The challenge of blue light, the power of urine, and our evolutionary history
Chemistry, Biology, Physics: Three scientists talk through big recent developments in their fields.
This article is a preview from the Summer 2015 edition of New Humanist. You can find out more and subscribe here.
Physics – Ceri Brenner
2015 is the International Year of Light and Light-based technologies, a chance to reflect on the impact light has on science and our daily lives. Electric light is vital to a progressive civilisation; just try to imagine a world without lighting and screens. The statistics say it all: 20-30 per cent of electricity worldwide is used for lighting alone. For this, we can thank applied physicists, who see a technology gap and discover the physics needed to close it. One example is the discovery of blue LED technology, awarded the Nobel Prize in Physics in 2014 – for its impact on mankind.
Light emitting diodes (LED) convert electricity straight into light. They are much more efficient than filament lightbulbs that emit light by flowing electricity across a wire to heat it until it glows. When electrons flow through certain types of specially constructed material, the electrons fall into “holes” in the structure (they’re not holes as we know them, let’s say spare places that electrons can reside in). These hole-residing electrons are left with excess energy, which they get rid of by emitting light (electroluminescence). The light given is of a single colour, which depends on the LED material you are using.
Red and green LEDs were developed in the 1950s. But in order to produce a white LED that could be used to light rooms, a blue LED was needed. The primary colours of light are red, green and blue and any colour can be produced by combining these three in different ratios. Combining them under equal intensity gives you white light.
For decades, physicists struggled to build a blue-emitting LED system. Physicists knew how electroluminescence worked, but the crystals of material couldn’t be produced with high enough purity and enough “holes” to be effective. In the late ’80s, Japanese researchers developed a method for growing pure crystals of gallium nitride. Not long after this, they discovered that bashing the crystal surface with electrons, or heating it, can further improve the “hole” structure. As these Nobel laureates ventured into the blue, they revolutionised lighting technology.
Ceri Brenner is a physicist who works for the Science and Technolocy Facilities Council
Biology - Lydia Leon
Today’s technological revolution is taking place in the virtual realm, but in past millenia the medium was stone. It has long been thought that complex tool-making began with the genus Homo, the evolutionary lineage that modern humans (Homo sapiens) belong to. Following research by Louis Leakey in Tanzania 80 years ago, the oldest stone tools discovered were dated at 2.6 million years old. The time-window matched separate evidence from East Africa of the oldest known Homo fossil, defined by its tall stature and large brain, which supported the view that complex stone tools developed because of the evolution of Homo: bigger brains equal better technology.
A recent discovery challenges this timeline. A group from Stony Brook University in New York excavated stone tools in Kenya, dated to at least 700,000 years earlier than any tools previously found.They were working in the wake of a controversial 2010 discovery in which cut-like marks were found on ancient hominin fossils dating to 3.4 million years ago, which some suggested meant stone tool use earlier than previously thought. The Stony Brook group found dozens of ancient stone-tool flakes, including one that fit perfectly into a stone core – showing that the tools were deliberatey made, not just found and used. (This is what man’s closest relatives, chimpanzees and bonobos, do.) The surrounding sediment was 3.3 million years old.
So who made these tools? What was the cultural context? Were they a flash-in-the-pan or are they early examples of the cultural development that eventually led to humans’ long tradition of tool-making? The debate rages amongst archaeologists and scientists studying early hominin evolution. Recently, the discovery of an ancient hominin jawbone in Ethiopia pushed back estimates of the Homo lineage’s beginnings to 2.8 million years ago – 500,000 years earlier than previous estimates. Were ancient hominins more dexterous and intelligent than we thought, or were we wrong about when our more human-like Homo ancestors appeared? Either way, this discovery taps into the heart of an evolutionary milestone in human history.
Lydia Leon is a PhD student at University College London
Chemistry – Mark Lorch
Do you ever read this magazine on the toilet? Well, you might want to give some thought to what you are wasting. This spring there’s been a sprinkling of interest in pee power. Or, more accurately, in urine-based microbial fuel cells. Fuel cells use chemical reactions to produce electrical energy. They all consist of two connected electrodes (the anode and cathode) and a liquid electrolyte in which the electrodes are submerged. The reaction at the anode generates electrons which flow to the cathode, generating usable electricity. Microbial fuel cells do the same, except the chemical reactions are already nicely packaged up in bacteria. The bacteria are immobilised on an electrode and fed with an appropriate electrolyte. As the bacteria use up the feed, they produce electrons. These get donated to the anode and generate electricity just like any other fuel cell.
The key points are finding bacteria that can carry out the reactions and an electrolyte that contains all the necessary chemicals to sustain the bacteria. This isn’t particularly difficult; the first microbial fuel cells were constructed in 1911. But now a team from Bristol BioEnergy Centre are making use of bacteria that love urine, which means they can turn an abundant waste into useful energy.
To start with, the team have embedded electrodes and a dormant film of bacteria onto a small tetrahedron of
waterproofed paper. When they peed into the small origami device, the bacteria awoke and got to work on the urine, in the process generating power for a small radio transmitter. One suggestion is that the device could be used as a lightweight emergency beacon of last resort. When all else fails, all you need is a little bit of something from your bladder. The same group are using a steady stream of student pee to generate an illuminating experience. A prototype cubicle, situated at the University of West England’s Student Union Bar, collects urine and then utilises a microbial fuel cell to power the lights. The student bar is a great place to test the devices, but the hope is that they could be used on refugee camps and other out-of-the-way areas to provide a ready source of cheap power. You can flush now.
Mark Lorch lectures in chemistry at Hull University