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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97 views

Is a non-accelerating object far from a gravity source moving at the speed of light through time?

I'm trying to understand the Minkowski spacetime better. If an object is not undergoing acceleration, and is far from any large mass, does it travel maximally "fast" through time? Can we calculate a ...
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0answers
94 views

Which physical entities equal “distance times time”?

Are there useful physical quantities with dimensions of distance-time? The background for this question is a differential equation which I try to make sense of: ...
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1answer
85 views

How do we presently understand time?

How do we presently understand time? Can a second be related directly to physical phenomena? What is a second really? Why are we sure that time is linear?
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5answers
809 views

Does coordinate time have physical meaning?

I have always been a little confused by the meaning of the "$t$" which appears in spacetime intervals or metrics in general relativity. I concluded that $t$ was just a mathematical thing which allow ...
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0answers
83 views

When did people start to regard “time” as a physical quantity? [closed]

I was trying to figure out how people came to know about time then I realized that people started keeping track of time to know about sunset and sunrise. But I can't figure out how did time came into ...
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1answer
202 views

Are we comoving observers of space expansion?

In cosmology: A comoving observer is the only observer that will perceive the universe, including the cosmic microwave background radiation, to be isotropic. (Wikipedia) According to this ...
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1answer
457 views

Does time invariance conclude conservation of energy? [closed]

I find it hard to understand that time-translation invariance necessarily implies conservation of energy. As I understand it, Noether's theorem says that there is an energy conservation because the ...
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3answers
9k views

What is a good definition of 'time'? [duplicate]

I know this is a silly question, but I'm only asking this because I honestly can't seem to find a good definition of time that doesn't include another word that relies on the definition (or logical ...
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2answers
477 views

Is time infinitely divisible? [duplicate]

Simple question (I think). Is time infinitely divisible? I heard that it was, although not from a particularly explanatory source. If so, are we sure that it is, without a shadow of a doubt?
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1answer
149 views

Can two distinct events occur at precisely the same moment in time?

I am writing a simulation and am having difficulty resolving the order in which two distinct forces occur. The simulation will give different results if the forces are applied to the state in ...
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1answer
75 views

How have the duration of the martian day changed in the past?

There is a panspermia theory which claims that life might have begun on Mars and I currently read a post that the human circadian rhythm is closer to the martian day length (about 25h) than the day ...
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2answers
576 views

Entanglement and simultaneity

According to the special theory of relativity, distant simultaneity depends on the observer's reference frame. And, according to the quantum theory, in the case of two entangled particles, a measure ...
2
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1answer
206 views

The Big Crunch and perceived entropy

I'm aware of the Big Crunch theory, that once at capacity, the universe may collapse in on itself. Hawking once theorized that time may go backwards during this crunch. So, that got me thinking: how ...
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0answers
36 views

Antimatter traveling back in time and gravity [duplicate]

I've been reading on the construct of considering antimatter as matter traveling backward in time, which seems like an useful tool. There seems to be some discussion around this concept, if ...
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1answer
309 views

Is imaginary time a fifth dimension? [duplicate]

I've read that by introducing the concept of imaginary time, the dimension of time can be treated like a spatial dimension mathematically. Assuming, without imaginary time, one considers the universe ...
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0answers
56 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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4answers
321 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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0answers
25 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
123 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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4answers
1k views

Relationship between Energy and Time [closed]

Is there a relationship between energy and time? What is it?
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1answer
87 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 ...
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4answers
131 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
96 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
5k 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
142 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 ...
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5answers
164 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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6answers
816 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 ...
5
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0answers
122 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 ...
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2answers
817 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 ...
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1answer
149 views

Gravitational Time Dilation Formula? [closed]

What is the equation for calculating the dilation of time at different levels of gravitational force?
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0answers
51 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 ...
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0answers
52 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
189 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 ...
1
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3answers
106 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 ...
1
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2answers
143 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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2answers
1k 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
128 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 ...
2
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0answers
89 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
461 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
379 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?
2
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1answer
94 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
329 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 ...
0
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1answer
72 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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1answer
86 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?
1
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1answer
125 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 ...
9
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2answers
427 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 ...
0
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0answers
60 views

Argument for the Smallest Division of Time? [duplicate]

Okay so a couple of months ago I was watch Vi Hart's video on how .999999... is equal to 1. Some really interesting arguments that I had never heard before. Yesterday, I came across an article on ...
4
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1answer
270 views

Imaginary time is to inverse temperature what imaginary entropy is to …?

The Wick-Rotation rotates imaginary time into inverse temperature (as can be seen from its "rotating" the Schrödinger equation into the heat equation). Now since entropy is temperature's conjugate, I ...
0
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0answers
129 views

Calculating time of being in a lift only by weight & travel distance

If someone is in a lift and normally weighs 90kg, when the lift starts accelerating the person weighs 100kg. After the lift has maintained a constant speed for a while it starts slowing down. While ...
0
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1answer
307 views

The Law of Conservation of Energy and Time

The Law of Conservation of Energy essentially states that in a given closed system, the total energy at any instance of time should be equal. This includes the kinetic energy, gravitational potential ...