How Does Light Actually Work?

the newborn universe hummed and frosted with boundless energy, even after the raging furnace of the first few minutes died out, temperatures throughout the universe exceeded one hundred million degrees for thousands of years, this primordial heat burned the cosmos of plasma, a super hot mixture of particles. and radiation until one day it changed forever that day came when the universe was almost 400,000 years old and had cooled to about 3,000 Kelvin in this now comparatively warm soup, lone electrons, methylone protons and were finally able to come together forming the first atoms, but this was not all for each electron and proton united a small amount of energy was released a packet of energy that escaped the cosmic speed limits the speed of

light

a particle of energy born in the formation of a hydrogen atom a particle we call photon particle of

light

itself, this photon was far from the first, but as the universe began to transition from plasma to a neutral gas, light was for the first time able to flow freely through its reaches and so, as the long journey of the photons began, it headed first into the darkness of the universe.

Long before the first stars burned, a time before the first galaxies formed in the mysterious darkness, gravity attracted mass to mold the first seeds of cosmic structure, the photon accelerated and noticed nothing, finally the first Stars came to life around him, massive and swollen. These ancient suns burned up in the blink of a cosmic eye when the first supergiant black holes grew rapidly between them as they eagerly devoured mass, but the photon sped up and noticed nothing the first galaxies began to gather the sky lit up with the fires of Countless young stars throughout the cosmos when they began to fuse the initial hydrogen and helium atoms into heavier elements, but the photon accelerated and did not notice anything.

Millions steadily turned into billions of years, and as the galaxies grew and matured, eventually the intense light of young stars began to shine. The photon's journey could have lasted forever into eternity, but after nearly 14 billion light years of travel, a large spiral galaxy steadily came into view. Their destination was set near a small blue dot orbiting a small white star after crossing the last few thousand light years. The photon collided with a piece of metal that is part of a human-built telescope that orbits near planet Earth. The photon's energy was completely absorbed, energizing the electrons and registering in the detectors, but when the photon faded from existence, its billion-year journey was complete, it remains simply I didn't realize because for the photon the trip never took place. 13.8 billion years of cosmic time disappeared in an instant.

However, how can this be? Light has existed in the universe since its earliest moments and will continue to exist long after humanity and the stars disappear. crush it to dust how it

work

s and how it can last seemingly forever perhaps the most important thing is that even if it is light, it is fast, it only takes 0.13 seconds to circulate around the globe via slowing down fiber optic cables by a third, but it still means that with Surf Shark changing your virtual location is almost instantaneous, so if Shark has been kind enough to sponsor this video and it's the simplest best VPN service out there, you can change your country quickly and easily to stream what you want from wherever you want.

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Light had played a fundamental role since the beginning of the cosmos in these earlier times, it had only existed for the briefest of moments colliding with accelerated particles before they had the chance to travel anywhere, one piece of light died when another was born, However, our packet of light was born in a very different and very transparent Universe, with the cosmic maelstrom of the Big Bang finally subsiding, our photon was able to begin its immense journey. Unhindered as he traveled, many generations of stars led to our sun and billions of years after that humans began walking on the surface of our small rocky planet.

Finally, when our photon was a couple thousand light years away from Earth, those humans started wandering. all men by nature want to know an indication of this is the delight we take in our senses and above all the sense of sight this above all the senses makes us know and brings to light many differences between things the ancient Greeks wondered Yes light emanated from the eyes that touch and feel the world around us, but clearly there are times when it is dark when we cannot see anything, so they concluded that light must be something external, something captured by our eyes.

Islamic scientists continued to unravel the properties of light. Finding the Reflection Rules and Magnifying Properties of Glass Lenses Light was clearly a natural part of the universe around us, but it took the advent of the Scientific Revolution and a struggle between two giants of science for it to finally be realized. They would discover the deepest secrets of light. 1652 and Dutch physicist, astronomer, mathematician and all-round genius Christian Huygens was exploring optical phenomena. He had noticed how light traveled through lenses and bounced off reflective surfaces and was particularly interested in the phenomenon of refraction, where the path of light is bent as it passes.

From one medium to another, Huygens noticed that his instruments often split light into rainbow colors and sometimes strange patterns of light and dark were produced, clear evidence to him that light was a kind of wave. , a kind of traveling oscillating phenomenon. Oscillations can be found throughout nature, from planetary orbits to vibrating electrons, but let's start with a simple image: think of a child on a swing as he swings, his position oscillates from one position to the next and then back again as a pendulum that drives the regular ticking and speaking of a grandfather clock when the oscillations act in unison but slightly out of step waves are formed a stone thrown into a flat pond drags the water down but the water bounces back this splash of water attracts its neighbors inducing them to oscillate which in turn attracts its own neighbors, these oscillations unfold throughout the pond as a constant pattern of waves.

Waves are everywhere, from sound waves. They cross through the air to waves of ocean water driven by the wind and the moon. Seismic changes can generate violent and destructive earthquakes on our planet. planetary crust, while similar waves ripple in the atmosphere of the Sun and other stars, so light also appeared to be a wave, but this left an obvious question: if light is a wave, what was the wave doing in Britain? Robert Hook also came to a similar conclusion. about the nature of light and he realized that this image of wavy light could explain much of the phenomenon he had seen.

This was cutting-edge science at the time, but Hook had a problem and that problem was a man. There are no surviving portraits of him. Robert Hook and over the years a rumor spread from generation to generation that this powerful man was to blame for having conveniently lost the painting upon assuming his directorship of the Royal Society in London, since Robert Hook had a powerful enemy and the That enemy's name was Isaac Newton from then on. Cleared of any wrongdoing in the absence of contemporary images of Hook, there is still little doubt that the two men were not friends.

In addition to his momentous discoveries in mathematics and gravity, Newton also had an interest in optics and the nature of light itself. and he didn't like what Hook or Highgens had to say, in fact it was Newton who discovered that white light could be split into a rainbow by passing it through a prism and, like Hook, he had continued to reflect on this, but Unlike Hook, Newton did not conclude that light was a kind of wave. For Newton, light consisted of corpuscles. For Newton, light was made of small individual particles. Newton's focus was on the phenomenon of diffraction. they curve around a sharp edge he knew the sound a wave in the air bending as it traveled Beyond the sharp edges, it was clear that a conversation could be heard from a corner without being able to see the gossipers.

You could hear it from behind an object but you couldn't see it, so he reasoned that light simply couldn't be a wave and he didn't. But we don't stop there, Newton went much further and reasoned that light as a stream of particles would even feel the pull of gravity. In his book Optics, published in 1704, he wrote: Do not bodies act on light at a distance and by their action bend its rays? and although he was right in this, he was not proven right for centuries, so it was Newton's corpuscular theory of light that reigned supreme due more to his weight of personality and scientific standing than to his ability. to explain the complex observations of light over the years.

However, as the tide steadily began to turn away from Newton, in 1800, scholar Thomas Young Shawn shone light into a pair of narrow slits and observed an interference pattern on a background screen. This was not the first demonstration of interference, but it was the clearest of how Newton could The image of light as particles explains Young's observation about interference how could light be produced as small bullets passing through a slit or of the other? The pattern observed by simply throwing a couple of pebbles into a still pond reveals that the interference is produced naturally by waves either in water or In light, other observations of light supported its wave nature, including the polarization of light through of a material called calcite, but for centuries the big secondary question remained unanswered: if light was a wave, what was it doing?

The strange particle of rippling light was born when a proton captured it. An electron launched into the universe powerful and energetic, but as it traveled and the universe expanded it began to lose some of that energy, the light originally blown into our eyes steadily transformed through the colors of the rainbow and soon faded. joined the red. By other energetic light shining from countless billions of newly formed stars, there were different types of light, as well as light of exceptionally high energy and light with barely any energy, the universe was flooded, of course, our light did not know that they would be invisible for us. human eyes because it would be many billions of years until eyes existed and in fact these X-rays and radio waves, as we call them, were unknown to us until the end of the 19th century, in this new era it was thought that they would be transmitted by radio gulielmo.

Marconi was on his father's estate near Bologna in Italy. He was still a young man of only 20, but his education had opened his eyes to an unseen world in the decades before the nature of light had been steadily unraveled and Marconi was ready to use this newfound discovery. knowledge to change everything by looking at his equipment Marconi was expecting to see a faint spark in the darkness with the bundle of wires and coils of his Workshop such a spark could not be surprising but the impetus of this spark was not in the equipment in front of him. was on similar equipment located several miles away, of course the 19th century had seen the arrival of the telegraph, where electronic pulses were sent over cables crossing entire countries and continents, but this required cables to be strung across of the air and under the oceans.

Marconi had no If he needed such cables, he would be sending messages not through pieces of copper, the messages would simply fly completely invisible through the air, but how the answer lies with one of the greatest geniuses of science. The answer lies in James Clark Maxwell when a young James Clark Maxwell arrived at the University of Cambridge in 1850 and was told that attendance at the 6 a.m. church service was difficult. It was mandatory for all students. The Scottish-born Prodigy had long been a night owl and simply responded: I guess I could stay up so late.late.

Her name is written in large letters. The modern world's greatest achievement was to unite two seemingly disparate phenomena and create something extraordinary. Electricity and magnetism have been known since ancient times, seen in the strange attraction of stolen materials and mysterious stones that knew how to find the North, but in the 19th century. It was becoming clear that these two were not really different: a flow of electric current could generate a magnetic field and a changing magnetic field could generate a current in a wire, but when Maxwell looked at these equations he began to see a deeper picture instead of separate them. relationships, he saw that electricity and magnetism could be united in a single hole, a united set of mathematics that encompassed all electrical and magnetic phenomena, but Maxwell's great intuition was not only concerned with electromagnetic complexity, as he asked about From the simplest situation of all electromagnetism in the nothingness of the vacuum, how

does

light travel through the vacuum of space?

Maxwell knew that electromagnetic fields filled all space even in a vacuum, but he imagined that in empty space these fields would be null, they were effectively not there, but what would happen if one of these fields were taken? either electrical or magnetic so that these fields were not at zero somewhere. Maxwell pondered this question using his equations to explore how the situation would evolve and the answer was surprising: Think about pinching the skin on the back of your hand, what happens when you stop? When you pinch yourself, the skin returns to its non-pinched state quickly if you are young and a little slower if you are older.

Maxwell's equations told him that the electromagnetic pinch would evolve to zero, but that this was not the end of the pinch story. The electric field would generate a similar pinch in the magnetic field and the pinch in the magnetic field would generate a pinch in the electric field and these pinches did not simply fade to zero, but oscillated regenerating each other from one moment to the next and like waves in A pond. These oscillations traveled like waves and then Maxwell realized that these oscillations had the property of light. He realized that it is a self-propagating electromagnetic wave, but what was causing the waves, what was the electromagnetic equivalent of the stone thrown into the pond?

He saw that they were electrical charges, something we now know as electrons, since these charges shake and oscillate, they disturb nearby electric and magnetic fields, and these disturbances propagate as electromagnetic radiation, which we call light. He also realized that the converse must be true when light enters the eye and falls. In the retina, light oscillations must cause the electrons in the atoms in the eye to move and it is this movement of electrons in the center of the eye that is the signal to the brain that we perceive as vision. Finally Maxwell understood what was stirring and what caused it. waves and one more thing, he knew that light had waves with a length of about a millionth of a meter, but his equations showed no limitation on the wavelength of his electromagnetic waves, so he concluded that there must be light with lengths both long and short waves. which is invisible to the eye, it would take two more decades for the answer to this enigma to be presented decades in which Maxwell died of cancer at the age of only 48 years.

In 1886, Heinrich Hertz,

work

ing at the University of Karlsruhe, was the first to find these invisible waves called Hertzian waves after their discoverer had born a new revolution, we now refer to these Hertzian waves as radio Hertz was understandably very pleased with his discovery, but when asked about the practical use of these radio waves, he apparently didn't answer anything, I guess. However, it was these radio waves that just a few years later Marconi was using to send messages across miles and then across oceans and across the vastness of the globe. In 1909 Marconi received the Nobel Prize for his work on wireless telegraphy.

Hertz, however, died in 1894, at the age of 36, never seeing the true promise of his discovery, the world was destined to be filled with invisible light as the 20th century began and the mystery of the properties of light began. light seemed resolved until 1905. A remarkable year for a German. Clerk's patent the universe continued to change and evolve as our light particle traveled the mixture of light that joined it on its journey reflected that change bursts of radio waves and high-energy gamma rays that became increasingly frequent this Energy surged through space much of it flowing between the stars and in the dark, but some found lone atoms in The Emptiness of the Void, low energy radio waves very gently shook and energized these atoms like an ocean wave. calm breaking on a sandy shore, just as we would expect from Maxwell's image of electromagnetics. waves, but the behavior of high-energy gamma rays was different, they delivered their energy to the atoms with a violent blow that knocked out the electrons, not a ripple, but an isolated shock, the gamma rays hit the atoms not as waves but as hard and low energy. particles, but how could Maxwell be wrong?

Could light sometimes be more like Newton's vision and act like a particle, and if so, what would those occasions be at the moment? We have to work on both theories. On Mondays, Wednesdays and Fridays we use the wave. theory on Tuesdays, Thursdays and Saturdays we think of currents of quanta or flying energy corpuscles Alfred Nobel had made his fortune thanks to his inventions and his businesses, especially in the field of explosives and weapons, so perhaps it is not unfair in an 1888 obituary in a French newspaper that was called The Merchant of Death, this surprised Nobel firstly because he was still alive but secondly and more distressingly because he realized what his historical legacy was going to be so that in his will he decided to leave most of his fortune to a series of prizes. that would honor those who have given the greatest benefit to humanity through science the Nobel Prizes are perhaps the most prestigious the list of winners filled with the Giants of science for more than a century and in 1901 the inaugural Nobel Prize of physics was awarded to the German Wilhelm Rundgan for his discoveries on the nature of light because it was he who discovered X-rays.

Ronkin's experiments with various materials discovered that only the densest ones could stop X-rays. He even managed to convince his wife Bertha to place her hand on it. The beam after realizing that its much smaller than visible light rather than radar, which was much longer, it took several decades to conclusively demonstrate that this was the case, although in the meantime the medical application of x-rays to repair bones and save lives grew. without limits, which meant that by the beginning of the 20th century Maxwell's vision of electromagnetic energy - waves beyond the visible - had been undoubtedly confirmed, all the secrets of light discovered, even the electron had been discovered, everything that What remained was to find the rest of the light, we couldn't see gamma rays, microwaves and more to fill the last gaps in the electromagnetic spectrum and To conclude the story, but, of course, if physics considers a job done, A hard blow is usually just around the corner.

In Maxwell's picture of light, it could be considered as a continuous wave. Scientists had discovered that when light hits most materials, it continually shed energy that energizes the electrons causing them to be emitted, this was called the photoelectric effect, by reducing the intensity of the light, the energy took longer to deposit and therefore It usually took longer for the electrons to start spitting out, usually because that was not what was observed when light was shown on certain metals, the electrons would apparently be instantly ejected from the surface of the metal and the really confusing observation came when adjusting the color of the light shown.

Blue light would result in very energetic electrons being emitted. The green light resulted in less power. Electrons and red light did not produce electrons at all. This made no sense if all colors of light carry energy. Why couldn't the Red Light energize the electrons? This mystery was solved and new Mysteries were born in a very special year. This was not just any year. a miraculous year because it was the year Albert Einstein changed physics forever. Most people are familiar with Einstein's Anna mirabilis. 1905 the year he wrote the special theory of relativity, but that was just the beginning.

Einstein received the Nobel Prize in Physics in 1921. The citation noted that the award was for his services to theoretical physics, however, one topic in particular was singled out for recognition and it was not his work on relativity, it was especially for his discovery of the law of the photoelectric effect when Einstein explored the photoelectric effect. He had to radically revise Maxwell's view of light and realized that when light interacted with electrons it could not do so as a continuous wave of energy, but rather the energy had to be concentrated and discharged into an electron as a packet of light. instant.

Einstein declared that it should be quantified. Being pieces of energy, they must interact like a particle. Einstein went on to explain that each packet of energy was proportional to the frequency of light. A red light packet carries less energy than a green light packet. A green light packet carries less energy. than a blue packet, so in experiments red light simply did not deliver enough energy for an electron to escape. This enigmatic package of energy did not receive its current name until 1926, when in an article in Nature magazine, Gilbert Lewis coined the name Photonic evidence for the particle nature of light grew rapidly and it was in 1923 that Arthur Compton organized an important experiment , but one that was based on a strange fact that light can drive this might seem strange to say how can light that has no mass. thrust, but Maxwell's equations showed that, in carrying energy, light also carries momentum.

Today, he can easily purchase a Crooks radiometer as an executive toy for his desk which consists of four veins in a vacuum glass tube, one side black and the other white when placed in sunlight. the veins begin to spin, supposedly pushed by the impulse of nothing more than sunlight, as always. The physics of the Crux radiometer is more complex than this simple explanation, but the force of sunlight pushing through the veins is real and some Visionaries imagine future Humanity flowing through the veins. However, Arthur Compton's experiment was a little different from his experiment. Compton aimed a beam of high-energy and recoiling electrons Compton discovered that Maxwell's picture of a wave of energy and momentum simply didn't work.

Instead, Compton had to treat X-rays and electrons like colliding billiard balls, since when an X-ray hit an electron, it gave up its energy and momentum. As a discrete packet, when an X-ray hit an electron, they definitely interacted as hard particles. Newton's vision of light particles was reborn, but was this definitive proof that light was a particle? Not quite, of course, there was still a mountain of evidence of his vibe. -like nature in any case, scientists were more confused than ever even though Maxwell's image of electromagnetic waves turned out to be extremely powerful and successful, these experiments in the early 20th century demanded that light be a particle and therefore That's why people started to wonder if there was any answer to be found.

We started this story by following a photon of light as it traveled through the universe. Maxwell tells us that this photon was formed by the changing energy of an electron and that it disappears when it is finally absorbed by the electrons at the end of its journey, but what happens in the middle is this. Epic Journey Simply Governed by Fate Does the photon really fly in a random direction and hurtle towards an electron at some arbitrary point in its future? This question is the next part of our early 20th century story. We realized that this simply could not be. the case in the language of quantum mechanics photons The journey has nothing to do with chance not only is the universe Stranger than we think Stranger than we can think We begin on a cold morning in France in January 1793 . with a whistle of a guillotine blade, King Louis XVI no longerexisted during this turmoil, chaos reigned throughout France.

Victor Francis, the second Duke of Broy, fought for his king, but eventually, like many other members of the aristocracy, fled France to seek safety abroad, the de Bruises eventually returned to their native France. to shape the country after the turmoil of the Revolution and after a series of statesmen, diplomats and writers in 1892 was born into the de bruy family the man who would change our understanding of everything his name was Louis Victor Pierre Ramon 7th duke dubroy but In the annals of physics, he is known simply as the broy. At the beginning of the 20th century he witnessed the birth of quantum mechanics and the growing confusion over whether light was a particle or a wave.

For Deborah, however, there was an obvious, if counterintuitive, solution. a light was neither and both at the same time, it was clear that light when it traveled traveled as a wave producing the effects of interference and diffraction, but when it interacted it interacted like a particle, it seemed to exhibit properties of being both a particle and a particle. cool, but it wasn't really cool either. De Broyer's remarkable insight was the realization that this was true not only of light but of the entire quantum world. Here he claimed that there were no true particles and no true waves.

Everything De Broyer told us was some kind of quantum thing. and so, in his doctorate in 1924 he stated that electrons that were clearly particles should also exhibit wave properties and in 1929 he received the Nobel Prize when, through experiments or his predictions, there was an important philosophical discussion about this wave-particle duality. in quantum mechanics. but the observational consequences of it are incontrovertible: a series of single photons or electrons sent through multiple slits still result in interference patterns and even large, complex molecules have been shown to have properties of both waves and particles; the largest so far tested has a size of 2,000 atoms and So, with quantum mechanics in hand, the quest was to understand how light and electrons interacted with classical physics.

Maxwell's physics. The electrons moved as electromagnetic waves passed by like seagulls bobbing in a choppy ocean, and as they moved, the electrons emitted their own electromagnetic waves. Waves were added to the mix, but the quantum picture had to be different, since the quantum world was one of reactions of quanta and particles. Despite these opposing situations, it was not long before a solution was found and it was another scientific titan, Paul Adrian Maurice Dirac. who began cracking the code in the late 1920s, was working to unite two of the biggest advances in modern physics. The strange world of quantum mechanics and Einstein's special theory of relativity.

Dirac's story has been told many times about his famous distraction and lack. of communication skills Quantum pioneer Niels Bohr even went so far as to call him the strangest man, but there was absolutely no doubt that Iraq was a revolutionary genius and it was through his work on quantum mechanics that Dirac left his mark on history science to understand the modern world. From the point of view that he helped achieve, we have to accept that everything is really felt. These fields are different from things like classical electric and magnetic fields. In quantum field theory, there are electron fields.

Photon fields fields for the various quarks and more a wave, for example, in the electron field is an electron and a wave in the photon field a photon thinks of an atom What do you see in our minds? We often have the image that Niels gave us. Bohr of electrons orbiting a nucleus like a planet orbiting a star and when an electron jumps from a higher orbit to a lower orbit a photon of light is emitted, but when considering the quantum world this is not entirely correct in quantum field theory We think of an electron in orbit as a vibrational pattern in the electron field, the higher energy orbit is one particular pattern and the lower energy orbit is another in the language of physics, the electron field and the photon field.

They are coupled and jump between the upper and lower orbits of the electron. The field generates a vibration in the photon field. Quantum field theory has grown to become arguably the most successful theory of our world to date, describing almost everything in our universe through 24 quantum fields that correspond to the various possible interactions of the Standard Model and is so simple that all is. Fields and fields interact, but of course, as often happens in the quantum world, things are about to get a lot stranger. Many of the brightest minds in quantum mechanics were involved in this movement toward strangeness, but perhaps the best known is a man from Far Rockaway, with a broad Brooklyn accent, a man named Richard Feynman, born in 1918, began his career as part of the Manhattan Project and was recommended by Oppenheimer himself to Berkeley in a now famous letter sent in 1942.

He is, according to all the Lords, the most brilliant young man. physical here and everyone knows it. I can give you two quotes from men he has worked with. Beta has said that she would prefer to lose two other men besides Feynman in this current job and Vigna said that he is a second Iraq, only this time he is human. In his 1985 autobiography, You're Surely Joking, Mr. Feynman was a revelation to many, not only because of his numerous contributions to science, but also because of his outgoing personality and his complex private life, including a club strikeout. striptease;

These aspects did not fit the stereotypical view of a man. In fact, Professor Murray, another giant of quantum mechanics, once even joked about Feynman. Feinman was a great scientist, but he devoted much of his effort to generating anecdotes about himself. And yet, when it came time to think about the quantum world, for many physicists Feynman changed everything. While Feynman's famous quip that no one really understands quantum mechanics may have been true, Feynman himself certainly understood the depth of the underlying mathematics, this gave him the insight to think about the true nature of light and how it interacts.

It all starts with a solitaire. electron in Maxwell's electromagnetism the charge on the electron results in an electric field surrounding it and a charge in an electric field feels the presence of the electric field in this situation there must be energy in the interaction but the question was to what extent the problem Each Every time Feynman tried to calculate the amount of energy the answer was the same Infinity, so Feynman did something quite radical: he discarded the classical notion of the electric field as defined by Maxwell in his Nobel Prize acceptance speech. Prize in 1965 Feynman said that I suggested to myself that electrons cannot act on themselves, they can only act on other electrons and a strange new picture of the interaction between light and electrons emerged.

The best visual representation of this interaction is the diagram named after Feynman himself. Feynman diagrams are often a complicated mix of lines, motions, and loops, but in essence, Feynman diagrams describe all possible interactions in quantum mechanics. To separate a Feynman diagram, it is best to start with the simplest interaction, the interaction between electrons and light. Feynman diagrams represent an interaction in space and time. lone electrons. Trace paths in straight lines through space-time. A path known as his world line. The electron is

actually

just a vibration in the quantum electron field and, without interactions, it happily traces a simple straight line.

Along the way, we also know, however, that the electron field can couple with the photon field and when this happens, the vibrations in the electron field change in an atom, the electron jumps from a high energy orbit to a low energy orbit, but for conservation of the momentum of the free electron. It means that the electron changes direction if we imagine this in space-time the world line of the electron has a distinctive Kink and this occurs where and when the photon is emitted usually represented as a wavy line. This structure this union is known as a vertex and is the basic Lego piece to build all Feynman diagrams, of course, complete Feynman diagrams are more complex than a single vertex, they generally combine several different pieces, the photon emitted by a electron is eventually received by another electron, two vertices join together to provide a complete interaction.

Two twisted electron paths were joined by the wavy line representing the photon, but what governs the coupling between the electron field and the photon field is related to the charge of the electron and one of the constants of nature, the constant of fine structure, this is electromagnetism and the exchange of the photon between two electrons is the electromagnetic force in action and, in Feynman's opinion, we say goodbye to the electromagnetic field. Instead, we simply have two electrons interacting by exchanging a photon and when large amounts of these photons are exchanged, it approximates the electromagnetic force at work.

Classical force, although ultimately this electromagnetic force is a quantum phenomenon and is not just electromagnetism, since it is also true for the fundamental strong and weak nuclear forces, for the strong force it is gluons instead of photons that are exchanged between quarks and for the weak force it is through the exchange of massive particles known as w and z and again all these forces can be presented by a combination of Feynman vertices, but this was not the end. Feynman had an even stranger card to play when it came to light, he had said that one electron acts on another and this happens through the exchange of a photon producing the complete Feynman diagram of the interaction, but

does

this mean that an electron fired a random photon?

Did this photon go out into the universe with only a remote chance of being absorbed by another electron counterintuitively, the answer Feynman said was no, he told us that the photon only passes between two electrons that have agreed to the exchange, but something strange is happening here if we are in the middle of the journey of the photon, its emission of one electron occurred in the past while the absorption of the photon by the other electron will occur in the future, so when did the electrons communicate and agree to exchange the photon? How did they even know of each other's presence?

Clearly it cannot be through the electromagnetic force since this is precisely what the photon exchange really is. So what is the solution? As is the case with a lot of quantum mechanics. What is the mathematics? Interpretation. The question of what is really happening is the biggest challenge. and so Feynman with his supervisor John Wheeler put on the table an amazing possibility, the suggestion is something that we now call transactional interpretation, they said that the two electrons shake hands and accept the exchange of the photon, but that this handshake is taken over time, an electron. messages from the past and others from the future this may sound ridiculous but it fits completely with the mathematics of quantum mechanics and so on a dark night when you look at a distant star an electron in your eye and an electron in the atmosphere of that The stars spoke to each other through time and agreed to exchange the photon you see and, going even further, for the lone photon we met at the beginning of our story.

Two distant electrons shook hands across billions of years of time, billions of light years of space and agreed. that the photon should set out on its cosmic journey the strange world of quantum mechanics never disappoints and yet there is one last even stranger mystery to reveal about light and our solitary photon in the blackness of space as it travels along many billions of light years. the photon experience that we have followed our photon for many billions of years, finally, the end of the journey, the universe it inhabits is very different from the one of its birth, but there is a disconnect, because once this photon was almost as old as the universe itself and remained eternally useful galaxies formed in the void stars were born lived and died entire superclusters splintered and collapsed and the photon Misty doll because to the photon time itself meant nothing this might seem a bit strange to say that the photon clearly had an existence in time but with the arrival of Einstein and his special theory of relativity, it was realized that time was

actually

flexible, relatively dependent on who or what was measuring it and light takes this idea to the surface. extreme.

What would the universe look like if you were riding on it? the end of a beam of light at the speed of light in the mid-17th century only Rome was bewildered working on theParis Observatory Rome watched IO one of Jupiter's bright moons as the Moon clocked orbiting the giant planet in just over 42 hours Fading from view as it drifted in and out of Jupiter's Shadow except there seemed to be something strange about this Cosmic Clock Rome noticed that the timing of the IO eclipses varied and realized that the timing of the IO eclipse was somehow tied to the Earth's orbit changing from earlier to later and vice versa when the Earth was closer. or further away from Jupiter and it was then that Rome realized that the culprit was light and, in particular, its speed.

He reasoned that the drift in Io eclipses must be due to a finite speed of light as the Earth moved in its orbit, the distance to Jupiter changed and the change in time was due to the light having to pass through these different distances. His initial estimate of speed was fast, very fast, 220,000 kilometers per second, and eventually more precise measurements. he pegged the speed of light at almost 300,000 kilometers per second, but what this speed was in relation to it had been the belief for centuries that there was a medium. The ether that carried light waves surely, therefore the speed of light was relative to this medium from Plato to Newton had long suggested this ether as a solution to various questions in physics, but never firmly detected that Experiments in search of evidence had failed again and again, so in 1905, during his miraculous year, Einstein announced the definitive death of this invisible. medium special relativity, the truth is that the speed of light was the absolute and invariant universal measured to be the same value for all observers throughout the cosmos.

Much has been written about special relativity, and while much of it seems confusing and paradoxical, there is a simple central message at its heart: particles with mass, like electrons, chart their own time as they travel through spacetime. Imagine two clocks located in the same location synchronized to show exactly the same time. Now take these watches on two separate trips at full speed. In Newton's vision of the universe of absolute time, if these clocks were put back together and their faces compared, they would have remained synchronized, but this is not the case in Einstein's vision, the relative motion of the two clocks would have influenced their relative passage of time and as they trace their different paths through space-time, when they meet, their times will now be out of sync.

This mind-blowing aspect of Relativity seems too strange to be true, but numerous experiments have proven this to be true. The way the universe works, from globe-trotting atomic clocks to high-speed particles and accelerators, time is definitely relative, but what does this mean for light? light had occupied a central place in Einstein's New Vision of the cosmos. Everyone in space-time should measure the speed of light had exactly the same value, but in demanding this something else had to give and so space and time themselves had to bend and become flexible and rubbery to accommodate the consistency of The speed of light.

In fact, an immediate consequence of Einstein's ideas was that light would sense the existence of gravity and, as it traveled through the universe, the path of light would be deflected by the presence of mass. Newton's statement from two centuries earlier was reborn. In fact, experiments have worn this down again and again and the results have become increasingly precise massive objects, like stars. and galaxies can even behave as gravitational lenses that magnify distant galaxies in the early universe and reveal the presence of dark matter. The beauty of these natural telescopes is clearest in deep space images like the first revealed by the James Webb Space Telescope and therefore the flexible one.

The nature of space and time had truly seen the end of Newton's vision of a rigid universe, but what about light? What did this mean for the experience of light from space and time traveling at the fastest speed possible in the universe? The effects of relativity become extreme, very extreme. all distances reduce to zero as does the time needed to cover these zero distances and therefore for photons, no matter how far they travel through the universe, we will not take a single instant of time, although this light has existed in time and space. For many years or light years, although it would clearly have been formed by an electron in one place and disappeared by being absorbed by another electron in another place, the space-time distance between these two events would be exactly zero.

The photon is born and dies in Precisely the same moment we begin this story following a lone photon from its creation just after the beginning of time to its final destruction in the detector of a telescope that today orbits our planet and yet The photon itself saw none of this, not the intense light of stellar birth, the catastrophic explosions that come with stellar death, or the formation of planets and the eventual emergence of life in our own pale blue dots. The photon did not notice anything. You've been watching the whole story. of the universe don't forget to like and subscribe and leave a comment to tell us what you think thanks for watching and see you next time abroad.