[thedoc (OP)]

Muhammad Al-Hakeem  asked the Naked Scientists:
   
How can the string theory reconcile quantum mechanics and general relativity? And why do they contradict each other?

Many thanks.

What do you think?

[Soul Surfer]

This is very difficult to give a short answer to and several books have been written on the subject.

The two theories are essentially different in nature

Relativity is a classical theory where things are described as continuous mathematical equations. The basic principle is that the laws of physics should not change according to your location, direction or movement.

Quantum theory is a discontinuous theory where things are described in terms of individual probability functions which are essentially integrals over all space and time. Based on particles which are point sources.  It is extremely successful and accurate for describing atomic particles and their interactions it also includes relativistic effects and so is compatible in this respect with relativity but does not work with gravity because the intergrals all explode and give infinite numbers of infinite results.

String theory is similar to quantum theory but the points are extended slightly in space time to turn them into lines this helps to take out the infinities and include gravity but there are so many different string theories no one knows how to chose the right model out of around 10^500 possibilities.

What we need is a fundamentally different approach to the whole problem that could point us towards the right sort of string theory.  So far no one has found one that enthuses people yet.  I could offer a good suggestion but to go much further than this would enter the realm of "new theories".  Suffice it to say that I prefer taking an analytical approach to a "theory of everything" based on an evolutionary principle of physical laws in which the most probable way is chosen for all universes including ours to create and seed new universes. This produces in effect a fractal multiverse in which the physical laws are quite likely to be favourable to the development of complexity at all levels.

[Emc2]

is it possible that no unified theory exists ?

I mean, suppose that matter just follows a different set of rules once it has "acquired" a certain level of mass, and it is as simple as that.

 just the same way that mass comes about upon combinations, maybe this process in of itself, requires said mass of particles to now follow these new rules..

[Soul Surfer]

The changing of physical laws with conditions in no way precludes a theory of everything.  you must bear in mind that there are some physical laws that will apply in ANY universe even if others change.  for example the second law of thermodynamics.

[Emc2]

ok, i will agree that some laws are universal, but could some also be depending on the mass of any given object.

   so if you have E = MC2

 you might also get  (laws ) = M x complexity of atomic structure ( or something like that )


  is this at all possible ?

[imatfaal]

we hope not.  much of our physics and science in general relies on an almost unspoken axiom that there are no special circumstances within which the laws of physics are changed.  we don't know these laws yet - but we believe that they will be universal.  to an extent SR and GR grew from Einstein's conviction about this - there was no absolute time, nor absolute space; every inertial frame had the same set of laws (incl speed of light).

[Emc2]

one neuron is nothing, combine billions and presto - you get consciousness, as of yet, unexplainable.

  maybe matter is like that, once you get so complex - presto = have to follow different rules.

  I imagine it like this. 

  something - maybe the higgs, or something else, provides mass and structure to atoms once the achieve a certain size, once matter reaches a certain size, the thing that gives it mass and holds all them atoms together, maybe just makes this new construct have to operate differently, ie. new rules, or old rule yet undiscovered .

  gravity is the one of the key's I believe, but it don't want to play by "our" rules yet...


  complexity changes a lot of things..