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You're not the only one with a lot of confusion about special relativity! The thing to focus on is what is happening locally for an observer, vs what is happening far away for that observer. Someone …

You have it right. $O$ sees $O'$ aging more slowly and himself aging normally, while $O'$ sees $O$ aging more slowly and himself aging normally. Let us say we have two ships meet in the ocean. Each s …

No, it does not stop. "Infinite Time Dilation" means a photon of light does not evolve in time. None of its properties ever change unless it interacts with something. This is one reason physicists kno …

You may be interested in the Barn Door paradox. Here are some important points regarding your setup: The "Stationary Setup" seems to show that both halves are moving at the same speed, while the "Mov …

Editing my answer to better address the original question. It is mainly an algebra difficulty, and albeit the math is a bit subtle. I will show you the algebra Einstein left out in his paper. I'll g …

You have to be careful. If rest mass $M_1$ of the system is when it is first placed in space, $M_2$ is the mass after the starlight is collected and the energy stored in the machine (with batteries or …

Here is a great reference that walks you through spacetime diagrams. The majority of questions about SR can be cleared up by seeing the diagram rather than reading words. I suggest printing out the im …

I'm not sure there's a meaningful way to derive it apart from the full Lorentz Equations, but one thing reflected in the equation is that a time interval $t'$ for one observer will correspond to partl …

Mass is not converted to energy. Mass is energy. Sometimes mass energy can be converted into heat energy or light energy, or vise versa (as in chemical or nuclear reactions). Thermodynamics always …

Periodic events are "events separated in time at regular intervals." I think not only are these the only possible measurement of time – they are the definition of time itself. Assigning a number $t= …

The invariance of light speed and its particular value are both observed facts, which cannot be derived from any current physical theory. Any theory we create is built up around these facts. That is …

Your problem is when you say, "The traveling Observer 2 sees the light pulses traveling toward himself at equal speeds..." None of the observers see the light pulses in transit. They only see them whe …

One misconception here – we do not feel gravity as acceleration. We feel resistance to gravity (e.g. standing in a suspended elevator on Earth) as indistinguishable from acceleration (e.g. standing i …

As someone pointed out, the original source has a mistake. It should be $$K= \int m\frac{d(γu)}{dt}\frac{dx}{dt}\color{red}{dt}$$ This is via the chain rule: $$dx=\frac{dx}{dt}dt$$

Consider diagram (a) carefully. In the reference frame of the laser source, the opposite wall is not moving. So in this frame, there is no reason to expect the beam to strike the opposite wall any cl …