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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1answer
37 views

Time a fundamental force? [closed]

If time is emergent especially immediately after big bang then is it a fundamental force that appeared at that moment
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If time is an illusion, then is free will also an illusion under such illusion? [closed]

Space time has existed from the beginning of the universe and until its end and humans exist on 3D plane. Due to its limitations, it is only able to experience one period of spacetime, like being ...
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Laws of nature and relative motion [closed]

According to the principle of relativity, the laws of nature should be independent of the relative movement of different frames. My doubt is the meaning of "laws of nature". So, suppose a ...
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A 'better' definition of time [closed]

I have been annoyed by official definitions of time from many Google searches and decided after listening to Sean Carroll's podcast to write my own. Here is what I did so far: What is time? A state ...
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Welche physikalische Wechselwirkung hat die Zeit in der Natur? Bei Temperaturen unter 0 Grad Celsius wird Wasser zu Eis [closed]

Welche physikalische Wechselwirkung hat die Zeit in der Natur? Bei Temperaturen unter 0 Grad Celsius wird Wasser zu Eis. What physical interaction does time have in nature? At temperatures below 0 ...
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Force from time and velocity

Let's say I have a goal velocity $(v)$. In $n$ amount of time $(t)$ (let's say two seconds). What is the formula for finding the amount of force I would need (not counting other forces like drag/...
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Can Toroidal High Voltage Capacitors Cause Time Dilation?

I read in NASA's Warp Mechanics, they managed to warp space time with a high voltage toroidal capacitor, as detected by an interferometer. So I was wondering, is it possible to dilate time with this ...
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Are zero meters equal to zero seconds? [closed]

Is $0\,\mathrm m=0\,\mathrm s=0\,\mathrm g$? This would seem somewhat logical given the mathematical properties of physical units, but also not necessary.
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Three Questions On Special Relativity [duplicate]

Twins Paradox Using the simplified version of the paradox, where acceleration to near light speed and the turning of the spaceship are almost instantaneous, the paradox is completely symmetrical - in ...
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1answer
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Generalised Gell-Mann and Low theorem for explicitly time-dependent hamiltonians

Is there a generalisation of the Gell-Mann and Low theorem that applies to the case of explicitly time-dependent hamiltonians? Any good references on it? (Not on the original proof which is for $H=H_{...
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Change with time

I was going through a silly doubt, but aren't able to find its answer. If we say something is changing with time, what do we mean by that? Should we multiply the quantity with time or divide it? Like ...
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Black holes and time dilation: how we could see interaction with other objects?

I have a question on the observable behavior of a Black Hole. So, I am not asking what is going on “now” at the Event Horizon or how can I “see” (get particles or waves). The question is how should it ...
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Energy conservation as non-time-dependence in SIMPLE terms

In Berkeley Physics Course volume 1 on Mechanics, on page 144 it says "The law of conservation of energy states that for a system of particles with interactions not explicitly$^1$ dependent on ...
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Is there a time component for each probable state of the wave function?

In other words, when does time or a time direction come into play or does it in the equations? Is there time or time directions associated with each probable state of a quantum system or does time ...
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2answers
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Is anything truly continuous? [closed]

Is any 'continuous' thing (fluids, light, time, etc...) truly continuous? Or is it really batch but at just such a high frequency that it appears to us as continuous? I.e. it appears to me that the ...
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Whats "integration time" in two photon microscopy?

What is the meaning "integration time" in Two-photon excitation microscopy? Why a mode-locked signal (laser) can reduce the "integration time" in Two-photon excitation microscopy?
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The time component of a geodesic [closed]

A geodesic is the path taken by a falling object so if the person is standing still he is not following a path, he is stationary on a path. This could be called "standing still" on the ...
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Does Gravity Causes Time Dilation?

Let's say there are 2 people, A and B. They both are at the sea level. A gets higher than B. Does time moves faster to A then B? (Does height -in other words gravity- causes Time Dilation?)
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Quantitative relation between entropy and time

Increase in entropy gives us the arrow of time. But is there any quantitative relation between these two quantities that relates the entropy change with time interval? Any literature/text/paper on ...
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Do photographs/microscopes capture instantaneous moments in time?

According to physics, our current understanding has space and time as continuous entities. Photographs generally work by letting light modify a surface by striking it and it forms the picture. The ...
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1answer
61 views

Does this relationship hold for the time derivative of an operator?

The derivation for the Ehrenfest Theorem that I've seen uses the chain rule across $\frac{d}{dt}\langle\psi|\hat{A}|\psi\rangle$ giving three terms: $(\frac{d}{dt}\langle\psi|)\hat{A}|\psi\rangle + \...
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How the information is related to time in physics?

The interpretation of information in physics is confined to assuming instant interactions and stationary states. Today we started to learn that when having higher resolution measurements, even most ...
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1answer
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Time dilation in the center of the earth [duplicate]

The time dilation seem to slow time in stronger gravitational fields. Lets say we put a person with a clock in the center of the earth. It will feel no gravity since it's pulling from every direction ...
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1answer
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How is atomic time defined in Hartree units?

As in Planck units, I believe Hartree units have a fundament unit of time, Atomic Time, something like $2.4188843265857(47)×10^{−17}$ s. My question is what exactly is it that happens in this time? ...
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Two ships meeting in the distorted spacetime of a Krasnikov tube - what happens?

Given a Krasnikov Tube: a speculative mechanism for space travel involving the warping of spacetime into permanent superluminal tunnels. The resulting structure is analogous to a wormhole or an ...
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Does "absolute time" exist, in any sense? [duplicate]

When physicist Steven Weinberg (who, sadly, just died recently) wrote a book about "The First Three Minutes" of the universe, doesn't this imply that there really was a distinct period of ...
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Is time taken by light to travel any distance 0 or finite? [duplicate]

According to relativity, Light does not experience any time. So it must travel any distance in no time. But, we know that light has finite speed $c$. So it should take finite time.
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Clock in gravitational field

Weinberg writes in his book: Consider a clock in an arbitrary gravitational field, moving with arbitrary velocity, not necessarily in free fall. The equivalence principle tells us that its rate is ...
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Condition for a time-dependent transformation to be a canonical transformation [duplicate]

I'm looking for a sufficient condition to determine if a given transformation is a canonical transformation. I have found two conditions, but they are only valid for the case that the transformation ...
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Two bodies A and B fell from rest Compare the time of arrival of objects A and B to Earth [closed]

Two bodies A and B fell from rest from a height of 100 m, and body A reached the ground Directly while body B hits an inclined surface making its velocity horizontal as shown in the figure, Compare ...
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1answer
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How to find time at any point on the path of a projectile motion?

I know how to find the time of flight and all but what if I chose a random point on the path of the projectile (no air resistance) and ask the time at which the particle is present there, then how can ...
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1answer
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How can we perceive light if light doesn't move through time? [duplicate]

From my understanding in space-time everything moves at the speed of light $c$ in some direction of this four dimensional space. Light itself moves only through space, so it doesn't move at all in ...
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Should time be a loop or a line?

It's interesting to see that torus was so popular in physics, that it worked so well. There was famous Gauss–Bonnet theorem which stated basically $$\oint_S K dS= 2\pi \chi(S)$$ where K was the ...
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Infinite bouncing in finite time?

Is it possible to calculate the time in which a bouncing ball with restitution coefficient $k$ which first hits the ball with velocity $v$ will be considered stopped? Note that each collision lasts $\...
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Block universe and entropy [duplicate]

I understand “Block Universe Theory” says past, present and future all exist at together and time is emergent (and not fundamental). I wonder how physicists who support this theory explain the ...
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1answer
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What is the relation between Time and Energy? [closed]

According to the formula $E = hf$, it can be re-arranged like $E = h/t$ where, $t =$ time, $E =$ energy, and $h =$ Planck's Constant. So from this, it would be reasonable to derive a relationship ...
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1answer
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What is the Poincare recurrence of the OBSERVABLE universe?

I have heard about a number called the Poincare recurrence time on Numberphile. It did not seem that exact in the way that it calculated this number, which was a power tower of 10s. What is the ...
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If I add one particle to the system at a time, When does the time reversal symmetry breakdown?

Suppose I have a system in my mind which consists of two elementary particles interacting with each other via fundamental interactions. We know that fundamental interactions have $T$-symmetry and ...
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Is time the collapse of quantum superposition across the universe?

Just to preface, I admit I'm not a physicist, or even well-read on science-related things (though I do read articles from various aggregate sites and sometimes purchase New Scientist) but I am ...
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Does real life have "update lag" for mirrors?

This may sound like a ridiculous question, but it struck me as something that might be the case. Suppose that you have a gigantic mirror mounted at a huge stadium. In front, there's a bunch of people ...
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What does it mean in practical terms that time inside a black hole gains space-like properties?

I've seen time inside a black hole described as gaining space-like properties - essentially swapping its properties with space, which becomes time-like, meaning there is only one possible direction of ...
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1answer
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Is time still (frozen) for a single isolated particle?

I understand entropy is called the arrow of time because it is the only physical property which always increases in an isolated system (based on 2nd law of thermodynamics). On the other hand, entropy ...
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1answer
56 views

Lifetime of pulsars

According to many textbooks, pulsars have lifetime (the time it would take the pulses to cease if $d(P)/dt$ were constant). Lifetime is $P/[d(P)/dt]$, $P=$period Why do P/[d(P)/dt] means the lifetime?
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Does time-independence of potential energy imply time-independence of the Hamiltonian in Quantum Mechanics?

Consider a quantum mechanical system for a particle with Hamiltonian $\hat{H}=\frac{\hat{p}^2}{2m}+\hat{V}$ where $\hat{V}$ is the potential energy operator. and now let us assume that $\hat{V}$ is ...
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Can we find the time after which thermal equilibrium is reached for 2 substances in contact?

The Zeroth Law of Thermodynamics states that if two systems are in thermodynamic equilibrium with a third system, the two original systems are in thermal equilibrium with each other. It says that ...
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Proper time in General Relativity and change of coordinates

Let $M$ be the spacetime manifold and let us consider a local coordinate system \begin{align} \varphi_i:\,U_i&\subset M\to \varphi_i(U_i)\subset \mathbb R^n, \end{align} which associates $p\in ...
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Imaginary Hamiltonian

The Hamiltonian for nuclear spin independent parity violation in atoms is given by: $$H_{PV} = Q_w\frac{G_F}{\sqrt{8}}\gamma_5\rho(r)$$ Here $Q_w$ is the weak charge of the nucleus (which is a scalar),...
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995 views

Why is absolute time considered an axiom of Newtonian mechanics? What statements are based on this axiom?

I guess absolute time is associated to classical mechanics because people like Newton believed in that concept, but are there actually any statements whose derivation is based on this assumption? I've ...
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1answer
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Can a frame of reference travel with the speed of light? [duplicate]

I read that nothing with mass can travel at the speed of light. Therefor one can not ask what happens when an observer in a car moves with the speed of light. But, is it possible for a frame of ...
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1answer
46 views

Two clocks in a room, different in motion and distance to the gravity center

According to the special and general relativity, lets say we have a room with two clocks. Clock A stands motionless on a table, while clock B is moving fast from on side of the table to the other one,...

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