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This section explores some of the scientific concepts featured in the His Dark Materials books.

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Dark Matter

An image of a galaxy cluster showing the
effect of a ring-like dark matter structure
One of the key elements in His Dark Materials, the mysterious Dust, is revealed to be dark matter. Dark matter is matter which doesn’t interact with electromagnetic radiation which means it cannot be seen. Dark matter cannot be observed directly, but there is much indirect evidence of its existence such as the movements of galaxies and galaxy clusters, temperature distribution of gas inside galaxies and gravitational lensing. Gravitational lensing means that when light passes near a massive object, gravity bends the light beam so that the object acts like a lens focusing the light which passes near it. This phenomenon is predicted by the theory of general relativity. Dark matter has gravity in the same way that ordinary matter does, but its composition is unknown. It could be some sort of previously unknown elementary particles. Dark matter fills the entire universe and there is in fact more of it than ordinary matter. Cosmological studies indicate that 22 % of the total energy density in the universe is composed of dark matter while only 4 % is regular, visible matter. The remaining 74 % is dark energy, which is even more mysterious.

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The many-worlds interpretation of Quantum Mechanics

In His Dark Materials there are numerous parallel universes. Lord Asriel tells Lyra that these worlds came into being as a result of possibility and that whenever there are several possible outcomes (at the level of atomic particles) the Universe splits into several parallel worlds each with a different outcome realized. This idea is based on the many-worlds interpretation (MWI) of quantum mechanics.

Quantum mechanics is a fundamental branch of physics which studies energy and matter interactions especially at the level of elementary particles. It says that some physical properties, such as the energy of an atom, are not continuously distributed, but can only have certain discrete values. Quantum mechanics (QM) has been tested and proven to work with astonishing accuracy; however, some elements of QM appear paradoxical and bizarre. There are several schools of thought (or interpretations of QM) attempting to explain these apparent paradoxes. The many-worlds theory is one of these interpretations.

The idea behind many of the apparent paradoxes of QM is that quantum mechanical systems (for example atoms) can have many possible outcomes and that they exist in all possible states at once. Yet, when an observation is made the system is always in one particular state. The conventional interpretation of QM, namely the Copenhagen interpretation, states that the observation collapses the system into one of the possible outcomes. The many-worlds interpretation does not assume such collapse, but postulates that the system splits into many branches each with different possibility realized. It could be said that the whole universe splits into several and we observe whichever outcome happens to be in our world. According to the MWI, the parallel universes are completely separate as opposed to His Dark Materials where one could travel from one world to another. As far as the predictions of the theory are concerned they are the same as those of the Copenhagen interpretation and so far there hasn’t been any way to tell which one is correct.

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Quantum Entanglement

Quantum entanglement is a phenomenon in quantum mechanics in which two (or more) objects are “linked”, or “entangled”, in such a way that the properties of one are correlated to the properties of the other. In His Dark Materials quantum entanglement is given as an explanation of how the lodestone resonator, a communication device used by the Gallivespians, works. Chevalier Tialys explains that in the world of the Gallivespians there is a way of entangling all the particles of a common lodestone and splitting it in two. That way the two parts resonate together and offer a way to communicate over great distances.

In reality it is indeed possible to prepare a quantum mechanical system consisting of several particles so that their physical properties are correlated. For example two electrons can have an entangled spin (angular momentum) so that if one electron is observed to be “spin-up” then the other will inevitably be observed to be “spin-down”. There is no possible outcome where the spins of both electrons are the same. If a person performs a measurement on one part of the entangled system that will immediately affect the other part. However, according to our current understanding it would be impossible to use quantum entanglement for communication because there is no way of predicting which state of a particular quantum system will be observed. Basically if one person makes a measurement on one part of the entangled system that also affects the other part, however, if the person on the other side performs a measurement on his part of the system he will not be able to tell whether the first person has done anything to the system or not. The receiver wouldn’t be able to tell the difference between the transmitter sending him information and a random measurement.

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String Theory

The Calabi-Yau manifold model of
extra dimensions in string theory
In the Amber Spyglass, when Mrs. Coulter is approaching the Clouded Mountain, the stronghold of the Authority, it is noted that it reminded her of a theory proposed by one of the scientists that there are more spatial dimensions than the familiar three, but the additional ones exist on the very small scale. Most likely this is a reference to string theory.

String theory is a model of physics according to which everything is made of so called strings, extremely small one-dimensional objects which vibrate at certain frequencies. Thus all the fundamental particles in nature are different vibrations of these objects. According to string theory there are indeed six or seven extra dimensions, but they are too small to be observed.

In His Dark Materials it is also said that this very same scientist had constructed a model of these extra dimensions, which probably refers to a Calabi-Yau manifold which is indeed a model of extra dimensions in string theory.

String theory is an attempt to combine quantum mechanics and gravity, which is one of the main goals in modern science. However, so far the theory hasn’t been confirmed experimentally.

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The Aurora

The aurora as seen from space
Several key characters in His Dark Materials are fascinated with the aurora, a mysterious occurrence of colourful light displays which can be observed in the far North. The aurora is an atmospheric phenomenon which occurs around the magnetic poles of the Earth at altitudes above 100 kilometres. The aurora occurring in the northern is called “aurora borealis” or “Northern Lights” and the one in southern hemisphere is known as “aurora australis” or “Southern Lights”.

The aurora is a result of charged particles (mostly electrons but also protons and various ions) entering the Earth’s atmosphere and hitting the atoms and molecules of various atmospheric gases. The particles come from magnetosphere which is a region of space around the Earth dominated by the Earth’s magnetic field. The magnetosphere captures charged particles that are radiated by the sun (solar wind) and also particles from the Earth’s ionosphere which is the uppermost layer of the atmosphere where particles are ionized by solar radiation. Some of the particles in the magnetosphere are guided along the field lines of the Earth’s magnetic field and enter the atmosphere in the vicinity of the magnetic poles where they collide with the atoms of atmospheric gases.

The charged particles of the magnetosphere possess a great amount of energy when they collide with the atoms and molecules in the atmosphere and part of that energy is transferred to the atoms and molecules they collide with. The atoms and molecules become “excited” which means that their energy is elevated above their normal energy level. However, the excited states are unstable and the atom (or molecule) soon returns to its usual energy level and radiates the excess energy as light (photons). This is where the light of the aurora comes from. Different atmospheric gases emit light of different wavelengths which is why the lights of the aurora have different colours. Because the higher layers of the atmosphere consist mostly of atomic oxygen the lights of the aurora are usually dominated by green and red colours, but molecular nitrogen often adds blue and violet.

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