Science is about making sense of the world. Most of us are endowed with a least 5 major senses: sight, hearing, touch, smell and taste. Other senses include that of temperature, pain and time, for example. Some senses are common to our own experience. For instance, a hawk has sense of sight just like we do except that its vision is generally much sharper than ours. Other senses, such as magnetoreception (the ability to detect direction based on the Earth’s magnetic field) is alien to us but observed in bees. And, of course, there is this other sense which is not so common at all: common sense.
So, to make sense of the world, we capture whatever information we need through these different senses and process it all in our brain to finally come up with our perception of the world. Sometimes our senses aren’t sufficient and we therefore have to use extensions of our senses to gather the extra bit of information needed. A telescope allows us to see further than our eyes can ever see. Hearing aids are required for people whose sense of hearing have been damaged. Not all senses are (yet) extensible. Our sense of taste is limited, for now, to our own taste buds. We have no known devices that can make us taste more flavours than we are already aware of. Perhaps, one day, there will also be extensions to our sense of touch so that we are able to perceive many more textures than we are currently limited to. In spite of their limitations, our senses have been shaped through millions of years of evolution to enable us to adapt to our environment. Our hearing is tuned to a certain range of frequency that is most common and useful in our habitat. Our taste has developed so as to warn us against potentially poisonous plants while being able to appreciate those which provides essential nutrients. To understand our senses, we not only have to look at them from the evolutionary point of view but, more importantly, from the more fundamental physical perspective. Let me explain.
Sight, for example, is the ability to detect the presence of light. For this to happen you need something, a sensor or some sort, that can react to radiation of a certain kind; to electromagnetic radiation. Light, visible light, is but a subset of electromagnetic radiation or waves. Ultra-violet (UV) radiation or microwaves are other forms of electromagnetic radiation – see Spectrum for a more detailed description. The human eye has adapted to recognise only one part of this radiation: the rainbow part. That is, only the part where we can see the colours ranging from red to violet. Anything below red or above violet is invisible to the human eye. Some insects, however, can detect UV. So, no matter what type of sight there exists, it is such that it reacts to electromagnetic radiation. There is an actual physical change in the eye (or part of the eye) when it is exposed to light. The physical change is, more precisely, a chemical change. (Chemistry, of course, is a subset of Physics – any chemical change implies an underlying physical one.) There is a molecule, in the cells that make up the retina, called rhodopsin which reacts to light. A solution of rhodopsin immediately changes from pale yellow to pale purple when exposed to light. This shift in colour is absolutely critical in sending the information, via the optic nerve, that the presence of light has been detected. There again, the signal sent via the optic nerve to the brain, there is a physical phenomenon involved. Small electrical signals are sent via the nerve. Electricity is ultimately responsible for sending information through the nervous system. The most interesting thing about this, though, is not that it all depends on physical properties such as electricity and electromagnetic radiation (this is almost a given); no, what is astounding is that rhodopsin, the light detecting molecule, is present in not just humans but throughout the animal kingdom. Whether it’s a bull’s eye or a butterfly’s eye or even organisms that don’t even have an eye, per say, such as a bacteria, they all have rhodopsin. This is absolutely surprising for it shows that, yet again, all the organisms have, at the very least, one common thread. Organisms which existed millions, if not billions, of years ago have the same molecule for light-detection that the organisms we encounter today. Rhodopsin can be traced back to the very early stages of evolution of life on our planet.
You see, our sight is not just a means for us to see things around us. It is a highly advanced system, that has evolved over millions of years, to enable us to make the most of our environment, adapt and survive. While sight has to do with detecting electromagnetic waves, hearing is about detecting another type of wave: sound wave. Sound is the vibration of air molecules transmitting a form of energy we call sound energy. Ears have evolved to capture those sound waves and transmit them to the brain to be decoded. All this decoding and processing of information requires a lot of brain power. Imagine processing the information received from most, if not all, inputs at the same time. Imagine rubbing the rough peel of a certain fruit. Touch is of course essential in detecting the roughness of the peel. As our fingers rub against the textured surface it makes a sound – again, we can hear that. We can also see the fruit – its bright reddish hue. And it is perhaps even emanating a nice odour – we can smell that it is ripe. Already there are four senses actively sending information to the brain to be processed – a very intensive operation indeed. Now imagine if one of these senses were deactivated. Let’s say we could not see. What would then happen is that the brain power, now made available by deactivating sight, is distributed over the remaining three senses, namely hearing, smell and touch. Furthermore, if smell was also deactivated then hearing and touch would take up the remaining brain power. So all the processing is now focussed on just decoding sound waves and information sent from our finger tips. The point here is that, if one or more senses become redundant then the other remaining ones are heightened. We can hear better if we close our eyes.
How about touch? What is the physical basis of this sense? If sight and sound are about detecting waves, touch is a mixture of different senses. It is about detecting changes in pressure, temperature, and even pain. Pressure and temperature, you would agree, lie within the realm of physics. As for smell and taste, these are based on detecting molecules; aromatic molecules. Again, on one level this has to do with chemistry – understanding how the receptors in our nose and on our tongue are reacting to the molecules. But the actual interaction of these molecules are governed by physical laws. By the mechanisms laid down according to the principles of physics.
The world, therefore, comes to us through our senses. How we then interpret the information we receive is up to us. Another sensation which is also very subjective is that of the passage of time. And, right now, I sense that it is time we conclude on this parable. To understand our world we have to go right down to the fundamentals; right down to the first principles. What more exciting way is there to do this than to explore the wonderful world of science?