# 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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### When Matter condensed — the condenser

Did gluons, quarks, and electrons first appear at the same age of the universe or was one first?
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### Can gravity act through time? [closed]

I know, that gravity acts through time and space, as it propagates at the speed of light, through space. I mean to discuss if the concept of gravity has an effect in space, along the time axis. I'm ...
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### Why would time behave differently in different parts of the galaxy? [closed]

I watched Interstellar and I got really confused around different time thing. How can it be possible at all that time is different at different places in the universe? Please explain.
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### Is time constant the same for linear system for all time?

I have heard that if you take a measurement $T_1$ and wait, then take another measurement $T_2$ and then find $\Delta T = T_2 - T_1$. Then 63% of $\Delta T$ + $T_1$ will represent the measurement when ...
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### Time quantization [closed]

There is no evidence to support that time is quantized. So wouldn't the use of discrete values like $dt$ in calculus suggest time is quantized and comes in discrete durations of $dt$?
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### Relativity and the observation of distant objects [closed]

If two identical telescopes orbiting earth take a picture of a far away galaxy, would relativistic effects lead them to significantly different observations? If so, how?
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I recently read about the early universe and found that first quarks were made 10^-12 seconds after the inflation or the beginning. But what was the cause of this minute delay ? Since inflation ...
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### Why does time flow? [duplicate]

People have explained how time flows but not why time flows or how time flow is possible at all. How does science explain time flow?
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### Question about uniform acceleration [closed]

I am studying for my university test and I have this question and it goes like this. A marble that starts from rest, slides down a slope of $30^\circ$. If there's no friction, what will be the speed ...
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### What could be introduced to provide a source of propulsion through time? [closed]

This Ape has been suspended in a 4 dimensional anti-higgs field time sphere, where as the only source of gravity interfering with this chimp is the interior materials and the chimp itself. What could ...
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### Why is the photon clock equivalent to all clocks?

I can understand why, if the speed of light is invariant, a photon clock would tick slower. I find this explanation very useful in terms of introducing the idea of time dilation (also because it ...
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### What would be the increase of gravity if we create a new world slightly bigger than the earth? [closed]

I need to know what would happen if I increased the earth's size by a small percentage to make a fictional world similar to earth. So my thought process is this: My thinking started with increasing ...
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### How to determine the correct time using quadratic functions if there are multiple “correct” roots exist in a 3D system? [closed]

Time can be calculated from a modified kinematics quadratic formula using the initial velocity, displacement, and acceleration. However, the acceleration vector isn't limited to 1 axis. When applying ...
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### Time dilation in Einstein's train

Wikipedia states that a clock that is moving relative to [observer] will be measured to tick slower than a clock that is at rest in their frame of reference and they explain it using two pictures: ...
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### Time dependency of inductor dimensions as a function of inductor geometry

While perusing the text book "Foundations of Analog and Digital Electronic Circuits" by Anant Agarwal, I came across this text in the section on inductors: Why are the dimensions of the ...
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### Time (or rather, $dt$) as a Vector? [duplicate]

I want to preface this by saying that I'm by no means experienced with the field of physics, but while on my commute this morning, I started thinking: Basically, I thought about time being a fourth ...
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### What is the smallest time that the current technology can measure?

Many physical phenomena are associated with unbelievably small time scales. Let me give a few examples. The time scale associated with visible light is $\sim$ a femtosecond ($10^{-15}$ sec), The ...
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### Difference between coordinate time and proper time in general relativity

I was watching a video on relativity on YouTube that talked about the difference between coordinate time $t$ and proper time $\tau$ and I have a couple of questions. As I understand it, the video said ...
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### How to get radius of trail with velocity and angular velocity?

If I know the velocity of something and the angular velocity of something, how could I figure out the distance between the object and the center it is rotating at? I just need an equation for the ...
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### How can I calculate the UV LED dose having few parameters such as wavelength and output power of LED?

i have UVC led with 270nm wavelength and output power of 70mW. The total length of the passage for the de-contamination is 40cm and the total time is 60 seconds. Is it possible to calculate the UV ...
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### Looking for a simplified explanation for why you cannot measure velocity and pin point location

Because of uncertainty, you cannot measure both velocity and exact position. Is this because when you measure the position of a particle, it is freezing it in its frame of reference? When measuring ...
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### Why are spatial derivatives of a field not used to define the conjugate momentum? [duplicate]

In mechanics, the conjugate momentum is defined to be $\pi=\dfrac{\partial L}{\partial \left(\frac{dx}{dt}\right)}.$ This can be regarded as a partial derivative with respect to a derivative of a ...
91 views

### Do all continuous gauge theories use Lie groups?

The article about gauge theory on Wikipedia contains the sentence "Lie group". How can we prove that the gauge transformations that are given in an article form a Lie group? I give you an ...
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### Time Reparametrization Invariance in GR

I've heard that the time reparametrization invariance in GR can be thought of as a gauge symmetry. Could someone specifically explain how, while also explaining if there is any connection with the ...
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### Problem 1: Sophism MIR publication [closed]

I am trying to solve the very first problem from the book "Physical Paradoxes and Sophism" The problem is as under: 1.1. The Amazing Adventure of a Subway Passenger: Every morning a ...
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### Confusion regarding the derivation of pressure in Kinetic Theory of Gases

I was studying the derivation of the relation between pressure ($P$) and root mean square speed ($v_{\text {RMS}}$) of an ideal gas from Fundamentals of Physics by Halliday, Resnick, Walker. (The same ...
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### Is it possible for physical constant to change in time? [duplicate]

There are many physical constants, like Boltzmann constant, light speed, dielectric constant of vacuum and so on. But is it possible to have physical constant that changes in time, for example it ...
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### Partial derivative of the function with respect to $t$ in total derivative

In the formula description there is one extra partial derivative compared to the example solution. What's the difference here? What's the physical implication of the last partial derivative in the ...
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### How can light travel the distance of nuclear size in negative time? [closed]

at first i thought time cannot be negative or zero but after going through the statement "time taken by light to cross a distance of nuclear size is 10^-23" iam confused
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### Is there an optimal intergalactical travelling speed? [closed]

In our perceiveable world, an increment of speed typically results in needing less time to travel a given distance. When I go by car, it takes less time then going by bike. However, there is the ...
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### Free falling into a black hole: time to the singularity doubt!

I have trying to get a more precise insight into the calculation of the time to the singularity of a test mass into a non-rotatic uncharged black hole. Prelude: the lagrangian for a massive particle ...
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### How do we introduce an hour as a time unit?

Historically, people measured time with the help of naturally recurring phenomena (say, a day). Then a day was split into smaller chunks (an hour, a minute, a second). Suppose we define an hour as 1/...
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### Position in generalized coordinates

In Lagrangian mechanics, when talking about a particle position expressed in generalized coordinates it is usual to find the expression: $$\mathbf{r}(q_0,...,q_k,t)\tag{1}$$ what it means this ...
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### Thought process at higher velocities

Time passes slower for objects that move at near speed of light . Since brain activity is based on signals that also need time to travel a certain distance, does the effect cancel itself out, or would ...
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### Quantum: Is it possible to determine the past knowing the present?

Due to quantum randomicity, it's impossible to determine the future knowing the present. But is it possible to determine the past knowing the present? As far as I understand, it is impossible because ...
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### Why exponential terms like $\exp (i\omega t)$ make no contribution when averaged over a long time?

In the physics of waves, I often see expressions like $$A\exp(i\omega t) + f(t)$$ where $A$ is a constant, $w$ is the angular frequency and $f(t)$ is an arbitrary function that depends on time. It ...
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### Do we know anything about the age of the universe?

I am looking to understand how the age of the universe is calculated according to modern physics. My understanding is very vague as the resources I have found do not seem to state consistently whether ...
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### Are the laws of physics eternal? [duplicate]

It is scientifically assumed that objects on a planet or heavy bodies fall towards it, when not supported by some ground; irrespective of time. Over a million years this does not change. Its the same ...