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What Is Light Made of? A Brief History of the Wave-Particle Duality Idea

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The idea of the wave-particle duality of light (and not just light, as we will see) is one of the most puzzling and profound in all of physics.

For thousands of years, the nature of light has remained a mystery for philosophers and scientists. Sure, you can tell that there’s something there, because when there’s no light source, like during the night, or in a dark room, you can’t see. But what is it exactly, what is made of, and does it work?

The first person to try to explain the nature of light in scientific terms was Isaac Newton, in his 1704 treatise called Opticks. For him, light was made out of particles he called corpuscles which behaved just tiny balls, obeying the famous laws of motion he himself put forth earlier. This theory, for example, could explain reflection (in terms of ball-like particles bouncing off a surface) and refraction (when passing from one medium to another, the particles are briefly attracted by the second medium, which gives them a slight kick in speed). Newton’s theory was accepted at the time because it made sense (and also because he was Newton), but the idea that light was actually a wave didn’t completely fade into obscurity.

This idea made a great comeback about a century after Newton’s treatise with the experiment of an English scientist named Thomas Young. Known as the double-slit experiment, it involved shining a light two narrow openings in a wall and observing the pattern it displays when hitting a screen. If light is made out of particles, we’d expect to see a couple of bright lines directly behind the two slits and nothing else. If light is a wave, however, like the ripples you see on the surface of a pond when you drop something in it, you’d expect the two like beams to interfere with each other. When Young did this experiment, he found the latter was true.

Illustration of the pattern observed when shining a laser through a single-slit and a double-slit. You can clearly see the interference pattern in the second example.

Illustration of the pattern observed when shining a laser through a single-slit and a double-slit. You can clearly see the interference pattern in the second example. Image: Wikimedia Commons

The image above illustrates what this looks like with a laser (Young himself, working 200 years ago, used sunlight). So why do we see a series of bright bands with dark bands between them? Well, these are caused by the beam of light splitting into two waves which then spread out and interfere with each other. We know that a wave has a peak and a trough. Where two peaks or two troughs meet, the amplitude of the wave is increased – we call that constructive interference. Where a peak and a trough meet, they cancel each other out (destructive interference). This is why we see a series of bright and dark spots on the screen behind the two slits. We can also see that, if there’s a single opening for the light to go through, there’s no longer any interference pattern.

So the debate seemed to have been settled: light was not made of particles, but was actually a wave. But a century after Young’s experiment, another great scientist would come along and, at least partially, vindicate Newton’s views on the nature of light – a scientist called Albert Einstein. One of the hugely influential papers he published in 1905 tackled precisely this subject. Attempting to explain a series of recent observations and experiments, Einstein postulated that light was actually made up of discrete units, or quanta. Particularly important is the fact that this idea explained the photoelectric effect, an observation that metals emits electrons when shining a light onto them. This explanation was so elegant and effective that, out of all his great achievements in physics, it was this one that was specifically mentioned when Einstein was awarded the Nobel Prize in 1921.

By this time, physicists were beginning to realize nature was a lot more complicated than previously thought. One of the consequences was that they no longer attempted to describe light simply as a particle or as a wave – but rather as both. This is what’s called the wave-particle duality of light. Other experiments would subsequently find that not only light behaves like this, but also electrons, individual atoms, and even huge molecules like carbon-60 buckyballs. So the age-old search for the nature of light has ultimately revealed something profound and astonishing about everything in nature: we are all made up of both particles and waves!

Who doesn’t enjoy listening to a good story. Personally I love reading about the people who inspire me and what it took for them to achieve their success. As I am a bit of a self confessed tech geek I think there is no better way to discover these stories than by reading every day some articles or the newspaper . My bookcases are filled with good tech biographies, they remind me that anyone can be a success. So even if you come from an underprivileged part of society or you aren’t the smartest person in the room we all have a chance to reach the top. The same message shines in my beliefs. All it takes to succeed is a good idea, a little risk and a lot of hard work and any geek can become a success. VENI VIDI VICI .

Engineering

Testing the longest quantum network on existing fiber optics in Boston

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Imagine a world where information can be transmitted securely across the globe, free from the prying eyes of hackers. Its incredible power lies in the realm of quantum mechanics, making it a groundbreaking advancement with immense potential for the future of telecommunications. There have been obstacles to conquer, but there has also been notable progress, exemplified by a recent achievement from researchers at Harvard University.

Using the existing fiber optics within the city of Boston, the team successfully demonstrated the longest transmission between two nodes. The fiber path covered a total distance of 35 kilometers (22 miles), encircling the entire city. The two nodes that connected to the close path were situated on different floors, making the fiber route not the shortest but rather an intriguing one.

Quantum information has been successfully transmitted over longer distances, showcasing remarkable advancements in this experiment that bring us closer to the realization of a practical quantum internet. The real breakthrough lies in the nodes, going beyond the mere utilization of optical fibers.

A typical network utilizes signal repeaters made of optical fiber. These devices incorporate optical receivers, electrical amplifiers, and optical transmitters. The signal is received, transformed into an electrical form, and subsequently converted back into light before being transmitted. They play a crucial role in expanding the reach of the original signal. And in its present state, this is not suitable for quantum internet.

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The issue lies not in the technology, but rather in the fundamental principles of physics. Copying quantum information is not possible in that manner. Quantum information is highly secure due to its entangled state. The Harvard system operates by utilizing individual nodes that function as miniature quantum computers, responsible for storing, processing, and transferring information. This quantum network, consisting of only two nodes, is currently the most extensive one ever achieved, with nodes capable of such remarkable functionality.

“Demonstrating the ability to entangle quantum network nodes in a bustling urban environment is a significant milestone in enabling practical networking between quantum computers,” stated Professor Mikhail Lukin, the senior author.

At each node, a tiny quantum computer is constructed using a small piece of diamond that contains a flaw in its atomic arrangement known as a silicon vacancy center. At temperatures close to absolute zero, the silicon vacancy has the remarkable ability to capture, retain, and interconnect pieces of data, making it an ideal choice for a node.

“Given the existing entanglement between the light and the first node, it has the capability to transmit this entanglement to the second node,” elucidated Can Knaut, a graduate researcher in Lukin’s lab. “This phenomenon is known as photon-mediated entanglement.”

The study has been published in the prestigious journal Nature.

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Physics

What are the consequences of flying over an earthquake?

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Have you ever pondered the potential consequences of being aboard a commercial flight at a significant altitude when a colossal earthquake occurs? Presumably, you would be in an altered state of consciousness that would hinder your ability to perceive and comprehend any sensory experiences, correct? The answer to that question is contingent upon several factors.

Seismic activity and atmospheric conditions
Although it may appear improbable, an earthquake can potentially lead to several consequences that could pose challenges for a flight, depending on the circumstances. However, it is important to first examine the connection between the atmosphere and the earth before delving into that topic.

Attila Komjathy, a scientist at NASA’s Jet Propulsion Laboratory (JPL) of the California Institute of Technology, explained on NASA’s website that when the ground shakes, it generates small atmospheric waves that can travel all the way up to the ionosphere. This is a region known as the exosphere, which can reach a distance of up to 1,000 kilometers (600 miles) from the Earth’s surface.

Consequently, an earthquake has the potential to induce certain atmospheric disruptions, but is this sufficient to disrupt the operation of an aircraft? Simply put, the answer is no. However, if we delve deeper into the matter, the answer remains a resounding no, but with some intriguing nuances.

Earthquakes emit seismic waves, which manifest as pressure waves (P waves) and shear waves (S waves). S waves are restricted to propagating through solid media, such as the ground, while P waves have the ability to transmit through different types of media, including liquids and gases. Consequently, they have the ability to enter the atmosphere. When sound is transformed into soundwaves, they often have a frequency below 20 hertz, which is the minimum level for human hearing. Consequently, these soundwaves, known as infrasound, are usually inaudible.

Nevertheless, as these waves propagate through the air, their intensity diminishes. This phenomenon is known as attenuation, and it essentially refers to the decrease in sound intensity as the distance between the source and the listener increases. It is also a phenomenon that diminishes the intensity of sunlight as it passes through different layers of the atmosphere or other substances, such as the ocean.

Consequently, an aircraft traversing an earthquake, regardless of its intensity, would remain unaffected by the seismic vibrations beneath. Once the P waves have propagated through the rock and subsequently the air, their intensity will have significantly decreased, rendering them overshadowed by the plane’s own noise and movement.

Nevertheless, airplanes are not exempt from risks during an earthquake. The concerns at hand pertain to navigation and safety, albeit of a distinct nature.

In 2018, a self-proclaimed United States Air Force pilot and aero engineer named Ron Wagner provided a response on Quora to a question inquiring about the impact of earthquakes on an aircraft in flight. Wagner’s response was sufficiently captivating that Forbes subsequently shared it again.

Wagner claims that he piloted an aircraft during an earthquake, causing disruptions to air traffic control. During this occurrence, the earthquake resulted in a loss of electricity at the ground base, which consequently affected the plane’s navigation instruments and its capacity to communicate. The power outage resulted in the loss of radar signals for air traffic control, rendering them unable to determine the location of Wagner’s flight. Nevertheless, these problems were quickly resolved when the emergency power of the ground base was activated.

Although this may sound alarming, it serves as an illustration of potential occurrences. Typically, air traffic control stations possess ample emergency backup generators to handle such situations. In addition, they have meticulously developed contingency plans for system-wide events, which include strategies for addressing potential scenarios such as volcanic eruptions, nuclear fallout, floods, acts of terrorism, and earthquakes.

If you find yourself flying during an earthquake, you can rest assured that there is very little cause for concern. Typically, you will be unaware of the occurrence until you touch down.

All “explainer” articles undergo verification by fact-checkers to ensure their accuracy prior to publication. Information can be updated in the future by modifying, deleting, or adding text, images, and links.

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Physics

According to physics, your enemy’s enemy is actually your friend

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People are social animals, and their relationships are complicated and change all the time. Several fields of study and theories have tried to figure out how these social networks work and how they change over time. The social balance theory was one of them. It was first put forward in the 1940s. Using statistical physics, researchers have now been able to prove it.

Just like the name says, social balance theory is based on the idea of balance. People in their networks want and try to keep relationships balanced. There should be rules to keep the system balanced. Relationships that are positive are balanced, but relationships that are negative or mixed are not. The classical model is based on the simple idea that relationships that are good are “friends” and relationships that are bad are “enemies.”

First, a friend of a friend is still a friend. Now, this is a made-up example, so don’t think right away of that friend of yours that you hate. Another rule says that a friend of an enemy is also an enemy, and of course, an enemy of a friend is also an enemy. We need to protect our friends. The last rule is a bit more subtle: a friend of an enemy is a friend of an enemy. It looks like the new analysis mostly meets this need, but the scientists had to add a lot of complexity before they could model it.

It’s finally possible to say that social networks match up with expectations that were set 80 years ago, said Bingjie Hao, the study’s lead author from Northwestern University. “Our results can also be used in many different ways in the future.” Because of how we do math, we can put limits on the connections and take into account what each entity in the system wants. That will help when making models of systems other than social networks.

Two things were very important to the new model: not everyone knows each other in real life, and some people are more positive than others. When you use both constraints, you get a social network that is exactly the same as the one Fritz Heider predicted 80 years ago.

“We always thought this social intuition worked, but we didn’t know why,” said István Kovács, who was the lead author of the study. “All that was left was to do the math.” There have been a lot of studies on this idea, but they don’t all point to the same conclusion. We kept getting it wrong for decades. It’s because real life is hard sometimes. We realized we had to deal with both problems at the same time: “who knows whom” and “some people are just friendlier than others.”

The study has been written up in the Science Advances journal.

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