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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186 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 ...
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1answer
37 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?
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0answers
22 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
72 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 ...
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1answer
34 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
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1answer
64 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
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2answers
43 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
52 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
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0answers
25 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
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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
57 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
865 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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1answer
45 views

Standardising shadow length on sundials

The sundial is fundamentally flawed in that the length of each hourly shadow changes with the seasons. If the base of the sundial was engineered to move cyclically on an anual basis however, the ...
1
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1answer
46 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 ...
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2answers
48 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 ...
9
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4answers
3k 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
23 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 ...
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1answer
41 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
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1answer
375 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 ...
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2answers
491 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 ...
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9answers
1k 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 ...
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1answer
62 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
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1answer
55 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?
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3answers
94 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
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1answer
136 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
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1answer
272 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. ...
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1answer
115 views

Does time freeze at Absolute Zero? [closed]

Time has many definitions per se, but the basic idea being it's "the measurement of change" so as we know, all matter looses it's ability of changing with the loss of kinetic energy. and the where it ...
0
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1answer
35 views

Observing from a black hole proximity

Suppose that you could get close enough to a black hole that time slowed down significantly for you, and you looked at a giant clock back on earth through a telescope. Would you see the earth clock go ...
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1answer
116 views

Understanding gravitational time dilation / Schwarzschild metric

I've had a look at the answers to these sorts of questions already, but feel like I'm still missing something. Starting with this question, and this one and even this one here. I'm looking at this ...
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2answers
76 views

Can photons decay without interaction?

Can photons decay like other particles without interacting with other particles or fields, i.e. by just "being"? In case the answer is "no" - does this have anything to do with them travelling at c, ...
0
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0answers
15 views

Is there a “framerate” for the universe? [duplicate]

I've been wondering this for quite some time. I just can't wrap my head around the idea of truly continuous time. If time is truly infinitely divisible, then how can any object in the universe move? ...
3
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3answers
105 views

Force and Acceleration, is there a delay?

Suppose we have a mass $m$. We can talk about two of its parameters : The net force applied on it $f(t)$ and its net acceleration $a(t)$. I want to know whether there is any delay between $f(t)$ and ...
4
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5answers
159 views

How can we justify dropping the absolute time hypothesis?

In some approaches to Special Relativity the theory is motivated talking about the Michelson-Morley experiment and how this relates to the postulate that the speed of light is the same in every ...
0
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1answer
38 views

Symmetric Time Dilation in Uniform Relative Motion

I feel (and hope) this is an easily answerable question among physicists versed in GR. I promise that I searched for other answers on the forum. Here goes: Observer 1 starts at X distance from ...
1
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0answers
25 views

The speed of light sets a lower limit to the rate at which a reference frame can pass through time. Is there anything that sets an upper limit? [duplicate]

Is there any "slowest" velocity that sets a cap on how fast a reference frame passes through time, or can you pass through time infinitely fast given a "slow" enough velocity?
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4answers
110 views

What's the differences between time in Physics and time in everyday use?

OK. This question might sound as not a good question, but the word 'time' is so confusing to me. I mean thermodynamics says time is the product of entropy. Relativity says time is relative. Quantum ...
9
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3answers
1k views

Is there a constant/baseline for how fast time passes?

Say we have an object completely unaffected by the effects of gravity/velocity. Is there a way to measure the passing of time for this object? Since time moves slightly slower for us on or near ...
1
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2answers
96 views

Speed of light and perception

So I'm reading a book called "The Elegant Universe" and here is a part of it Imagine two countries that have been at war are sitting down to sign a treaty ending hostilities while traveling aboard a ...
2
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2answers
721 views

Time Reversal in a Black Hole

I had a lively discussion with a person about black holes recently, and was making the point about gravitational acceleration in GR being paralleled by speed in SR. One thing that I know people talk ...
89
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4answers
12k views

Why do electrons, according to my textbook, exist forever?

Does that mean that electrons are infinitely stable? The neutrinos of the three leptons are also listed as having a mean lifespan of infinity.
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2answers
101 views

Is time dilation based on the formula for period of a pendulum?

The theory Albert Einstein put forward about special relativity mentions a possibility for time dilation, in which he states gravity has a considerable effect on time. And in high school physics we ...
2
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5answers
371 views

What is the exact mechanism by which time dilates?

What is the exact mechanism by which time dilates for a fast moving object? Can the time dilation be explained by any theory other than relativity?
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1answer
125 views

Age of the universe [closed]

Does the fact that the edge of our observable Universe contains information from the beginning of the Universe give us an ability to determine its age? The edge of our observable universe surely has ...
2
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1answer
68 views

Does time really differs drastically?

As I heard/read time moves slower and slower for me as I speed up, but does it change drastically? Our current formulas say, If I go at a speed very close to light's, time almost stops. I've seen ...
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3answers
101 views

Time period related to acceleration due to gravity

The period of a pendulum is given by $$ T = 2\pi \sqrt{\frac{L}{g}}. $$ If we take a pendulum where there is no gravitational field, then $g=0$, therefore the period should become infinity. In such a ...
1
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2answers
399 views

Is the second defined arbitrarily? [duplicate]

According to the definition a second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of ...
0
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2answers
173 views

Does the universe have a different age to different observers?

Although I understand that the universe is approximately 12 billion light years wide, and that may mean that it took the light photons 12 billion years at 186,000 miles per second to reach the ...
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1answer
87 views

Could time be considered a force

I think I understand the basic concept of spacetime, at least some of it. And when people talk about spacetime they don't call gravity a force, but rather the result of mass interacting with it. And ...
0
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2answers
61 views

Movement of accelerating points with maximum speed (i.e. running away from tiger) [closed]

I'm walking through a forest and suddenly I see a tiger. And now I have a problem. I want to know how much time I have left but I don't know how to calculate it. Or more formally: Let's ...
9
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3answers
807 views

How do we know that the cesium-beam frequency used in atomic clocks is always the same?

Atomic clocks use cesium-beam frequency to determine the length of a second. This has shown that the period of orbit of the earth is decreasing. But what experiment showed that cesium-beam's period ...