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
1
vote
1answer
122 views
Is time the rate at which one moves through space
I'll start out with the cliche attempt in a protective shield of my dignity. I am a young highschool kid just eager to learn and understand. If I'm way off or this is already a known idea, or maybe ...
7
votes
1answer
316 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 ...
2
votes
1answer
823 views
Anti-matter black hole and time
I have recently read some hard science-fiction story based on an assumption that if time stops (from external observer's perspective) on the event horizon of black hole, then in an anti-matter black ...
1
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1answer
76 views
A clock devoid of motion
My understanding is that every clock mechanism we have depends on motion of something w.r.t the observer. From atomic transitions to clockwork gears. So, does this property/constraint makes every ...
2
votes
3answers
173 views
In a very small static universe with only a particle, does it make sense to talk about time?
I am sorry if this question is silly; it′s just one of those things I wished I asked before leaving university.
If there were a static universe only as big as the size of two particles, say ...
3
votes
2answers
243 views
Atomic clocks and how to synchronize them
During teaching measurement section in the class, Our teacher told us about atomic clocks. I have two questions:
What is exactly an atomic clock?
and how do we synchronize two atomic clocks far ...
3
votes
2answers
119 views
Why do we treat time as parameter in non relativistic QM instead of treating position as parameter?
Why do we treat time as parameter in non relativistic QM instead of treating position as parameter?
What is actually a parameter?
I have read this Wikipedia page, but could not understand why should ...
1
vote
2answers
126 views
Is it possible to hear the past?
From this Stack Exchange Physics Post, I am certain that it is possible to view the past.
But then this interesting question came to me.
Is it possible to hear the past?
Ok, you might say, "Well, ...
0
votes
1answer
175 views
Does the Earth's revolution around the Sun affect radioactive decay?
Premises:
The radioactivity is either hastened or slowed inside a fast moving aircraft.
Speed of fastest aircraft: 3,529.6 km/h.
The earth's revolution is: 107278.87 km/h.
The earth's ...
-1
votes
1answer
148 views
Calculate time to go from one point to another point [closed]
in a 2D football game I want to calculate cycle(time) until ball go from one point
to another point.
in this link exist all fomulas that we need for my problem but anyone does not have any parameter ...
0
votes
2answers
295 views
Is it true looking at an object from a great distance with a telescope will show the past version of the object?
Once again from my son's workbook.
It discussed standing on a planet 65 million light years away from Earth, with an extremely powerful telescope pointed at Earth. It claimed that then you could see ...
2
votes
3answers
117 views
How can an action be dependent on both its past and future?
Is it true that whenever an action takes place it is dependent on both its past and future? I mean if we already know that whatever we are doing is dependent on future as much as it is dependent on ...
32
votes
8answers
2k views
Is time continuous?
I was making universe simulations, and I noticed that I implemented discrete time (the only type possible on computers). By that, I mean that I had an update function, that was called many times per ...
8
votes
4answers
508 views
Is a 1D vector also a scalar?
A vector in one dimension has only one component. Can we consider it as a scalar at the same time?
Why time is not a vector, although it can be negative and positive (when solving for time the ...
0
votes
0answers
478 views
Create general equation of racing cars with head start [closed]
Cars A and B are racing each other along the same straight road in the following manner: Car A has a head start and is a distance $d_A$ beyond the starting line at $t=0$. The starting line is at ...
0
votes
3answers
148 views
Time slowing down problem
When someone moves, time slows down for him. Let, a man standing still and another moving very very very fast, this happens for an hour (as measured by the standing man). Time has moved slower for the ...
1
vote
1answer
79 views
What is the difference between “at all times” and “at any particular time”?
Morrison writes in "Morrison, Michael A. : Understanding quantum physics : a user's manual"
$ |\Psi(x,t)|^2 \xrightarrow[x\rightarrow\pm \infty ]{} 0$ at all
times t [bound state]
$ ...
4
votes
1answer
321 views
Is there really time reversibility in physics?
First, how i got to the question.
I was randomly looking at this page:
http://en.wikipedia.org/wiki/Langton%27s_ant
describing some sort of cellular automaton.
Here is the path of this automaton ...
3
votes
2answers
287 views
Is there an observable of time?
In Quantum Mechanics, position is an observable, but time may be not. I think that time is simply a classical parameter associated with the act of measurement, but is there an observable of time? And ...
-3
votes
4answers
189 views
How can we be sure about the constancy of atomic clocks as in the Hafele and Keating time dilation test?
Atomic clocks were used in Hafele and Keatings experiment which supposedly helped to prove time dilation.
Time Dilation Proof - Hafele and Keating
How can we be sure other forces didn't act upon the ...
2
votes
4answers
333 views
Why are objects at rest in motion through spacetime at the speed of light?
I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
2
votes
0answers
254 views
Is large-scale “time reversal” (Poincaré recurrence) possible given infinite time?
The following are some assumptions I'm basing my question on, from what (little) I understand of physics. I list them so an expert can (kindly) tell me where I'm going wrong.
There is a probability ...
1
vote
2answers
141 views
What's the relationship between quantum entanglement and the relativity of time?
Apologies in advance for what may be a stupid question from a layman. In reading recently about quantum entanglement, I understood there to be a direct link between entangled particles, even at ...
3
votes
2answers
257 views
Time to establish saturated vapour pressure above liquid
Thought experiment - a liquid is in a closed container in equilibrium with its vapour, and then suddenly all the vapour is pumped away. Switch off the pump so that instantaneosuly there is no vapour ...
1
vote
0answers
74 views
“Time” by epistemic subdivision of a closed system [closed]
There is the idea that there is no time in a completely closed (thus unobservable) system. Within such a system, a subsystem may be imagined to be split off by some virtual boundary. However, one ...
4
votes
2answers
296 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 ...
1
vote
1answer
82 views
How precisely can we date the recombination?
The early universe was hot and opaque. Once it cooled enough, protons and electrons were able to form hydrogen atoms. This made the universe transparent, and was known as recombination. We can see the ...
3
votes
1answer
113 views
There are plans to develop a better definition of a “second”. How does the current definition fall short?
The current definition of a second is stated here and I found a presentation on the BIPM site which discusses plans to change to a "better" definition of a second. You can find the presentation here. ...
0
votes
2answers
264 views
1
vote
1answer
465 views
Relation between comoving distance and conformal time?
In cosmology, we have two quantities and I want to understand the physical relation between these two :
$\chi = \int_{t_e}^{t_0}c\frac{dt'}{a(t')}$ : the comoving distance with $t_e$ the time at ...
3
votes
1answer
91 views
How did Cook and other astronomers time the 1769 Venus transit?
The 1769 transit of Venus was observed and coordinated by over one hundred astronomers around the world. How did they measure time so accurately, key to the observations having any scientific value? I ...
0
votes
1answer
2k 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 ...
2
votes
4answers
311 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 ...
3
votes
1answer
87 views
Is GPS time measuring the proper time on the mean sea level or the GPS station itself?
LeapSecond.com states:
Global Positioning System time is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves.
Does GPS ...
-2
votes
11answers
494 views
Are there any theories that explain the very beginning of absolutely everything? [closed]
Of course there's the theory of The Big Bang, and there are theories on what caused The Big Bang, but what was the cause of the very first thing that ever happened? What started every
I also won't ...
2
votes
3answers
688 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
$$t = \frac{t_0}{\sqrt{1-v^2/c^2}}$$
...
4
votes
5answers
491 views
Why isn't the symmetric twin paradox a paradox?
Two twin sisters synchronize their watches and simultaneously (from the earth frame) depart earth in different directions. Following a predetermined flight plan, each sister accelerates identically to ...
1
vote
1answer
205 views
Two identical rockets, time dilation, and possible weirdness [duplicate]
Possible Duplicate:
Why isn't the symmetric twin paradox a paradox?
Suppose there are two identical rockets, each carrying one of two identical clocks and one of two identical ...
2
votes
3answers
205 views
Is there a point in universe that is observable at present?
We know that we can see distant galaxies only billions years before now. We can observe the nearest stars just several years before the present. Something on the Moon can be observed only some seconds ...
2
votes
3answers
172 views
Slow thermal equilibrium
I have a question which is inspired by considering the light field coming off an incandescent lightbulb. As a blackbody radiation field, the light is in thermal equilibrium at temperature $T$, which ...
1
vote
3answers
782 views
Hours of light per day based on latitude/longitude formula
I'm looking for a formula that will return the number of hours per day given a specific location. I was thinking that can be calculated as a difference of sunrise and sunset, but I see that there are ...
-1
votes
1answer
67 views
Does the movement of things in the universe will cease one day?
To start or change the movement, we need a force. This force, according to Newton's second law, is variation of quantity of motion from the object per unit of time.Therefore, if the variation does not ...
1
vote
1answer
276 views
What is actually meant by 'sun set' and 'sun rise' times, when taking into account the mirage due to light bending in the atmosphere
I’ve heard from the likes of Brian Cox that what we see of the sun during a sunset and sun rise is actually the mirage of the sun. The Sun has actually set/risen and we see it due to the way light is ...
1
vote
1answer
120 views
How to calculate the amount of night time during a flight?
I have been asked to find a way to calculate the amount of time that a flight takes during night time.
So far, I have the departure latitude and longitude and the time of takeoff, the arrival ...
-2
votes
3answers
401 views
How does Time traveling work in practice?
There are multiple theories about time traveling. One is "proven": The time slows down according to your speed. The satellites in space are traveling faster than us, thus their clocks slows down a ...
4
votes
5answers
3k views
How can something happen when time does not exist?
I saw this documentary hosted by Stephen Hawkins: www.youtube.com/watch?v=WQhd05ZVYWg
And if I didn't get it wrong, it says that there was no time before the big bang, time was created there.
So how ...
4
votes
3answers
173 views
Twin paradox - observers counter orbiting Earth
Imagine three observers - one (A) stationary on the surface of Earth (latitude 0 deg) and two others orbiting the planet in the same circular equatorial orbit just in the opposite direction. When the ...
1
vote
1answer
490 views
How to determine day/night based on latitude, longitude and a date/time?
Is there a simple method of determining, given a UTC date/time, whether it is day or night at a given lat/long coordinate?
I am currently using a formula based on a Sunrise/Sunset Algorithm from the ...
4
votes
2answers
589 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 ...
5
votes
3answers
480 views
Does this Zeilinger group result provide experimental proof of backward-in-time causation?
Does this recent Zeilinger group delayed choice entanglement experiment imply backward-in-time influences?
http://arxiv.org/abs/1203.4834
From the abstract: "This can also be viewed as “quantum ...
