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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3
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2answers
339 views

Why time is considered a dimension?

Why is time considered to be a dimension? And the other 7 (except the 3 dimensions of space, and the dimension of time) dimensions that string theory suggests, why can't they be realized?
4
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1answer
59 views

Can you use pulsar observations to determine absolute time? How long can you go without anything else?

In this old answer of Steve Allen's, he quotes this nice passage Imagine for a moment what would happen if, just as a practical joke, someone found a way to stop all atomic clocks, just for a ...
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2answers
91 views

are clocks always wrong? [closed]

So I was sitting thinking earlier and I remembered an experiment that I heard a couple days back about how scientists put a stop watch on a jet and it had a different time then one on earth because ...
11
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3answers
486 views

If time standard clocks and any memories about the time standard are destroyed, can we recover the time standard again?

Assume the time standard clocks and any memories about the time standard are destroyed. Can we recover the time standard again exactly? Recovering the time standard again means we can determine the ...
0
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1answer
53 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 ...
1
vote
1answer
99 views

What is the difference between a parameter, a variable, and an operator in QM?

On the question why time isn't an operator, people will usually say that time is a parameter in QM (Time as a Hermitian operator in QM?) and not a variable. Can someone please distinguish between a ...
0
votes
1answer
51 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 ...
3
votes
1answer
147 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 ...
8
votes
2answers
373 views

Time crystals : fake or revolution?

This article about "crystals of time" just appeared on the PRL website. Viewpoint: Crystals of Time (http://physics.aps.org/articles/v5/116) The authors (including famous Frank Wilczek) claim that ...
0
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2answers
51 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 ...
1
vote
2answers
70 views

Theory of relativity. Relative to what? [duplicate]

If I properly understand relativity, time ticks faster for an object sitting still than for an object passing by. So, in a universe with only two objects which have the same "age", object A is ...
0
votes
1answer
47 views

Doesn't the Big Bang negate the law of conservation of matter? [duplicate]

I was watching Hawking (2004 film) and in the movie, Hawking has a sudden insight that all the matter and energy observed in the known universe may, in fact, have sprung out from nothing (singularity) ...
0
votes
1answer
83 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 ...
0
votes
2answers
1k views

Does travelling light help us see past versions of an object?

I saw a passage in my son's homework book, constructing a scenario in which a person standing on a planet 65 million light years away from Earth, with an extremely powerful telescope pointed at Earth, ...
7
votes
4answers
900 views

Special Relativistic Time Dilation — A computer in a very fast centrifuge

Ok, I've stumbled onto what I think is a bit of a paradox. First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on ...
0
votes
1answer
30 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 ...
1
vote
3answers
122 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 ...
23
votes
7answers
5k views

Is there a maximum frames per second (FPS)?

Take a video camera and crank up the frames per second rate. Disregarding current technological advancements, could a camera's FPS go so fast that any two captured images be identical? Would ...
0
votes
0answers
23 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 ...
-1
votes
2answers
54 views

Relativity asymmetry?

If you have two bodies that move towards each other at a constant velocity, each body will observe the other body experience time faster. This does not make sense to me because if you had a person ...
0
votes
0answers
42 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 ...
1
vote
2answers
409 views

If two observers pass each other in opposite directions at $.5c$ what would effect on each others clocks be?

Assume an alternate universe with same physical laws as here. In this universe nothing exists except 3 observers, each in a transparent box with a clock. Observer A is travelling at .5c. Observer C is ...
5
votes
4answers
1k views

How long would it take to travel through a wormhole?

Assuming wormholes exist and you put some matter into one, how long would it take to reach the other end versus how far apart the two ends are? Basically, by how much does a wormhole stretch ...
-2
votes
1answer
28 views

Find Distance with Acceleration and Time

I'm working on Physics homework and have run into a problem I can't figure out. Any help would be much appreciated! Problem: Allison exerts a steady net force of 50N on a 22-kg shopping cart ...
0
votes
1answer
68 views

What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
0
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0answers
39 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?
0
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1answer
68 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 ...
1
vote
2answers
65 views

Time Dilation: One observer at rest, two observers in motion

I am currently taking a course in Modern Physics mainly focused on Special Relativity and came up with the following problem: Let $O_1$ be an observer at rest. A second observer $O_2$ is moving to ...
0
votes
3answers
104 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?
11
votes
3answers
508 views

Space is expanding so what is time doing? [duplicate]

Space is expanding and as we know space and time are intrinsically linked to be now known as spacetime. What is happening to time during expansion? Is there more time, longer time or is the time part ...
4
votes
2answers
205 views

How do physicists and astronomers handle leap seconds?

I'm confused by the many contradictory descriptions I see about how UTC leap seconds are accounted for. I understand that there are various ways to handle them in common practice, and I've seen a ...
0
votes
1answer
90 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 ...
5
votes
2answers
270 views

What time scale is used by the JPL HORIZONS system?

I'm confused by the ust of the term "UT" in the description of time scales used by the JPL HORIZONS system. Their manual states that UT is Universal Time This can mean one of two non-uniform ...
3
votes
4answers
221 views

QFT and violation of Heisenberg uncertainty principle

In some QFT books is said that a free electron can emit a virtual photon as long as it reabsorbs the photon and returns to its original state within a time: $$\Delta t<\dfrac{\hbar}{2\Delta E}$$ ...
0
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0answers
18 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 ...
6
votes
6answers
9k views

How many colors exist?

How many "colors" do exist? Our perception: As far as I know, colors are just different frequencies of light. According to wikipedia, we can see wavelengths from about 380 nm und 740 nm. This means ...
11
votes
3answers
328 views

Is there a prediction of quantum mechanics that could be construed as representing an “energy-time uncertainty relation?” [duplicate]

As the title suggests. Is there a prediction of quantum mechanics that could be construed as representing an "energy-time uncertainty relation?" Does there exist any reference to such a prediction, or ...
-1
votes
2answers
145 views

Proof that time exists [duplicate]

Is time just an axiom? Or can it be proven to exist? Correct me if I'm wrong, but our whole understanding of the universe is based on directly observing the world and building out axioms that are ...
0
votes
1answer
65 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 ...
1
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0answers
65 views

Looking for more information about these two hypotheses

Big Lurch - This was one I read about in a special issue of Scientific American from 2014. It was explained as The Big Lurch is a theoretical scientific model suggested as one of the ...
0
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1answer
42 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 ...
0
votes
2answers
74 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 ...
1
vote
3answers
317 views

Gravity on the International Space Station - General Relativity perspective

My question is an extension to this one: Gravity on the International Space Station. If all the outside views of the ISS was sealed, then the crew inside would not be able to tell whether they were ...
5
votes
1answer
212 views

In the calculation of sunrise, where do the magic numbers come from?

In this question about how to calculate sunrise, there is a link to a page that describes a algorithm to calculate sunrise sunset. But when I start to follow the instructions I find that there is a ...
3
votes
3answers
3k views

How to calculate time dilation in approaching speed of light

If a spaceship travels close to the speed of light (say, at 0.9c), how do I calculate the time as the spaceship pilot experience it? I thought the formula was $$t = \frac{t_0}{\sqrt{1-v^2/c^2}}$$ ...
2
votes
1answer
125 views

The Big Crunch and perceived entropy

I'm aware of the Big Crunch theory, that once at capacity, the universe may collapse in on itself. Hawking once theorized that time may go backwards during this crunch. So, that got me thinking: how ...
0
votes
1answer
73 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 ...
2
votes
4answers
1k views

Which Schrödinger equation is correct?

In the coordinate representation, in 1D, the wave function depends on space and time, $\Psi(x,t)$, accordingly the time dependent Schrödinger equation is $$H\Psi(x,t) = ...
1
vote
0answers
88 views

Do past and future exist? [closed]

Ok, first thing I want to say is that I'm a layman. No high school math background whatsoever, so I'd be greatful if you could provide an explanation without equations. Now I'm quite interested in ...
0
votes
1answer
49 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 ...