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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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7answers
119 views

What happens to velocity when Time equals zero?

I am not formally educated in Science but natural questions have always intrigued me.The way I put it is that I am married to Commerce but Science has been a childhood love. Now I have this very basic ...
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0answers
47 views

What is “Time Convection” ? Can it exist, how can we imagine it? [on hold]

Talk ... I want to know what is the therm "Time Convection" ? Can it exist, how can we imagine it, and how can it be represented ? And I mean CONVECTION not convention ... lets not forget that ...
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0answers
16 views

Effect of variation in day length on timekeeping

I was reading about atomic clocks when I came to know that precise measurements of time have shown that the time for earth's rotation is slightly more that 24 hrs (on the order of 10^-3). I was ...
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0answers
25 views

Clock equivalence [on hold]

As far as anyone knows, has an extremely precise experiment been ever conducted to determine whether a pendulum clock is identical in terms of keeping time to when compared to an electromagnetic force ...
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1answer
41 views

Convective derivative vs total derivative

I was wondering what is the difference between the convective/material derivative and the total derivative. We were introduced to the notion of material derivative $$ \frac{D\vec{u}}{Dt}=\frac{\...
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0answers
40 views

How old would earth be if altering systems velocity [closed]

Time dilation explains why two working clocks will report different times after different accelerations. For example, at the ISS time goes slower, lagging 0.007 seconds behind for every six months. ...
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1answer
72 views

What is the physical interpretation of the Wick rotation?

What is the physical interpretation of the Wick rotation? How is it that we can just propose there's a new time coordinate tau? Are physicists saying time is modeled by an imaginary number? Isn't ...
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1answer
22 views

Would not the oscillation of light slow down the wave? [duplicate]

Would not the oscillation of the light wave slow down the wave? Does light travel at "c" of its net position over time, or does it travel at "c" on the wave?
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1answer
34 views

How do you calculate conformal time?

I've got several references that indicate that conformal time is the integral of the scale factor: $$\eta=\int_0^t \frac{1}{a(t)}\mathrm dt.$$ So I tried to calculating this over a range of {0, ...
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1answer
143 views

Is the M87 black hole really a black hole? [duplicate]

I apologize if this is a silly question, but... From what I've been told, new black holes cannot form, because time slows to nearly stopped as matter approaches the event horizon. Instead, a new ...
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0answers
66 views

Is now a universal constant? [duplicate]

As I'm typing this question, there is probably a star, somewhere in the universe, going supernovae. These two events are occurring now. At the same moment in time. Simultaneously. I may never observe ...
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2answers
152 views

Why the time period of pendulum with infinite length is $84.6$ minutes? [closed]

In a book I was reading about SHM it stated: If the length of a simple pendulum is increased to such an extent that $\ell\to\infty$, then its time period is given by, $$T=2\pi\sqrt\frac{R}{g}\...
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1answer
29 views

Aging while traveling faster than speed of light? [closed]

theoretically, if organic matter was able to travel faster than the speed of light, without becoming "pure energy", and since theoretically traveling faster then the speed of light would travel ...
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4answers
12k views

How can a day be exactly 24 hours long? [closed]

The longest solar day of year is approximately 24 hours 0 min 30 seconds (occurs at mid to late December) while the shortest solar day of year is approximately 23 hour 59min 38 seconds. If I average ...
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3answers
538 views

Why are time dilation and length contraction needed to fix time? [duplicate]

In many textbooks and online answers I have heard people go on about how time dilation accounts for the gap of time experienced between two observers. However, they continue that in reality this is ...
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0answers
23 views

Is there a “smallest unit of time”? [duplicate]

I am aware of the planck-length, being the smallest unit of space. I was wondering if there was such a thing as the smallest, undividable unit of time, something like 1 x 10 to the power of -35 ...
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2answers
96 views

Clocks only measure repetitions and not time [closed]

To measure time, we use clocks. From sophisticated atomic clocks to everyday wall clocks. When we measure the length of a time interval using a clock, we are really measuring the number of times the ...
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0answers
15 views

Does time flow or do we move through time? [duplicate]

I hear time spoken of as something that flows like a river. Something that stops. I've also heard of time called a dimension. Something through which we move. These two ideas seem incompatible. Does ...
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3answers
99 views

What is the best way to conceptualise a 'division' [closed]

This may seem like a strange question, but my question is more along the lines of trying to figure out how people were able to 'discover' the formulas which have shaped our understanding of the ...
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3answers
48 views

Inserting an arbitrary phase in the equation for driven damped oscillations

In Classical Mechanics by Taylor, we find the solution to the differential equation of a damped oscillator with a sinusoidal driving force: $$\ddot{x} + 2\beta\dot{x} + \omega_0^2x = f_0\cos\left(\...
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1answer
50 views

Integer multiples of fundamental time period? [closed]

If we define harmonics to be positive integer multiple of fundamental frequency What will we say to positive integer multiples of fundamental period?
3
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0answers
46 views

Can Noether's theorem be applied to cyclic time symmetries? [duplicate]

Noether's theorem relates continuous symmetries in the time evolution of a system to a conserved value. Many conserved values, such as conservation of momentum, can be described via this theorem. I'...
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2answers
142 views

Why is it necessary to keep UTC within 0.9 seconds from UT1?

Why is it necessary to keep UTC within 0.9 seconds from UT1? I thought that UTC in fact more accurate than UT1, so why should it be based on UT1 within that range? Another question would be, why isn'...
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1answer
44 views

Einstein's Theory of Relativity Time Dilation

My friend claims that this proves that time moves faster on a mountain than at sea level. He says that since both of these people start and end at the same angular position and are both traveling at ...
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2answers
95 views

Relativity Confusion

In the time dilation formula $\Delta t=\gamma\Delta t_0$, I am confused about what $\Delta t$ and $\Delta t_0$ measure. If we have two people, Tom and Bob, moving at constant velocity relative to ...
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1answer
103 views

Solution of Friedmann equation in terms of conformal time

We know that for the flat geometry of lamda CDM model, the solution for Friedmann equation is $$ a(t) = \left\{ \frac{Ω_{m,0}}{Ω_{Λ,0}} \sinh^2 \left[\frac{3}{2} \sqrt{Ω_{Λ,0}} H_0(t - t_0)\right] \...
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2answers
112 views

Does time stop inside a black hole? How about at it's singularity?

I'm a layperson who just read Brief Answers to Big Question and in the book, Hawking proposes that: A typical black hole is a star so massive that it has collapsed in on itself. It’s so massive ...
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0answers
78 views

How is time “homogeneous”?

My book$^1$ states: Let's consider a clock moving freely over a curve such as: \begin{equation} \frac{dx^i}{dt}=\text{const} \tag{1.20} \end{equation} We define the proper time $\tau$ as the ...
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2answers
121 views

A theoretical limit of accuracy?

Is there an agreed upon/conjectured theoretical limit to our ability to resolve the accuracy of time?
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2answers
155 views

With drag, why does it take longer for an object thrown upwards to fall back down than it does for it to reach its highest point? [duplicate]

Why does it take longer for an object thrown upwards to fall back down than it does for it to reach its highest point? We can draw a free body diagram for when the object is falling down and for when ...
1
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1answer
65 views

Recordings of journey traveling near speed of light

If you had two identical video cameras and started recording synchronized atomic clocks recording at the same speed and you put one on the spaceship and sent it out traveling at 99% of the speed of ...
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1answer
44 views

Is the answer to the question “How many moments in time exist between any two particular moments?”, infinitely many? [duplicate]

This question is related to Xeno's paradox, and to the discrete/continuous time debate, but it comes from a slightly different angle. If the answer is infinitely many, why would this not be a ...
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1answer
54 views

Imaginary time concept in S.Hawking's No Boundary proposal, extra-time dimensions and the Big Bang

In this post I will be refering to S.Hawking's lecture: http://www.hawking.org.uk/the-beginning-of-time.html I have a couple of questions regarding the Imaginary time and the Big Bang. In the ...
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1answer
64 views

Graviton particles travelling backwards

I know that time travelling backward particles are anti-matter particles but what about graviton time travelling backward?
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1answer
61 views

What is the meaning of $d$? [duplicate]

What is the meaning of $d$? Is is Delta? If it is Delta, why is it then not $\Delta$? I am still confused with that. Can someone help explain it to me?
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4answers
105 views

Present vs Past in Cosmological time

My question is in regard to “seeing back in time” when observing objects in space. I understand the concept that light takes a certain amount of time to reach the earth and we can determine the ...
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1answer
21 views

Amount of Time the Moon remains overhead at Night?

I was wondering, as the Moon moves across the night sky, at midnight, when the Moon is overhead, how long does it technically stay over head before moving to the other side of the night sky? I was ...
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0answers
43 views

What would be the time dilation standing on a neutron star in comparison to earth?

What would be the combined gravitational and velocity time dilation one would experience if they stood on the surface of a neutron star in comparison to standing on the earth's surface? Specifically, ...
2
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1answer
51 views

Small oscillations in the given potential

The task is to find the period of small oscillations in the potential $$U=U_0\tan^2{\Big(\frac{x^2}{a^2}\Big)}.$$ I started with finding the stable equilibrium points: $\frac{dU}{dx}=0$ $2U_{0}\...
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0answers
44 views

Time derivative in rotating frame

In Goldstein (2ed) sec 4.9 - Rate of change of a vector, why does he say that the instantaneous angular velocity $\omega$ is not a derivative of any vector? $$ (d\textbf{G})_{space} = (d\textbf{G}...
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2answers
79 views

Would a human age faster if these certain conditions are met?

So, a human would travel in a rocket in outer space. There is little to no gravity, and the pressure may or may not have an affect (?) on what i'm about to ask. It has been proven that when a human ...
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1answer
30 views

Does $L=T-V$ still hold when $L$ is NOT time-dependent?

I am aware that the Lagrangian $L=T-V$ where $T$ is the kinetic energy and $V$ is the potential energy when $L$ depends on, for example, $r, \dot{r}, t$. My question is, does this still hold when the ...
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2answers
75 views

Reason why dot notation isn't used for time derivatives in Maxwell's equations [closed]

Maxwell's equations seem to be usually written: \begin{align} \nabla \cdot \mathbf{E} &= \rho/\epsilon_0,\\ \nabla \cdot \mathbf{B} &= 0,\\ \nabla \times \mathbf{E} &= -\frac{\partial \...
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1answer
70 views

Do gravitational waves affect the flow rate of time?

Since LIGO has been able to detect the presence of gravitational waves, this implies that there is a density wave traveling through space with a high potential front and a low potential back side. ...
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2answers
46 views

Is simultaneity of events relative or just our observation of it?

I have already read this post about Relativity of Simultaneity but it doesn't seem to answer my question or it confuses me even more. Please feel free to close this if I am mistaken. I (think I) ...
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2answers
686 views

Are Mirrored Universes With Opposing Directions of Time Theoretically possible? [closed]

I found an article that talks about this here, entitled "Big Bang May Have Created a Mirror Universe Where Time Runs Backwards". I know any notion of backwards time is probably a dead horse in this ...
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1answer
42 views

Physics of time running backwards

Although it would seem weird to analyze physical phenomena when time runs backwards, it seems to have a logical sense, at least for me: Entropy would tend to decrease: two balls having energy ...
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1answer
21 views

Lagrange's equation for system not having time translation

While we are deriving Lagrange's equation from D'Alembert's principle, when we argues as; $$\delta \vec r_\alpha = \sum_i \frac{\partial \vec r_\alpha}{\partial q_i }\delta q_i + \frac{ \partial \...
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2answers
69 views

Spatial and temporal dimensions orthogonality

It seems that the spatial dimensions are orthogonal: a particle can move along one axis without changing its position in relation to other two axes. It seems that the temporal dimension is somewhat ...
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0answers
48 views

One Electron Universe - Bumping particles back in time? [closed]

I understand that John Wheeler's 'One Electron Universe' proposal is not generally accepted, but it's obvious that in disproving such a proposal, or at least discrediting it, we can gain insights to ...