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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5answers
12k views

How can time be relative?

I don't understand how time can be relative to different observers, and I think my confusion is around how I understand what time is. I have always been told (and thought) that time is basically a ...
2
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5answers
294 views

Two clocks along different worldlines [duplicate]

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, ...
0
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3answers
196 views

Question about rain when an object is moving

So here's the question: A train window is 1 meter high and 10 meters long. A raindrop rolls down the window at a vertical speed of 5 meters per second(when stationary). If the train is moving at 30 ...
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1answer
91 views

Can we observe a star collapse into a black hole? [duplicate]

Let's say that I happen by a star that has just burned out and is collasping into a black hole. I seat at infinity to watch it as a Schwarzschild observer. Will I ever see the black hole collapse into ...
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1answer
1k views

Does the universe update time in some finite interval? [duplicate]

I was listening to a lecture by leonard susskind and one of the analogies he used was a coin having two states and he "broke" time into intervals. He continued to say that at each interval of time, if ...
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4answers
957 views

What isotope has the shortest half life?

Question: What isotope has the shortest half life?
2
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7answers
10k views

I need help with finding distance traveled

How do I find the distance traveled of an object if the speed is not constant?
3
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3answers
607 views

Accuracy and Error of Atomic Clocks

I'm quoting a passage from my notes: The development of clocks based on atomic oscillations allowed measures of timing with accuracy on the order of $1$ part in $10^{14}$, corresponding to errors ...
0
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3answers
120 views

What is the pace of absolute time

How fast or slow compared to my alarm clock time does time passes in a place where there is no gravitational pull and where you are not moving. I don't know if my question is clear, but is there some ...
2
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2answers
242 views

What would a closed timelike curve look like?

What exactly are closed timelike curves. In a metric in which they would exist, what would they look like. What would it be like travelling through them? It obviously wouldn't look like a door. Would ...
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1answer
120 views

Does time stand still at a phase transition?

For second order phase transition thermodynamic properties can be described in very general terms by their critical exponents. So at every transition the correlation length $\xi$ should diverge as ...
1
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2answers
826 views

If time stops for an object, does that object feel gravity?

As far as I understand The GTR, it is said that Mass bends space-time which causes gravity. So every Mass in this universe is flowing through space-time example earth is moving along with space-time ...
0
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1answer
61 views

Relationship between gravitational time dilation and energy?

The rate that a stationary clock slows down near a massive object, relative to one far away, can be read off from the Schwartzschild metric: ...
2
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3answers
163 views

What does it mean to say that “remembering the future and not the past?”

I encountered a rather stupid question which I don't quite understand. - "Why can we remember the past but not the future?" It sounds cool when I first read about it but I think about it more, about ...
0
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1answer
127 views

Calculate Time travel with Time Dilation [closed]

Does the following hold: If we have: person A moving at a speed of $0$; person B moving at a speed of $xC$ (where $C$ is speed of light, $x$ a fraction) And if time passes for $m$ ...
13
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9answers
8k views

Is there a proof of existence of time?

It seems to me that there is no such thing as time. There is only movement in the universe and we compare our own movement to a different object to have a sense of time. It can be a clock or a atomic ...
0
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0answers
28 views

Discrete time like a computer program [duplicate]

Has anybody thought about the effects of discretizing time in the way most computers do? In computer programming; collision detection for example, or updating a trajectory of a particle, everything is ...
8
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1answer
383 views

Cancelling special & general relativistic effects

We know that for a GPS we need to make a correction for both general and special relativity: general relativity predicts that clocks go slower in a higher gravitational field (the clock aboard a GPS ...
11
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3answers
18k views

Is time a Scalar or a Vector?

In Wikipedia it's said that time is a scalar quantity. But its hard to understand that how? As stated that we consider only the magnitude of time then its a scalar. But on basis of time we define ...
9
votes
3answers
8k views

How fast will the sun become a red giant?

I've read many accounts of our sun's distant fate, but what I've never heard is on what time scale these events occur. For instance, when the sun runs out of hydrogen, I presume it doesn't just WHAM! ...
0
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0answers
45 views

What is time except “Dimension”? [duplicate]

I know everybody says that time is the fourth dimension. But I want to know what is the definition of Time without just saying that it's the Fourth Dimension.
0
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1answer
258 views

A problem on rectilinear motion in a car [closed]

Today, I attempted the third question in the first chapter (Physical Fundamentals of Mechanics) in the book Problems in General Physics by I. E. Irodov. The question goes like this: A car starts ...
0
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1answer
61 views

By what factor would you have to slow down time for water to feel like glass?

I have been told that though glass seems like a solid, it is somehow, in theory, a liquid -- but is just somehow a liquid that is so thick that it appears to be solid. (Of course --- if this premise ...
1
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1answer
71 views

Understand the relation of time and the space dimensions of spacetime?

I assume the relation of the three spacial dimensions and the time dimension is handled purely in the mathematical domain, usually. But is there any intuitive description of this relationship, how ...
1
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1answer
392 views

How are the higher derivatives (jerk, jounce) of position with respect to time used in physics?

I don't see them much in any physics lesson or course, but that's probably because I'm not into physics as much. I can understand why velocity and acceleration are useful, but why would someone want ...
7
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3answers
203 views

Physics without time

The structure of physical law as we generally recognize it today is firmly held together by the existence of time. Although physical laws can both predict and retrodict (reversible time does not break ...
-1
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1answer
56 views

Is it possible to travel forward and backward along with time? [closed]

Is it possible to travel along through time if we found a thing that is more speeder than light?
0
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0answers
26 views

What's the difference between cosmic time and conformal time? [duplicate]

When they say that the age of the Universe is about 13.7 billion years, they are giving the age in cosmic time, is that right?. There's this other thing called conformal time which I don't understand. ...
0
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2answers
129 views

Meaning of Proper time

Sorry for a bit of a basic question, but want to clarify things in my head. Is proper time quantified by the amount of physical process that an object, or physical system undergoes, for example the ...
2
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1answer
66 views

How can bubble collision happen if there is no space and time outside the universe?

The question is almost self-explanatory. What I am trying to say is that if there are no space-time outside our universe, how does collisions even happen. I am having a hard time explaining this ...
0
votes
1answer
70 views

Time dilation and space time [closed]

I know a little about space time, and I know that space time is adding the time component into the three- dimensional world and creating an abstract universe. But my question is that why time is ...
0
votes
2answers
90 views

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 ...
0
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1answer
63 views

Is gravitation time dilation simply c/v?

Recently, I've been very interested in forms of time dilation. I'm relatively new to relativity, so I apologize for any stupid mistake I may make. I was messing with the equation for gravitational ...
0
votes
0answers
63 views

How power spectral density in time domain can be understood?

I got some data which basically gives me the variation on the time of a PSD measured across specific frequency bands ranges, for instance [10Hz-30Hz]. However I have not found any good explanation ...
0
votes
0answers
49 views

What perpetuates change? [duplicate]

People say that our notion of "time" comes from entropy which in turn is just a large scale effect of the laws of physics, but what is it that perpetuates the laws of physics from one state into the ...
0
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0answers
60 views

If time somehow went backwards would this violate one of the laws of thermodynamics?

If time somehow went backwards and all the physical events that had occurred in a sequence , would some of the events occurring 'backwards' or in the reverse order violate the principle of entropy or ...
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2answers
1k 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 ...
2
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1answer
52 views

Cellular automata and time T

Reading around about various CA models I saw that there are even those who are following the track to provide a single mechanicist model of the universe. For example Gerard van 't Hooft claims that ...
-1
votes
2answers
51 views

Can I sum-up time?

If a kinetic process takes 1 second to complete(reach a point), and that process is repeated $n$ number of times, is this formula correct $t_t$=$n\times 1$ = total time in seconds? It's similar to a ...
10
votes
4answers
4k 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 ...
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3answers
25 views

How can we be sure that a new frequency standard is better than the old one?

Lets assume for this question that at one point in scientific history everyone was running along well with their cesium frequency standards, and someone has a brilliant idea and builds an active ...
-1
votes
1answer
55 views

Time dilation: reference frame [closed]

So I'm calculating how long it will take for half of some muons to decay for in a stationary observers frame of reference. They have a half life of 2.2 * 10^-6 and are moving at a speed of .98c ...
3
votes
1answer
487 views

Is time the property of an object?

I don't know if the title makes much sense, but hopefully it will become clear with the text. Temperature is not a property of a point in the three dimensions, but actually of the object occupying ...
0
votes
2answers
710 views

Why does time exist? [closed]

So I have been thinking about some subjects and one of it involves time. And I tried writing a story/question on here to summarize the bigger picture but it's not going to happen it's too complicated ...
7
votes
9answers
2k views

Did relativity make Newtonian mechanics obsolete?

Did Einstein completely prove Newton wrong? If so, why we apply Newtonian mechanics even today? Because Newton said that time is absolute and Einstein suggested it relative? So, if fundamentals are ...
1
vote
1answer
69 views

How much is time slowed down inside a planet or star?

An answer to What would be the rate of acceleration from gravity in a hollow sphere? states "that according to General Relativity time passes more slowly inside a hollow massive sphere than it does ...
0
votes
1answer
61 views

Has the effect of magnetic fields on time ever been examined experimentally?

Relativity of time can be examined with satellites as gravitational or acceleration. Is there any similar experiment with intense magnetic fields?
1
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3answers
103 views

Does Time change over temperature? [duplicate]

I am not a physicist, I am just an engineer. But I dared to ask whether the temperature changes the perception of time. Let's consider a particle that "stops" at absolute zero. I was thinking as a ...
2
votes
1answer
147 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 ...
2
votes
1answer
326 views

How come the concept of an instant of time is such a controversial topic with relativity, but with entanglement it's completely acceptable?

When talking about relativity most people say that a universal instant of time doesn't exist, but when talking about entanglement most will say that the particles are both measured instantaneously. ...