Jack Oughton - Einstein, Hubble and The Expanding Universe.doc


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Jack Oughton - Einstein, Hubble and The Expanding Universe.doc

  1. 1. First Principles “Man is equally incapable of seeing the nothingness from which he emerges and the infinity in which he is engulfed.” – Blaise Pascal Cosmology is a field where physics and the metaphysical collide. As the study of everything, it is a area that often threatens to follow esoteric tangents into the spiritual. Cosmology also has come to a point where human comprehension is perhaps not enough, yet. The origin of our universe, and possibly everything to ever exist, was christened the Big Bang by Fred Hoyle in 1949. The big bang is a monumentally important concept. Understanding the conditions in which our very universe formed has deep implications for a deeper universal understanding, both scientific and spiritual. Decades of evidence now suggest that the Universe is expanding. Simple deduction indicates that an expanding universe must be expanding outwards from something. It is that something it came from, and the reason why, which poses one of science’s greatest unfolding mysteries. Einstein’s contribution to expanding universe
  2. 2. When the General Theory of Relativity was proposed in 1915, the state of the observational knowledge was not yet ready to put his theory to the test. Soon after it’s completion, Einstein began using these equations to describe the global properties of the whole Universe. He soon came to a serious quandary. If, at a given time, all the galaxies in the Universe are stationary, and provided the Universe was finite in size, mutual gravitational attraction would cause them to begin to converge inwards; the universe would collapse in on itself. It could not remain static. To have the universe remain unchanged would be like a pencil balanced on its point; possible, but highly unlikely and not liable to last for very long. One way or another, it would fall. Einstein found he could ‘fix’ this problem by adding a simple constant term to the equations. An invisible force to immobilize the universe. This "cosmological constant" Einstein admitted, was only "a hypothetical term." It was "not required by the theory as such nor did it seem natural from a theoretical point of view”(Einstein 2007) Observational Evidence Arrives.. In the 1910s, Vesto Slipher was the first to observe the shift of spectral lines of galaxies, making him the discoverer of galactic motion. (Slipher 1913). However, Slipher’s measurements of radial velocities had effectively reached their limit, his 24-inch refractor at the Lowell Observatory , unable to penetrate further into space and record spectra from the numerous fainter nebulae. Enter Edwin Hubble, and his 100 inch telescope on Mount Wilson..
  3. 3. Hubble’s Contribution "The redshift of distant nebulae has smashed my old construction (the cosmological constant) like a hammer blow" – Einstein In 1925 Hubble published an extensive paper, in which he reported his observations of NGC 6822. Using Cepheid Variables as standard candles to measure distance he determined a figure of 700 000 light-years and concluded: “N.G.C. 6822 lies far outside the limits of the galactic system”(E. P. Hubble 1925) This was a monumental moment; this was the first system beyond the Magellanic Clouds to have its distance accurately determined. It instantly changed our cosmological understanding. The galaxy was no longer the universe. Who knew how many more galaxies there could be? By 1929, the work of Hubble had established our present picture of an expanding universe, consisting of galaxies moving away from one another. For his dissertation Hubble decided to study a series of nebulae. In a now famous diagram, he plotted the redshifts (velocities) of the
  4. 4. receding galaxies against their distances, and thus Hubble’s Law was written. Hubble’s Law: Galaxies are receding from us at a velocity that is proportional to their distance from us. Galaxies appear to be moving away from us at speeds proportional to their distance. This observation supports the expansion of the universe and is a powerful argument that the universe was once compacted. Too much knowledge? I would compare the implications of expanding space to our discovery that the world was not flat. Just because it appears one way does not make it so. In cosmology, intuitive was not enough, and we must once again acknowledge the possibility that our minds may not be capable of comprehending the bigger picture. A common trend throughout history is denial of the truth, if the truth challenges doctrine or, if it hurts too much. Both Einstein and Hubble had trouble facing up to the implications of their discoveries. In 1917 de Sitter produced a set of equations that could describe the
  5. 5. universe as expanding. An expanding universe implied a beginning, which Einstein did not appreciate. In correspondence with him, Einstein stated frankly of a non-static universe; “To admit such possibilities seems senseless.”(Edwards 2001, p.19) This would not be the first time that Einstein’s humanity clashed with the science he was developing. Hubble was a cautious man and determined to leave a ‘perfect’ scientific legacy by making no predictions that could later be mistaken. Lick Observatory astronomer C Donald Shane later revealed "Hubble had a desire to show that the red shift was not actually expansion, because he seemed always to be seeking some other explanation for it"(Bartusiak 2009) In his Rose Memorial Lectures on Hubble said of redshifts: "Their significance is still uncertain" – and described the expanding universe as a "dubious world"(Edwin Hubble 1937) Despite Hubble’s own personal reservations with his discovery, redshifts brought about big changes. A contemporary scientific theory was Fred Hoyle’s steady state Universe. An old astronomical paradigm of an eternal unchanging universe, it all but had its foundations pulled out from underneath it by Hubble’s observations. However, galactic motion’s implications were to go far deeper… The Plurality Of Worlds, Continued.. Hubble’s evidence of an expanding universe disrupted both religious and scientific beliefs. His observations contributed to an increasingly larger cosmos, and perhaps by comparison, an increasingly small place in this universe for humanity. In 1543 Copernicus’ De Revolutionibus smashed the belief that the earth was the centre of the universe. Hubble had now showed that this universe was much, much larger than we thought. It was becoming evident that we were not particularly unique in the cosmos (at least not in a cosmological sense). Expanding from what? "The actual point of creation lies outside the scope of presently known laws of physics" - Stephen Hawking "The instant of creation remains unexplained." - Alan Guth
  6. 6. In 1922, Alexander Friedman corrected an error in Einstein’s field equations. His solutions of an open or closed universe argued strongly for a universe in motion. (Friedman 1922) Then, in 1927 Lemaître proposed his 'hypothesis of the primeval atom' (Milne 1949). He had independently derived the same expanding mathematics that Friedman had. Their calculations would later be combined in the FLRW metric. This standard model of cosmology describes an expanding or contracting universe. Mathematical and observational evidence was mounting. An awkward question started to rear its head. If the universe was in motion, it is changing, and furthermore if expanding, what was it moving away from? Einstein’s response to the idea of an expanding universe was essentially the same to both men’s mathematics: he found no errors in the mathematics of the theory, yet he was convinced that from the physical point of view it was “tout à fait abominable”’(Kragh 2007, p.56). However, physical law does not care for human sensitivity. Decades later, Hawking and Penrose mathematically demonstrated that every solution to the general relativity’s equations guarantees the existence of a singular boundary for space and time in the past. This is now known as the "singularity theorem"(Hawking 1976). The ‘primeval atom’ now existed in a strong mathematic framework. Questions Posed By The Origin – Nothing and Infinites? The singularity presents ideas that are extremely hard to comprehend. Areas that take us into a domain of philosophy and questions that are hard to answer with science. Some believe that space didn’t exist before the big bang. This in itself is a perceptual and philosophical challenge to human instinct. What is nothing? I do not think we can comprehend it. The closest to nothing I can imagine is blackness. But blackness can be defined, it is a colour, or an absence of light. In wrestling with the nature of nothing Descartes stated; I think therefore I am; postulating that the foundations of knowing reality to be true are that we can think about them. Extending this idea further, perhaps the fact that we think there could have been something at origin, means that perhaps it exists at least as a perception of collective human belief, but
  7. 7. maybe not in a physical reality? Can nothing exist? Surely in existing it is something, it exists as nothing, and therefore is. Therefore there must have been something, even if defined as nothing. These are rhetorical arguments which do not offer anything in the way of an explanation, but may be important in a more philosophical sense, helping humans deal with the great uncertainties inherent in facing oblivion, and using semantics to challenge and expand our comprehension. Infinites.. If something grows in size, by definition it takes forever to become infinite. Therefore, if our Universe is infinite in size today then it must also have been infinite in the past. Furthermore, it must already have been infinite in size at the moment of the Big Bang. Though the primordial singularity is described an infinitely small, at this point it may have been everything. This introduces the philosophical concept of differing infinites, which at the very least utterly counterintuitive to human comprehension. Time Our definition of time is another victim of the big bang. Can we say that the Big Bang ‘happened’ at some definite moment in time? The problem is in General Relativity, time itself is hypothesized to have began at the Big Bang. Furthermore, in an area of infinite mass (such as the primordial singularity), relativity demands that gravitational time dilation would essentially cause time stand still. The Big Bang cannot even be considered as the ‘first event’ since that would require it to have happened within time. If time was essentially static at this point (essentially moving infinitely slow), ‘when’ did the big bang happen? Einstein himself held unusual views about time. He believed the flow of time to be illusory and even expressed it when consoling the bereaved widow of a close friend. He told her that she should take comfort knowing that the present moment is no more special than any other in the past or the future; all times exist together. This however doesn’t make it any easier for the layman to grasp.
  8. 8. More Big Bang Questions Apart from a string of existential headaches, the origins of the big bang have been the catalyst for an explosion of new physical theories. The questions asked by an expanding universe have produced many wildly disparate, tentative answers at the cutting edge of science. One theory says the universe began as the result of the motion of a particle falling towards a black hole singularity, and that our universe exists locked inside an Einstein-Rosen black hole.(Poplawski 2009) Another argues the big bang was the result of a collision between two membranes floating in higher-dimensional space; an idea dubbed the Ekpyrotic Universe. (Khoury et al. 2001) Yet Another says that our universe was created as a bubble in energy fluctuations, in the seething quantum foam of a different, parent universe. This multiverse has no beginning or ending, and the theory is known as the Chaotic Inflation.(Linde 1986) Asides from the three mentioned above there are many, many more theories dealing with origin. Evidence supporting the big bang As optical technology and mathematical tools have evolved, the expanding universe has been strengthened by observational evidence. Redshift The first piece of evidence comes from Hubble’ Law. When a large number of galaxies are studied, it might be expected that roughly half would be blue-shifted and half red-shifted. This would be if the overall universe were static and the galaxies were moving randomly. This however, is not the case. On a smaller scale, galaxies close to the milky-way are converging with mutual gravitational attraction (Courteau 2000), but the majority of galactic observations see them moving away in accordance with Hubble’s law(Collins et al. 1986) The ratio of the velocity and a galaxy’s distance is now established at a constant, termed the Hubble parameter. Its value is now estimated to be around seventy kilometers per second per megaparsec, where a megaparsec is the distance light travels in about three million years.
  9. 9. Cosmic background radiation Secondly if the universe was initially extremely hot, as the singularity suggests, we should notice some remnant of this heat. In 1948 George Gamow predicted that if the Big Bang had occurred, the radiation from it should be observable in the microwave portion of the spectrum(Alpher et al. 1948). However, the technology for observing at these wavelengths did not yet exist to test his theory. In 1965, Radioastronomers Arno Penzias and Robert Wilson accidentally discovered a 2.725 degree Kelvin Cosmic Microwave Background radiation (CMB) throughout the entire universe. This is thought to be the energy that Gamow predicted. Penzias and Wilson shared in the 1978 Nobel Prize for Physics for their discovery. Later observations of cyanogen excitation in molecular clouds provide further support for the CMB. Cyanogen is a gas which responds to photons emitted from the CMB. The observed level of cyanogen excitation is consistent with direct satellite measurements of the cosmic microwave background radiation (Roth & Meyer 1995), and also agrees remarkably well with the Cosmic Background Explorer Satellite’s (COBE) measurements.
  10. 10. Spectrum of the Cosmic Microwave Background Radiation as measured by the COBE satellite. Within the quoted errors, the spectrum is precisely that of a perfect black-body at radiation temperature T = 2.728 ± 0.002 K(Fixsen & Mather 2002) Although we are unable to ‘see’ it, all of this is the footprint for our primordial fireball (a black body object) and strong evidence for the hot big bang hypothesis. Cosmic Neutrino Background Additional evidence comes from the existence of ripples of primordial origin in the Cosmic Neutrino Background (Trotta & Melchiorri 2005). Measurement of these ripples was made by combining data produced by the NASA WMAP (Wilkinson Microwave Anisotropy Probe) satellite and the Sloan Digital Sky Survey. These neutrinos are thought to have decoupled from the singularity when the universe was around 1-2 seconds old. It is estimated that today the CNB has a temperature of roughly 1.95K
  11. 11. Standard Candles In Distant Galaxies All type 1a supernovas are believed to shine with approximately the same absolute magnitude of brightness. The absolute magnitude for the Type Ia supernovae has been calibrated to be M = -19.33 0.25 (Universe Review n.d.) Suppose one observes 2 such supernova, and one appears to be 4 times brighter than the other. If the expansion of space were constant, the redshift of the dimmer supernova would be twice the redshift of the brighter one. Graphing redshift vs. brightness would yield a straight line, and if the expansion were decelerating, the line would curve downward. Studies of these supernova show an upward trend (an accelerating universe) (Phillips 1993). Because of this, scientists tentatively conclude that the expansion is accelerating. However, there is significant variation in the brightness of the supernovas; the intrinsic colours of Type Ia supernovae at maximum light are not identical, and the curve of the graph is very close to a straight line. More measurements at greater distances are required before we can be completely certain of the results. Olber’s Paradox If the galaxies were distributed according to the inverse square law in space, it is calculated that the light flux in the night sky would be at least as bright as the average star. ‘Dark’ background space would glow with the light from an infinite field of stars (Wesson 1991). However, the expansion of the universe ensures that the flux is constantly reduced as the universe expands, the light has further to travel, consequentially it is made fainter. Thus, the Visible Universe (our tiny corner of space) does have an observable edge (a limit on how much light gets to us) even if the Universe as a whole does not. This is caused by expansion. Finally, we can turn Olbers’ paradox on its head and make the statement the real proof that the Big Bang happened is that it gets dark at night. (Al-Khalili 1999) Conclusion Today ample evidence outweighs challenges to the expanding universe
  12. 12. hypothesis. The big bang and expanding universe are arguably the new cosmic paradigm. However, the scenario poses more questions than it has answered. Mainly in what caused the event, and what could have happened before it. In this way, these theories are the stepping stones for more scientific understanding to come. Understanding conditions at origin could be very important in formulating a Grand Unified Theory which could very possibly unite all the fundamental interactions in physics. Though we still have ample questions to answer, the relentless march of science has contributed to less and less uncertainty in understanding the Universe’s origins. Religious fundamentalists may be unwilling to confront this directly, but as extent of the known Universe expands, the God of The Gaps shrinks. With a coherent understanding of the beginning of the universe, Religion’s place may be confined purely to dealing with the end of the universe and the death of physical consciousness (if such a thing is true). And Perhaps one day science will get to that as well? Whatever Happens, Everything Ends. Cosmology is a purely observational science, it is very hard for us to create physical experiments which simulate the early universe. This is because we cannot observe past the point that photons were energetically bound in the early universe (the cosmic dark age), regardless of how good
  13. 13. our optics become. Nor can we properly simulate the bizarre conditions in which the universe began, as we may never know what they are. However, technology such as particle accelerators may allow us to peak into the fundamental building blocks of matter by smashing hadrons into the quark gluon plasma which is thought to have permeated the universe at origin (Masera & Alice Collaboration Project 2003). This may help us answer questions associated with the singularity; such as the origin of mass, where missing antimatter may have gone, and perhaps allow us a peak at extra dimensions.(CERN 2008) Finally, an expanding universe also deals with issue of mortality (by making it unavoidable, on a cosmic scale!). At this point, there are 3 main scenarios for the end. A Big Crunch in which we are annihilated in a contracting, superheated, superdense universe. A Big Rip in which a repulsive force in accelerating universe eventually overcomes all the other forces, and literally tears matter and all it’s constituents apart. Finally there is Heat Death, in which eventual entropy conquers everything, and we are left with a cold ‘dead’ universe where even fundamental particles have decayed. The full transition of mass to energy is made complete. Many physicists, such as Hawking; see time as a measurement of entropy. The universe, in its current expanding direction, is becoming more and more disordered- entropy is increases and has been doing so since the inception of the universe, Like a sun that cools into cosmic darkness, a building that surrenders to gravity, or a person who succumbs to age, as time progresses, the ultimate movement is always towards disorder. Perhaps it isn’t elegant, perhaps it’s hard to deal with, but who said the universe had to be fair? An universe in motion may be an easy concept to grasp intellectually, but it’s eschatological implications could be terrifying to the human mind that cannot properly comprehend infinites or the void. References Al-Khalili, J., 1999. Black holes, wormholes & time machines , Bristol UK ;;Philadelphia PA: Institute of Physics Pub.
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  17. 17. Wesson, P.S., 1991. Olbers's paradox and the spectral intensity of the extragalactic background light. The Astrophysical Journal , 367, 399.