In Newton's world (first iteration) anything which could be done could be undone: for example we could collect many atoms together to make a planet, but we could then also prise these atoms apart to break the planet back to individual atoms. The existence of such black holes marked a very unusual step in the development of physics. This process is called the gravitational collapse of the star, and it results in the formation of a black hole. That is, it would get more and more dense as it compresses, till it becomes an infinite density point which forms the singularity. Computations show that if a star is more than 3 times heavier than the sun, then it would compress in a runaway fashion. When stars run out of the fuel they can burn, they start to compress under their own gravitational attraction. In fact more is true: once things fall through the horizon, they must keep moving towards the center of the hole, where they eventually get crushed at a location called the singularity. There is a boundary surface called the horizon: things can fall in through the horizon, but they cannot come out. In this theory the curvature of spacetime can be made such that we get a trapping region: i.e. A key feature is that no form of matter - particles or waves - can move faster than the speed of light. The behavior of matter in general relativity is given by a natural extension to curved spacetime of the behavior one had in flat spacetime.In this theory the effects of gravity are incorporated by making space and time curved rather than flat. Gravity is described by Einstein's theory of general relativity.The situation changed with the work of Einstein. Thus we see that with Newtonian physics, nothing is really 'trapped' by gravity, and we cannot get a black hole. But he can sit in a rocket, and the thrust provided by the rocket can lift him out to empty space, away from the star. He cannot jump up and escape the gravitational pull of the star. Consider a person standing on such a star. Even though light and other objects may not be able to fly out on their own from such dark stars, they can still be extracted out by applying a suitable force. Are such dark stars therefore black holes? If we add this assumption to our Newtonian thinking, then it would seem that nothing can fly out of a dark star. Today we have learnt that nothing can travel faster than the speed of light. Using these principles, John Michell conjectured in 1783 that sufficiently massive stars may be invisible: the gravitational pull of the body may be so strong that even light cannot escape from their surface and reach our eyes. The motion of particles is described by Newton's laws of motion, where the acceleration of a particle is proportional to the force acting on it.Gravity is described by Newton's law of gravitation, where the attraction between two bodies falls off as the square of their separation.In each new iteration, we incorporate a new principle of physics, and find a change in what can and cannot be trapped. The story of black holes has gone through 4 iterations. The theory of black holes is therefore the cutting edge of research into the ultimate laws of nature. It is likely that the best way to arrive at a final theory unifying all principles is to look for a consistent description of the black hole. Quite remarkably, the answer to this question has changed each time we have incorporated a new principle of physics in our thinking. The question then is: Can this gravitational force trap objects that fall in, so that they can never come out? If we put a lot of mass in some region, then any object coming near this region will be strongly pulled in by the gravitational attraction created by this mass. Gravity is a universal force that makes everything attract everything else. Why should we think such regions might exist? The reason is gravity. Can there be a region of space where one can go in, but from which one cannot come out? Such a region is called a black hole. The central idea behind black holes is the notion of trapping.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |