Afterwards, information on the increase of its mass would not be able to be "communicated" outside the black hole. Otherwise, black holes should all show the same mass (= gravitation): the mass which is necessary to initially form a black hole. Since black holes of different masses are observable, are we not able to conduct that they can send out gravitational waves with this information? If gravitational waves (which have not been detected so far) were not able to leave a black hole, nothing outside a black hole would notice changes in the gravitation of the black hole. Hm, Hurkyl, is it really true that gravitational waves cannot leave a black hole?Ĭhanges in a gravitational field are supposed to be "communicated" by gravitational waves. so any gravitational waves that are inside the hole never make it out. This is allowed because it is not a local speed.Of course, anything that happens inside the black hole cannot propagate to the outside. ![]() As another example, there are some distant stars in the universe that are moving away from each other at a speed faster than light. If a different beam of light was sent from earth to the North Star and did go through the worm hole with you, there is no way you could outrun it. This is allowed because you never locally exceeded the speed of light. In other words, you would have reached the North Star first. Compared to a bit of light that traveled from earth to the North Star and did not go through the wormhole, you would have been traveling faster. For instance, if wormholes exist, you could use one to take a shortcut from earth to the North Star. A more accurate statement of the principle would be, "nothing can locally travel faster than light." This means that we can indeed acquire effective speeds faster than light if we use non-local scales. The restriction that nothing can travel faster than light is not as limiting as it seems. However, there is so much evidence now supporting relativity that, if it is wrong, it will have to be wrong in a small way that does not change these basic principles. You might say that maybe Einstein's theories of relativity are wrong. In fact, the phrase "faster than light" is physically meaningless. Because the concept of "speed" requires measuring a certain amount of distance traveled in space during a certain period of time, the concept of speed does not even physically exist beyond the speed of light. Therefore, this tells us that nothing can ever go faster than the speed of light, for the simple reason that space and time do not actually exist beyond this point. A reference frame with zero width and with no progression in time is really a reference frame that does not exist. If you look at the equations which are at the core of Einstein's theories of relativity, you find that as you approach the speed of light, your spatial dimension in the forward direction shrinks down to nothing and your clock slows to a stop. Instead, space and time can warp and bend. ![]() In other words, space and time are not a fixed background on which everything takes place in the same way it always does. It is difficult to visualize this if you have never heard about it before, but scientists have found that the faster you go, the more your spatial dimension in the forward direction shrinks and the slower your clock runs when viewed by an external observer. The universal speed limit, which we commonly call the speed of light, is fundamental to the way the universe works.
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