Quantum mechanics is the mathematical foundation of quantum physics, the branch of science that describes the behavior of systems at atomic and subatomic scales. While Newton’s laws form the basis of classical mechanics—which explains how bridges, planes, and other everyday objects work—quantum mechanics abandons the precise results of those laws for a system based on probability.
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In the quantum world, particles such as electrons are “quantized,” meaning they can only hold specific values of energy or momentum. These particles also behave like waves, with their wave function predicting where they might be found at any moment as probability clouds called orbitals.
Newton's laws form the core of classical mechanics, suitable for everyday objects and speeds. The term is relatively new, distinguishing the branch of physics from quantum and relativistic mechanics.
Light and electrons can act like particles when observed, but behave like waves in motion, creating patterns through interference. Even larger objects, like baseballs, have wavelengths but are negligibly small.
Semiconductors, crucial in electronics, operate based on quantum superposition. Lasers use stimulated emission, a quantum process, and MRI machines leverage the quantum spin of hydrogen atoms for imaging. Atomic clocks measure time with unprecedented precision using quantum transitions.
All objects above absolute zero emit electromagnetic radiation, with the amount and distribution determined by temperature alone. The shape and intensity of this radiation follow Planck’s law, while Wien’s law governs the peak wavelength.
When scientists first tried calculating the radiation emitted by a heated object, their assumption was that energy was equally distributed across wavelengths and produced infinite energy at low wavelengths. This contradicted observations, which showed near-zero energy intensity at those values.
Smartphone cameras use sensors like CMOS or CCD to capture light by converting it into electrical signals using the photoelectric effect. Einstein explained this effect by showing that light behaves as particles called photons—not just as waves—which earned him the Nobel Prize.
When electrons within the atom drop to a lower energy level closer to the nucleus, they lose energy and produce light with energy equal to the difference between energy levels. Electrons can also move up to higher energy levels if they absorb light with appropriate energy.
Unlike Bohr’s fixed paths, the quantum model describes electrons as exhibiting wave-like behavior and forming standing waves with nodes and antinodes. Their exact positions can’t be known, only the probability of where they might be within orbitals.
Just as waves are extended objects whose heights change across space, quantum waves dictate that the probability of an object existing in different locations across space varies. Like water waves, the probability waves can combine, changing the heights—and therefore probabilities—in different locations.
Since the time our ancient human relatives began using stone tools to perform tasks, humans have harnessed scientific knowledge and new technologies to advance our ability to feed ourselves, increase our health, expand the boundaries of our knowledge, and much more. From artificial intelligence and quantum computing, to optimizing the human body in pursuit of a long and healthy life, and much more—learn about these topics and more with our smart-but-digestible overviews and expert-curated resources.