Everything Everywhere Daily: History, Science, Geography & More - The Fundamental Forces of Nature

Starting point is 00:00:00 Everything in the universe, from galaxies to the atoms in your body, is driven by just a few fundamental forces. It took centuries for a physicist to identify these forces, but once identified, they believed that some of these forces were merely different manifestations of the same underlying phenomenon. And once they realized this, some physicists felt that all the forces in nature could be explained by a single theory of everything. Learn more about the fundamental forces of nature, and the quest for a grand unified theory, and a theory of everything on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed.

Starting point is 00:00:59 It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. Before we get into the weeds on what the fundamental forces of nature are, I should explain what a fundamental force of nature is. A force is a push or pull that acts on an object causing it to move, change direction, or deform. And there are many forces in the world. You could push or pull on an object yourself and exert a force on it. A fundamental force is one that cannot be explained as the result of any other force or interaction. It's a basic,

Starting point is 00:01:41 irreducible interaction of nature that governs how particles and matter behave. In the case of you pushing an object, you can keep reducing it down to the muscles in your body, then the food you weight, and then the energy in the molecules released by changing molecular bonds. All observed forces in the universe arrive from combinations or manifestations of these fundamental forces. There are generally considered to be four fundamental forces in the universe. Gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. And I know that some of you right now might be raising a technical objection, but I will be getting to that in a bit. So let's start with gravity, the weakest of the four fundamental forces.

Starting point is 00:02:30 It has an infinite range and always exerts an attractive force. It acts between all objects with mass and is responsible for the structure of the universe on large scales, such as the orbit of planets, the behavior of stars, and the formation of galaxies. To appreciate just how weak gravity is, lift your hand in the air. Your arm is able to counteract the entire gravitational pull of the planet Earth. The discovery of gravity as a fundamental force evolved over centuries, culminating in Isaac Newton's groundbreaking work in the 17th century. In the ancient world, philosophers like Aristotle believe that objects moved

Starting point is 00:03:10 towards their natural place, such as stones falling towards the earth. And this was a qualitative idea, not a universal or mathematical one. A more scientific approach to gravity began with the work of Galileo Galilei in the early 1600s, who conducted experiments that showed all objects fall at the same rate, regardless of mass, contradicting Aristotle's views. The true formulation of gravity as a universal force came with Isaac Newton. In 1687, he published the Philosophé Naturalis Principia Mathematica, where he proposed the law of universal gravitation. Newton declared that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

Starting point is 00:04:00 Although Newton described how gravity works, he didn't explain what it is. That deeper understanding came with Albert Einstein in 1915, who showed in his general theory of revelativity that gravity is the result of the curvature of space time caused by mass and energy. The second fundamental force is electromagnetism, which is much stronger than gravity and also has an infinite range. It acts between charged particles and is responsible for electricity, magnetism, light, and most of the interactions you encounter daily, like friction and chemical bonding. Opposite charges attract and light charges repel. The discovery of electromagnetism as a fundamental force unfolded over centuries,

Starting point is 00:04:46 beginning with separate observations of electricity and magnetism before their unification in the 19th century. In ancient times, people observed that amber, when rubbed, could attract light objects, which was an early observation of static electricity. Likewise, natural magnets were known for their ability to attract iron. These phenomena were thought to be unrelated until much later. The modern understanding began in the 18th century with scientists like Benjamin Franklin, who experimented with electricity and proposed the concept of electric charge. However, the turning point came in 1820, when Hans Christian Orsted discovered that a current

Starting point is 00:05:24 carrying wire could deflect a magnetic compass needle. This was the first evidence that electricity and electricity and and magnetism were connected. This discovery launched a wave of research. Andre Marie Amperre soon showed that electric currents produced magnetic fields and formulated mathematical laws describing this relationship. Michael Faraday then discovered electromagnetic induction in 1831, showing that a changing magnetic field could induce an electric current.

Starting point is 00:05:51 The unification of these insights came through James Clerk Maxwell, who in the 1860s formulated a complete set of equations, now called Maxwell's equations that described how electric and magnetic fields are generated and interact. The third fundamental force, the strong nuclear force, is the strongest of the four forces, but acts only over extremely short distances, about the size of an atomic nucleus. It holds protons and neutrons together in the nucleus and binds corks inside of protons and neutrons. The discovery of the strong nuclear force arose from the mystery of how atomic nuclei stayed together despite the powerful repulsion between positively charged protons.

Starting point is 00:06:37 Since light charges repel each other, something stronger than electromagnetism had to be at work inside the nucleus. This problem became evident after the discovery of the atomic nucleus by Ernest Rutherford in 1911. His gold foil experiment showed that atoms have a dense, positively charged core. But if the nucleus was made up only of protons, the repulsive electromagnetic force should blow it apart. Something had to hold it together. In 1932, James Chadwick discovered the neutron, which helped clarify the structure of the nucleus. Physicists now understood that atomic nuclei consisted of protons and neutrons, collectively called nucleons. But the puzzle deep

Starting point is 00:07:20 Since neutrons carry no charge, their presence didn't explain how they could help bind the nucleus together. To solve this, physicists proposed the existence of a new, powerful force, which acts only at very short ranges of about a femtometer. In the 1930s, Hideki Yukawa developed the first theoretical model of the strong force. The final of the fundamental forces is the weak nuclear force, which is responsible for radioactive decay and nuclear fusion. stars. It also operates at very short distances and can change one type of subatomic particle into another, such as turning a neutron into a proton during beta decay. The story begins in the early 20th century with the study of beta decay, a type of radioactivity where the nucleus emits an electron or positron. In 1896, Henri Beccarell discovered radioactivity and soon after

Starting point is 00:08:15 beta radiation was identified as one of its components. But a puzzle emerged. In beta decay, energy and momentum seemed not to be conserved. To resolve this, Wolfgang Polly proposed in 1930 that an invisible, neutral particle must be escaping along with the electron. He called it a neutron, but it was later renamed the neutrino after James Chadwick discovered the actual neutron in 1932. Enrico Fermi incorporated this idea in 1934 into the first full theory of beta decay, introducing the concept of a new fundamental force, the weak force. Before I mentioned that some of you may have raised an objection when I said that there were four fundamental forces.

Starting point is 00:09:01 For the purpose of studying basic physics, four are usually given, but in reality, based on our current understanding, there are three. and this is because it turns out electromagnetism and the weak force are actually the same thing. And they're now known as the electro-weak force. The unification of the electromagnetic force and the weak nuclear force into a single force was one of the major breakthroughs in 20th century physics. This discovery came not from a single experiment, but from theoretical insights in the 1960s, followed by key experimental confirmations in the 1980s.

Starting point is 00:09:37 The starting point was that both the electromagnetic and weak forces shared some important characteristics. They act on leptons, such as electrons and neutrinos. They obey quantum field theory, and they both are mediated by subatomic particles known as bosons. Photons in the case of electromagnetism and W&Z bosons for the weak interaction. In 1967 and 1968, Sheldon Glasshouse, Stephen Weinberg, and Abduxon, Salaam independently developed what became known as the Electro-Week theory. They proposed that at very high energies, electromagnetism and the weak forces are not distinct,

Starting point is 00:10:18 but two manifestations of a single underlying force. In 1983, the W and Z bosons were directly observed at CERN and Switzerland using the super proton synchrotron. Their observed properties of mass, charge, and interaction behavior match the predictions of the Electro-Weak theory almost exactly. So there are really three fundamental forces then. Well, many physicists believe that the electro-week force and the strong nuclear force might also be the same thing.

Starting point is 00:10:52 This is a central goal of theoretical physics at the moment and is known as the Grand Unified Theory. After the Electro-Week unification was confirmed in the 1970s and early 80s, physicists sought a deeper unification that would combine all three of the known quantification. forces, electromagnetism, the weak force, and the strong force. At extremely high energies, trillions of times higher than those currently achievable by particle accelerators, it is hypothesized that the strong and electro-week forces become indistinguishable and are described by a single force with a unified set of fundamental particles and interactions.

Starting point is 00:11:31 So if at some point in the future, physicists can prove the grand unified theory to be accurate, then there would be two fundamental forces. So could these two forces also be unified? This is known as the theory of everything. Merging gravity with other fundamental forces, however, is extremely difficult, because gravity, described by Einstein's general relativity, is a classical theory based on the smooth curvature of space time, while the other three forces are described by quantum field theory,

Starting point is 00:12:04 which operates with probabilistic particle interactions. Attempts to quantize gravity leads to mathematical inconsistencies, particularly infinities that render the theory inoperable at extremely high energies. And if you recall my episode on the ultraviolet catastrophe, this type of mathematical problem was how quantum mechanics was initially founded in the first place. Theoretical efforts such as string theory and loop quantum gravity remain unproven. This fundamental incompatibility between quantum mechanics and general relativity remains one of the greatest unresolved challenges in physics.

Starting point is 00:12:43 So, depending on what can be proven in the future, there might be three or two or just one fundamental force. Except that might not be true either. Putting aside the unification of forces that I've just discussed, some physicists are proposing that there might be a fifth fundamental force, or maybe even more. In recent years, a team of Hungarian physicists reported evidence for a possible new force-carrying particle they dubbed X-17 based on anomalies in the decay of excited beryllium-8 and helium atoms. Some cosmological models propose that dark energy, the mysterious energy driving the universe's

Starting point is 00:13:23 accelerated expansion, might be explained by a new long-range force acting on cosmic scales. This force would be extremely weak and could interact with mass or space time in some novel way. Also, some theories extend general relativity by adding a new force that interacts with matter and gravity. These models predict an extra fifth force that can vary in change with time or environment. So, of the fundamental forces in nature that affects us every day, were positive that there are at least four, which is really three. but it might be two or even one, but could be as many as five to seven. Absente a breakthrough in theory or a major discovery or the construction of a massive particle accelerator,

Starting point is 00:14:12 the ultimate answers to these questions will probably have to wait. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Oakden and Cameron Kiefer. I want to thank everyone who supports the show over on Patreon. Your support helps make this podcast. possible. I'd also like to thank all the members of the Everything Everywhere community who are active on the Facebook group and the Discord server. If you'd like to join in the discussion, there are links to both in the show notes. And as always, if you leave a review or send me a boostagram, you too

Starting point is 00:14:46 can have it read on the show.

Everything Everywhere Daily: History, Science, Geography & More - The Fundamental Forces of Nature

There aren't comments yet for this episode. Click on any sentence in the transcript to leave a comment.