Questions tagged [time]

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

Filter by
Sorted by
Tagged with
0
votes
3answers
77 views

Why is the motion described by $F = -kx^{2n+1}$ periodic?

I understand the motion when: $$ F=-kx $$ which leads to the an ODE that then has solutions expressed as: $$ x(t)=A\cos(\omega t)+B\sin(\omega t) $$ This is periodic since a cosine function is ...
1
vote
0answers
41 views

Swing - time taken [duplicate]

I was thinking about how I would go about calculating the time taken for a swing to swing from one side to the other, assuming that there only exists a gravitational force and discarding all other ...
0
votes
1answer
213 views

How is four-velocity automatically normalized?

This is a page from Sean Carroll's Spacetime and Geometry.There is a line in this page which says that the four velocity is automatically normalized.This absolute normalization is a reflection of the ...
2
votes
2answers
218 views

How does calculating Hubble time work?

For calculating we take $t=\frac dV$, where $V=Hd$ . But velocity isn't uniform for an object as distance also increases with time. And if velocity isn't constant the equation $t=\frac H d$ also isn't ...
0
votes
2answers
293 views

What would the position vs. time graph look like if the velocity vs. time graph was a curve?

In my physics class we are learning about velocity vs. time graphs and position vs. time graphs for an object. We have learned that if the object is moving with constant velocity (this would be a ...
-5
votes
1answer
43 views

What do you think of this conceptualization of the universe and time dilation? [closed]

So the universe is ever-expanding. It's been expanding in all directions since the Big Bang, like how a sponge expands when you give it water. The universe is made of a fabric known as space-time. The ...
-3
votes
1answer
428 views

Why is the MKS unit of time the same as the CGS unit? [closed]

There are many system of units used in physics. In the CGS, the units are, length : centimetre mass : gram time : second And in the MKS system the units are, length : metre mass : kilogram time : ...
0
votes
0answers
32 views

What formulas do I need to calculate the time it takes for a room with opened window to become the same temperature as outside?

I want to calculate how long I have to open my window to become the same temperature as outside. To make things more easy let’s assume there’s almost no wind helping the exchange of temperature.
0
votes
2answers
53 views

Calculation of Gravitational Collapse time

The answers to Gravitational collapse and free fall time (spherical, pressure-free) describe the calculation of collapse time for a gas. For the case of neutral hydrogen gas with number density $10^4$/...
0
votes
0answers
14 views

Is it possible that D-T graph could be linear , but V-T graph will be log?

So , I have plotted the V-T & D-T plots for solar sail using the parameters (Using euler's method for solving the ODE based on Solar sail, estimate force & Here's my program :- https://github....
0
votes
1answer
20 views

Average Velocity Question (isolation?)

So there is this question i've been having trouble with for the past hour. It involved a child going down a ramp on a sled at and angle theta with a total system of mass. accelerates down a hill of ...
12
votes
6answers
3k views

Why does a sign difference between space and time lead to time that only flows forward?

Ever since special relativity we've had this equation that puts time and space on an equal footing: $$ds^2 = -dt^2 + dx^2 + dy^2 + dz^2.$$ But they're obviously not equivalent, because there's a ...
0
votes
1answer
101 views

Does light know the future? [duplicate]

As I understand it, if light is traveling at the speed of light, then from it's point of view space is fully compressed in its direction of travel. Does that mean that from it's point of view, light ...
0
votes
1answer
43 views

Interdependence of time, the speed of light and distance in General Relativity

In the relation $$ \text{time}\cdot\text{speed of light} = \text{distance}\,,$$ by definition, the speed of light is constant. When bringing a clock, like in a GPS satellite, up into orbit, i.e. ...
0
votes
2answers
73 views

Why did Einstein pick his definition of synchronous clocks?

In his paper "On the Electrodynamics of Moving Bodies", Einstein defines synchronous clocks as clocks which satisfy $t_B-t_A=t'_A-t_B$. $A$ and $B$ are two points separated by empty space, and ...
-1
votes
3answers
61 views

If things travel at different time rates due to relativity wouldn't one of them disappear from my perspective? [closed]

If I travel to a 3d location where Einstein was known to have existed at some other time, I do not expect to see him, because his 4d location is different! Why then can I send a clock around a black ...
0
votes
0answers
23 views

Equations of motion due to gravity [duplicate]

This question has probably been asked before, but I couldn't immediately find anything with a search. Two masses of $m_1$ and $m_2$ are in space separated by a distance of $x$. They now accelerate ...
6
votes
3answers
3k views

Does time speed up or slow down near a black hole?

The Schwarzchild geometry is defined as $$ds^2=-\left(1-\frac{2GM}{r} \right)dt^2+\left(1-\frac{2GM}{r} \right)^{-1}dr^2+r^2(d\theta^2+\sin^2(\theta) d\phi^2)$$ Lets examine what happens close to ...
1
vote
1answer
61 views

Can we always choose a gauge in GR in which time is constant?

In General relativity the metric describes the curvature of 4D space-time. But due to diffeomorphism invariance, many metrics describe the same physics. Can we always choose a metric such that we can ...
2
votes
3answers
85 views

If I could halt all motion would I stop time? [duplicate]

I've never really understood time. Time is not a force. It isn't energy or matter. Time doesn't MAKE anything do anything. Time doesn't make a clock tick (motion or batteries do). Time doesn't make ...
1
vote
1answer
30 views

How do we write free body diagram for an object that is rebounding?

How do we write free body diagram for an object that is rebounding? Here's an illustrated example Let us assume that the object has an initial force. So, I want to draw free body diagram for each ...
2
votes
2answers
124 views

What does it actually mean to say that time “speeds up” or “slows down”?

I was thinking lately about relativistic time dilation and time passing differently on other planets (which both, eventually turned out to be caused by the same principle). Now, quite naturally (as ...
-1
votes
1answer
69 views

Does a black body in zero gravity emit EM radiation? [closed]

I have just recently thought of this query. However, I can find no evidence of any experiments ever being carried out on the effect of zero gravity on black body radiation.Perhaps someone here has ...
0
votes
1answer
80 views

Can body of one temperature ever cause higher temperature in another body?

If you have one body that radiates heat at a constant rate and, forgive my simple assumption, thus constant temperature, and a body that may absorb this heat, may the temperature of second body ever ...
2
votes
1answer
93 views

Time Travel, CTC and Causal Loop

What is the difference between a closed timelike curve and a causal loop? If someone is travelling in a closed timelike curve, are they also in a causal loop?
-1
votes
1answer
87 views

Is speed of light is the only way to measure time [closed]

After reading up on special relativity, I understood that because of Einstein's postulates -the speed of light in free space is a universal constant Everytime we measure time for an event, directly ...
-3
votes
1answer
75 views

What are the relativistic arguments for existence of space? [duplicate]

One of the interpretation of special relativity states that the time is an illusion and does not really exist. This interpretation promoted Einstein himself in his condolence letter after the death of ...
4
votes
3answers
139 views

Concept of time in General Relativity

I am starting to read General Relativity, and from what i have understood, in this theory, time is a derived notion. An event is not associated with a particular time. But then what is the physical ...
0
votes
1answer
36 views

What does “Real-time” mean?

In the context of describing Real-time dynamics of Lattice gauge theories, have they specifically mentioned real-time in order to differentiate it from imaginary-time. Or does it have any other ...
3
votes
1answer
55 views

Are there other processes theoretically out there that can cause time dilation besides gravity and velocity?

I am just wondering if there is anything else besides gravity or velocity that causes time dilation in regards to special relativity or other theoretical models of our universe.
-1
votes
1answer
40 views

If time was non-existent would we be able to move? [closed]

If time would stop, would we be able to move, or would we be "frozen"? also if we could move, would we be able to move at a infinite speed ?
1
vote
2answers
130 views

How to get the UT1 directly? or How to get the UT1-UTC

I have a question to consult you. Even though I know the relationship between time scales like UT1, UTC, TAI, and TT, I do not know which one is the key point for the computation. That is, from which ...
0
votes
0answers
17 views

How time dilated is the average particle relative to the big bang? [duplicate]

Particles created during the being bang have experienced time dilation by means of gravitation and general acceleration for the past 13.8 billion years. On average, how time dilated is the average ...
2
votes
2answers
450 views

What is the meaning of the negative sign in $\Delta s^2 = \Delta x^2 + \Delta y^2 + \Delta z^2 - (c\Delta t)^2$?

In the equation of the spacetime interval formula $\Delta s^2 = \Delta x^2 + \Delta y^2 + \Delta z^2 - (c\Delta t)^2$ is there meaning for the minus sign before the $(c\Delta t)^2$ or is it just a ...
0
votes
1answer
425 views

Is time passing really differs on other planets/in interstellar? [duplicate]

I am aware of the idea of time dilation (which I, by the way, asked another question about) on speeds, that get close to the speed of light. Though, I wonder what other (if any) forces and laws affect ...
1
vote
1answer
53 views

Gravitational attraction between two kilogram weights [duplicate]

Imagine two weights, each of mass one kilogram, floating in outer space. Starting one meter apart, and under no forces other than their own gravity, how long would it take before these two weights ...
-1
votes
1answer
65 views

Why are pendulums' time periods amplitude-invariant? [closed]

Whether the angle is low or high, it returns at the same time. How come this is true?
9
votes
4answers
896 views

Twin paradox in curved space time [duplicate]

In a flat space, where special relativity works, a travelling body can only return to the same point if we apply some kind of acceleration to the body. So twin paradox is not a paradox because a ...
1
vote
0answers
28 views

Event Horizons and Events [duplicate]

How can two black holes with event horizons merge within the lifetime of the universe? Basically events are happening where events stop (to the outside observer) so does an event horizon actually ...
1
vote
2answers
99 views

Conversion from Planck unit to SI [closed]

Good evening, I'm reading the paper Prehawking radiation by William G. Unruh where it says: ...a time scale of order of $m^{3}$ in Planck units, or $10^{53}$ ages of the current universe for a ...
1
vote
0answers
126 views

Testing if antimatter is backwards-travelling matter?

I've read about how antimatter can be modeled as matter traveling backwards in time before but always viewed this as a sort of mathematical curiosity. With this question I'm not so much asking if ...
0
votes
2answers
130 views

What is the “rate” of the “passage of time”? How does a physicist define and measure time? [duplicate]

I'm trying to separate common concepts of time from the use of time as a standard measurement in physics. One thing I'm struggling to define is the "rate of the passage of time". For example, ...
0
votes
3answers
69 views

What are the units of time when planck's constant is equal to 1?

If I express a Hamiltonian $H$ in units of Hz by dividing the energy terms in the Hamiltonian by hbar $\tilde{H}=\dfrac{H}{\hbar}$ which means you set $\hbar =1$. Then what are the units of time? Also ...
2
votes
1answer
79 views

Is the violation of time-reversal always associated with the violation of time-translation and vice-versa?

Is the violation of time-reversal symmetry always associated with the violation of time-translation symmetry? What about the converse? Is it possible for one to be violated while the other remaining ...
14
votes
6answers
1k views

If photons don't experience time, does that mean time is a consequence of mass? [closed]

If photons don't experience the passage of time because they have no mass, does that mean time is a consequence of mass? To me that's a profound conclusion yet not one I see printed. Is it right?
3
votes
2answers
122 views

Effect of time dilation in Cs atomic clocks?

Let's say, Observer A is at rest and Observer B is in a spaceship moving at a significant fraction of speed of light. B synchronized his atomic clock with A's when his spaceship just passed A. Now, ...
26
votes
4answers
6k views

With what velocity are we moving along the time dimension?

Does the question make sense? Velocity along time axis means $v_t=\mathrm dt/\mathrm dt$? If it doesn't, please explain where the flaw is. Taking time as measure like length? Or do we need to ...
1
vote
0answers
26 views

Can time flow backwards? [duplicate]

Is there any equations in physics or laws that say time can flow backwards instead of forward?
0
votes
1answer
55 views

Is the formula for time dilation applicable only in 1D?

According to time dilation formula $$ \Delta t_{observer} = \frac{\Delta t_{proper}}{\sqrt{1-(v/c)^2}} $$ I have basically two questions: (1) Is this formula applicable only for 1D motion, i.e. ...
1
vote
2answers
433 views

How to deal with explicit time dependence of the Lagrangian?

Clearly, if the Lagrangian in explicitly time dependent, the Euler-Lagrange equations being satisfied does not extremise the action. I am unclear as to how to deal with systems with an explicitly time-...