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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54 views

Could a flat battery make a watch run fast?

My watch used to keep good time but as of about a month ago it runs fast (gains about 5 mins per day). Could a flat battery be responsible, or is this physically impossible? It's a quartz crystal ...
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1answer
82 views

How long is a 'sun year'? [closed]

I know that a 'sun day' is the time that a sun spot takes to orbit one time across the suns surface (25-30 days dependent on location I think) and what is actually defined as a 'sun year' is how long ...
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2answers
196 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
91 views

Standardising shadow length on sundials

The sundial is fundamentally flawed in that the length of each hourly shadow changes with the seasons. If the base of the sundial was engineered to move cyclically on an anual basis however, the ...
0
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1answer
38 views

Determine time over known distance, constant acceleration and starting speed [closed]

Problem: I have an object covering a specific distance (say 100m) at a starting speed (say 10m/s) and a constant acceleration of 1m/s/s. Which equation can I use determine how long it will take the ...
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2answers
395 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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4answers
109 views

How does light travel?

How does light travel, does this not contradict the idea that going the speed of light stops time? Because if going the speed of light stops time and light goes the speed of light shouldn't it be ...
6
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2answers
1k views

Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?

Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon? If so, can quantum mechanics describe the universe at high energies where there is no ...
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2answers
111 views

Can less gravity speed up time? [closed]

We know more gravity slows down time per Einsteins Theory of Relativity. However will a significantly less gravitational pull speed up time? Or is "our time" aka earth standard of time the fastest ...
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1answer
89 views

Expanding Universe Balloon Analogy - Anything Similar for Time?

It is difficult to imagine the infiniteness of space and how it itself is expanding rather than the universe expanding into something else. A helpful analogy is that of drawing little dots ...
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0answers
26 views

Introductory time dilation confusion [duplicate]

I'm a little bit confused about the nature of symmetrical reference frames and how they relate to time dilation. To clarify my question, I've written a scenario. Bob stands on a platform as a train ...
1
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1answer
240 views

What is meant by 'probability of transition per unit time'?

Today I came across a term used by Feynman in his thirteenth lecture: 'probability per unit time' to go from $| 1\rangle$ to $|2\rangle$ while initially being at $|1\rangle$. This is the excerpt fom ...
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3answers
95 views

Calibration of a clock [duplicate]

I was inspired by this interesting question on this forum: How do I measure an earth year without a clock? Say you're stranded on an alien planet without any significant tools. How would you ...
2
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1answer
103 views

Does General Relativity espouse “block time”?

Brian Greene talks about spacetime as a loaf of bread. https://www.youtube.com/watch?v=eR8DYZzmin0 His analogy does seem to imply block time, so I was wondering if the theory of General Relativity ...
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4answers
186 views

Astronaut travels 16 lightyears and ages 15 years - am I misreading this question?

The astronaut is travelling to a star sixteen lightyears away. During this trip he ages fifteen years. What is the speed u at which the astronaut travels? It's obvious he can't be traveling at ...
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1answer
204 views

Is there a place in the universe where time doesn't exist?

I've been reading that, all laws of nature and the universe stop existing at a singularity. So where there is a singularity, there cannot be time. A singularity is created when a property of a system ...
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7answers
1k views

Clocks in special relativity

One book on special relativity says: Any observer at rest relative to his own timepiece will see that other clocks moving with respect to him run fast - the greater their speed, the faster they ...
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10answers
4k views

What are the mechanics by which Time Dilation and Length Contraction occur?

What are the mechanics of time dilation and length contraction? Going beyond the mathematical equations involving light and the "speed limit of the universe", what is observed is merely a phenomenon ...
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2answers
87 views

How to literally slow time [closed]

Let's say there is this car in a bubble of some sort. I want to slow time for that car in the bubble, let's say, by half so if the car is going 40 mph, outside of the bubble, people see it as going 80 ...
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1answer
61 views

expansion of space and time vs passage of time [closed]

Is passage of time is due to expansion of space and time?And the "dilation of time(by general relativity)" due to the force of gravity held against the expansion itself,like time slows down near ...
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1answer
82 views

How is movement possible? [duplicate]

This is a weird question that I wasn't sure where to ask. Say I have two points A and B. I roll a ball from A to B. Between A and B there are an infinite number of points right? Wouldn't it take an ...
3
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4answers
352 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 ...
1
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1answer
117 views

Time Dilation When In Orbit

Imagine a space ship orbiting the sun at near relativistic speeds, when compared to Earth (say from the reference frame of the sun) there would be x amount of time dilation. This would mean people on ...
2
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3answers
202 views

Is it possible that photons lose a small amount of energy over time to become redshifted instead of being redshifted because of an expanding universe? [duplicate]

Can photons lose a small amount of energy over time when traveling large distances due to either weak interactions with magnetic fields (Faraday Effect) or due to the way all objects cool and give off ...
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1answer
134 views

Pre Big Bang knowledge

I have read that no one knows what preceded the Big Bang, but is this true? The Big Bang process (with or without inflation) followed known rules which “existed” prior to time zero. For example, some ...
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1answer
94 views

Is time a finite resource? [closed]

I am struggling to find an answer for this question because time as we know it would end when we reach the heat death of a universe. Which would imply that is the end of time. I think I have a ...
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1answer
105 views

Is there a difference between 0.18 and 0.180 seconds? [closed]

Q. Is there a difference between 0.18 and 0.180 seconds ? In our databases we are collecting timestamps and there are 2 time instants which are the same for the hour, minute and seconds but the ...
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2answers
77 views

Estimation of the age of Earth

By calculating the ratio of U-238 to Pb - 209 the age of the earth can be estimated. Is it not a possibility that non radioactive lead already there formed during the birth of earth it self alter the ...
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4answers
651 views

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 ...
5
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3answers
5k 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
185 views

Quantum entanglement and special relativity PARADOX [closed]

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
239 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 ...
0
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1answer
66 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
42 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
258 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
164 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
42 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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2answers
76 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
55 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
64 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
190 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 ...
3
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2answers
169 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 ...
5
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3answers
815 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 ...
20
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5answers
13k views

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
32 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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votes
1answer
265 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. ...
0
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1answer
104 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
19 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
425 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
66 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) ...