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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2answers
54 views

Origin of time or origin of space-time? [on hold]

This might be a mere theoretical concept and I might even get down voted for asking this. I read in several sources that winding back general relativity equations leads to $t=0$, origin of time. ...
-5
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2answers
60 views

If the Earth was the only planet and there was no Sun how would time be measured? [on hold]

The human race has developed a system to measure "time" and naturally the human race has come to understand there must be a "time" to measure. If there is only a "now" and "past" is purely ...
2
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1answer
63 views

How can the size of the universe change over time when time is part of the universe?

Bit of an awkward way to phrase it, but basically: Time in relativity is just one of four dimensions of space-time. Nothing really special about it. Yet the universe was once smaller than it is now ...
2
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1answer
82 views

GR says that time and space are aspects of the same thing, yet there is no observable for time in QM

I understand that the topic of a time operator in quantum mechanics has come up more than a few times so forgive me if this is a repeat question but I couldn't find anything specific to my question. ...
1
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0answers
31 views

How difficult is it to construct the time inverse of a state? [closed]

This is a vague question, but I hope it can have some sort of answer. Given an isolated state, classical or quantum, of finite size, how difficult is it to actually produce a state that is the time-...
2
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2answers
74 views

What happens to Pauli's argument (that says that there is no time operator) when applied to $X$ operator for some simple systems?

An argument by Pauli is usually referred to in the literature when it is stated that there cannot be a time operator in quantum mechanics. This argument can be found as a footnote to P63 of W. Pauli, ...
1
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2answers
56 views

How can I slow down? Or, How can I speed up time? Reverse twin paradox

Everyone know the standard Twin Paradox. I have my clock synchronized here on Earth with my twin. I leave Earth, Travel for a time at 0.9c, turn around, come back at .9c and then my clock is slow ...
0
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2answers
60 views

Synchronization of clocks using material waves

I am not a physicist by training, but I have studied special relativity enough to understand why simultaneity is a relative concept, and so why if you synchronize clocks in one inertial frame, an ...
0
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0answers
71 views

In a moving light clock, does the velocity of the clock add to the velocity of the light?

Currently going through the class Space, Time and Einstein from worldscienceu. On module Time in Motion an example is given of 2 light clocks, one moving and one stationary. The point is made that ...
4
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0answers
50 views

Why isn't there a Time Operator in Quantum Mechanics? [duplicate]

I was wondering about a scenario where you subject a quantum particle to an intense gravitation field. Why can't we apply a sort of time operator to the particle to see how time changes for the ...
-1
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3answers
304 views

About time and time dilation [closed]

This question is related to this answer of John Rennie. He says: The length of the red line is the same in both figure 1 and figure 2 I guess his meaning of red line is the space-time distance ...
1
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0answers
122 views

Why does the clock work slowly at higher speed? [duplicate]

I know nothing about relativity but I cannot accept that there is a phenomenon called time dilation. However I have no problem with it because of mathematics behind it. I have no problem if time is ...
0
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3answers
108 views

Can we have a physics by using other mathematics except calculus? [closed]

We (I) always have been said that we don't need to real values, we just need to differences. For example, $\mathrm du=C_v\mathrm dT$ and $\Delta u=\int_{T_1}^{T_2}C_v\mathrm dT$. So, I have some ...
1
vote
2answers
73 views

Any alternative to time? [duplicate]

Just curious to know. Suppose physicists start from the very beginning, i.e defining the fundamental quantities, figuring out the math etc. So will they see the universe differently than what we have ...
0
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1answer
61 views

Is it possible to dumb down the idea that “Time didn't exist until the big bang”? [duplicate]

So, I've asked questions before that have been met with "Time (and our laws of physics) didn't exist before the big bang" and other answers to that effect. This is massively confusing to me, for ...
46
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3answers
6k views

Do pear-shaped nuclei really have anything to do with time travel?

Recently (in the last week or two), various articles about pear shaped nuclei have appeared, such as this one from Science Alert and this from the BBC The Science Alert article includes the quote ...
2
votes
1answer
69 views

Is the age of the Universe relative to where you are within it? [duplicate]

The accepted age of the Universe is 13 billion years give or take. If you were a super space being and hypothetically had spent a large portion of this time sitting next to a black hole then your ...
1
vote
2answers
39 views

Lagrangian mechanics not relying on time or independent of time [closed]

If neither the potential energy nor kinetic energy depends on time, then Lagrangian is explicitly independent of time I find this statement a little bit odd because velocity is distance over time or ...
-1
votes
1answer
35 views

Water Boiling Time Calculator

Is there a way to calculate out how quickly a body of water will boil? My primary concern is to measure in relationship to different temperatures. For example, heat at 100 degrees Fahrenheit versus ...
0
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0answers
79 views

What would a universe with 2 time dimensions be like? [duplicate]

In a universe with 2 dimensions of time, and 3 spatial dimensions, the equation for finding the change in time is: $\Delta T= \sqrt{(\Delta \alpha_1)^2+(\Delta \alpha_2)^2} \geq 0$ Where $T$ is the ...
3
votes
1answer
95 views

Is there any Hamiltonian that contains time derivative? [duplicate]

Quantum mechanics is governed by Schrodinger's equation: $$\hat{H}\psi=i\hbar\partial_t \psi$$ It seems that Hamiltonian acts on wave functions like a time derivative. Just out of curiosity, is ...
0
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1answer
58 views

What is Hawking's, “No Boundary Conditions”? [closed]

In his "No Boundary Conditions", is Hawking stating that time is eternal? And what is the difference between Real Time and Imaginary Time? Is he saying there are two different arrows of time, and ...
23
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3answers
2k views

Is there an actual proof for the energy-time Uncertainty Principle?

As I understand, the energy-time uncertainty principle can't be derived from the generalized uncertainty relation. This is because time is a dynamical variable and not an observable in the same sense ...
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3answers
93 views

How can time be a dimension when it is relative? [closed]

I understand that by definition dimension is defined by just another coordinate to pin-point something in space-time. Therefore we need to know not only where but when. At the same time, this somehow ...
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3answers
86 views

Is “time” a singular dimension or multiple dimensions? [closed]

We know of x, y, and z dimensions. We also know of "time"... Another dimension we are aware of, which is a "non-physical dimension" called a "temporal dimension". Now, we all look at "time" as a "...
2
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1answer
36 views

Is Entropy Maximized, or Just Increased?

Do different real processes involve different rates of change of entropy? (Is the rate of change of entropy constant with time throughout all regions of space, or perhaps in other words, constant with ...
1
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1answer
43 views

Reference for Reichenbach synchronisation and non-standard special relativity

My professor introduced in the last lesson a new method for clock synchronisation, which he called "Reichenbach synchronisation". In this new method, two clock A and B synchronise themself with the ...
0
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0answers
25 views

Does photon experience time? [duplicate]

According to the special theory of relativity, for all observers the speed of light is c. Any observer travelling at the speed of light c does not experience time. Hence even protons shouldn't ...
0
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0answers
8 views

Power scaling behavior in Detrended Fluctuation Analysis

I am trying to apply DFA in my time-series, however, remain the the determination linear relationship of the log fluctuation vs. log scale plot i.e. slope which indicates to the power scaling behavior ...
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votes
1answer
98 views

Calculating speed in four dimensions [closed]

If you are moving at $c$ in 3D space and $c$ in time axis too, What would be your total speed? Edit: Since question has been voted to be closed, I shall make an Edit. In 4D world all objects move ...
1
vote
1answer
91 views

Period of a pendulum [closed]

In the book 'Calculus the Early Transcendetals' at page 776 (7th edition) they give that the period of a pendulum with length $\text{L}$ that makes a maximum angle $\theta_0$ with the vertical is: $$\...
4
votes
4answers
174 views

Is time an observable in Relativistic Quantum Mechanics?

Relativistic Quantum Mechanic is based, as far as I know, in the Dirac Equation. Now, the Schrödinger equation, in the abstract state space takes the form: $$i\hbar \dfrac{d|\psi(t)\rangle}{dt}=H|\...
0
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3answers
132 views

What does it mean that the laws of physics are time reversible?

The Universe, as far as we can tell, only operates according to laws of physics. And just about all of the laws of physics that we know are completely time-reversible, meaning that the things they ...
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1answer
27 views

Is the time for light to go a certain distance the same amount of time sped up through relativity?

If you were to stand on the tower of my Lemmon and had an atomic clock that was exactly synchronized with one at tucson, (6734 feet difference) for 24 hours, it was shown to be roughly a 20 nano ...
0
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0answers
25 views

Special Relativity and its relation to refractive index [duplicate]

As is known, light slows down (compared to vacuum) whenever it enters a medium. Also, Special Relativity effectively puts a limit on the max. speed of any body. So is it possible for a body (in a ...
1
vote
1answer
45 views

Traveling slower by traveling in opposite direction as the Earth rotates

I know that if I were to travel fast, the time would pass by fast for me. But if I were to travel fast in the opposite direction of the earths rotation while I'm still on earth, would the time pass by ...
0
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1answer
68 views

How does pressure change over time in an open box?

Imagine that you have a 1 cubic meter metal box with two 20 mm diameter holes. One of them is connected to an air-compressor that constantly pressurizes the inside of cube. Let's say 5 atm. The other ...
0
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2answers
69 views

Is time a coordinate or a parameter in Newtonian mechanics?

In classical (Newtonian) mechanics we only ever seem to consider 3-dimensional space, with physical quantities being represented by 3-vectors. My understanding for this is because in classical (...
0
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0answers
30 views

How much time a ball stays at rest when throw up?

You throw a ball straight up in the air. The ball attains its maximum height when it is momentarily at rest,(v=0). How mutch time is this moment? If we take time has continuous it is an infinitesimal ...
0
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0answers
21 views

Are there any specific examples of the application of Lewis-Riesenfeld procedure to time dependent Hamiltonians in QM?

Lewis-Riesenfeld invariant theory is a theory applicable to solve time-dependent Schrodinger equations. I have always encountered the theory related to the procedure, however never encountered any ...
0
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1answer
87 views

What is the best way to calculate impact time with collisions?

I've been teaching myself physics and I've been wondering about the impact time in collision calculations. The scenario I've been using to learn is an object with a mass of 4000 kilograms colliding ...
0
votes
1answer
113 views

How can Big Bang happen without time?

I had recently watched a video and he says big bang could have happen by the slow collision rather than a fast collision. But I know that there was no time before the big bang and fast and slow are ...
2
votes
2answers
410 views

Stanford: “Objects in spacetime all move at constant speed $c$.” Are they right? [duplicate]

In this Stanford University lecture on Relativity, it is stated: Likewise, objects in spacetime all move at constant speed c in spacetime but if you change its direction, say by moving at speed v in ...
1
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3answers
69 views

Did time also began from big bang?

Did time began from big bang? If not then what existed before big bang? If time had a beginning, then does it have a end, or pause because if time had a pause then we would not have known about it, ...
-4
votes
1answer
64 views

How time and speed of light are related? [closed]

I want to know how speed and light and time are related? How will motion with highspeed effect time? I am not a physics student. I want an answer which is free of mathematical relations. I want an ...
-1
votes
1answer
60 views

Equation for everything?

Suppose, I throw a ball and it bounce. If we observe it from the time of it hitting the ground, we can see it moves due to the initial velocity it had and the interaction it had with the ground. We ...
0
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1answer
25 views

What does Time tells about mass of an object? [closed]

According to theory of relativity Time becomes slower in presence of an heavy object. And In theory on concentration it is said when we are in deep concentration our perception of Time changes and it ...
0
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0answers
45 views

Gravity's effects on time

So, in the movie Interstellar they say that one year by the black hole is about 35 years back on Earth (excuse any lack of accuracy in the numbers, I haven't seen the movie in over a year). Now, the ...
4
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4answers
194 views

Distance in General relativity

I read a few lines about general relativity and one of the first equations is the one defining the eigentime of a time - like curve. But observers should also be able to measure length, right? So is ...
1
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2answers
106 views

Atomic Clocks: How is time measured?

I am trying to understand atomic clocks better. I am not getting HOW the cesium oscillation is actually being counted. So from my understanding of an older atomic clock: cesium gets heated-> ...