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The answer is straightforward. The formula shows that there is no dilation when your speed is zero, which is what you would expect, otherwise length dilation would be observable in connection with sta …

If A changes their velocity then you can say absolutely that A has accelerated, since acceleration is not a relative effect. That said, you still cannot say in any absolute sense who is moving, since …

If you were at the centre of the balloon, it would appear to be a sphere. The speed at which the balloon was expanding away from you would appear to be reduced owing to the Doppler red-shift effect. I …

Since SR is entirely symmetrical, you can imagine the train and crate are initially at rest, and the crate is then thrown through the window at some speed. Since in that frame, in which the train and …

The answer to your first question is that in your frame of reference the light will take one second to reach you. The answer to the second is that B will measure a longer time than you did, because li …

There is no paradox. You are confusing two separate quantities, 1) being the time taken for information to travel to the moon from Angie, and 2) being the elapsed time for parts of the message to arri …

You must be using the word motion in a very specific sense, because in the more general sense of the word motion is clearly observable. Motion is a change of position over time, and we can clearly ob …

You are overlooking the relativity of simultaneity and misunderstanding the symmetry of time dilation. Suppose the light flashes when the mid-point of the observers on the train passes the mid point o …

The light goes wherever you point it. If you point the light vertically in either frame it follows a diagonal path in the other. The same applies if I climb a ladder vertically in one frame, I move di …

There is no paradox. The question you pose is exactly analogous to this: Two presidents must sign a treaty at 6pm or a bomb will go off. They sign it at 6PM London time, so the bomb doesn't go off. B …

You are right to say that the box and its contents will slide to the left when the attractive external force is applied, and will continue to slide at a constant speed when the force is switched off. …

Your comment 'but shouldn't time always move slower when you are in motion' is the clue to why you might be struggling to understand what is happening, so let's see if we can help... Firstly, let's im …

At the risk of making the experiment sound more complicated, there are two considerations here. The first is that the local duration of a flash is frame dependent. In a frame in which the flash occurs …

It is a common misconception that time dilation is some effect that impedes the action of clocks as a result of their motion, which then leads people to ask how come different types of clocks are affe …

Where you are going wrong is to assume that the time axis of the observer on the train is the same as the time axis of the observer on the platform. If the lightning strikes are simultaneous in the p …