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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180 views

Does the universe have a different age to different observers?

Although I understand that the universe is approximately 12 billion light years wide, and that may mean that it took the light photons 12 billion years at 186,000 miles per second to reach the ...
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1answer
95 views

Would Special Relativity Predict Time Dilation of a Geostationary Satellite Compared to an Observer on Earth?

Consider a geostationary satellite at some arbitrary distance above the Earth's equator and consider a person directly below it, standing on the Earth's equator. Both satellite and person exist on the ...
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1answer
69 views

Why do I different values compared to my theoretical time?

I'm having an experience about time needed to charge the capacitor to the 63.2% voltage of the batteries. There are resistance, capacitor and batteries in the circuit. When I calculate the ...
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3answers
149 views

Formation of the event horizon seems impossible with singularity inside seems impossible [duplicate]

According to what I was reading, the formation of an event horizon appears if the mass becomes compact enough. Unfortunately, due to time dilation the time for mass to fall into the event horizon ...
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3answers
117 views

What is time, with respect to universe? [closed]

I want to know what is actually time, not like the measurable quantity. But with some scientific terms Someone said that "time is entropy". Is that true? also what makes time unique?
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2answers
126 views

Which will collide first, the moon and Earth, or Sun and Earth?

As time progresses, which scenario will happen first? The moon colliding with Earth, or the Earth colliding with the Sun? I figure the Moon and Earth will happen first, based on proximity, but the sun ...
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1answer
53 views

Can relative speed be faster than c [duplicate]

If there are two spaceships moving away from each other(in opposite directions) at a speed 0.6c, then wouldnt that make the relative speed of one from the other's frame of reference 1.2c? Does this ...
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1answer
240 views

Is imaginary time a fifth dimension? [duplicate]

I've read that by introducing the concept of imaginary time, the dimension of time can be treated like a spatial dimension mathematically. Assuming, without imaginary time, one considers the universe ...
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1answer
66 views

Special Relativity: Four possible time spans between events?

I've got another question regarding time in special relativity. I'll start with the standard configuration: there are two observers O and O', their x-axis are aligned, in the rest frame of O observer ...
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1answer
99 views

Distance as a function of time where acceleration changes with respect to distance

I was thinking the other day about gravity. I know that acceleration in a magnetic field changes with respect to distance from the center of the field. So I was thinking, how would one find the total ...
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2answers
198 views

I understand the Big Bang Theory (BBT), but how was the matter in the BBT created?

I understand the Big Bang Theory to consist of all of the matter being pulled into one great gravitational pull. such a great force that it expelled the matter out causing the idea of Red-Shift and ...
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1answer
309 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 ...
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1answer
296 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 ...
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1answer
257 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 ...
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1answer
80 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 ...
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2answers
169 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 ...
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2answers
155 views

Time Delays in General Relativity

If gravity propagates at, or less than, the speed of light, and is therefore not instantaneous, does that introduce time delays to gravity? For example: suppose that we, the observer, sit within the ...
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1answer
312 views

What really happens with Time Dilation? [duplicate]

I know if you move your time moves slower than someone who is stationary, by Lorentz's transformation. However, I don't get how this happens. What does it mean when time moves slower? How does it ...
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2answers
103 views

The speed of light through space and its effects on black holes

I was curious about a couple of things that don't quite make sense to me: (and probably won't when I get the technical answer, but I'll ask it anywise.) When light travels through space, is its ...
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1answer
235 views

General Relativity and the effect of mass on time [duplicate]

My question is related to the first page of this article regarding the big bang theory and refers to this specific sentence: Armed with the best physics of the 20th century, Albert Einstein came ...
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1answer
137 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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1answer
225 views

Deriving infinitesimal time dilation for arbitrary motion from Lorentz transformations

I'm trying to derive the infinitesimal time dilation relation $dt = \gamma d\tau$, where $\tau$ is the proper time, $t$ the coordinate time, and $\gamma = (1-v(t)^2/c^2)^{-1/2}$ the time dependent ...
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1answer
11k views

Finding deceleration and velocity using distance and time

A car is moving down a street with no brakes or gas. The car is slowing due to wind resistance and the effect of friction. The road is flat and straight. The only data I have are timings taken at 100m ...
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1answer
192 views

If you removed every particle from space…? [closed]

I'm trying to find something Einstein (I think) said about time...It was something like.. "If you removed every particle from space and were left with only one pocket watch (clock, timepiece?), time ...
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0answers
24 views

How long does it take for disturbed water to stop making sound?

Suppose I have a bowl with water or another liquid. The water from the bowl is perfectly quiet. Then I throw a stone in the water and I wait. How can I calculate the time after which the water is ...
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0answers
18 views

Why does time stand still for light? [duplicate]

The source for this is the book "Einstein for Dummies", page 330, chapter 10.
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1answer
29 views

Are measurements of time and distance independent or always coupled by the speed of light

In texts about special relativity the light clock is usually described as a tool to measure time $t$. It counts how often light travels along a given distance $d$, i.e. $t = d/c$, where $c$ is the ...
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0answers
25 views

Smallest measurable time increment

What is the smallest increment of time which can be measured using modern methods, and is not theoretical?
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0answers
28 views

Discrete time like a computer program [duplicate]

Has anybody thought about the effects of discretizing time in the way most computers do? In computer programming; collision detection for example, or updating a trajectory of a particle, everything is ...
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0answers
35 views

What is time except “Dimension”? [duplicate]

I know everybody says that time is the fourth dimension. But I want to know what is the definition of Time without just saying that it's the Fourth Dimension.
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0answers
23 views

What's the difference between cosmic time and conformal time? [duplicate]

When they say that the age of the Universe is about 13.7 billion years, they are giving the age in cosmic time, is that right?. There's this other thing called conformal time which I don't understand. ...
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0answers
32 views

How power spectral density in time domain can be understood?

I got some data which basically gives me the variation on the time of a PSD measured across specific frequency bands ranges, for instance [10Hz-30Hz]. However I have not found any good explanation ...
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2answers
51 views

What is the least count of the timer clocks used in RADAR?

I was checking out some videos in YouTube regarding the working principle of RADAR. To quote some HOW IT WORKS: World War II Radar (720p), part 1, How does RADAR work? | James May Q&A | Head ...
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0answers
49 views

What perpetuates change? [duplicate]

People say that our notion of "time" comes from entropy which in turn is just a large scale effect of the laws of physics, but what is it that perpetuates the laws of physics from one state into the ...
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0answers
57 views

If time somehow went backwards would this violate one of the laws of thermodynamics?

If time somehow went backwards and all the physical events that had occurred in a sequence , would some of the events occurring 'backwards' or in the reverse order violate the principle of entropy or ...
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0answers
15 views

Is there a “framerate” for the universe? [duplicate]

I've been wondering this for quite some time. I just can't wrap my head around the idea of truly continuous time. If time is truly infinitely divisible, then how can any object in the universe move? ...
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1answer
38 views

Symmetric Time Dilation in Uniform Relative Motion

I feel (and hope) this is an easily answerable question among physicists versed in GR. I promise that I searched for other answers on the forum. Here goes: Observer 1 starts at X distance from ...
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1answer
69 views

Is our locally measured time actually conformal time?

The FRW metric at the origin $r=0$, with $c=1$, is given by: $$ds^2=-dt^2+a(t)^2dr^2$$ Now one can change variables so that near the origin the FRW metric is approximated by the Minkowski metric ...
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1answer
58 views

Time relativity / paradox [duplicate]

After watching the movie Interstellar, the theory of time relativity / paradox really mind-boggles me. If it is true that gravity controls everything even to the extent of time, then it might as well ...
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2answers
56 views

Eulerian mass conservation on a stream line to Lagrangian mass conservation

if the density of a fluid particle is conserved on a streamline, $$\frac{d\rho}{dt}=0.$$ Why does this mean $$\frac{\partial \rho}{\partial t}+(\mathbf{v}\cdot\nabla)\rho=0$$ is true everywhere? Why ...
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0answers
27 views

Do physicists theorize an origin to the big bang?

Do we have any theory that covers a possibility of the big bang's origin? This seems like the most difficult question of all. Logic tells us that every effect has a cause. But every cause must be the ...
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0answers
45 views

How can matter reach the singularity of a black hole if time stops at the event horizon? [duplicate]

Black holes are said to be composed of two parts: A singularity at the center, where all the mass of the black hole is condensed in a point of zero volume. A black and empty ball delimited by the ...
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0answers
51 views

Does the rotation of the Earth affect time?

If the Earth were to spin from east to west instead of west to east, how would that affect time or our perception of it?
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1answer
102 views

Immortality within the multiple worlds interpretation of quantum mechanics [closed]

I understand the multiple worlds interpretation of quantum mechanics as follows: Any time an event happens, all of the possible outcomes take place ("split the universe") If I then think about a ...
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0answers
27 views

Why is solar culmination not local, solar noon plus the value of the equation of time?

I understand (at least partially) why solar noon is not always 12:00PM clock time. However, I do not understand how to calculate the clock time of culmination with the equation of time. I thought that ...
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2answers
130 views

Is the intuition of “absolute simultaneity” necessarily wrong?

I read about Einstein’s theories of relativity with all the interesting stuff like time dilation, mass increase and whatnot. And also about the relativity or conventionality of simultaneity. The ...
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1answer
47 views

Is it possible to tell time within a steady state?

(Inspired from this question (A) which unfortunately the link in the selected answer is now 404 broken (which might have contained my answer), thus cannot read any deeper than that) From the above ...
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1answer
79 views

Time in a perfect vacuum? [duplicate]

If we were able to make a perfect vacuum with no forms of energy in, including all forms of light would time still go on in that vacuum and if it doesn't how would we tell that it doesn't? Then if we ...
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1answer
58 views

a question regarding relative velocity

"Consider a gravity-free hall in which an experimenter of mass $50~\text{kg}$ is resting on a $5~\text{kg}$ pillow, $8~\text{ft}$ above the floor of the hall. He pushes the pillow down so that it ...
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0answers
56 views

With the new time cloak technology could it be possible to stop time for everything except one person

So I was just reading up on some new research on national geographic from the Cornell University scientists and it seems that they've managed to bend waves of light around something to hide it from ...