View Full Version : Gravity and its weakness???

allwase wounder
2011-Jun-16, 04:39 PM
nube here,

I was told by a friend{not a very smart one ether}. That gravity is phasing in and out between universes/damnation's. and that that's the reason for its weakness?

this sounds wrong for a lot of reasons! is it?

2011-Jun-16, 05:12 PM
There is a speculation by a subset of String Theorists that there should be a reason gravity is so weak compared to the other forces. Or more specifically why it has such a low coupling constant. One of the ideas is that gravity acts across multiple brane universes so kind of leaks away. The idea is very speculative - so I wouldn't get too fond if it. It may be right, but there are so many unproven bits to it that we cannot honestly assign it even a probability of being right.

Tim Thompson
2011-Jun-16, 06:21 PM
The real truth about physics is that it can tell you how things happen, in great detail and with great precision, but it cannot tell you why things happen that way.

The "how" part arranges all of physics into the contest of four fundamental forces. Two of those forces have been known to classical physics for a long time: Gravity (http://en.wikipedia.org/wiki/Gravitation) (Isaac Newton (http://en.wikipedia.org/wiki/Isaac_Newton) & Albert Einstein (http://en.wikipedia.org/wiki/Albert_Einstein)) and Electromagnetism (http://en.wikipedia.org/wiki/Electromagnetic_interaction) (Michael Faraday (http://en.wikipedia.org/wiki/Michael_Faraday) and James Clerk Maxwell (http://en.wikipedia.org/wiki/James_Clerk_Maxwell)) and both act over very long distances. The other two are relatively recent discoveries from quantum mechanics, boringly titled Strong (http://en.wikipedia.org/wiki/Strong_interaction) & Weak (http://en.wikipedia.org/wiki/Weak_interaction), and both act over only very small, nuclear scale distances. The electromagnetic force is something like 1036 times stronger than the gravitational force (see "Fundamental Forces (http://en.wikipedia.org/wiki/Fundamental_interaction)"), in the sense that the electromagnetic repulsion between an two protons is about that much stronger than their gravitational attraction. That's what is meant by the observation that gravity is so much weaker, but one must be careful not to over-interpret nature. Electromagnetic forces tend to cancel each other because there are usually as many negative charges as there are positive charges (or nearly so) in most environments, whereas gravity only has one "charge", that being plain old ordinary positive mass (http://en.wikipedia.org/wiki/Mass). Hence the gravitational attraction between two stars easily overwhelms their electromagnetic attraction or repulsion, because any net electric charge will be relatively small compared to the mass, and the electromagnetic forces of opposite sign will cancel each other.

That's a really nut-shell version of how the forces compare, but why they compare that way has been an unanswerable question, until recently. The advent of string theory has provided a way to answer the question. Of course, there is no way to tell whether or not the answer is correct. Indeed, there is no way to know that the answer is not really silly. But it is an answer, and the first time anybody has ever had a real excuse to claim to be able to answer the question with any potentially physically realistic idea.

String theory (http://en.wikipedia.org/wiki/String_theory) is a quantum theory of gravity (http://en.wikipedia.org/wiki/Quantum_gravity), and like other such theories provides a way around the singularity of the Big Bang and opens the door to pre Big Bang cosmology. In the context of string theory, this is done by the unintuitive means of mathematical/physical structures called branes (http://en.wikipedia.org/wiki/D-brane), which inhabit spaces of more than 3 spatial dimensions (that's mathematically "easy" but physically challenging to say the least). The argument is that the Strong, Weak & Electromagnetic forces are confined to individual branes, whereas gravity is not. So since it is spread over more spatial dimensions, it is necessarily weaker.

That's a reason for the weakness of the gravitational force, but whether or not it is the reason is a long way from being established. While criticisms that string theory cannot be experimentally verified are simply not true, it is still the case that string theory is in its scientific childhood, and is really more of an hypothesis than something most people would call a theory. So one should not put a lot of faith in the answer proposed here. It's an idea, but it really is no more than slightly educated speculation at the moment.