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. ubergewehr273

    Time Dilation: Doubts & Questions Answered

    Why must time slow down when a body moves with respect to a reference frame at rest ? Why should its mass and length increase and decrease respectively when a body travels faster and faster ?
  2. L

    Can time dilation cause confusion in the twin paradox?

    Hi, In the often cited example of a person in a rocket traveling past Earth at high speed - I think I understand that both the person on Earth and on the rocket could view the other as being the party that's actually moving. And so if they could view the other party, they would both see the...
  3. H

    Time dilation - effect on clock or 'time' itself?

    I understand that this topic have been discussed many times, but I just haven't found the answer, at least one I could understand. I'm not a physicist, just curious. I've been reading all around the internet about time dilation and SR. I understand that time dilation is real, at least when it...
  4. O

    Gravitational Time Dilation: Observing Planet Life

    Hello , my question is : If we could observe a planet life so far away from the Earth with so much gravity that it makes time pass more slowly on that planet , what would we see? Like what can we say about motions of lifeforms living on that planet? Would they be moving in slow-motion in the...
  5. M

    Is Grav & SR Time dilation additive?

    Just wondering if you are observing someone from a far out distance and they are in a gravitational field going at a high speed would the time dilation from their speed add on to the gravitational time dilation?
  6. B

    Time Dilation/Length Contraction Qs: Exploring SR Basics

    It pains me to even type these out. I realize how many threads there are with very similar questions and to someone well versed in these topics, these questions probably all seem the same. But after reading what seems like all the questions, I feel I'm still confused. 1) In regards to the light...
  7. D

    Time dilation -- light clock on a train thought experiment

    Who first came up with the light clock on a train thought experiment.
  8. aditya ver.2.0

    Time dilation through velocity of a moving body

    Why does time dilation occur due to the velocity of a moving body, according to SR?
  9. J

    Equation for time dilation of body in orbit around Kerr black hole?

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  10. C

    Time Dilation Notation in SR: Clarifying the Differential Form

    So I have seen time dilation written as all three of the following: t=τγ, Δt=Δτγ, dt=dτγ. I'm assuming this not to be the case, but just wanted to clarify that the third (differential) notation does not imply that t=∫τγ? That really wouldn't make sense (to me at least), so I'm assuming that...
  11. applestrudle

    Special Relativity Time Dilation Santa question

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  12. R

    Understanding Time Dilation: Exploring the Effects of Speed on Time

    A question about time dilation.. I find myself in an argument / discussion about the theory of time dilation, and it seems to me, that the terminology is really the problem. Would it not be more accurate to say that the effects of time slow, as speed increases ? To say that our test of clocks...
  13. G

    Time Dilation: Layperson Question About Gravity's Effect on Time

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  14. P

    Time Dilation Effect on High-Speed Object Orbiting Massive Object

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  15. johann1301

    Time Dilation: Do Astronauts See Events on Earth Slower?

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  16. Q

    Length contraction and time dilation in spacetime

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  17. V

    Minimal Special Relativity - Reciprocity of Time Dilation

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  18. kmm

    Time Dilation, Twin paradox etc.

    I know there have been a lot of other threads on this topic but I wanted to get some feedback on my thoughts on this. Time dilation is a result of Einstein's second postulate of SR, although the first postulate is what gives rise to the apparent twin "paradox". The common solution to the paradox...
  19. R

    How does one get time dilation, length contraction, and E=mc^2 from spacetime metric?

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  20. S

    Time dilation on the surface of a planet and escape velocity time dilation

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  21. P

    Relativity problem involving a muon

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  22. A

    Special relativity - time dilation

    Consider two events that take place at the origin of the frame of an inertial observer O' . At times t_1 ' = 0 and t_2 ' = T . O' moves with a constant speed v w.r.t. another inertial observer O . 1. Use the Lorentz-transformations to show that these events occur at x=vt in the frame...
  23. V

    How Can Two Clocks Be Synchronized if One is Accelerated?

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  24. R

    Time Dilation Issues: Expert Answers

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  25. E

    Gravitational redshift with time dilation?

    Hello, thanks for reading this. I need help trying to find a way to calculate the time dilation due to gravity, from a satellite 50,000km above the surface of the Earth, traveling 10,000km/h relative to a stationary observer on Earth. A signal is being sent from the satellite to the observer...
  26. D

    Lorentz contraction and Time dilation (Special relativity)

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  27. J

    If time time dilation is infinite at v=c, then time stands still only

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  28. Ascendant78

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    Homework Statement A rocket ship carrying passengers blasts off to go from New York to Los Angeles, a distance of about 5000 km. (a) How fast must the rocket ship go to have its own length shortened by 1%? (b) Ignore effects of general relativity and determine how much time the rocket...
  29. F

    Deriving the time dilation? equation of Lorentz transformation

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  30. L

    (self study) Time Dilation on Earth

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  31. E

    Time dilation due to changing the speed of rotation of the earth

    I was wondering about how to speed up time because I was bored, so I considered rotating my body clockwise (in the northern hemisphere) in order to speed up the rotation of the Earth by creating angular momentum opposite to that of the earth. I was thinking that this would then speed up the...
  32. P

    Time dilation formula explanation?

    Can anyone explain how the time dilation formula works? T=t/(√(1-v^2)/c^2))... ... What does the 1 stand for? Why include it? Can you write down the process of the formula?... How does ((C*t)^2))/c^2-v^2 lead to the time dilation formula? Please explain the process.
  33. H

    Mathematical name of time dilation curve

    In mathematics, what is the name (type) for a curve given by velocity and time dilation? Specifically, I want to find a name for the curve y=1/(1-x^2)^{1/2} This curve is derived from the equation of a unit circle (x-a)^2+(y-b)^2=r^2 where y=(1-x^2)^{1/2}
  34. I

    Muon Time Dilation: Exploring Earth's Perspective and Resolving the Muon Paradox

    when muons are created in the atmosphere and fall to Earth the Earth clock runs faster. Thus, the "slower" muon clock allows more of them to reach the Earth's surface. But from the muons' perspective, the Earth is moving towards the muon. Shouldn't the muon's clock run "faster" and there should...
  35. Art_Vandelay

    Time Dilation with Two Spacecraft

    I want to write a science-fiction story concerning the rapid increase in technology affecting the speed at which spacecraft travel and passengers age (relative to each other). Theoretically, would it be possible that a son leaves a certain time (a number of years) before his father to...
  36. O

    On the question of experimental evdidence for 'real' SR time dilation?

    Do experiments like 1971's Hafele & Keating show that SR relativistic effects of time dilation are not mere products of measuring symmetry? Does such an experiment show that for the jets it is their clock that has kinematic time dilation in relation to the other clock that 'remains'...
  37. Greg Bernhardt

    Time Dilation Definition: What is Time Dilation?

    Definition/Summary Time dilation is the factor by which an inertial observer measures another observer's clock as going slow. Time dilation is composed of two factors: 1) a relative factor of \sqrt{1\ -\ v^2/c^2} for Lorentz time dilation, which depends only on the velocity of the clock...
  38. C

    Atomic Vibrations & Time Dilation: The Reality Behind Our Perception

    We measure time based off of atomic vibrations, so time dilation from gravity and velocity are nothing more than pressure applied to the atoms, slowing their vibrations. This isn't an accurate measure of what we consider time, but more of a measure of the reaction of atomic vibrations under...
  39. O

    Is Time Dilation Relative in Special Relativity Experiments?

    If velocity is relative and if we cannot say which is moving away from what *objectivley, how do we say that time dilation is relative as well if we can tell who experienced the time dilation, as special relativity shows - and other experiments (muon concentrations etc). For example the jets...
  40. F

    Time dilation measurement and events

    Hello Forum, An event is a point in spacetime with spatial coordinates and a time coordinate: (x,y,z,t). An event does not have a duration since it only lasts for an instant t. We can talk about time duration to mean the temporal separation between two different events, correct? In the...
  41. Tranceform

    Does Time Dilation Affect Observations in Baseball?

    Homework Statement A baseball player at home plate hits a pop fly straight up (the beginning event) that is caught by the catcher at home plate (the ending event). Which one or more of the following obeservers record(s) the proper time interval between the two events? (a) A spectator sitting...
  42. S

    Gravitational Time Dilation and Age of Astronaut

    Hello Everyone, I am new to this forum. I understood from sources that space-time is like a fabric. The massive bodies bend the space around it, hence the gravity. If time is 4rth dimension, so, the space is bent in time due to mass. that pretty much explains stopping of time in black holes as...
  43. W

    Time dilation and curved space

    I am trying to get an understanding of general relativity one tidbit at a time. I have a vague concept of why curved spacetime causes the effect we call gravity. However, there's an aspect of it (ok, there' are quite many aspects of it, but I'm concentrating on this one right now) that I can't...
  44. R

    Muons: Why time dilation takes precedence?

    I was browsing through old threads and a user named universal_101 kept asking about why we can use muons as a direct measurement of time dilation but only an indirect measurement of length contraction. It was pointed out that the two go together and cannot be separated, but it got me thinking...
  45. J

    Time Dilation of Charged Particle "p

    Picture: - - - ---------------------------------- p -> ---------------------------------- + + + Positively charged particle "p" is initially moving to the right between two capacitor plates. Is the...
  46. Rookie

    Time Dilation, Spaceship Problem

    Homework Statement A spaceship has traveled for 14 years at an average speed of 90% of the speed of light. Its round trip from Earth has taken 14 years according to clocks on the ship. (a) How long has the journey taken according to Earth clocks? Homework Equations t = t’ / (1-v2/c2)-1/2The...
  47. A

    Special relativity time dilation question

    Out of interest I'm studying a book "A first course in general relativity" which is a great book in my opinion because it explains the subject very well. I'm a beginner though and I have a hard time understanding one particular thing mentioned quite early in the book. I'm attaching a scan of a...
  48. J

    Kinematic time dilation in black holes

    Black hole A moves at slow velocity, and there's an Einstein light clock hovering near the event horizon. Black hole B moves at high velocity, and there's an Einstein light clock hovering near the event horizon. The black holes are identical. And the light clocks are at the same...
  49. T

    Does Time Dilation Really Happen?

    I will just describe a common thought experiment to do with special relativity and a question I have about it. Note this question only applies to the realms of SPECIAL relativity. Imagine a scenario in which there are 2 spaceships A and B. Each spaceship has its own clock. Spaceship B moves...
  50. J

    How Does Gravitational Time Dilation Affect Human Physiology and GPS Technology?

    Hi people, please could someone enlighten me on gravitational time dilation. I have read online that some places, such as neutrons stars, warp time so much that time can pass 100 times slower than it does on Earth. I was just thinking about a human heart beating. If a healthy heart rate on Earth...
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