Ideas that changed our notion about the Universe.
1. Aristotle Fallacy; A notion that objects need force for their movement. It contradicts the idea of inertia. Newton corrected this by introducing the first law, things continue in their state of motion, a quality called as inertia, without requiring force and the motion changes due to application of force.
2. Earth is flat; that there is a boundary where you fall off its edge. [I am not going to explain or tell you how and when we found this was a horrendously hilarious and misleading notion we had. But it might have been used in the past by parents to discipline their teen-age kids. Don’t go out, you will fall off earth. That would have kept them in check.]
3. Rotational Dynamics; Earth is accelerating in a near circle in addition to about itself, so additional forces are acting that changes our observation about the world. Newton tried to understand this (not successful) in his last days, by rotating a bucket full of water, his laws could not explain the effects observed. His laws needed to be modified slightly. The same thing makes objects feel weightless by a given amount if they are accelerating towards a gravitational field (eg merry go round, satellites) This is the basis of many works of Einstein. First came Mach’s Principle which says observations made from objects that are accelerating in circular paths are to be corrected by fixing frames of references to stars that are so far away that the rotational motion is neglected. [if you shake your head while looking at stars and shake your head by looking at nearby objects such as a light post, evidently the light post shakes more and the stars less]. This helps in correcting observed phenomena from earth. Earth moves at 30 kms/second wrt sun and 0.5 km/second wrt itself. So a radar on earth will measure inaccurately all phenomena it measures. This can be corrected by measuring wrt a distant star rather than earth locations. Accelerated objects provide us non-inertial frames of references and non-accelerated* objects the inertial frames of references. (*objects with stationary location or stationary speed called as uniform velocity, no change in direction, no change in speed are defined as inertial frames, since the state or quality of inertia is associated with velocity. If velocity is not changing of an object, such objects provide inertial frames. )
4. Since Earth is not flat, not stationary in its location and not stationary in its speed, that is earth does not provide an exact inertial frame of reference, how to measure its exact state of inertia. It was wrongly assumed that our world is floating in a stationary matter called aether. Due to that everything can be measured wrt that aether since aether is not accelerating. Michelson, American Physicist, before Einstein’s time, performed a measurement known as Michelson Morley experiment, where light is made to travel in two different directions. If there would be aether we could measure the difference of path traveled by light, due to any relative motion of light wrt aether. There was no such path difference of light’s motion, throwing the notion of aether as a fallacy. So it was not only known that there is no aether or absolute inertial frames, it was also evidenced that speed of light is constant no matter where you measure it from.
5. These two above, Mach’s Principle and Aether Fallacy were the ground on which Einstein’s further revolutionary work was based on. He also equivalenced non-inertial motion with gravity. The reason why objects would feel weightless. The difference of position (distance) became a function of speed of objects from where observations are made. This was already the case with earlier ideas, known as Galilean Relativity. But now the time also became a function of speed of objects from where time is measured. So time and distance both being function of speed, time and space were no more as simply connected to each other as were predicted by Galilean Rules. You can say this is Galiean Fallacy. Physics works by removing the fallacies accrued by generations previous to the concurrent generation. But now not only position and time became function of speed of objects, but also mass became a function of speed of objects from where it is to be measured. In general every physical variable became a function of every other physical variable, this was of-course so before as well, but now the relation between the variables known as Transformation Laws became more complicated and more accurate than before.
6. At the same time when it was realized that, gravity and acceleration are equivalent because they are merely a curvature of space (and time and mass and speed and so on) it was also realized (mathematically as well) that space and time, electric field and magnetic field, mass and energy are also equivalent. That is for a given amount of one variable there is always a given amount of another equivalent variable that can be determined from a specific worked out Transformation Law. The laws and the transformation laws (the latter being a rule that relates quantities from one frame of reference to another or one operation to another) are together called as Law of Physics or Laws of Nature as befits your taste. (Physics is what we know about nature and not what nature ought to be like, so rather “laws of nature as we understand today” )
7. It was also realized that particle-objects and wave-phenomena are but two aspects of the same reality. Earlier there were Newtonian or Einsteinian laws of Particles and the same for waves. Now the same law would describe both, in a way consistent with what we observe. They are no more different laws for waves and different laws for particles. Its consequence was unprecedented. eg particle laws say particles always have mass. Wave laws say while waves have momentum and energy they don’t have mass. But now particles are there without mass and waves have particles associated with them, so waves also have mass. Earlier particles were specifed to one point like location. They did not have extensions. [point like particles]. But now point like particles are no more localized. Like waves they wander from Queen’s toes to Kings hair. A point particle, that electron is can exist simultaneously at many different locations with a probability for each location. Its likely that the electron is at an angle of 60 degree to the nucleus with a likelihood of say 30% and at 120 degree with a likelihood of say 20%. [These are fictitious examples I just gave] But altogether the electron must be found all the time around a fuzzy sphere around nucleus, with a likelihood of 100%. Then there are tons of other such counter-intuitive examples of the consequences of wave-particle duality.
From Aristotle through Newton to Einstein one thing led to another before we could see light as a wave as well as a particle. The fact that electrons are as particle like as they are wave like, not showing both qualities at the same instant is known as Complimentarity of wave and particle. But the fact that particle-electron has a wave-momentum and particle-momentum and they are the same also means that particle’s wavelength is given by its momentum.
[For a wave this was already the case: wave momentum = constant/wave-wavelength. That is they are inversely proportional, a concept that leads to wave-number. The momentum and wavelength of a wave are related the same way the Energy and the frequency of the wave are, inversely, this time by the concept of wave-timeperiod. Its for this reason there is de-Broglie relation, there is space-momentum uncertainty and there is energy-time uncertainty. These are just the formal variables, now everything is uncertain wrt everything else. ]
So wave and particles being the different aspect of same reality and that there are so many new ideas that replaced our fallacies or notions we have reached a far more counter intuitive modern world than ever before. The particular instance of interest is when a particle can have zero mass (zero mass is a wave property) in addition to the fact that a particle can also have a constant limiting velocity. (waves have zero mass hence a limiting velocity of 2.99 x 10 8 m/s, known as speed of light). This is the reason light has a limiting velocity in all frames of references, simply because its wave had a zero mass. If waves were also not particles it was impossible to see how photons which are zero mass particles could have that speed. Its simply that the waves had zero mass and c= 2.99 x 10 ^8 m/s speed but now it has agreed to proxy itself through the particle. A particle represents the waves properties. As simple as that. If you marry me you can carry my credit card.
Imagine if Aristotle’s fallacy was held to be sacrosanct we wouldn’t be knowing satellites and TV and LASER and telescopes today. We would be stuck like nomads that we were one day.