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
51 views

Time dilation and freefall (follow up and simplification) [closed]

A person is four miles up in the atmosphere, and freefalls towards earth. Another person is standing on earth, watching them come down. During this period of freefall, which person experiences more ...
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2answers
50 views

How to interpret irreversibility in time?

I'll quote Feynman's Lectures, chapter 52 (Symmetry in Physical Laws) of volume 1: [...] If we see the egg splattering on the sidewalk and the shell cracking open, and so on, then we will surely ...
3
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2answers
98 views

How do you think about time as an axis/dimension?

I'm studying mathematics, but (obviously?) have an interest in physics. I've been thinking, how do people in physics think about time as an axis or dimension (as they would be called in mathematics)? ...
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0answers
32 views

Is there a fundamental frequency of time? [duplicate]

Our eyes and brains can only perceive frequencies as individual frames up to some limit, after which we perceive the motion to be "continuous." Is there such a frequency of time? Along the same ...
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3answers
98 views

Is time created by movement through a higher dimensional object? [closed]

In a comment I read on this page, someone mentions a theory where time is created by moving through and slicing "moments" of a higher dimensional object. For analogy, a 2-D creature living on a plane ...
3
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2answers
80 views

Questions regarding the Feynman-Stueckelberg interpretaion

I am studying for an introductory particle physics exam, and I am having some problems with the Feynman-Stueckelberg interpretation of antiparticle states. Background: The course was being thaught ...
2
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2answers
877 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.
4
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0answers
78 views

What determines time flow? (arrow of time) [closed]

I've been reading up on the arrow of time and there is one thing that is being omitted from every explanation that I've found: time flow. I am rewording this question to make it clearer. From the ...
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0answers
34 views

What would you experience if the universe ceased existing whilst you were under extreme time dilation?

Hypothetical situation, if you were in the center of a supermassive black hole (and managed to not be immediately obliterated), time dilation would be so that billions of years may pass outside the ...
4
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1answer
62 views

Which magnet will last longer?

Say you have a magnet that is used in a brush-less generator. If the brush-less motor was ran (by external force such as water or human interaction) for 400 years, would the magnet that was under use ...
1
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2answers
48 views

Question regarding gravity and time

I and my friend (Age 15) were discussing about light and speed of light when we thought of a question. Imagine you are travelling in a spaceship at the speed of 2.9*10^8 m/s circling the earth. ...
1
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1answer
44 views

Can we see ourselves slower due to time relativity?

Please bear with me because I'm noob at physics. Numbers don't have to be calculated, these are just examples, I'm just asking conceptual stuff. Just double check: Objects traveling at $0.99c$ in ...
0
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1answer
157 views

Relativistic time dilation on Mars compared to Earth?

What is the time dilation in Mars, compared to earth? Can we accurately calculate it? What information is needed to do these calculations?
6
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2answers
428 views

Why do we treat time as parameter in non relativistic QM instead of treating position as parameter?

Why do we treat time as parameter in non relativistic QM instead of treating position as parameter? What is actually a parameter? I have read this Wikipedia page, but could not understand why should ...
0
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2answers
81 views

Age of universe?

Well relativity teaches us that time interval between two events is a frame dependent quantity, then how can we say that our universe is 13.8 billion years old? Should it not depend on who is asking ...
31
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8answers
5k views

What is $\Delta t$ in the time-energy uncertainty principle?

In non-relativistic QM, the $\Delta E$ in the time-energy uncertainty principle is the limiting standard deviation of the set of energy measurements of $n$ identically prepared systems as $n$ goes to ...
2
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1answer
287 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 ...
70
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10answers
11k views

Is time continuous or discrete?

While working on physical system simulation software, I noticed that I had implemented discrete time, which means that there was an update mechanism advancing the simulation for a fixed amount of time ...
-2
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1answer
45 views

Reversal of time, an absurd concept? [closed]

Consider a specific case of a hourglass. Here, because of gravity sand flows down and reaches the equilibrium state when all the sand is in the lower half. This way we can keep a measure of time. From ...
0
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1answer
94 views

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 ...
1
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1answer
79 views

A fast object (0.8c) getting overtaken by another fast object (0.9c): why don't times agree?

I'm trying to work on an exercise in Wolfgang Rindler's book "Introduction to Special Relativity" and I'm stuck on the following exercise: Two particles move along the x-axis of S at velocities ...
6
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3answers
1k views

Cooling of atomic clocks

I have read of cooling atoms to one-quarter of one-thousandth of a degree above absolutely zero. According to Physicist William Phillips, this improves the measurement of the ticking frequency. I have ...
2
votes
6answers
140 views

Wouldn't backwards time travel break the law of conservation of mass? [closed]

We know from the law of conservation of mass that the amount of mass in the universe is constant. Suppose there were a way for a person to travel backwards in time. Let's call this mass $m_t$ for some ...
0
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3answers
26 views

Looking at past events by observing sky? [duplicate]

Since solar system (and our galaxy) is constantly in motion at a great speed, is it possible that we can look at our own image as it was sometime ago? Since the light of that age takes sometime to ...
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8answers
4k views

Is time travel possible? Is it possible to go back in time?

I read somewhere that according to relativity, black holes and other space related stuff it is possible to jump into past. Is it possible for anything to go back in time either continuously or by ...
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2answers
100 views

Traveling through time, reaching the past - POSSIBLE? [closed]

I was obsessed in studying the "faith" and I've made several great discoveries. I don't want to publish anything yet, but I have a semi-proven (proven partially) / theories / so I am curious on bones. ...
7
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3answers
525 views

Do gravitational waves cause time dilatation?

The effect of gravitational waves in transverse traceless gauge on matter is represented by the expansion and contraction of a ring of test particles in the direction of polarization of the wave. ...
2
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1answer
270 views

Huggins Displacement Theory and Retrocausality

I was looking at the Wikipedia entries on Time Travel and the Grandfather paradox and noticed a paragraph on the so-called Huggins Displacement Theory. I haven't been able to find the source although ...
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2answers
161 views

Is there a time operator in quantum mechanics?

The question in the title has been asked many times on this site before, of course. Here's what I found: Time as a Hermitian operator in QM? in 2011. Answer states time is a parameter. Is there an ...
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0answers
29 views

Age difference between hands and feet due to relativity?

According to relativity time passes faster the faster something moves, and gravity slows time. My head is moving faster than my feet (assuming I'm not at one of the poles). My head is further away ...
1
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1answer
104 views

Time Travel: Is it Possible to return to an earlier time? [duplicate]

(Please note: I've seen some other questions asked like the one I myself am asking, I realize that I am indeed late to the party, but I am genuinely curious and none of the previous answers have ...
-4
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1answer
453 views

The time is a type of energy ?

You know energy is necessary for the occurrence of an event . Time is also exactly neccessary for the occurrence of an event. If there is no time , there will be no event. I mean time is a type of ...
0
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0answers
31 views

How person in different gravity field be seen?

We know that gravity affects time. More the gravity, slower the time, and vice-versa. Now consider a hypothetical condition where two people are walking next to each other. One person is subjected ...
7
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6answers
5k views

Why are objects at rest in motion through spacetime at the speed of light?

I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
1
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0answers
27 views

Non-time orientable quotient of de Sitter space

Examples of non-time orientable spacetimes are pretty scarce, but it seems the big one is quotients of de Sitter space of the form $dS^n/\pi_1$, where $\pi_1$ is some subgroup of the isometries of de ...
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0answers
29 views

Does the Heisenberg uncertainty principle hold up for events in the past? [duplicate]

I was watching this youtube video on predicting the future if you can know the exact position and momentum of every particle in the whole universe. But you can't ever know that says Heisenberg. But ...
1
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5answers
15k views

Why doesn't mass of bob affect time period?

The gravitation formula says $$F = \frac{G m_1 m_2}{r^2} \, ,$$ so if the mass of a bob increases then the torque on it should also increase because the force increased. So, it should go faster and ...
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1answer
34 views

Calculate the relativity of time of an event occurred in different frames

Imagine we have a train which is moving with a velocity and there's an observer inside of that train and there is an observer that is outside of the train observing the train moving. There's a ball ...
1
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0answers
49 views

Hamiltonian in commutator contradiction [duplicate]

Consider the following: $$[ \hat H, \hat x]=\left[-\frac{\hbar^2 \hat p^2}{2m}+V,\hat x\right]\ne0 \text{ in general}$$ But $$[ \hat H, \hat x]=\left[i\hbar \frac{\partial }{\partial t},\hat ...
14
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9answers
635 views

How to explain (pedagogically) why there is 4 spacetime dimensions while we see only the 3 spatial dimesions?

I have been asked this question by a student, but I was able and in the same time incapable to give a good answer for this without equations, so do you have ideas how one can explain this in a simple ...
1
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0answers
39 views

Biological concept behind time dilation [duplicate]

What is the exact mechanism which makes aging process slow for persons travelling at higher velocity relatively. How does our body cells responds to gravity and undergo aging?
0
votes
1answer
106 views

Wave Function State Reduction As a Result of Quantum Measurement

This is a question about indirect quantum measurement, involving an observable of an object of interest and a probe that is used to measure that observable. In this experiment, an observable of the ...
1
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2answers
97 views

Time in general relativity

A physical quantity is introduced by its operational definition. In general relativity we use a differential manifold to describe the 4-dimensional space-time and, to identify a point in it, we use a ...
25
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6answers
3k views

Can black holes form in a finite amount of time?

One thing I know about black holes is that an object gets closer to the event horizon, gravitation time dilation make it move more slower from an outside perspective, so that it looks like it take an ...
0
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0answers
44 views

Can we choose any dense subset of $\mathbb{R}$ to represent time?

Is there any particular reason for choosing time to be real? Is choosing time to be represented by say rationals going to give problems? Can someone give a physical reason that requires it to be ...
2
votes
2answers
81 views

Would a person in a gravity well observe the sky as rapidly moving due to time shift?

Inspired by the movie Interstellar (2014) - I was wondering about the crew on the surface of the planet which was deep in the gravity field of the black hole (Gargantua) - if they would look up at the ...
1
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0answers
55 views

Is there a model of the universe with the transfinite (space)time?

In mathematics there is a concept of ordinal numbers where one can count to infinity and beyond. For example the least number that is greater than all the finite numbers is denoted by $\omega$. Such ...
5
votes
6answers
686 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 ...
13
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5answers
1k views

Time dilation all messed up!

Okay! There is a problem with my logic and i cannot seem to point out where. There's a rocket ship travelling at close-to-c speed v without any acceleration (hypothetically), and there is an observer ...