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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2answers
46 views

Can only one now imply every future? [closed]

In logic, A implies B, if B is always true in instances where A is true. Obviously, there can only be one possible future, for every potential now, that is, in all instances where a certain now is ...
20
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3answers
9k views

Oh-my-god particle: How can it get through Milky way in 10 seconds?

My question is concerning wikipedia article on Oh-my-God particle, to be precise, this paragraph: This particle had so much kinetic energy it was travelling at 99.99999999999999999999951% the ...
4
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3answers
555 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?
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3answers
213 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 ...
1
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3answers
121 views

What would happen if you went back in time to get a random number?

For example, you go to a website that generates a random number. You get the number 8. What would happen if you went back in time a few minutes, and repeated the same actions. Would you get the same ...
6
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5answers
586 views

Do clocks really measure time?

Each time I listen to this quote from The man from Earth, I'm absolutely intrigued: Dan: Time... you can't see it, you can hear it, you can't weigh it, you can't... measure it in a laboratory. It ...
0
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1answer
55 views

How to measure size of x in time (“time thickness” and not “lifetime”)? [closed]

My question is a consequence of a personnal hypothesis which might be wrong. Everything which exists has a size mesurable in 3D space with different size of rulers. This stands for any particle, ...
2
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0answers
69 views

Should we consider space and time as separate entity?

In general relativity, we think of space and time in spacetime framework. As some people say, metric tensor sign difference, along with our inability to go backward in time suggests that space and ...
1
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1answer
135 views

Does antimatter travel faster than light

I have read in the answers here that an electron traveling backwards in time would behave as a positron. I also read in another there that antimatter is matter traveling backwards in time As far as I ...
0
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0answers
35 views

Time. Is it really a dimension? [duplicate]

I have trouble accepting that time is a dimension, in the same way that space has three dimensions. Wherever there is space and matter, it has spatial properties. You can move back and forwards in ...
33
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6answers
4k views

What is the proper way to explain the twin paradox?

The paradox in the twin paradox is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible. There are a thousand explanations out there ...
0
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1answer
173 views

Does Inertial time dilation demonstrate that Time is not a dimension? [duplicate]

If time is a dimension and 'now' simply an expression of your position with respect to that dimension, the progress of any object along that dimension should remain in step with all other objects. By ...
0
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3answers
145 views

Is time unidirectional because of 4th spatial dimension? [closed]

We heard about an expanding universe. Consider an expanding sphere. Consider the surface of the sphere as our 3 dimensional universe. Can time dimension be the radius $R$ of this sphere? And because ...
2
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3answers
71 views

Can the passage of time be measured in the absence of motion? [duplicate]

All of the ways I have heard of to measure the passage of time involve measuring some sort of motion (e.g. vibrations of a cesium atom, movement of the hands on a clock, etc.). Can the passage of ...
1
vote
1answer
261 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 ...
2
votes
2answers
2k views

What is the difference between UT0, UT1 and GMT time?

Every reference I find says that they are "essentially" the same, which we all know really means that they are not the same, but different only by a some small amount that someone else other than me ...
-1
votes
1answer
27 views

Is there any naturally occurring light wave with a constant frequency that has a terminable decimal. [closed]

I was wanting to think of a natural unit of time, if one exists, that is known exactly. I started thinking about it with the Voyager plaque and the 21 cm Hydrogen line (HL). When I looked into the HL, ...
1
vote
1answer
59 views

Does travelling towards something at relativistic speed cause it to appear to speed up?

If one were to travel towards a giant TV floating in space, at a fraction of the speed of light, would a video playing on the TV appear to play faster? I'm guessing the answer is no. From what I ...
0
votes
2answers
49 views

How Can a Singularity contain different things? [closed]

According to the Big Bang model, space and everything in it was squeezed into a infinitely small point which subsequently expanded. But if everything is squeezed into a point of zero size than there ...
1
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1answer
199 views

Could time be considered a force

I think I understand the basic concept of spacetime, at least some of it. And when people talk about spacetime they don't call gravity a force, but rather the result of mass interacting with it. And ...
1
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3answers
526 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, ...
15
votes
5answers
10k views

Did time exist before the creation of matter in the universe?

Does time stretch all the way back for infinity or was there a point when time appears to start in the universe? I remember reading long ago somewhere that according to one theory time began shortly ...
3
votes
4answers
645 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 intervals can always be split up into smaller units (it is infinitely divisible), we can always be more ...
1
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1answer
40 views

Scientific definitions of “moment (of)” and “instant”? [closed]

What are the scientific definitions of "moment (of time)" and "instant"? Are they different with their definitions in everyday language? I also don't know the definitions in everyday language, of ...
-8
votes
1answer
79 views

Explaining The Quantum Mechanics Weirdness [closed]

Academic replies only; I would like feedback on this, so yes i am asking you to poke holes in it, it is about explaining the time weirdness of quantum mechanics and how particles behave. When the ...
1
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0answers
58 views

Smallest possible spinning clock?

The earth's rotation acts as a clock and defines a rather precise unit of time called the day. We could go out in outer space and spin a marble and get a reasonable clock. On the other hand, it is my ...
0
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0answers
40 views

complete layman trying to understand time relativity [duplicate]

I am trying to understand intuitively why time slows down as speed increases. I have watched many pseudo-documentaries explaining the concept, but I cannot get at the core of the explanation. The ...
4
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0answers
42 views

What ticks in an optical clock?

After reading several articles about current state of the art clocks, I'm still wondering one thing: What ticks? As I understand it, in cesium clocks time is measured in cycles of a microwave ...
1
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2answers
98 views

Three questions about time [closed]

Since I don't want to abuse to the ASK QUESTION form, and since those questions are all about time, I decided to write them all here. Hope it's ok. First Question Could it be possible (how?) to ...
3
votes
1answer
383 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
2
votes
3answers
118 views

Can there be motion without the flowing of time? [closed]

tldr - Can we reject the notion of the passage of time, but still accept that motion is real? This question is a follow up to comments between myself and the author of this answer to the question, ...
-1
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3answers
95 views

How time dilation happens by velocity?

i got many explanation and proving that relative velocity causes time dilation. Einstein's moving light experiment proves it. but that is a clock works with light detector. as detecting the light gets ...
10
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3answers
1k views

Why do we remember the past but not the future?

The question is sometimes referred to as the "psychological arrow of time" (Hawking, 1985). Here the past is understood as a moment or time when the entropy of the universe was lower, and contrarily ...
0
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1answer
58 views

What dictates the rate in which time passes? [closed]

I understand that special relativity tells us that our perception of the passage of time can change depending on reference frames. But why does time pass the rate at which it does in my reference ...
4
votes
1answer
2k views

Formula for getting time of sunrise at a particular location?

Is there a formula that can get sunrise at a particular latitude and longitude (and elevation from sea level)? If so, what it is? (Why does it work?)
1
vote
1answer
102 views

Is the cosmological time grosso modo isochrone?

Is the cosmological time grosso modo isochrone? by analogy with space isotropy. Or else do we have possibly great differences by analogy with great voids in the space. We know that it's not strictly ...
1
vote
0answers
22 views

Time in the early universe [duplicate]

When it is said, for example, that grand unification took place "Between 10−43 second and 10−36 second after the Big Bang", how are these figures of time derived? Moreover, do these figures have any ...
0
votes
1answer
86 views

Does time and time dilation exist in a black hole?

Since being near stronger gravitational fields causes time dilation, can this be generalized to the region beyond the event horizon? i.e , is it meaningful to say that someone outside the black hole ...
1
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1answer
63 views

Is it correct to think about a point in time as the set of positions of all “things”?

Is it correct to think about a point in time as the set of positions of all "things" (photons, electrons, etc) that exist in the universe at that moment, despite the fact that simultaneity is ...
2
votes
2answers
107 views

How can we say time began at big bang?

I have seen many times scientists refer to time when Big Bang took place and space and time born out of singularity. 'Beginning of Time' is a very misleading statement,because process of beginning ...
1
vote
1answer
63 views

Cosmology: equation of motion for a scalar field in conformal time [closed]

So, I've derived the equation of motion for a scalar field in "normal" time, $t$: $$ \ddot{\phi}+3H\dot{\phi}+\frac{dV(\phi)}{d\phi} $$ Then, using the expressions for the scalar field density, ...
0
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0answers
59 views

Time Vs Entropy [duplicate]

Entropy is a property of thermodycamical systems. We know that entropy measurement it's determinated by preassure P and temperature T (for simplicity). At the same way we consider that the entropy of ...
0
votes
2answers
42 views

What is the relationship between the flow rate of time and gravitational field?

I have heard, qualitatively, about the fact that time's rate of flow slows when the gravitational field is "strong". Here I am looking for some more rigorous descriptions of this phenomenon. My first ...
0
votes
1answer
74 views

Trouble in understanding spacetime

I have a problem in understanding spacetime. What i understood from the conversion of time to distance is that the interval between any two events is always the same for any observer. But how is that ...
0
votes
1answer
73 views

Time Travel possibility and Paradoxes of The Past [duplicate]

can one travel back in time and if not so, what laws prevent time travel to the past. this is quite a challenge to understand.
-2
votes
1answer
44 views

Can motion be characterized without time as independent variable? [closed]

I was just thinking about speed = distance/time which relatively describes how fast something is moving wrt some still object. So if by some wishful thinking or some coordinate system I remove the ...
4
votes
1answer
77 views

Are there waves of time? [duplicate]

If I understand correctly, gravitational waves are ripples in the fabric of space-time itself created by the movement of mass. Moreover, space and time are just dimensions of the same space-time ...
3
votes
1answer
51 views

How quickly does the temperature rise in a water container submerged in a hot water bath?

Let's assume I have a small bottle (neglecting any insulation from the walls of the bottle) containing e.g. 150ml water at 4°C and place it in a larger pot with sufficient water at 80°C so that the ...
0
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1answer
82 views

Interpretation of time dilation

Is there any interpretiation of time dilation for photons? I mean, how does time work for them? Do photons have any distinction between their own and observer's time? Or is it something like ultimate ...