by Marcus Chown
Despite the fact that the mass of the neutrino is extremely small, neutrinos could still have important consequences for the universe. Prodigious quantities of them flood out of the Sun, not to mention every other star in the galaxy, and they were also created in uncountable numbers by processes in the Big Bang that created the universe 13.82 billion years ago.33 Neutrinos are the most elusive entities in nature, as close to nothing as anything we know of and apparently spectators rather than participants in the life of the cosmos. However, they turn out to be the second most common particles in nature, after photons. In terms of sheer numbers, we live in a neutrino-and-photon universe.
So even though neutrinos have ultra-tiny masses, they could still make up a significant fraction of the mass of the universe. In fact, if there exists an as-yet-undiscovered massive neutrino, neutrinos could be a component of the universe’s mysterious dark matter, which is known to outweigh the visible stars and galaxies by a factor of about six.34
But this is not the only way in which neutrinos could be the key to the universe. Experiments showing differences between the rates of creation and destruction of neutrinos and antineutrinos hint at a fundamental asymmetry between matter and antimatter. It may one day explain one of the biggest mysteries of the universe: why we live in a universe of matter that contains virtually no antimatter.35
Once Reines’ team detected the neutrino in 1956, he was far from finished. In 1987, he was a member of one of two teams that detected a total of nineteen neutrinos coming from another star. Supernova 1987A marked the detonation of a massive star in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. It was the first supernova seen in our galaxy for four hundred years.
When a massive star reaches the end of its life, it runs out of fuel to generate the internal heat necessary to oppose the gravity trying to crush it. As the core shrinks catastrophically, heating up to ferocious temperatures, the elements built up by nuclear reactions over the star’s lifetime come apart into protons, neutrons and electrons. Electrons are squeezed into protons to create a superdense ball known as a ‘neutron core’, in the process unleashing a tsunami of neutrinos. In the case of Supernova 1987A, this amounted to 1058 – or ten billion trillion trillion trillion trillion – neutrinos. Although a supernova can shine as bright as a galaxy of 100 billion stars, it turns out that a mere 1 per cent of its energy is emitted in the form of light; 99 per cent consists of neutrinos.
It is the neutrinos flooding out of the star that turn the implosion of the core into a supernova explosion, blowing the exterior envelope of the star into space. This contains elements which enrich interstellar gas clouds, destined to become stellar nurseries when they fragment into the new generations of stars. Without neutrinos, the elements essential for life would remain locked up inside stars. ‘Why does nature need them? What use are they?’ asks the English physicist Frank Close.36 The remarkable truth of Pauli’s ‘impossible particle’ is that it is more critical to the universe than anyone could possibly have imagined. Without it, you would not be reading these words; in fact, you would not even have been born.
Notes
1 Proceedings of the 13th International Conference on Neutrino Physics & Astrophysics, edited by Jacob Schneps et al. (World Scientific, p. 575, 1989).
2 ‘Frederick Reines Dies at 80; Nobelist Discovered Neutrino’ by John Noble Wilford (New York Times, 28 August 1998: http://www.nytimes.com/1998/08/28/us/frederick-reines-dies-at-80-nobelist-discovered-neutrino.html).
3 KSU Physics Ernest Fox Nichols Lecture by Herald Kruse, 1 March 2010: https://www.phys.ksu.edu/alumni/nichols/2010/kruse-lecture.pdf.
4 ‘Deadly Legacy: Savannah River Site Near Aiken One of the Most Contaminated Places on Earth’ by Doug Pardue (The Post and Courier, 21 May 2017: https://www.postandcourier.com/news/deadly-legacy-savannah-river-site-near-aiken-one-of-the/article_d325f494-12ff-11e7-9579-6b0721ccae53.html).
5 Ibid.
6 Quoted in Great Physicists by William Cropper (Oxford University Press, New York, 2001, p. 257). Pauli is reputed to have said this during his student days in Munich, when Einstein lectured at a crowded colloquium.
7 ‘The Average Energy of Disintegration of Radium E’ by C. D. Ellis and W. A. Wooster (Proceedings of the Royal Society, vol. A 117, 1 December 1927, p. 109).
8 Letter to Oskar Klein, 10 March 1930.
9 ‘The Romance that Led to a Legendary Science Burn’ by Esther Inglis-Arkell (Gizmodo, 17 February 2015: https://io9.gizmodo.com/the-romance-that-led-to-a-legendary-science-burn-1686216120).
10 No Time to Be Brief: A Scientific Biography of Wolfgang Pauli by Charles Enz (Oxford University Press, 2010, p. 210).
11 Letter from Wolfgang Pauli to Gregor Wentzel, 7 September 1931.
12 Pauli was so badly affected by the break-up of his marriage that after his divorce on 26 November 1930, he appealed to none other than Carl Jung for counselling. The great psychoanalyst recognised immediately that Pauli was an academic whose social life had been neglected at the expense of his intellectual life. He judged that Pauli needed a woman, not a man, to bring some balance back into his affairs, and referred him to his pupil. Erna Rosenbaum, a relatively inexperienced analyst, asked Pauli to send her his dreams so that she might interpret them, something she may have regretted when, over time, he sent her a total of 1,300 (No Time to Be Brief: A Scientific Biography of Wolfgang Pauli by Charles Enz (Oxford University Press, 2010, p. 243)).
13 The Historical Development of Quantum Theory, Volume 1, Part 1. The Quantum Theory of Planck, Einstein, Bohr, and Sommerfeld. Its Foundation and the Rise of Its Difficulties, 1900–25 by Jagdish Mehra and Helmut Rechenberg (Springer, Heidelberg, 1982).
14 ‘Pauli’s Letter of 4 December 1930: The Proposal of the Neutrino’: https://fermatslibrary.com/s/the-proposal-of-the-neutrino.
15 h/2*pi, where h is Planck’s constant, a tiny quantity equal to 6.62607004 × 10–34 m2kg/s.
16 The Last Man Who Knew Everything by David Schwartz (Basic Books, New York, 2018).
17 ‘Fundamental Forces’ (Eric Weisstein’s World of Physics: http://scienceworld.wolfram.com/physics/FundamentalForces.html).
18 Wolfgang Pauli. Writings on Physics and Philosophy, edited by C. P. Enz and K. Von Meyenn (Springer, Berlin, 1994).
19 Wonder Boys by Michael Chabon (Fourth Estate, London, 2008).
20 The God Particle: If the Universe Is the Answer, What Is the Question? by Leon Lederman and Dick Teresi (Mariner Books, Wilmington, 2006).
21 ‘Discovery or Manufacture?’ Tarner Lecture, 1938. Reprinted in The Philosophy of Physical Science by Arthur Eddington (University of Michigan Press, Ann Arbor, 1958).
22 ‘The Reines–Cowan Experiments: Detecting the Poltergeist’: http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-97-2534-02.
23 ‘A Proposed Experiment to Detect the Free Neutrino’ by F. Reines and C. L. Cowan, Jr (Physical Review, vol. 90, 1 May 1953, p. 492).
24 KSU Physics Ernest Fox Nichols Lecture by Herald Kruse, 1 March 2010: https://www.phys.ksu.edu/alumni/nichols/2010/kruse-lecture.pdf.
25 Ibid.
26 ‘Detection of the Free Neutrino: A Confirmation’ by C. L. Cowan, Jr, F. Reines, F. B. Harrison, H. W. Kruse and A. D. McGuire (Science, vol. 124, 20 July 1956, p. 103). ‘The Neutrino’ by Frederick Reines and Clyde Cowan, Jr (Nature, vol. 178, p. 446).
27 Unfortunately, Clyde Cowan died in 1974 and so did not share the Nobel Prize with Frederick Reines.
28 Possibly, Reines had confused events with an earlier episode with a drunken Pauli. In late 1953, when news had reached Pauli of Reines and Cowan’s first faint hint of the existence of the neutrino at Hanford, he and his friends finished their dinner and climbed the Uetliberg mountain above Zurich. On the way down later that evening, Pauli, wobbly from the wine he had drunk at the meal, had to be supported on both sides by his friends to avoid falling over (No Time to Be Brief: A Scientific Biography of Wolfgang Pauli by Charles Enz (Oxford University Pr
ess, 2010)).
29 KSU Physics Ernest Fox Nichols Lecture by Herald Kruse, 1 March 2010: https://www.phys.ksu.edu/alumni/nichols/2010/kruse-lecture.pdf.
30 For the discovery of the solar neutrino problem, Ray Davis shared the 2002 Nobel Prize in Physics.
31 The proof that neutrinos oscillate between three ‘flavours’ as they fly through space and therefore have mass was obtained independently by Takaaki Kajita at the Super-Kamiokande detector in Japan and Arthur McDonald at the Sudbury Neutrino Observatory in Canada. They shared the 2015 Nobel Prize in Physics.
32 So John Updike was incorrect to say, in his poem ‘Cosmic Gall’, that neutrinos ‘have no charge and have no mass’, and he was also wrong to say that neutrinos ‘do not interact at all’ since they interact (admittedly rarely) via the weak nuclear force, and of course via gravity. But I like the poem!
33 One of the most amazing images in the history of science was created by the Super-Kamiokande neutrino detector, deep underground in the Japanese Alps. It is an image of the Sun taken at night, not looking up at the sky but down through 12,700 kilometres of the Earth, and generated not by light but by neutrinos. If there is ever an illustration of how, to neutrinos, the Earth is the most rarefied of fogs, it is that image.
34 If there were many more than three generations of neutrinos, the gravity of their extra mass would have braked the expansion of the Big Bang fireball, causing the universe to stay denser and hotter for longer, so that nuclear reactions forged a different amount of helium than astronomers observe. It is possible to have more than three types, however, if they are of a type known as ‘sterile’. The normal neutrinos, although antisocial, do interact with normal matter occasionally via nature’s ‘weak nuclear force’. Sterile neutrinos would not even do this; their sole interaction with normal matter would be via the gravitational force.
35 ‘Neutrinos Suggest Solution to Mystery of Universe’s Existence’ by Katia Moskvitch (Quanta Magazine, 12 December 2017: https://www.quantamagazine.org/neutrinos-suggest-solution-to-mystery-of-universes-existence-20171212/).
36 Neutrino by Frank Close (Oxford University Press, Oxford, 2010).
* We now know that in beta decay, a ‘neutron’ in a nucleus changes into a proton. Since both protons and neutrons are composite particles made of triplets of ‘quarks’, we can be more specific: a down-quark in a neutron changes into an up-quark, turning the neutron into a proton.
† This is not strictly true. It is ‘angular momentum’ that is conserved. Spin is simply intrinsic angular momentum.
‡ Cosmic rays are high-speed atomic nuclei, mostly protons, from space. Low-energy ones come from the Sun, while high-energy ones probably come from supernovae. The origin of ultra-high-energy cosmic rays, particles millions of times more energetic than anything we can currently produce on Earth, is one of the great unsolved puzzles of astronomy.
§ In quantum theory, fundamental forces are caused by the exchange of force-carrying particles. A weak force is therefore one in which force-carrying particles are exchanged rarely, and a strong force is one in which they are exchanged frequently. This is why neutrinos, which are subject to weak force, interact with other particles so rarely.
¶ A light year is the distance light travels in a vacuum in a year. It is roughly equal to ten trillion kilometres.
6
The day without a yesterday
The radiation left over from the Big Bang is the same as that in our microwave oven but very much less powerful. It would heat your pizza only to minus 270.4ºC – not much good for defrosting the pizza, let alone cooking it!
STEPHEN HAWKING
The elements were cooked in less time than it takes to cook a dish of duck and roast potatoes.
GEORGE GAMOW
Holmdel, New Jersey, Spring 1965
For the best part of a year, they had faced nothing but delay and frustration. For the best part of a year, a stubborn hiss of radio static had prevented them from doing the slightest bit of astronomy. But now, as they put on overalls and boots and climbed into the gaping mouth of the twenty-foot ‘horn’ with their stiff brooms, Arno Penzias and Robert Wilson were convinced that their nightmare would soon be over.
The horn, a giant metal funnel the size of a railway carriage, stood on Crawford Hill, a wooded knoll near Holmdel, New Jersey. It belonged to Bell Labs, part of AT&T, the giant American phone company, and it had been built in 1959 to test the feasibility of beaming phone and TV signals around the Earth via a ring of communications satellites.
The idea of such satellites had been proposed by the British science-fiction writer Arthur C. Clarke.1 In an article in the October 1945 issue of Wireless World, he had pointed out that the further a body is from the Earth, the weaker it is gripped by the planet’s gravity and so the more sluggishly it orbits. At a special distance – 35,787 kilometres from the Earth’s centre – the body circles so slowly that it orbits the planet once every twenty-four hours. Observed from the ground, such a satellite would appear to hang motionless in the sky.
Clarke’s idea was to have three communications satellites equally spaced around this ‘geosynchronous orbit’. Sending a phone conversation from England to, say, Australia would then involve broadcasting a radio signal from a transmitter in England to the nearest satellite, which would relay it to the next satellite and the next one, before beaming it back down to a receiver in Australia.
In 1945, the idea of a planet girdled by communications satellites was the wildest of science fiction. But Clarke, while serving as a radar technician with the Royal Air Force, had vivid memories of the Nazi bombardment of London by V2 ballistic missiles, and had realised that such rockets could just as easily be fired straight upwards as at a distant city. He was not alone in thinking this. On 24 October 1946, a V2 rocket captured by the Americans and launched from the White Sands Missile Range in New Mexico escaped the atmosphere and took the very first photograph of the Earth from space.
Clarke’s belief that science fiction was rapidly becoming science fact was confirmed on 4 October 1957, when the Russians launched the first satellite. Sputnik 1, a metal sphere fifty-eight centimetres in diameter that beeped incessantly as it circled the Earth, terrified the Americans, who feared the Russians dropping an H-bomb on a city like New York. It marked the birth of the ‘Space Age’ and kick-started the space race between the world’s two superpowers. Almost immediately, AT&T and many other companies realised that they needed to get into the satellite business, and fast.
The best way to communicate with a satellite was via ‘microwaves’, radio waves with short wavelengths of between a few centimetres and a few tens of centimetres. The problem with microwaves is that everything glows with them – people, trees, buildings, the sky, and so on. The challenge for the AT&T engineers was to pick up a weak microwave signal from a tiny source in the sky – a satellite – amid much stronger signals coming from every other direction.
The microwave horn on Crawford Hill, the construction of which had begun in the summer of 1959, was the AT&T engineers’ solution. When its twenty-square-foot opening was directed at a point-like object in the sky, microwaves from all other sources had difficulty bending their way into the horn, meaning that only microwaves from the desired source were funnelled down to the tapered end of the horn, where they were detected by a radio receiver.
The first test of the twenty-foot horn was Echo 1, a kind of Stone Age communications satellite launched by NASA in 1960. It was, in effect, a 100-foot-diameter silvered inflatable beach ball, off which radio waves from the microwave horn could be bounced and picked up (a radio horn has the ability to both transmit and receive radio waves). Hot on the heels of Echo 1 came the first modern communications satellite. Telstar did not simply passively bounce back radio waves transmitted from the ground; it boosted them in strength before retransmitting them. In 1962, it relayed the first-ever television pictures between America and Europe. Telstar caused a global sensation, and pop records were even recorded about t
he satellite.
By 1963, when the world had well and truly entered the age of communications satellites, AT&T no longer needed the twenty-foot horn on Crawford Hill, so decided to hand it over to some radio astronomers. This was not an altruistic act. Such astronomers were in the business of detecting ultra-weak signals in the sky, just as AT&T was, and the company reasoned that it might benefit from giving the horn to science. In fact, it was not AT&T’s first venture into astronomy. In the 1930s, the company had employed Karl Jansky to identify sources of radio interference which were playing havoc with wireless reception. By picking up radio waves from the Sun and a mysterious source at the centre of the Milky Way that later turned out to be a ‘supermassive’ black hole, Jansky earned the title of the ‘father of radio astronomy’, and the unit of radio power is called a Jansky in his honour.
Arno Penzias, a dynamic thirty-one-year-old New Yorker whose family were refugees from Nazi Germany, had arrived at Holmdel in 1962. Robert Wilson, a taciturn twenty-eight-year-old from Caltech in Pasadena, came in early 1964, and in the summer of that year, the pair teamed up.
Wilson had the suspicion that the Milky Way, our galaxy, which is shaped rather like a CD, might be embedded in a spherical halo of extremely cold hydrogen gas left over from the galaxy’s formation. If so, the gas would be glowing with very faint radio waves, and the horn, because of its ability to reject spurious radio waves from its surroundings, had a unique ability to pick up such a signal.
