Wave-particles duality of light

 Properties of light had been a topic of discussion for a long time. It started back to Democritus (5th century BC) continued to Newton and ended at Maxwell and Einstein. Quantum mechanics is vast branch which incorporate quantisation of energy, wave-particle duality, the uncertainty principle etc. Here I will focus majorly on wave-particle duality of light. Now, what does this term mean? It states that every particle weather light or electron exhibit both wave and particle nature.

Source: Livescience.com

Actually, earlier some scientists believed that light shows particle nature and some believed on wave nature. But later with the work of many prominent physicists it was proved that light shows both wave and particle nature. In 1670 Isaac Newton developed corpuscular theory of light. He said that as light follows rectilinear propagation it must be composes of particles as only particles could travel in perfectly straight lines. Newton argues that reflection and refraction are possible only because light is composed of particles. At the time when Newton was confident of his corpuscular theory Robert Hooke and Christian Huygens explained the wave nature of light. According to Huygens principle ‘Each point of the wavefront is the source of a secondary disturbance and the wavelets emanating from these points spread out in all directions with the speed of wave. After this the wave nature was further proved by Thomas Young's famous double slit experiment. Polarisation of light, black body radiation could also be explained with the help of wave nature.

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Around 19th century the wave model was well established. But we know that wave requires a medium to propagate but light can travel through vacuum also. How is this possible? This problem was solved by James Clerk Maxwell around 1855 with the help of his electromagnetic theory of light. The changing electric and magnetic field result in the propagation of electromagnetic waves in vacuum. In 1900 Max Planck gave his theory which said that radiation emitted or absorbed occurs in the form of small packets known as quantum and energy of these packets is proportional to the frequency. He gave the equation as E=hf where he is plank's constant(6.626×10^-34 J-sec). By using plank’s quantum theory Einstein in 1905 successfully explained the photoelectric effect. When a light of certain frequency is allowed to fall on a metal of low ionization energy the electrons emitted known as photoelectrons and this phenomenon is known as photoelectric effect.

Observation given by:

1) On increasing the frequency of light kinetic energy of electrons increase.

2) On increasing the intensity of light number of photoelectrons increases however kinetic energy remains constant.

This experiment showed that light consist of particle. These particles are called photon. Einstein was also awarded Noble prize for discovering photoelectric effect. Later in 1924 Louis-victor de Broglie said that all matter has wave nature. He gave the formula ƛ=h/p where p is momentum. For this he was awarded with noble prize in 1929.

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With the efforts of prominent scientists like Newton, Huygens, Young, Bohr, Plank, Maxwell, de-Broglie, Einstein etc, it was proved that light shows both particle and wave nature. To verify one phenomena we need particle nature and for another we need wave nature. Together they explain all the phenomenon of light.

Black Holes

 Black holes have fascinated scientists from the early 18th century. The term black hole was coined in 1969 by American scientist John Wheeler. A black hole is a dense object from which even light cannot escape. A star after supernova explosion turns into a black hole. But there is a condition. Only star which has mass more than one and a half times the mass of the sun will turn into a black hole otherwise it will become a white dwarf or a neutron star. This mass is known as the Chandrasekhar limit, after the name of its discoverer Subrahmanyan Chandrasekhar. Black holes are not visible because the light could not escape the strong gravitational field and would not reach us. But still its presence would be felt because of the gravitational attraction on nearby objects.

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There are two parts of a black hole the event horizon and the singularity. The boundary of a black hole is called the event horizon. The central, most dense part is called singularity. Cygnus X-1 was the first identified black hole. The nearest known black hole is about 1000 light years away. Though most on it are theoretical but implementation of equations of General Relativity was first done by Karl Schwarzschild in 1916. The ‘No hair theorem’ explains that the information about the body must be lost only its mass and rate of rotation can be calculated. Stephen hawking showed that large black holes emit slow radiation and slow ones emit a large radiation because of which they glow. This thermal radiation because of quantum effects is known as Hawking radiation.

source: wallup.net

The first picture of a black hole was taken in 2019 using 8 telescopes around the world known as Event horizon telescope with the effort of more than 200 scientists. This black hole was spotted at the centre of M87(Messier 87) about 55 million light years away. The algorithm that created the first image was developed by Katie Bouman. The mysteries of black hole have not been fully solved. But scientists around the world are working continuously in revealing it and consequently revealing the beginning of the universe.

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Optical Lattice Clock

 Time is very important factor for everyone. Sometimes a few seconds is a lot time to reach the milestone. Time is a storm in which we all are lost. So first of all let us know the standard unit of time and its defenition. The SI unit of time is second. But what is '1 second'? The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. There are many devices to measure time. In earlier times, Sand clocks, water clocks and Sun dials were used. Now we have quartz watches, atomic clock, smart watch etc. But the most accurate of all the clocks is Optical Lattice Clock. 

Optical Lattice Clock is designed by Jérôme Lodewyck and his team at the Paris observatory. It is the most accurate clock and could 'redefine the second'. The cesium fountain clock operate about 1x10^-16 relative precision whereas optical atomic clock has a relative precision of 2.5x10^-19. It is accurate to within 1 minute every 18,000 million years. It uses laser beams and interference phenomena. Like, it is formed by the interference pattern of two laser light beams that are propagating in precisely opposite directions through the same medium. A laser is used to excite, high-frequency transition in the strontium atom to reach upto a standard frequency that provides extremely precise measurment of time.

The new clock is located at the National Institute of Standards and Technology (NIST)
in Boulder, Colorado, USA. "An inch of time is an inch of gold but you can't buy that inch of time with an inch of gold". Therefore we should have clock which measures time with the highest precision and now we have one! 

Quantum Stealth

 Remember the invisibility cloak from Harry Potter, after wearing which he becomes invisible. We have seen or heard about invisibility in fantasies or in fiction but now its possible. Yes, you heard it right. Now it’s possible for human beings to camouflage themselves. A material called Quantum stealth made it possible. Quantum stealth is based on light bending technology.

   

Quantum stealth is developed by Hyperstealth Biotechnology corp. whose CEO is Guy Cramer. Hyperstealth found in 1990 is a Canadian company which manufacture military camouflage uniforms. Quantum stealth is one of the materials developed by Hyperstealth for military to make them invisible. Now, how actually this happens that something become invisible? To know this, first we should know that how are we able to see something. We can see an object when the light reflected from that object enters our eyes. This makes a real inverted image of that object on our retina which is further erected by brain. So, we see objects when light ray is reflected from it. What will happen if light not get reflected? Of course, we will not be able to see that object. This principle was used to develop quantum stealth. It bends the light wave around the target thus making it covert. It even makes the shadows invisible. This material also works against IR scopes and Thermal optics.

This material is not available and will not be in near future for general public. This technology is only made for military purpose. But I wish that some technologies be developed for commercial purpose also, so that I can also get camouflaged and eat my sister’s chocolate 🤣.