# Questions tagged [time-dilation]

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### What is time dilation really?

Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for ...
6k views

### Is gravitational time dilation different from other forms of time dilation?

Is gravitational time dilation caused by gravity, or is it an effect of the inertial force caused by gravity? Is gravitational time dilation fundamentally different from time dilation due to ...
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### Can a ultracentrifuge be used to test general relativity?

With today's ultracentrifuge technology, they can spin so fast that the sample can be subjected to accelerations of up to 2 millions Gs. That is equivalent to two solar masses. Has someone tried to ...
9k views

### How can time dilation be symmetric?

Suppose we have two twins travelling away from each other, each twin moving at some speed $v$: Twin $A$ observes twin $B$’s time to be dilated so his clock runs faster than twin $B$’s clock. But twin ...
7k views

### Is time dilation an illusion?

It is said that we can verify time dilation by flying a very accurate clock on a fast jet or spaceship and prove that it registers less time than the clocks on earth. However, the clocks on earth ...
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### Time dilation all messed up!

Okay! There is a problem with my logic and i cannot seem to point out where. There's a rocket ship travelling at close-to-c speed v without any acceleration (hypothetically), and there is an observer ...
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### Why isn't the center of the galaxy “younger” than the outer parts?

I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are ...
4k views

### What is the correct formula for gravitational time dilation for a satellite in a circular orbit?

In the Wikipedia article on Gravitational Time Dilation I see two formulae for the gravitational time dilation. One contains $\sqrt{1 - r_0/r}$ but the other $\sqrt{1 - 1.5 r_0/r}$. What formula ...
285 views

### Dancing twins, one travelling in a rocket ship, looking through telescopes at each other [duplicate]

Suppose two twins are put asleep. One is put in a rocket ship and accelerated to 90 percent of the speed of light. They are then both awakened, after which they both train their telescope on each ...
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### A clock in freefall

Time dilation calculated using Schwarzschild metric for a non rotating spherical body is: $$t_0=t_f\sqrt{1-\frac{2GM}{rc^2}}$$ For such a non rotating spherical body, what would the time dilation of ...
1k views

### So Black Holes Actually Merge! In 1/5th of a Second - How?

I've read a lot of conflicting answers in these forums. However, today saw the awesome announcement of gravitational waves. Two black holes merged: http://www.slate.com/blogs/bad_astronomy/2016/02/11/...
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### Time dilation clock experiment: what would happen if the clock were flipped 90 degrees?

I have seen and understood the classical thought experiment where you imagine a "light clock" sending a light ray between two mirrors while moving in a perpendicular direction to the lights direction ...
412 views

### Relativity and Galaxy Rotation Speed

If time travels slower nearer gravity wells, why can't the galaxy rotation speeds being faster on the outer edges than the inner areas be explained by relativity? What necessitates dark matter?
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### 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 ...
926 views

### What is the highest speed time dilation has been tested?

What is the highest speed time dilation has been tested? How close to the Special Relativity prediction did it get?
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### Does STR imply that time dilation is effected by an orientation of clocks?

Many texts about STR time dilation use as an example thought experiment with 2 mirror photon clock. The conclusion of this experiment is: In a frame moving relative to the clock, they will appear to ...
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### Can you calculate unix timestamps (universal clock) from any planet?

Given the definition of unix timestamp as the number of seconds elapsed since January 1st, 1970 as GMT+0, without leap seconds, is it possible to create a universal clock that will generate the ...
606 views

### Would time speed up near a large body of negative mass relative to observers in micro gravity?

Time tends to slow down near objects with large amounts of positive mass relative to observers in micro gravity. Considering that negative mass is the opposite of normal mass and would time tend to ...
388 views

### Why does a light beam in a moving light clock follows a V shaped path?

If I am standing on a platform moving along the X-axis and I throw a basketball vertically upward along the z-axis, the ball also travels along the x-axis. Does the same apply to a photon? According ...
352 views

### Are gravitational force and gravitational time dilation proportional?

Particles in gravitational fields are subject to gravitational time dilation. The closer a particle is near a gravitational source, the slower is running its clock. I would like to know more about the ...
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### Can radioactivity be slowed through time dilation?

Can radioactivity be slowed using the effect of time dilation? If you put cesium, tritium or uranium in a cyclotron at relativisitic speeds, do their half lives become longer in our frame? Could ...
7k views

### According to special relativity, has the future already happened? [closed]

According to special relativity, a photon traveling at the speed of light, does not “experience” time. It is traveling into the future at an infinite rate, right? That would mean that everything that ...
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### Movie Interstellar - Question about Escape Velocity

The movie Interstellar shows people on a water planet where time is dilated so much that 1 hour is equal to 7 years back on Earth. Even though they lift off from Earth using a Saturn-V two stage ...
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### Why don't two observers' clocks measure the same time between the same events?

Person A in reference frame A watches person B travel from Star 1 to Star 2 (a distance of d). Of course, from person B's reference frame, he is at rest and is watching Star 2 traveling to him. ...
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### The twin paradox and positively curved space

I'm reading about the twin paradox in special relativity - if there are two identical twins, one of whom who sets off in a high speed rocket to a planet, and then heads back, will find the twin who ...
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### Twin Paradox Without Acceleration [duplicate]

So I've been doing a lot of reading about the twin paradox and have encountered several different explanations that strive to resolve it. First off let me start by saying general relativity is not an ...
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### What's inside a frozen star?

Consider a specific black hole whose whole mass is located at the event horizon. How such a black hole can form is beyond he scope of this question. Perhaps a spherical shell made of the neutron star ...
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### Can light travel faster?

I'm on Earth. Joel is on a planet orbiting near a black-hole's horizon. Every year on Joel's planet is equivalent to 10000 years on Earth due to the gravity of the BH. The two planets are 10000 light-...
564 views

### How can a photon oscillate when it experiences no time? [duplicate]

How can light experience change if it is motionless in time?
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### Practical time travel: time dilation above the event horizon [duplicate]

Imagine there is a huge black hole with very small gravity gradient so that one doesn't get killed by spaghettification after even nearing the event horizon. Now imagine a very curious creature ...
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### Is there such thing as imaginary time dilation?

When I was doing research on General Relativity, I found Einstein's equation for Gravitational Time Dilation. I discovered that when you plugged in a large enough value for $M$ (around $10^{19}$ ...
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### If you hover just above the event horizon of a black hole, would you see the future of the universe?

Let's do this thought experiment. You have an insanely powerful rocket and it can accelerate to 0.999999c. Now you fly to a supermassive black hole and hover just above its event horizon, where the ...
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### Can a photon that is emitted from a denser part of the universe to a less dense part appear redshifted?

Galaxy one is located in a dense area of the universe and galaxy two is located in a less dense part of the universe. Would galaxy one appear red-shifted to galaxy two? Is the mass density at our ...
718 views

### A spool in Einstein's theory of special relativity

I would like to know how can we model a simple spool that unrolls at speed close to light (in the frame of the wire remaining on the ground AND in the frame of the translatory motion of the rolling ...
3k views

### Do strong magnetic fields cause time dilation?

Does a strong magnetic field cause time dilation? If you have a strong magnetic field, and a magnetic radio active material, does the half life of the material change due to field?
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### Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
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### Does time dilation correct for the Doppler effect?

Knowing that a body in motion experiences time dilation, "also" knowing when two objects travel at a great speed away from one an other, both observers experience the others clock as moving slower ...
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### Why is light affected by time dilations in space-time curvatures

My previous question on this site gave me an answer to what affects light - space warping or time warping. The answer is- both. But what now doesn't make sense to me is why light is affected by time ...
445 views

### Time dilation due to space expansion

As we observe a remote galaxy, we see it with a redshift. The most distant galaxy discovered to date is GN-z11 visible with the redshift of $z=11.09$. For simplicity, let's assume no gravitational ...
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### Time dilation and Lorentz transformation

I have trouble understanding the Lorentz transformation to proof the dilation of time. If I use: $$dt ^{'} = \frac{dt}{\sqrt{(1-(v^2/c^2))}}$$ Understanding that $S^{'}$ is the moving frame of ...
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### A sees B's clock running slow and B sees A's clock running slow? [duplicate]

This paradox is very common it seems, in which A sees B's clock running slow and B sees A's clock running slow. Here is the question a little more concretely. Let's say B flies by A's spaceship. If B'...
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### Relativistic time dilation on Mars compared to Earth?

What is the time dilation in Mars, compared to earth? Can we accurately calculate it? What information is needed to do these calculations?
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### Time Dilation When In Orbit

Imagine a space ship orbiting the sun at near relativistic speeds, when compared to Earth (say from the reference frame of the sun) there would be x amount of time dilation. This would mean people on ...
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### How close should you get to speed of light, in order for time to be dilated?

Recently I was watching Carl Sagan's Cosmos: A Personal Voyage. In episode 8 ("Journeys in Space and Time") there is a scene presenting the idea of time dilation, due to traveling close to the speed ...
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### The Time Freezing Room - Theoretically possible?

Imagine a room in your basement with a very special property: The time inside this room runs 60 times faster compared to the outside world. That means when you enter the room and spend there 1 day ...
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### Relativity tangential light clock

I summarised the question in the final para, if you prefer to skip all my rationale and trig. btw, I have looked at Using light clocks, can one derive the length contraction formula without the '...
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### Time dilation under different references paradox [duplicate]

I couldn't figure this out... I understand that if Alice is moving relatively to Bob at a high speed, Alice's time elapses slower than Bob's. So when Alice is back to Bob and compares the clock, ...
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### Can an observer B move in such a way that his clock will run faster than that of a fixed observer A?

My understanding of Special and General Relativity comes from books which attempt to explain them to non-experts in these fields. Let A and B be observers, which at some time t(0), are together at ...
### Why is the momentum of a particle $\gamma mv$?
I am very new to relativity, and as I was going through Resnick & Halliday, I saw that momentum was no longer $mv$, rather $\gamma mv$. This was the proof: p = mv = m \frac{\delta x}{\delta ...