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. A

    Get confused about time dilation

    When the observer B is traveling at a very high speed, the observer A on the ground will record a time dilation. But at the same time,from the point of view of B, A is also traveling at a very high speed relative to B. Here comes the question:does that mean they both record the time...
  2. E

    How does time dilation affect the perception of light speed in a moving plane?

    Homework Statement A plane is moving at a constant speed of 300m/s. If you are inside and you shine a light towards the back of the plane, how will light appear to move from the Earth's frame of reference? Homework Equations None The Attempt at a Solution Light always moves at 3x10^8 m/s so...
  3. Labyrinth

    Looking for 'absolute still' with time dilation

    I looked through this thread here regarding how fast we're moving relative to the CMBR, but I wonder if it would be hypothetically possible to get an even better measurement while also looking for a decent value for 'absolute still' using the apparent asymmetry of time dilation/constriction. A...
  4. Serious Max

    Time Dilation Explained by Stephen Hawking: 1 Day = 1 Year?

    Here (at ~3:50) they say if the ship reaches 99% of the speed of light, a single day on the ship = year on Earth. But it looks like it's going to be one week on Earth. http://cosmology.com/images/3TimeDilationTable1.jpg Is it just a simplification of some sort in the video?
  5. dragoneyes001

    Exploring Time Dilation: The Effects of FTL Communication on Twin Observers

    EDIT: split from "twin paradox with a twist" thread Re: https://www.physicsforums.com/threads/twin-paradox-with-a-twist.791673/page-5#post-4985729 one question: on the charts I understand the reflections as being at the speed of light correct? what would change in the case of FTL...
  6. Einstein Devotee

    Time dilation why or how, Special Relativity causes

    I understand the theory of special relativity and the mathematics which support it. I even understand that the time dilation has been proven. Therefore I am going to ask a question which on first blush may appear that I disagree with it but that is not the case. The question I can not seem to...
  7. W

    Exploring Gravitational Time Dilation & Event Horizons

    I want to ask a question about science/physics. To me and my level of education, this has not been answered, though I am sure there is someone out there that can provide the answer. It regards something I have been pondering due to gravitational time dilation (and space dilation I suppose, if...
  8. N

    Time Dilation and Relative Time

    I was reading in Clifford M.Will's book "Was Einstein right? Putting General Relativity to the Test" that there was an experiment done where in October 1971 an experiment was done with radioactive clocks, and plane trips taken going with the spin of the earth, and against it. He reports: "The...
  9. L

    Why does time appear to slow down on a moving spaceship?

    Please forgive my ignorance in STO, but I don't understand something about the following thought experiment. Spaceship flies from Earth with large speed. We observe the clock inside the spaceship from Earth with strong telescope. We see the clock showing 12:00. When we see on the clock 12:05 (in...
  10. H

    Time Dilation at Near Light Speed: Answers to a Thought Exercise

    I'm fairly new to the concepts provided by special and general relativity, and was wondering if someone could provide an answer to a thought exercise I came across regarding time dilation on an object going near light speed. Say a spaceship were connected by a live video feed to a monitor on...
  11. CaraKboom

    Metric Tensor: What is it and how does it relate to Riemannian geometry?

    I've been trying to get my head around time dilation in order to understand the relationship between space and time. I do not have a maths brain, I tend to understand things better as narrative concepts. I've read a lot of introductory material, but I'm having trouble making the link between...
  12. A

    Time Dilation: Photon Reflecting Surface Experiment

    I don't understand the thought experiment where a photon hitting a reflecting surface and traveling back to the observer is viewed from two frames of reference and the concept of time dilation is suggested arguing that the distances traveled by the photon are not the same in both the frames even...
  13. S

    Does Gravity Affect Time Dilation on a Flat, Non-Rotating Earth?

    On a science test that I took the other day, one of the questions inspired me to ask a question of my own. The original question was a multiple choice question that went something like this: if someone shoots a gun horizontally and simultaneously drops another bullet, which one would hit the...
  14. Ganesh Ujwal

    Why isn't length contraction permanent even though time dilation is?

    Why isn't length contraction permanent even though time dilation is? It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that object goes back to "rest", it...
  15. M

    Special Relativity and time dilation

    Homework Statement Two spaceships are traveling with a relative velocity of 1.2x10^8 m/s, both carrying clocks. According to the captain of each ship, the other captains clock ticks more slowly than his own. By what factor do the clocks disagree? Homework Equations 1/(1-(v^2/c^2))^1/2The...
  16. D

    Time dilation as seen by different observers

    Let's say the gravity around a planet of mass M is accurately modeled by the Schwarzschild metric. Then an observer (A) at infinity sees a stationary clock (B) at distance R from the center of the planet being gravitationally time dilated by the factor ##\sqrt{1-\frac{2GM}{Rc^2}}##, i.e. if B...
  17. M

    Geometry of Time Dilation

    I was recently exploring time dilation from Gravity and from velocity and I came up with an interesting derivation that I have not seen before. I was wondering if there is a paper published showing these relationships like this before and where I could find it? First you start with the...
  18. 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 ?
  19. 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...
  20. 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...
  21. 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...
  22. 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?
  23. A

    Exploring Space-Time: Dilation & Concentration

    Hi all, I was wondering if anybody else here thinks the concept of space-time dilation/concentration (curvature) is a little bit funny, not in the sense of it having an effect on the neighbouring particles, but in the sense of actually stretching or contracting, as though it itself had certain...
  24. 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...
  25. D

    Time dilation -- light clock on a train thought experiment

    Who first came up with the light clock on a train thought experiment.
  26. 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?
  27. J

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

    Inspired by the movie Interstellar which featured a planet orbiting a rotating supermassive black hole with an extremely high time dilation factor (slowed by a factor of 60,000 relative to observers far from the black hole), I was wondering if anyone knows of an equation for time dilation of...
  28. 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...
  29. applestrudle

    Special Relativity Time Dilation Santa question

    I am doing a presentation and want to make sure I'm not misunderstanding something very fundamental. My argument goes like this: t0 = ϒt Santa is moving very fast and from his point of view he is in proper time. This means that if it takes him t0 seconds to deliver a present, the amount of...
  30. 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...
  31. G

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

    I have what might be a silly question about time dilation caused by gravity. My understanding (very basic) of it thus far is as follows: 1. A clock (time) will tick slower when close to a gravitational source that a clock that's positioned farther away. 2. This affect has been measured in the...
  32. P

    Time Dilation Effect on High-Speed Object Orbiting Massive Object

    I browsed a lot this forum to find an answer, but it always ends up in the same way : no constant answer. I understand how time dilation relative to speed or to gravity separately work. But what about an object orbiting at high speed (natural ans stable orbit) an other object with a...
  33. johann1301

    Time Dilation: Do Astronauts See Events on Earth Slower?

    If I am an astrounaut in orbit, i would "see" events down at Earth happening at a slower rate. For example; if i watch a dragrace between two cars down at the surface from the orbit, i would see the cars driving slower then what i would see if i were standing at the racetrack. Offcourse, when i...
  34. Q

    Length contraction and time dilation in spacetime

    Observers that pass each other with a relative speed close to the speed of light will observe length contraction and time dilation at the other observer. In a spacetime diagram, this would be represented by two worldlines making an angle, right? Some textbooks suggest that some of the length...
  35. V

    Minimal Special Relativity - Reciprocity of Time Dilation

    Hello, I hope somebody can help me with this question. Homework Statement I have to prove that time dilation is a reciprocal effect by only using the Postulates of Minimal Relativity Theory: 1. Let I be an inertial frame, then I' moving with a constant velocity in a rectilinear motion with...
  36. 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...
  37. R

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

    How does one get time dilation, length contraction, and E=mc^2 from the spacetime metric? Suppose all that you are given is x12 + x22 + x32 - c2t2 = s2 How do you derive time dilation, length contraction, and E=mc^2 from this? What is the most direct way to do this?
  38. S

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

    If an object falls through a planet's entire grav. field, before impact it's velocity will be the escape velocity. I assume the time dilation for an observer on the object will be the same as for an observer on the planet. They're not added together. Another point - since time dilation on a...
  39. P

    Explaining Why Accelerating a Spacecraft to Light Speed is Impossible

    Homework Statement In terms of the energy involved (using formulas provided), explain why accelerating a spacecraft to the speed of light is impossible. Homework Equations time, mass and length dilation formulas, and a few astrophysics formulas, E = Ek + mc2, projectile motion formulas The...
  40. 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...
  41. V

    Time Dilation in accelerated frame

    Homework Statement Hi, I have an exercise where we are supposed to find a condition for which two clocks are synchronise if one clock is accelerated. Homework Equations The time dilation in an inertial frame moving with velocity v is well known. t'=\frac{t}{1-\frac{v^2}{c^2}} The Attempt at a...
  42. R

    Time Dilation Issues: Expert Answers

    I really need an expert for these two: 1. How can we correct the clock of a satellite due to time dilation effect due to its motion relative to the ground when ground-based clocks can be equally considered in need of correction due to their motion relative to the satellite? Both equally valid...
  43. 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...
  44. D

    Lorentz contraction and Time dilation (Special relativity)

    A quick question. It's been a long time since I had anything to do with special relativity, so I really can't remember much. But last night I was thinking about the "proof" of special relativity with the case of muons. So basically: Muons are created when particles hit the atmosphere. They...
  45. J

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

    How can speed of light be absolute yet that fact and relativity of sublight speed implies relativity of space and time intervals; if time time dilation is infinite at v=c, then time stands still only from that reference frame, but light takes a longer time relative to any other reference frame...
  46. Ascendant78

    Lorentz transformations (time dilation)

    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...
  47. F

    Deriving the time dilation? equation of Lorentz transformation

    Homework Statement It is not an official question but a request for pointers. I am trying to derive the Lorentz time equation to understand the intuition behind it. My math skills are not very good so it might be an obvious question for you. Please see below for my attempt. The variables are...
  48. L

    (self study) Time Dilation on Earth

    Hello, Firstly, let me point out that I do not have much knowledge in physics. However, after reading a certain book, I wanted to find out more about time dilation. I spent a few days reading about it. Here is the problem: Homework Statement I would like to be able to calculate the...
  49. 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...
  50. naima

    Neumark dilation and entanglement

    Do you know if there are experiments on particles having interacted which illustrate the Neumark dilation theorem?
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