# Tag Info

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The equation for time dilation is $$\Delta t =\frac{\Delta t_{0}}{\sqrt{1-\frac{v^2}{c^2}}}=\Delta t_{0}\gamma$$ Where $\Delta t$ is the time that passes for the moving observer (according to the stationary observer), $\Delta t_{0}$ is the time that passes for the stationary observer, $v$ is the relative velocity between the two observers. There is also ...

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Similar questions have cropped up on this site many times, and the debate surrounding them is usually fractious because people misunderstand each other's use of words like exist. One of the lessons of General Relativity is that any observer has to choose a locally convenient coordinate system that may not be globally convenient. We on Earth (quite sensibly) ...

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As I understand Hawking, the point that he is trying to make is that Newton's theory of gravity is actually incomplete and needs to be improved. So Hawking finishes on page 36, saying that Einstein tried to find that better theory of gravity for 6 years and finally in 1915 published his general theory of relativity. In this theory it takes now also 8 minuets ...

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I don't see your problem. We are dealing in hypothetical situations that lead to paradoxes and inconsistencies, so there is no problem with postulating what would happen if...?, even if the "if..." is impossible. He could have as easily said what would happen if the sun moved suddenly, we would see it move after 8 minutes, but gravitationally feel it move ...

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It's a matter of what you mean by "see". Even for a distant observer, it will take a small amount of time for the gravitational redshift effect to become essentially infinite. If your collapsing gas star redshifts to the point where it won't emit a single photon in the age of the universe, it may not have yet technically "redshifted to zero", but it has ...

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In Special Relativity CTCs can't exist (or at least I don't think so) but General Relativity has solutions that include CTCs. The best known is probably Gödel's solution for a rotating universe. The Alcubierre drive could also be used to construct CTCs, as could any FTL mechanism. Also see the Tipler cylinder, and probably many other examples I can't ...

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The world lines of both clocks pass through two particular events ('points' in spacetime), the event of your leaving the home and the event of your returning. The worldline of the clock at home is straight while the worldline of the clock in your pocket must be curved due to the acceleration you undergo during your near light speed trip out and back. A ...

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Let's say we have two clocks. Let's call the (coordinate) times of these two clocks $t_A$, and $t_B$, respectively. I leave one at home and keep one in my pocket. Then, I started running [...] then come back to my house. If I compare those two clocks how would they differ in time? If it is also given (corresponding to the comment by the OP ...

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Technically they wouldn't differ in time because to come back to your house you would have to decelerate and accelerate, which is under the realms of general relativity or as seen in comments below (thanks to @dgh) we can use comoving frames. You could use two frames one moving towards school and one away from school and Lorentz transform between the two, or ...

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If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed. Similarly, to A it APPEARS that B's clock is moving slower, but B sees his own clock moving at normal speed. [...] Is this true or false Foremost: it is improper. (In a ...

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Is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed. Similarly, to A it APPEARS that B's clock is moving slower, but B sees his own clock moving at normal speed. This is true. If the above is true, then ...

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Time dilation actually occurs with objects that are moving at some portion the speed of light relative to any observer "that is to say" relatively stationary to that object compared with light speed; However to the "OBJECT" in relative motion, it would of course see this effect on the stationary observer as the one's clock moving slow. but that is only ...

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Isn't saying that time doesn't exist without motion equivalent to saying that sound doesn't exist when no one is around to hear it? You can't rule out time's existence in this way. Then again, why focus on time? When you propose an empty space, does space exist? Normally space is detected as a separation between objects. If no objects exists, as per scenario ...

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My answer to your question is: no one can reliably answer your question. The model of the universe based solely on General Relativity says something about the beginning of the universe. If one follows the evolution of the universe backwards in time, one finds a singularity of infinite energy density "before" which the concept of time has no meaning. ...

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Isn't dt something that cannot change? In Special Relativity, time $t$ is a coordinate rather than a (universal) parameter. To locate an event in spacetime in a particular reference frame, one must specify 4 coordinates, 3 spatial and 1 temporal. So, a quantity like $\frac{dx}{dt}$ is a coordinate velocity; it is the rate of change of one coordinate ...

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The operation that seems to be causing you confusion is called a boost. A boost is an operation on minkowski space-time that in many ways is analagous to a rotation in three dimensional space. So let's make sure we understand the analogous situation dealing with rotations in three dimensional space. Rotations Let's imagine we have a stick which has a ...

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As the comments say, you have to be precise about your reference point when you talk about time dilation. Time dilation is always relative to something else. But there is an obvious interpretation to your question. Suppose you have an observer well outside the Solar system and stationary with respect to the Sun. For that observer your clock on Earth is ...

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Time is relative. When it comes to Time Dilation, you actually see dilated time of another observer. So, your own time flow won't get frozen in any case. Hypothetically, you can see another one's time frozen if she is traveling at speed of light (time dilation by speed) or she is at event horizon of Black Holes (gravitational time dilation). Unfortunately, ...

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The answer to (2) is simply that no-one knows, and further that it's unlikely we will ever know. It's impossible to prove that the universe is infinite, but it's just possible we might prove it closed and therefore finite if the length scale is around the size of the currently observable universe. The paper Topology of the Universe: Theory and Observations ...

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You are right that there are two effects at play here. Firstly, suppose that we turn relativity off --- suppose that we consider our universe to be Newtonian, with a finite speed of light propagation. It would indeed be the case that if an observer A were moving relative to another observer B, and emitting a light signal towards B, then the rate at which ...

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Assuming you're willing to accept General Relativity as a valid theory, your question has a well defined answer because we can solve the equations of GR for an empty universe. The result (well, the simplest result) is Minkowski spacetime. You might think that nothing much can happen in an empty universe, but even though no matter or energy is present there ...

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Now what about something like a gravitational field? Could that also be excluded from acting within a perfect vacuum? As pointed out in this Wikipedia article on gravitational shielding, the ability to shield gravitational fields would violate the equivalence principle which is inconsistent with both Newtonian mechanics and Einstein's general ...

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In both cases, the person who jumps has inertia of motion and hence will land in front wrt the earth's reference frame. It is the same effect which makes you jump forward and keep moving for a while when getting down from a slowing bus/train.

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Time is perceived threw moving objects, changes and things transitioning from order to disorder (positive entropy). But time itself is a dimensional axis much like length, height and width. "but as far as the discussion on entropy" it is dynamically highly improbable and could mean harnessing all the energy in the universe in order to reverse it. "but then, ...

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People defined time as a variable going forward long before entropy was defined. Biological/consciousness time, which you also discuss, forced the concept of time and a way /unit to measure it, as cultivation and buildings forced a concept of space and units to measure it. The celestial clock of sun moon and planets was used even by primitive people. ...

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Let me address Anupam's experiment, because it seems to me this is the real thrust of your question. It seems to you that different things happen depending on the frame. In one frame the egg survives while in the other it's broken. To explain why this doesn't happen let me modify your experiment slightly: This starts the same as Anupam's experiment. In ...

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This is not an "answer" as such but an attempt to be very clear about the difficulties with the question. You are not being clear enough about making it possible for all observer to verify what happened when and where. You say in the Einstein's rail experiments which he mentioned in his book. In this experiment we preassume events A and B are ...

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The error would be in the order of 10^-14. This is mathematically similar to the sense of errors you have on your hand watch, caused by mechanical inaccuracy - probably in the range of 1 second per week, or 1 second per year if its a Rolex :) One should note however, that such a very small inaccuracy in time measurement in atomic clocks is perhaps less than ...

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It means that if the clock begins set to the correct time, then after time $t$ the clock will be wrong by no more that $(\pm 10^{-14}) t$. Or as a physicist would be likely put it $$\frac{\delta t}{t} \le 10^{-14} \,.$$ This kind of expression of "fractional errors" is very common in many fields of quantitative science. Now, to be concrete, a year is ...

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