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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27 views

How Do we Know How Old the Universe Is? [duplicate]

It is common knowledge that the universe is 13.8 ± 0.037 billion years - but how was this calculated?
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0answers
21 views

Are these Kinematics Equations Correct? [on hold]

Can someone make sure that these kinematic equations I derived are accurate please? Thanks in advance. I'm new to this forum, so if I'm doing something wrong, let me know. I understand the below ...
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0answers
29 views

FINDING THE ANSWER [on hold]

Equiptment- Micronair air barrier sprayer (60 gal tank) Output Rate-2 gal/min Swath width-6 feet Product demand CS Rate 5 oz/1000 1, square feet is 22225 sqft 2.How many gallons of mix will we ...
3
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5answers
210 views

Two clocks along different worldlines

I have been reading and watching videos about this subject for a while now. I just can not seem to grasp the idea. Let's say we have two clocks. I leave one at home and keep one in my pocket. Then, ...
3
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0answers
65 views

QFT and violation of Heisenberg uncertainty principle

In some QFT books is said that a free electron can emit a virtual photon as long as it reabsorbs the photon and returns to its original state within a time: $$\Delta t<\dfrac{\hbar}{2\Delta E}$$ ...
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3answers
221 views

Where in, Einstein’s “On the Electrodynamics of Moving Bodies” (Relativity), is “Time” reasonably shown to exist, or why is it a valid assumption? [closed]

Given the widespread acceptance that “Einstein’s Relativity” reasonably proves the existence of Space-‘Time’, and thus “Time”... Can any member of the Physics StackExchange please show precisely ...
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6answers
36k views

How exactly does time slow down near a black hole?

How exactly does time slow down near a black hole? I have heard this as a possible way of time traveling, and I do understand that it is due in some way to the massive gravity around a black hole, but ...
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0answers
24 views

Relativity question [duplicate]

If a rocket is traveling away from earth, why does time pass slower for the rocket if from the rocket's perspective, earth is going away from it?
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2answers
77 views

Consistent answers in special relativity [closed]

I was doing a question about if a train fits in a tunnel. From the train frame it does not and from the tunnel frame it does. Then the question asked are these two answers consistent? What does this ...
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1answer
548 views

1D Kinematics - Relative Motion involving non-inertial frames of reference

I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
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4answers
61 views
0
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1answer
42 views

What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
2
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4answers
70 views

Why is coordinate time frame dependent? [duplicate]

Here is what I understand by coordinate time. It is the time difference measured between two events, using two synchronized clocks, one present at each event, and the difference is measured in an ...
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2answers
53 views

Does information paradox in the Many Worlds interpretation cause a problem? [closed]

I'm taking a philosophy of time travel class. In one of the lectures, the teacher was discussing problems with the Many Worlds interpretation. He talked about how since anything that can possibly ...
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2answers
93 views

Why does time slow down when traveling at high speeds [duplicate]

One of the effects of traveling at high speeds is slowing down of clocks. I can understand gravity time dilation effect but not how would velocity affect clock speeds. How correct it is, if I say ...
0
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0answers
43 views

How fast time goes in zero gravity [duplicate]

I understand that the effect of gravity is warping of space because of which object travels more through space dimension and less through time dimension, this is the reason for time slowing down in ...
1
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5answers
219 views

A question about motion and time dilation

I was thinking that if you are in empty space with another person (with no other objects around), and from a distance you see that the other person is approaching you a constant speed, you wouldn't ...
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5answers
103 views

About the perception of the flowing of time

The user John Rennie suggested I ask the following as a new question: If time is continuous why would the perception of time being continuous or flowing be an illusion?
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5answers
163 views

Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
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0answers
40 views

SciFi Stasis Field and the Quantum Zeno Effect

The Quantum Zeno Effect concerns the use of repeated measurement of a particle to prevent the time evolution of the wave function, and hence "freeze" it in the observed state. A Stasis Field is a ...
0
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2answers
59 views

If a photon is exists in 'timeless' state, how can objects around it move? [duplicate]

My understanding is that light does not experience time. In attempting to understand what the universe would be like from the perspective of a photon, the answer I get is that the universe would be ...
1
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3answers
81 views

Is the world we are living in discretized? [duplicate]

I do not know how to use professional words to ask my question, so I will try to use a layman language. Please bear with me for a moment. A ROUGH GUESS The world our eyes are seeing every moment is ...
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1answer
45 views

Gravitational Time Dilation Formula? [closed]

What is the equation for calculating the dilation of time at different levels of gravitational force?
1
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0answers
44 views

Do time dilation tests prove that it exists or that atomic clocks are faulty? [duplicate]

Are the experiments that prove that time dilation exists, actually proving that an atomic clocks ability to keep time is affected by gravity/acceleration? How do we know 100% that that is not the ...
2
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4answers
901 views

Which Schrödinger equation is correct?

In the coordinate representation, in 1D, the wave function depends on space and time, $\Psi(x,t)$, accordingly the time dependent Schrödinger equation is $$H\Psi(x,t) = ...
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0answers
237 views

Why discrepancies in the Schrödinger equation? [duplicate]

Why is there seemingly two definitions of the Schrödinger equation? \begin{equation} i\hbar\frac{\partial}{\partial t}\Psi=\hat H\Psi. \end{equation} And \begin{equation} i\hbar ...
3
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1answer
627 views

Time evolution in quantum mechanics

We know that an operator A in quantum mechanics has time evolution given by Heisenberg equation: $$ \frac{i}{\hbar}[H,A]+\frac{\partial A}{\partial t}=\frac{d A}{d t} $$ Can we derive from this ...
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1answer
51 views

What is the longitudinal difference between the sub­solar point and the magnetic poles at time $t$ (hours)?

I'm trying to convert geomagnetic coordinate to geographic, but there are some steps in the paper which I'm reading, that I don't understand. I have the geomagnetic latitude centered around the ...
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0answers
28 views

Ultimate Planck Frequency [closed]

Is there an upper limit to the Planck Frequency? Does it simply depend upon the inverse of the Planck Time unit?
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2answers
76 views

Time should run slower near massive body

We have considered that time should run slower near massive body like Earth, BH. There is no gravity in space, means time is faster in space compare to earth. Then How is it possible that man who ...
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2answers
396 views

Regarding time dilation and particle entanglement

I have a question regarding time dilation and particle entanglement. As I have read a few forums and questions here, I am aware both aspects do not contradict each other. Still, a question that I am ...
1
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1answer
425 views

How does time relate to mass and velocity

I understand that the larger the mass the greater gravity is and the slower time is, as well the faster an object is traveling the slower time passes. My question is that since the faster an object ...
1
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2answers
95 views

What would be the consequences of time not being “relative” [closed]

So far nobody proved Einstein wrong about Theory of relativity and time but I'm curious: What would be the consequences or problems if someone would prove him wrong when it comes to relativity of ...
2
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1answer
71 views

How many hours will there be in a day 5,000,000,000 years from now?

It is known that the moon is moving away from Earth 2cm a year, and in doing so makes the days longer. I want to know how many hours will have one day, when our planet is near its end.
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3answers
102 views

Can time be calculated without actually involving any matter?

Humans typically measure time by the change in material things. The movement of hands on a clock. The oscillations of a cesium atom. But can time also be measured by just changes in energy, and in ...
15
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5answers
1k views

Can black holes form in a finite amount of time?

One thing I know about black holes is that an object gets closer to the event horizon, gravitation time dilation make it move more slower from an outside perspective, so that it looks like it take an ...
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0answers
62 views

What is the true fundamental 'stuff' of physics? [closed]

It seems to me that most if not all of the publications and the institutional education of physics 'jump in' and start describing detailed phenomena without spending too much time describing and ...
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0answers
63 views

Commutation relation of a operator with Hamiltonian [duplicate]

Given that the eigenvalues of a Hamiltonian operator $H$ are bounded below, will a Hermitian operator $T$ exist such that $[T, H] = i\hbar{\bf 1}$ identity operator?
2
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1answer
46 views

How to find “Time” from “Force vs. Velocity” graph? [closed]

If I have Velocity on the $y$ axis and force on the $x$ axis how can I calculate the total time it takes to reach 4000 newtons? Is this just a case of integrating the gradient of the line?
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0answers
20 views

Converting between cosmological times

David Hogg's 'Distance Measures in Cosmology' is my go-to reference for all things cosmological. It's missing a discussion of time measurements however. How does one convert between different ...
1
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1answer
61 views

What is the physical clock ticking inside a living cell? [closed]

What is the physical process which determines the timescale of the aging of a living cell? It might be that on the macroscopic scale, i.e., aging of the human, the gravitational force is one factor ...
2
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1answer
88 views

Death by entropy

An idea struck me as I was walking to class today. According to Wikipedia, entropy is defined as the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a ...
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1answer
56 views

Special Relativity: Four possible time spans between events?

I've got another question regarding time in special relativity. I'll start with the standard configuration: there are two observers O and O', their x-axis are aligned, in the rest frame of O observer ...
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10answers
5k views

Is time continuous or discrete?

While working on physics simulation software, I noticed that I had implemented discrete time (the only type possible on computers). By that I mean that I had an update mechanism that advanced the ...
9
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4answers
2k views

Lagrangian to Hamiltonian in Quantum Field Theory

While deriving Hamiltonian from Lagrangian density, we use the formula $$\mathcal{H} ~=~ \pi \dot{\phi} - \mathcal{L}.$$ But since we are considering space and time as parameters, why the formula ...
2
votes
1answer
9k views

Need help with the position of a particle in a velocity-versus-time graph

I am having trouble with a velocity-versus-time graph. I recently took a Physics test that asked this question: The graph shows the velocity versus time for a particle moving along the $x$ axis. The ...
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1answer
54 views

Can time be Quantised? [duplicate]

Can time be quantised? Would it be the smallest distance between two photons moving in the same direction or the shortest wavelength?
9
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2answers
265 views

Is reflection instantaneous?

I was wondering while reading "On the Electrodynamics of moving bodies" by Albert Einstein (1905) (Translated to English). In the paper, he describes the time as being: by definition that the ...
1
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1answer
71 views

Time dilation: faster or slower?

I was wondering about Time-dilation in Special Relativity. I am still a middle school student who wonders so please excuse me if I missed any important aspects. Let us assume we have a system of ...
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5answers
335 views

Are events in this experiment simultaneous if observed in platform's frame?

In some contexts e.g. on Wikipedia it is defined as a matter of happening . In others(e.g. as defined by Einstein in his book "Relativity the special and general theory") it is defined as a matter of ...