Monthly Archives: January 2012

Physics for Future Presidents

A quick break from the science basics I’ve been laying down!

When I was an undergrad, my university had a pretty amazing course for non-scientists called Physics for Future Presidents. The basic idea was to cover a lot of day-to-day phenomena from a scientific angle, forgoing any unnecessary background, and the professor for the course, Rich Muller, was very charismatic and an excellent lecturer. While I am trying in my posts to build up some scientific concepts so that I can write about some of the interesting phenomena out there, the approach of Physics for Future Presidents was to treat physics as a second language that you learn through total immersion. An interesting approach, and they covered lots of physics from the headlines such as UFOs, nuclear weapons, and solar energy.

I bring this all up to point out that the lectures for the course are available online here, and you can access some of the book chapters online such as those covering radioactivity and climate change. It’s a great resource for improving scientific literacy, which even scientists can benefit from.

Charged with Meaning

The further you delve into the physics of electronics and materials, the more you will hear about the importance of electric charge. What charge particles have determines much of how they interact with other particles. In materials many of the electronic and magnetic effects are, at a basic level, due to charge. So what is it?

Electric charge is a fundamental property of matter. How much charge a particle has determines the force it will experience from an electromagnetic field, and such a field can be generated either by other charged objects or by the motion of magnetic objects. This is similar to mass, which is another fundamental property that determines the gravitational force an object will experience as it interacts with other massive objects. There is one key difference between charge and mass, however: there are two types of charge, positive and negative, whereas mass can only be positive (or zero). From the particle perspective, we can have particles like protons that have a positive charge, particles like electrons with a negative charge, and particles like neutrons that have no charge. Anything with a charge creates an electromagnetic field, and other charged particles nearby will feel a force from that field.

Now, say that we have two particles sitting near each other. Each one will have an associated electromagnetic field, and the total field will be a sum of the individual fields. The size of the electromagnetic force experienced by each particle due to the other depends on the magnitude of the two charges. But whether the charge on each particle is positive or negative is important for the following two reasons:

  1. Similar charges repel.
  2. Dissimilar charges attract.

So with our two particles, if they both have positive charge, or they both have negative charge, they will each feel a force directed away from the other charge. But if one is negatively charged and one is positively charged, they will experience the same size force toward each other. This force is part of what holds atoms together. Protons and electrons have equal and opposite charge. In atoms, we have a nucleus of protons and neutrons surrounded by a cloud of electrons. If there are more protons than electrons, the atom as a whole will be positively charged and will be attractive to nearby electrons. But if there are more electrons than protons, the atom is instead negatively charged, and the electrons within it are not as strongly bound.

We can already see that the charge of a particle is extremely important on the atomic scale. As we look at collections of atoms, the interactions will get more complicated, but the pieces to remember are:

  1. Charge is an inherent property of matter.
  2. Charged objects create an electromagnetic field.
  3. How strong a force an object feels from such a field is determined by that object’s charge.

What is an atom?

Much of the interesting science in modern electronics stems from the properties of quantum-size objects, at very small scales. So the most sensible place to start is at the bottom, with atoms.

There are many different kinds of matter, but most of the matter on Earth that humans interact with is made from atoms. What makes atoms non-intuitive for many people is their size, which is so small that we are able to get through day-to-day life never having to think about the atomic nature of matter. An atom like hydrogen is so small that you could line up ten million of them in a millimeter. In the same way that the universe is made of trillions of stars, in differing arrangements made up of differing materials, our bodies are made of trillions upon trillions of atoms.

Helium Atom

A helium atom. The inset shows a detail of the nucleus, which has two protons and two neutrons. The entire atom is about an angstrom in size, which is less than a billionth of a meter.

Atoms were originally proposed as indivisible units of matter, hence the name which comes from a Greek word meaning indivisible or unable to be cut. However, what we now call atoms do have smaller objects inside them. Atoms are comprised of a central ball of protons and neutrons, called a nucleus, surrounded by a cloud of electrons. The nucleus is very heavy compared to the electron cloud, because protons and neutrons are approximately 2,000 times heavier than electrons. This means that in a collection of atoms, there are many dense nuclei, and the disperse electron clouds around them. Much of what we perceive as solid matter is actually made up of empty space, because of the low density of electron clouds. Nothing on Earth as dense as a nucleus is big enough to see by eye.

Within an atom, there can be different numbers of protons, neutrons, and electrons. What name we give to an atom is depends on the number of protons in its nucleus. The number of protons and the number of neutrons affect the size of the atomic nucleus. So if we compare a nucleus with one proton and no neutrons, which is a kind of hydrogen, with a nucleus that has eight protons and eight neutrons, which is a kind of oxygen, we find that the oxygen nucleus is physically larger than the hydrogen nucleus.

The number of electrons in an atom has a large effect on how the atom interacts with other atoms and with its surroundings. The numbers of protons and electrons impact each other as well, which we’ll get into when we go deeper into the quantum nature of atoms. But the numbers of protons, neutrons, and electrons give us many types of atoms, also called atomic species, which can be used as building blocks for matter.

But, from here we can begin to talk about what makes materials different, which largely depends on atomic properties and interactions. Even though many people don’t think about atoms when they go out into the world, much of our lives does stem from happenings in the world of atoms.

The History of Public Engagement with Science – Part II

Slightly further along from Newton science began to get really exciting for the public – Evolution! Electricity! The periodic table! Science seemed to be travelling along in leaps and bounds, and what’s more, the scientists doing the discovering were also the ones bringing it into the public sphere. Charles Darwin’s publication of On the Origin of Species in 1859 sparked debate worldwide – journalists and fellow scientists alike publishing their own reactions to the work and spurring discussions both logical and theological.

Throughout the Victorian era public lectures on scientific topics grew in popularity – the Royal Institutes Christmas lectures began in 1825 and have continued to this day, exploring a wide range of topics from  ‘The chemical history of a candle’ to ‘Wireless messages from the stars’ and ‘The release and use of atomic energy’. Lecturers such as Michael Faraday and William Thomas Brande were both pioneers in their field but also engaging public speakers and educators. John Tyndall, a well-known Irish physicist, progressed through various posts to become Professor of Natural Philosophy (Physics) at the Royal Institution. Not only was he leading research on diamagnetism and thermal radiation but he was also an insanely popular lecturer who drew huge crowds at lecture halls in both the UK and the States. He also wrote 17 science books, some of which were translated into languages such as German, French, and Chinese, and some of which are still in print today. In the foreword to his 1867 book Sound he says:

“In the following pages I have tried to render the science of acoustics interesting to all intelligent persons, including those who do not possess any special scientific culture. The subject is treated experimentally throughout, and I have endeavoured so to place each experiment before the reader that he should realise it as an actual operation.”

Other scientists and engineers filled theatres and lecture halls with their talks – names such as Tesla drew in fascinated, terrified audiences, and venues such as the Crystal Palace hosted the Great Exhibition, dedicated to showcasing the most recent technological and social advancements. Onwards from that scientific communication began to branch into other types of media as well;  radio shows and television programmes were produced detailing the wonders of the world, and scientific films and public health advertisements flourished.

Moving into today’s media it is easy to see the veritable saturation of sources with scientific information, from online newspaper articles and journals to webcomics, television programmes and podcasts. Over the coming weeks I’ll be looking at some of the more noteable examples of each of these, highlighting the achievements and drawbacks of each and exploring the current ‘public’ relationship with scientific discovery and information. In other words, I’m giving myself an excuse to do what I like best – reading about science and the people who do it. I can’t wait!

The Weird Quantum World

One of the first and most effective tricks of teaching any subject is making analogies. A concept that initially doesn’t click may make more sense when compared to a common experience or narrative. In the sciences this can come up a lot, where the mechanical motion of balls can be compared to things we’ve seen in sports, or laws of heat transfer compared to experiences cooking food. Scientific inquiry is, among other things, an inquiry into the rules of the world around us, so it makes sense that while exploring those rules, we try to place them in the context of that world.

But as we examine the world at a smaller and smaller scale, looking at components much tinier than we have any normal experience thinking about, the rules begin to change. As you approach the scale at which the constituents of matter become indivisible, the behavior of these constituents is nothing like what we are used to at our scale, the macro scale, with bouncing balls and boiling water. This is the quantum world, so-called because many aspects of reality are quantized and discrete rather than continuously variable . And the trouble with learning about the quantum world is that there are very few analogies to the world we know, even though the quantum world is what underlies our own!

One example of weirdness in the quantum world is particle-wave duality. This terms stems from the history of research on light: from the 17th century through the early 20th, many of the best scientific minds were divided on whether light was a particle or a wave. Initially light was assumed to be an indivisible particle, observed to travel along straight lines. But the way that light can bend, or refract, around corners seemed more similar to the behavior of a wave. An experiment was devised to test which theory was true, with two narrow slits cut into a thin plate, in front of a screen. Classical particles would be expected to form an image of the two slits on the screen, whereas a wave traveling through the two slits would form a complicated interference pattern on the screen due to overlapping wavefronts. When light is sent through the double slit, the interference pattern is seen, implying that light is a wave. But, if you set up a detector to determine which slit each light particle is passing through, then the screen shows an image of the two slits. Thus light has both a particle and a wave nature, and in fact this is true for many other “particles” such as the components of atoms: protons, neutrons, and electrons. Each of these particles has wave properties as well.

But something about the double slit experiment may have struck you as even stranger than light being both a particle and a wave. It appears that whether we see evidence for the wave or the particle nature of light depends on the measurement we do: if we measure which slit the light passes through, we see particles, and if we do not, we see waves. It turns out that another example of strange quantum behavior is the importance of measurement.

Within quantum mechanics, the mathematical system devised to describe quantum behavior, it turns out that in addition to discrete quantum states, it is possible to have superpositions of states. So, in addition to having an atom aligned to the left or to the right, we can have a state which is “left plus right”, that is not just zero. There is no analogue for this idea in the macro world, and the whole strange setup leads to the question: If we measure the state “left plus right” for alignment, what do we get? Left or right? It turns out that we have an equal probability of measuring either one, but what’s even stranger is that before we perform the measurement, the system is not really in either state. It is in both, and neither. The measurement itself causes a fundamental physical property of the system to change, meaning that the traditional scientific idea of observing a physical system without affecting it must be discarded!

Both of these ideas, particle-wave duality and the importance of measurement, have a lot of tricky implications and can be explored in much more detail than I’ve given so far. And they take awhile to wrap your head around! For many people, their first reaction to these concepts is a creeping unease, an inability to place these in any “real world” context and a sense that something must be wrong. To me, that is precisely what is so fascinating about the quantum world. It’s completely unlike anything that we have practical experience with, and yet it has been verified by experiment after experiment that the quantum world is a reality that underlies everything we see, a bizarro-land hidden behind all the things with which we are familiar. What a place to explore!

The History of Public Engagement with Science – Part I

The act of science communication is a prime example of two great hallmarks of humanity – the desire to discover and explore and the desire to communicate with those around us. It’s not too hard to imagine early man discovering fire and then excitedly – or perhaps in a bit of a panic – hooting to his fellows about what he’d found. Throughout history there are examples of men and women undertaking ground breaking research and then enthusing their peers with their discoveries and what they might mean for the future. And often, those that are best at communicating their enthusiasm and passion for what they do – and why it’s important – are the ones that gain the recognition and support to go further.

Any ‘big name’ scientist from history – that is, one you’ve probably heard of – has left a mark in history because of the discoveries they’ve made. That’s not all they’ve left, however. There’s likely also letters, publications, and other evidence of their processes, their thoughts and ideas. Isaac Newton published numerous treatises on his various areas of studies, including the Principia Mathematica, which lay the foundation for an entire technological revolution to come. He was also a subject of popular science writing, both for adults and for children, as in John Newberry’s 1761 The Newtonian System of Philosophy starring Tom Telescope explaining a wide array of subjects.

All our ideas, therefore, are obtained either by sensation or reflection ; that is to say, by means of our five senses; as seeing, hearing smelling, tasting, and touching, or by the operations of the mind. Before you proceed farther, says Mrs, Twilight, you should, I think, explain to the company what is meant by the term Idea.?

Not only did Newton and his fellows desire to explain their findings to the public but also the scientific mindset itself – important to grasping the concepts and ideas they were exploring was the notion of inquiry, of curiosity, of meticulous experiments and proof. Robert Boyle was devoted to the Baconian method, Gottfried Leibniz advocated the setting up of scientific societies across Europe and encouraged the cataloguing and indexing of titles from across the globe. as well as the creation of an empirical database across all of the sciences. Coffee houses, debating societies, salons and lodges all sprung up around the idea of allowing people to come together to hear and discuss the great ideas of the day, and it was in such venues that the Enlightenment truly took off.

Introducing Jessamyn!

The world around us is amazing, the natural world as well as the world of everything that we humans have created. And the deep awe we feel looking at the whole is only enhanced by examining the parts in detail. Many perspectives can be useful in this examination: the function and purpose of a thing, or its artistic merit, or the consequences it has on its environment.

I have been trained to use the physical and scientific lens to look at the world, exposing beauty and intrigue that’s usually inaccessible. I recently finished a PhD in physics and nanoscience at the University of Pennsylvania, focusing on the transport of optically generated electrons in nanocrystals. I found the material fascinating, but I also found that I enjoy talking with many different people about both the science I do and other scientific topics. So, my goal writing here is to discuss some of the things I find interesting in a way that non-scientists can understand.

We’ll look at some of the cool things that you start to see around you when you learn about physics, with an eventual focus on the electronic behaviors of materials. I will cover a lot of topics that I find interesting, from logical computing to sensors to bioelectronics. And I’ll go over some background topics, too, like atoms, mass, charge, and the weirdness of quantum physics, to show how electronic behavior also affects things like biological functions and the properties of materials. This affects the life of anyone with a computer, a mobile phone, or access to an Internet connection: more of us each day.

It’s interesting to know a bit more about how the devices you rely on work. But it’s also another perspective on day-to-day life, and the more perspectives we gather, the more we’re truly able to see.