# Tag Info

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If you define "now" to be all those points in space and time that have hypothetical, pre-synchronized, stationary clocks that read the same time as your clock, then there "currently" exists a hypothetical observer somewhere, who is moving relative to us, for whom "now" includes Earth, circa 1900. But these notions of "now" are different for the two ...

4

If the twins never meet, but just continue travelling in a straight line at constant velocity then each twin will see the other as being younger. The *paradox*$^1$ only occurs if one or both of the twins is accelerated, which of course is necessary for the twins to meet again. $^1$ it's not a paradox of course, just an unintuitive result!

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Yes. More specifically, if $d$ is the distance between the planets in their rest frame, then in the astronaut's frame the distance between the planets will be $\frac{d}{\gamma}$ so the travel time as measured from his frame will be \begin{align} t_\mathrm{astro} = \frac{d/\gamma}{v} = \frac{1}{\gamma}\frac{d}{v} \end{align} Notice that the quantity $d/v$ ...

4

If you say that earth's velocity around the sun is 67,000 mi/h, your reference point is the sun itself, which makes the aeroplane's velocity 68,000 mi/h, not 1000. Using special relativity only, and (A) observing from the sun, a clock on the plane would seem to run slower than a clock on earth. A person (B) on earth would measure also measure an ...

3

I'll concentrate on cellular automata in this answer, because it's a good example, and should help to give a good intuition about algorithms in general. The answer is: most cellular automata do have an intrinsic time direction, but some don't. The most famous example of a cellular automaton is John Conway's Game of Life. This is an irreversible cellular ...

3

Muons are single-particle excitations (states) of the $e-\mu-\tau$ quantum field, except that these states don't have definite values of energy (they are in a superposition of states that have definite energy). Because states with different energies change at different rates, this superposition changes with time. After some time has elapsed, the ...

2

Yes, you'll gain extra hours, but you'll lose them on the way back, unless you keep going round. Let's assume you're in a plane flying along the equator, moving at 800 km/h (in the direction of the earth's travel) - a normal jetplane speed. The earth is rotating so that a point stationary on the equator moves at 1600 km/h. That means that, for every km you ...

2

What if without meeting they send a light pulse to each other, such that they can know each other's age The result will still be the same - each twin judges the other twin to be ageing more slowly than themselves. However, sending a light pulse to each other involves other factors that must be taken into account such as time of flight and ...

2

Basically what your asking is if information can be transmitted faster than the speed of light. According to quantum mechanics, it is impossible to use quantum entanglement for transmitting data faster than light. This is know as Eberhard's theorem, more details about can be found here (i'll try to provide a link with full access to the article). ...

2

Time dilation (and also length contraction) always occurs with respect to an observer in a different frame of reference. You, in your own inertial frame, will not notice any difference. However, when you compare your measurement to that of an external observer, you will see a discrepancy in the results. If you enter a spaceship and go on a journey through ...

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I'm not entirely sure I understand what you're asking but here is how I've interpreted your question: It seems like all of the laws of physics are reversible in time. That is, given the state of a physical system, it's possible to both go forward in time or backwards in time from that state. Assuming this is the case for physical laws and the equations ...

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Not only the position in the gravitational field is important, but also the velocity. Consider the Schwarzschild metric $$\text{d}\tau^2 = \left(1 - \frac{2GM}{rc^2}\right)\text{d}t^2 - \frac{1}{c^2}\left(1 - \frac{2GM}{rc^2}\right)^{-1}\left(\text{d}x^2 + \text{d}y^2 +\text{d}z^2\right),$$ where $\text{d}\tau$ is the time measured by a moving clock at ...

1

There is a standard way to find out if the spacetime around you is curved. Surround yourself with a sphere of small test masses and wait and see what happens. If the sphere stays exactly the same shape you're in flat spacetime but if it changes shape or volume you're in a curved spacetime. In the case of the ISS the test masses nearer the Earth than you ...

1

The first statement is very much true. Light moves a finite, if very fast, speed. Even ignoring any movement/ relativistic effects this simply means that observers closer to earth will see it in it's most recent state. It may sound strange for light, but we see exactly the same phenomenon in sound, an observer noticeably closer to the source of a sound will ...

1

My question is, do other types of mathematics, say a cellular automata as an example, have the intrinsic time direction that the equations lack? With a CA, all steps have to be completed sequentially. A reversible system is not related to whether it is differential equation, algorithm or cellular automata. It is the underlying model, or physics, ...

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Basically, the universe has a speed limit. No object can ever exceed the speed of light. Now imagine you decide to prove Einstein wrong by building a train capable of nearly reaching the speed of light, and then shooting a bullet forward in that train, so that the bullet will break the speed of light. In order to preserve this speed limit, time for you and ...

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A clock near the surface of the earth will run slower than one on the top of the mountain. Rather: the geometric (and kinematic) relations between two (or more) given, distinct, separated clocks must be determined and taken into consideration in order to compare intervals (from any one indication to any other indication) of each clock to each other, on ...

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Think about this In your brain there is a clock too. In other words, everything has a clock in itself. The clock in this meaning is the electron and molecule activity. Both gear and battery is electron and molecule activity. And inside your brain is another kind of electron and molecule activity Time dilation is about the reality that all electron and ...

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