In Legacy of Light, modern-day astrophysicist Olivia makes a breakthrough when she discovers the first evidence of a planet in formation. This kind of discovery beyond our solar system requires a lot more than the classical mechanics >envisioned by Isaac Newton >. The question is, what kind of physics is most needed to understand? That of quantum mechanics, which deals with the very small, or Einstein’s relativistic mechanics, which deals with the very large? Or, do we need a new, more complete picture of the universe?
“Anyone who is not shocked by quantum theory has not understood it.” – Niels Bohr
Quantum mechanics is essential to our understanding of all the fundamental forces of nature except gravity.
Quantum mechanics is the foundation of several branches of physics, including electromagnetism, particle physics, condensed matter physics, and even parts of cosmology. Quantum mechanics is also essential to the theory of chemical bonding (and hence all of chemistry), structural biology, and technologies including electronics, information technology, and nanotechnology. A century of experiments and of work in applied science has proved quantum mechanics successful and practical.
Quantum mechanics began in the early 20th century, with the groundbreaking work of Max Planck and Niels Bohr. The wider physics community soon accepted quantum mechanics because of its highly accurate empirical predictions, especially in systems where Newtonian mechanics >fails. A major early success of quantum mechanics was its explanation of particle/wave duality, or how subatomic particles and waves share many similar properties.
Particle/wave duality is perhaps the easiest way to get acquainted with quantum theory because it shows, in a few simple experiments, how different the atomic world is from our world.
Double Slit Experiment
The results of the double-slit experiment led scientists to ask many questions, not only about what happens at the microscopic level of the universe. What is the role of an observer in any experiment? How does probability weigh in? These questions led Niels Bohr to what is now known as the Copenhagen Interpretation: Nothing is real unless it is observed.
So, if quantum mechanics grapples with the very small, what about the very large? Two hundred years after Newton, a Swiss patent lawyer named Einstein changed our understanding of how our universe works on the largest scale. Grappling with light, gravity, and the space-time continuum, Einstein showed the world that the universe looked very different from the one envisioned by Newton.
PBS Nova special, The Elegant Universe: Einstein’s Relativity
If we have a certain kind of physics to understand our world on the level of atoms and the world’s building blocks and another kind of physics to understand celestial objects, we’re all set, right?
Wrong. When looking at the sky, some problems seem to require BOTH a small-scale and large-scale interpretation. But when scientists try to combine them, the answer is gibberish. This is because quantum mechanics does not grapple with the force of gravity and Einstein’s universe does not grapple with the rules that specifically apply to matter on the smallest scales.
Now, some scientists think they may have found a way to link the theories in a “theory of everything.” This theory is known widely as “string theory.” Currently, science does not have the ability to test experimentally if the theory is correct, because no modern instrument can see matter that small. Time will tell, but string theory is currently the best hope of the field to unite everything we know about our world and universe.
Here are some videos from the PBS Nova special The Elegant Universe that dig deeper into string theory.
