Recent content by yinfudan

Yes, my top right diagram and bottom right diagram are both wrong. The bottom right one should look exactly as the top left one. The top right one should have the 4th ray emitting diagonally upwards and bouncing back to the new position (dashed) of the light bulb. Can you take a look at my...

Though I believe I have understood some basic ideas, theories and mathematic formulas of SR, I still have a pretty fundamental question: Many textbooks start SR with a light clock consisting of two mirrors and a light blip bouncing in between, claiming that when the light clock moves, the...

Thanks for the replies. I think bcrowell's statement below especially answers my question: So my top right diagram is wrong. Since the light clock (light bulb + mirrors) are moving towards right together as a whole, the observer in the light clock reference frame will see uniformed light...

As stated in SR and the principle of equivalence, there is no privileged reference frame or reference frame at absolute rest. However, I went across the following idea that seems to be able to tell if a reference frame is moving or at rest. Please help me point out what is wrong in my idea...

Wikipedia does not imply the black hole is a consequence of the singularity. It seems that no matter in Newtonian gravity or general relativity, as long as the mass is concentrated in the Schwarzschild radius, it forms a black hole that light within the range of Schwarzschild radius cannot...

Wikipedia and some other web sites mention that: At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature. This means that a black hole's mass becomes entirely compressed into a...

Thanks Jesse for your quick reply! General relativity says that mass can curve the spacetime fabric around it. I do not have a very deep mathematic background, but I suppose that, although the spacetime can be curved, its topology cannot change. Think of a 2-D scenario, no matter how you warp...

Since I only learned special relativity but not yet general relativity, please bear with me that our discussion will be limited to the scope of special relativity, that is, suppose we would not utilize special spacetime topology, such as worm hole and black hole. I ran into some video about...

I suppose it works for length as well:) The length of one side of the rhombus must be sqrt((1+v2)/(1-v2)). If longer (or shorter) than this value, when the rhombus is normalized to a unit square, and the original square is warped to a new rhombus, the length of one side of the new rhombus...

I think I have an easier way to understand why both the area of the square grid for the rest frame O must be equal to the area of the rhombus grid for the moving frame O'. If the area of the rhombus grid is not the same, say, bigger. Now if I normalize the rhombus grid, that is to make the...

Yes, the determinant of lorentz boost is 1. However, my question here is why it has to be 1. Is it a coincidence or does it have certain meaning in physics? What is the consequence if it is not 1, yet still a linear transform?

I have an interesting finding in spacetime diagram - The area of the square grid for the rest frame O, is the same as the area of the rhombus grid for the inertial frame O'. More specifically, the area of the square for frame O (0, 0), (0, 1), (1, 1) and (1, 0) is 1 The area for the...

I hope I could try to answer boysherpa's question, although I just learned Special Relativity lately. Boysherpa has a very good point - what is the definition of time. It is important to understand what makes time before we discuss if time is a dimemsion. I have a feeling that physics cannot...

Thanks Fredrik and Jesse! Another quick question: Due to length contract, the volume of the rod also decreases. Will the mass density of the rod increase for the observer?

The length contraction in special relativity says that a rod moving along its axis will appear shorter by γ to a stationary observer. I think, however, not only the rod will appear shorter, but also each small segment of the rod will show its snapshot of different time as in the moving frame, in...