'... [the] vision of the universe arranged in harmonies of sounds and relations is no new discovery. Today, physicists are simply proving that what we call an object... an atom, a molecule, a particle, is only an approximation, a metaphor. At the subatomic level, it dissolves into a series of interconnections like chords of music. It's beautiful.'

'Yeah, but there are boundaries, aren't there? I mean, between you and me, for instance. We are two separate bodies, aren't we? That's not an illusion. Is it? Are you saying that there is a physical connection... between you and me, and you and the wall behind you... and the air and this bench?'

'Yes. At the subatomic level there is a continual exchange of matter and energy between my hand and this wood, between the wood and the air, and even between you and me. I mean a real exchange of photons and electrons.

Ultimately, whether we like it or not... we're all part of one inseparable web of relationships.'

[Mindwalk, Bernt Capra]

A brief insight into the historical aspect of the modern physics 

'In these days of conflict between ancient and modern studies, there must surely be something to be said for a study which did not begin with Pythagoras and will not end with Einstein, but is the oldest and youngest of all.'

[A Mathematician's Apology, G.H.Hardy]

The idea of the atom was long forecasted by a few Ancient Greek philosophers, amongst them Leucippus and his student Democritus. Yet it was vehemently criticized by several European scientists in the mid-19th century. Boltzmann suffered ostracization from the scientific community for trying to reintroduce this concept as the basis of all matter, which ironically we hold as a pretty conventional notion these days. There is a tendency in the scientific world for old ideas to be regenerated and surface under various forms in distinct time frames, or in other words, to be repeated. Indeed, most great insights tend to be provoked through previous reflections upon some inspiring work!

For instance when Einstein attempted to understand the problem with Maxwell's equations and Galilean transformations, he soon realized that essentially Galileo's intuition concerning the notion that velocity is only relative and inertial systems are equivalent could not be wrong. Yet Maxwell's insight that any interaction is mediated by a field could not be incorrect either. Still, there was difficulty in putting the two together because it was thought that one was of limited validity in terms of the other and thus not equivalent. The seeming contradiction rested upon the fact that physicists were subconsciously taking an incorrect assumption in their deductions. Einstein's wonderful contribution was in amending the wrong assumption that simultaneity was well defined. The history of physics is riddled with instances where a scientist discerns an erroneous hypothesis in merging two theories together so as to account for both of them (sometimes by borrowing from yet another theory).

Maxwell's dream of Unification extended

' "I have long held an opinion," says that illustrious experimentalist, "almost amounting to a conviction, in common, I believe, with many other lovers of natural knowledge, that the various forms under which the forces of matter are made manifest have one common origin; or, in other words, are so directly related and mutually dependent, that they are convertible, as it were, into one another, and possess equivalents of power in their action." '

[Vril, The Power of the Coming Race, Sir Edward Burton-Lytton]

Near the turn of the 19th century, it was widely held that the great problems in physics had been solved and what was left to decode were a few details. One of these 'details' was known as the ultraviolet catastrophe, which emerged from applications of statistical physics to complicated systems, such as energy distribution among different frequencies in blackbody radiation. A blackbody is one that perfectly absorbs all incident radiation and then releases all of that radiation. The puzzle was essentially a product of friction between the theoretical predictions and empirical observation; it was predicted that an infinite amount of energy was concentrated at the highest frequency yet this was not observed experimentally. A curious reassigning of this problem by Max Planck explained the seeming dichotomy. He discarded the assumption of classical physics that energy radiated continuously in and out of the blackbody and instead suggested that radiation was emitted (or absorbed) in discrete energy packets called quanta, whose energy content is proportional to the frequency of radiation where the constant of proportionality was taken to be a universal constant of nature, today widely known as Planck's constant.

The idea of quanta was explored further by then a young patent clerk, Albert Einstein, while pondering about yet another unresolved mystery, the photoelectric effect. Einstein noticed that if one had to consider the light ray as a beam of persisting quanta, the apparent mystery would vanish due to Planck's claim. The collision of a photon with the metal surface would result in the emission of an electron from the surface only if the original photon exceeded a certain frequency (threshold frequency). Such discoveries were just the beginning of a truly wonderful era.

Figure 1

The weirdness of Quantum Mechanics 

'A red dragonfly hovers above a backwater of the stream, its wings moving so fast that the eye sees not wings in movement but a probability distribution of where the wings might be, like electron orbitals: a quantum-mechanical effect that maybe explains why the insect can apparently teleport from one place to another, disappearing from one point and reappearing a couple of meters away, without seeming to pass through the space in between.'

[Cryptonomicon, Neal Stephenson] 

As the physicists probed deeper into the nature of the atom to discover the behaviour of particles at the subatomic level, they discovered some really strange affairs which seemed to contradict all intuition. One of the very first experiments with bizarre outcomes was the double-slit experiment, which in terms of classical behaviour could be explained as the particle behaving both as a particle and as a wave. Amongst the other uncanny outcomes of quantum mechanics was Heisenberg's Uncertainty Principle, which describes the fuzziness involved when trying to detect the momentum of a particle at a specific position simultaneously. Such inherent probabilistic computations relates to the measurement problem which is beyond the fact that scientists use classical equipment to evaluate microscopic phenomena.

Figure 2

One may ask: but how can it be that the discrete nature of energy levels in the quantum world is to be reconciled with the continuous temperament of the macroscopic world? The bizarre world of quantum mechanics has been considered profoundly shocking even to the physicist, let alone to the layman. But perhaps this is only because as humans, we are embedded in a three dimensional macroscopic framework and unfamiliar with the Planck scale of quantum particles. Thus arises the confusion in language and misconceptions of ideas, like the wave-particle duality, the thought experiment of Schrödinger's cat and the EPR paradox as a corollary of the Copenhagen interpretation. There is also a whole mesh of confusion over the divergent interpretations of QM.

The puzzle of Quantum Gravity: towards a paradigm shift? 

'...what we really should be discussing is 'the interpretation of classical mechanics' – that is, how can the classical world we see - which is only an approximation of the underlying reality, which in turn is quantum mechanical in nature – be understood in terms of the proper quantum mechanical variables? If we insist on interpreting quantum mechanical phenomena in terms of classical concepts, we will inevitably encounter phenomena that seem paradoxical, or impossible.'

[The Physics of Star Trek, Lawrence Krauss]

The problem at hand necessarily translates to the fact that the formalisms of Quantum Mechanics and General Relativity are incompatible with each other: QM is expressed using an external time variable which is discordant with GR since the latter did not appeal to the Newtonian mechanistic concept of time. Newton held that the flow of time was the same for all. Indeed, one of the triumphs of relativity was its illustration that the passage of time was not the same for all observers but depends upon the velocity of the subject; the difference would essentially be negligible from Newtonian applications at very small speeds. In GR, objects are not localized with respect to some temporal or spatial frame of reference (there is no fixed background structure). Localization is only with respect to the field and not with respect to some arbitrary coordinate system. On the other hand, in QM the dynamical field is quantized and also follows probabilistic superposition states. The question thus is: How can we fully describe quantum spacetime?

 Figure 3

Exploring Quantum Gravity: reconsidering the notion of gravity 

'Everything in our past experience tells us that the two descriptions of Nature we currently use must be approximations, special cases which arise as suitable limits of a single, universal theory. That theory must be based on a synthesis of the basic principles of general relativity and quantum mechanics.

This would be the quantum theory of gravity that we are seeking.'

[The Ashgate Companion to Contemporary Philosophy of Physics, Abhay Ashtekar]

The pursuit of quantum gravity is mainly split into three main lines of research, known as covariant, canonical and sum over histories. The initial investigation route was the construction of Quantum Field Theory by considering the metric fluctuations over a flat Minkowski space (since this is the metric space we most conveniently use for relativistic considerations), which eventually led to string theory. A consequence of this theory is the multiverse, where the initial conception of our universe would not be described by a cosmic inflation from seemingly nothingness (big bang), but rather the fusion of two universes into one or a universe's separation into two baby universes. The big dilemma about this theory is that there aren't testable predictions which can be verified, so despite the fact that theoretically it satisfies the unification of QM and GR, we do not yet know if it gives us a description of the physical universe even at extreme situations like the singularity of a black hole.

The canonical research involved in developing a quantum gravity theory was based directly on Einstein's geometrical formulation, known as Loop Quantum Gravity. In this theory, one can regard space as a fine network of finite loops so that the structure of spacetime is discrete. But unlike string theory, LQG makes some definite predictions, which implies it may well be tested before string theory is. The cosmological implications of this theory is that there is no big bang singularity; instead, the universe's history can be traced far into the past in an infinite regress known as the Big Bounce.

Figure 4

The sum over histories inquiry (or path integral formalism) comprises Feynman's ideas and Hawking's mostly through Euclidean quantum gravity. There is still much unfinished work in this approach. Also, there have been other ideas working alongside these three principal ones, but so far none of them have been developed into a full theory of quantum gravity. Peter Bergmann, one of Einstein's collaborators, had this to say during the 1963 Conférence internationale sur les théories relativistes de la gravitation,

'In view of the great difficulties of this program, I consider it a very positive thing that so many different approaches are being brought to bear on the problem. To be sure, the approaches we hope, will converge to one goal.'

Although the vogue in physics has been to understand gravity at the atomic level, one should apprehend that some concepts used to describe the natural world would be deficient on different scales, for instance water is wet but its molecules would not be described as such. Just because a theory makes fairly accurate predictions for atoms for instance, this does not imply that we can extend this theory to apply to the planetary scale. The same pertains to gravity; we perceive the effects of gravity acting on masses, but is it indeed present on the atomic scale? Can we measure the 'curvature of spacetime' inflicted by a pair of atoms? In this sense, it would be considered as an emergent phenomenon. Erik Verlinde, who has been working on a new theory of gravity, harbours such ideas. So that instead of gathering information on the behaviour of every specific particle - which would be impossible because of the uncertainty involved - one can study the behaviour of the entire gas or system as a whole.

Reconsidering the pursuit for a grand unified theory 

'We often think that when we have completed our study of one we know all about two, because 'two' is 'one and one'. We forget that we have still to make a study of 'and'.'

[unknown source, Arthur Eddington]

The rapid accumulation of scientific knowledge in the last few centuries can be accounted for because of specialization - detailed analysis of a specific area of study. However, efforts are being generated towards a unification of ideas, synthesizing these discrete branches of physics into an integrated whole. Although this endeavour is to be highly esteemed, one must claim that such efforts would be prolonged unless one reflects on the problem at hand thoroughly. One question which still remains unanswered is: Are the four fundamental forces simply different aspects of one fundamental entity, in the same fashion that electricity and magnetism turned out to be manifestations of the same one spectacle?

Another curious mystery is the fact that gravity is so much weaker than the other three forces, namely the weak force, the strong force and electromagnetic force.Nonetheless, the Standard Model has not been able to account for gravity at the smallest of scales; although a new particle graviton has been hypothesized to account for gravitation, this has not been found yet despite countless experimentation. The other forces have already been integrated through the Standard Model, though gravitation eludes us still on the microscopic level.

Finally, the definition of everything as provided by the Oxford Dictionary of English incorporates 'all things' whereas current physics is concerned only with the ordinary universe, which amounts to 4.9% of the total mass-energy of the known universe. Although these claims seem to verge on the pessimistic, they need to be taken into consideration if we are to find a true generic understanding of the world.

Figure 5

Notation

Although it is pretty clear, I declare these acronyms for those reading the article and are unfamiliar with certain notation;

QM: Quantum Mechanics, GR: General Relativity, LQG: Loop Quantum Gravity

References

  1. Carlo Rovelli, Quantum Gravity, draft version http://www.cpt.univ-mrs.fr/~rovelli/book.pdf 
  2. Cosmology and Quantum Gravity: Loops and Spinfoams (Carlo Rovelli) http://www.youtube.com/watch?v=_7WRbUgnWgM 
  3. Erik Verlinde: gravity doesn't exist https://www.youtube.com/watch?v=hByJBQXjXU 
  4. Erik Verlinde: a new explanation of gravity https://www.youtube.com/watch?v=vyomGtZCsmI 
  5. Einstein Online, Max Planck Institute for Gravitational Physics, Loop Quantum Gravity http://www.einstein-online.info/elementary/quantum/loops 
  6. Michio Kaku explains String Theory https://www.youtube.com/watch?v=kYAdwS5MFjQ 
  7. http://www.oxforddictionaries.com/definition/english/everything
  8. Why String Theory? a layman's journey to the frontiers of physics, 'Quantum Gravity: Towards the Holy Grailhttp://whystringtheory.com/research/quantum-gravity/