# 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. ### B Gravitational Time Dilation Inside the Sun

How can time dilation, lets say 500000 km inside the sun be calculated ?
2. ### How Does Time Dilation Impact Physics Forum Discussions?

Will post a question and view responses
3. ### I Integrate time dilation with derivative

I need to integrate time dilation with derivative, how could I do that?
4. ### I Sabine Hossenfelder says time dilation is due to acceleration

Sabine Hossenfelder says time dilation is due to acceleration in the twin's paradox. Is this true? At 12 minutes into this video , Hossenfelder states, "This is the real time dilation. It comes from acceleration." Looking at the equations for time dilation, time dilation comes from...
5. ### B Time Dilation: Is This a Reasonable Explanation?

I thought of this description recently and I think it's pretty intuitive, but I've gotten some side eye telling it to friends and family (maybe because relativity is screwy, maybe because I'm confused, maybe both?) so I want to get some confirmation that it's reasonable. Here goes: If you're in...
6. ### Time dilation for a clock thrown vertically

The non-moving clock will see the other one move upwards and land as predicted by Newton's laws, so using the equation ##z=v_0t-\frac{1}{2}gt^2##, and assuming the moving clock starts at ##t=0##, it will land at ##t=\frac{2v_0}{g}##. Now, using SR only, and the Minkowski metric (with signature...
7. ### B Explaining Distant Time Dilation & Enhanced Gravitation

When we observe distant time dilation effects, usually indicated by redshift, there are three possible explanations: 1) The speed of light, is slower there and then; 2) Space, is contracted for light there and then; 3) The frequency, of specific light is slower there and then. However, it is...
8. ### B Is Time Dilation About Particle Motion Rather Than Time Itself?

Hi, i am not a physicist but i have the intuition that time dilation is just slow in the movement of particle's and causality instead of slow in time itself and that this does not affect photons. I understand that there is no way to distinguish between a slow in time and a slow in movement and...
9. ### B Mick's Spooky Time Dilation Puzzle

Hmmm, , Does gravitational time dilation (speed up) cancel out earth orbit time dilation (slow down) for astronauts, , , it must do, to a certain extent Hmmm, , ,Mick's been thinking = the present is a continuous but fleeting moment, that allows the future to flow into the past, , ,so does the...
10. ### Effect of time dilation on Earth/space communication?

Let's say there is an audio oscillator on earth sending a 440 Hz audio tone over radio to a spacecraft. There is also an audio oscillator on the spacecraft sending a 440 Hz audio tone over radio to earth. Time is slower in the high gravity of earth than the weak gravity in space. Is the 440...
11. ### I Time Dilation Paradox: Geosynchronous Satellites

Time moves faster when higher above the earth. Time move slower the faster you are moving. A geosynchronous satellite has to be very high to be geosynchronous so it's time should be fast, but it also has to be orbiting the earth extremely fast to keep up with a geosynchronous position, so it's...
12. ### I Effects of time dilation for near-speed-of-light travel

Hello everyone, I've been learning about special relativity, and so far I believe based on what I read that if you are traveling at a velocity of .6c, you will experience time 20 percent slower than people on earth. Each second in the spaceship will be 1.25 earth seconds. Each second on earth...
13. ### I Time dilation from galactic gravitational mass

I've been thinking about how rotational speeds don't fall off high distances from galactic centers, for which dark matter is generally an explanation for the increase in acceleration Speed = distance / time But time is relative What "time" is used in these calculations? Wouldn't time be...
14. ### B Time dilation - what is the time on the Earth?

If I understand it well, 10 s did really passed in the rocket, it is according to the observer on the Earth, but if the man in the rocket measured the time, he would measure 10 s. But when we say that the man in the rocket is in an inertial frame of reference as well, he can claim that because...
15. ### I Time Dilation & Length Contraction: Graphically Explained

The thread "twin paradox without math" inspired me try to find fully graphical solution of length contraction. Here is the result: Graph is 3D as I think that is ilustrative to make all in one graph, but I am sure that it is possible to do it in 2 or 3 2D slices. X and Y are spatial axes, T is...
16. ### 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...
17. ### 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...
18. ### 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?
19. ### 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...
20. ### 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?
21. ### 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...
22. ### 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...
23. ### 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...
24. ### 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...
25. ### 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...
26. ### 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...
27. ### 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...
28. ### 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...
29. ### 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...
30. ### 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...
31. ### 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...
32. ### 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?
33. ### 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...
34. ### 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...
35. ### 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...
36. ### 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?
37. ### 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?
38. ### 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?
39. ### 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...
40. ### 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...
41. ### 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...
42. ### 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
43. ### 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...
44. ### 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...
45. ### 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?
46. ### 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...
47. ### 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...
48. ### 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?
49. ### 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...
50. ### 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...