# Tagged Questions

Time is defined operationally to be that which is measured by clocks. The SI unit of time is the second, which is defined to be

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### Understanding gravitational time dilation / Schwarzschild metric

I've had a look at the answers to these sorts of questions already, but feel like I'm still missing something. Starting with this question, and this one and even this one here. I'm looking at this ...
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### Movement of accelerating points with maximum speed (i.e. running away from tiger) [closed]

I'm walking through a forest and suddenly I see a tiger. And now I have a problem. I want to know how much time I have left but I don't know how to calculate it. Or more formally: Let's ...
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### Is the intuition of “absolute simultaneity” necessarily wrong?

I read about Einstein’s theories of relativity with all the interesting stuff like time dilation, mass increase and whatnot. And also about the relativity or conventionality of simultaneity. The ...
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### What is the correct way to treat operators that has “time” in QM? [duplicate]

I don't know if this question has already been resolved but considering that $i\hbar\partial_t$ is the energy operator, and $\partial^2_t$ is the waves operator (or helmholtz), I can't accept that $t$ ...
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### What are the effects of increased mass on persons traveling at near light speed?

It's been a long time since I studied physics (and then only very superficially), so please bear with my gross naivete. This question's been running around in my head for about two weeks now, and I ...
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### How to build a clock? [closed]

You have unreliable clocks that fire in the interval $(t,t+\delta)$ with probability density $f(t;\lambda)=\lambda\exp(-\lambda x)$. How will you build the best clock using these unreliable components ...
2k views

### Relationship between Energy and Time [closed]

Is there a relationship between energy and time? What is it?
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### Is proper time an intrinsic value of Minkowski space?

What is proper time? Is it a part of Minkowski space (that is a mere spacetime interval)? Or is it an intrinsic characteristic of massive particles (a sort of "aging")? Example: In the following ...
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### Would infinite time elapse relative to an outside observer if an object was completely at rest?

Here's my reasoning... time dilation due to velocity: t'=t√(1-v^2) v expressed as a % of the speed of light. If you are moving through distance at the speed of light, to an observer at rest relative ...
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### Is there no fourth dimension (time) in the universe? [closed]

In this article (and numerous others) http://phys.org/news/2011-04-scientists-spacetime-dimension.html and http://www.rebelscience.org/Crackpots/notorious.htm they suggest that there is no time ...
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### Twin Paradox: Whose time is slow? [closed]

What I understand about the twin paradox is that if a person stays at rest with something lets say the earth and a traveller moves with a great velocity with respect to the firsy person, then the time ...
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### How can a clock work if the uncertainty principle is true?

If the uncertainty principle and Copenhagen Interpretation are true, then how can a clock tick? Supposedly particles can do all sorts of things when not measured, then how can they be formed into ...
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### Do photons see shorter distances due to space contraction?

I may be wrong, but this is just what I've heard. People often talk about what would happen if we, humans, were able to make a spaceship travel at the speed of light. If I'm not mistaken, then we ...
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### Will we gain some extra hours if we travel in the direction of the rotation of the earth? [closed]

I heard that If we travel for long distances in the direction of the rotation of the earth, we can gain some extra hours in the journey. Is it true? What if we travel in the opposite direction?
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### If time travel to the past is not possible why is this situation considered in Feynman diagrams?

I recently read R.P Feynman's QED:A Strange Theory of Light and Matter. It is believed that time travel to the past is not possible. Then why is particles going backward in time considered in the book ...
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### Does time pass fastest in isolated, resting space?

While it is fairly established that both fast movement and the presence of gravity make time pass slower as compared to a system at rest / free of gravity, does that mean that there is no way for time ...
458 views

### Time travel, is it possible? [duplicate]

I see there are many questions with this title, but this one is different, so please give it due thought: Is time travel possible? If so, Can we go both forwards and backwards in time? Paradox: I ...
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### Could it be a limit in our measuring the speed of photon, instead of photon having a speed?

Are we (not) limited by our own speed through time (1 sec / sec) to measure highest possible speeds(c)? I fire a laser which hits a mirror and comes back and I precisely measure the time, and knowing ...
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### How do we know that time and distance are not discrete?

I know that it is believed that energy is discrete, in that it travels in quanta. I was wondering if there is any evidence which either proves or disproves something similar with both time and ...
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### Time Dilation in relation to Acceleration

What I am looking for is a layman's explanation on the equations required to work out Time Dilation at high speeds including acceleration and deceleration of velocity. Or I would greatly appreciate it ...
321 views

### Approximate Time Dilation at Rocket Speeds

How do you calculate the time dilation effect experienced by a traveler traveling at a relatively low speed? Specifically, how much time dilation would a traveller moving at $v=0.0007 c$ (speed of ...
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### Is relativistic motion equivalent to fluctuating gravitational fields?

The theory of relativity makes very precise predictions about how an object's motion through space-time affects the passage of time for both the object and observers in other frames of reference. I ...
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### When are we now? Time coordinate system [closed]

The Second and the metre are well defined. We have those units available. Of course units are meant to express measurement, tools to compare with precision, and interchange that information ...
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### What is Hawking's, “No Boundary Conditions”? [closed]

In his "No Boundary Conditions", is Hawking stating that time is eternal? And what is the difference between Real Time and Imaginary Time? Is he saying there are two different arrows of time, and ...
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### How does pressure change over time in an open box?

Imagine that you have a 1 cubic meter metal box with two 20 mm diameter holes. One of them is connected to an air-compressor that constantly pressurizes the inside of cube. Let's say 5 atm. The other ...
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### How to measure size of x in time (“time thickness” and not “lifetime”)? [closed]

My question is a consequence of a personnal hypothesis which might be wrong. Everything which exists has a size mesurable in 3D space with different size of rulers. This stands for any particle, ...
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### Does Inertial time dilation demonstrate that Time is not a dimension? [duplicate]

If time is a dimension and 'now' simply an expression of your position with respect to that dimension, the progress of any object along that dimension should remain in step with all other objects. By ...
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### How Can a Singularity contain different things? [closed]

According to the Big Bang model, space and everything in it was squeezed into a infinitely small point which subsequently expanded. But if everything is squeezed into a point of zero size than there ...
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### What dictates the rate in which time passes? [closed]

I understand that special relativity tells us that our perception of the passage of time can change depending on reference frames. But why does time pass the rate at which it does in my reference ...
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### Time Travel possibility and Paradoxes of The Past [duplicate]

can one travel back in time and if not so, what laws prevent time travel to the past. this is quite a challenge to understand.
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### What makes things move in a universe with blocktime? [closed]

In a universe with blocktime the past, present and future all exist at the same time. But what makes it appear that for example my body is going from one movement ...
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### Coordinate Time and Proper Time/Simultaneity [closed]

At close to the speed of light, clock A is running slower than "stationary" clock B. Does clock A enter the future time reference of clock B as it slows down? Trying to understand where the forward ...
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### Deriving proper time invariance from first principles

I'm trying to learn special relativity right now, and for various reasons I'd like to start by getting the invariance of proper time, rather than starting with the Lorentz transformations - if you can ...
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### Why does the light beam moves diagonally?

In almost all articles that explains Relativity or Time dilation. They start by saying the the Light is absolute and isn't affected by the inertial frames of reference yet when they start to explain ...
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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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### Can less gravity speed up time? [closed]

We know more gravity slows down time per Einsteins Theory of Relativity. However will a significantly less gravitational pull speed up time? Or is "our time" aka earth standard of time the fastest ...
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### What is the difference between the expansion of space and the Alcubierre drive?

The Alcubierre drive violates causality. As far as I know the expansion of space does not. The usual explanation for why space is allowed to go FTL is that the matter doesn't move. The Alcubierre ...
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### With respect to what does time itself change? [duplicate]

We all have an intuitive notion that time itself "changes" - before it was the past, now it is the present, later it will be the future, and as time "changes" or moves forward what was the present ...
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### If time is relative, how could time pass? [duplicate]

EDIT: I appreciate people who answered below. But it does not answer the question, so I will clarify my questions: -It seems like everyone is saying that time passing is actualized by physical ...
1k views

### Does the universe update time in some finite interval? [duplicate]

I was listening to a lecture by leonard susskind and one of the analogies he used was a coin having two states and he "broke" time into intervals. He continued to say that at each interval of time, if ...
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### Calculate Time travel with Time Dilation [closed]

Does the following hold: If we have: person A moving at a speed of $0$; person B moving at a speed of $xC$ (where $C$ is speed of light, $x$ a fraction) And if time passes for $m$ ...
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### Is gravitation time dilation simply c/v?

Recently, I've been very interested in forms of time dilation. I'm relatively new to relativity, so I apologize for any stupid mistake I may make. I was messing with the equation for gravitational ...
127 views

### What is the least count of the timer clocks used in RADAR?

I was checking out some videos in YouTube regarding the working principle of RADAR. To quote some HOW IT WORKS: World War II Radar (720p), part 1, How does RADAR work? | James May Q&A | Head ...
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### Has the effect of magnetic fields on time ever been examined experimentally?

Relativity of time can be examined with satellites as gravitational or acceleration. Is there any similar experiment with intense magnetic fields?
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### Is time dilation based on the formula for period of a pendulum?

The theory Albert Einstein put forward about special relativity mentions a possibility for time dilation, in which he states gravity has a considerable effect on time. And in high school physics we ...
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### Naked Time ( Is there such a thing ?) [closed]

I have lately been concerned with time and whether or not it is an illusion. For argument's sake let's assume it is. Then time should stand on its own. Can anyone describe, (or point me to a paper ...
275 views

### Does the universe have a different age to different observers?

Although I understand that the universe is approximately 12 billion light years wide, and that may mean that it took the light photons 12 billion years at 186,000 miles per second to reach the ...
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### Would Special Relativity Predict Time Dilation of a Geostationary Satellite Compared to an Observer on Earth?

Consider a geostationary satellite at some arbitrary distance above the Earth's equator and consider a person directly below it, standing on the Earth's equator. Both satellite and person exist on the ...