Paul Dirac versus Richard Feynman

Feynman and Dirac, two great physicists who made invaluable contribution to quantum mechanics and Nobel prize winners, were poles apart.

While Richard Feynman idolized Paul Dirac, they disagreed on many things. One remembers Dirac as an extremely shy person, who hesitated to speak. Feynman, on the contrary, was a chatty man whose anecdotes spread contagious laughter.

Dirac won the Nobel prize for correctly predicting the existence of anti-matter. Three decades later, Feynman won the coveted prize for his work with elementary particles.

Both physicists had a very distinct view of science. Dirac was inclined towards mathematics and considered beauty in one's equations to be important. While Feynman preferred the equation to stand the test of experiment.

Feynman said - Physics is not mathematics. Mathematics is not physics. One helps the other.

Dirac was of the view - It is more important to have beauty in one's equations than to have them fit experiment.

You can say that in this regard Feynman and Dirac were rivals as they say "Raibaru" in Japanese. They did not seem to agree on this one thing.

Yet, as a young man Feynman idolized Dirac. He said - 

Dirac made a breakthrough, a new method of doing physics. He had the courage to simply guess at the form of an equation, and to try to interpret it afterwards.

This equation is now called Dirac equation. It is a beautiful, small equation that predicts counterpart of matter, anti-matter. In 1932, Paul Dirac was recognized by Nobel prize in physics for his work.

Later on, Feynman's views changed.

Being a mathematical physicist, Dirac was of the view that if an equation has beauty, then one must be working correctly, on the right path. Feynman disagreed that beauty is paramount, but he still remained a Dirac fanboy.

Feynman's evolved thought was

No matter how beautiful an equation is, no matter who made the equation or how genius he was, if it disagrees with experiment, it is wrong!

In 1962, the two great minds Feynman and Dirac met at a science conference.

Feynman a chatty fellow talked at length while a meek old man Dirac listened quietly. In the end, Dirac blurted out a question - I have an equation. Do you have one too?

Earlier in 1948, Feynman had invented a diagram to pictorially represent the interaction of subatomic particles. For this simplification work, Feynman won the Nobel prize in 1965. It is then interesting to note that both scientists won the Nobel prize in physics for proposing a simple solution.

One key takeaway from this story is that it takes courage to challenge your idol. Feynman admired Dirac all his life, but it was not wrong for him to disagree with his hero once in a while. Isn't that how science progresses? When great minds collide?

10 Examples of Physics In Daily Life

Physics is not just about solving the problems and finding the right answer. From atoms to galaxies, everything is governed by physical laws. Not only is physics responsible for modern technology but also an active part of day to day life without us even realizing.

Following are ten such examples of physics in daily life:

1. In winter season, the act of rubbing your hands together to create warmth is a norm. Friction generates heat as well as responsible for static electricity. Have you heard sparkling noise while removing woollen clothes?

2. The refrigerator is made up of sheet metal so we can have thermal insulation between the strong metal and the food inside. That is why we use the surface of fridge to hold up a magnetic note or picture.

3. As we throw a basketball into the hoop or hit the soccer ball with foot, the curve traced by ball is called a parabola, and there is a certain angle at which you need to throw the projectile so it covers maximum distance. Athletes use this physics all the time.

4. Feeling the pressure change when riding in an elevator. Not only that, when you move from plains to mountains, there is also a pressure change and breathing becomes more difficult. This also happens with divers.

5. Using glasses or contact lenses to correct vision. Approximately 64% of adults use some form of vision correction, including eyeglasses, contact lenses, and/or vision correction surgery. Also, rear view mirror in vehicles is a convex mirror, bulged outward, to give a wider field of view.

6. Semiconductor physics used in electronic devices like smartphones, laptops, and TVs. When we buy a new smartphone, we tend to compare which chip the device is powered by.

7. When a baseball pitcher throws a curveball, the spin on the ball creates a pressure difference on its surface, causing it to curve due to Bernoulli's principle.

8. Ferrofluids are used in high end speakers to improve sound quality. Ferrofluids are liquids that become strongly magnetized in the presence of a magnetic field, thus dampening vibrations, and cooling the speaker coils.

8. Flicking a light switch involves a combination of mechanical and electrical processes. When the switch is flipped, it completes an electrical circuit, allowing current to flow and illuminate the light bulb.

9. The popping of popcorn kernels occurs due to the buildup of steam inside the kernel as it heats up. When the pressure inside the kernel exceeds its structural integrity, it explodes, turning inside out to form the fluffy snack we enjoy.

10. Elasticity is everywhere around us - from springs to rubber bands to bouncing a ball. Even trains are powered by thick metal springs. Springs are also used as a power source in mechanical watches.

Why Light Bends Because of Gravity If It Has No Mass?

Gravity affects light not because light has mass or not, but because gravity disturbs the fabric of spacetime itself. According to Einstein's theory of general relativity, massive objects like stars or planets, even mountains to some extent, bend the space around them.

Imagine space is a flexible, three-dimensional rubber grid. For example: planets like Earth or Jupiter, bend and create an impression in this grid. This curvature makes smaller bodies, their moons, follow the planets around in a circle.

Near massive objects, like a star or a black hole, spacetime is more curved, and objects move along more curved trajectories like an elongated ellipse.

Light, like moons and planets, also follows the curvature of this warped spacetime, causing it to appear as if it's being "bent" by gravity.

Does light have mass?

No, light does not have mass. Light consists of massless particles called photons.

The masslessness of photons is a fundamental property that contributes to some unique characteristics, such as traveling at the speed of light and having no electric charge.

Has general relativity been tested?

Albert Einstein proposed his theory of gravity, known as the theory of general relativity, in 1915 in a sequence of four papers. Time and time again the theory has been proven right, for instance in explaining the rotation of Mercury's orbit.

That's why general relativity is extensively used in modern technological applications such as atomic clocks, GPS, etc.

5 Amazing Inventions By Physicists We Use Every Day

Did you know that one of the first video games was invented by a physicist? Why do you have to put your bags through a machine when you enter airport? In this post, we will look at five simple or somewhat complicated inventions by physicists that are used in daily life.

Although, from Wi-Fi to smart TV - physics is everywhere around us in the form of modern technology. The following are inventions we rarely talk about, or are thankful for, despite making use of them on regular basis.

1. Lever

Archimedes said, “Give me a firm place to stand and a lever and I can move the Earth." That was never tested but a lever is put to use in many forms today: Stapler, a pair of scissors and seesaw. There are different classes of levers:

a) Class I lever is when fulcrum is between load and effort. Example: Seesaw.

b) Class II lever is when load is between fulcrum and effort. Example: Door.

c) Class III lever is when effort is between fulcrum and load. Example: Stapler.

2. Video games

Physics has had an important impact in the early development of video games. In 1958, physicist William Higinbotham created what is thought to be the first video game. It was called Tennis For Two, a very simple game that shaped the history of computer games.

3. Electric generator

Physicist Michael Faraday invented the first electric motor in 1821. Shortly after, Faraday invented the electric generator, based on electromagnetic induction discovered by him. This is used to generate electrical power - which in turn is used to run electrical appliances.

When Faraday first presented induction, he was asked by some politician or reporter: What use is it in the practical world? To this Faraday replied, What use is a newborn baby?

4. Battery

While Faraday invented a way to generate electrical power by fluctuating magnetic fields, another physicist Alessandro Volta had invented a way to store electrical power in 1800. In honor of Volta, the SI unit of electric potential is called Volt. Today, almost all the toys that children play with use batteries.

5. X-ray

Some say that Nikola Tesla discovered x-rays by accident. Others credit Wilhelm Roentgen for inventing a way to generate x-rays in 1895. Whatever the case may be, did you know that x-rays are not only used in healthcare but also in the security industry? Every time your luggage passes through a security machine, an officer can see what is inside your bags.

How Rutherford Became Father of Nuclear Physics

"It is JUST AS surprising - as if a gunner fired a shell at a single sheet of paper and for some reason or other, the projectile BOUNCED BACK."

This is how New Zealand physicist Ernest Rutherford described the result of alpha particle scattering experiment - conducted by his students Geiger and Marsden.

Introduction

Geiger and Marsden aimed high speed alpha particles at a very thin gold foil - it was only 1000 atoms thick. Around the gold foil was a zinc sulphide screen which glowed every time alpha particles would hit it.

If Thomson's plum pudding model of atom were correct, the fast moving and relatively heavier alpha particles would have passed straight thought the target, since electric field generated by evenly distributed charge is very minimal.

But the experiment revealed that a few alpha particles were deflected by small angles, while 1 in 20,000 particles got deviated by angle greater than 90 degrees.

Rutherford set out to explain these unusual findings by creating a new model of atom, because Thomson's model had failed.

Early life and career 

Ernest Rutherford [1871-1937] was a multi-talented student who did phenomenally well in mathematics, catching everyone's attention at his school as a consequence.

He won the scholarship to study at Canterbury College, University of New Zealand, where he participated not only in the lab but also in the debating society.

Rutherford was the head boy in college and played the rugged sport of rugby. He completed three degrees in this college - ba, ma and bsc.

Thereafter, he travelled to England in order to study under the guidance of J. J. Thomson at the Cambridge University. Rutherford worked with cathode ray tubes under Thomson's mentorship. 

In 1899, he heard about Henri Becquerel's discovery of radioactivity and became interested in exploring alpha and beta decay. Rutherford was among the first to prove that alpha particles were Helium nuclei.

"All science is either physics or stamp collecting." Rutherford used to say, but ironically he won the Nobel Prize in chemistry in 1908 for his pioneering work with on the chemistry of radioactive substances.

Discovery of Nucleus 

As discussed earlier, alpha particle scattering experiment was conducted by Rutherford, Geiger and Marsden in the year 1909, by passing alpha particles through a thin gold foil.

Rutherford argued that since most of the particles passed straight through the gold foil, the atom must be made up of mostly empty space - not a positive soup as Thomson had thought.

In fact, the atom is about 100,000 times the diameter of the nucleus. It is like putting a grain of sand in the middle of a soccer ground!

Positive charge must be localized, Rutherford argued, in a very small point at the center of atom, which explained bouncing back in a small fraction of alpha particles, since positive positive repel.

Negative charges in the atom must be located somewhere on the outskirts ... which explained smaller deflections.

Summing up

By creating a new improved model, Rutherford became the father of nuclear physics, as he initiated a whole new branch of physics. Scientists decided to probe further into the nucleus and many subatomic particles were discovered as a result.

Upon the discovery of atomic nucleus, Rutherford said: "I have broken the machine and touched the GHOST OF MATTER." But he regretted not being able to explain something deeper - "when we found the nucleus, we found the basis of everything, the greatest secret of all - except of life."

10 differences between astrology and astronomy

1. Every newspaper in the world has a daily column on astrology. How many papers carry even a weekly column on astronomy? – this is a major, disappointing difference between the two fields, as pointed out by Carl Sagan.

2. Astronomy is a practical science built upon technical skills such as in observation, mathematics and computer programming. Astrology does not demand such complicated knowledge.

3. If you delete all of human history, astronomy will come up again in exactly the same manner since it is based upon facts and figures. Whereas, astrology is a product of the human imagination and will acquire different shapes and forms.

4. There is a Nobel Prize for astronomers who make great advances to our understanding of the universe – astronomy being a branch of physics. In astrology, there is no such honor.

5. According to astrology, the position of a planet such as Saturn can trigger a life changing influence on an individual located on some corner of the Earth. Astronomy denies this claim.

6. After decades of research, astronomy has reached to the conclusion that life on earth is made from elements that were forged in the core of dying stars – a poetically beautiful truth. Astrology could not have reached to this sophisticated result.

7. Historians say that astrology is 2,500 years old. On the contrary, astronomy is vastly older. The first human beings depended on astronomical events for various activities, such as in agriculture and navigation. This developed into questions like, "What's out there?" and into inventions like the telescope.

8. Hence, astronomy is a natural tendency (aka curiosity) whereas astrology is derived, from observations and results in astronomy. Astrology is something that people turn to thinking it would have answers to life's problems.

9. Astronomy is a healthy activity for kids to get involved in. Astrophotography is one way to get started. Whereas, a sincere belief in astrology puts children inside boxes and they grow up asking dumb questions like, "What's your star sign?" to measure compatibility.

10. Reading astrology may be comforting to some people, but at only a superficial level. On the contrary, astronomy appeals to the very core of a person and may inspire them to paint a timeless piece like the "starry night".

5 Niels Bohr Quotes On Quantum Mechanics

Niels Bohr was a Danish physicist who made pioneering contributions to understanding atomic structure and quantum theory, for which Bohr was recognized with a Nobel Prize in 1922. Bohr was an active participant in the new quantum theory revolution that shook the foundations of classical physics.

Einstein, who was not ready to accept Heisenberg's uncertainty principle, as one of the cornerstones of modern physics, commented: God does not play dice with the universe. Bohr made peace with the uncertainty principle by developing the principle of complementarity.

According to complementarity, particles have certain pairs of interdependent properties that cannot all be observed or measured simultaneously. For example: position and momentum make such a pair.

Bohr regarded complementarity as an essential feature of quantum mechanics. It is said that Bohr replied to Einstein, who preferred the determinism of classical physics over the probabilistic new quantum physics: (1) "Stop telling God what to do."

In 1920, Bohr met Heisenberg for the first time. Bohr said, (2) What is it that we humans depend on? We depend on our words... Our task is to communicate experience and ideas to others. But when it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images and establishing mental connections.

Some physicists depended on mathematical analysis to make sense of the quantum world. However, Bohr was not satisfied. (3) Even the mathematical framework helps nothing, I (Bohr) would first like to understand how Nature avoids the contradictions. (1927)

Bohr said further: Our experience in recent years has brought light to the insufficiency of our simple mechanical conceptions and, as a consequence, has shaken the foundation on which the customary interpretation of observation was based.

We can still use the objectifying language of classical physics to make statements about observable facts. But we can say nothing about the atoms themselves.

In the 1927 Solvay conference, Bohr and Einstein went head-to-head on the metaphysical and philosophical implications of quantum mechanics. Two legends, one defending the new-age probabilistic physics and another fighting for classical determinism. At the end, it was Bohr who emerged victorious and successfully established the probabilistic character of quantum measurement.

Niels Bohr wrote in 1934: (4) Isolated material particles are abstractions, their properties being definable and observable only through their interaction with other systems. Everything we call real is made of things that cannot be regarded as real.

In a 1952 conversation with Heisenberg and Pauli in Copenhagen, Bohr quipped: (5) "Those who are not shocked when they first come across quantum theory cannot possibly have understood it." This was most likely a reference to Einstein, who not only contributed to the new theory but also immediately taken aback by its bizarre results.

Richard Feynman Explains The Circle of Life

Nobel prize winning American scientist, Richard Feynman, was fascinated by simple things. From rubber band to fire, Feynman was delighted to explain the physics of day to day items in easy and poetic language. Here, Feynman described the life cycle of a tree as an example to illustrate that life comes full circle.

Where does the structure of the tree come from? To find out, we must start at the beginning. It is understood that seed sown in the ground will develop shoot of the plant, as it reaches out for the sunlight. At the same time, a root spreads deep in the soil searching for water.

Capillary action helps bring water up into the roots when the soil has higher concentration of water than the root cells. It is like putting a wick in oil lamp. But capillary action can only pull water up a small distance, when the plant is small.

In a mature tree, liquid water flows into the woody stem and then into green leaves where photosynthesis will occur. How does it work against the effects of gravity? The answer is cohesive forces that help to move water to the furthest leaf.

In the green leaves, some part of the water is used for photosynthesis. The other part, due to heat from sunlight, escapes into the atmosphere as water in gaseous form. In fact, if you wrap a plastic bag around a leaf, you can actually see vapor condense inside the bag.

Since molecules of water in the root and stem stick tightly to one another because of cohesion, the vapors which escape from the leaves, kind of pull the remaining water, as a single unit, upward behind them. This process is called transpiration.

Going back to, where does the structure of the tree come from? Feynman comments: it is generally thought that plants grow out of the ground. However, apart from water and vital nutrients, the ground does not contribute in the building up of the tree.

Mass of the tree is primarily carbon and where does that come from? The atmosphere, but not in pure form, it comes as carbon dioxide. (In its lifetime, a tree soaks up tons of carbon dioxide from the air, which is why it is advised to plant more trees).

The absorbed carbon dioxide is reduced to pure carbon when acted upon by the sunlight. Trees utilize these carbon molecules to construct their body tissues, for example in the stem. The useless oxygen molecules, on the other hand, are spit back into the air.

Thus, a combination of water, air and light as they come from the ground, atmosphere and sun respectively, mediate the flowering and growth of the tree.

There is a beautiful end to the story. The tree is used as a fuel for combustion. When pieces of wood are rubbed, for example, heat is built up by friction and that leads to reunification of carbon molecules in the tree with oxygen molecules in the air, generating a "tremendous catastrophe" as Feynman puts it, fire.

If you think about it, this light and heat of the fire is the light and heat of the sun, that went in! Feynman says: it is kind of a "stored sun", that is coming out when you burn a log. Isn't it wonderful how nature manages to come back in a full circle?

Why We Can Never Build The Time Machine

It has been a long, unfulfilled dream of humankind to obtain control over the passage of time. One cannot help but fantasize about bending time backwards, pause its eternal flow and dodge the inevitable death if technologically possible.

Clearly, time is a captivating phenomenon. That is why, a common theme in all science fiction is time travel. However, is building the time machine so trivial as depicted in the movies, like Back to the future? Is it theoretically as well as practically allowed?

What we gather about time travel from fiction is that it is either going back to a bygone era or jumping forward in the future. Time travel is a trip not in space which has three dimensions, but it is a journey in the fourth time dimension, the one we do not understand fully.

Theory of relativity

In non-relativistic physics, time was absolute, independent of the observer and same throughout the universe. This was proposed by English scientist Sir Isaac Newton when he thought that time progressed at consistent pace for everyone everywhere.

But in relativity, as theorized by German physicist Albert Einstein, time is no longer an absolute concept.

Firstly, time is treated like an alternate dimension to spatial dimensions of length, width and height. In other words, time is a new corridor to pass through.

Secondly, time is not the same for everyone everywhere as Newton had assumed. Time slows down as you travel faster, for example.

In fact, when subatomic particles are accelerated to nearly the speed of light, their lifetimes expand dramatically. They would usually decay faster, but when moving at relativistic speed inside the particle accelerator, they experience time more slowly (relative to other particles) and live longer.

Furthermore, from general theory of relativity, an upgraded version of special relativity, it is known that time passes more slowly for objects in strong gravitational fields, than for those objects which stay far from such fields.

As a result, if there were twin brothers and one of the twins orbited a black hole while the other around the earth, can you guess which of the twins would be older?

Coming back to the question: Is time travel as shown in the movies like Looper or Back to the future practical? Many scientists agree that the idea of time travel at the push of a button is not possible as it would violate the law of causality.

The paradox

Time's flow is like a river as it speeds up, meanders and slows down. Time can also have whirlpools and fork into two or more rivers, says American physicist and futurist Michio Kaku.

As soon as the button of the time machine is pressed, it may be possible for one to go backwards in a parallel world. Therefore, deprived of the opportunity to change the turn of events in the reality one came from. A new reality would be built from scratch, avoiding the grandfather paradox.

This idea of time travel was proposed by British physicist David Deutsch who used the terminology of multiple universes to solve the widely debated grandfather paradox.

The paradox comes from the idea that if a person travels to a time before their grandfather had children, and kills him, it would make their own birth impossible.

Deutschian time travel solves the paradox only theoretically. The time traveler emerges in an alternate universe, but very similar to his own. Can such universes pop in and out of existence merely on the whim of the time traveler? The idea sounds good on paper but its practical possibility is highly doubtful.

What is possible

As per most scientists and engineers, time travel is impossible as you have seen in the movies. The late English astrophysicist Stephen Hawking once joked: "I have experimental evidence that time travel is not possible." Hawking hosted a party for time travelers in 2010, but no one came.

Yet, we have observed that time slows down and does not always run at the same pace everywhere, which can help to travel forward in time, at least, relative to another. As shown in the realistic movies like Interstellar (2014).

Also, when we observe the universe, we are looking back in time. Our own Sun’s light, for instance, takes about 8 minutes to reach on earth. We see the Sun the way it was 8 minutes ago; so if the Sun disappeared this instant, we wouldn't know.

You will be surprised to know that NASA's James Webb telescope can study light that was emitted by the most ancient galaxies 10 billion years ago. This means, we can peek at the birth of the universe, more or less, if we design an even larger, better telescope.

Summing up

Time travel at the push of a button is out of the question. To construct such a machine violates not only the laws of physics but also common sense. It is much like building a perpetual motion machine, a hypothetical machine that can do work infinitely without an external energy source.

Lastly, reiterating that time travel is far more impossible technically than it is theoretically. There may still be undiscovered physics that allows construction of a time machine. It might be possible but would involve vast amounts of energy and money.

4 Unsolved Mysteries About The Higgs Boson

On July 4, 2012 the Higgs Boson particle was discovered at the Large Hadron Collider that is operated by CERN, the European organization for nuclear research. It took 60 years to first detect the elusive particle and there is still a lot to learn about it, scientists say.

CERN closed the largest particle accelerator for maintenance work that was extended due to delays caused by the pandemic. In 2022, scientists celebrated the 10th anniversary of Higgs Boson discovery. They now hope to uncover more as LHC has gotten back in action after 3-year hiatus.

1. Is the Higgs connected to dark matter?

Since dark matter makes up about 30% of the universe's mass and considering Higgs boson's relation to mass, scientists want to find if the two are connected somehow. They may explore, for example, whether or not the Higgs boson particle decays into a dark matter particle.

As of current understanding, scientists know that the Higgs boson particle can decay into boson, fermion and muon. The goal is to see which other kind of mysterious particle the Higgs boson particle can decay into. So far no unusual particles have been detected in collider experiments.

2. Does the Higgs boson interact with itself?

Matter particles (such as electron) move through the Higgs field and acquire their characteristic mass. More interaction means more the mass attained by the particle. Scientists hope to run experiments to find if the Higgs boson particle interacts with itself as predicted by the standard model.

This is the main question about the Higgs particle right now, say scientists working at the council for nuclear research. According to the standard model, when the Higgs particle self-interacts, it would create pairs or triplets of Higgs bosons, that are yet to be detected in the experiments.

3. Are there other Higgs particles?

The Higgs boson is an excitation of the all-pervading Higgs field that helps other particles pass through it and acquire mass. For this reason, it was nicknamed the God particle by the media, although some scientists refer to it as the Goddamn particle as it took so long and multi-billion dollars to find it.

The particle which was found in 2012 has zero spin and no electric charge. Theories alternate to the standard model predict the presence of more than one kind of God particle. Detection of additional Higgs particles in the collider experiments would mean that there must be new physics out there.

4. How does the Higgs interact with matter?

One thing scientists know for sure is that the more massive a given particle, the greater its interaction with the Higgs field must be. The nuances of this are yet to be understood even though the measurements thus far match the predictions of the standard model, the precision of these measurements isn’t great enough.

Models other than the standard model propose the existence of one kind of Higgs particle that interacts only with heavy particles and another that interacts with only lighter particles. Similar exciting challenges in particle physics await scientists working at the large hadron collider.

5 Richard Feynman Quotes on Quantum Mechanics

American physicist Richard Feynman won a Nobel Prize for physics in 1965 for his work in quantum electrodynamics. Feynman was a man who always jumped into an adventure: as an artist, a story-teller and an everyday joker whose life was a combination of his intelligence, curiosity and uncertainty.

Despite making fundamental contribution to the field of quantum mechanics, Feynman was often perplexed by its complexity. Feynman said, We don't know what an atom looks like but we can calculate its behavior. It is like a computer trying to calculate how fast a car is going without being able to picture the car.

Following are five quotes by Richard Feynman that reflect his views on quantum physics. As students, we may derive one or two equations, solve few problems and be done with it. But it is a great insight to look back as to how a previous generation of physicists grappled with the bizarreness of quantum mechanics.

1. Personal struggle: I always have had a great deal of difficulty in understanding the world view that quantum mechanics represents. Because I'm an old enough man that I haven't got to the point that this stuff is obvious to me, okay? I still get nervous with it. And therefore, some of the younger students, you know how it always is, every new idea, it takes a generation or two until it becomes obvious that there's no real problem. It has not yet become obvious to me that there is no real problem.

2. Nature is absurd: What I am going to tell you about is what we teach our physics students in the third or fourth year of graduate school. It is my task to convince you not to turn away because you don't understand it. You see my physics students don't understand it... That is because I don't understand it. Nobody does. Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is - absurd.

3. Relativity VS quantum mechanics: There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, (Einstein) because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics.

The difficulty really is psychological and exists in the perpetual torment that results from your saying to yourself, "But how can it be like that?" which is a reflection of uncontrolled but utterly vain desire to see it in terms of something familiar. But nature is not classical, dammit, the imagination of nature is far greater than the imagination of man.

4. The mystery of atom: It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time.

How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypotheses that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple.

5. On nature of reality: Does this then mean that my observations become real only when I observe an observer observing something as it happens? This is a horrible viewpoint. Do you seriously entertain the idea that without the observer there is no reality? Which observer? Any observer? Is a fly an observer? Is a star an observer? Was there no reality in the universe before life began? Or are you the observer? Then there is no reality to the world after you are dead? I know a number of otherwise respectable physicists who have bought life insurance.

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5 Major Differences Between Sgr A* and M87*

Take a close look at the two black hole images and you can ascertain a few differences by your own. Notice the speed of accretion disk, which is a gas-like flow around the black hole. Or the size of dark spots in the center that give you a faint idea of the black hole event horizon.

The latest image by event horizon telescope is that of Sagittarius A*, a black hole in the center of our Milky Way galaxy. That this is a supermassive black hole was first recognized by physicists Reinhard Genzel and Andrea Ghez, for which they won the Nobel Prize in 2020.

Event horizon telescope or EHT is a worldwide network of radio telescopes that took the first ever picture of a black hole in 2019. It was that of M87*, an enormous supermassive black hole in the heart of Messier 87 galaxy in the constellation Virgo.

While the two black hole pictures look almost similar, for the laws of physics that govern their behavior are the same, the new image is more exciting than before. For one, it is located in our neighborhood; and second, it was way too difficult to catch a glimpse of.

1. Schwarzschild radius: It is the size of the sphere from which even light will fail to escape. For supermassive M87* this is 18 billion km, four times the radius of our solar system! For Sgr A*, Schwarzschild radius is only 12 million km.

2. Relative size: Our black hole is 31 times wider than the Sun, as shown in the figure below. Whereas the black hole in Messier 87 is 27,000 times wider than the Sun. If Sgr A* was the size of a doughnut, then M87* would be the size of a football stadium.

3. Distance: Our neighborhood black hole Sagittarius A* is obviously closer, located 25,000 light years away from the earth. Whereas M87* is 55 million light years away! So if it took 1 hour to get to Sgr A*, then it would take 91 days to reach M87*.

Despite being closer, observing Sgr A* was more challenging than expected. Scientists had to look through the galactic plane and filter out the noise from intermediate stars and dust clouds in their data, collected across continents.

4. Mass: M87* is 6 billion times more massive than the Sun whereas Sgr A* weighs 4 million Suns. Thus, our black hole Sgr A* is 1500 lighter in comparison.

5. Speed: Around the black hole is a bright ring of materials that swirl at great velocities. The material disk of M87* rotates over a course of many days at roughly 1,000 km/s, while it takes only a few minutes for material to move around Sagittarius A* because it is much smaller.

Why is the picture of our black hole kind of blurry? One of the reasons is that we don't have a direct view of the object while sitting on one of the arms of the galaxy and secondly, its accretion disk is spinning very fast compared to M87* so it's like taking a picture of a toddler who cannot stand still.