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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7
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4answers
996 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 ...
3
votes
0answers
51 views

What is the shortest controllable time?

I was reading http://en.wikipedia.org/wiki/Planck_time and noticed a reference to: http://phys.org/news192909576.html where it is stated that: 12 attoseconds is the world record for shortest ...
2
votes
1answer
108 views

Expectation value of Hamiltonian in different pictures of quantum mechanics

We start with the familiar Schrodinger equation: $$ i\hbar \frac{\partial \left|\psi_S\right\rangle}{\partial t} = \hat{H}_S \left|\psi_S\right\rangle $$ As we switch to a different picture than ...
0
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1answer
133 views

Distance travelled given velocity at various moments of time [closed]

I am trying to solve a problem where I need to find the distance travelled at the end of the nth second and my input data contains only velocities at different time instances. Say for instance I ...
4
votes
1answer
167 views

Time-Energy Uncertainty Principle and Operators

In most of examples, I notice that uncertainty principle for time & energy is given between mass & lifetime. The UP for time and energy is $$ \Delta t\,\Delta E\geq\frac h{4π} $$ where $$Δt ...
1
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5answers
222 views

A question about motion and time dilation

I was thinking that if you are in empty space with another person (with no other objects around), and from a distance you see that the other person is approaching you a constant speed, you wouldn't ...
1
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4answers
110 views

Relation between Force, Time, and Energy

Is energy involved independent of force applied over time? In other words, if I wish to apply a force for much more time would I require more energy?
0
votes
1answer
153 views

Time to heat/cool a room

So, I have a basic, very basic, understanding of thermodynamics. I don't take it until next semester. I'm attempting to write a program which plots a temperature over time graph of a room being ...
0
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3answers
91 views

How can a clock work if the uncertainty principle is true?

If the uncertainty principle and Copenhagen Interpretation are true, then how can a clock tick? Supposedly particles can do all sorts of things when not measured, then how can they be formed into ...
1
vote
1answer
130 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
3
votes
1answer
114 views

How is UT1 being computed?

I've recently read up about time standards and now understand that UTC is a second-corrected version of international atomic time so that it is kept within 0.9s from UT1. And then UT1 is defined as ...
-3
votes
3answers
116 views

Can it be considered as time travel?

India is about 8.5 hours ahead of US. If some person starts from India at 9 pm(according to his wrist watch) and reaches US in 2 hours(just assume),at that time his wrist watch will b showing 11 pm ...
0
votes
1answer
172 views

How does a black hole slow time? [duplicate]

I've been reading about black holes, and I keep coming across the fact that time runs slower near a them. My questions are: Does this mean that if you left Earth at age 30 and spent 30 years near the ...
16
votes
2answers
1k views

Inflation and the Meaning of Time

I'm not quite sure how to ask this so that it can be answered in layman's terms, but I have lately seen, in several places, that with cosmological inflation, there was a point where the universe ...
6
votes
2answers
511 views

How can photons interact with anything?

I read photons do not age because they move at the speed of light. So when a photon interacts with my eyes, aren't they apart in space-time by the difference of the time in the frame of reference of ...
0
votes
0answers
60 views

Time relativity - 'philosophical' question

I'm aware that time is relative to the observer. But, does this also extend to the perception of time? For example, let's consider a fly (there's research suggesting that flies perceive time passing ...
0
votes
1answer
51 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 ...
7
votes
3answers
349 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. ...
0
votes
1answer
133 views

What's the meaning of the age of the universe?

I'm not asking about how we worked backward from an expanding universe to the age of the big bang, but rather what is the meaning of time in a near infinitely dense point in the context of general ...
-1
votes
1answer
130 views

Determine the distance from time-velocity graph [duplicate]

A small car that we made in class was travelling and its time was recorded at 1,2,3, and 4 meters. The points in the form (seconds, meters) are as follows: ...
0
votes
0answers
83 views

Calculating impact velocity and time with non-uniform acceleration [duplicate]

Here goes: imagine a spacecraft with engines shut off in a free fall towards some celestial body x. let's say the distance to surface is $100 000$ $\text{meters}$. initial vertical velocity is ...
22
votes
2answers
2k views

The age of the universe

Many times I have read statements like, "the age of the universe is 14 billion years" . For example this wikipedia page Big Bang. Now, my question is, which observers' are these time intervals? ...
-3
votes
3answers
174 views

Is Space conserved [closed]

Can space be created or destroyed? Is space conserved? I am not asking for matter,energy and time. Its just a question about conservation of space PS: I am asking for what was there before big bang. ...
15
votes
9answers
3k views

Is the flow of time regular?

Is the flow of time regular? How would we come to know if the our galaxy along with everything in it stops for a while(may be a century) w.r.t to the galaxies far beyond our reach. Is there a way to ...
0
votes
1answer
171 views

Calculate impulse based on mass, acceleration and time elapsed [closed]

I want to move to Sprite Kit framework offered by apple which has physics integrated right into it. The back bone of the physics engine is famous Box2D. Sprite Kit has made it pretty easy by wrapping ...
1
vote
1answer
128 views

Does the light speed change in media? [duplicate]

Does the light speed change? The Theory of Relativity says that the speed of light in vacuum is the same and unchangeable, while I read that the speed of light in glass is lower than in air, and that ...
2
votes
0answers
56 views

What's the connection between being homogeneous in energy and having a proper time scale?

Towards the end of page 8 of this scientific paper, I have found the following sentence: ...given the fact that the system is homogeneous in energy, or equivalently, that it has no proper time ...
0
votes
1answer
73 views

How does time dilation work in this situation?

It is my understanding that when moving near the speed of light, time slows down relative to other things not moving so fast. Based on this principle, would it be theoretically possible to travel a ...
0
votes
1answer
75 views

Increase thinking capability through relativity

As Einsteins relativity suggests that everything slows down along with the speed of light. So, if we were to live in space would our thinking capability (essentially speed) increase or decrease (due ...
-2
votes
1answer
80 views

What is the formula for determining time dilation (as the object in motion)? [duplicate]

The formula for calculating how much time passes for a still observer is T=TO/(1-v^2/c^2)^1/2. How do I calculate what TO is?
0
votes
2answers
284 views

Mistake in Briefer History of Time by Stephen Hawking [closed]

I was reading A Briefer History of Time by Stephen Hawking and Mlodinow. I found something silly. On page 36 at the bottom, it says the following : If, say, the sun suddenly disappeared, Maxwell's ...
2
votes
2answers
410 views

How long does it take for a black hole to form?

The well-known fable of an astronaut sending signals out to an external observer while falling toward an event horizon states that the time lapse between such signals becomes greater even if in the ...
2
votes
0answers
158 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 ...
2
votes
1answer
306 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 ...
2
votes
1answer
99 views

Regarding the possibility of Closed Timelike Curves

I've been looking a lot at Closed Timelike Curves, and how if a theory allows for these curves it doesn't respect causality. I understand that about the curves themselves (Grandfather Paradox), but ...
3
votes
5answers
211 views

Two clocks along different worldlines

I have been reading and watching videos about this subject for a while now. I just can not seem to grasp the idea. Let's say we have two clocks. I leave one at home and keep one in my pocket. Then, ...
1
vote
0answers
81 views

What are characteristic ranges of time, distance, energy regions for physics and chemistry? [closed]

I've constructed such table from many different sources for my thesis introduction: I'm trying to make a bit of philosophy it the thesis first chapter. Are they realistic or not? Could you make any ...
0
votes
2answers
148 views

How could mass exist before Big Bang?

I heard that before Big Bang the temperatures were so high that mass and energy constantly converted to each other. After big bang the temperature became less and the conversion stopped that is what ...
1
vote
5answers
336 views

Are events in this experiment simultaneous if observed in platform's frame?

In some contexts e.g. on Wikipedia it is defined as a matter of happening . In others(e.g. as defined by Einstein in his book "Relativity the special and general theory") it is defined as a matter of ...
1
vote
2answers
193 views

Does our current notion of velocity/acceleration (based on calculus) require absolute time?

When people explain special relativity, they say that a velocity in one frame leads to time dilation in that frame relative to a stationary frame. When we say something like ...
2
votes
1answer
163 views

Time Dilation Effects from simply being on a spinning planet orbiting a star in a rotating galaxy in an expanding universe.

I am a layman, so take this with a grain of salt. I saw a TV show the other day which showed a Russian Cosmonaut who had spent more time in space than any other human. The relativistic effects of ...
2
votes
2answers
743 views

Can Flow of time become still?

According to theory of time dilation, flow of time slows down significantly at the speed of light.Is there any conditions practically or theoretically when flow of time is reduced to zero means it ...
3
votes
1answer
356 views

Does time dilation correct for the Doppler effect?

Knowing that a body in motion experiences time dilation, "also" knowing when two objects travel at a great speed away from one an other, both observers experience the others clock as moving slower ...
8
votes
5answers
558 views

Does time exist in a vacuum?

Imagine a perfect vacuum devoid of all matter and radiation. Irrespective of whether such a space can even exist, my intuition tells me that time would not exist within such a space. What this thought ...
-2
votes
1answer
74 views

Displacement inside the moving Object

Suppose say a person is standing over the moving bike and he jumps while bike is moving, bike will move forward & person will land in same point at which he jumped, relative to earth position ...
-1
votes
2answers
121 views

Backward Time Flow?

Physicists say that time is moving foward because entropy always increases. But have physicists considered that we might be mistaken? Since there is no ultimate reference frame, it could be possible ...
0
votes
2answers
148 views

Breaking the simultaneity

I have expressed my self in a detailed way. I've labeled the points to which I want an answer. I have doubt in the Einstein's rail experiments which he mentioned in his book. In this experiment ...
2
votes
2answers
283 views

Accuracy and Error of Atomic Clocks

I'm quoting a passage from my notes: The development of clocks based on atomic oscillations allowed measures of timing with accuracy on the order of $1$ part in $10^{14}$, corresponding to errors ...
5
votes
9answers
910 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 ...
1
vote
1answer
163 views

Is there a physical quantity which is the reciprocal/multiplicative inverse of time?

Is there a physical quantity which is the reciprocal/multiplicative inverse of time? If time =distance/speed what is speed/distance. Please forgive my ignorance if there is a really simple ...