I do not understand general relativity?

Question

if general relativity deals with acceleration then why the fuss over super strings [ie. gravtons]

Answer 1

Einstein never got it all together with his theories. In this case, "all" means the four fundamental forces in our universe: strong and weak atomic forces, gravity, and electro-magnetic (EM). Using Al's equations and thoughts, the best anyone can do is unify the atomic and EM forces...gravity remains an outcast.

One reason physicists want to unify the forces (put them all under the same set of equations) is because they postulate that these forces were in fact unified during the first few seconds of the big bang. So, to explain the big bang better, they have to unify the four fundamental forces in their equations. (There are other reasons, but this is a major one.)

String/M theory is a set of untested, unproved approximations that can be mathematically used to unify all four fundamental forces...even gravity. In fact, these equations actually predict the four fundamental forces, including gravity. But there are some real detractions in them.

First, they are based on the assumption of an infinitely thin vibrating string of Plank length, which is 10^-33 cm in length. I'm not at all clear on what "infinitely thin" means; is that the same as having no width or depth? It has length, but no diameter?

Second, to make the equations work (solvable with the right answers), they have to go into higher dimensions (eleven at last count). What the heck is that? What does that mean in our real-world of four dimensions?

Third, the equations are only approximations...they invoke something called perturbation to solve. As any engineer knows full well, the devil is in the details. And it's these details that perturbation equations leave out.

Finally, none of these string theories (there are actually several), can be validated through experiments because the tests would require more energy than technology can produce currently. There is some hope the Large Hadron Collider will produce enough energy to test some (small) aspects of string/M theory. But we have to wait until it comes on line.

Answer 2

For a very long time science has been trying to tie together the four fundamental forces of nature--electromagnetism, strong nuclear force, weak nuclear force, and gravity. Einstein's relativity has failed to accomplish this goal. String theory is a complex mathematical system devised in hopes of formulating the Grand Unified Theory.

Answer 3

General relativity simply states that no matter what point of view you see a situation in, the same physical laws apply.

Answer 4

.:: the abc of relativity - bertrand russell - fourth revised edition edited by felix pirani - 220 p, london, 1985

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p.12 - ... if einstein were with you, you would understand him more easily than the ordinary mortal would, because you would be free from a host of preconceptions which prevent most people from understanding him.

p.53 - What really is measured by a clock?

p.71 - We are concerned with events, rather than with bodies. In the old theory, it was possible to consider a number of bodies all at the same instant, and since the time was the same for all of them, it could be ignored. But now we cannot do that if we are to obtain an objective account of physical occurrences. We must mention the date at which a body is to be considered, and thus we arrive at an "event" that is to say, something which hapens at a given time. When we know the time and place of an event in one observer's system of reckoning, we can calculate its time and place according to another observer. But we must know the time as well as the place, because we can no longer ask what is its place for the new observer at the "same" time as for the old observer. there is no such thing as the "same" time for different observers, unless they are at rest relatively to each other. We need four measurements to fix a position, and four measurements fix the position of an event in space-time, not merely of a body in space. three measurements are not enough to fix any position. that is essence of what is meant by the substitution of space-time for space and time.

p. 99 - But now suppose that, instead of taking a small piece of the earth's surface which can be regarded as flat, you consider making a map of the world. An accurate map of the world on flat paper is impossible. A globe can be accurate, in the sense that everything is produced to scale, but a flat map cannot be. I am not talking of practical difficulties, I am talking of a theoretical impossibility. For example: the northern halves of the meridian of Greenwich and of the 90th meridian of west longitude, together with the piece of the equator between them, make a triangle whose sides are all equal and whose angles are all right angles. On a flat surface, a triangle of that sort would be impossible. On the other hand, it is possible to make a square on a flat surface, but on a sphere it is impossible. Suppose you try on the earth: walk 100 miles west, then 100 miles north, then 100 miles east, then 100 miles south. You might think this would make a square, but it wouldn't, because you would not at the end have come back to your starting-point. If you have time, you may convince yourself of this by experiment. If not, you can easily see that it must be so. When you are nearer the pole, 100 miles takes you through more longitude than when you are nearer the equator, so that in doing your 100 miles east (if you are in the northern hemisphere) you get to a point further east than that from which you started. As you walk due south after this, you remain further east than your starting-point, and end up at a different place from that in which you began. Suppose, to take another illustration, that you start on the equator 4,000 miles east of the Greenwich meridian; you travel till you reach the meridian, then you travel northwards along it for 4,000 miles, through Greenwich and up to the neighbourhood of the Shetland Islands; then you travel eastwards for 4,000 miles, and then 4,000 miles south. This will take you to the equator at a point about 4,000 miles further east than the point from which you started.

p.117 - It is only our obstinately earth-bound imagination that makes us suppose a geometry separate from physics to be possible.

p.122 - if people could leave the earth and travel about for a time and then return, the time between their departure and return would be less by their clocks than by those on the earth: the earth, in its journey round the sun, chooses the route which makes the time of any bit of its course by its clocks longer than the time as judged by clocks which move by a different route. This is what is meant by saying that bodies left to themselves move in geodesies in space-time.

p.139 - That means to say that, if we have expressed a law correctly in terms of one set of co-ordinates, it must be expressed by the same formula in terms of another set of co-ordinates. Or, more exactly, it must be possible to find a formula which expresses the law, and which is unchanged however we change the co-ordinates. It is the business of the theory of tensors to deal with such formulae. And the theory of tensors shows that there is one formula which appears more appropriate than others as being possibly the law of gravitation. When this possibility is examined, it is found to give the right results; it is here that the empirical confirmations come in. But if the new law had not been found to agree with experience, we could not have gone back to the old one. We should have been compelled by logic to seek some law incorporating the relativity of motions, distances and times, and expressed in terms of 'tensors'. It is impossible without mathematics to explain the theory of tensors; the non-mathematician must be content to know that it is the technical method by which we eliminate the conventional element from our measurements and laws, and thus arrive at physical laws which are independent of the observer's point of view. Of this method, Einstein's law of gravitation is the most splendid example.

p.147 - the supply of uranium in the planet is limited, and it might be feared that it would be used up before the human race were exterminated, but now that the practically unlimited supply of hydrogen can be utilised, there is considerable reason to hope that the race may put an end to itself, to the great advantage of such less ferocious animals as may survive. But it is time to return to less cheerful topics.

p.160 - Science does not aim at establishing immutable truths and eternal dogmas: its aim is to approach the truth by successive approximations, without claiming that at any stage final and complete accuracy has been achieved.

p.172 - All this is rather speculative; it is very likely that the universe evolved from a highly condensed state, and it is even more likely that such a highly condensed state represents the earliest time about which there will ever be any scientific information. Whether such a state actually occurred is not at present under dispute. Unfortunately, some people are inclined to refer to the highly condensed state as 'the beginning of the universe' or 'the time when the universe was created' or something of that kind. These phrases mean no more than 'the earliest time about which there is ever likely to be any scientific information', and it is better to avoid them, because they carry undesirable metaphysical implications. As things stand at present, certain of the model universes derived from relativity theory and predicting expansion from a highly condensed state are readily reconciled with the astronomical data. All of them have defects, of which the most obvious is that they give only a smoothed-out picture which does not account for the size or composition of the galaxies and clusters. The construction of an entirely satisfactory model depends on the resolving of some serious mathematical difficulties; which of the available models is to be preferred at any particular time must depend on the astronomical data.

p.189 - The planets move round the sun because that is the easiest thing to do - in the technical sense of'least action'. It is the easiest thing to do because of the nature of the region in which they are, not because of an influence emanating from the sun.

p.190 - If people were to learn to conceive the world in the new way, without the old notion of 'force', it would alter not only their physical imagination, but probably also their morals and politics. The latter effect would be quite illogical, but is none the less probable on that account. In the Newtonian theory of the solar system, the sun seems like a monarch whose behests the planets have to obey. In the Einsteinian world there is more individualism and less government than in the Newtonian. There is also far less hustle: we have seen that laziness is the fundamental law of the Einsteinian universe. The word 'dynamic' has come to mean, in newspaper language, 'energetic and forceful'; but if it meant 'illustrating the principles of dynamics', it ought to be applied to people who sit under trees waiting for the fruit to drop into their mouths. I hope that journalists, in future, when they speak of a 'dynamic personality', will mean a person who does what is least trouble at the moment, without thinking of remote consequences. If I can contribute to this result, I shall not have written in vain.

p.216 - What we know about the physical world, I repeat, is much more abstract than was formerly supposed.

p.220 - The final conclusion is that we know very little, and yet it is astonishing that we know so much, and still more astonishing that so little knowledge can give us so much power.

Answer 5

......duh? what fuss???