De voorspelling van antimaterie

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1 De voorspelling van antimaterie
Paul Dirac voorspelde het bestaan van het positron in 1928 Dirac’s vergelijking impliceert: positron massa = elektron massa positron lading = +e The first of these is antimatter, predicted by the British theoretical physicist Dirac in 1928 when he was developing an equation to describe the behaviour of the electron. Dirac was a very shy man; you see it in his demeanour as he gives a lecture. However the respect in which he is held is shown by his plaque in Westminster Abbey, placed there in 1995, which is reputedly the only equation in the Abbey. For Dirac the equation was obvious; however he could only find a solution to it describing the behaviour of the electron if there was also another solution which seemed to describe something with negative energy. This solution he eventually ascribed to the positron, the antiparticle of the electron.

2 De voorspelling van antimaterie
Dirac AntiDirac The first of these is antimatter, predicted by the British theoretical physicist Dirac in 1928 when he was developing an equation to describe the behaviour of the electron. Dirac was a very shy man; you see it in his demeanour as he gives a lecture. However the respect in which he is held is shown by his plaque in Westminster Abbey, placed there in 1995, which is reputedly the only equation in the Abbey. For Dirac the equation was obvious; however he could only find a solution to it describing the behaviour of the electron if there was also another solution which seemed to describe something with negative energy. This solution he eventually ascribed to the positron, the antiparticle of the electron. De enige vergelijking in Westminster Abbey?

3 E = mc2 e Wat is antimaterie?
+ - Elektronen en positronen annihileren en produceren g-straling (energie) E = mc2 The simplest way to describe antimatter is in terms of its behaviour - when particle and antiparticle meet they annihilate and their mass is turned into energy in the form of g-rays, also called photons. This process is governed by the second and last equation you will see this evening, and surely known to the whole audience - Einstein’s famous equation E=mc2. Not only is this true for electrons and positrons, it also occurs for quarks and anti-quarks and more complicated objects like protons and anti-protons. You would also be in trouble if you met your anti-you. However this possibility is still someway off; it was not until 1996 that anti-hydrogen, the simplest anti-atom was produced. Energie en materie zijn equivalent Energie kan naar materie getransformeerd worden en vica versa.

4 De ontdekking van antimaterie
Four years later the positron was discovered by the American Carl Anderson in one of his pictures of the tracks of particles in a detector known as a cloud chamber. This device was in a magnetic field produced by the coils of cable you see in the photograph. The magnetic field has the effect of bending charged particles. From the direction of bend it is deduced that the particle has positive charge. From the amount of energy it loses as it passes through the plate in the middle of the chamber it is possible to deduce its mass. Note the size of his detector. Later we will see others, somewhat larger, but with similar features. We now know that all particles have antiparticles and I will now take a minute or two to discuss antimatter since it is not just the stuff of Star Trek science fiction, it is also science fact. Anderson (1932) ontdekte het door Dirac voorspelde positron

5 Antimaterie is meest efficiënte energiedrager
Neem 1 gram antimaterie Dit levert E = 2mc2 Waarom factor 2? = 2(0.001 kg)(3x108 m/s)2 = 1.8 x 1014 J aan energie!!! Energieverbruik per persoon per jaar 150 GJ/jaar = 1.5 x 1011 J/jaar Antimaterie is meest efficiënte energiedrager

6 Het ATHENA experiment op CERN
CERN 1996: 9 antiatomen gemaakt CERN experiment ATHENA in 2002: antiatomen waterstof gemaakt Star Trek’s warp drive? Alle antiatomen op CERN gemaakt in een jaar: 100 W lamp, kwartier

7 Antimaterie Voor ieder deeltje bestaat er een antideeltje.
Tegenovergestelde eigenschappen: bijvoorbeeld de lading, e- en e+. Maak deeltjes en antideeltjes uit energie volgens E = mc2. Als een deeltje en antideeltje van dezelfde soort elkaar ontmoeten, dan verdwijnen ze in een flits van pure energie. Dit heet annihilatie. De vrijgekomen energie volgt ook uit E = mc2.

8 Grootste versnellers staan op CERN - Geneve
Ring van 27 km omtrek 100 meter onder de grond 4 interactie punten waar protonen botsen

9 E = mc2 g Elektron-positron botsingen e- e+
Annihilatie produceert energie - mini Big Bang Elektron (materie) Deeltjes en antideeltjes worden geproduceerd Positron antimaterie g e- e+ E = mc2

10 E=mc2: creatie van Materie en Antimaterie
Als materie uit energie wordt gemaakt, dan wordt er altijd evenveel antimaterie geproduceerd

11 Big Bang Cosmology Evenveel materie & antimaterie Materie domineert!

12 Big Bang Expansie van sterrenstelsels Big Bang Nucleosynthese
Edwin Hubble in 1929 expansie Big Bang Nucleosynthese CBR – Kosmische microgolf achtergrondstraling 24% primeordial 4He Gamow (1948) materie  0.04 kritisch Bell Telephone Lab. in 1965

13 Ontdekking v/h nagloeien
1965 Penzias & Wilson

14 NRC HANDELSBLAD Woensdag 12 februari 2003
Hubble Deep Field – overal materie Proton/foton 1/109 Woensdag 12 februari 2003

15 Speuren naar antimaterie in het universum
Omringend universum wordt door materie gedomineerd: Afwezigheid van anti-nuclei in kosmische straling in ons sterrenstelsel Geen annihilatiestraling van sterrenstelsels in botsing met antimaterie Alpha Magnetic Spectrometer

16 Speuren naar antimaterie in het universum
Het zichtbare universum wordt door materie gedomineerd!

17 Waar is de antimaterie gebleven?
In 1966 liet Andrei Sakharov zien dat creatie van netto baryongetal vereist: Processen met schending van baryongetal (bijv. protonverval) Geen evenwichtstoestand tijdens expansie van het universum Schending van C en CP symmetrieen

18 Materie-antimaterie asymmetrie
In 1964 werd ontdekt dat het radioactive verval van antimaterie een klein verschil vertoont met het verval van materie (CP schending). Sindsdien is de voortgang in ons begrip erg traag geweest: experimenten zijn uiterst moeilijk (VU – SLAC, CERN); astronomie is een waarnemende wetenschap, geen experimentele (we kunnen de Big Bang niet herhalen). MAAR we hebben geleerd dat de materie-antimaterie asymmetrie enkel kan optreden indien er drie paar quarks bestaan.

19 Nobel Price in Physics 2008 Yoichiro Nambu Makoto Kobayashi Toshihide Maskawa "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics" "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature"

20 Evolutie met materie-antimaterie symmetrie
Uiteindelijk zal zulk een universum enkel uit fotonen bestaan (dat is bijna het geval voor ons Universum – kosmische microgolf achtergrond) For example, let’s try to understand what would happen to the Universe if at that time, a billionth of a second after the beginning, equal numbers of particles and antiparticles exist. This is a reasonable assumption since it is what we observe in our experiments at accelerators where the energy density is the same. The density of particles at this time is enormous. They collide and annihilate producing photons, which then turn back into particle and antiparticle pairs. The number of photons and particle-antiparticle pairs is roughly equal. Eventually, after about one second, the energy of the photons is too small for any more particle-antiparticle pairs to be produced and only the annihilation process continues. Since we started with equal numbers of particles and antiparticles we cannot have an excess of either and, indeed only photons will be left in the Universe. This is manifestly what did not happen - our Universe is different. However it’s not so different. The Universe does contain huge numbers of photons, by now at very low energy and known as the ‘microwave background’. Measurements shown that there are about 109 photons in the Universe for every proton. How this number arose is an area of great interest to particle physicists and astrophysicists.

21 Een Universum met asymmetrie
Misschien veranderde een in elke 109 antiquarks in een quark tijdens de geboorte van ons Universum Na de materie-antimaterie annihilatie bleef een kleine hoeveelheid materie over (ongeveer een proton voor 109 fotonen) Ignoring the third condition, except to say that non-thermal equilibrium almost certainly occurred early in the Universe, let’s see the consequences of our discussion. Let’s imagine one antiparticle in 109 turning into a particle in the first billionth of a second after the Big Bang. The same annihilation process we saw earlier continues, but when it has finished we now have one particle left over for every 109 photons, just as we find in the Universe today. We thus conclude that, although matter consists of two different quarks and the electron, we could not be here today if the other quarks did not exist to play their crucial role in the first billionth of a second of the life of the Universe. Thus we may not have an answer to Rabi’s question about the muon - Who ordered that? - but we may begin to see why these other objects have to exist.

22 Relatie met het heelal BigBang scenarium Gebruik laboratorium experimenten om de fysica wetten vast te leggen voor de condities van het beginnend heelal >10-10 s na t = 0…

23 Wat er gebeurde op tijden voor 10-10 s na de Big Bang is onzeker
What happened in that era is therefore debated amongst physicists with great fervour. Nevertheless there are some general principles that we understand.