ANGELS & DEMONS
SNIPPET LESSON PLAN: ANTIMATTER
Ages: 14+: High School;
Length: Snippet: 6.5 minutes.
Students will learn about the properties that make antimatter different from matter at fundamental level and the energy released in different kinds of explosions.
The film clips provide an excellent supplement to vary the classroom experience for a unit on fundamental particles of physics.
DESCRIPTION OF SNIPPET
A flask containing recently produced antimatter is stolen from the research facility at CERN and used to threaten Vatican City with mass destruction. The explosion actually takes place but high up in the sky with only minor destruction at ground level.
So, what is antimatter? Most explanations given in books and documentaries do not answer this question. Instead, they tell us how antimatter behaves, what it does when it comes in contact with “ordinary” matter. It is repeatedly said that antimatter is in a form that is opposite to ordinary matter. But in which sense is it “opposite”?
The usual answer is in terms of electric charge: the “opposite” of an electron would be a particle with an identical mass but positive electric charge. This anti-electron is also known as a positron. However, if it all comes down to electric charge one might ask what all the hype is about. We are familiar with objects of opposite electric charge and how they attract each other without an apocalyptic explosion. There must be something deeper about antimatter than just opposite electric charges.
Paul Dirac first predicted the existence of antimatter in the specific case of the anti-electron, which has an electrical charge opposite to that of the electron. However, the fundamental difference between the two is of a deeper nature and the different electrical charge is just one manifestation of that fundamental difference. In the case of a neutron and an antineutron, for example, their electrical charge obviously does not play any role, as they both are electrically neutral.
In order to take the explanation of the constituents of matter one level deeper, scientists talk in terms of quarks. Quarks and electrons are members of a family of fundamental particles known as leptons. The famous Higgs boson is also lepton. They are the most fundamental level of matter according to the Standard Model.
***Quarks are ascribed various fundamental properties which are called charges, the electrical charge being just one of them. Other quark charges are known as isospin, color and flavor (the names of the latter two not being at all related to their usual meanings). In antiquarks both electrical and other charges are of opposite sign, while other properties such as mass, mean lifetime and spin remain unchanged. It happens similarly with leptons and their own different set of fundamental properties. Let us therefore bear in mind that matter and antimatter are “opposite” in a more fundamental way than just electrical charge, even though this is commonly used as the easiest way to explain it.
Of course, transposing the question of what antimatter is to the next deepest level may still not seem to provide a satisfactory answer: why would an encounter between quarks and antiquarks with their opposite charges be so different from letting two electrically charged particles of opposite signs attract each other up to their closest possible approach? Why do scientists and sci-fi authors alike talk about destructive annihilation?
In order to understand this a little better, let us review how Paul Dirac imagined it. Paul Dirac was the scientist whose theoretical work first hinted at the existence of antimatter. Even if his imagined model for antimatter is now superseded, it helps us to appreciate the fundamental difference between attraction between opposite charges and matter-antimatter annihilation.
To proceed we need to introduce the concept of “negative” energy. The “ordinary” energy we are familiar with in our everyday lives is always positive. In Physics, energy is understood as the “capacity of producing a physical change on an object”. So, the passage of electrons through a thin wire heats it up and can even make it give out light, as we can see in incandescent bulbs (the term “negative” for the electrical charge of electrons being just a label with no more fundamental meaning). Or gravitational attraction is able to pull a ball down a slope and speed it up. In both cases the energy used to produce changes in temperature and speed, respectively, is a positive number. It is like cash: you may have more or less, or none at all, but the amount you can handle is always positive. However, as in the case of money, you could imagine handling debt. If this debt is put on paper, you could imagine the corresponding pieces of paper as “negative” money.
So, in order to explain some results from his theoretical calculations, on the specific case of the electron, Dirac postulated that there is an endless “sea” of electrons that goes unnoticed because in its usual state, that sea is completely full and occupies the whole of space. On occasions some very energetic physical process is able to extract one electron from that sea, and we are left with an empty “hole” in its place. A hole in a sea of negative electrical charges behaves as a positive charge, and this is what we would detect as an anti-electron or positron. If an electron encounters the positron it will “fill in “the hole, disappearing in the undetected electron sea and releasing the vast amount of energy that went into extracting the electron that left the hole.
There we have a fundamental difference between different electrical charges attracting each other (such as a proton and an electron) and the annihilation of antimatter and matter when brought together (such as a positron and an electron, but also a neutron and an antineutron, etc.).
Particle physicists are making fast progress in the creation, trapping, and storage of antimatter, in particular of antiprotons, or anti-Hydrogen nuclei (as a Hydrogen nucleus actually is a single proton). Vast amounts of energies, which can only be generated in huge particle accelerators like those at Fermilab (http://www.fnal.gov/) or CERN (http://public.web.cern.ch/public/) are needed to create tiny amounts of anti-hydrogen. But trapping and storing it poses an even bigger challenge, as it needs to be kept away from any ordinary matter in order to avoid annihilation.
The fiction of Angels and Demons anticipated the progress that is being made in reality in this regard. It depicts the successful creation of a chunk of antimatter and its storage in a special flask that keeps it away from the walls of the container and is powered by a battery that needs to be reloaded or replaced. The amount of anti-hydrogen produced, and therefore the magnitude of the explosion that can occur if annihilation takes place is fictional.
1. Read the Helpful Background section of this Guide.
2. Be familiar with the location of the clips on the DVD, check for accuracy of the minute and second locations of the clips on the DVD, and practice getting quickly from one film clip to the other.
Clip #1 Minute 4:45 to 7:15 (2 minutes, 30 seconds). This shows the movie´s depiction of the moment in which antimatter is produced at CERN and is trapped and kept in storage in specially devised flasks prepared to keep it in suspension.
Clip #2 (optional): you may want to show the clip from 18:30 to 19:00 (30 seconds) in which the scientist summoned by the Vatican explains the destructive power of the stolen antimatter flask. If this proves unpractical, this information can be verbally mentioned together with the fact that the flask was stolen with the purpose of letting it explode in the Vatican in order to destroy the Catholic Church.
Clip #3 Minute 1:44:00 to 1:47:30 (3 minutes, 30 seconds). The stolen flask is about the run out of the power that keeps antimatter suspended and away from ordinary matter, and there is no time to reload or change the battery. The flask is flown up to the sky where it finally explodes. No mass destruction occurs at ground level, but the shock wave causes certain damage.
3. Cue the DVD to the beginning of the first clip.
STEP BY STEP
1. Show the first and (optionally) the second clips to the class. If you are not showing the second clip tell the class that the flask was stolen with the intention to let it explode within the Vatican due to its huge destructive power, mentioned in the clip to be of 5 Megatons (about 5 times the most powerful nuclear weapons currently available in US arsenals, and 330 times the Hiroshima bomb – for reference, the most powerful bomb ever, the Tsar hydrogen bomb was tested by the Soviet Union at 50 Megatons). The movie then tells the story of the chase of the flask in order to avoid such destruction.
2. Ask students what they imagine under the term antimatter. Many ideas and concepts will be mentioned, containing the words “opposite” and “annihilation”. By further questioning these concepts you can show them that it is probably unclear for all or most in which sense antimatter is “opposed” to ordinary matter.
3. Explain antimatter as outlined in the Helpful Background section above.
4. As a concluding finale, show the third clip with the explosion. We see the huge explosion take place, preceded by a kind of suctioning implosion. The latter was undoubtedly meant to represent the kind of void we intuitively associate with the word “annihilation”, but in reality, we would directly a more ordinary-looking explosion, as it all comes down to the release of energy, regardless of the underlying physical process. This leads to point 5.
5. Concluding Assignment Suggestions: Students can be asked to put this explosion into context by comparing the efficiency in energy release (i.e. destructive power) of different types of explosives: quick combustion in explosions involving oxygen reacting with flammable substances; the fision reaction in which an atom is split; the fusion reaction that is the basis for hydrogen bombs, and finally; and most efficiently, annihilation of matter and antimatter. The aim is that they come up with a scale like this:
- Exothermic chemical reactions transform mass into energy (according to E=mc2) with an efficiency of 1/100.000.000 (meaning that one part in one hundred million of the mass involved is actually converted into energy, the rest comes out still as mass);
- Fision reactions do so with an efficiency of 1/100;
- Matter-antimatter annihilation transform matter into energy completely!
Due to the rapidly progressing nature of this field, we do not give direct links to the latest news on research on antimatter, which would soon become obsolete. The best source for the latest advances is the aforementioned sites of Fermilab (http://www.fnal.gov/) or CERN (http://public.web.cern.ch/public/). Both sites include sections aimed specifically at educational purposes.
An excellent book on this topic at popular-science level is “Antimatter” by Frank Close (Oxford University Press, 2009).