# Tagged Questions

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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### 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 ...
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### 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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### 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 ...
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### Why Sun light can reach us if Time is dilating?

I understand that if something is moving with constant speed in respect to an observer, the time of the moving one runs slower, so the more your speed is, the more your time ticks slower. Which ...
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### 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 ...
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### How difficult is it to construct the time inverse of a state? [on hold]

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-...
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### Does time and time dilation exist in a black hole?

Since being near stronger gravitational fields causes time dilation, can this be generalized to the region beyond the event horizon? i.e , is it meaningful to say that someone outside the black hole ...
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### 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. ...
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### 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, ...
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### 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 ...
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### 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 ...
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### Calculate Time from Distance, Initial Velocity and Final Velocity [closed]

How can I calculate the time given the traveled distance, initial velocity and final velocity? I've found some algorithms that include acceleration, but in this case there is constant acceleration. ...
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### Presentism: doesn't everything exist at the same moment? [closed]

The Help Center recommends I 'fix' this question: (original question) "It seems self-evident that everything exist in the Now. Notwithstanding time-dilation and different rates of the passage of ...
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### 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 ...
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### 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 ...
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### 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, ...
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### How is time not a constant?

I am a visual person, so it's hard to imagine the information I keep getting, but shouldn't time be a constant? If you were traveling at the speed of light and your able to cover $299{,}792{,}458$ ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### I heard that at quantum level the past-present-future is not in order, is this true? Is time really messed up there? [closed]

I heard that, at the Quantum level, events can happen out of order making causality invalid. Thus the future can happen in the present and the present in the future. Is this true?
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### 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 ...
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### Why does time dilation cause you to age slower? And is time considered relative to the observer?

I understand that the higher your velocity the slower light will move. But how does time itself slow down while you are moving faster?
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### 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 ...
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### 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 ...
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### Hafele-Keating revisited with a gravity clock

Most modern clocks use electromagnetic phenomena to measure time. There are perhaps some older clocks that involve gravity to some degree (hour glass, pendulum), but I believe they still have a ...
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### What is the least count of the timer clocks used in RADAR?

I was checking out some videos in YouTube regarding the working principle of RADAR. To quote some HOW IT WORKS: World War II Radar (720p), part 1, How does RADAR work? | James May Q&A | Head ...
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### 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 ...
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 ...