Grade 12 ↓
Modern and quantum physics
Modern physics focuses on two major breakthroughs of the early 20th century: relativity and quantum mechanics. Classical physics, which includes Newton's laws of motion and Maxwell's electromagnetism, is extremely effective at describing everyday phenomena. However, it begins to break down when dealing with the very fast, the very large, the very small, or the very intense. In modern physics, we venture into these areas to understand how nature behaves in these extreme cases.
Relativity
Albert Einstein's theory of relativity revolutionized our understanding of space, time, and gravity. There are two parts of relativity: special relativity and general relativity.
Special relativity
The special theory of relativity, introduced by Albert Einstein in 1905, addresses the behavior of objects traveling at high speeds. It is based on two principles:
- The laws of physics are the same for all observers, regardless of their relative speed.
- The speed of light in a vacuum remains constant for all observers, regardless of their relative speed or the speed of the light source.
A major consequence of these notions is time dilation, which means that time passes slower for moving objects than for a stationary observer.
Δt' = Δt / √(1 - v²/c²)
In this equation:
Δt'is the time interval measured by a moving observer.Δtis the time interval measured by a stationary observer.vis the velocity of the moving object.cis the speed of light.
Example
Imagine a spaceship passing the Earth at 90% of the speed of light. An hour passes on the spaceship, but much longer has passed on Earth. This shows how time slows down for a fast-moving object.
General relativity
General relativity, proposed by Einstein in 1915, explains gravity not as a force, as Newton did, but as a curvature of spacetime due to mass. According to this theory, massive objects such as planets and stars distort the fabric of spacetime, and these distortions guide the motion of smaller objects.
Visualization of curved spacetime
In this simple diagram, the circle represents a massive object, and the line represents how spacetime is curved around it.
Quantum physics
Quantum physics, developed in the early 20th century, is the branch of physics that deals with the behavior of very small particles. It challenges many classical intuitions with surprising predictions about the nature of reality.
Wave–particle duality
One of the most fascinating aspects of quantum physics is wave-particle duality. This theory states that every particle, like an electron or a photon, can exhibit both wave-like and particle-like properties, depending on how it is viewed.
Double slit experiment
In a double slit experiment, light or electrons are fired through two parallel slits. On the other side, a screen shows an interference pattern of multiple bands, indicating wave-like behavior. However, when the particles are observed passing through one slit, they behave like particles.
In the SVG above, particles come in from the left, pass through the slits, and create an interference pattern on the right.
Quantum entanglement
Quantum entanglement describes a phenomenon in which two particles become intertwined, such that the state of one particle instantaneously affects the state of the other, no matter how much distance there is between them. This was one of the ideas that puzzled Einstein, leading him to describe it as "spooky action at a distance."
Visualization of entangled particles
This image shows two entangled particles, one blue and one red, connected by entanglement (dashed line).
Fundamentals of quantum mechanics
Uncertainty principle
The uncertainty principle, formulated by Werner Heisenberg, states that certain pairs of physical properties, such as position and momentum, cannot both be known precisely at the same time. The more precisely one is known, the less precisely the other can be known.
Δx * Δp ≥ ħ/2
Here:
Δxis the uncertainty in position.Δpis the uncertainty in momentum.ħis the decreasing Planck constant,hdivided by 2π.
Quantum superposition
According to quantum superposition a particle exists in all of its possible states simultaneously until it is measured, after which it 'chooses' a state. A famous example of this concept is Schrödinger's cat, a thought experiment depicting a cat that is both alive and dead until it is observed.
Schrödinger's cat thought experiment
A cat is placed in a sealed box containing a poison that can be released by a random quantum event. According to quantum mechanics, until the box is opened, the cat is in a state of being both alive and dead. This thought experiment highlights the unique nature of quantum superposition.
Conclusion
Modern and quantum physics have vastly enhanced our understanding of the universe. By exploring the minuteness of particles and the vastness of space, these theories provide a foundation for technological advancement and deepen our understanding of the physical world. Although often contradictory, these fields depict a universe that is far richer and more complex than what can be seen through the lens of classical physics. Both relativity and quantum mechanics challenge, enlighten, and inspire us, giving us a deeper understanding of the complexities of our universe.