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Questions tagged [time]

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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Finite time approximation for transition amplitude

Can I use periodic boundary conditions for calculation of transition amplitudes for a large but finite time, using the Feynman $i \epsilon$ prescription in the path integral formalism?
Peter's user avatar
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Continued calibration of atomic clocks

First off I am not well versed in physics, but as I understand things the second is defined by the ceasium fountain clock which is calibrated as follows How was the first atomic clock calibrated?. Now ...
Emma Harris's user avatar
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Time limits in path integral for free field theory

I just wanted to clarify one thing from this question , what if there is no interaction, no time-dependent sources? In this case, is it necessary to integrate over entire real line?
Peter's user avatar
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I need an explanation for the time derivative omissions in Landau’s Mechanics: Chapter 1 [closed]

So I have been self-studying Landau and Lifshitz’s Mechanics for a little bit now, and I have been working through the problems, but Problem 3 is giving me some trouble. I solved the Lagrangian ...
Justyn's user avatar
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Kinematics and law of motion [closed]

An object is under a motion with velocity v as function of distance V=(x^2+10x+3). What will be the velocity as function of time for same object following the same motion??
Divyanshu Kumar.'s user avatar
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Do clocks tick faster when gravitational forces are weaker?

A professor last year taught us that "gravity slows clocks," when teaching about the relationship between gravity and time. This led me to think about places, such as intergalactic space, ...
William Solomon's user avatar
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1 answer
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Probabilistic behavior of quantum mechanics [closed]

In a hypothetical scenario, if I were to measure the quantum spin of an electron and it showed "up," and then I traveled back in time without changing the initial conditions, would measuring ...
Vishnu's user avatar
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2 answers
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Does Hamilton's principle allow a path to have both a process of time forward evolution and a process of time backward evolution?

This is from Analytical Mechanics by Louis Hand et al. The proof is about Maupertuis' principle. The author seems to say that Hamilton's principle allow a path to have both a process of time forward ...
Raffaella's user avatar
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How exactly did Harrison's chronometer circumvent the impulse problem of time-keeping on a moving ship?

According to folklore, around the time of the exploration of the New World, there was a quandary regarding how to measure time on the open sea. Time keeping then was based on the pendulum clock, which ...
Fomalhaut's user avatar
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1 answer
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Multiple time dimensions in the eternal inflation model

From a lecture by Prof. Kaiser, I reckoned that according to the Eternal Inflation model, it is possible that all of the 10500 topologies posited by string theory could exist somewhere in the region ...
groaking's user avatar
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Extrapolating time to infinity for a particle moving spirally outward

If I have a particle moving radially away from me in a straight line and I extrapolate time to infinity, I could see the particle in a particular direction (given enough time for the light to reach me)...
Matrix23's user avatar
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Could chaos theory and butterfly theory prove that time only exists in the present? [closed]

I am sorry if this were to sound dumb but, chaos theory is about reconizing patterns and the universe itself can only repeat it self , would that mean that time only exist in the present cause if time ...
Anonymous 's user avatar
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If time reversal symmetry was preserved would past and future notions be defined

If time reversal symmetry was preserved would someone be able to define future as a time interval from a given time moment as measured by a clock (assuming they would still function as normal)?
John greg's user avatar
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2 votes
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Gravitational time dilation near the Earth [closed]

I recently read the statement that near the Earth, in the Newtonian weak gravitational field, gravity is 99.9999% mainly due to "curvature of time" (ie gravitational time dilation), and only ...
Rene Kail's user avatar
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Does it make sense to talk about time in absence of matter? [duplicate]

The equations of general relativity should predict (although I might be wrong) that in absence of mass the spacetime is everywhere flat. That is, time is the same everywhere. However, I'm not sure ...
Elvis's user avatar
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1 answer
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Does quantum entanglement arise from perpendicular time vectors? [closed]

From what I understand, "quantum entanglement" is a phenomenon where certain information travels instantly between entangled particles, regardless of distance in space. When thinking of ...
Quantum Wonder's user avatar
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1 answer
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Does time arising from entropy agree with GR?

There's a theory that the direction of time arises from entropy and the correlations (interactions) between bodies. However, I don't see how this would incorporate the effects of General Relativity, ...
Flamethrower's user avatar
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1 answer
97 views

Speed is equal to distance divided by time but is this correct?

In this study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9784821/, the distance the punch travelled from start to impact is 0.49 meters and the time taken from start of punch (that's it, they define ...
SnoopyKid's user avatar
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4 votes
3 answers
1k views

Is the meter relative to time?

Is the meter relative when we are near the speed of light? I was reading a physics book and I found that the meter is the length that light travels for an amount of time, so since time is relative ...
Angel Echavarria's user avatar
3 votes
1 answer
137 views

Non-orientable time

Consider the following toy classical physical theory. Let the theory take place on a fiber bundle $(E, M, \pi, F)$ such that $M$ is a one dimensional manifold interpreted as time. Define an action $S[...
Silly Goose's user avatar
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1 vote
2 answers
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How do I interpret the time axis in a diagram with multiple light cones?

Light cones are often drawn on a spacetime diagram that has a directional time axis like the fourth one on this page: There is a time axis, and all of the light cones are align with it because this ...
Jim's user avatar
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Can anyone please give some explanation in terms of the frequency domain of the time evolution?

This might be a silly question. But I was puzzled for a long time, even some comments are greatly appreciated. Is it possible to claim that "All the time domain evolution can be thought of ...
MathArt's user avatar
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For an observer on a spaceship moving near the speed of light away from Earth, would Earth be moving near the speed of light in the other direction? [duplicate]

There is something I don't understand about time relativity in examples given in internet, television, etc. Supposedly if a spaceship takes off from Earth and moves closer to the speed of light, time ...
Pablo's user avatar
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A change in the unit vector over a finite time interval

how we can write the change in unit vectors over a finite time interval, the change in unit vectors in an infinitesimally small-time interval 'dt' is given by the magnitude of the really small angle ...
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Is there any difference between Wick time order and Dyson time order?

Reading A Guide to Feynman Diagrams in the Many-Body Problem by R. Mattuck, I am getting the feeling that I missed something subtle related to time order. When deriving the Dyson series for the ...
Mauricio's user avatar
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2 answers
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To understand relativity in time with time dilation experiment

The time dilation experiment involves two frames in relative motion, let one at ground and other at train with velocity V. The light clock runs faster in rest frame, as seen by an observer A at rest ...
Raja's user avatar
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3 votes
1 answer
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Why is the term 'Accuracy of 1 part in $x$' used?

My question stems from how we measure the accuracy of Caesium clocks. Most Caesium clocks are said to have an accuracy of '$1$ part in $10^{14}$.' I understand that the terminology means to convey ...
Smarika Singh's user avatar
1 vote
1 answer
81 views

Entrainment of air and timekeeping of a mechanical watch at high altitude (problem attributed to A. H. Compton)

S. K. Allison told1 this Fermi problem: During the war, Professor A. H. Compton, Enrico Fermi, and I [Allison] were traveling together to visit the Hanford Plutonium Plant in the state of Washington. ...
Alessandro Jacopson's user avatar
3 votes
3 answers
329 views

Comparison of clocks running at different heights in a gravitational field

I hope this question has not yet been asked. If so then please link me to the answer. If I build an apparatus which, on flicking a switch, sends a light beam, a distance to a mirror, and reflects it ...
Paul Hinrichsen's user avatar
1 vote
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Relativity explained using sound instead of light

A friend of mine asked me to explain Einstein relativity to him, and I tried to use a methaphore using sound, however for some reason it does’t quite work: imagine there are 2 people with a clock, ...
Alberto's user avatar
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Clarification regarding the meaning of Universal Time UT1

I've been reading the book "From Sundials to Atomic Clocks: Understanding Time and Frequency" by James Jespersen and Jane Fitz-Randolph which is available at https://www.nist.gov/system/...
russell.price's user avatar
11 votes
1 answer
866 views

Northern lights / aurora borealis "pre-warning" - how does this work w.r.t timing and different particle / wave speeds?

There is an article in the newspaper today entitled "Northern lights predicted in US and UK on Monday night in wake of solar storms". I assume that the reason that someone can make this ...
jaimet's user avatar
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2 answers
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Condition for synchronizing clocks in the special relativity paper

I'm reading Einstein's special relativity paper and couldn't understand the condition for synchronizing given in the following paragraph taken from the paper - If at the point A of space there is a ...
Rishabh Kumar's user avatar
5 votes
3 answers
239 views

Time dilation rotating around the center of mass

If 2 objects connected by a massless rod or wire, rotate around the center of mass, do they experience time dilation ? I'm thinking that the smaller one will move faster so time will pass slowly, but ...
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0 answers
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Time taken for an object to fall [duplicate]

Time taken for an object to fall is generally given by $$t=\sqrt{\frac{2h}{g}}.$$ But this is only true under the assumption that gravitational acceleration is constant. With variable gravity what ...
Star Gazer's user avatar
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0 answers
52 views

Was "flow of time" equally fast during the life of universe? Is Doppler Effect the only interpretation of "shift to red"? [duplicate]

I'm an IT developer and recently I created a project where I tried to send signals between two threads in a slowing down environment. I simulated two points with their own clocks and tried to send a ...
aerion's user avatar
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1 answer
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How does the distribution of floor choices of your co-passengers affect your time of arrival in an elevator?

Note: This is a wiki post. Suppose you are late for a meeting and you have to take an elevator. The floor choice of your fellow passengers influences how late you will reach your destination. If ...
AlphaLife's user avatar
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3 votes
1 answer
122 views

What is the problem with two time dimensions? [duplicate]

I am reading a book "General relativity: The theoretical minimum" by Leonard Suskind. In page 168-169, the author explains the reason why we don't consider the case with two time dimensions ...
Zjjorsia's user avatar
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2 votes
1 answer
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Need help to clarify understanding example of time nature from Hawking's book "Briefer History of Time"

I'm reading Hawking's book "Briefer History of Time" both in Ukrainian and Russian languages and found a possible translation mistake in this paragraph (last page of "Chapter 6. CURVED ...
Oleksandr Bratashov's user avatar
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1 answer
73 views

Can a homogenous electric/magnetic field vary in time?

In either case I was thinking their curl is cero since they're homogenous. But that only leaves with $- \frac{\partial B}{\partial t}=0$ for example, but then?
MarioPEM's user avatar
2 votes
0 answers
76 views

An unusual calculation of our universe's age? [closed]

Does the following make sense? And has anyone else come across this odd ~’cosmological coincidence’ before?… …If we posit that our total universe mass is: (1) $$M_{U}=\frac{{M_{pl}}^4}{{M_{p}}^...
user86742's user avatar
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0 answers
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Symmetrical Time Dilation [duplicate]

I have lately been researching time dilation and relativity, and thought about this phenomenon: Take two people, Observer A, and Observer B, who are both carrying clocks. Observer A travels through ...
user392759's user avatar
-1 votes
4 answers
98 views

Does the speed of light determine how slow time can move?

Since moving faster makes time move slower. Does that mean that there is an absolute minimum rate at which time passes? If so. Is there also a maximum?
NewToPi's user avatar
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0 answers
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How much time passes relative to the protons inside the LHC?

The time depends on the speed of movement. Protons in the LHC move at near-light speed. Therefore, they perceive a different time than the scientist who is observing them. My question is how much time ...
nilecrocodile's user avatar
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0 answers
42 views

Time direction ambiguity in stationary observer's 4-velocity

Working in the mostly + convention, for a timelike geodesic in Minkowski spacetime we have the requirement that (c=1): $$u^\alpha u_\alpha=-1$$ and that it of course obeys the geodesic equation. If we ...
Mario's user avatar
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1 vote
2 answers
169 views

How come time does not commute with $i\hbar\dfrac{\partial}{\partial t}$ but it does so with $H$? [duplicate]

Are they not supposed to be the same operator according to Schrödinger equation? $$ i\hbar\dfrac{\partial}{\partial t}\psi = H\left(\vec{r},-i\hbar\nabla,t\right)\psi $$ Apparently $[t,i\hbar\dfrac{\...
K. Pull's user avatar
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4 votes
1 answer
671 views

Intuitive explanation of COSMIC TIME?

I came across the following statement, while studying a Newtonian model for cosmic expansion: "If $R(t)$ is the scaling factor, we can define the Hubble parameter as $H(t)=\frac{\dot{R(t)}}{R(t)}...
Ruba18's user avatar
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0 votes
2 answers
53 views

Gravitational effects on a celestial body and the difference between a pendulum and a regular clock

Imagine a planet with the same properties as Earth, this time moving in an elliptical orbit around a heavy star of a large number of solar masses. Also imagine that the surface of this planet is as ...
Apsteronaldo's user avatar
0 votes
2 answers
554 views

Can we define time as a field? [closed]

The main objective is, can we relate time in terms of a field, I know time differs in many properties from an usual field. But I always imagine time as an forward moving field and we all know it is ...
Ash's user avatar
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0 votes
3 answers
209 views

Why is it that objects inside a moving train tend to move at the same speed as the train itself?

I mean I get people saying because it's Newtonian mechanics. Everything inside the train will have same speed as that of train but my question is why ? Why is it like that ? And How does that happen ? ...
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