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. D

    I Realistic Time Dilation for Objects > Subatomic Particles

    Time travel, or more precisely time dilation, has been a well known proven result of Relativity. It has been demonstrated most notably in satellites traveling thousands of mph around the world with GPS. You can only go forward with our current understanding of physics. Have there been any...
  2. S

    B Attribution of Reference Frame: A Dilettante's Question

    I can't find an answer on my dilettante question about how we attribute reference frame to complex objects, where different parts move with different velocity or where different parts experience different influence of gravitation. For example, we can take a human's body. If we take the full...
  3. P

    Difference between time / length equations for time dilation

    What is the difference between time dilation (t is the stationary reference frame) t = Description: If two successive events occur at the same place in an inertial reference frame, the time interval 􏰋t0 between them, measured on a single clock And this equation for time, if we take t' as the...
  4. D

    B Time Dilation Dialogue: Understanding the Concept

    I'll confess, I joined this forum solely to understand the reasoning behind the concept of time dilation, and to see if it is correct or not. If anyone could help me understand it better, and converse with me, I'd greatly appreciate it.
  5. B

    I Issue With Derivation of Gravitational Time Dilation

    Why do we use the equation ##\frac {1}{2}mv^2 = \frac {GmM}{r}## to derive potential velocity, and then put that in the Lorentz factor in order to derive gravitational time dilation? Shouldn't we be using the relativistic definition of kinetic energy -> ##mc^2(\gamma - 1)## to derive the...
  6. A

    I Falling Into a Black Hole: Time Dilation & Hawking Radiation

    I know that has been discussed elsewhere but never could find for a satisfying answer, so I try this here again. Let us not take into account that an observer (an astronaut or a clock or just let us take both: an astronaut with a clock) falling into a black hole (BH) will be killed and torn...
  7. mrSpring

    I Time Dilation Effects - Understand without Clocks

    So I am having some hard time understanding exactly the effect of moving near light-speed on time. Most of the examples mention clocks as a way of measurement but I can understand why would a clock which is a mechanical or electrical device for measuring time would be effected with motion. That...
  8. N

    How can the time dilation equation explain faster moving clocks running slower?

    Since for the two events of Samir starting the stopwatch, and the stopwatch reaching 10.0s, Samir and his stopwatch are stationary from his own frame of reference, I said it was the proper time and that delta t0 = 10s. Then the speed of the moving frame of reference was 0.6c. I thought placing...
  9. S

    B How much time dilation is there as time passes?

    I'm not a Physicist, I just have this question that has bothered me for a long time. This came up again recently when I was listening to some people talking about evolution. We know the universe is expanding, and we know that time is stretched with it. So if I'm looking back a million years...
  10. S

    Effect of time dilation on a satellite

    I've got the start of a plot forming in my mind, and I'm wondering if it's likely to be supported by physics at all. My basic understanding: when astronauts go to the International Space Station, due to the speed at which it is travelling, time passes ever-so-slightly slower for them. This...
  11. benorin

    B Can Atomic Clocks Yield the Same Time Dilation Equation as Light Clocks?

    Ok so I've got a question after walking through the time dilation derivation that used 'light clocks' (think a beam of light bouncing back and forth between mirrors) to derive ##\delta t^\prime = \frac{\delta t}{\sqrt{1-\frac{v^2}{c^2}}}##. So my Q is could you derive the same equation if you...
  12. Buckethead

    B Time Dilation: Accelerating vs Inertial Frame

    This is probably common knowledge to relativity aficionados but at Example 7.3 in this paper: https://www.farmingdale.edu/faculty/peter-nolan/pdf/relativity/Ch07Rel.pdf I was surprised to read the author showing that a ship accelerating at 1g from rest for 1 hour and reaching a speed of...
  13. sweet springs

    B Time Dilation and thermal motion

    [Mentors' note: This thread was split off from another thread about the cosmic ray muon measurements] The particle at rest in the moving ship is moving against the Earth. The particle at rest on the Earth is moving against the moving ship. A scientist in the moving ship measures the life time...
  14. M

    Length Contraction & Time Dilation

    Homework Statement A spaceship of proper length L is moving with respect to the ground with speed v. As measured on the ground, how much time does a light signal need to get from the front to the end of the spaceship. Homework Equations L'=L/γ t'=tγ The Attempt at a Solution The right answer...
  15. Z

    I Gravitational Time Dilation: Radius & Clock Rate Variation Explained

    (Apologies I posted this initially as a conversation. Not familiar with the format) I used the ‘gravitational time dilation’ equation to see how the clock rate varies with distance from the center of an object. I got the opposite result to what I was expecting.From Wikipedia; Gravitational...
  16. P

    B Does Gravitational Time Dilation Affect How We Measure Time on Earth?

    So I know gravity correlates with time dilation. If you have two individual equal size black holes close to each other, then at a point between them, gravity is equal to zero. Would the time dilation at that point be a sum of each individual black holes gravity or would the two time dilation...
  17. G

    B Muons traveling to Earth, time dilation question

    Hello learned people, I've been looking at special relativity of muons formed in the upper atmosphere... If I can summarise what I do understand (i think)... A muon has 12km to travel to the Earth from the atmosphere at 0.994c. Alice records this as taking 40.2 micro seconds. Now a muon has a...
  18. A

    I Calculate mass from time dilation

    Based on the exponential growth of time dilation 0.0 - 1.0 if given the radius of an object how do you calculate the mass of the object? Time dilation is a function of gravity. Which can be thought of as escape velocity from a gravitational field. So if you have to achieve .866 c to escape...
  19. DaveC426913

    B Cause of time dilation when net gravity is zero

    I'm armchair knowledgeable about GR, but I've come up against something I can't eloquently explain (to someone who asserts otherwise and wants an unassailable answer). What property results in time dilation even when net gravity is zero?The net gravity at the centre of the Earth is zero, but...
  20. E

    I Second Derivative of Time Dilation Equation

    Hello all. I was playing around with the time dilation equation : √(1-v2/c2) Specifically, I decided to take the derivative(d/dv) of the equation. Following the rules of calculus, as little of them as I know, I got this: d/dv(√(1-v2/c2) = v / (c2√(1-v2/c2)). Now, this seems reasonable enough...
  21. W

    B Time dilation and Einstein's theorem

    Hello! Einstein's theorem is in the last sentence of the following quote (bold) [1]: "If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its...
  22. T

    How do proper time and time dilation differ?

    Homework Statement I am currently stuck on a problem as shown below. My confusion really come from the fact that I can never seem to understand the difference between proper time and time dilation. As in some books they seem to mean the same thing and never give a clear indication Homework...
  23. H

    B What Happens When We Cross the Event Horizon of a Black Hole?

    When we approach a black hole, the effect of gravity is such that relative to us, time far from the black hole would approach infinity as the distance to the Event Horizon approaches zero. But what happens when we cross the Horizon? How do we measure time outside? Will infinite time have have...
  24. S

    B Can gravitational time dilation explain the galaxy rotation curve?

    Hello everyone, By considering the effects of the gravitational time dilation the speed of the inner stars must be higher for the local observer than for the external one. So why the gravitational time dilation can not potentially explain the galaxy rotation curve? I already read that the...
  25. N

    B Time Dilation Problem with Mesons

    At the suggestion of some of the members here, I am reading the book Space-Time Physics by Wheeler. The last problem in the first chapter states: "In a given sample of mesons, half will decay in 18 nanoseconds (18 x 10-9)), measured in a reference frame in which the mesons are at rest. Half of...
  26. L

    B I got confused about SR after trying to reply to another

    So let us say that there are 3 separate alien species that somehow speak and write the same language. Let us say that 2 of these have always lived and died in their spaceships/asteriod ... going at speeds close to that of light. Alien species 3. A3 leaves behind a message saying that at time t0...
  27. C

    B Time Dilation Theory Flaw: How Can They Be Different Ages?

    The theory regarding two persons experiencing different amounts of time dilation due to the two persons being influenced by different amounts of gravity states that while one person stays on Earth under its gravity and another person travels through space under less influence of gravity (less...
  28. Ennio

    I Gravitational field in the galaxy and Schwarzschild´s time dilation

    Is it possible to estimate the gravitational force of the center of a Galaxy (it could be Andromeda or the Milky way) to any point (such as a planet) of its Orbit? Furthermore is there such as Schwarzschild solution that calculates the time dilation of any point of an external Galaxy (e.g...
  29. R

    B Does time dilation prove the existence of an absolute zero velocity?

    You may think you've seen this before, since I've seen similar discussions in the archives of this, but I think I've distilled the thoughts down to a couple of facts that contradict the common beliefs regarding relativity. Let me preface this with a basic observation: Lorenz invariance does not...
  30. bland

    I Accuracy of time dilation measurement *in principle*

    Sorry that's the best wording for a title I could come up with. Anyhoo my question is one that I have wondered about for a long time, and I am prompted to post now after seeing this article on the new atomic clock. Let's assume that we have clocks that can measure time to an arbitrarily...
  31. P

    B Exploring Time Dilation and the Galaxy: Effects of Gravity and Angular Velocity

    I'm just wondering about time dilation in regards to both special and general relativity within our galaxy. Does time move slower or faster relative to us within the inner parts of the galaxy? I know at the horizon of the black hole time is effectively not moving. This implies that locations...
  32. Freonpsandoz

    I Gravitational Effects on Age of Earth's Core

    The Wikipedia page on gravitational time dilation (https://en.wikipedia.org/wiki/Gravitational_time_dilation) states: "Relative to Earth's age in billions of years, Earth's core is effectively 2.5 years younger than its surface." A clock subjected to less acceleration (gravitational or...
  33. Sandip Patel

    B Which Watch Will Have Slower Time: Object 1 or Object 2?

    Assumption: Object 1 is moving and object 2 is static. It is impossible to say which object is moving without any reference object 3. There are three scenarios possible. 1. Reference object 3 is at same position in space time with object 2, then object 1 is moving and object 2 is static. 2...
  34. S

    B Take on Length Contraction at relativistic speeds

    Hello everyone and apologize if my questions seem a bit off, please have patience with me. I want to have the following, rather simple, thought experiment. Let's say that we have a moving object O with the proper length L, when at rest. Let's say that object O starts moving at 0.9c (90% the...
  35. D

    I Time dilation for the Earth's orbit around the Sun

    If we have 2 atomic clocks on Earth's orbit around the Sun, one on Earth's surface, at one pole, and the other on a spaceship, far from Earth, but traveling with the same speed around the Sun, the clocks would suffer the same kinematic time dilation or not? I'm asking this because the clock on...
  36. P

    B Math-Based Time Dilation Paper: Seeking Suggestions

    I'm writing a mathematical paper on time dilation. Does anyone have any suggestions on how to incorporate math into the topic? I'm considering applying a Loedel diagram. The emphasis needs to be on the math, and not the physical aspects, though they can be introduced through the use of math. The...
  37. K

    I Gravitational time dilation derivation

    If a beam of light is shot from a fast space ship, it travels a distance c*t1 according to their reference frame. The same beam of light seen from an outside observer goes at an angle and travels a distance c*t2. The distance the spaceship travels is equal to v*t2. Using the triangle made from...
  38. S

    How Can Time Dilation Be Achieved Near a Black Hole in Sci-Fi?

    Super frustrated English major here trying to do calculus! Please help! I'm in way over my head... So, I'm writing this manuscript that involves humans with genetically inherited teleporting abilities. Near the end of the book, my protagonist wants to fling the antagonist close enough to a...
  39. Exidor

    I Time dilation vs. the Doppler effect

    If you had an object moving away from you at near C and it was emitting light that was pulsed at 1 Hz (from the point of view of the object) and you were to view it from a stationary position (earth), what would you see? It would be red shifted and the pulse rate would be slowed down? Would the...
  40. zox00

    I Deriving Lorentz from time dilation and length contraction

    Is it possible to derive the Lorentz transformation from time dilation and length contraction? If so, how should I start? I know how to derive it while considering 4 scenarios finding values of A, B,D,E in x'=Ax+Bt t'=Dx+Et and the transformation is: x'=(x-vt)/sqrt(1-v^2/c^2)...
  41. Biker

    I Time Dilation in SR: Exploring Clocks & Perception

    I don't really understand how time dilation works in SR. I just know this that "Now" in one reference frame is not the same in another so for example when Observer A says his time is 10s then at the same moment he will say Observer B's time who is moving relative to him is 5s for example. The...
  42. Mr C Odd

    Time dilation in a magnetic field

    Hi all. I was wondering if time is dilated whilst traveling in a stable magnetic field that is generated by the object travelling, and if so, does this vary if you reduce or intensify the magnetic field? Also, what happens if the object is generating two opposing magnetic fields, would...
  43. J

    Should I use time dilation or length contraction?

    1. Homework Statement [/B] This is a problem that was in my Physics HW. Two powerless rockets are on a collision course. The rockets are moving with speeds of 0.800c and 0.600c and are initially ## 2.52 × 10^{12} ## m apart as measured by Liz, an Earth observer, as shown in Figure P1.59. Both...
  44. P

    SR - Time dilation, space-time diagram, and radio signals

    Homework Statement P.S.: I'm not sure if it is allowed to ask multi-part questions. Two equally old sisters Alice and Barbara leave Earth simultaneously in opposite directions. The following velocities and distances have been measured in the Earth system. Alice travels with a speed of ##v_A =...
  45. jha192001

    I Time Dilation: A & B's Age Difference

    This is a gendenke experiment. You(A) and your friend (B) are on earth. Now your friend sits on a spaceship that can fly at speed of 0.1c. He flies for 5 year straight ahead(away from earth) and then returns back slowly. The answer that i get is B would have aged. Assuming this answer is right...
  46. J

    B Gravitational Time Dilation: Math Formula for Clock-Slowing Factor

    What is the mathematical formula for the time dilation (clock-slowing factor) for a clock in a gravitational field g, equivalent to the Lorentz factor γ for a clock traveling at a relative speed v?
  47. Jazzyrohan

    I Time Dilation Explained: Feynman Lectures 15-4

    Feynman Lectures 15-4 Transformation of time first para http://www.feynmanlectures.caltech.edu/I_15.html How is it possible that the moving clock slows down and also shows more time elapsed to the man outside?
  48. Amaterasu21

    I SR Light Wavelength & Direction: Questions Explained

    Hi all, I have two questions about light in Special Relativity. (I'm going to pad these questions out with a few statements about my understanding of length contraction and time dilation, so you can see how I currently think about it and clear up any misconceptions if I've got the basic idea...
  49. Jazzyrohan

    I What is the physical cause behind time dilation?

    Time dilation can be shown mathematically but what is the physical phenomenon due to which it occurs?
  50. N

    I What I understand about Time Dilation

    As I understand it, time dilation can occur under gravity or acceleration, which can be referred to as Gravity Time Dilation and can also appear to be happening when two things are in different frames of reference, which can be referred to as Velocity Time Dilation. With Gravity Time Dilation...
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