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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351 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 ...
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156 views

Is it possible to defy time using speed? [closed]

I have always wondered if we were to travel at past the speed of light (even beyond the current capability) would we be able to slow down time around us? I have asked my teacher at school and he has ...
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215 views

Will the black hole evaporate in finite time from external observer's perspective?

There is the problem that is bothering me with the black hole evaporation because of Hawking radiation. According to Hawking theory the black hole will evaporate in finite time because of quantum ...
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2k views

Why doesn't mass of bob affect time period?

Please correct me if I'm going wrong - By the gravitation formula: $F = \frac{G m_1 m_2}{r^2} $, So if the mass of a bob is greater then the torque on it should increase because the Force increased ...
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What is the term $t$, in the expression $E=t^{0}m^{1}c^{2}$? [closed]

$E=(t)^{0}(m)^{1}(c)^{2}$. Here, $m$ = mass of the body. $c$ = velocity of light. Is $t$ the time?
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109 views

I heard that at quantum level the past-present-future is not in order, is this true? Is time really messed up there?

I heard that at Quantum level events can happen out of order making causality invalid. Thus the future can happen in present and the present in the future. Is this true?
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124 views

What about continuity of Space and possible discreteness of Time? [duplicate]

Is time continuous or discrete? Is even this question a valid question? If you say, it all depends on resolution then assume the best possible resolution achievable. If it is discrete, then what about ...
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2answers
596 views

Big bang and time

I heard Carl Sagan talking about the Universe 15 Billion years ago, and the Big Bang. He made the statement that it was the biggest explosion of all time (at first I thought this a subtle pun). This ...
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Relativity in Real Life

I have no formal training at all in relativity. But I was just wondering if our perception of time is altered by different events. Here are some examples I had in mind: If I touch a stove for 10 ...
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2answers
142 views

The heat equation in relation to smoothing algorithm

Recently I learned about a technique in image processing, which has its roots in something called the 'heat equation' from physics. The original creators of this technique were inspired by the physics ...
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70 views

Is the universe we know just shaped due to time? [closed]

Call me a daydreamer, but I could not stop myself for asking this question. I was idle when something ticked me and struck my head. I was thinking about universe, speed of light, and how time works. ...
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Do you age at different rate at different speed?

This is probably answered many times, but my confusion is the following. In special relativity it is said that there is no preferred coordinate system. Does that mean that for the people at rest ...
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123 views

What is difference between $\frac {dr}{dt}$ and $\frac {\partial r}{\partial t}$? [duplicate]

What is difference in physical meaning of partial time derivative and ordinary derivative of $r$? $$\frac {\partial r}{\partial t}\quad\text{and}\quad \frac {dr}{dt}.$$ I know that ordinary time ...
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2answers
215 views

Energy time complementarity from unitary evolution

I am looking for a well posed experimental situation that illustrates energy time complementarity. I know of Einsteins box, which is discussed quite nicely in Bohr's article Discussions with Einstein ...
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1answer
2k views

Is time quantized? Is there a fundamental time unit that cannot be divided? [duplicate]

Is the present just a sharp line between the past and the future with no time at all, or is the present a short frozen unit of time? Could time be quantized into a fundamental units? Like Planck ...
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473 views

What accounts for the discrepancies in my calculations of year lengths?

A common exercise in many introductory astronomy texts is to use the lengths of various kinds days to calculate the approximate length of the corresponding year. For example, ratio $k$ of the length ...
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1answer
781 views

Is time slowing down and disappearing from the universe instead of the expansion of universe? [duplicate]

Are we fooled into thinking that expansion of the universe is accelerating, when in fact, time itself is slowing? Or if dark energy does exist?
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1answer
2k views

How to derive the Time Dilation formula given: [closed]

Since I do not have 10 reputation I will fit this all in one image: If you have any questions please dont hesitate to ask. EDIT: http://img16.imageshack.us/img16/8604/myquestion2.png
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1answer
237 views

Calculating the length of day at any time of the year? [duplicate]

Is it possible to calculate the length of the day at various location (distances) from the sun? I hear agricultural scientists are able to do that. To make calculations easier assume there is no axis ...
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1answer
91 views

Nonlinear combination of velocities implies no absolute time?

Landau 1961 begins with a brief presentation of special relativity. This question is about the validity of a certain argument that they use in building up the foundations of the subject from scratch, ...
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1answer
121 views

How can we observe lights properties if it travels at the speed of light, or can we? [duplicate]

Special relativity says that anything moving (almost) at the speed of light will look like its internal clock has (almost) stopped from the perspective of a stationary observer. How do we see light as ...
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3answers
2k views

What is “first order“ and “second order” in time?

What is the meaning of the text quoted below? In the physical world, if a system is described by an equation that is first order in time, the system is general dissipative (has energy loss). ...
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1answer
88 views

Could a bipolar nebula be produced by a time gradient?

M2-9 is an example of a bipolar nebula that resembles two back-to-back rocket nozzles. Is it possible that this shape (somewhat unusual for an explosion) is the result of a time gradient? A rotating ...
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45 views

Estimating the present state of stars [duplicate]

Many time while reading through astronomy articles on the stars most of then thousand of light years away from earth. I have wondered how do astronomer know about the present state of star if we are ...
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1answer
112 views

Synchronization of clocks and observations of time in special relativity

I have thought up a situation that I cannot understand with my understanding of special relativity. I don't know general relativity, but as the situation doesn't involve gravity or acceleration, I'm ...
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1answer
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If time stops at the speed of light is a photon 'everywhere' at once? [duplicate]

I am not a physicist so excuse my question if it's paticularly stupid. As a particle gets closer to the speed of light time slows down as for that particle as compared to a reference from the ...
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Does one second exist? [closed]

Let us assume .5 second has passed. Now similarly let .9 seconds also passed.. Then let's say that .99 second has passed...we're still not done because 1 second hasn't passed. Then follows .999 ...
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How can the big bang occur mathematically?

As we know time began with the big bang. Before that there was no time, no laws, nothing. Mathematically how can an event take place when no time passes by? How did the big bang took place when there ...
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2answers
265 views

Imaginary time in QFT

I'm reading chapter 4 of Introduction to Quantum Field Theory by Peskin & Schroeder. In the $\phi^4$ theory, the authors state that the ground state of the interaction theory $|\Omega\rangle$ can ...
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1answer
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Question about Time Dilation

I just have a quick question about time dilation/proper time because my physics book makes it a little confusing. Let's say we have an observer on Earth, and then an observer on a space ship. The ...
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1answer
102 views

How do we know that time and distance are not discrete?

I know that it is believed that energy is discrete, in that it travels in quanta. I was wondering if there is any evidence which either proves or disproves something similar with both time and ...
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318 views

Why is my approach to the equation of time off by a constant?

I'm trying to better understand the causes for the equation of time by deriving an approximation from first principles. My naive approach, $EOT_{NAIVE}$, is to take the difference between the right ...
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1answer
214 views

Is period of rotation relative?

My question is inspired by the following answer by voix to another problem: "There is a real object with relativistic speed of surface - millisecond pulsar. The swiftest spinning pulsar currently ...
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When is the right ascension of the mean sun 0?

I understand that the right ascension of the mean sun changes (at least over a specified period) by a constant rate, but where is it zero? I had naively assumed that it would be zero at the most ...
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How to find time taken for a spinning top to stop? [closed]

The angular position of a spinning top is given by $\theta = t^3 - 72t$, where $t$ is in seconds and $\theta$ in "radian".
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242 views

Does the collapse of the wave function increase entropy of the atomic system itself?

Does wave-function collapse cause the entropy of the atom (ie. the sub-atomic particle system that makes up the atom) to increase?
7
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3answers
261 views

Do velocity and acceleration time dilation factors add?

For a spinning space station such as in 2001, A Space Odyssey, what would be the time slowing in the perimeter of the spinning space station with respect to the center axis of the station? The ...
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2answers
191 views

Does it make a sense to speak about age of electron or atom?

It's possible that this question is too soft or even quite senseless for this forum, but I will ask nevertheless. Everyday (macroscopic) things, like a grandfather's pendulum clock or the grandfather ...
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2answers
567 views

What is the fastest process or shortest time in nature?

We know about some events that happen very quickly. For example, the dielectric relaxation time is about $10^{-14}\, \mathrm{seconds}$. I'm interested in other processes that switch extremely fast ...
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2answers
1k views

What is the common difference between partial time derivative and ordinary time derivative? [duplicate]

What is difference between partial and ordinary time derivative? for example: what is difference between $\frac {\partial v}{\partial t}$ and $\frac {dv}{dt}$? where the $v$ is velocity.
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1answer
120 views

The status / acceptance of block time?

What is the current status or acceptance of block time as it relates to Einstein's theory of relativity? Has quantum mechanics ruled it out or is it still the favored view of the world? Perhaps there ...
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0answers
123 views

Wormholes and the illusion of time?

I was watching a video on Youtube by Brian Greene, "the illusion of time."http://www.youtube.com/watch?v=j-u1aaltiq4 In that video, he introduces to me the idea of a "brane," or a slice of the ...
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4answers
312 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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0answers
124 views

Time ordering and Fermions

Having time ordering operator for fermions, should it reverse sign if it swaps operators with opposite spin variable? In other words should $T[c_{t_1,\uparrow}c_{t_2,\downarrow}^\dagger]$ return ...
8
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1answer
248 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 ...
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2answers
263 views

Is this a great flaw in big bang theory? [duplicate]

Einstein said that, Time & Space cannot exists without one another. Big bang says, time didn't exist before the big bang. So the Primordial ball referred in the Big Bang theory didn't had any ...
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1answer
2k views

Did space and time exist before the Big Bang? [duplicate]

I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
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1answer
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Are “timed” measurements actually revealing error-distributions of the measurement apparati?

A thought experiment: Given some object moving (swinging) from left to right and back with constant velocity, imagine a camera set up to take a picture of the scene at a fixed interval so that we can ...
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4answers
475 views

Time inside a Black hole

If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black ...
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1answer
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Anti-matter black hole and time

I have recently read some hard science-fiction story based on an assumption that if time stops (from external observer's perspective) on the event horizon of black hole, then in an anti-matter black ...