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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votes
0answers
46 views
Mass term in the Minkowski metric and an oscillation model in Lorentz group [closed]
This is my first post at stackexchange.com. A few weeks ago, I submitted
a physics paper to a journal and finally I received a reply from editor 2
days ago with referee's comments. Before answering ...
-2
votes
0answers
39 views
How to derive an oscillation period formula? [closed]
Given that the position function of a object flowing on a circle is $y = w-a\sin(y)$.
Why does the oscillation period $T = \int dt$ ? Why does this make sense?
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votes
0answers
50 views
what makes time proceed [closed]
some philosophers look at reality as some kind of machine that requires a "Mover"
this "Mover" is the force or power which moves time.
This is not consistent with the physics way of defining force ...
1
vote
1answer
83 views
+50
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 ...
1
vote
1answer
143 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 ...
0
votes
1answer
87 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?
2
votes
1answer
58 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 ...
-5
votes
1answer
91 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
3
votes
1answer
57 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, ...
-3
votes
0answers
44 views
Where the speed of light is constant how big bang evolve per time? [closed]
I mean where the $\frac{dc}{dt}=0$ how could world evolve by time during big bang?
How is time evolution of energy possible where the velocity of light doesn't vary by time?
0
votes
1answer
54 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 ...
1
vote
3answers
84 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). ...
0
votes
0answers
41 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 ...
2
votes
1answer
47 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 ...
6
votes
2answers
164 views
How fast can time flow? A question of time dilation
(I would describe myself as an illiterate physics enthusiast, so I hope you'll forgive me if my ignorance is borderline offensive.)
If I've understood anything of the concept of time dilation, your ...
2
votes
1answer
83 views
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 ...
-6
votes
3answers
89 views
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 ...
0
votes
0answers
22 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 ...
1
vote
4answers
122 views
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 ...
3
votes
2answers
112 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 ...
4
votes
3answers
75 views
Does the expansion of the universe soon after the Big Bang affect the amount of time that light takes to reach us?
If faster than light travel is impossible, how is it that light emitted from matter so close together in the time soon after the Big Bang is only now just reaching us? I would assume that there would ...
0
votes
1answer
76 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 ...
-3
votes
1answer
30 views
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".
3
votes
1answer
101 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 ...
13
votes
1answer
160 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 ...
7
votes
3answers
129 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 ...
4
votes
2answers
87 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 ...
0
votes
2answers
70 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.
1
vote
2answers
58 views
Area under a displacement graph
If the area under an acceleration-time graph denotes velocity and the area under a velocity-time graph denotes displacement, what exactly does the area under a displacement-time graph denote?
0
votes
0answers
40 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 ...
1
vote
4answers
184 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?
7
votes
1answer
121 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 ...
0
votes
1answer
147 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?
1
vote
1answer
21 views
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 ...
1
vote
0answers
85 views
General physics question involving Heisenberg Uncertainty Principle
Question:
An unstable particle produced in a high-energy collision is measured to have an energy of $483\ \mathrm{MeV}$ and an uncertainty in energy of $84\ \mathrm{keV}$. Use the Heisenberg ...
2
votes
4answers
208 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 ...
2
votes
1answer
164 views
Need help with the position of a particle in a velocity-versus-time graph
I am having trouble with a velocity-versus-time graph. I recently took a Physics test that asked this question: The graph shows the velocity versus time for a particle moving along the $x$ axis. The ...
3
votes
2answers
313 views
Is time Scalar or Vector
In
http://en.wikipedia.org/wiki/Time_in_physics
its 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. ...
0
votes
4answers
171 views
Bear with me, this is a stupid question. Talking on the phone and time
So a few days ago I noticed (im sure we all just know this) that when talking on the phone you receive the messages a few seconds after it is said by the sender.
So person A says "hello" to person B.
...
4
votes
3answers
324 views
Is there a mechanism for time symmetry breaking?
Excluding Thermodynamic's arrow of time, all mathematical descriptions of time are symmetric. We know the arrow of time is real and we know the equations describing physics are real so is there any ...
3
votes
3answers
185 views
How do we know for certain that space is expanding?
How do we know for certain that space is expanding?
Let's say that in the year 1950, we observe that galaxy 1 is 5 billion light years away from us and galaxy 2 is 10 billion light years away from ...
3
votes
3answers
131 views
Looking out into the universe means looking back in time - how does that work?
This is a question that has been gnawing on me for many years now. Back a long time ago, as I recall in reference to a scene in a popular science show on TV, I was asked the following.
The claim is ...
-1
votes
1answer
81 views
US time zones and Daylight saving time, energy efficient? [closed]
As a foreigner, United States has a very complex time system for me. Central Time Zone, North American Eastern Time Zone, ...
3
votes
4answers
214 views
Why a day is divided by 12/24 hours? Why the number 12?
Why a day is divided by 12/24 hours? Why the number 12? Why not using 10 or 6 or 14, 16? Who invented this? Any physical reasons behind this?
1
vote
0answers
76 views
Do particles travel backward and forward in time? [duplicate]
All these classical ideas are pointless and obsolete today, because in quantum mechanics, the particles are completely different objects, defined by quantum motion of fields, not by the location of ...
0
votes
1answer
94 views
Does our local time speed up as the Universe expands?
Starting from a simplified radial Freidman Walker metric we have
$$ds^2 = -c^2 dt^2 + a(t)^2 dr^2 $$
How does one measure one's proper time operationally?
One times a light beam along an element of ...
0
votes
1answer
62 views
Time Dilation in relation to Acceleration
What I am looking for is a layman's explanation on the equations required to work out Time Dilation at high speeds including acceleration and deceleration of velocity. Or I would greatly appreciate it ...
3
votes
1answer
98 views
How much time has passed for Voyager I since it left the Earth, 34 years ago?
34 years have passed since Voyager I took off and it's just crossing the solar system, being approximately at 16.4 light-hours away. How much time have passed for itself, though?
1
vote
2answers
188 views
Will observers moving on a sphere experience time dilation?
A single source of light exists at a fixed point in space relative to two observers. The two observers move on the surface of a shell with a fixed radius with the light source at its centre. They move ...
5
votes
1answer
125 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?
