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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The time derivative term in the continuity equation
The integral form of the continuity equation is written as:
$$\frac{dq}{dt} + \oint_{S} \textbf{j} . d\textbf{S} = \Sigma$$
where $q$ is the amount of quantity in a certain volume $V$, $t$ is the time,...
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What about just "postulating" that time runs only forward?
I understand that $v \cdot t$ is a spatial dimension. And I understand that mathematically, the processes are the same if I move it in time or in space direction.
However, time is different to space: ...
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Questions about E. Minguzzi's article on Synchronization (arXiv:1009.3005)
Only recently I learned of E. Minguzzi's article
"Clocks' synchronization without round-trip conditions", [gr-qc: arXiv:1009.3005] ...
(Notably, the article available for download is dated ...
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Since we observe stars, galaxies, etc in their past - is it correct to say that our present is only present for us but is in the past from afar? [closed]
So - I know that when we observe galaxies, we are observing their past. And that if the same past-them were to be looking at us, they would see our past. But when we look at their past - that is a ...
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Calculate mass from time dilation
Hi not a physicist in any way so was wondering if I know the age (time passed) and mass of an one object and the age (time passed) of another object, can I calculate its mass?
So Object 1 is Earth:
...
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Relationship between clock rate and speed
Let's consider example:
The propagation of light from the middle of a moving train to its left and right ends. From the point of view of a train passenger, the light will reach the right and left ends ...
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Equality of variables for small values of time, when the time derivative of the variables are equal to one another
It is given that $\frac{ds}{dt} = \frac{d\theta}{dt}$, i.e. the time derivative of s and $\theta$ are equal to each other.
Does it follow that for small values of $t$, $\Delta s ≈ \Delta \theta$? My ...
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Intuition behind energy not being conserved in Rheonomous mechanical system [closed]
firstly, this is what Rheonomous System means. So, in such a system, the kinetic energy is not exactly just a quadratic function of generalized velocities because one of the generalized coordinates ...
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Reality of speed and time [closed]
I have a very simple question. How does a faster object takes less time for the same distance? A car with a speed of 100km per hour takes one hour to travel 100km while a car with the speed of 50km ...
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How to explain the time dilation effect non-mathematically (without Lorentz transformation)?
I read many good and rigorous mathematical explanations of the time dilation effect, but I didn't see any non-mathematical explanations.
Is it possible to explain the time dilation effect non-...
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How to measure time in reference frame with clock?
I considered example of time dilation with light clock. I have a question about measuring time in reference frame with clock.
If we know that clock move from A to B in the reference frame with clock ...
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Time dilation query [closed]
In the light clocks, time ticks via the motion of light and since speed of light is constant therefore when the clock is in motion ,the photon has to cover a greater distance by the perspective of an ...
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Why is the Accuracy in the measurement of Time so important in GPS?
I read in a physics book that
Without clocks of extreme accuracy, the Global Positioning System (GPS) that is now vital to worldwide navigation would be useless.
What would be effects on navigation ...
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What exists in the world according to the special relativity? [closed]
Before I learned about special relativity, I thought that only one 3-dimensional state of the world exists. Then, like in game of chess, in one "turn" previous state is destroyed - and the ...
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Has the age of the universe changed in 2023?
I teach high school physics and physical science. I was going through the definitions of theory and law when a couple of my students (of different periods) asked about some recent development that ...
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Does special relativity imply that there's such a thing as absolute time, or base time?
If time measured by one observer moving at a greater velocity than another observer is observed to be passing more slowly, does this imply that there's such a thing as "absolute time" or &...
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Theoretical: what is the meaning of nothing? [duplicate]
Before the big bang, there was a point surrounded by nothing (no space or anything). Then the big bang happened and the universe expanded. so beyond the universe's limits, there is nothing? I don't ...
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What is the reason of different clock's measurements in different frames? [closed]
I tried to understand what is the reason of different clock's measurements in different frames.
For this I looked at easy example with distance S traveled by man with moving clock (velocity V1=2m/s) ...
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I need a ship at rest to accelerate under preferably constant acceleration/deceleration to arrive at rest at an object 55 AU away [duplicate]
I'm working on the story and I need help with the plot point. Assume that the energy needed for constant acceleration is not a problem. And there's no need to complicate this with outside forces.
I ...
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How to derive the period of non-circular orbits? [closed]
By conservation of mechanical energy:
$$
E(r_0)=-\frac{GMm}{r_0}+\frac{1}{2}\mu \left (\dot{r_0}^2+r_0^2 \omega_0^2 \right)
$$
where $r_0 =r_{max}$. Because our body is located at the apoapsis: $v_r = ...
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In spacetime time is a coordinate. Does it mean there is a single objective timeline for the Universe?
If every event can be defined with x, y, z, t coordinates - does it mean all events with the same t are composing the whole Universe at the moment t?
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How is pressure related to time?
I was studying physics for my exams when I came up with a question:
there is this relationship $1Pa=1kg/(m*s^2)$ , which I reckon to be true as you can define pressure as $F/A$ and also by Newton's ...
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SLM pulse shaping to delay (and advance) ultrashort pulses in time
I am trying to replicate some of the experiments discussed in this excellent publication:
SLM for pulse shaping
In particular, I replicated the setup configuration in Figure 14 and I want to use the ...
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Is heat death absolutely and really inevitable? [duplicate]
As the second law of thermodynamics indicates, entropy would continue to grow in the universe until it reaches a maximal value (in an expanding universe with a cosmological constant, like ours) or ...
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How does the lifetime and temperature of a black hole scale with mass in higher dimenstions?
I've tried to find out how the lifetime and temperature of a black hole scale with mass in a universe with more then 3 spatial dimensions. I've spent a while trying to look up an answer to this ...
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Can it be accurate to say that time is also a length?
So a type of measurement, in units, is length, position, mass, etc, and a unit is meters, kilograms, etc.
Is it accurate to say that "an hour" is a time measurement, but also a form of ...
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How to measure time difference in different frames of reference in relativity
I saw this post about measuring the time difference between two clocks and I couldn't understand Ajay Mohan's answer even after his edit.
I tried to draw a picture of what I think actually happens.
...
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Notation confusion about time derivative of a vector in a rotating frame
As far as I can tell, this question, or similar ones, have been asked a number of times:
Derivation of the time-derivative in a rotating frame of refrence
Time derivatives in a rotating frame of ...
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Could you take a point on the surface of the earth as the frame of reference in the Hafele-Keating experiment?
I was recently reading about the Hafele-Keating experiment and asking, how does time in the plane which has flow westwards could have passed faster than on the surface of the earth if the frame of ...
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Lack of independence between the spatial dimensions and time within space-time
I am having a conceptual difficulty understanding the following issue regarding space-time: it is clear to me why a full description of coordinates requires three spatial dimensions plus time. However,...
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Speed of Light and Time [closed]
I'm an amateur and this is my first question here, I'm trying to formulate question about a general representation I have in mind after trying to grasp the idea of relativity and the concept of space-...
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Why would we correlate dark energy to the rate of universal expansion: $dS(x,y,z)/S(x,y,z)$ and not to the flow rate of cosmic time $dt/t$?
Cosmic time, which is the same from one place to another (at a given instant), is it also the same from one moment to the next?
To compare the cosmic time at two different instants,
we would need ...
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What changes do we have when we consider time dilation of light clock? [closed]
According to the special theory of relativity, in moving body all physical processes are slower than they should be for a stationary body according to the time counts of a fixed (laboratory) frame of ...
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To what extent does Time Dilation occur?
Time Dilation is a fundamental concept in the theory of relativity, encompassing both special and general relativity. It describes the phenomenon where time appears to pass differently for observers ...
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Local Gravitational Time Dilation Effects on Entangled Particles
If Alice is located just beyond the event horizon of a black hole, and Bob is at some other point in space with de minimis gravitiational effect, what, if any, effect would it have on the "spooky ...
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If an object is travelling at say 35 mps, if I somehow stop the time, is the speed zero or 35 mps? [closed]
I know we only go close to zero, not equal zero, but if that somehow happens, will it be zero as it is at rest or 35mps as when you resume the time, the speed is 35mps?
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What is stopping optical clocks from redefining the second?
Optical clocks, based on optical transitions either in cold atomic lattices or trapped ions, have been shown to up to one million times better accuracy/precision compared to the cesium microwave ...
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Defining the second by an alien civilization [closed]
(The above question could be phrased better, so feel free to suggest.)
Like many, I was imprecisely told that the second is 9192631770 oscillations of caesium valence electron (or smth along those ...
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Topology of Time
I came across the concept of topology of time and causality in Reichenbach book, "Philosophy of Space and Time". It would be nice to have list of references of recent developments of the ...
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Average Time since the Big Bang
Can we define an average time for the entire universe relative to the Big Bang and call this the universal time since the beginning of the universe? (time, averaged relative to all possible reference ...
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Why can clocks not be compared unless they are meeting?
In the answer here to a special relativity question about clock synchronization: https://physics.stackexchange.com/a/485517/141472 it says (bolding mine):
As long as the two space ships are not ...
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Time of collision of two relativistic speed particles
Suppose I have two particles, one moving at $0.9c$ to the right, starting at $(-0.9c,0,0)$ in the lab frame at $t=0$ and the second one moving at $0.9c$ to the left, starting at $(0.9c,0,0)$. In the ...
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How to prove that time slow down on all type of clocks? [duplicate]
I read about time dilation and how to prove time dilation existence with light clock.
But how to prove that time slow down on all other type of clocks (biological, mechanical, digital, electric, ...
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Neutrino oscillations imply neutrino mass — Does the usual argument really hold?
An argument that people put forth is that because neutrinos can undergo changes in lepton flavor midflight, they must "experience time." Since massless particles must travel at the speed of ...
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What has coherence time to do with Energy-time uncertainty?
we know that the coherence time $t=\frac{1}{\Delta f}$can be derived from Fourier transformation.
But if we look at the Energy Time Uncertainty which is given by $\Delta E \Delta t ≥ \frac{h}{4\pi}$ ...
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Is nature discretizable? [duplicate]
From mathematical perspective, can we describe all the realistic quantum mechanical phenomena at any given moment by functions alone, or is it correct that distributional behavior can also be observed ...
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Justification of string breakage in Bell's Spaceship paradox from observer's frame
In Bell's Spaceship Paradox, are there any direct observations that the stationary observer can make that would justify the breaking of the string without taking into consideration as to what's taking ...
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Effect of the length $\ell$ on a pendulum
Currently, I am trying to intuitively understand how the length $\ell$ affects the period of a pendulum. I understand that the shorter the length $\ell$, the shorter the time period $T$. When we have ...
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Commutator of energy and unitary time evolution operator
Edited:-
$\hat{H} = -\frac {\hbar^2}{2m} \frac {\partial^2}{\partial^2 x}~+~V$
$\hat{U}(t) = e^{-iHt/\hbar}$
The Robertson Uncertainty Principle states:-
$\sigma^2_A\sigma^2_B \ge (\frac {1}{2i}[\hat{...
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A unit of time $\frac{GM}{c^3}$ [closed]
I have come across a time unit $M$ that should be equal to $\frac{GM}{c^3}$. I cannot find anything at all about this anywhere.
I came across it while doing flux analysis on the flux from black hole ...
