# Questions tagged [time-dilation]

This tag is for questions regarding the 'time dilation' which is the lengthening of the time interval between two events for an observer in an inertial frame that is moving with respect to the rest frame of the events (in which the events occur at the same location).

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### Time dilation as an observer in rocket [duplicate]

If a rocket was moving away from earth at say 0.5c, why do we consider the earth as stationary object and the rocket is moving? Can we assume that the rocket is stopped but the earth is moving ...
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### Relativistic Time-Keeping and Sharing

Suppose there are 2 ships which keep time using atomic clocks. The atomic clocks are the same build so it is know that the two keeps keep proper time at the same rate. Suppose that the two ships ...
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### Time dilation at event horizon and outside universe [duplicate]

From what I know, time dilation is almost infinite at the event horizon of a black hole. Therefore, infinite time should pass from an uninfluenced observer’s reference frame compared to the reference ...
1 vote
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### What are the differences between the Michelson-Morley experiment and the Kennedy-Thorndike experiment?

I am trying to understand the differences between the original Michelson-Morley experiment and the Kennedy-Thorndike experiment, but there aren't a lot of readily available resources that do a good ...
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### Question about gravitational time dilatation

For $g_{00} = 1 - 2GM/c^2r$ , the time interval $\Delta T$ measured in a stationary frame at a distance $r$ from the source and the time interval $\Delta t$ measured by a frame at $r= \infty$ are ...
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### Variation on twin paradox involving a common timekeeper [closed]

To try to understand the twin paradox better I thought of a variant involving a third party time keeper that both twins can agree on, and am trying to understand what each party would actually observe ...
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### Is there gravitational time dilation as we look further out into space (and therefore further back in time)?

There is a formula for gravitational time dilation which relates the slowing of time to a changing force of gravity. ...
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### Acceleration and gravitation are locally equivalent ? I find not

In a gravitational field, the above and below clocks do not run at the same rate. The acceleration equivalent means that the simultaneity changes. During acceleration there would be a gravitational ...
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### How would a clock with hands behave if half of it is outside a black hole and half inside? [closed]

I am thinking of a clock moving close to the speed of light at a tangent to the event horizon so it doesn't fall in instantly Would the time like spacetime inside the black hole be reflected in the ... 1 vote
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### Relative to the amount of time that passes for someone in a black hole, how much time passes for an observer outside of it?

Time slows immensely for someone at the event horizon of a black hole. From the viewpoint of an observer outside the black hole, it appears time stops at the event horizon. How can we know the actual ...
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### Hafele–Keating Experiment. What are the forces acting on the moving clock?

According to the Hafele–Keating Experiment, time dilation is the reason for the differences between the earth bound clock and the moving clock. ...
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### How to re-solve the Schwarzschild solution after inverting one of the assumptions?

The Schwarzschild solution is based on the following assumption: ...the geometry of the spacetime is unchanged under a time-reversal $t \rightarrow -t$. I’m interested in what the derivation and ...
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### How do we know the assumptions of the Schwarzschild solution are valid?

The Wikipedia article on the derivation of the Schwarzschild solution (https://en.wikipedia.org/wiki/Derivation_of_the_Schwarzschild_solution) lists 4 assumptions. The second of which is: A static ...
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### A clock falling at escape velocity; another blasting off at escape velocity

Imagine two clocks a distance $r$ from a non translating, non rotating planet. One clock is falling towards the planet at the escape velocity $v_e$ the other is blasting off from the planet at the ...
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### How much of Earth's history can a spaceship traveling at near speed of light record in an astronaut's lifetime?

I'm asking this question to better understand how "abrupt" a frame of reference change is when a spaceship accelerates. Apologies if this is not the right forum, and for the unrealistic ...
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### Understanding consequences of spacetime relativity

If I understood right, time flows slower where there is more gravitational force, compared to where there is less: that means that if we put a first timer in a point A in which there is more gravity, ...
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### How can I calculate gravitational time dilation between two planets? [duplicate]

I am writing a school paper and chose to do it about gravitational time dilation. I wanted to calculate the time that passed on Mars when 1000 years on Earth went by. (probably a tiny difference). I ...
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### Does Shapiro time delay apply to massive objects? [closed]

The diagram below I have borrowed from another question about Shapiro Time Delay: Impossible dilemma about Shapiro delay and momentum conservation My question is if Shapiro time delay applies to ...
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### Quantum Theory and Time [closed]

I read somewhere that quantum theory requires absolute time and not a dynamic time as described in relativity. Can anyone confirm this and further describe in laymen's terms what quantum theorists ...
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### Special Relativity [duplicate]

With respect to SR, the concept of each clock running slower than the other in different inertial frames is not intuitive (and is actually contradictory) unless either: each clock merely APPEARS to ...
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### Clocks at a moving reference frame

This is an example which I'm not grasping quite well in Special Relativity: A train $S'$ is moving at speed $.5c$ with 3 clocks inside 1 meter apart. Someone on a resting platform (lab frame $S$) ...
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### Simultaneity of events

Apologies, this thought has been bugging me and I am... Simple Consider two observers. One on Earth (stationery) One travelling away from Earth at some appreciable % of c If the spaceship sent a ...
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### Asymmetry in infamous Muon example

The immediate example usually given in relativity courses after teaching relativistic time dilation is concerned with the detection of muon flux on earth's atmosphere. The problem is that the average ...
1 vote
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### Sequential Lorentz transformation on an accelerating frame of reference?

A rocket takes off from Earth and increases its speed by 0.001 c every second. When the speed reaches 0.99 c, it decreases its speed by 0.001 c every second until its speed returns to 0. Then, it ...
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### Time dilation between now vs right after the Big Bang should imply the universe is much older than 13.8 bn years? [duplicate]

The universe is said to be 13.8 bn years old. But if we go back in time towards the Big Bang singularity time will slow down more and more and eventually stop because of the density of the singularity....
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### Can an object appear to be moving faster than light due to time dilation?

If I were to travel tword earth from a distant star at .9 C, I would see that earth would be experiencing more time than I would, but does this mean that I would see earth approaching at more than the ...
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### Why light travel along with light clock? [duplicate]

I am interested in exploring time dilation effects. I came across a video and I learned that when we move a light clock in constant velocity the light bounce will take a longer time with more speed. ...
1 vote
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### Describe a nuclear bomb near a black hole relative to a bomb in open space, due to $E=mc^2$

The energy of a nuclear bomb is described by $E=mc^2$. Near a black hole we have tremendous time dilation, so the rate of time and the speed of light is slower relative to open space. To an outside ...
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### Length contraction experienced by a person "at rest"?

If a person was riding a train going .999C tword a person standing on the train track, and the train track and everything on it were the only things in the universe, the person on the train would see ...
1 vote
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### Deriving time dilation from a moving photon clock

This is my attempt of simple derivation of time dilation from a moving photon clock. Consider this schematics: A) is photon clock as seen from a photon clock reference frame (or as by observer ...
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### Entangled electrons and time dilation where each observer opens box first to cause random collapse ("cause"/random selection paradox?)

Suppose two entangled electrons are put into separate boxes, and these boxes are made to travel in separate frames close to the speed of light (relative to the other frame). A person traveling with ...
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### If a car ahead of me suddenly speeds up close to the speed of light, what would I and the car observe each of us? [closed]

Suppose I and the car is beside each other and the car went a little ahead of me, then instantly speeds up close to the speed of light. Will I observe the car is going too slow or stuck at one place ...
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### What would an observer inside of a collapsing shell observe?

What does and observer inside of a collapsing shell observe? Lets say we have a shell of matter collapsing to a black hole. What would observers near the center see? How would the rest of the universe ...
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### When we use the word 'time' in spacetime and time dilation are we understanding that time has the same meaning for both entities?

When we talk about time dilation are we talking about spacetime or is time dilation a separate kind of time?
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### Exact meaning of Lorentz transformations [closed]

This is my first year in Physics and we have been shown about S.R very superficially, just having a bunch of equations to apply. However, I feel rather confused about results such as time dilation, ...
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### Is there a way to express gravitational time dilation as a scalar field?

The formula for gravitational time dilation is $t' = t\sqrt{1-\frac{2GM}{rc^2}}$. This gives a value of t for an observer at rest relative to the mass in question, compared to an observer infinitely ...
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### How to take the integral of the gravitational time dilation formula

The formula for gravitational time dilation is $t' = t\sqrt{1-\frac{2GM}{rc^2}}$. That gives us a value of $t'$ at some distance $r$. But is it possible to find the integral value over two different ...
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### What is the correct intuition for time dilation?

I'm a high school student and I recently thought of an intuitive, but incorrect way of thinking about time dilation. My trouble lies in understanding why this intuition does not work. It should be ...
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### How would a super long object orbiting a black hole be affected by time dilation? [closed]

Assume there is a long enough rod orbiting a black hole. Such that the time dilation occurring on the two ends of the rod is noticeably different. So, for example, the end that's closer to the black ...
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### Can length contraction be applied in Einstein's train thought experiments?

The thought experiment I am referring to in this question is similar to this: https://aether.lbl.gov/www/classes/p139/exp/experiment5.html Essentially, let the length of the light clock be $d$ ...
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### What did Einstein mean in his 1905 paper when exposing the relativity of simultaneity?

This question pertains to the section § 2. On the Relativity of Lengths and Times of Einstein's original 1905 paper "ON THE ELECTRODYNAMICS OF MOVING BODIES". I'm trying to figure out ...
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### Redshift and expansion and time

From the Weinberg 1972 book Gravitation and Cosmology Principles, we have the following ($R(t)$ is the scale factor): I understand everything, except the first part of equation (14.3.4), how does the ...
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### Interpreting the observations from a moving clock in special relativity

Consider a clock in motion and another at rest with respect to us, both frames are inertial. The moving clock will measure the time differently than ours, let's say for every 2 seconds that we measure ...
1 vote
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### Interval at time of emission and observation between two photons

In deriving how scale factor is related to redshift $1 + z = \frac{1}{a(t_e)}$, we started by saying the first light wave obeys: $c\int^{t_o}_{t_e}\frac{dt}{a(t)} = r$, where r is comoving distance. ...
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### How can a photon bouncing between two mirrors on a moving train illustrate perceived time dilation? [closed]

An outside observer couldn't see it; there would have to be a photon - a stream of photons - emitted back from that bouncing photon to the observer's eye or measuring device - absurd. Or the photon ...
1 vote
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### Relativity of simultaneity very confused

In the observer's frame the events A and B are simultanous ($\Delta t = 0$) and are separated by $\Delta x$ We can get the corresponding time between events in the car frame using the Lorentz ...
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### Can Lorentz transformations hold only One-way from a preferred frame?

I there any problem with assuming that Lorentz transformations hold only One-way from a preferred frame, let’s say stationary with respect to CMB. Still speed of light is constant and laws of physics ...