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. A

    Question regarding light clocks and time dilation.

    Hello. I am trying to gain a more intuitive understanding of relativity, and hopefully someone may be able to help me. Suppose there are two light clocks on two different spaceships - ship A and ship B. If the two ships are moving past one another with a constant velocity, then an observer on...
  2. D

    Time dilation flashlight problem

    I have a copy of "Relativity and Early Quantum Theory" by Robert Resnick. On page 78 there is a problem from chapter 2: A, on earth, signals with a flashlight every six minutes. B is on a space station that is stationary with respect to the earth. C is on a rocket traveling from A to B...
  3. W

    Do I have time dilation right?

    Hello all, First let me say that I have been battling with time dilation for years, all the videos seem to drive me more into confusion and reading does the same. The past few weeks I have been really trying to get a grasp on it better. I understand the concepts, theories, and postulates but...
  4. H

    Mass inflation exactly equals time dilation?

    Two spacecraft in inertial motion have relative velocity .5c. The ships have identical "grandfather" clocks very much like earthly grandfather clocks, except that the force of gravity is replaced by Coulomb repulsion. [The clocks have charged plates on either side of a charged pendulum...
  5. M

    Length Contraction causes Time Dilation?

    I had a big epic discussion on another board after someone stated that "if I were to travel to Betelgeuse at a sufficient velocity I would reduce the distance between myself and Betelgeuse until it is say, 2 light years, which means I would only experience 2 years or so during my journey", this...
  6. F

    Time dilation yes, why no contraction?

    The example I have read to show time dilation is that of a light clock on a train. Two mirrors are one metre apart. Light is beamed from the first mirror to the second. An observer on the train sees that it takes the amount of time for light to travel 1m for the light to reach the second mirror...
  7. S

    Understanding Light Clock & Time Dilation

    Hi guys, I am having trouble getting my head around the light clock scenario which demonstrates time dilation. I can't help but intuitively feel that it seems like a fault of the clock, rather than time dilation. I hope you can understand what I'm getting at. If someone could try to give an...
  8. N

    Time dilation and length contraction

    Can someone please clear this up for me? Lets say the distance of Point A from Earth is 10.4 light years. Some spacecraft is traveling 0.95c. So. The person in the spacecraft will see Earth contract but Earth will see the spacecraft contract in length too. The thing I'm confused on is...
  9. B

    Why do clocks appear to run at different speeds when traveling at high speeds?

    I don't understand this: http://casa.colorado.edu/~ajsh/sr/timevbig_gif.html if the mirror is moving fast enough, why won't the light just miss it? why is the light traveling towards at an angle instead of straight?
  10. G

    Is time dilation relative, or absolute?

    I explain my question through an example. If we brought down a GPS clock, would it show the normal time, because it was accelerated before launch, but it has been slowed down by time dilation? Or we have to accelerate those clocks in order to compensate for the time loss, till the signal from...
  11. A

    Calculating Time Dilation on an Airplane in Special Relativity

    Homework Statement An airplane travels 1250 km/h around the Earth in a circle of radius essentially equal to that of the Earth, returning to the same place. Using special relativity, estimate the difference in time to make the trip as seen by Earth and airplane observers Homework...
  12. F

    A good video explaining time dilation

  13. W

    Time Dilation: Does Length Contraction Apply?

    Suppose I am standing on the Earth surface and observing a rockhet of very high speed then i will see the length the rocket contracted and abserver on the rocket will also see my length contracted(I am not sure about it)in the direction of motion. Is the same case takes place with time...
  14. A

    Need help understanding time dilation

    I keep reading that an observer will find the clock moving relative to him to be slower than his own local clock. But isn't his own local clock measuring proper time, which should be a shorter time period than the moving clock? How can the slower (moving) clock measure a longer time period...
  15. G

    Visualizing Time Dilation: Exploring the Effects of Relativity on Twin's Journey

    Are there any graphs that depict the amount of time dilation that occurs by the fraction of the speed of light for the traveling twin?
  16. V

    Can Particles Exist in Multiple Times Through Quantum Time Dilation?

    What if quantum mechanics is combined in an experiment with time dilation? Not that unheard of as subatomic particles can travel very fast, until they are relatively close to the speed of light. Take a ship moving very fast, say .25c. Now take a particle that would travel at either .25c in...
  17. R

    Understanding Time Dilation and Age Differences in Twin Paradox Experiments

    Homework Statement Twins, A and B. A goes off in a straight line traveling at .96c for 7 years as measured on his clock, then reverses and returns at half the speed. B remains at home. When they return, what is the difference in ages between A and B?The Attempt at a Solution My answer is 19.958...
  18. J

    How Does Time Dilation Work? Solving a Space Journey Time Question

    Homework Statement im not sure how to work this equation out ! please help! imagine that one pf a pair of twins takes off on a long space journey to Vega, 25 Light years away, at a speed, relative to Earth, of 99.5% of c (gamma = 10). once there he decides he doesn't like the Vegans, so...
  19. Erland

    Time dilation and simultaneity: easier to see with a train

    Many people have difficulties to understand how time dilation can be consistent with he special relativity principle: "According to the observer on the Earth, the observer at the spaceship is aging slower, but according to the observer at the space ship, the observer on the Earth is aging...
  20. S

    Time Dilation or Mass Dilation

    Hi, I'm a first time poster and wanted to share a thought I had concerning disproving time dilation. It is said that time is relative depending on the observer's speed because speed = distance/time and because light's speed appears the same no matter who measures it, therefore either time or...
  21. S

    I can't understand time dilation in absence of absolute motion.

    According to theory of relativity there is no absolute standard of rest. Now, if Alice and Bob are two observers floating in space, so that Alice thinks that she is at rest and Bob is moving away from her at a speed comparable to that of light and Bob thinks that he is at rest and Alice is...
  22. E

    Special Relativity - Time Dilation and Length Contraction

    Homework Statement I have a two part question where one has to solve for a velocity to make a moving clock run half the rate as one at rest. Then the second part is what velocity would an object have to move in order to make its length halved. Homework Equations t'=t\gamma...
  23. R

    Does a proton age differently when accelerated at high speeds?

    Very quick question here that's bugging me. I go to the LHC and send a proton around at 0.999999991c. After 5 seconds of that speed I stop it and take it out. Has the proton become younger or older, by x years, than when it was put in? Thanks!
  24. C

    Time Dilation Paradox: Interstellar Race

    Hi, I asked a theoretical question here a month or two ago and someone was able to help me. I have another: Imagine an interstellar race. Starship 1 heads from Earth toward Alpha Centauri at a constant rate close to the speed of light, then makes a loop and returns home. Ship 2 is faster, and...
  25. M

    Why does time dilation apply for objects moving with a velocity less than c?

    I am confused with some of the aspects of time dilation. I read the derivation (the one with the mirrors) and I understand it and it seems to make sense to me. In the usual derivation (http://www.drphysics.com/syllabus/time/time.html) , person A who moves with the apparatus (mirror-light...
  26. L

    Time Dilation: Understanding the Formula

    I do not fully understand the time dilation formula, if the answer is nearer to 1 does that mean time itself under perspection has slowed or increased?
  27. T

    Time dilation in horizontal clock

    hi, when talking about time dilation we base our idea(as i understand) such that; static observer relative to other one claims that lights' path is longer for him/her and since lights' speed is c for each of them time dilation occurs. This is quite obvious in vertical clocks but in horizontal...
  28. L

    Time dilation question for a sci-fi story premise

    Greets! Sorry for the random question... I realize this forum is about real physics, so I apologize if this post is inappropriate. I'm not speculating that this is possible -- it's more of a thought experiment about how it would appear if it were. :) I'm pondering a sci-fi plot where...
  29. M

    Time Dilation: Exploring the Phenomenon of Speed and Time

    Would I be correct to say that time would not dilate at all if I were to be sedentary throughout my life? & is it also correct to say that even for us individuals time dilates relative to each other? For example, we all move around, do things & time passes by, but though the difference may be...
  30. D

    Understanding Time Dilation: How Do Clocks Differ in Space Travel?

    Homework Statement At 3 pm a rocketship passes extremely close to the Earth with a speed of 0.800 c. Observers on the ship and on Earth agree that it is 3 pm. At 3:40 pm, as indicated on the rocketship clock, the ship passes a small space station that is fixed relative to the Earth and...
  31. C

    WIKI and Time Dilation: The Possible Error in Relative Velocity

    WIKI has possible error with time dilation. Does anyone agree? http://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_due_to_relative_velocity
  32. M

    Time Dilation: Object & Lightbulb

    Let's say there is an object at one place and the light bulb at another place. The light bulb switches on, when object sees that it starts to accelerate to the light bulb. After some time object reaches 0.866c relative to the light bulb, now the object and the light bulb is in inertial frame of...
  33. J

    What Happens to Time Dilation at a Black Hole's Event Horizon?

    I'm looking at this equation for gravitational time dilation: T = \frac{T_0}{\sqrt{1 - (2GM / rc^2)}} I understand the relation of time dilation and velocity, and how v must be less than c, but I don't understand what exactly is implied here. At a certain point, M could be great...
  34. Drakkith

    Time Dilation Light Clock Example

    I'm missing something here on the light clock example from http://en.wikipedia.org/wiki/Time_dilation. I understand the math on the picture, but I'm missing how that applies to time dilation. Why does the light pulse take on a diagonal path for the moving observer? Is the light pulse still...
  35. K

    Time Dilation Vs. Length Contraction

    I'm having a major mental block to special relativity - i understand it the principle of it but seem to be struggling with time dilation and lenth contraction. I've spent a while thinking that time dilation and length contraction happen both togethor like you can't get one without the other...
  36. C

    Negative moving coordinates and Time Dilation

    I have question. Want to know time dilation for clock at negative coordinate in moving frame to reach origin of rest frame. Let's use P' = ( -7/8ls,0,0 ). Use v =3/5c, then γ = 5/4. ls is light seconds. Now, do you apply Lorentz Transforms like this t' = ( t - vx/c² )γ But, we do...
  37. Vorde

    Time Dilation Paradox: Exploring What Prevents it From Happening

    I was discussing the possibility of intergalactic travel with a friend and suddenly this occurred to me. Classically, if someone speeds away at the speed of light (or near to it), he returns without having aged as much as everyone else. But to him everything else sped away in the opposite...
  38. C

    Time Dilation: Explaining the Basics for a Sci-Fi Story

    Hi all. I'm working on writing a sci-fi story and I'm really just getting into researching relativity and time dilation. I'm a layman, but the ideas excite me, so I'm trying to figure these things out the best I can. Here is my hypothetical: Say someone were to have a vehicle that could...
  39. M

    Black Hole time dilation + biological paradox

    If a spaceship housing humans were to travel near a black hole, time would slow down due to the increased gravity. However, with what we currently know about cellular biology and gravity, humans need to stay around 1g to proliferate properly. Now if the spaceship generates an artificial...
  40. S

    Near Light Speed Travel & Time Dilation I don't get it.

    I recently came across an article relating to Gliese 581 g and some theoretical information about getting there. It said something along the lines of "while it is 20.3 light years from Earth, passengers aboard a vessel traveling at nearly the speed of light would perceive the journey as nearly...
  41. P

    Time dilation formula for constant acceleration on a circular path

    Time dilation formula for accelerated circular and spherical motion A traveler goes in an accelerated circular motion of radius r from spacestation A to spacestation B with a constant proper acceleration alpha, e.g. there is also a tangential acceleration...
  42. M

    Time Dilation & Stem Cell Therapy: Twin A vs Twin B

    I believe in the future stem cells will cure everything and stop the aging process, and I also think that any mammal traveling at high speed would be affected by failing organs and a weaker immune system (just my opinion). So, two people of the same age are on Earth. They are identical twins...
  43. M

    Special relativity, time dilation and rockets

    Homework Statement Lights are placed at points A and B, which are 100m apart as measured in the rest frame of the earth. As a rocket moving at speed v = 3/5c, passes point A the light turns on. As the rocket passes point B, the second light turns on. As read on the rockets clock, the time...
  44. G

    Infinite Past and Future: Surprising Consequences of Time Dilation

    From the equation of time dilation we can deduce a consequence that surprise me . If we know that in our frame system is future and in other frame system is past , and from pointview of the other frame system must be another frame system that is past from our pointview and so on from the...
  45. E

    Can proper time be calculated for varying velocity along a worldline?

    Ideal clocks are taken from event A to event B along various worldlines. then that the longest proper time for the trip is indicated by that clock whcih follows the straight worldline. How it can be showed. thanks
  46. S

    Event horizon: light delay and grav. time dilation

    Hello, I know that time dilates while approaching the event horizon of a black hole, but explanations failed to make me understand HOW MUCH of each phenomena causes this as an object approaches the EH. On the one hand there is photon delay due to gravity acceleration approaching the speed of...
  47. 1

    An issue I'm having with time dilation and other effects of speed

    Here's my issue. We will say that from our reference Object A is stationary and Object B is moving. Object A witnesses Object B traveling 6/7 the speed of light, thus Object B's "onboard clock" is running half as fast as Object A's, though it appears normal to Object B. If Object B does...
  48. H

    Solving the Time Dilation Paradox - Special Relativity Explained

    Consider A and B are moving in a linear motion, A claims B to move, and B claims that A is in motion, now when they look at each other they would clearly see which clock is running slower. Let us denote the resting object by x and the moving object by y. The special relativity explains, that...
  49. B

    How Do Observers in Different Frames of Reference Perceive Time Dilation?

    Ques) 2 observers, A on Earth and B in rocket ship whose speed is 2x10(^8) m/s, both set their watches at 1:00 when ship is abreast of the earth. (a) When A's watch reads 1:30, he looks at B's watch through telescope, (b) When B's watch reads 1:30, he looks at A's watch through telescope...
  50. A

    Help with time dilation and length contraction

    Homework Statement How fast must a pion be moving on average to travel 25 meters before it decays? The average lifetime, at rest, is 2.6 x 10-8s. Homework Equations \Deltat =\Deltat0/ sqrt(1 - v2/ c2) l = l0 * sqrt (1 - v2/ c2) The Attempt at a Solution I think that 2.6 x...
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