Physics can be pretty mind-boggling, especially when you look at the laws that govern the quantum world. It can be easy to dismiss any news about physics as irrelvant to us, something for the scientists to worry about. But physics is at work all around us, in fascinating ways that we can sometimes take for granted.
The Good Human wants to remind you of just how incredible this planet is, by stopping and really thinking about phenomena that we accept as part of life, without really thinking about how they work. We have compiled a list of some of the most fascinating examples of physics at work in nature.
Let’s start with the spectacular light show that we witness from time to time during a storm. Lightning is a spectacle of nature that can have children and pets running for cover, while many adults hasten to the window to enjoy the display. While the production of lightning is not fully understood, we do know what must be happening inside the clouds prior to electrical discharge.
Storm clouds are a turbulent place, filled to bursting point with water droplets, ice particles and wind currents. Temperature differences in the water droplets cause some to rise, while others fall, creating the perfect environment for collisions. As the droplets and ice particles bash together, negative electrons are ripped off, separating them from the positively charged droplets.
Meanwhile, warm moisture is busy rising to the top of the cloud where it meets freezing temperatures at the higher altitude. This causes the droplets to cluster together, becoming negatively charged as they freeze solid and begin to sink. Positively charged water droplets are attracted to the frozen particles and surround the cluster.
As the cluster continues to sink, air currents knock the positively charged water droplets off, allowing them to rise again. Over time this can result in polarisation of the cloud, with a positive charge at the top and a negative charge at the bottom.
A statically charged cloud such as this begins to have an affect on the world around it. First of all the surrounding air undergoes a transformation, ionising as it’s components shed electrons. This leaves a conductive plasma made up of positive ions and free electrons.
In addition to this, the ground below the cloud also begins to change. The Earth’s electromagnetic field is affected, with negative electrons being repelled by the negative cloud bottom. This leaves the ground positively charged, which is of course attractive to the negative electrons at the bottom of the cloud.
If the charge is strong enough, streamers from the cloud down, and the Earth up begin to reach out toward one another in a zig-zag pattern through the plasma. If a complete conducting pathway is mapped out, and the two connect, then lightning will begin.
Enormous amounts of electrons are discharged along the conducting path, at speeds of up to a staggering 50,000 miles per second. The sheer amount of this rapid flow of charge emits light, and causes the surrounding air to expand violently. This is what we hear as thunder.
Lightning tends to re-strike a few times in rapid succession, usually 4 times, but as many as 30 re-strikes have been recorded. It is also common for lightning to strike between clouds, when two polarised clouds affect one another and cause a discharge of electrons as described.
Sense of Smell
The answer to the question ‘how do we recognise smells?’ is one that has come under debate in recent years. The widely accepted theory was known as the shape theory, which maintained that tiny molecules made up of atoms of a certain shape travel via the air up the nose where they meet around 400 receptors.
Different molecules trigger various combinations of receptor cells, which inform the nerve cells that a particular smell is present. The nerve cells pass this on to the olfactory bulb in the brain, which also happens to be the area associated with memory.
You have a specific-shaped molecule fit into a specific-shaped receptor. And that would fire off the receptor ~ Jenny Brookes, fellow at University College London.
While this makes sense on the surface, once you test the theory there are a number of flaws. For one thing, while the lock and key mechanism is the accepted theory for enzymes, the same process doesn’t occur with smell….i.e. there is no chemical reaction taking place in the nose.
A further concern with the shape theory is that different molecules of the same shape can be easily distinguished as separate smells by participants.
So, if the shape theory is incorrect, how do we smell? The answer may be far weirder than you imagine. Quantum mechanics could be at play, right before our eyes every time we sniff!
The alternative to shape theory is the ‘vibrational theory‘. Research led by Luca Turin in this area investigated whether ‘olfaction recognizes odorants by their shape, their molecular vibrations, or both’.
Luca suggests that different smells are determined in the nose by the vibration of the molecules rather than the shape of them. Using the quantum mechanic theory that an electron can behave as a wave as well as a particle, we can accept that at sometimes atoms pass through barriers that we wouldn’t normally expect them to.
So, if a molecule vibrates at a certain frequency, which matches an energy recognised by a certain receptor, this may open a kind of pathway, allowing a process described as ‘electron tunnelling‘, which enables us to discern one scent from another. So in essence this is a kind of teleportation.
It is a controversial theory as you can imagine, but many studies are supporting the idea. Shape theory is widely accepted as incorrect, but quantum mechanics in the nose has not exactly been embraced to date. It is a niche area of science, with little impact on human health, so it may be some time before we know exactly how we recognise smells.
Colours of The Rainbow
Most of us remember how a rainbow is formed from science lessons at school. But do we know the whole story?
This was the story in my mind, maybe yours too: Light waves from the sun refract when they reach droplets of water in the air and this breaks the waves into a spectrum of colours, which is reflected out as a rainbow.
This explanation is clearly missing some big chunks of information, and the following description aims to fill in the blanks a little.
We know that visible (white) light is made of up a spectrum of various wavelengths of light, with each associated with a separate distinct colour. When the sunlight goes through a water droplet, it acts as a tiny prism which disperses the light. Dispersing the light means breaking it open into it’s separate coloured wavelengths.
The waves of light move more slowly through water than through air, so as they enter the droplet the beams are forced to slow down and this makes them bend slightly (refract).
The beam of light reflects again on the inner surface of the droplet refracting once more and exiting at another point, where it speeds up again upon reaching the air. The refraction of light at these two points causes the dispersion of light into it’s spectrum of colours as visible to our eye. The pathway of a single light wave is shown in the diagram below.
This is where it becomes more complicated. First let’s look at why the rainbow is presented in the specific order of red, orange, yellow, green, blue indigo and violet.
Each light wave travels at a slightly different speed through water, and therefore refract at slightly different angles. The diagram shows the difference between the shortest wave (indigo) compared to the longest wave (red). The others all fit neatly between the two. The shorter waves refract at a slightly greater angle than the longer waves. This is described as the angle of deviation.
Next, let’s ask why we only see light exiting the droplet at one point? Does all of the light enter the droplet at one specified location (as per the simplified diagram above)? The answer is no. Light waves enter the droplet many different points, and are refracted inside and beam out in a jumble of colours. So why do we see the colours individually in a neat row? This is because of the angle of deviation.
Each individual wave in the spectrum refracts at a specific angle as we have said, with the red refracting out of the droplet at a slightly steeper angle than orange and so on. So, although the light enters and exits at many points, and refracts into a number of individual spectrums, there is always a maximum point at which each wave can exit. This greatest concentration of outgoing waves of each individual colour is located at the pre-determined angle of deviation, and to the observer it is here that it shines the brightest.
This also explains the next part of the question. Why is the sky lighter underneath a rainbow? Past the maximum angle of indigo’s deviation there can only be a mixture of colours – where the exiting waves converge again, which results in white light, meaning that the sky is lighter.
Why does a rainbow form an arc? A full rainbow is actually a circle, but from the ground we can only see a part of it.
Why do we sometimes see two rainbows? Secondary rainbows are fainter to the eye than the primary rainbow, and if you look carefully you will notice that they display the colours in reverse, with red at the bottom and indigo at the top. They are formed when the light waves are reflected twice inside the inner surface of a water droplet.
Photosynthesis is another of those theories that many people recognise by name. ‘The process by which plants convert sunlight to energy, using chlorophyll inside the leaves (which make them green)’ is the regurgitated phrase many people would use to describe it. There is actually an awful lot going on inside a leaf, far more than we imagine.
Plants have special light-gathering macro-molecules at their surface, which are composed of chromophores. The chromophores are astonishingly good at transferring energy from sunlight to a chemical energy that can be used by the plant. Around 95% of the sunlight gathered is converted almost instantaneously.
How does this happen? Scientists are beginning to suspect that quantum mechanics is at work. To set the scene let’s remind ourselves of the quantum theory that light can behave as both waves and also particles. The particles of light are known as photons, individual tiny packages of light.
Meanwhile, chromophores on the surface of the plant appear to vibrate and pulse in a continuous, coherent motion, which allows energy exchange between each molecule (explained in the following quotation).
Energy transfer in light-harvesting macromolecules is assisted by specific vibrational motions of the chromophores. We found that the properties of some of the chromophore vibrations that assist energy transfer during photosynthesis can never be described with classical laws, and moreover, this non-classical behaviour enhances the efficiency of the energy transfer. ~ Dr Alexandra Olaya-Castro (UCL Physics & Astronomy), supervisor and co-author of the research
When a single photon excites the chromophores it is able to travel down many different energy pathways at once, searching for the most efficient route to the reaction centre (where the actual chemical reaction takes place). To reiterate, a single photon travels down numerous vibrational pathways simultaneously – it is in many places at the same time!
This is known as superposition.
This was analysed in a study which looked at the behaviour of a single molecule of purple bacteria. The fact that the photons of light seemed to behave according to quantum theory was a real surprise for scientists who did not expect such a thing under biological conditions. The following is an extract from the abstract of the report.
The crucial step in the conversion of solar to chemical energy in photosynthesis takes place in the reaction centre, where the absorbed excitation energy is converted into a stable charge-separated state by ultrafast electron transfer events.
However, the fundamental mechanism responsible for the near-unity quantum efficiency of this process is unknown.
We reveal the presence of electronic coherence between excitons as well as between exciton and charge-transfer states that we argue to be maintained by vibrational modes.
Furthermore, we present evidence for the strong correlation between the degree of electronic coherence and efficient and ultrafast charge separation. We propose that this coherent mechanism will inspire the development of new energy technologies.
The final point in the abstract is the most interesting. If we can really understand what is happening inside a plant we could mimic the process to develop ultra efficient and incredibly fast ways of harnessing sunlight into usable energy. I am sure we will hear a lot more about this in the future!
What do you think? Have we missed out an essential example?
We would love to hear from you!