Category Archives: Physics

What Is Life? And Other Interdisciplinary Questions

Scientists, like most people, want to understand the world they live in. We examine the physical structure of the world, in the hope that understanding the rules governing it will also lend some clue as to what it all means. Ironically, as the boundaries of scientific knowledge grow, the possibility of any individual scientist grasping this entire meaning gets smaller and smaller. Even within science, the traditional disciplinary boundaries—biology, chemistry, physics—often separate scientists who should really be talking to each other. I have always loved talking to people who know different things than I do, prompted by curiosity and encouraged by family. But it can be rare to see famous scientists doing the same.

Erwin Schrödinger, a physicist famous for his mathematical and philosophical development of quantum mechanics, tried to reach across these boundaries and ask the question that compels so many of us, namely ‘What Is Life?’ His historic lectures were given in 1943, against the backdrop of world war and 75 years behind our current understanding of biology. And in a wise move for anyone trying to understand something new, Schrödinger began by admitting what he didn’t know: to him, the difference between what physics and biology had to say about life was the difference between “a wallpaper and a Raphael tapestry”.

And yet, connecting physical understanding to biology has provided significant insights. When these lectures were given, the DNA molecule itself had already been discovered, but the double helix structure was yet to be found, along with much of our modern understanding of how this blueprint for life works. And yet the stability of the DNA molecule in the cell is directly due to the quantum basis of chemical bonds. Schrödinger expresses amazement that even with the perturbations caused by heat and environment at the molecular level, the naive physicist’s expectation of wild variability is incorrect, and chemical stability holds. While DNA does sometimes mutate in ways that persist through generations, forming the basis of natural selection, its ability to reproduce error free throughout our lives is amazing from a physics perspective. Especially when one considers the consequences of uncontrolled mutation, as the world would see only two years later as radiation-induced mutation caused terrible illness in the survivors of Hiroshima and Nagasaki.

In trying to define life, Schrödinger comes to the idea of order and disorder, and the physicist’s idea of entropy. Although entropy, which is a measure of disorder, is bound to increase over time subject to the Second Law of Thermodynamics, Schrodinger posited that living beings were effectively decreasing their local entropy by exporting it, increasing order within the cell even if the broader environment became less ordered. Cheating the Second Law of Thermodynamics is a necessity for living cells, living beings, and even our planet to maintain local order. Schrodinger then concludes that living beings must be ‘negative entropy machines’, converting energy to local order, a perspective only a physicist could have come up with.

Schrödinger’s willingness to admit what he did not know, and try to combine modern biology and modern physics even during wartime to unify humanity in knowledge, put me in mind of another, less famous, transdisciplinary scientist.

A man pipetting.

My father, Eric Fairfield, was a biochemistry professor who left academia to work on the Human Genome Project. We talked about science a lot, especially once I chose to pursue physics. I know he was proud of me for becoming a scientist, even though as a biochemist he could not resist ribbing me for my limited understanding of biology. When I read Schrodinger’s statement:

THE CLASSICAL PHYSICIST’S EXPECTATION, FAR FROM BEING TRIVIAL, IS WRONG

I could nearly hear it in my dad’s voice. The “naive physicist’s approach” to understand the cell by looking to statistical physics and randomnessi misses the stability of chemical bonds in the DNA molecule and other cellular components. In a messy, changeable environment, the blueprints that make us have persisted through thousands of generations. As my dad used to say, biology had this figured out a long time before we even knew what questions to ask.

But this isn’t to say that physicists have no business asking questions in biology, or vice versa. Biology is built on the laws of physics and chemistry, even if the exact details of how are still being puzzled out today. And questions that my dad put to me, as part of his own research, often had me questioning both physics and biology. How does a cell know what organ to build a piece of? What biochemical signals lead to the evolution of our own sensory organs, like ears or eyes? How does higher level order arise from molecule level decisions?

I enjoyed discussing these questions with him, and asking my own about the chemistry of the nanomaterials I studied, and their current and possible future biological applications. But the last big biological questions my dad asked ended up being about cancer, a scientific issue that has absorbed the careers of many researchers. Colon cancer took my father’s life last year, and when I have a question about biology, I can no longer call him to see if he’s thought about it before. At his memorial service, many friends commented how much they enjoyed talking science with my dad, whether they had a scientific background or not. He enjoyed discussing and debating these topics with anyone, even if and sometimes especially if they had a vastly different perspective to his own. But I think science would get a little bit further if we had more scientists like my father, or like Erwin Schrödinger, who were willing to cross disciplinary boundaries, admit what they don’t know, and see where they can go from here.

My scientific colleagues may find this to be a very personal response to a scientific matter. But Schrödinger himself dedicated What Is Life? to the memory of his parents. We are all searching for answers together, inspired by those who have come before, and certain to be surprised by what comes next.

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When Your Science Hero is Problematic

We all have heroes, people we look up to and whose achievements spur us on to do our own personal best. And, especially in this era where women are saying #metoo and finally being heard, we have probably all had the experience of finding out that one of our heroes has done some less than heroic things. This has come up a lot for me recently with the deaths of some very famous scientists and science fiction writers, men I greatly admired when I was a kid, who I’m now discovering were frequently awful to women (i.e., people like me).

I think this happens more than usual in science, a traditionally male-dominated field where a culture of elitism and privilege has been embedded for a long time. And it’s tempting to view things in black and white: either my hero is amazing for their achievements or they are garbage for their behaviour. We know in our personal lives that people are multi-faceted, yet we’re slow to allow public figures that same understanding. If a famous male scientist discovers lots of things, and is a great collaborator with other men but acts differently toward women, consciously or unconsciously, how are we meant to think about that?

As a physicist who loves to write, I’ve had to consider this before, because one of my early science heroes was Richard Feynman. Feynman was a brilliant theoretical physicist, a Nobel laureate, and worked on the Manhattan project building the atomic bomb in my hometown of Los Alamos. He also wrote a series of very enjoyable popular science books, which were also quite personal and effortlessly engaging. A quote from an interview that immediately stuck with me:

Omni: As we came back to the office, you stopped to discuss a lecture on color vision you’ll be giving. That’s pretty far from fundamental physics, isn’t it? Wouldn’t a physiologist say you were ‘poaching’?

Feynman: Physiology? It has to be physiology? Look, give me a little time and I’ll give a lecture on anything in physiology. I’d be delighted to study it and find out all about it, because I can guarantee you it would be very interesting. I don’t know anything, but I do know that everything is interesting if you go into it deeply enough.

As someone who is omnivorous about knowledge, I found that quote resonated with me deeply. Science is fascinating because it shows us how the world works, how things which might appear separate are deeply connected, and the overlapping intricacies behind the everyday we take for granted. I now do my research on nanoscience, a strongly interdisciplinary field that draws from chemistry, electrical engineering, materials science, and plenty more beyond the physics that I got my degrees in. I admired Feynman for not letting other people dictate the questions he could ask, for being a physicist in what felt like a subversive and wide-ranging way. He was also famous for his sense of humour, his love of non-scientific things like playing bongos, and for generally not being as formal and rigid about anything as physicists tend to be.

The author having a Feynman bongo moment at the No-Ball Prizes. Photo by Ian Bowkett.

Of course, if you read Feynman’s books you’ll also find less inspiring stories, if you are a female scientist. He writes about doing his calculations in a Hooters, negging women in bars, and pretending to be an undergraduate to pick up grad students’ wives. This is less subversive, and more what we might generously call ‘of a time’. Feynman did plenty to promote the status of women in physics, encouraging his own sister to study it and eventually get a PhD. But reading through these differing accounts of his behaviour, female physicists are left wondering whether this great man of science would have seen them as colleagues and equals, or as prey.

I still find a lot in Feynman to look up to, as a physicist who did amazing work but cared about communication and didn’t give in to pressure to conform. However I can still acknowledge the women he mistreated, or perhaps even drove out of the field which is a terrible loss to science. He had a complexity to him, and my initial hero-worship of Feynman when I was younger has been replaced by equally complex feelings, of respect for his scientific and communication work alongside frustration at his mistreatment of women. But there’s no such thing as a perfect hero anyway, and if I needed one in physics, I might be waiting a long time. We have many historical women in physics to look up to, like Lise Meitner or Emmy Noether, and yet often these women were denied resources and opportunities that their male colleagues had, which can make them feel like amazing but also tragic figures. I would hope that women working in science today can be heroic without the tragedy.

Perhaps looking for heroes in science is a fundamentally flawed endeavor. Science is at its heart collaborative, and the sheer scope of human knowledge means that it is impossible for one person, toiling alone, to conquer it all. We must talk to each other, work together, and build on existing work, as famously stated by Isaac Newton: “If I have seen further it is by standing on the shoulders of giants.” The great man theory is as flawed when it comes to science as it is when it comes to history. We all seek out role models, but we must recognize that they worked with others, seen and unseen, and that science is a societal effort and not the work of a lone genius.

While Feynman is long gone, there are other scientists still living, still contributing, and still behaving badly. It’s important that we not let them off the hook. Feynman lived decades ago, and certainly the standards of behaviour were different then, but today’s harassers and discriminators have no such excuse. If science is truly a collaborative effort, then it loses strength every time a person is pushed out of science by harassment. We can have complicated feelings about prominent scientists of the past, but there are a lot of people working in science today who are doing it right, and can serve as inspirations.

For example, tomorrow is the first ever LGBT STEM day, being celebrated with events around the world. Our Irish LGBT STEM network, House of STEM, has done so much to organise and promote this event, and founder Shaun O’Boyle explains why it’s desperately needed here:

The past is full of problematic yet successful scientists. Yet I’m hopeful that the future will have a broader array of amazing scientists, working together, who are also amazing people.

Threading a Nano-needle

One of the most exciting things about working in nanoscience is the incredible level of precision with which we can probe the world around us. This includes not just the physical world but also the biological world, which is a lot messier than most physicists are comfortable with!

There is currently intense interest in sequencing DNA via translocation through a nanopore, like threading a needle with the molecule that contains instructions for building life. Protein nanopores are the basis of new technology for DNA sequencing that made the news recently, costing only $1000 for full DNA sequencing with a palm-sized device from Oxford Nanopore. The protein nanopore is pictured in the image below, with DNA unspooling to pass through the pore.

But these nanopores can also be created in silicon, graphene or other thin materials. These solid state nanopores emulate the very small biological pores which can be found in the lipid bilayer around cells and their nuclei. Macroelectrodes in solution on either side of a solid state nanopore drive an ionic current in the carrier solution through the nanopore. As the DNA passes through the nanopore, it physically blocks the ionic current through the nanopore, allowing detection of translocation events. Additional electrodes can be added across the nanopore to enhance sensitivity to DNA. While research in this area is ongoing, it is thought that noise in the electrical signal through the nanopore can eventually be lowered—by applying coatings, slowing translocation speeds and improving fabrication techniques—to enable base pair sensitivity for DNA sequencing. Using solid state nanopores for sequencing could lead to more reliability and lower costs than protein sequencing, and is a major research area of the Drndić group at UPenn, the group I worked in for my PhD!

To me, nanopore sequencing is an amazing example of how direct electrical interaction with nanostructures can yield important information about not just the world around us, but our own place in it.

Cassini’s Grand Finale

After nearly 20 years in space and a final series of dives through Saturn’s ring, the spacecraft Cassini is on its last descent. It will crash into the planet later today, ending an incredible scientific mission to an amazing place.

Cassini and its instruments helped investigate Saturn’s atmosphere, its rocky rings, its strange polar hexagon. It also expanded our knowledge of Saturn’s moons, from the geysers and hidden oceans of Enceladus to the rocks and lakes on the surface of Titan. Cassini’s Huygens probe, which landed on Titan, was the furthest space landing of anything humanity has built.

Originally launched in 1997, Cassini’s mission was supposed to end in 2008. But it received two major mission extensions, nearly doubling its lifetime. It has sent 635 gigabytes of data back, which mightn’t sound like a lot except that all of it was on 1997 era technology, through a billion kilometers of space.

The spacecraft is being crashed into Saturn because it’s running out of fuel for orbital maneuvers, and scientists don’t want to risk accidentally crashing it into one of Saturn’s moons which might contain life, and contaminating them. I feel personally invested in Cassini’s mission and final resting place, because my signature is on board! When I was growing up, one of my Girl Scout troop leaders was an astrophysicist working on the Cassini Plasma Spectrometer before the spacecraft was launched. She arranged for us to all come in and get to see some of the instruments, and in the end our signatures were all added to the 600,000 signatures on the disc of human culture that was included with the spacecraft. This disc, modeled on the Golden Record aboard Voyager, is a time capsule of human culture for other spacefaring civilizations to find. But while the Voyager discs are traveling beyond our solar system, Cassini will be meeting its end here, to become part of the planet it studied.

Cassini’s voyage has been such an inspiration, a feat of technical and scientific exploration which I, along with millions of others, have loved watching from here on Earth.

You can read much more about Cassini’s scientific discoveries here, and watch Cassini’s final descent today starting at 7AM EDT here, on the NASA livestream. Godspeed, Cassini.

Sound and Waves

When I hear my mother’s voice, it sounds different from my father’s voice, and different from a bird or a drum. Why are the sounds we hear so varied, and how do they travel to our ears?

soundwaves

Sound is created when something moves rapidly, and creates a wave in the air around it. Our vocal cords do this, as does the skin on a drum, pushing the wave out into the world. This wave is made up of bands of air: more pressure, less pressure, high and low, back and forth as long as the sound lasts. Sound can only travel through something whose pressure can be changed, like air and water. So if you’re floating in space: perfect quiet.

But have you ever noticed how sound changes as it echoes around a gym? That’s because sound waves change when they bounce off things. A musical note will sound differently in a glass room than in one lined with velvet cushions. This affects musical instruments too! And the size of an instrument influences the sound it makes, from the deep growl of the tuba to the light chirp of a flute. Generally, bigger instruments make deeper sounds, with fewer waves per second.

And sound is not just high or low. Of course, it’s also soft or loud. But more interesting are differences that lead to a new tone or feel. For example, a violin and a flute might play the same note at the same volume, but they still won’t sound the same. Waves have amazing abilities to send subtle differences within a sound. And luckily for us, our ears use delicate hairs to detect these waves as they move through the air. Nerves connect the hairs to our brain, connecting us to the full orchestra of sound.

Gravitational Waves Discovered by LIGO

The world is abuzz with news that gravitational waves have been detected for the first time. This is a huge leap forward for scientists’ understanding of gravity! For all that we experience gravity every day as we (mostly) stay grounded on the Earth, figuring out exactly how it works has been a challenge.

Gravity draws things together, but how ? One of the most brilliant discoveries of Albert Einstein was realizing that objects with mass actually warp spacetime itself. If we imagine space as an enormous sheet, throwing a light object like a tennis ball onto it would only pull the sheet down a little, whereas a bowling ball would pull the sheet down significantly more. Everything with mass distorts the sheet though, affecting other objects on the sheet and even massless things like light as they pass through.

Spacetime_curvature

Seeing that gravity affected light was actually the first major proof of Einstein’s theory of general relativity. During an eclipse in 1919, light from a cluster of stars was seen to distort from its normal pattern as it passed close to the temporarily obscured Sun. But another consequence of Einstein’s work was the idea that the speed of light is a maximum speed for any particle or force, including gravitation, however it’s propagated. This implies that gravitational interactions can only happen so fast, and that if a huge gravitational event were to take place emitting a lot of gravitational energy, that energy would have a maximum speed to move through the universe.

What kind of huge gravitational event? Well, the strongest gravitational interactions we have been able to observe take place around black holes, whose mass causes gravitational forces that overcome even basic quantum mechanical ones that prevent matter from piling up on itself. So black holes are supermassive point objects, singularities with exceptionally strong gravity. And if two of them were to come together, their movement might create gravitational waves in spacetime itself that could be strong enough for us to detect.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) has been looking for gravitational waves using light as a ruler to measure whether spacetime is being warped. LIGO compares the length of two 2.5 mile long tunnels, set at right angles to each other, which would warp in alternation if a gravitational wave were to pass through them. The precision needed to see even very strong gravitational waves is tremendous, as we know from the fact that we don’t just observe our living rooms getting bigger and smaller in response to cosmic events. LIGO has been searching for gravitational waves since 1992, and improving its precision since then. Finally this week, they announced a signal!

LIGO_measurement_of_gravitational_waves

The gravitational waves detected come from two black holes merging, a billion light years from our planet. These black holes were enormous, 36 and 29 times the mass of our Sun. They merged into a black hole 62 times the mass of our Sun, converting three solar masses into energy as gravitational waves. It is these waves that the LIGO researchers managed to detect, corroborating their results at two separate facilities in Louisiana and Washington. The difference in lengths of the LIGO tunnels due to the gravitational waves was less than a millionth of the size of an atom, an astounding physical feat, and yet the LIGO collaboration is confident in its measurements to 99.9999%.

Validating a prediction made over a hundred years ago about the way mass warps spacetime is impressive enough, especially considering that gravity is still the least well understood of the four fundamental forces. But it’s also a beautiful new way to look at the stars, and at the massive universe beyond our planetary doorstep.

Color and the Size of Light

What is color, and what does it mean for an object to have a specific color? Well, color comes from the fact that light can have different sizes, the way objects reflect that light, and the way our eyes can see it.

Light is made up of these tiny packets of energy, photons, which travel as waves that can move through air or space. And there’s a distance between the peaks of the waves, the same way there would be for waves in water, which is the size of the light. Light can have a whole range of different sizes, so the microwaves that you use to cook food or the radio waves that carry sound through the air are both different sizes of light. But there’s a special range of light, the visible range, which contains the sizes of light that our eyes can detect.

wavelength_size

So in the visible range, we have shorter lengths of light, which our eyes see as more blue, and longer lengths of light, which our eyes see as more red. In between, you have the full rainbow, which has all the colors we can see. The sun shines light on us with the whole range of sizes, but different objects will reflect different sizes or colors back at us. So an orange is absorbing most visible light but reflecting orange light, and then our eye detects that light and our brain tells us it’s orange.

But we need special cells in our eyes to detect color. Most people have three kinds of color-detecting cells, called cones, that pick up blue, green, or yellow light. From these three colors, our brain puts together the rest of the rainbow, like an artist does when mixing paint. People who have fewer or more kinds of cones will perceive color differently, maybe being color-blind or seeing even more colors than average, even though the light itself is the same!

If you want to know more, we have some nice posts in the archives about visible light and why the sky is blue.