# Tag Info

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So, here's the deal. "Time is relative" means a lot of different things to a lot of different people. In order to make a solid step forward, Einstein and company basically needed to clarify what they were trying to say. What they were trying to say looks something like this: "if you see a train passing by you, you're going to see things happen in slightly ...

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Time doesn't really flow according to how we usually think of time flowing. Time is just our mind's understanding of the changing environment around us. It is the changing environment that determines how fast time is moving. Assuming that the expansion of the universe is tied to the energy therein, so that if expansion were to stop the energy also would be ...

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Time doesn't really flow according to how we usually think of time flowing. Time is just our mind's understanding of the changing environment around us. It is the changing environment that determines how fast time is moving. Assuming that the expansion of the universe is tied to the energy therein, so that if expansion were to stop the energy also would be ...

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If you think about time as we know it does not actually exist/flow - it is our mental manifestations of the world around us that we think of as time. For example, what we see is not actually there how we view it. Whatever the object is sends us light-waves (only a small portion possibily of what the object really is), our eyes then have to decode the light ...

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That is a very interesting question, but you have to pay close attention. The current value of the speed of light in a vacuum (c) is 299 792 458 m/sec. Assuming that 1 g is exactly 9.8 m/$sec^2$, then the time to accelerate from rest to c is just 299792458 / 5 * 9.8, or 6 118 213.4 seconds, or just under 71 days. But. Let's put it this way - as an ...

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As mentioned by WhatRoughBeast, caesium offers several advantage over other microwave standards. Its most important feature is the presence of an atomic transition with a very small linewidth. This allows the energy of this transition to be established very accurately (see the uncertainty principle). However, caesium is not the only atom with a narrow ...

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The notion of absolute time for all observers in all reference frames has been debunked by Einsteins theory if special relativity. Prior to that, scientists believed that there might be an ether that permeated all space, and from which a universal reference frame could be derived. However, when Michelson and Morley did their famous experiments attempting to ...

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I do not understand what the accuracy of $1$ part in $10^{14}$ means. [...] reviewed the definitions of accuracy and error [...] In definitions of "accuracy" or "error" you should have noticed mentioning of the true value of some particular quantity, referring to the trial(s) under consideration, and the corresponding, commensurate value(s), ...

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There isn't a such thing as "absolute time." Some events – they are called space-like events – can't even be agreed to happen in an "objective order." Only time-like events can be universally agreed to happen in a particular order, but there's no such thing as "universal time." For you, time will always tick per one second by second, and that will apply to ...

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Is there an absolute pace of time, no. Is your clock , in a region without gravity, (and at "rest" relative to other objects) "ticking" faster than your alarm clock on the Earth's surface, yes. But obviously you physically cannot escape the effect of gravity, no matter how far away the mass-energy sources are, so this will vary from observer to observer, ...

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As other users have said, it has one stable isotope, so that's nice. It's also the SI standard. We define the second by Caesium. Specifically: The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. So, if we were to use another ...

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I'm afraid you're overcomplicating things, aepryus. Yes, most modern clocks use electromagnetic phenomena, but your pendulum clock employs gravity in much the same fashion as your water-drop clock. The clock rate doesn't depend on gravitational potential, it depends on the first derivative of potential, the "slope" as it were. The force of gravity. And this ...

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The choice of cesium is due to various factors. It's worth noting that your statement "Modern atomic clocks only use caesium atoms" is simply untrue. At the very least, rubidium and hydrogen clocks are common, and you can get rubidium standards on eBay for well under $200. But the best performance comes from using cesium. In part this is because it was ... 72 "Because that is how the second is defined" is nice - but that immediately leads us to the question "why did Cesium become the standard"? To answer that we have to look at the principle of an atomic clock: you look at the frequency of the hyperfine transition - a splitting of energy levels caused by the magnetic field of the nucleus. For this to work you ... 4 Because one second is defined as (from the SI brochure): the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom,${}^{133}\mathrm{Cs}$. Thus, using any other atom is irrelevant (even if calculate some correction time factor). 4 To know what a closed timelike curve looks like, you just do like every spacetime metric. You compute geodesics and field equations and all of that. Unfortunately, things start getting complicated. Closed timelike curves have a lot of weird behaviours, especially when it comes to matter fields upon them. They may not have a properly defined Cauchy problem, ... 0 A closed timelike curve wouldn't actually "look" like anything because it's an abstract thing. You can't actually see any lightcones or worldlines. A metric is an abstract thing too, to do with your measurements of distance and time, typically made using the motion of light. And the crucial point is this: you don't travel along your worldline. You move ... -4 The speed of light wouldn't stop time but make it extremely slow. After u have traveled the distance light travels in a sec then you will pass 1 second in space time assuming you are still whole and have not turned into a photon which would break so many rules. 1 Is it possible for two events happen at the exact same time? No. Even at any one event itself there can be several (or in though-experimental principle even arbitrarily many) distinct participants (encountering and passing each other, momentarily). All their individual distinct times (indications) are attributable to this one event of their meeting. ... 2 Is it possible for any two thing to occur at the exact same time This is a physics question and answer site. In physics our examination of nature has shown that there exist many frameworks for defining "events" , as in your title, or "things" as in your question. The main frameworks where "simultaneity" and "event" have to be defined so as to make the ... 0 Events are points$(x,t)_S$onto a chart$S$on some space-time manifold and in this respect whenever two such points$P_1 = (x_1,t), P_2=(x_2,t)$have the same$t$-coordinate in that reference frame then yes, they do occur at the same time for the observer described by the chart$S$. For another observer, represented by a different chart$S'$, the ... -1 In a non-relativistic point of view, yes. Events occurring in less than$5.39106 × 10^{-44} s$(the Planck time) are considered to be simultaneous. The Plank time is the time it takes light to travel$1.1616 × 10^{-35}m$, about$1/(2.67×10^{24})$the size of the hydrogen atom. The Plank time is also, considered to be the smallest time lapse that could ever ... 2 You ask: If the clock is running slowly compared to a distant clock is this equivalent to the clock having a lower energy compared to a distant clock? but you have to very careful what you mean by energy in general relativity. As it stands your question too vague to be usefully answered. However in the weak field limit there is a sense in which time ... 0 What's being referred to here is roughly the question that Einstein called the "problem of the now". That is, our experience suggests a tensed, flowing time, and the phrase is only "absurd" insofar that it seems to clash with our experience. The underlying problem is to answer why or how it is that we seem to perceive time as flowing, and the phrase is most ... 1 If time was reversed we would remember only things we hadn't done yet and nothing that had happened. The laws of physics work equally well forwards or backwards, yet our everyday experiences of cause preceding effect, not the other way around makes this seem counter-intuitive. Just imagine some kids playing cricket in a universe where time is reversed. In a ... 0 In this case one could argue that 'remembering the past' would be a methaphorical expression to describe being able to predict the future. Experimental evidence says that people that have declared being able to predict the future are either scammers, delusional, self-fulfilled prophecies or just extremely intuitive. As far as I can tell, there hasn't been ... 1 John, have a look at the simple inference of time dilation due to relative velocity. If you and I are identical twins, and you take a fast out and back trip, when you come back we agree that you've experienced less time than me. As you pointed out, we can relate this to the Lorentz factor and write: $$\Delta t' = \frac{\Delta t}{\sqrt{1-\frac{v^2}{c^2}}}$$ ... 0 Following the wikipedia link to "Time:Time as Unreal" from Glenn the Udderboat's answer I read :- Time as "unreal" In 5th century BC Greece, Antiphon the Sophist, in a fragment preserved from his chief work On Truth, held that: "Time is not a reality (hypostasis), but a concept (noêma) or a measure (metron)." If I can paraphrase your hypothesis: ... 1 A vector is a scalar with direction. So Time can be a vector, but what it means depends on the context. In 1D it has only 2 directions, positive and negative with zero being positive. In 2D it can be an angle between ÷/-Pi radians. And so on. Time can be a single dimension attached to the familiar 3 Euclidian spacial dimensions and in this case it is ... -2 NOOOOO!!! This is wrong. Granted the pendulum formula (T = 2 * pi * sqrt(L / g)) does not take into account mass of the bob, much less the pendulum, mass can and does affect the pendulum period. The Pendulum Formula is accurate and i give it credit, but its variables are broadly defined. T represents time or period, and g represents gravitational ... 2 You can easily get that answer by noticing that in when you have constant acceleration the average velocity after a time$t$is: $$\langle v\rangle_{acc.=w}=\frac{v_{start}+(v_{start}+w t)}{2}$$ for your case$v_{start}=0$and then$\langle v\rangle_{acc.=w}=\frac{wt}{2}$. For the deceleration we get the same result. Now you ... 2 Contrary to popular misconception, below a specific temperature, glasses do not flow. At all. A glass by definition is a solid sans repeating crystalline structure. Anything which flows (see "pitch-drop experiment which drops every 80 (or something) years") is a liquid, however viscous. Liquid glasses tend to have reasonably high viscosity, but once ... 3 I once read of a science fiction scenario where on a planet the distance from a specific center was time. Life in that format progressed in height from the center, grew contours of certain height and became flat at death. The consciousness of those entities had time defined by their changes but humans just saw a completed contoured landscape unchanging in ... 2 As the equations of motion are of second order, the higher derivatives give no new information (but follow uniquely from the initial conditions of position and velocity), therefore they usually are not discussed. (Note: As Timaeus pointed out there are specific scenarios, e.g. Norton's dome where intial values for the higher order derivates will change the ... 1 Actually we can't reach to a thing that is more speeder than light. Because as we read in the Einstein's theory, the speed of light is constant. When you reach the speed near the speed of light, the time will be stretched, and more you get close to the speed of light, more the time will be stretched and YOU WILL NEVER GET TO THE SPEED OF LIGHT. So, due to ... 2 I think you are mixing up two different concepts, which is muddying the waters. Firstly, relativity (both special and general) is a geometrical theory and the proper time for an observer has a precise definition as the length of a world line along which the observer travels (give or take a factor of$c$). This length is calculated using the metric. As ... 3 Proper time of an observer is time as measured by the observer's own clocks. So it's obviously frame-independent because calculating proper time of a given observer requires to use his own frame of reference. 0 I assume you're thinking about bubble universes in the context of inflation. In this case the universe consists of an (infinite?) inflating manifold with the bubble universes embedded in it. So the bubble universes are just a region of the whole manifold. The terminology is a bit confusing - the problem is that there isn't a clear definition of the term ... 2 You are mixing up time with the flow of time. Search this site for more on this topic. Although we're all used to the fact that for us humans time flows, the flow of time does not exist in relativity. Time is just a coordinate like the spatial coordinates$x$,$y$and$z$. We identify points in spacetime by the four coordinates$(t, x, y, z)$, so time is ... 0 "How exactly the RADAR works? Is it possible for RADAR to work with 1940s clocks?" is, of course, two questions, and the second is easier to answer: in the sense that we talk about it today, where a signal is analyzed and a digital readout provides timing information, 1940's radar did not do that at all, and therefore did not "work with clocks" at all. The ... 1 Your problem is that$E=mc^2$is false here. That's only rest energy: the complete formula would be$E=mc^2 + \frac12 mv^2 + mgh\$ (in the non relativistic limit).

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One does not need a precise clock for radar because the time that a radar system is measuring is very short, on the order of a few microseconds to maybe a millisecond (that's already 300km of distance!). The long term stability of the timing system is therefor irrelevant, but it's long term stability that makes precise clocks hard to build. In terms of ...

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