is: t = t₀ • 1 / √(1 - v²/c²) Let's take a photon that travels at c. In my opinion, for a photon "clock doesn't tick" and its life is just a moment. But when we calculate time dilation by this formula, then c over c is 1 and the root of 1 minus...
  3. A

    B Time Dilation & Bosons: Decay Rate Changes?

    Hi, It is easy to find discussions about time dilation and muon Half-Life. Is it meaningful to discuss whether bosons capable of pair production can have their decay rate changed if they pass through material?
  4. E

    I Time difference caused by length contraction

    The goal is to calculate the difference in the passage of time between two ends of a cabin which is accelerating upwards due to length contraction. To help in the calculations we can consult: https://arxiv.org/pdf/1807.05338.pdf There is an old problem called the 4/3 problem which has been...
  5. IXWELL

    B General Relativity & Grav. Time Dilation Qn

    hello I'm korean high school student and sorry for my poor English. I saw ## t_0=t_f\sqrt{1 -\frac{ 2GM}{rc^2}} ## in wikipedia. does ## \sqrt{1 -\frac{ 2GM}{rc^2}} ## of this equation have name like lorentz factor ## \frac{1}{\sqrt{1 -\frac{v^2}{c^2}}} ##of ## t=\frac{t_0}{\sqrt{1...
  6. A

    Time Dilation in the ISS: 2 Seconds in a Year

    Using the above formula I get that the time goes 6.5∗10−86.5∗10−8 percent faster in ISS. Thus, this is approximately 2 seconds in a year. But the answer is much lower. Where am I making a mistake?
  7. R

    B Calculating Time Dilation w/ Light Clock - Implications & Mistakes?

    In this picture it shows a light clock. Let's use the moving light clock example. Am I essentially calculating the b component of moving clock. Assume the moving frame is the B frame. Assume the stationary frame is the A frame https://simple.wikipedia.org/wiki/Light_clock Or essentially the b...
  8. DavidBalut

    I The Theoretical Minimum: Length Contraction and Time Dilation

    Hello, My name is Dave and I'm a physics major at UIUC. It looks like I will be taking the special relativity course (phys 225) this fall. I've always been fascinated by the theory so I decided to get a head start with Lenny and Art's perspective on it. My first head-scratching moment came in...
  9. D

    B Proving Reciprocity Of Time Dilation

    Hopefully the answer on this question is positive. This forum has a very good reference about the Experimental Basis of Special Relativity. The tests of the Twin Paradox conclude that faster moving clocks tick/run slower, however this seems to be an 'absolute' fact. They do not show symmetry or...
  10. B

    B Time Dilation & Muon De Broglie Wavelength: Explained

    I understand it's experimentally verified muons traveling at relativistic speeds relative to an observer will be observed to have longer half-life than would be observed in the rest frame of the muons, which is explained theoretically by a relativistic time dilation effect. Does this correspond...
  11. P

    I Exploring Time Dilation: A Layman's Perspective

    According to a video I watched recently 'time' allegedly runs a tad slower in places on the Earth where the magnetic field is stronger. No doubt that has been tested and confirmed by atomic clock experiments.. to my simple mind that just suggests a timing error caused by the difference in...
  12. T

    B Time Dilation on Rotating Disk: Clocks on Disk Perspective

    Obviously, a third observer who is at rest with respect to the disk will see that the clock on the outside has a much faster velocity than a clock on the interior of the disk, so clearly the outside clock will show that it has measured less time. But that's one question. What about looking at...
  13. J

    B Gravitational Time Dilation on Mountaintops: New Member Questions

    New member here; just a physics hobbyist. There is probably a simple answer to this question but I could not find it. We know time flows faster on mountaintops relative to sea level due to gravitational time dilation. Over millions of years, wouldn't there be a cumulative effect making the...
  14. D

    B Build a Time Dilation Clock for 8th Grade Science Project

    A science teacher ask if I could help one of her students build a "Time Dilation Clock" so, at launch the Ships chronometer and the local time are in sync. with a 3g continuous thrust, at some point the time, the time at the launch site will be going twice as fast as the ships chronometer. so...
  15. S

    I Time Dilation Paradoxes Near C: Exploring the Twin Paradox of Special Relativity

    I'm struggling to wrap my head around the twin paradox in special relativity especially when dealing with multiple vectors. In my thought experiment say I have a set of twins. Both set out in opposite directions and intend to sling shot around two different black holes(luckily equidistant from...
  16. PainterGuy

    Time dilation and length contraction for a rocket

    Hi, It's not a homework but still thought to post it here as advised in the past. A rocket is going to leave Earth's surface and it is decided that a data pulse encoding emission time of pulse will be sent every second from Earth station to the rocket, and the rocket would do the same. The...
  17. Reinhardt Walzer

    I Time Dilation along Multiple Axes

    Been studying Special Relativity in Uni. and I've noticed that all examples of relativistic motion provided are motions only along a single axis, like the one below: The particle's Reference Frame is moving only along the X axis in the example above. In this case the Lorentz Transformation for...
  18. M

    B Time Dilation: 2 Clocks in Same Ref Frame?

    Question about time dilation. What if two clocks used the same reference frame? For instance, 2 countdown clocks using a particular pulsar as a measure of time. One stays here, the other is sent 100 million miles away at a very high velocity. Would they still reach 000 at the same time?
  19. diazdaiz

    B Help Me Determine Validity of Time Dilation Formula

    I recently trying to learn General Relativity by first scraping the surface on ScienceClic's general relativity playlist, and then I stumbled upon a video where it said that we actually move through spacetime on a constant speed of c, and then I remember about time dilation because how speed on...
  20. guyvsdcsniper

    B Check my understanding of Time Dilation and Length Contraction

    I just started learning about Special Relativity and have come upon the topics of Time dilation and Length contraction. Its a bit abstract for me and I just want to cross ref my knowledge here and see if someone can tell me if I am understanding this correctly. I've attached an excerpt of a...
  21. H

    A Time Dilation in Reissner-Nordström Metric: Even or Odd?

    In the Reissner–Nordström metric, the charge ##Q## of the central body enters only as its square ##Q^2##. The same is true for the Kerr-Schild form. This would seem to imply that all effects are even functions of ##Q##. For example, the gravitational time dilation is often written as $$\gamma =...
  22. S

    I Time Dilation at Moving Black Hole Event Horizon

    Hello everyone, I have a hard time to conceptualize the case of a moving black hole. We know from SR that time slows down for moving objects; but time dilation at the event horizon is already equal (tends) to zero. It seems that it can create some sort of conflict for the black hole movement...
  23. curiouschuck

    I Gravity & Time Dilation: Quantum Level Questions

    If gravity is the affect of time dilation because of the distance from the bottom of an object to the top then wouldn’t that mean that gravity doesn’t exist at the quantum level?
  24. BadgerBadger92

    I Time Dilation vs. Doppler Effect: Similarities & Differences

    Does time dilation in Special Relativity relate to the Doppler effect? If you move near the speed of light you experience time differently and the sound is stretched. Are these similar phenomenon?
  25. S

    B Confused about time dilation and cosmic speed limit

    [Moderator's note: Thread spun off from previous thread due to topic/forum change.] Time dilation sounds really weird, can i assume it has a logical explanation?
  26. T

    B Time Dilation: How Does Speed Affect Aging?

    Hello everyone, I wanted to know how speed can dilate time. For example, if there is a star 100 light years away from Earth and I started traveling at light speed, how long would it take for me to get there? I understand that the time differs from the point of reference (ie time from Earth's...
  27. A

    I Time Dilation on 3D Torus: Clock Speed & Why It Matters

    Assume that space is a three-dimensional torus ( a 3D donut) . If there is a clock traveling at a CONSTANT speed in a direction parallel to the torus (inside out of the hole) and one clock that is still. Which clock ticks faster and why? I know that the clock rotating will tick slower, but I...
  28. ronald_hinh

    I Time Dilation: Gravitational & Velocity Effects Explained

    I'm trying to understand what the time dilation looks like when moving through space and then approaching a planet's gravity field. So I have the broad understanding that if you are moving near the speed of light in a spaceship, your clock ticks normal but the clocks on other stationary objects...
  29. S

    Time measured by two clocks (involves time dilation)

    Proper time (to) is the time interval between two events measured by an observer who sees the events occur at the same point in space. I am confused how to determine which one is proper time for this question. How to know which events occur at the same point from the question sentence? Thanks
  30. S

    B Time Dilation in a Galaxy: Calculating Mass Effects

    Hello everyone - The gravitational force near the edge of the galaxy at point A (see attached image) can be calculated by assuming that all the galactic mass is located in the center of the galaxy. - In order to calculate the gravitational force in the middle of the galaxy (point B) we take...
  31. I

    I Kinetic vs Gravitational Time Dilation: Perceived Speed

    As an object approaches a black hole’s event horizon, it experiences increasing gravitational time dilation, causing it to appear to an outside observer to slow down, until, at the event horizon, it appears to stop. An object traveling in space that increases its velocity from one...
  32. V

    B Time Dilation: Traveling to a Distant Star in 4.5yr

    If there is a spaceship traveling at 0.999c, the time to reach a star 100 lyr away would be approx 100 yr (assuming no accel and decel). But on the spaceship, It would be 100 yr * sqrt(1-0.999^2) = 4.5yr. Why do we take 100 yr as the time seen on Earth and not the time on the spaceship?
  33. P

    Question on special relativity from "Basic Relativity"

    Summary:: Require confirmation regarding answers to a question posed by the book "Basic Relativity" by Richard A. Mould. Here is a problem which I encountered while going through Basic Relativity by Richard A. Mould- I'd like to receive a confirmation regarding the answers I've come up with to...
  34. M

    I Does time dilation occur due to the speed limit of light or c?

    The universal speed limit is c, and as a consequence light is confined to that limit. I was thinking about the time dilation in SR and was wondering if this is result of reaching speeds close to the speed of light or because of reaching speed close to c? For example, let's say light could be...
  35. M

    I Time Dilation in Gravitational Fields vs Acceleration on Earth

    If I'm standing on Earth, is my time dilation actually greater than if I was in a rocket accelerating at 9.8m/s^2 in deep space due to me being in a gravitational field on top of the acceleration? Geodesics experience time dilation in gravitational fields, so it seems like there is an additive...
  36. L

    I Time Dilation: Variables Beyond Speed & Gravity?

    Can time dilation vary without a gravity well or accelerating a viewer towards light speed? Are there other variables that affect the flow of time?
  37. N

    Time dilation for a simple problem — Light propagating inside a moving bus

    So I drew the problem and tried to derive t1 for an external observer by making the following assumptions. Inside observer sees light travel a distance of d0 meters in t0 seconds at a speed of c m/s. Bus moved Δd meters in t1 seconds at V m/s. Outside observer sees light travel a distance of...
  38. AdvaitDhingra

    B Time Dilation: Does Observer See Your Time Speed Up?

    If time slows down for an observer traveling at some speed relative to your proper time, shouldn't the traveling observer also see your time slow down relative to his proper time? Or does the observer see your time speed up relative to his proper time. Also, is dilation exactly the same in...
  39. S

    B Time Dilation Effect: Corrections to Clocks on ISS

    Hello All The Hafele-Keating experiment in 1971 confirmed measurable time dilation effects on atomic clocks flown around the Earth on aircraft. Presumably clocks aboard the International Space Station suffer worse time dilation because of their greater speed in orbit. How often are corrections...
  40. Dukon

    A Kerr Metric Time Dilation Formula: Deriving Absolute Form

    Just as the time dilation formula for the Schwarzschild metric in terms of the position ##r## away from center of mass for a gravitational body and the Schwarzschild radius ##r_s = {2GM}/{c^2}## is given by $$ \tau = t \sqrt{1 - \frac{r_s}{r} } $$ so I'd like to know the corresponding...
  41. morrobay

    B Time like spacetime interval, proper time, and time dilation

    Since the time like spacetime interval is equal to proper time for stationary or traveling observers, then it seems time dilation (proper time) seen with traveling clock is necessarily frame invariant. Then the so called time between ticks of both identical clocks, with stationary and traveling...
  42. R

    I Length contraction and time dilation

    A long time ago, I was very impressed by a lecture on elementary special relativity which showed in simple math how the correct conclusion to the null results of the Michelson-Morley experiment were obtained by concluding a constant c but then adding a length contraction and time dilation. I...
  43. stevendaryl

    I Time-Dependent Lagrangian Leads to Time Dilation?

    This is just something unexpected that I noticed recently, and I hadn't heard anyone mention it before. The relativistic Lagrangian for a particle moving under a scalar potential ##\Phi## is this: ##L = \frac{1}{2} m g_{\mu \nu} \dfrac{dx^\mu}{d\tau} \dfrac{dx^\nu}{d\tau} - \Phi## This leads...
  44. Nick tringali

    I Hyperbolic Time Chamber: Is Time Dilation Theoretically Possible?

    Has anyone ever watched dragon ball Z before? In this TV show, there is something called the hyperbolic time chamber. 1 day on Earth is equivalent to 1 Year in the time chamber. In other words, if you stayed in the chamber for a full 24hours than exactly 1 year would have passed when you left...
  45. Julius Ceasar

    B Time Dilation Question: Two Men's Watches Differ after Space Travel

    Sometime in the future two men meet at a space port and they synchronize watches, one boards a spacecraft and goes on a round trip around the solar system, when he returns the two men compare wristwatches to find they have different times. Q. Do the two men still exist at the same time or not?
  46. C

    B Conflict Between Time Dilation and Red/Blue Shift?

    Experiment 1: Astronaut travels away from Earth at near the speed of light, then travels toward the Earth at near the speed of light. Einstein tells us she barely aged, but red shift/blue shift don't seem to agree with that. While traveling away, both Earth and astronaut observe each other...
  47. Buckethead

    B Clocks Vanishing into Thin Air - Gravitational Time Dilation

    With regard to relativity of simultaneity and the "block" universe and reflecting on the notion of skewed time slices associated with frames moving relative to each other, one observer sees one event a distance away (parallel to the direction of motion) occurring before another event a distance...
  48. MacWylie

    B Why Aren’t ALL SR Effects Cumulative?

    Why aren’t all the SR effects cumulative like Time Dilation? Why should the Space dimensional effect become null when v—>0 while the Time dimension does not revert back to the 2 frames being in sync if Space and Time are treated on an equal footing. Clearly, Space and Time are not treated on an...
  49. Guillermo Navas

    I Thorne's error in explaining gravitational time dilation

    In Box 2.4 of the book "Black Holes & Time Warps" by Kip S. Thorne, he explains gravitational time dilation using the equivalence principle. For this he uses an experiment thought analogous to the one used by Einstein in 1911 to postulate the existence of a gravitational Doppler shift, but...
  50. M

    Why Is Time Dilation Considered a Real Phenomenon?

    Good day. I have read many books, forums, and articles, and watched many youtube videos, all in an effort to understand special relativity and time dilation. Or rather, more precisely, trying to find a valid explanation that does not result in contradictions and paradoxes, and if it does, one...
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