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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What is a clock?

Relationalists love to define time operationally as what clocks measure, but this begs the question of what counts as a clock. Clearly, it's a measuring instrument and what it measures is supposedly ...
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1answer
79 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 ...
4
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4answers
4k views

That 10km/day error predicted if GPS satellite clocks not corrected for relativity

Some authorities have stated publicly and without explanation that if the theories of Special and General Relativity were not taken into account in the design of the GPS (by building the satellite ...
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2answers
156 views

Quantum entanglement and special relativity PARADOX [on hold]

Imagine two entangled atomic clocks. After we entangle them, we measure the time: it does has to be the same , right ? Now lets suppose that we entangle them , but don't measure them, then we plant ...
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5answers
129 views

Why isn't time just a function of the speed of light being finite

Time is generally referred to as the fourth dimension and seems frequently to be treated as an equivalent to the 3 spatial dimensions. But then people seem to get tied in knots as to why time has an ...
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0answers
27 views

what is the real physical sense of moving only in time? is that actual question for today? [on hold]

Best regards, I'm not physicist, but knoweledge that you possess as specialists, is very inspiring for me. My question: It's simple... But possible answer could be interesting. Einstein's theory ...
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1answer
50 views

Time relativity

Lets say that I am on a spaceship moving with the speed of 0,90c and I am looking on my friend who stayed back on earth. My friend is looking on me. From my perspective, my friend is moving 7 times ...
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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 ...
3
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2answers
158 views

Can you express mass in other dimensional units?

I'm just started a Physics I course, and while I've paid attention, I'm stuck on one of the first problems: Express mass ($M$) in terms of acceleration($a$), density($D$), area($A$), and time($t$). ...
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1answer
108 views

If there is a boson that carries mass, why not space, or time? [closed]

If the Higgs Boson carries mass, why doesn't there exist more bosons that carry other fundamental properties such as volume/distance (space), time, or even spacetime? Also if bosons carry force, but ...
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1answer
32 views

Ligth clock with spaceships side-by-side

In the reference frame of an observer, two spaceships travel in a straight direction (e.g. x axis) at a very high velocity and side-by-side; the distance between them is always d (km) = c (km/s) x 0.1 ...
2
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4answers
372 views

Is it possible for two events happen at the exact same time?

Is it possible for any two events to occur at the exact same time? As I see it, because time can always be split up into smaller units (it is infinitely divisible), we can always be more and more ...
2
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2answers
50 views

Do photons experience every moment in time and position in space simultaneously? [duplicate]

Would it be more correct to say that a photon, traveling at the speed of light, would experience all points in time simultaneously, and therefore be everywhere at once? It might be just our ...
0
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1answer
40 views

What is the difference between the expansion of space and the Alcubierre drive?

The Alcubierre drive violates causality. As far as I know the expansion of space does not. The usual explanation for why space is allowed to go FTL is that the matter doesn't move. The Alcubierre ...
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1answer
54 views

Time is what keeps everything from appearing at once [closed]

This is a question about time. In this talk http://ed.ted.com/lessons/einstein-s-brilliant-mistake-entangled-states-chad-orzel Chad Orzel makes the point that if the same quantum experiment is ...
2
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1answer
79 views

Why isn't the time-derivative considered an operator in quantum mechanics? [duplicate]

Based on my understanding when doing quantum mechanics we deal with a small set of mathematical objects: namely scalars, kets, bras, and operators. But then in the Schrodinger equation we have this ...
2
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2answers
135 views

How to understand the lifespan of large-scale cosmological structures?

When a star is said to live for 1 billion years, is that relative to the 'average cosmological time unit' or local time in the star's gravitational field? Also, if the sun is said to have 5 billion ...
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3answers
750 views

Big bang and time

I heard Carl Sagan talking about the Universe 15 Billion years ago, and the Big Bang. He made the statement that it was the biggest explosion of all time (at first I thought this a subtle pun). This ...
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5answers
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The meaning of imaginary time

What is imaginary (or complex) time? I was reading about Hawking's wave function of the universe and this topic came up. If imaginary mass and similar imaginary quantities do not make sense in ...
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2answers
30 views

On a graph, can the compositions of both the x and y variables involve the unit time?

Time seems to be so fundamental to the calculations that we make, that it seems to be at the core of everything we do. Indeed, this is not just philosophically true, time is very often the x axis, by ...
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1answer
223 views

Absolute time as a common basis of quantum gravity? [closed]

Quantum mechanics has an absolute time concept, and general relativity has the dynamic time concept of spacetime. The incompatibility of both concepts is called the problem of time in quantum gravity. ...
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2answers
66 views

Time in general relativity

A physical quantity is introduced by its operational definition. In general relativity we use a differential manifold to describe the 4-dimensional space-time and, to identify a point in it, we use a ...
0
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1answer
66 views

With respect to what does time itself change? [duplicate]

We all have an intuitive notion that time itself "changes" - before it was the past, now it is the present, later it will be the future, and as time "changes" or moves forward what was the present ...
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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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2answers
131 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
357 views

Time contraction

This is my first time posting on this site. I am a computer programmer that stumbled across a physics text book and have a question on special relativity. So firstly, I understand that there is no ...
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1answer
47 views

Fixing time in Feynman phase space path integral

The phase space version of Feynman's path integral expression for the free particle propagator involves a (formal) sum over paths in phase space with fixed $q$ endpoints and (as far as I'm aware) ...
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3answers
175 views

Isn't the aether existent?

Before you say I'm wrong consider this, Einstein is supposedly the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them right ...
4
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2answers
776 views

Why don't two observers' clocks measure the same time between the same events?

Person A in reference frame A watches person B travel from Star 1 to Star 2 (a distance of d). Of course, from person B's reference frame, he is at rest and is watching Star 2 traveling to him. ...
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1answer
63 views

Will two clocks moving in opposite directions measure the same time as one at rest?

A rocket passes the earth and synchronises its clock with the earth. Years later, a rocket passes it going to the earth and synchronises its clock with the first rocket. When it reached the earth, ...
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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 ...
0
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3answers
130 views

If time is relative, how could time pass? [duplicate]

EDIT: I appreciate people who answered below. But it does not answer the question, so I will clarify my questions: -It seems like everyone is saying that time passing is actualized by physical ...
1
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1answer
183 views

Wormholes and the illusion of time?

I was watching a video on Youtube by Brian Greene, "the illusion of time."http://www.youtube.com/watch?v=j-u1aaltiq4 In that video, he introduces to me the idea of a "brane," or a slice of the ...
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1answer
43 views

About Time and the Big Bang [duplicate]

In a TV ducumentary, I heard that time started with Big Bang, and it is meaningless to talk of "before". This was given without any further explanation, in the peculiar, irritating style of ...
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0answers
53 views

Is time infinite? [duplicate]

If time has a beginning, must it not exist for some amount of "time"? If not, it exists from the point when existence started and if there was ABSOLUTELY no existence there may not exist something ...
9
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11answers
2k views

understanding time: Is time simply the rate change?

Is time simply the rate of change? If this is the case and time was created during the big bang would it be the case that the closer you get to the start of the big bang the "slower" things change ...
2
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0answers
35 views

What is the definition of time? [duplicate]

I wanted to know the definition of time just like as we define displacement, current etc. **Note:**There should be no mention of time period or time interval in the definition.
2
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2answers
77 views

Does anti-matter increase or decrease in entropy over time?

Antimatter is matter going backwards through time. From a matter-based observer does antimatter: Increase in entropy (and therefore decrease in entropy in its own time) OR Decrease in entropy ...
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3answers
183 views

If traveling at the speed of lights stops time, why does it take light 8 minutes to reach Earth?

I just learned that, according to Einstein's relativity theory, time reaches zero for an observer (light) when traveling at the speed of light, so everything is supposed to be at the same place in the ...
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2answers
37 views

Is there a time difference for people traveling at different speeds during a long period of time?

I'm just throwing this out there for discussion/answering: If person A sat in a chair all his life, in a house on earth (let's say 100 years), and person B flew around in earth's atmosphere at let's ...
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1answer
52 views

Time and gravity relation

I was reading about relativity when I crossed by the applications of relativity in real life, and they said that as the elevation increase time increase so gravity decrease Can someone explain to me, ...
2
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2answers
494 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 ...
7
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3answers
932 views

Anti-matter as matter going backwards in time? (requesting further clarification upon a previous post)

I understand this question has already been asked here, however, I don't have enough reputation points to place a comment (I suppose that's the reason) on a specific answer to request a reference. A ...
1
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3answers
84 views

Would a giant see our year as a second? [closed]

If there were an enormous being whose arm span is one light year across, how would that being perceive time? Wouldn't what we perceive as a year be virtually nothing to that being? Explanation: ...
0
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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 ...
12
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5answers
9k views

How can time be relative?

I don't understand how time can be relative to different observers, and I think my confusion is around how I understand what time is. I have always been told (and thought) that time is basically a ...
2
votes
5answers
283 views

Two clocks along different worldlines [duplicate]

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, ...
0
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3answers
110 views

Question about rain when an object is moving

So here's the question: A train window is 1 meter high and 10 meters long. A raindrop rolls down the window at a vertical speed of 5 meters per second(when stationary). If the train is moving at 30 ...
1
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1answer
75 views

Can we observe a star collapse into a black hole? [duplicate]

Let's say that I happen by a star that has just burned out and is collasping into a black hole. I seat at infinity to watch it as a Schwarzschild observer. Will I ever see the black hole collapse into ...
0
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1answer
1k views

Does the universe update time in some finite interval? [duplicate]

I was listening to a lecture by leonard susskind and one of the analogies he used was a coin having two states and he "broke" time into intervals. He continued to say that at each interval of time, if ...