Oxford Literary Festival talk

I gave a soapbox talk in the Blackwell’s book tent in the Bodleian Quad in Oxford at lunchtime on Saturday 6th April, on my new book: “MATTER, A Very Short Introduction”, which was published by Oxford University Press on 28th March 2019. Excellent turnout, well received with all seats taken, and standing room only. Lots of interesting questions, and books were signed. Thanks to my daughter, Rebecca, for the photo.

Nine faces of matter

Here is a distillation of nine key ideas from my forthcoming book: “Matter – A Very Short Introduction” (Oxford University Press to be published in 2018).

In my book, I have focussed on key concepts using hardly any equations. These include the properties of atoms, the different forms of ordinary matter, how matter is defined as mass and energy, weird quantum matter, antimatter, fundamental particles, the origin of the elements, and mysterious dark matter and dark energy.

  1. What is matter?

Matter is the stuff from which you and I and all the things in the world around you are made. If you had the most powerful microscope imaginable you could look inside your body and see that you are made of atoms. Inside every atom is a tiny nucleus and orbiting the nucleus is a cloud of electrons. The nucleus is made out of protons and neutrons, and by zooming in on a nuclear particle you would find that inside it there are even smaller particles, quarks. Quarks are the smallest particles that we have seen, and lie at the limit of resolution of the most powerful microscopes of matter. As far as we know, electrons and quarks are not made from anything smaller and so they are called fundamental particles.

2. Atoms

Take an apple and chop it up into smaller and smaller pieces.  Eventually a point is reached where no more chopping is possible, revealing the ultimate graininess of matter, atoms. The word atom comes from the Greek word atomos, meaning indivisible. This prescient idea that the world is made of atoms was conceived of 2500 years ago by the Ancient Greek philosophers Leucippus and Democritus. Their conjecture was remarkable because atoms are too small to be seen with the unaided eye. The reality of atoms was only finally accepted in 1905 when Albert Einstein analysed the constant jiggling of tiny pollen grains suspended in water, being randomly battered by hordes of smaller unseen particles, the molecules. This jiggling about is called Brownian motion.

3. Different forms of matter

When large numbers of of atoms and molecules aggregate to form a piece of matter, they assemble into the lowest energy state available. The three familiar states of matter, solid, liquid and gas, result from the competition between the attractive forces between particles, and their thermal motion which pushes them apart. Temperature has a central role in controlling when, for example, water molecules join together to form ice or disperse as a gas, steam. At very high temperatures, electrons are knocked off atoms, and a gas transforms to the so-called fourth state of matter, an electrically conducting plasma. Plasmas occur naturally in the stars, lightning, and in high energy astronomical bodies.

4. Defining matter

What are the key defining properties of matter? Isaac Newton identified one as the inertial mass. This is a measure of the resistance (or inertia) that a body feels to being accelerated. An advanced view of matter emerged from  Einstein’s special theory of relativity; there,  space and time and merge into a single entity: spacetime, which is deformable, in the sense that different observers moving at high uniform speeds see lengths as being contracted and clocks running slowly. Mass and energy turn out to be the same thing, only expressed in different units. Large scale concentrations of rest mass and energy in the universe in the form of stars, galaxies, and black holes, exert gravitational influences which warp spacetime and bend light rays. Mass curves space, and the curvature of space in turn tells bodies how to move. The gravity that binds the Moon in its orbit is a result of the ‘dent’ in spacetime made by the mass of the Earth.

5. Quantum particles

On human size scales, we imagine lumps of matter moving through space along sharp classically defined trajectories. This Newtonian conception is more than adequate to get a man to the Moon and back. However on microscopic atomic scales, particles reveal their quantum wave nature, enabling them to spread out in space as fuzzy entities. In the quantum world one cannot speak of particles following sharp single trajectories, but only about the probabilities of particles following various motions and paths. Quantum theory describes nature very accurately and particles behave in a mind-boggling manner. They can for example pass through classically impenetrable barriers (quantum tunnelling), and occupy many states simultaneously. Quantum tunnelling occurs in the energy producing reactions in the heart of the Sun. Without this process we would not exist. All ordinary matter is made from two basic types of particles: matter particles are fermions (for example electrons), and force-carrying particles are bosons (for example the photons of light).

6. Quantum matter

While microscopic particles are governed by quantum laws, aggregates of particles can sometimes reveal large-scale quantum behaviour. In a coherent quantum fluid  billions of particles move together as a single entity, rather than moving around haphazardly as individuals. A metal contains vast numbers of free electrons which form a quantum fluid at ordinary temperatures. At very low temperatures some metals become superconductors and conduct electricity without any electrical resistance. There are also exotic atomic fluids, such as superfluid helium, in which the atoms move frictionlessly through extremely fine tubes, and appear to defy gravity by climbing out of a vessel.

7. Fundamental particles

In the 1920s, quantum theory was developed to describe particles moving at near-light speeds, and the theory predicted antimatter. The first antimatter particle discovered was the positron (a positively charged electron). When a positron encounters an electron, the two particles mutually annihilate each other, producing a burst of light. All the rest mass energy is converted to radiation energy. As quantum theory developed further, all of space was viewed as being filled by a number of quantum fields. Elementary particles such as electrons or quarks emerge from an ocean of quantum wave energy, as fluctuations in the underlying fields. One of these is the Higgs field which interacts with elementary particles to confer upon them their intrinsic masses. Most of the mass of ordinary matter (this mass resides in atomic nuclei) is associated with the quark force fields operating inside the nuclear particles.

8. Where do the elements come from?

The 92 naturally occurring chemical elements come from three sources. The lightest, hydrogen and helium, were made a short time after the Big Bang, 13.8 billion years ago. The middle weight elements, up to iron, were (and still are) being made inside the cores of burning stars by nuclear processes which release fusion energy. But to build elements heavier than iron, energy input is needed. This energy comes from the explosions of massive stars, supernovae; there, involving particles accelerated to extremely high energies. The remains of a supernova can contain an exotic, gravitationally collapsed object: a neutron star in which matter is squeezed so tightly that a teaspoon of would weigh as much as Mount Everest. All the  atoms in your body and in the solar system were made in the lives and deaths of stars, billions of years ago.

9. Dark matter and dark energy

The planets move in roughly circular orbits in the attractive gravitational field of the Sun, in which the outward centrifugal force of a planet is balanced by the inward force of gravity. Because the Sun’s gravity gets weaker the further out a planet is, orbital speeds in the solar system decrease with distance. This motion can be used to ‘weigh’ the Sun. The same method has been used to weigh spinning galaxies, containing trillions of stars, by measuring the rotational stellar speeds. However, it turns out that the speeds  do not decrease with distance from the centre, but are constant. This indicated that the masses of galaxies are much larger than we had previously thought, and could not be accounted for by the known masses of the stars and gas.  Galaxies therefore contain extra invisible ‘missing mass’, or ‘dark matter‘, in a mysterious form, one which exerts gravity but does not emit or absorb light. Searches for dark matter, either in the form of hypothetical subatomic particle or as other larger masses, have so far drawn a blank.

Even more enigmatic is dark energy. In the 1990s, the light from exploding stars (supernovae) in distant galaxies was used to measure the expansion of the universe. This showed that the galaxies  are further away than we had thought. The space, through which the light from the supernovae had travelled, had been stretched more than expected – the expansion of the universe is accelerating.  Dark energy is the name for whatever is believed to be causing this acceleration. Whatever dark matter and dark energy are (and we don’t know), they dominate the cosmos. Normal familiar matter, as discussed above, account for only 5% of everything there is. The remaining 95% is a complete mystery!

10 Interesting Things About Telescopes: Oxford Literary Festival Talk

Oxford Literary Festival: 25 March 2017: Talk in Blackwell’s Marquee

Telescopes: A Very Short Introduction

There are one hundred billion galaxies in the observable Universe, and each of them has a hundred billion stars. We know this because of one instrument: the telescope.

I am going to tell you 10 interesting things about telescopes …

  1. Who invented the telescope?

No one knows. The Romans knew about the focusing properties of water-filled glass spheres because Seneca wrote about them two thousand years ago. 400 years ago the availability of lenses in Europe lead to the discovery of the telescope. Two lenses are needed. The first lens collects the parallel rays of light from the object and focuses it. The second produces a parallel beam.

  1. What’s the most important property of a telescope?

It is its light collecting power. As the light from a star spreads out into larger volumes of space, it gets diluted. A star 10 times further away is 100 times dimmer.

Larger telescopes can see the most distant objects. Galileo’s spyglass could gather 64 times as much light as the naked eye. The largest 10-metre telescopes today collect 10 million times more.

The further away an object is, the longer it takes light to reach us. We can now observe galaxies 13 billion light years away and see back in time, almost to the Big Bang. Galaxies then looked very different from those today.

  1. Why is Galileo and his telescope so important?

In 1609 Galileo took a Dutch spyglass and increased the magnification from three to 20 times. The military and commercial significance of being able to see ships approaching Venice, before they became visible to the naked eye, was not lost on him. He gave a telescope to the doge, who rewarded him with a tenured professorship.

Galileo raised his telescope to the heavens and made discoveries of historic importance. His book “The Starry Messenger” lies in the Bodleian Library.

Galileo’s greatest discovery was of the four largest moons of Jupiter. It provided evidence for the Copernican heliocentric model of the solar system, and got him into a great deal of hot water with the church.

Although Galileo improved the telescope’s power, what was really important was what he did with it. He contributed to the overturn of a 2000-year old cosmology that had placed the Earth at the center of the Universe.

  1. Why do big telescopes have mirrors?

Big glass lenses are heavy and sag badly. The largest refractor ever made was the 1-metre telescope at Yerkes observatory of the University of Chicago.

Isaac Newton made the first 2½-inch reflecting telescope in 1668. There’s no size limit to a reflector, which uses a dish-shaped mirror to collect light.

William Herschel built many telescopes. But it was with a 6-inch reflector that he discovered Uranus, from his garden in Bath. There is an example of such a telescope in Oxford’s Museum of the History of Science.

The big 10-metre Keck telescopes use mirrors segmented into hexagons. They are located on a volcanic summit in Hawaii 4 km high.

They have looked into the heart of the Milky Way, and traced the orbits of stars, haplessly caught in the thrall of the supermassive black hole lurking there. Telescopes perform better high up, where the air is thinner, and less infrared is blocked.

  1. Why do we need space telescopes?

Our own atmosphere limits what we observe from the Earth. First the atmosphere blocks all the high-energy light from the cosmos. Second the atmosphere is turbulent. While turbulence makes the stars twinkle prettily, it blurs telescope images.

In space there is no atmosphere to limit the performance of telescopes, and they can realize their full potential. This applies across the whole of the spectrum: from gamma rays to radio.

  1. What can you see with a radio telescope?

The atmosphere is transparent to radio waves. Radio wavelengths are a million times longer than light, so the detail that a single dish can see is limited. The solution is to assemble many dishes as elements of a much larger telescope.

This opened up the Radio Universe – viewing the radio emission from Active Galaxies, spewing out vast quantities of energetic particles and radiation, and pulsars.

Pulsars are spinning neutron stars – matter so dense, that it is only one step away from a black hole.

A neutron star is the size of a city, and a teaspoonful weighs as much as a mountain!

Just by picking up this paper, I have used more energy than has ever been picked up by all the radio telescopes of the world!

  1. What are today’s big questions about the Universe?

They are:

  • What is dark matter?
  • What is dark energy?
  • How did the first galaxies form?


  • Are there habitable Earth-like exoplanets?

This includes the search for biomarkers – the fingerprints of extra-terrestrial: oxygen, carbon dioxide, and water.

  1. What is the next radio telescope?

It is the Square Kilometre Array, or SKA, which will have an aperture of one million square metres, and soon be the world’s largest scientific instrument.

It will bridge two continents, from South Africa, to Australia. Hundreds of radio dishes will be linked together, acting like a ‘zoom’ lens on a camera.

The SKA will observe gas clouds from the Cosmic Dawn. Its antennas will be sensitive enough to detect airport radar on a planet 50 light years away, and so could detect any extra-terrestrial signals. Within this distance there are over 100 stars similar to the Sun, many of which may possess Earthlike planets.

  1. What is the next space telescope?

It is the infrared, James Webb Space Telescope (or ‘Webb’ for short). It will be launched next year. Webb will have 100 times the resolution of the Hubble Space Telescope.

Why infrared?

The light from the earliest galaxies has been redshifted by the expansion of the Universe into the infrared part of the spectrum.

How do you squeeze Webb’s huge 6.5-metre mirror into a rocket?

Webb’s mirror is made from a mosaic of beryllium hexagons folded like origami. When the telescope is released, a million miles from the Earth, the segments will unfurl, like a butterfly emerging from a chrysalis.

Webb will peer inside cosmic nurseries where stars are born, search for planetary discs, and look for organic molecules and biomarkers. It will also search for the reflected light from exoplanets, which is difficult. It is like trying to see the dim light of a firefly next to a dazzling searchlight.

  1. What about the data?

In 400 years, the size of telescopes has doubled, every 30 years. Since the 1980s, the number of picture elements in light detectors has doubled every 2 years.

For the next telescopes therefore, we are talking about Big Data. The data rate will compete with the WWW – equivalent to 36 million year’s worth of high definition video!

The needles in the data haystack are the science discoveries. The big question is how to find them.

Two possibilities are:

  • ONE: Harnessing the eyes and brains of millions of volunteer citizen scientists to classify the data (e.g. the Zooniverse projects)
  • TWO: using autonomous pattern-recognition programmes to look for unusual features

To conclude: in addressing the key questions, the next telescopes will strain at the limits of what is technically possible.

Will telescopes show us that we are not alone in the Universe?                 

Oxford Literary Festival Talk

Was yesterday 25th March 2017  and went very well! There must have been around 100 people listening in Blackwell’s Marquee, on a beautiful sunny spring day. There was no electrical power and so no sound system; but I projected my voice to engage the audience. There were some interesting questions at the end – ranging from the emission mechanisms of pulsars, to the way that galaxies look when they are 13 billion light years away. Several books signed. Verdict: a very positive experience!

Talk at the Oxford Literary Festival

I will be giving a talk on “10 really interesting things about telescopes”, in support of my OUP Book: “Telescopes: A Very Short Introduction” at 13:15 in with Q&A:


Oxford University Press is proud to return to the FT Weekend Oxford Literary Festival with another series of soap box talks from the very short introductions series.  These free, 15-minute talks feature expert authors from the series and take place twice a day in the Blackwell’s Marquee, next to the Sheldonian Theatre.

Astrophysicist Dr Geoff Cottrell describes the basic physics of telescopes and explores their history from Galileo to modern computer technology. He explains the crucial developments in detectors and spectrographs that have enabled the high resolution achieved by modern telescopes, and the hopes for the new generation of telescopes currently being built across the world.