Passing Through General Relativity and Quantum Theory

Have you ever asked yourself the perplexing questions of life? For instance, whether the universe is all there is? or, if the universe began at some point in time or extends into the infinite past? If the universe did begin, then what exactly began it? Scientists, philosophers and theologians over the ages have proposed many solutions to the problems regarding the universe’s basic function and it’s more general questions of “metaphysical perplexity,” (so to speak) and have come to their own respective conclusions.

 However, interesting and relevant for discussion, physicist Lee Smolin has written fantastic books such as The Life of the Cosmos (1997), The Trouble with Physics (2006) and Three Roads to Quantum Gravity (2002) that deal very nicely with certain questions of physics and basic reality. In his book The Life of the Cosmos [1], he gives a very interesting discussion regarding these questions that have perplexed scientists for centuries. He writes:

What is the universe? Is it infinite, or finite? Is it eternal, or did it begin at some first moment? If it began, what began with it? Everyone has wondered about these questions, and every culture has told a story about them [ … ] Now at the end of the twentieth century we stand at the verge of another step in our growing understanding of the universe. We live in the middle of one of the great revolutionary periods in our understanding of nature, as we attempt to meld into framework what we had learned about relativity, the quantum and the expanding universe. [2]

However, some preliminary background might be in order. For those readers who have no clue regarding theoretical physics, general relativity or quantum physics, at the present moment that doesn’t necessarily matter. However, take for example Wim B. Drees’s paper in The Philosophy in Science volume where he writes, “In theoretical physics the major fundamental theories are general relativity (GR), quantum theory (QT), and thermodynamics” [3]. Though Frank Tipler (2007) outlines the subject more as

  • (1) General Relativity
  • (2) Quantum Mechanics
  • (3) Standard Model for Particle Physics,

The three theories above could easily be just as relevant as that seen in Drees’ paper (1990). However, let’s first discuss a central issue with respect to the conversation between General Relativity and Quantum Mechanics – the problem of quantum gravity.

Isaac Newton with his epic work the Principia in 1687 dominated the world of physics for over 400 years. It wasn’t until the dawn of the 20th century where Albert Einstein would shake all of what we know in regards to space, time, gravitation and motion. In General Relativity (GR), Einstein proposed the idea that gravity and motion were “intimately related” to each other and gave us new insight as to the geometry of space and time. Stephen Hawking explains:

According to Newton’s theory of gravity, at any given time objects are attracted to each other by a force that depends on the distance between them at that time. But the theory of relativity had abolished the concept of absolute time, so there was no way to define when the distance between the masses should be measured. Thus Newton’s theory of gravity was not consistent with special relativity and had to be modified. The conflict might sound like a mere technical difficulty, perhaps even a detail that could somehow be worked out without much change in the theory. As it turned out, nothing could have been further from the truth. [4]

Thus, Einstein later developed his own theory of gravity which he called general relativity. It wasn’t that much more than twenty years later until quantum theory (QT) was developed with new understanding’s in matter and radiation. However, there is a notable problem between GR and QT. As Smolin notes, “in spite of great progress over the century, they remain incomplete” [5].

In respect to GR and QT we are simply unable to combine the two due to the grounds that they are dispositioned to cover. In other words, at the level of the initial singularity of the Big Bang, all of physics seems to break down. Once we invoke subatomic proportions to cover this singularity, we now need to introduce some new theory of subatomic physics (‘Quantum Field Theory’). According to Science Daily (August 2009) in an article entitled, Rewriting General Relativity?: “Despite the success of general relativity, one of the most important problems in modern physics is finding a theory of quantum gravity that reconciles the continuous nature of gravitational fields with the inherent ‘graininess’ of quantum mechanics.”

Lee Smolin explains this point as one of the great problems of theoretical physics: “Problem 1: Combine general relativity and quantum theory into a single theory that can claim to be the complete theory of nature.” [6] Smolin thence discusses the issue of GR and QT as a problem of infinities. He writes:

General relativity has a problem with infinities because inside a black hole the density of matter and the strength of the gravitational field quickly become infinite. That appears to have also been the case very early in the history of the universe- at least, if we trust general relativity to describe its infancy. At the point at which the density becomes infinite, the equations of general relativity break down. [ … ] Quantum theory, in turn, has its own trouble with infinites. They appear wherever you attempt to use quantum mechanics to describe fields, like the electromagnetic field. The problem is that the electric and magnetic fields have values at every point in space. This means that there are an infinite number of variables. [7]

However, if it were possible to finally obtain this “quantum theory of gravity,” then we would have finally found what has often been called “the holy grail of physics.” This is demonstrated more so further by Smolin (1997): “Unification [ … ] is what theoretical physicists, at least most of us, dream of” [8]. Some theories of course, have been developed in order that they might fill this quantum gravity gap. An episode from The Big Bang Theory might demonstrate this point best:

________________

Notes:

  • [1] Lee Smolin, The Life of the Cosmos (Oxford University Press: 1997)
  • [2] Ibid., p. 11
  • [3] Wim B. Drees, Philosophical Elements in Penrose’s and Hawking’s Research in Contemporary Cosmology in The Philosophy in Science (vol. 4, 1990) p. 16
  • [4] Stephen Hawking and Leonard Mlodinow, The Grand Design (Bantam Books: 2010) p. 100
  • [5] Lee Smolin, Trouble With Physics (Mariner Books: 2006) p. 4
  • [6] Smolin 2006, 5.
  • [7] Ibid., pp. 5-6
  • [8] Smolin 1997, 48
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