Guest post by Nicky Dean, Team Manager Physics, Nature Communications.

For this week’s set of experiments in our poll we will stick to the 19^th century. Our first entry is from 1839, when Alexandre Edmond Becquerel invented the photovoltaic cell at the tender age of 19. While playing around in his father’s lab, Becquerel created an electrolytic cell from silver chloride in acid. After connecting it to platinum electrodes, he found that exposing it to light generated an electrical current. Currently, photovoltaics is one of the most active themes in materials research, as it may be key in our challenge to produce enough clean energy for the world for generations ahead.

Skipping ahead to 1887, our next experiment also unveiled some of the intricacies of the interaction between light and matter. While testing Maxwell’s theory of electromagnetic waves, Heinrich Hertz constructed a receiver device based around a gap between two metallic electrodes across which a spark could propagate. He realised that light promoted spark production but also found that this could be suppressed by inserting a piece of glass between the light source and his receiver. Crucially, this wasn’t the case for a sheet of quartz and from this, Hertz deduced that ultraviolet light, which glass absorbs but quartz does not, was responsible for easing the ejection of electrons from the metal electrodes, forming his sparks. Thus he discovered the photoelectric effect, in which electrons can be emitted from a metal by light.

Later on, Albert Einstein would explain this effect as arising from the quantum nature of light. Hertz didn’t think his findings were of any practical use and that they merely served to support Maxwell’s theories. Ironically, his investigations would eventually lead to such world-changing inventions as telegraphy, radio, and television.

While Hertz was busy submitting his findings to the Annalen der Physik, our final experiment was taking place on the other side of the Atlantic. The growing understanding of light throughout the 19^th century led people to believe that light needed a medium to transit through, much as sound travels through air and waves ripple across water. Scientists called this medium the “luminiferous aether” and it was believed to permeate all of space. As such, while the Earth was whizzing around the Sun, it must be moving relative to the aether and so it must surely be possible to detect its presence.

Michelson interferometer (Wikimedia)

Continue reading →

Guest post by Liesbeth Venema, Senior Physics Editor, Nature

We are basking in light. In our daily lives we encounter a multitude of light-based technologies from basic lighting, optical fibre communication, television and computer screens, to diagnostic techniques in healthcare. Sunlight energy harvesting will almost certainly be essential to match the world’s growing energy needs. The International Year of Light 2015, which is celebrating these achievements, and more, is now in full swing.

Of course, light plays a key role in scientific inquiry and discovery. To take a closer look, we have opened up a poll to find out what are the most striking, beautiful experiments with light. To have your say, please click here and simply select three experiments from the list of candidates that would be top of your list. Over the next few weeks, we will introduce the candidate experiments on this blog, in chronological order. The results of the poll will be announced here at the beginning of May.

So let us start – with Greek philosophers who of course already pondered the nature of light. They debated for example how we can see: with light emitted by our own eyes or by absorbing rays that reflect from objects?

Lighthouse Lens by Tonya Cook (Own work) (CC BY-SA 3.0, via Wikimedia Commons)