Every experiment ever conducted tells us something about the nature of science, whether a claim is false or not. Every new experiment results in new information, the fact that some experiments fail also provides us information about our knowledge and theories regarding the topic. But there are some experiments which change the course of science, that have a huge effect on the future, and change the way we think about the stuff around us. Here are 10 experiments, that I think changed the thinking and views held around that time, forever.
1. Rutherford’s Alpha Scattering Experiment (1909)
This was the time when we were not sure about the structure of atoms. One model predicted that atoms were like watermelons, with negative charge scattered around a positive region, keeping the whole atom neutral. Ruthurford’s alpha scattering experiment demolished this idea, and gave a bit more accurate model of the atom, the one high school students learn about, the classical atom. For his experiment, he fired beams of alpha particle( doubly ionised helium ions i.e a particle of two protons and two neutrons) on a thin gold foil. Rutherford observed that most of the alpha particles went through the foil without any deviations, or were deviated through very small angles. But, 1 in 8000 alpha particles, was deviated in very large angles, sometimes just reversing the path. Since alpha particles are positively charged, the deviation meant they were repelled by like charges(Opposites attract and similar repel in). The experiment showed that atoms were mostly empty space, with most of the mass concentrated in the centre, and this central nucleus was positively charged. To make this atom neutral, electrons had to orbit the nucleus as electron clouds. Thus the classical atomic model was introduced with proof.
2. Oersted and Faraday’s Experiments on Electricity and Magnetism (1820 and 1831)
Electricity and Magnetism were completely two independent process in the 19th century. But Things were about to be changed. These two experiments are arguably one of the most important experiments in the history. Oersted showed that current flowing in a wire produced a magnetic field, more importantly he showed whenever the current in a wire was changed, a change in magnetic field was observed by a nearby compass(Left Image). A decade later Michael Faraday demonstrated that without the presence of any batteries, changing magnetic flux from a bar magnet produced a current in a metallic wire (Right Image). He showed that when a magnet was moved in the vicinity of a conductor, the changing magnetic field cause a flow of current in the wire. the two experiments thus showed that electricity and magnetism were actually completely interrelated topics. One cause the other. These experiments gave rise to a completely different field of physics: Electromagnetism. Later on, light, and in extension all radiations were proved to be electromagnetic waves, when Maxwell proposed equations to explain the above observations mathematically. These experiments resulted in future experiments that demonstrated the immense applications of radio and x-rays. We have completely separate courses in electromagnetism in college, which shows the importance of the experiments and electromagnetism.
3. Issac Newton’s Scattering of Light (1660s)
Light. One of the most astonishing things was a complete mystery in the 17th century (not that it isn’t now). One of the most important experiments in optics would be the scattering of light by Issac Newton. He passed sunlight through a prism and saw a spectrum, a rainbow coming out of the other end. This changed the notion that white light was just a single component, but was actually made of a wide range of frequencies, which depending on their frequencies got scattered by different angles on passing through a prism, and the components of white light thus separated out. This also marked the existence of colours as a form of light, which together make up the white light of the sunlight. This experiment later gave birth to the method of spectroscopy in which light from different bodies was scattered and the resulting spectrum tells us about then different elements present in the radiating body. Below are two pictures by me a) a Halo formed by dispersion of sunlight and, b) a spectrum of mercury vapours observed during a spectrometric experiment:
4. Thomas Young’s Double Slit Experiments (1801)
Young passed a beam of light through a slit, and the light after passing through the slit passed through two other slits, and the resulting light fell on a screen. What was observed shocked every one. Young observed a pattern of alternate dark and bright fringes on the screen. This experiment proved ( or atleast showed) that light was a wave. The interference pattern (the crossing or superposition of waves is called interference) could only be explained if light was a wave, the cancelling of opposite vibrations produced dark bands, and similar vibrations produced bright bands.Light produced darkness! Even though phenomenon like photoelectric effect and compton scattering required light to be a particle, this experiment showed that it had wave nature too. This was not the end of the experiment’s future. Later it was showed that if a beam of electrons was passed through the slits, even they produced a similar interference pattern (provided the width was the slits were small enough), which meant even electrons behaved as waves under certain circumstances. This experiment marked the beginning of experimental quantum mechanics, all bodies have a dual nature, and behave as both particles and waves. More about this topic on my post on Schrodinger Equation: A Non-Mathematical Insight For Everyone. We ourselves have interference experiments in our graduate courses. Below are two interference patterns observed by me in my experiments: a) Newton’s Rings (Interference through wedge) and, b) Double slit Interference Pattern:
5. Miller and Urey Experiments (1953)
A series of experiments by biochemists Miller and Urey proved that evolution was a valid theory, and that life can emerge from carbon based compounds, under the right conditions. They passed an electric spark through a container with chemical mixture of methane, water, ammonia and hydrogen. It was observed that amino acids were beginning to form simultaneously in the mixture. Amino acids are the basic building blocks of proteins, which is necessary for life. Simultaneous production of these chemicals proved beyond doubt that under the balanced conditions, amino acids, and in extension carbon-based life could have originated in the medieval Earth.
6. Joule Demonstrating The Conservation Of Energy (19th century)
Joule conducted a simple experiment using different fluids to demonstrate the conservation of energy. His arrangement had a container with a fluid( water, whale oil etc), which had paddles around an axis, which was in turn connected to a weight through a rope that was hanging down a pulley. He made this weight fall down, which made the paddles churn the fluid, heating the fluid a few degrees after successive falls. By careful measurements and calculations he showed that potential energy lost by the weight was equal to the heat energy gained by the fluid, and thus that energy was and will always be conserved in an isolated system. In his respect, the work-energy equivalence constant is shown by ‘J’, and Joules is the unit of energy.
7. Discovery Of The First Anti-Particle By Anderson (1932)
Anti-particles were first predicted by Dirac, saying that quantum field theories allowed for both positive and negative charges for electrons and other particles. Antiparticles have all the same properties like mass, magnitude of charge, spin but have opposite charges. They were widely opposed, but in 1932, in August, Anderson while studying cosmic rays, discovered the first antiparticle, the positron, electron-but with a positive charge. When cosmic rays passed through a cloud chamber and lead under a magnetic field, particles similar to electrons were observed, but which curled in opposite directions to electrons. This showed that they had opposite charge as an electron (opposite charges curve towards opposite ,magnetic poles), but had similar mass. This was thus the first anti-particle to be discovered. Charge-less particles (like light photons) are their own anti-particles. When a particle and its anti-particle collide, they annihilate and produce two gamma photons.Till now many anti-particles like anti-proton(proton with negative charge), anti-neutrino and anti-tau have been discovered. This discovery marked the existence of a completely new world around us. This laid a benchmark for particle physics.
8. The Large Hadron Collider & The Discovery Of Higgs Boson (July,2012)
The Large Hadron Collider or LHC in Geneva, Switzerland, is the biggest experiment of science humanity has built yet,and gets updated every year, with much higher energy reaching capabilities. It has been the source of many discoveries in particle physics like up quark, down quark, gluons and many more subatomic particles, but one discovery stand apart. The discovery of higgs boson, or the so dubbed God’s particle. For a long time it was predicted that particles oved through an invisible field spread around the universe, and their interactions with this field gave them ‘mass’. the particle excitation of this mysterious higgs field was called higgs boson(Higgs predicted this field). Bosons are force particles in the standard model. What made it stand apart was that unlike quarks and gluons this was not predicted by the Standard Model, the most accurate model of particle physics yet. So basically, the mass you have, which is the result of the particles in your body ultimately, is because of their interactions with this invisible field. Massless particles like photons do not interact with the higgs field or higgs boson, and so have zero mass. More the interaction, more the mass. This discovery was a result of a bump in the actual curve of data with respect to the predicted curve, obtained from the proton collisions, at immensely high energies and almost light speeds.More recently the LHC predicted a fifth boson, and thus a fifth new force, and this month, five new particles.
9. Casimir Effect & Negative Energy by Casmir (1948)
In 1948, Dutch physicist, Hendrick Casimir showed that there was an attractive force between two chargeless plates in a vacuum because of quantum fluctuations, and this energy of vacuum is the negative energy(proposed power source for making wormholes), and the effect was called casmir effect. In a vacuum, due to quantum mechanics, and uncertainity principle, if one observes at very small scales, you will see particle-antiparticle pairs forming and annihilating simultaneously and randomly, and so in atomic scale vacuum is not possible. In the above experiment, the relatively less number of particles being produced in the thin space between the plates, to the number of particles on the opposite sides, resulted in a higher pressure on the opposite sides, which resulted in a net attraction between the plates. The energy resulting from this extraction, the energy of the vacuum is the negative energy, something right outside the sci-fi movies. Dirac showed that negative energy was possible, but normal particles cannot occupy states of negative energy because these are all completely preoccupied by antiparticles. Though the amount if negative energy generated in casimir’s experiment is too less to create a wormhole, it is a good start.
10. Measurement Of The Speed Of Light By Fizeau (1862)
Speed of light is a constant no matter how fast you move and is roughly 300,000 kilometres per second. But there was a time, when the speed of light was unknown. Galileo using crude methods had established that the speed of light was atleast 10 times more than sound, but the first accurate results were by Fizeau, and later a more accurate value was found when Foucalt improved his arrangement, which later was called Fizeau-Foucalt Experiment. Fizeau built an apparatus in which a cogwheel and a mirror were placed eight kilometers apart, and then sent pulses of light between them. He would rotate the cogwheel and observe how fast the beam of light traveled between the cogs of the wheel and the distant mirror, observing that if he spun the wheel very fast, the reflection back from the mirror was obscured because the light had struck one of the cogs.Fizeau suggested that the amount of time it took the wheel to move the width of a single cog was equivalent to how long it took for the light beam to travel to the mirror and back again. Since he knew how fast the cogwheel was rotating, and the width of a single cog, as well as the distance to the mirror, Fizeau was able to calculate the speed of light, obtaining the value 313,300 kilometers per second. This was still roughly 5% too high. Later, Faoucalt attached mirror to the cogwheel itself, and using the parameters available, calculated along with Fizeau, the speed of light to be roughly 299,796 kilometres per second.
This is already a long post, and I had to omit some experiments, like Galileo proving that all bodies take the same time to fall down, or the discovries of electron/protons and many others. Got any experiment that you found fascinating but I missed mentioning? Comment it below!The future holds many more great experiments and discoveries to be done. There is more to know about the nature of things around us, more to be proven wrong, more to be proven right, more to be learnt, and more to be discovered. Happy Reading!
-The Cosmogasmic Person
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