DOCSLIB.ORG

The Age of the Universe

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Age of the Universe the age of the universe WE’RE OBSESSED WITH measuring time. We celebrate new years, anniversaries and birthdays. We dedicate entire sports to seeing how long someone takes to get from one point to another. We take joy in counting the minutes before the end of a particularly boring English lesson (or before the beginning of a fantastically engrossing session of Physics). So it was only a matter of time before we made the ultimate measurement: how old is time itself? What is the age of the Universe? THE NIGHT SKY is dark. It might appear brighter than daylight. Of sound like an obvious statement, course, we know this isn’t true: but someone had to point it out if you take this sheet of paper before we realised that it actually to the middle of a field, in the has quite profound implications. middle of the night, and with no We used to think that the artificial light, you’re not going Universe was infinite - that is, it to be able to read it. Which can was always in existence, and went only mean one thing: the Universe on, forever, in every direction. But isn’t infinte at all. It must have a in 1823, the German astronomer finite age, and the light from the Heinrich Wilhelm Olbers realised most distant stars hasn’t had the that if this was true, then the time to reach us. night sky would be filled with an infinte number of stars and Heinrich Wilhelm Olbers Right: the original NEARLY A HUNDRED years later, velocity-distance graph the American astronomer Edwin plotted by Hubble Hubble used a technique known (below left). Although as redshift (see “painting the he had the right idea, his sky red”) to investigate the speed actual results were quite at which distant galaxies were inaccurate; we have since been able to produce more moving away from us. He plotted velocity-distance accurate results using the a graph (left) Hubble Space Telescope and found that the distance of a (below right). galaxy was more or less directly proportional to its speed; that is, a galaxy twice as far away from us as another galaxy, was moving twice as fast. This was an astonishing discovery, and not what anyone expected. What’s more, using some pretty basic physics and maths, it leads to quite a startling conclusion. If an object emitting a wave is painting the sky red: redshift moving away from you, then the You know that a wave, such as the light smaller frequency than blue light. So wave appears “stretched”, and the emitted from a star, has a wavelength as the wavelength gets longer, and the wavelength appears longer. - the distance between two consecutive frequency gets smaller, the light appears peaks or troughs. However, if the object redder - which is why this phenomenon is moving away from you, then the wave is known as redshift. If you measure the seems stretched and so the wavelength value by which the frequency decreases, appears longer. In turn, this means that you can then use a simple formula to its frequency appears smaller. calculate the speed at which the object is moving away from you - and this The frequency of visible light determines is what Hubble used to determine the what colour it is - red light has a speed of distant galaxies. IMAGINE THAT YOU’RE standing you are, that you’re observing further reading! on the side of a particularly long something similar to what Hubble If you want to find out more about stretch of road, when, at exactly saw in the stars: their speed away the origin of our universe, and its 12:00pm, two cars pass you at from you is proportional to their potential fates, check out A Brief exactly the same time. One is distance from you. But you have History of Time by Stephen Hawking, travelling at 30mph, and the an extra piece of information: or An Elegant Universe by Brian other is travelling at 60mph. At there was a time when both cars Greene. Although be warned: the first you take no notice, but then where at the same place at the former isn’t that brief, and the latter at 1:00pm, exactly one hour later, same time. Applying the same isn’t always that elegant! you decide to look through your logic to the stars, there must have telescope to see where they are. been a time when everything in references As expected, the first car is 30 the Universe was also at the same BW Carroll, DA Ostlie, An Introduction miles away, and the second car is place at the same time. We call it to Modern Astrophysics, 2nd Edition (2007, Addison Wesley, San Francisco). 60 miles away. You notice, being The Big Bang. the particularly bright person that If the distance to several objects is proportional to the speed at which they’re moving away from you, then there must have been a time when they were all in the same place at the same time. THE BIG BANG was when believed to be about 2.33 x 10-18 everything came into existence s-1. This means we now have a – so if we can calculate how relation between v and r, known long ago that was, then we’ll as Hubble’s Law – which states, know how old the Universe is. quite simply, that v = H0r. If we You know that quantities that rearrange the formula, we can are proportional to each other see that the Hubble Constant is are related by a proportionality equal to speed over distance (1, constant, and in this case, the left). Take the reciprocal, and we speed, v, and the distance, r, are have something that is equal to related by the Hubble Constant, distance over speed… or time(2). H0. We can find it by calculating So if we take the reciprocal of the the gradient of the graph, which Hubble Constant, we’ve got what turns out to be quite a simple we’re looking for. The age of the task, since it’s a straight line Universe. 14 billion years. - using data obtained from the Hubble Space Telescope, it is Who wants to buy the candles? LIST OF IMAGE SOURCES: Portrait of Olbers: Images of the Milky Way used http://upload.wikimedia.org/ for backgrounds: wikipedia/commons/a/a9/ http://www.astropix.com/HTML/ Heinrich_Wilhelm_Olbers_2.jpg D_SUM_S/MILKYWAY.HTM Portrait of Hubble: http://www.depts.ttu.edu/ http://lh4.ggpht.com/_ communications/news/stories/ opzY8FwgzCI/RxcpXLtIEwI/ images/milkyway_brunier-large. AAAAAAAAACA/y-d9N7wpREA/ jpg edwin+hubble.bmp http://apod.nasa.gov/apod/ The Hubble Space Telescope: image/0501/milkyway_garlick.jpg http://miguellopes.files. Portrait of Olbers: wordpress.com/2007/01/hubble. jpg Hubble’s Original Diagram: http://spiff.rit.edu/classes/ phys240/lectures/expand/ hubble_fig1_small.gif.
Load more

Recommended publications
  • The Age of the Universe Transcript
    The Age of the Universe Transcript Date: Wednesday, 6 February 2013 - 1:00PM Location: Museum of London 6 February 2013 The Age of The Universe Professor Carolin Crawford Introduction The idea that the Universe might have an age is a relatively new concept, one that became recognised only during the past century. Even as it became understood that individual objects, such as stars, have finite lives surrounded by a birth and an end, the encompassing cosmos was always regarded as a static and eternal framework. The change in our thinking has underpinned cosmology, the science concerned with the structure and the evolution of the Universe as a whole. Before we turn to the whole cosmos then, let us start our story nearer to home, with the difficulty of solving what might appear a simpler problem, determining the age of the Earth. Age of the Earth The fact that our planet has evolved at all arose predominantly from the work of 19th century geologists, and in particular, the understanding of how sedimentary rocks had been set down as an accumulation of layers over extraordinarily long periods of time. The remains of creatures trapped in these layers as fossils clearly did not resemble any currently living, but there was disagreement about how long a time had passed since they had died. The cooling earth The first attempt to age the Earth based on physics rather than geology came from Lord Kelvin at the end of the 19th Century. Assuming that the whole planet would have started from a completely molten state, he then calculated how long it would take for the surface layers of Earth to cool to their present temperature.
    [Show full text]
  • Hubble's Law and the Expanding Universe
    COMMENTARY COMMENTARY Hubble’s Law and the expanding universe Neta A. Bahcall1 the expansion rate is constant in all direc- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 tions at any given time, this rate changes with time throughout the life of the uni- verse. When expressed as a function of cos- In one of the most famous classic papers presented the observational evidence for one H t in the annals of science, Edwin Hubble’s of science’s greatest discoveries—the expand- mic time, ( ), it is known as the Hubble 1929 PNAS article on the observed relation inguniverse.Hubbleshowedthatgalaxiesare Parameter. The expansion rate at the pres- between distance and recession velocity of receding away from us with a velocity that is ent time, Ho, is about 70 km/s/Mpc (where 1 Mpc = 106 parsec = 3.26 × 106 light-y). galaxies—the Hubble Law—unveiled the proportional to their distance from us: more The inverse of the Hubble Constant is the expanding universe and forever changed our distant galaxies recede faster than nearby gal- Hubble Time, tH = d/v = 1/H ; it reflects understanding of the cosmos. It inaugurated axies. Hubble’s classic graph of the observed o the time since a linear cosmic expansion has the field of observational cosmology that has velocity vs. distance for nearby galaxies is begun (extrapolating a linear Hubble Law uncovered an amazingly vast universe that presented in Fig. 1; this graph has become back to time t = 0); it is thus related to has been expanding and evolving for 14 bil- a scientific landmark that is regularly repro- the age of the Universe from the Big-Bang lion years and contains dark matter, dark duced in astronomy textbooks.
    [Show full text]
  • The Reionization of Cosmic Hydrogen by the First Galaxies Abstract 1
    David Goodstein’s Cosmology Book The Reionization of Cosmic Hydrogen by the First Galaxies Abraham Loeb Department of Astronomy, Harvard University, 60 Garden St., Cambridge MA, 02138 Abstract Cosmology is by now a mature experimental science. We are privileged to live at a time when the story of genesis (how the Universe started and developed) can be critically explored by direct observations. Looking deep into the Universe through powerful telescopes, we can see images of the Universe when it was younger because of the finite time it takes light to travel to us from distant sources. Existing data sets include an image of the Universe when it was 0.4 million years old (in the form of the cosmic microwave background), as well as images of individual galaxies when the Universe was older than a billion years. But there is a serious challenge: in between these two epochs was a period when the Universe was dark, stars had not yet formed, and the cosmic microwave background no longer traced the distribution of matter. And this is precisely the most interesting period, when the primordial soup evolved into the rich zoo of objects we now see. The observers are moving ahead along several fronts. The first involves the construction of large infrared telescopes on the ground and in space, that will provide us with new photos of the first galaxies. Current plans include ground-based telescopes which are 24-42 meter in diameter, and NASA’s successor to the Hubble Space Telescope, called the James Webb Space Telescope. In addition, several observational groups around the globe are constructing radio arrays that will be capable of mapping the three-dimensional distribution of cosmic hydrogen in the infant Universe.
    [Show full text]
  • Galaxies at High Redshift Mauro Giavalisco
    eaa.iop.org DOI: 10.1888/0333750888/1669 Galaxies at High Redshift Mauro Giavalisco From Encyclopedia of Astronomy & Astrophysics P. Murdin © IOP Publishing Ltd 2006 ISBN: 0333750888 Institute of Physics Publishing Bristol and Philadelphia Downloaded on Thu Mar 02 23:08:45 GMT 2006 [131.215.103.76] Terms and Conditions Galaxies at High Redshift E NCYCLOPEDIA OF A STRONOMY AND A STROPHYSICS Galaxies at High Redshift that is progressively higher for objects that are separated in space by larger distances. If the recession velocity between Galaxies at high REDSHIFT are very distant galaxies and, two objects is small compared with the speed of light, since light propagates through space at a finite speed of its value is directly proportional to the distance between approximately 300 000 km s−1, they appear to an observer them, namely v = H d on the Earth as they were in a very remote past, when r 0 the light departed them, carrying information on their H properties at that time. Observations of objects with very where the constant of proportionality 0 is called the high redshifts play a central role in cosmology because ‘HUBBLE CONSTANT’. For larger recession velocities this they provide insight into the epochs and the mechanisms relation is replaced by a more general one calculated from the theory of general relativity. In each cases, the value of GALAXY FORMATION, if one can reach redshifts that are high H enough to correspond to the cosmic epochs when galaxies of 0 provides the recession velocity of a pair of galaxies were forming their first populations of stars and began to separated by unitary distance, and hence sets the rate of shine light throughout space.
    [Show full text]
  • The Anthropic Principle and Multiple Universe Hypotheses Oren Kreps
    The Anthropic Principle and Multiple Universe Hypotheses Oren Kreps Contents Abstract ........................................................................................................................................... 1 Introduction ..................................................................................................................................... 1 Section 1: The Fine-Tuning Argument and the Anthropic Principle .............................................. 3 The Improbability of a Life-Sustaining Universe ....................................................................... 3 Does God Explain Fine-Tuning? ................................................................................................ 4 The Anthropic Principle .............................................................................................................. 7 The Multiverse Premise ............................................................................................................ 10 Three Classes of Coincidence ................................................................................................... 13 Can The Existence of Sapient Life Justify the Multiverse? ...................................................... 16 How unlikely is fine-tuning? .................................................................................................... 17 Section 2: Multiverse Theories ..................................................................................................... 18 Many universes or all possible
    [Show full text]
  • Year 1 Cosmology Results from the Dark Energy Survey
    Year 1 Cosmology Results from the Dark Energy Survey Elisabeth Krause on behalf of the Dark Energy Survey collaboration TeVPA 2017, Columbus OH Our Simple Universe On large scales, the Universe can be modeled with remarkably few parameters age of the Universe geometry of space density of atoms density of matter amplitude of fluctuations scale dependence of fluctuations [of course, details often not quite as simple] Our Puzzling Universe Ordinary Matter “Dark Energy” accelerates the expansion 5% dominates the total energy density smoothly distributed 25% acceleration first measured by SN 1998 “Dark Matter” 70% Our Puzzling Universe Ordinary Matter “Dark Energy” accelerates the expansion 5% dominates the total energy density smoothly distributed 25% acceleration first measured by SN 1998 “Dark Matter” next frontier: understand cosmological constant Λ: w ≡P/ϱ=-1? 70% magnitude of Λ very surprising dynamic dark energy varying in time and space, w(a)? breakdown of GR? Theoretical Alternatives to Dark Energy Many new DE/modified gravity theories developed over last decades Most can be categorized based on how they break GR: The only local, second-order gravitational field equations that can be derived from a four-dimensional action that is constructed solely from the metric tensor, and admitting Bianchi identities, are GR + Λ. Lovelock’s theorem (1969) [subject to viability conditions] Theoretical Alternatives to Dark Energy Many new DE/modified gravity theories developed over last decades Most can be categorized based on how they break GR: The only local, second-order gravitational field equations that can be derived from a four-dimensional action that is constructed solely from the metric tensor, and admitting Bianchi identities, are GR + Λ.
    [Show full text]
  • Cosmic Microwave Background
    1 29. Cosmic Microwave Background 29. Cosmic Microwave Background Revised August 2019 by D. Scott (U. of British Columbia) and G.F. Smoot (HKUST; Paris U.; UC Berkeley; LBNL). 29.1 Introduction The energy content in electromagnetic radiation from beyond our Galaxy is dominated by the cosmic microwave background (CMB), discovered in 1965 [1]. The spectrum of the CMB is well described by a blackbody function with T = 2.7255 K. This spectral form is a main supporting pillar of the hot Big Bang model for the Universe. The lack of any observed deviations from a 7 blackbody spectrum constrains physical processes over cosmic history at redshifts z ∼< 10 (see earlier versions of this review). Currently the key CMB observable is the angular variation in temperature (or intensity) corre- lations, and to a growing extent polarization [2–4]. Since the first detection of these anisotropies by the Cosmic Background Explorer (COBE) satellite [5], there has been intense activity to map the sky at increasing levels of sensitivity and angular resolution by ground-based and balloon-borne measurements. These were joined in 2003 by the first results from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP)[6], which were improved upon by analyses of data added every 2 years, culminating in the 9-year results [7]. In 2013 we had the first results [8] from the third generation CMB satellite, ESA’s Planck mission [9,10], which were enhanced by results from the 2015 Planck data release [11, 12], and then the final 2018 Planck data release [13, 14]. Additionally, CMB an- isotropies have been extended to smaller angular scales by ground-based experiments, particularly the Atacama Cosmology Telescope (ACT) [15] and the South Pole Telescope (SPT) [16].
    [Show full text]
  • Arxiv:2002.11464V1 [Physics.Gen-Ph] 13 Feb 2020 a Function of the Angles Θ and Φ in the Sky Is Shown in Fig
    Flat Space, Dark Energy, and the Cosmic Microwave Background Kevin Cahill Department of Physics and Astronomy University of New Mexico Albuquerque, New Mexico 87106 (Dated: February 27, 2020) This paper reviews some of the results of the Planck collaboration and shows how to compute the distance from the surface of last scattering, the distance from the farthest object that will ever be observed, and the maximum radius of a density fluctuation in the plasma of the CMB. It then explains how these distances together with well-known astronomical facts imply that space is flat or nearly flat and that dark energy is 69% of the energy of the universe. I. COSMIC MICROWAVE BACKGROUND RADIATION The cosmic microwave background (CMB) was predicted by Gamow in 1948 [1], estimated to be at a temperature of 5 K by Alpher and Herman in 1950 [2], and discovered by Penzias and Wilson in 1965 [3]. It has been observed in increasing detail by Roll and Wilkinson in 1966 [4], by the Cosmic Background Explorer (COBE) collaboration in 1989{1993 [5, 6], by the Wilkinson Microwave Anisotropy Probe (WMAP) collaboration in 2001{2013 [7, 8], and by the Planck collaboration in 2009{2019 [9{12]. The Planck collaboration measured CMB radiation at nine frequencies from 30 to 857 6 GHz by using a satellite at the Lagrange point L2 in the Earth's shadow some 1.5 10 km × farther from the Sun [11, 12]. Their plot of the temperature T (θ; φ) of the CMB radiation as arXiv:2002.11464v1 [physics.gen-ph] 13 Feb 2020 a function of the angles θ and φ in the sky is shown in Fig.
    [Show full text]
  • Lecture 14: the Age of the Universe
    The Age of the Universe One somewhat low-pro¯le but important test of cosmological models is that the age of the universe implied by the models agrees with the age estimated using various methods. Here we'll talk about the age we get from models, and in the next lecture will discuss several observational handles on the true age. For a change of pace, and to give us some practice in evaluating complicated equations, we will start with the equation for the lookback time provided by Hogg in astro-ph/9905116, and see whether the units, limits, etc. make sense. The lookback time from now (z = 0) back to redshift z means the time that would have elapsed on the wristwatch of an observer moving with the Hubble ow between those redshifts. Hogg's expression is: 1 z dz0 tL = 0 0 3 0 2 : (1) H0 Z0 (1 + z ) ­(1 + z ) + ­k(1 + z ) + ­¤ p Here H0 is the current value of the Hubble parameter, and ­, ­k, and ­¤ each indicate their current (z = 0) values. Does this expression behave as it should? See Figure 1 for a graphical representation. As always, we check units ¯rst. Recall that the Hubble parameter has units of inverse time, so the prefactor 1=H0 has units of time. The integral is dimensionless because the redshift is, so indeed the units are correct. Our second easy check is to note that tL must increase with increasing z. Since the integrand is always positive, this is indeed the case. Our third simple check is to note that smaller H0 should imply a larger time back to a given redshift, because H0 = a=a_ today.
    [Show full text]
  • The Hubble Constant
    Astro-2: History of the Universe Lecture 3; April 11 2013 Previously.. On Astro-2 • The universe is much larger than the Milky Way (Gpc vs kpc) • There are billion of galaxies, the Milky Way is average Joe galaxy • Most galaxies can be classified based on their appearance as – Elliptical – Lenticular – Spiral – Irregular • Spirals rotate and have young stars, gas and dust • Ellipticals do not rotate and have old stars, no gas nor dust Previously.. On Astro-2 • It is difficult but very important to figure out the size and distance of things in the universe • One way astronomers do that is by using “standard candles”. • Examples of standard candles are cepheids variable stars and supernovae Two important questions • Are there black holes in galaxies? • What is a black hole? Two important questions • How do we know it? • Exactly in the same way we know the mass of the sun, or the mass of galaxies for that matter! Two important questions • If the universe is homogeneous and isotropic how do stars know that there is a center of a galaxy to orbit around? • It is a matter of scale: • On scale much larger than a Mpc the universe is homogeneous • On scales much smaller than a Mpc the universe is NOT homogenous, there are galaxies, for example. Assignments. Due Friday 4/19 4PM 1. To TA: Universe 24.42 - 24.43 - 24.45 2. On your own: 24.17 thru 24.30 Today.. On Astro-2 1. How far are galaxies? 2. Measuring velocities and “redshifts”. 3. Hubble’s law.
    [Show full text]
  • 22. Big-Bang Cosmology
    1 22. Big-Bang Cosmology 22. Big-Bang Cosmology Revised August 2019 by K.A. Olive (Minnesota U.) and J.A. Peacock (Edinburgh U.). 22.1 Introduction to Standard Big-Bang Model The observed expansion of the Universe [1–3] is a natural (almost inevitable) result of any homogeneous and isotropic cosmological model based on general relativity. However, by itself, the Hubble expansion does not provide sufficient evidence for what we generally refer to as the Big-Bang model of cosmology. While general relativity is in principle capable of describing the cosmology of any given distribution of matter, it is extremely fortunate that our Universe appears to be homogeneous and isotropic on large scales. Together, homogeneity and isotropy allow us to extend the Copernican Principle to the Cosmological Principle, stating that all spatial positions in the Universe are essentially equivalent. The formulation of the Big-Bang model began in the 1940s with the work of George Gamow and his collaborators, Ralph Alpher and Robert Herman. In order to account for the possibility that the abundances of the elements had a cosmological origin, they proposed that the early Universe was once very hot and dense (enough so as to allow for the nucleosynthetic processing of hydrogen), and has subsequently expanded and cooled to its present state [4,5]. In 1948, Alpher and Herman predicted that a direct consequence of this model is the presence of a relic background radiation with a temperature of order a few K [6,7]. Of course this radiation was observed 16 years later as the Cosmic Microwave Background (CMB) [8].
    [Show full text]
  • The Problem of the Age of the Universe and the Earliest Galaxies
    The Problem of the Age of the Universe and the Earliest Galaxies Roger Ellman Abstract A number of years ago the estimates of astronomers and astrophysicists were that the earliest galaxies took about 2½ - 3 billion years to form, that is, that they did not appear until 2.5-3.0 billion years after the Big Bang. Those estimates were based on analysis of the processes involved in star formation and in the aggregation and “clumping” of matter in the early universe. Since then improved equipment and techniques [e.g. Keck and Hubble telescopes and gravitational lensing] have resulted in reports of observation of early galaxies having stars that formed as early as 300 million years after the Big Bang. Such new data has led to the abandonment of the several billion years estimates of the time required for star and galaxy formation; however, an alternative response to the data would be to re-examine the Hubble theory from which the age of the universe and the distance to high redshift objects is determined. Roger Ellman, The-Origin Foundation, Inc. 320 Gemma Circle, Santa Rosa, CA 95404, USA [email protected] http://www.The-Origin.org 1 The Problem of the Age of the Universe and the Earliest Galaxies Roger Ellman Background of the Problem A number of years ago the estimates of astronomers and astrophysicists were that the earliest galaxies took about 2½ - 3 billion years to form, that is, that they did not appear until 2.5-3.0 billion years after the Big Bang. Those estimates were based on analysis of the processes involved in star formation and in the aggregation and “clumping” of matter in the early universe.
    [Show full text]