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The Origin of the Universe

Brief outline of the evolution of theories on the origin of the universe:

  • Ancient Greeks:
    • the geocentric universe:
      • earth is the centre of the universe, around which the sun & planets rotate
      • this held as the popular view almost to the end of the 18thC!!
    • Aristarchus' universe:
      • the only reference remaining is a critic by Archimedes, and this view appears to have been lost
      • sun & stars are fixed, earth & planets rotate around the sun.
  • Copernicus (1543AD):
    • published a view similar to Aristarchus but not widely accepted as opposed religious doctrine, removing humanity as the centre of all consideration, until Newton & others to spread it, even so, it was not widely accepted until late 18thC.
  • Newtonian “classical” physics:
    • Newton in 1687 published his Principia Mathematica, giving us the 1st mathematical model for time and space
    • time & space were a background in which events took place but which weren't affected by them
    • time was separate from space & was considered to be a single line with no beginning & no end & was constant
    • law of gravity:
      • if one changed the distribution of matter in one region of space, the change in the gravitational field would be felt instantaneously everywhere else in the universe, which implied, one could send signals faster than light & in order to know what instantaneous meant, it also required the existence of absolute or universal time
    • whilst Newton regarded light as corpuscular, Huyghens (1629-95) introduced the wave theory of light
  • Immanuel Kant's “antimony of pure reason”:
    • if the universe was created only a few thousand years ago as most believed, why had there been an infinite wait before the creation?
    • on the other hand, if the universe had existed forever, why hadn't everything that was going to happen already happened, meaning that history was over? 
      • why hadn't the universe reached thermal equilibrium, with everything the same temperature???
  • space as “ether”:
    • by the end of the 19thC, scientists believed they were close to a complete description of the universe, they imagined that space was filled by a continuous medium called the “ether”.
    • light rays & radio signals were waves in this ether, just as sound is pressure waves in air
    • all that was needed for a complete theory were careful measurements of the elastic properties of the ether, anticipating such measurements, the Jefferson Lab at Harvard University was built entirely without iron nails so as not to interfere with delicate magnetic measurements, however, they forgot that the reddish-brown bricks contain large amounts of iron.
    • it was expected that light would travel at a fixed speed through the ether, but if you were travelling in the same direction, the speed should appear lower, & the converse if travelling towards the light
      • unfortunately, no daily or yearly differences in speed of light were found in expts in 1887 when comparing speed of light in two beams at right angles to each other as the earth revolved around the sun - it was as if the speed of light was constant relative to where one was, no matter how fast & in what direction one was moving!
  • Einstein's theories:
    • photo-electric effect:
      • Einstein won his Nobel prize for his photoelectric theory in 1905
      • he interpreted results which showed that for each metal there is a critical wavelength above which no photo-electrons are emitted, as meaning that radiation could be regarded as made up of small 'packets' of energy, known as photons, when a metal is irradiated by such photons, some of the energy was used in ejecting electrons from the metal whilst the remainder was given up to the electrons.
      • the energy of a photon is dependent on the wavelength, or frequency, of the radiation concerned according to the basic equation of the quantum theory E = hv
    • special relativity:
      • Einstein in 1905, started with the postulate that the laws of science should appear the same to all freely moving observers, in particular, they should measure the same speed of light independent of their motion.
      • this required overthrowing the absolutes of 19thC science (& thus not accepted until mid-20thC): 
        • absolute rest, as represented by ether, and,
        • absolute or universal time
          • everyone would have there own personal time. The times of two persons would agree if they were at rest with each other, but not if they were moving.
            • this has been confirmed by a number of expts such as:
              • two accurate clocks flown in opposite directions around the world would become slightly out of sync by a fraction of a second.
      • this implied a theory of special relativity & an important consequence is the relation between mass & energy as, if the apparent speed was constant for everyone, then, no-one could travel faster than the speed of light, Einstein managed to then formulate his famous equation (E = mc2) which showed that as the energy increased so does the mass of the object which would then require an infinite energy to get to the speed of light. 
        • a consequence of this is the realisation that if the nucleus of a uranium atom fissions into two nuclei with slightly less mass, this will release a tremendous amount of energy!
      •  this theory then did not fit with Newton's law of gravity:
        • nothing could travel faster than light
        • “instantaneous” was meaningless as absolute time was abolished
    • general relativity:
      • in 1912, Einstein realised that if the geometry of space-time was curved and not flat, as had been assumed, acceleration and gravity can be equivalent only if a massive body curves space-time - this was the basis for his theory of general relativity 
      • this was confirmed in 1919 when a British expedition to West Africa observed slight bending of light from a star passing near the sun during an eclipse. This spurred the greatest change in our perception of the universe since Euclid wrote his Elements of Geometry in 300BC.
      • one cannot curve space without curving time, thus time has a shape
      • his equations did not allow for a static universe, unchanging in time as was generally believed, so he added a fudge which he called the “cosmological constant” rather than consider the universe was expanding or contracting
  • hyper-space:
    • hyper-space is space beyond 3 dimensions of space and 1 dimension of time.
    • ancient Greeks try to prove that hyper-space was impossible
    • in 1860s, Bernhard Riemann (1826-1866 - perhaps Vernhard is alternative spelling) proves that hyper-space was possible
    • in 1921, Kaluza showed that universes may exist in hyper-space
    • Einstein's equations give us the possibility to leap into hyperspace through a worm-hole to reach another universe, but this would require more energy than we have & we don't know how stable such a hole would be
    • it is now believed that the concept of hyperspace is required to unify the four fundamental forces, as these can be seen as ripples in hyperspace:
      • if the 5th dimension vibrates, the ripples are seen as light
      • if the other dimensions vibrate, the ripples are seen as nuclear force
    • time is like a river, it bends and flows around the Universe & may have whirlpools & may fork into 2 rivers, but for time travel, one would need Plank energy or the energy of a Black Hole
    • 90% of our Universe is made up of dark matter
  • the expanding Universe:
    • in 1920's, Edwin Hubble found (by Doppler Red Shift) that galaxies far from our own Milky Way are moving away from us, in fact, the further away, the faster they are receding, thus concluding the Universe must be expanding
    • using Einstein's general theory of relativity, one could then conclude that, tracing the expansion of the universe back in time, at the beginning of time, there would be a point of infinite density (of either energy or mass as these are equivalent) which is called a singularity.
  • quantum mechanics:
    • in the 1920's, Heisenberg, Dirac & Schrodinger developed a new picture of reality called quantum mechanics
    • no longer did tiny particles have a definite position & speed but introduced the Uncertainty Principle which stated that the more is known about the position of a particle, the less can be known about its speed & vice versa
    • these became the foundation of modern developments in chemistry, molecular biology & electronics.
    • 1924 de Broglie suggested that moving electrons had waves of definite wavelength which was demonstrated in 1927 and their wavelength = h/mv where h is Planck's constant, m is mass of electron & v is the velocity of the electron & if this is written as momentum x wavelength = h & thus relates the particle-like aspect of an electron ie. its momentum, to the wave-like aspect, ie. wavelength.
    • 1927, Schrodinger postulated based on his intuition without proof, that the wave pattern of an electron could be expressed as an equation relating a wave function, the total energy & potential energy of the system, mass of the electron, Planck's constant & the coordinates of the system.
    • 1927, Heisenberg put forward the Uncertainty Principle as a long wavelength can be measured with greater fractional accuracy than a short one, thus according to de Broglie's equation, a particle with small momentum has a correspondingly large wavelength which can be measured with some accuracy but at the expense of a relatively inaccurate determination of the small momentum.
  • the Big Bang theory of the 1960's & 70's:
    • based on particle physics:
      • matter consists of fundamental matter particles quarks & leptons (eg. electron, muon, tauon & neutrinos) with 6 flavours of each
      • 4 known fundamental forces, each mediated by a fundamental particle (quantum, known as a carrier particle):
        • Force Particle/quantum relative strength range (meters) strong nuclear gluon 1 10-15 electromagnetic photon 7 x 10-3 infinite weak nuclear W+, W-, Z 10-5 10-17 gravitation gravitron (tentative) 6 x 10-39 infinite
    • the cosmic afterglow:
      • in 1963, Arno Panzias & Robert Wilson detected the afterglow of the Big Bang, known as cosmic microwave background (CMB), which revealed that the Universe was once a very hot, hostile place & together with the expanding Universe concept, led scientists to deduce that the Universe began as an infinitely compact fireball.
      • the Big Bang describes how this fireball grew to form stars & planets, although it is erroneously thought of as being an explosion in one place, while it is is now thought as not forming from one central ignition point, but rather, that space was first created & then stretched.
      • according to physics, particles of matter & anti-matter should have been produced in equal quantities & if they meet each other, they would annihilate each other resulting in light - strangely we seem to have much more matter than anti-matter - this still has not been answered. 
      • initially, space was jam-packed with particles which prevented light from escaping, but after 300,000yrs, the Universe cooled to the temperature of the Sun's surface allowing the particles to join to form atoms which do not impede light & thus gradually light started to pour through the Universe
      • the afterglow from this event formed a bright halo, whose light then began to filter down through space & time.
      • as we look into space we also look back into time, if it would be possible to see this far, the cosmic halo would be the furthest visible point. Everything beyond this, from the birth of the Universe until this epoch will be invisible to us forever.
    • Stephen Hawking & Penrose: the beginning of time:
      • spacetime is curved not only by massive objects but also by the energy in it which is always positive, so it gives spacetime a curvature that bends the path of light rays towards each other.
      • light rays in our past light cone are bent back toward each other creating a pear-shaped light-cone with the base being the Big Bang
      • in 1968, won 2nd prize in a competition with a paper proving time is dependent on the universe & has a beginning - the Big Bang
      • to understand the origin & fate of the universe we would need a quantum theory of gravity
    • physicists attempted to trace back the universe to the big bang using mathematical equations and determined:
      • Big Bang happened ~ 14-15 billion years ago
      • matter was a soup of quarks & leptons at a temperature of 1016 deg.C
      • after a nanosecond, temperature fell to 1012 deg.C & protons & neutrons began to form
      • the electroweak force differentiated into electromagnetic and the weak force.
      • if matter and antimatter were perfectly symmetrical, the cooling of the Universe would have resulted in matter annihilation & the result being only photons, but for every 1 billion annihilations, a particle of matter remained forming the matter today, & thus ~99% of the current photons in the Universe are cosmic rays from these initial annihilations (photons from stars are a trivial contribution).
      • a plasma of electrons & nuclei existed for 300,000yrs until the temperature dropped to 5,000 deg.C when hydrogen & helium atoms formed
      • took a billion years to evolve into galaxies and stars
      • at about 9 billion years, our Sun exploded into action
    • but became stumped by the questions of the “Cosmic Singularity”:
      • what was the Big Bang?
      • what made the Big Bang happen?
      • did time start at the Big Bang?
    • and even worse, our current laws of physics break down at the instant of the Big Bang & thus no single theory could explain all of nature
    • in addition, particles could never be predicted to be where they should be
  • super-symmetry of the 1970's:
    • a new kind of symmetry was discovered that provides a natural physical mechanism to cancel the infinities arising from ground state fluctuations
    • one way is to say that spacetime has extra dimensions called Grassman dimensions, because they are measured in numbers known as Grassman variables rather than ordinary real numbers. Grassman variables anti-commute: x times y is same as -y times x.
    • super-symmetry was 1st considered for removing infinities in matter fields & Yang-Mills fields in spacetime where ordinary numbers & Grassman dimensions were flat, not curved.
    • one consequence of super-symmetry is that every field or particle should have a “superpartner” with a spin that is either 1/2 greater or less than its own
  • Stephen Hawking & Penrose:
    • in 1974, calculate the entropy of a black hole, thus showing that there is a deep connection between quantum gravity & thermodynamics & suggested that quantum gravity may exhibit holography
  • the super-gravity theory of the 1980's:
    • applied super-symmetry to ordinary numbers & Grassman dimensions that were curved resulting in super-gravity theories
    • predicted 11 dimensions but was temporarily displaced by the string theory's 10 dimensions
  • the inflation theory:
    • Universe was born by a spontaneous quantum energy bubble forming from nothing and then rapidly expanding from a size smaller than a proton to a grapefruit in a fraction of a second which then kick started the Big Bang 
  • the super-string theories of the mid 1980's:
    • an extension of quantum physics using strings (one-dimensional extended objects that vibrate) to represent the “particles”
    • at Planck-length (10-35meter) dimensions, Einstein's equations of general relativity result in such intense fluctuations that “space-time goes haywire”. 
    • if the strings  have Grassman dimensions as well as their ordinary number dimensions, the ripples will correspond to bosons & fermions.
    • thus, instead of boson & fermion particles, the universe is proposed to be made of Planck-length boson & fermion strings which must be stretched under tension to vibrate (excite) & unlike particle interactions which occur at a single point of space-time, strings collide over a small but finite distance & can vibrate in 10 dimensions, 6 of which are tightly coiled in on an unmeasurably small scale & 4 of which are conventional space-time
    • thus the basic element of matter is not particles but are super-strings which when vibrate create different types of matter
    • a string has 10 dimensions - 9 spacial + time
    • as string theories do not have infinities, they are good at calculating what happens when a few high energy particles collide & scatter off each other, however, are not good at describing how the energy of a very large number of particles curve the universe or forms a bound state, like a black hole - for these situations, one needs supergravity.
    • this explained many things but 5 string theories evolved (types I, IIA, IIB, heterotic-0, heterotic-E) and this was not satisfactory
  • Townsend's “p-branes”:
    • it was realized that strings were just one member of a wide class of objects that can be extended in more than one dimension
    • Townsend in late 1980's, named them “p-branes” where p is an integer indicating that it has length in p dimensions
    • p-branes can be of different shapes:
      • 0-branes are sub-atomic particles and thus form our laws of chemistry
      • 1-branes are strings
      • 2-branes are membranes (rolled up could form a torus)
      • 3-branes maybe a universe (a 3 space + 1 time universe)
    • all the p-branes could be found as solutions of the equations of super-gravity theories in 10 or 11 dimensions
  • the Membrane theory or M-theory of the late 1990's:
    • an extension of the string theory whereby strings have 11 dimensions (the 11th being gravity?)
    • this allows for the multitude of string theories and an infinite number of particle types as well as supporting super-gravity theories, thereby it was a duality - a model that shows other models are all essentially equivalent & are just different aspects of the same underlying theory
    • a universe consists of a membrane which connects all its component strings
    • maximum width of the 11th dimension is 1 trillionth of a millimetre but it may be infinitely long
    • there may be an infinite number of such universes, each with its own laws of physics within our “multiverse”
      • eg. a universe may consist only of electrons or only of neutrinos
    • when 2 membranes or strings collide, they create new membranes and new string
    • the Big Bang could then be a collision of parallel “universes” in the 11th dimension as the rippling “walls” of each universe collided with each other resulting in resonation of string creating a new universe
    • this theory finally can explain many previously inexplicable phenomena & thus be at last a single, unifying theory:
      • what created the Big Bang
      • the existence of time prior to the Big Bang
      • the reason gravitational force is so weak may be that it emanates from a distant, connected parallel universe at the end of the 11th dimension tunnel
    • some believe that a new universe could be created in the laboratory by effectively creating a new Big Bang thus creating a rapidly expanding universe by creating its own space, in a different dimension to ours & therefore not affecting our universe
    • each universe “bubble” may form as a quantum fluctuation of Nothing (quantum theory says that bubbles of energy can appear temporarily out of absolutely nothing! normally these “pop”, but to survive, it must have an intense outward push)
    • our universe can be viewed as:
      • the membrane of a 4 dimensional (3 space & 1 time) bubble with the centre filled with hyper-space.
      • the bubble is floating in 11 dimensional hyper-space
      • it may be connected to a parallel universe to explain the gravitational forces
      • the dark matter and black holes in our universe may actually be out-buddings of 'child' universes
      • one theory says that our nearest universe bubble may be 1 millimetre away from us
  • the F-theory:
    • held by only a minority of physicists, adds a 2nd time dimension to M-theory

 

References:

  • Stephen Hawking. The Universe in A Nutshell. 2001. Bantam Press.
photo/ast_origins.txt · Last modified: 2012/04/05 01:12 by gary1