Light waves do not need a medium in which to travel but sound waves do. Explain that unlike sound, light waves travel fastest through a vacuum and air, and slower through other materials such as glass or water.

When light rays enter a new medium at an angle, the change in speed causes them to bend and change direction. They change the speed causes the ray to bend or change direction. When light slows down even more when it passes from water into glass.

Light of different energy will change its speed by slightly different amounts, depending on the properties of that medium. Once you leave that medium and go back into a vacuum again, that light goes back to moving at the speed of light.

When a light beam goes from vacuum (air) into glass, the only thing that happens is that the wave gets delayed (takes more time to travel the same distance, because of the higher density). Once it passes the glass, the delay is gone so light resumes its previous propagation speed in air.

And the answer to your question for this kind of tachyon is that it cannot escape a black hole. Since the disturbance of a localized tachyon cannot spread faster than c, it therefore cannot escape the inside of a black hole’s event horizon.

Answer: Firstly, the physical consequence of traveling at the speed of light is that your mass becomes infinite and you slow down. According to relativity, the faster you move, the more mass you have. So, traveling at the speed of light in the conventional way is impossible.

Yes, due to the theory of relativity, the ship would move close to the speed of light, causing time dilation which would make time on the spacecraft move slower compared to that on Earth. However, earth’s age would have passed as many light years as the journey.

In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. In both views there is no symmetry between the spacetime paths of the twins.

The Einstein–Podolsky–Rosen paradox (EPR paradox) is a thought experiment proposed by physicists Albert Einstein, Boris Podolsky and Nathan Rosen (EPR), with which they argued that the description of physical reality provided by quantum mechanics was incomplete.

For there to be a clock paradox, there must be a paradoxical inconsistency. On the outbound journey, both T and S agree that the other’s clock pulses slower at frequency to(l – )3)y where /3 = v/c and 7 = (1 — f52)~1/2 and on the return they both agree that the other’s clock pulses faster [frequency o>(l + p)y].