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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How are rotations invariant by time reversal?
The title summarizes it. I'm confused as to how the anti unitary operators work. If it inverts the signal of the angular momentum and conjugates the rotation operator, I can see why the rotation ...
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$i\epsilon$ prescription for finite systems [closed]
What is physical interpretation of path integral for finite time and finite epsilon (i.e without taking limits time->+-inf, epsilon->0)? Does it mean you are doing some finite temperature qft ...
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What is the difference between material time derivative and total time derivative of a tensor field? [closed]
I consider material coordintes as $(X_1(t),X_2(t),X_3(t),t_0),$ ($t_0$ arbitrary) and space coordinates as
$(x_1(t),x_2(t),x_3(t),t).$
$\textbf{Remark.}$ I am interested just in dim=3.
We consider a ...
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Relation between energy and time
I would like help in understanding something that has been causing me a lot of trouble recently: Why is energy always related to time in physics?
Examples include the 4-momentum, the energy-time ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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)...
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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 ...
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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)?
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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[...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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, ...
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