Research led by Alina Yousaf

Ibrahim Sadat, Arhama Javed, Hamna Azeem

‍

Introduction

Physics is that basic science which studies the behavior of matter, energy, and the fundamental forces of nature. The field has been broadly categorized into two fields: the classical physics and modern physics. Though both fields try to understand and describe the physical world, they do so indifferent ways and apply to different scales and conditions. The differences between classical and modern physics are based on their principles, applications, limits, and how the scientific revolutions led to modern physics.

Overview of Classical Physics
Classical physics is that part of physics, which was developed before the 20th century. These are mainly the theories and laws formed by pioneers like Isaac Newton, James Clerk Maxwell, and Galileo Galilei. Classical physics deals with the macroscopic world; hence, it should relate to large objects with a scale much greater than that of the atom and moving at much slower speeds than light. Classical physics comprises a number of key areas:

Mechanics: The motion of bodies can be defined by Newton's laws of motion and the law of universal gravitation.

Electromagnetism: Maxwell's equations describe electric and magnetic fields, giving details of their interactions with charges and currents.

Thermodynamics: It refers to the laws of conduct described with a relation to heat, work, and energy in systems.

Optics: Gives an account on light’s behavior in interaction with matter.

The principles of classical physics are deterministic, with future behavior of any physical system being precise if known exactly its current state and governing laws. For example, given the initial position and velocity of a particle in classical mechanics, Newton's equations for motion can give an absolute prediction for the trajectory that it will follow.

Principles of Modern Physics
Modern physics was invented in the first decades of this century. It overcame the limitations of classical physics and developed new ideas that better explained the behavior of matter and energy at very small scales, or quantum level, and at very high speeds, near the speed of light. There are two important pillars to modern physics:

Quantum Mechanics: It explains the behavior of matter and energy at the sub-atomic and atomic levels for which the classical physics do not provide results. Introduces concepts like wave-particle duality, uncertainty, and quantization of energy levels.
Theory of Relativity by Albert Einstein: that discusses objects moving at high speeds and explains gravity as a curvature of spacetime.
Where classical physics was largely determinable, modern physics is probabilistic. The probability of finding an electron in a given state in quantum mechanics can be predicted, but its position and velocity cannot be determined simultaneously, due to Heisenberg's uncertainty principle.

Some Major Differences Between Classical and Modern Physics

a. Scope and Scale:
Classical Physics: It is concerned mainly with objects at the macroscopic level, from planetary motion to everyday forces. Itis not capable of explaining phenomena at the atomic or subatomic level.
Modern Physics: This branch explains phenomena at atomic and subatomic levels-quantum physics-and at extreme speeds where classical physics is not enough. This is concerned with particles smaller than atoms, photons, and objects moving nearly at the speed of light.

b. Laws and Predictability:
Classical Physics Based on deterministic laws; that is, the initial conditions define with certainty the future of a system. For example, Newton's laws do provide the possibility of determining definite values of an object's future position and velocity.
Modern Physics: Introduces probabilistic laws. Quantum mechanics is known to be based on probabilities rather than certainties. For example, it is not possible to know simultaneously both the position of a particle and its momentum with infinite accuracy (Heisenberg's Uncertainty Principle).

c. Speed of Light and Relativity:
Classical Physics: Assumes that time and space are absolute. According to Newtonian mechanics, the flow of time is taken to be uniform everywhere and space is flat.
Modern Physics: According to the theory of relativity by Einstein, time and space are relative and dependent on the motion of the observer. At nearly the speed of light, the temporal coordinate moves slowly and the length of objects contracts (time dilation and length contraction); phenomena which cannot be explained in classical physics.

d. Concept of Energy:
Classical Physics: Energy is continuous: it can take any value in a range. For example, an object can be travelling at any speed and thus can have any kinetic energy.
In small-scale systems, energy is quantized, meaning it cannot be divided further; rather, it comes in chunks called "quanta." Electrons occupy only specific energy states in atoms and may make transitions between these states by absorbing or emitting specific amounts of energy (photons).

‍
e. Electromagnetism and Quantum Electrodynamics:
Electromagnetism Classically: The theory of electromagnetism as quantified through Maxwell's equations works fine in systems at larger scales but fails to satisfy the needs for systems at smaller quantum scales.
Contemporary Physics: Quantum electrodynamics (QED) is the quantum theory of electromagnetic phenomena, describing light and matter behavior at the quantum level. It reveals why classical physics could not come up with a sensible explanation of blackbody radiation as well as the photoelectric effect.

‍
f. Gravitation:

 Classical Physics: Describes gravitation in terms of Newton's law of universal gravitation where gravity is supposed to travel at a finite speed through a distance.
Modern Physics: Einstein's general theory of relativity explains gravity as an effect of spacetime curvature because of mass, and not as a force acting over a distance. This has accounted for certain phenomena that can be explained neither by classical notions of gravity nor by electrostatic forces, such as the bending of light near massive objects and the existence of black holes.

‍
Classical Physics Limitations
Despite all this success in the explanation of motion of planets, everyday objects, and the behavior of fluids and gases, there is a limitation in the classical physics theory which can be described below:

Microscopic Scale: There is no explanation given by classical physics regarding the behavior of particles at the atomic as well as subatomic level. Due to such limitations, the phenomenon of quantum mechanics emerged.
High Velocities: At the speed of light or near it, classical physics breaks down. Einstein's special relativity shows the behavior of time and space to be very much unlike anything envisioned in classical mechanics.
Extremely high gravitational fields: Newtonian gravity cannot describe gravitational fields such as black holes or regions like at the Big Bang.

‍
Triumphs of Modern Physics
Many phenomena that could not be described by the classical physicist have been aptly explained by the modern physics. Some of the important achievements of modern physics are as follows:

Quantum Mechanics: This explains atomic structure, chemical bonding, and behavior of particles at quantum level. It hassled to the development of technologies like semiconductors, lasers, and quantum computers.
Special and General Relativity: Discusses the nature of space, time, and gravity. It has experimentally confirmed phenomena like bending of light by gravity and time dilation in particle accelerators.
The Standard Model of Particle Physics: Unifies electromagnetic, weak, and strong forces describing the behavior of fundamental particles, that is, quarks and leptons.

‍
Conclusion: Classical vs. Modern Physics
While classical physics does a good job describing the world at everyday scales, modern physics explains what is happening in the universe at very small scales, at very large scales, and at very high speeds. Both fields, of course, are complementary; classical physics turns out to be a limiting case of modern physics in the domains of low speeds, large sizes, and weak gravitational fields.

In brief, the main difference between quantum and classical physics is the difference between a ramp and a staircase.

In classical mechanics, events (in general) are continuous, which is to say the move in smooth, orderly and predicable patterns. Projectile motion is a good example of classical mechanics. Or the colors or the rainbow, where frequencies progress continuously from red through violet. Events, in other words, proceed incrementally up a ramp.

In quantum mechanics, events (in particular) are unpredictable, which is to say "jumps" occur that involve seemingly random transitions between states: hence the term "quantum leaps". Moreover, a quantum leap is an all or nothing proposition, sort of like jumping from the roof of one building onto another. You either make it or you break it! Events in the quantum world, in other words, jump from one stair to the next and are seemingly discontinuous

Electrons, for example, transition between energy levels in an atom by making quantum leaps from one level to the next. This is seen in the emission spectra, where various colors, indicative of energy level transitions made by electrons, are separated by dark areas. The dark areas represent the area through which electrons make quantum, and therefore dis-continuous, leaps between energy levels.

Classic physics is very useful in many areas of science and engineering, but modern physics opened up new frontiers, and therefore, has given new insights into the nature of reality at its most basic levels. From quantum mechanics' treatment of the atomic world to relativity's descriptions of the cosmos, modern physics has significantly changed our understanding of the universe.

‍

‍Quantum Physics: The Newest Understanding of the Universe

Quantum physics, more popularly summarized as quantum mechanics, is the revolutionary turn in the understanding of nature by humans. While classical physics has been great at describing everyday objects and forces, quantum physics delves deep into the strange, often counterintuitive behaviors of particles at the atomic and subatomic levels. It is a domain of science that introduces us to the quirks of nature: particles existing in two states at once, probabilities instead of certainties, and interactions faster than the speed of light. The theoretical playground of scientists has now formed a base for state-of-the-art technologies like quantum computing and secure quantum communication systems.

1. The Birth and Basics of Quantum Mechanics:
   Quantum mechanics emerged at the beginning of the 1900s, once physicists realized that classical physics couldn't explain the phenomena occurring at a microscopic level. For example, theories about the behavior of light and matter at very small-sized atoms and photons, respectively, were not explained by the classical theories.

Until 1900, the first serious step was made in the sense that Max Planck found that energy is emitted and/or absorbed only in quantized "packets" or quanta, rather than being continuous. In one fell swoop, this completely rejected the classical belief of continuity with respect to energy. He recorded in his groundbreaking study: "Energy is not emitted continuously but rather in discrete energy elements" (Planck, 1901). His discovery then provided a basis for the whole quantum mechanical theory. Not long thereafter, Albert Einstein furthered this idea. He explained the photoelectric effect, in 1905, in which Light itself acts like a stream of particles called photons. His work started to reinforce the idea that energy and matter did not always act in ways that classical physics had predicted. According to Einstein, "Light consists of quanta of energy, which move through space in a straight line" (Einstein, 1905).

This wave-particle dual nature of light became one of the cornerstones for quantum theory.
Another major breakthrough came in 1913, when Niels Bohr applied quantum ideas to the atom itself. He postulated Electrons move around a nucleus in specified energy levels and that only between those energy levels can they jump by the absorption or emission of quanta of energy. In one stroke, many puzzles of atomic behaviour fell into place, and its creator became celebrated as one of the founders of quantum mechanics.

2. Basics of Quantum Mechanics

‍a. Wave-Particle Duality:
Another interesting phenomenon in quantum physics is wave-particle duality. It is the principle dealing with how particles, such as electrons and photons, can be sometimes wave-like and might display wave properties under specific conditions and would otherwise exhibit particle-like properties at other times. A very popular experiment that demonstrates this is the double-slit experiment, where the electron traveling from its source passes through the two slits it is meant to pass through, matching the wave behavior, and interferes with itself at the screen placed behind the slits for observation. But if you then look at which slit which electron went through, it behaves much more like a particle. This duality doesn't occur within classical physics, and such observations are among those that demonstrate quantum systems are fundamentally very different from any classical systems.

b. Uncertainty principle
In 1927, Werner Heisenberg made a postulate now called the uncertainty principle, which states you cannot know with infinite precision both the exact position and the exact momentum of any particle in space at the same time. Heisenberg's deep realization was to understand that the more precisely we know one property-be it's the position-the less precisely we can know the other property-like momentum. Simply put, he described it: "The more precisely the position is determined, the less precisely the momentum is known" (Heisenberg, 1927). It is not because of any defect in our measuring devices that this uncertainty occurs; rather, it is an inherent property of quantum systems challenging predictability, which classical physics relies on.

c. Superposition and Entanglement
Superposition is a concept peculiar to quantum mechanics. Superposition postulates that until measurement, particles exist in states multiple. The famous thought experiment of Schrödinger's cat illustrates this principle-the cat in a sealed box is both alive and dead until you open the box and take a good look.

The phenomenon is coupled with the concept of quantum entanglement, in which two particles become so entangled that the state of one instantly affects the state of its peer, no matter the distance between them. Einstein, who felt uneasy from the implications of entanglement, termed it "spooky action at a distance" (Einstein et al., 1935).

3. Recent Developments in Quantum Physics
   Quantum mechanics is anything but an abstract branch of learning; it has become the very basis for a set of advanced technologies which, in the future, are bound to blow the lid off. The most impressive area is quantum computing, whereby scientists attempt to exploit strange features of quantum particles to process information in ways traditional computers cannot.

In 2019, Google had made headlines in claiming to achieve 'quantum supremacy' with their quantum processor called the Sycamore processor. This quantum machine finished a complex calculation in just 200 seconds, whereas a classical supercomputer would take around 10,000 years. As put by Google investigators: "Quantum processors based on superconducting qubits can now perform tasks beyond the reach of classical processors" (Arute et al., 2019).

This set off an interest in quantum computing, both in the tech industry and within government circles.

Another fast-moving area is quantum cryptography. In 2020, two researchers from China set a record-much like the satellite experiment-1,200 kilometers for the distance over which quantum communication, in this case via a secure QKD connection, could be achieved. It has great potential to construct unconditionally secure communication networks. Major projects are underway worldwide to unlock quantum's full power, including the Quantum Flagship, which is the major European Union-funded initiative that will drive research in quantum communications and quantum simulations, leading with funding of over €1 billion. It is among the many initiatives showing governments and enterprises that bet big on the future of quantum.

4. Major Ongoing Projects in Quantum Physics
   Various key projects happen to be at the leading edge in quantum research;

IBM Quantum System One: Devised by IBM, this is one of the most advanced quantum computers, and IBM provides access through its IBM Q platform. This open-source system allows the researcher or scientist to investigate the operability of quantum algorithms, part of IBM's vision to bring quantum computing into practical use in industries like finance, logistics, and healthcare. 

Microsoft Quantum Program: Contrary to that, Microsoft is charging forward to make the quantum computers with topological qubits that would be more stable than those from the current range of qubit technologies. The company is racing to develop a scalable, practical quantum computer that has the ability to solve real-world problems. China's Quantum 

Communication Network: Micius is the world's very first quantum satellite China launched into space in 2016 to test secure communications using the process of quantum key distribution. Its aim was to be able to establish an unbreakable quantum highway across the world, thus positioning it in the leading place for this type of technology. These projects are a signal and a sign of global competition and collaboration that is pushing quantum research forward. In the next few decades, quantum technology could revolutionize everything from computing and cryptography to medicine and beyond.

Conclusion:
Quantum physics has completely redefined the way we understand the Universe by providing ideas that, quite unmistakably, challenge the viewpoint associated with classical physics. From outlandish, utterly counterintuitive suggestions like wave-particle duality and superposition to the practical use of quantum computers, the scope of influence of quantum mechanics is humongous. Today, with major companies and governments investing tremendous sums in quantum research, the sky's the limit. The opportunities found in quantum technologies will be ultimately game-changing, shaping whole industries and our everyday lives in ways we can hardly begin to imagine as they continue to advance.

‍

Newtonian Mechanics

Newtonian mechanics, also known as classical mechanics, is a fundamental framework in physics that describes the motion of an object under the influence of forces. The true foundation of classical mechanics came with Sir Isaac Newton (1642-1727), whose work expanded upon the discoveries of earlier scientists. The mathematical principles of natural philosophy published by Isaac Newton in 1687 is one of the most influential works in the history of science, in which he formulated his three laws of motion and the law of universal gravitation. These laws govern how objects respond to forces, which can result in motion, rest, deformation, or equilibrium.

History of Newtonian mechanics:

The history of Newtonian mechanics traces back to ancient philosophers like Aristotle, who believed objects required continuous force to move. During the Renaissance, Galileo introduced the concept of inertia, laying the groundwork for Newton's breakthroughs. Sir Isaac Newton in his 1687 work principia, formulated his three laws of motion and law of universal gravitation, providing unified explanation for both terrestrial and celestial motion. These ideas revolutionized physics, giving rise to classical mechanics.

 Newton’s Laws of Motion:

Newton’s First Law (Law of Inertia):  An object at rest will remain at rest, and an object in motion will continue moving in a straight line at constant velocity unless acted upon by an external force. This law explains that forces are required to change an object’s state of motion. Without a force, an object velocity remains unchanged.

Newton’s Second Law (Law Of Acceleration): The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, mathematically it is represented as F=ma

Where F is the force applied, m is the mass of the object, and a is the acceleration. This law explains how the magnitude of force affects the motion of objects, with heavier objects requiring more force to achieve the same acceleration as lighter objects.

. Newton’s Third Law (Action and Reaction): For every action, there is an equal and opposite reaction. This means that forces always occur in pairs; when one object applies a force on another, the second object an equal and opposite force back on the first object.

‍‍

Types of Forces and Their Effects

 Gravitational Force: Gravity is an attractive force between two masses. Newton’s law of universal Gravitation describes it mathematically as: F = G(m₁m₂)/R².

Effects:

●     Weight: The weight of an object is the gravitational force acting on it, depending on its mass and the mass of the planet it is on. This weight affects how objects fall to the ground.

●     Orbital motion: Gravity governs the motion of celestial bodies, causing planets to orbit stars, moons to orbit planets, and satellites to orbit earth.

●     Free-fall motion: Objects near the earth's surface experience acceleration due to gravity‍

Frictional Force: Friction is the force that opposes the relative motion between two surfaces in contact. There are two main types:

●       Static friction: Preventing an object from moving until a force is applied.

●     Kinetic friction: Acts on moving objects and opposes their motion

  Effects:

●    Heat Generation: When two surfaces rub against each other, friction generates heat.

●     Wear and Tear: Friction can lead to the gradual wearing down of the materials, such as tires of a vehicle or the soles of shoes.

●     Reduction in motion: Friction slows down moving objects, like a sliding book eventually coming to rest.

‍

Tension Force: Tension is a force transmitted through a string, rope, cable or any flexible object when it is pulled tight by forces acting on opposite ends

 Effects:

●    Support systems: Tension supports objects in various applications, from hanging a picture frame to the cables holding up suspension bridges. The tension adjusts based on the weight and distribution of forces.

●    Motion control: In systems like pulleys, tension can change the direction of force application, allowing for more efficient lifting or movement of objects.

 Applied force: Any force that is intentionally applied to an object by another object or agent. It can cause acceleration, deformation, or motion, depending on the situation.

 Effects:

●     Acceleration: Applied force can change an object's velocity (as per newton's second law)

●     Deformation: If the object can not move (e.g. a fixed beam) the force may cause bending, stretching, compression .

 ‍

Spring force: This force is described by Hooke’s Law, that the force exerted by a compressed or stretched spring is directly proportional to its displacement from the equilibrium position. Mathematically, Hooke’s Law can be expressed as: F=-k . x

‍Effects:

●     Elastic deformation: when a spring is compressed or extended, it stores potential energy and exerts a force in the opposite direction.

●     Oscillations: springs often cause oscillatory motion, as in mass spring system or suspension system vehicles.

 ‍

Applications of Newtonian Mechanics

●    Engineering and construction:

               In structural engineering, Newtonian Mechanics is used to analyze forces, stresses and equilibrium in buildings, bridges and other structures. The stability of these structures rely on calculations based on Newton’s Laws to ensure they can stand forces like gravity, wind and seismic activity.

●    Automotive design:

  Newtonian mechanics is central to understanding how vehicles move. It helps in designing cars for better performance, fuel efficiency, and safety features as well as understanding crash dynamics to improve passenger safety systems like airbags.

 ●    Sports:

In sports like basketball, soccer, cricket, Newtonian mechanics describes how objects move through air under gravity influence. It allows athletes to improve their techniques.

 ●   Mechanical systems:

            Newtonian mechanics is central to understanding the design and analysis of simple machines like pulleys, levers and gears and more complex systems like engines. Understanding how the forces can be transmitted through mechanical components help in making more efficient machinery.

 ‍

Limitations of Newtonian mechanics

Newtonian mechanics, while highly effective in many conditions, has several limitations.

●    High velocities (close to the speed of light):

           Newtonian mechanics fail when objects move at speeds close to the speed of light. In such cases the effects predicted by Einstein’s theory of relativity becomes significant, and Newton’s laws no longer accurately describe the motion.

●    Quantum mechanics:

          Newtonian mechanics does not apply to the behavior of small particles like electrons, atoms and subatomic particles. Quantum mechanics is needed to explain phenomena at these scales.

●    Strong gravitational fields:

          In the presence of very strong gravitational fields, such as near black holes, Newtonian mechanics becomes inaccurate. General relativity, Einstein’s theory provides a more accurate description of gravity in such intense environments.

‍

‍