What Is the Twin Paradox? A Simple Guide to Einstein’s Theory of Relativity

Did you know that NASA conducted a study of the effects of spaceflight on twins. This was done to test Einstein's famous twin paradox experiment which is a result of relativity. Identical twins Scott Kelly and Mark Kelly were chosen and while Mark stayed on Earth, Scott spent a year aboard the international space station. You can read the results here.

What exactly is twin paradox? Let us understand Einstein's original idea first.

Time machine

Surely the idea of time machine takes our mind on a wild imaginary ride when we attempt to understand it. Time travel is a kind of travel not in space (which we know has three dimensions, length, width and height) but it is the travel in the fourth time dimension. Is it possible to travel in the past or in the future?

In non-relativistic or classical physics, the concept of time is that of absolute time, which is independent of any observer and is same throughout the universe. Same time flow on Jupiter as on Earth. This was thought of first by English scientist Sir Isaac Newton back in the day... who proposed that time progressed at consistent pace for everyone everywhere and is essentially imperceptible and mathematical in nature.

But in Einstein's relativity, time is not absolute. Meaning that time is perceivable and is not the same everywhere and for everyone. And we now know that the rates of time actually run differently depending on relative motion for different observers; time effectively passes at different paces so it might not be the same flow of time on Jupiter.

So, making a time machine might be possible if we can control the flow of time.

Twin paradox

There are two types of time travel: to the future and to the past. We already are moving into the future all the time at the tick of the seconds hand, but we're doing so at a regular rate. Could we make it so that this pace of time going forwards is increased, such that we go into the unseen future?

There is a way. Sending elementary particles on round trips in a particle accelerators at 99% of light speed is routine. The result is that the inner clock of such a travelling particle, say electron, runs much slower than that of a particle of the same species that remains at rest. Time slows for the fast moving particle.

Can this result from subatomic particles extend to larger human bodies? Einstein thought so... in his famous experiment "twin paradox" while he was working on the theory of relativity. In this, a hypothetical astronaut returns from a near-light speed voyage in space only to find his stay-at-home twin many years older than him, because travelling at high speeds has allowed the astronaut to experience only, let's say, one year of time, while ten years have gone by on the Earth.

The real paradox happens from the fact that there is "no favourable reference frame" in relativity. Why can’t the twin in the spaceship define himself as being at rest, let's say? And everyone on Earth is moving in that frame, oppositely. The Earth moves away at high speeds before returning to the still spaceship.

And if that is the frame, couldn’t the travelling twin apply time-dilation to everyone who stay on the Earth? By that argument, shouldn’t it be the humans of earth that remain younger once the twins are reunited? We all must eventually agree though that only one of the twins' perspective has to be the correct one. Which one is it then? So this is the actual "twin" or "dual" paradox of time dilation as put forth by Einstein in the 20th century.

Mind bending.

From general relativity, we can say that time passes more slowly for objects in strong gravitational fields than for the objects which stay far from such fields. There are all kinds of space and time distortions near black holes, where the gravity can become very intense. Thus if one of the twins is orbiting around a black hole and the other's orbiting around the earth the question of the paradox, "which twin is older" is answerable.

Back to the past

We have all watched "Back to the Future" and wondered how messed up it could get if we too did actually move backwards in time? And many scientists say the very premise of pushing a button and going back to yesterday violates the law of causality. However there are also some who think otherwise. Professor Michio Kaku has said, "Time is a river. It speeds up, meanders, and slows down. It can also have whirlpools and even fork into two rivers."

That last bit, "fork into two rivers," is important because then moving backwards in time could become at least thinkable. Because as soon as we push the button we go back into an alternate world or reality. We do not cause harm to our previous reality as in the case of "grandfather paradox". The idea was first proposed by British physicist David Deutsch who used the terminology of multiple universes to solve the grandfather paradox. Deutschian time travel involves the time traveler emerging in a different universe other than his own but very similar to his own.

Time travel will remain only conceptual and debatable except if we are able to develop enough advanced technology for it to become achievable. Until then we will use our earth bound telescopes as time machines. Because when you look into one you'd actually be looking into the past stages of the universe.. meaning that the star you observe today might not even exist in the first place. Turns out that if aliens knew exactly where to point their telescopes they could see dinosaurs at least in principle.

How Physics Affects Technology and Vice Versa

The knowledge of physics has resulted in a wide range of technological applications. Steam engine, for example, the first great industrial invention, arose from the discipline of thermodynamics, at the very start of eighteenth century. Within just a few decades, steam engines were being used in all sorts of applications including factories, mines, locomotives, and boats. Of course, the progress rate of human civilization increased manifold in a short time.

Then, in the nineteenth century, Faraday discovered the law of induction which became the basis for the invention of transformer. Further discoveries by Tesla and current war between Edison and Westinghouse led to the commercialization of electric power. Which created a ground-breaking change in the way we lived life as people. Radio came along soon when Hertz found the way to transmit and receive radio waves; the magic of long distance communication happened.

In first half of the twentieth century, two great inventions took the world by storm. Firstly, there was this enormous, uncontrolled atomic energy, employed as weapons of mass destruction in the second world war. Which would later be controlled in the nuclear reactors to harness clean electrical energy for the 21st century society. The second big invention of the early twentieth century was the television; all the world inside a box; first in greyscale then in color.

In next half of the twentieth century, humankind exceeded all their expectations. Landing on the moon, flying past the planet Saturn and invention of the internet. Towards the end of the twentieth century, personal computers became a reality. Productivity of man reached an all time high. Furthermore, the continually developing semiconductor physics led to manufacturing of even smaller computers and then ultimately smartphones.

From a mechanical age to electrical; from electrical to space age; and from space to a digital age; how far have we come; and marching onwards still! The main point is, that there is a fundamental connection between physics and technology. Without knowledge of physics, there could be no technological advances in the society. Let's see with the following table a list of some important technologies and the principles of physics they are based on.

Steam engine	Laws of thermodynamics
Nuclear reactor	Controlled atomic fission
Radio and TV	Generation, transmission and reception of electromagnetic waves
Laser	Stimulated emission of radiation
Computer	Digital logic
Rocket propulsion	Newton’s laws of motion
Radar and sonar	Reflection of sound
Ultra high magnetic field	Superconductivity
Electric generator	Faraday’s law of induction
Hydroelectric power	Conversion of energy
Airplane	Fluid dynamics
Particle accelerators	Lorentz force
Optical fibers	Total internal reflection
Electron microscope	Wave nature of matter
Photocell	Photoelectric effect
Fusion reactor	Magnetic confinement of plasma
Telescope	Reflection and refraction of light
Transistor	Semiconductor physics

 

Now a question arises: can technology give rise to new physics? Yes but rarely is it so. For example, measurement of time, an otherwise ancient technology, was perfected only in the era of Huygens and Galileo. This new form of technology was an accurate pendulum clock, which led Galileo to understand the physics of velocity and acceleration.

Another example of technology giving rise to new physics is the particle accelerator such as the large hadron collider. Inside a particle accelerator, there are a thousand possibilities; discoveries of strange particles. It is not surprising that whenever a new particle is found, new physics is unraveled.

Thus, the link is kind of two-way. However, physics leading to new advances in technology is far more likely than vice versa. Whatever is the case, the ultimate benefit, should be going back to the common people. It is the duty of those in power to make it so and to not misuse physics or technology to fulfill their eccentricities.

How A Rainbow Can Form Without Rain 😲

Rainbow is an optical phenomenon which is generally associated with rain, mist, and even fog. Some or the other form of water is thought to be required in order for a rainbow to form. But have you ever noticed a rainbow formation in a specific spot, like near a window at home? The conditions have to be just right, which makes it a cool little surprise when it happens!

Now, the sunlight keeps hitting the glass window all through the day so why is it that rainbow is only a rare occurrence? Dispersion or splitting of white light is a simple physical formation and yet rare to sight in day to day life. That is why, every time you spot a rainbow out of nowhere, it evokes a sense of joy and wonder isn't it?

For the rainbow effect to pop out, the light has to strike the glass window near a "critical" angle. The sun moves in the sky and it is only a specific moment in time when the angle of incidence is accurate enough for rainbow to appear. It is not a full arc like a sky rainbow because the geometry of a window pane is not the same as the spherical shape of a raindrop, but the physics is identical: refraction, dispersion, and a bit of reflection.

Why light splits into colors?

White light, or sunlight which is made up of all visible wavelengths, doesn’t bend uniformly, as each color, having different wavelength bends differently at a slightly different angle. As a general rule, shorter wavelengths, like blue, bend or refract more than longer ones like red.

Some cool facts about rainbow

1. No two people see the exact same rainbow since a rainbow is formed by light refracting through specific raindrops relative to your position. The exact rainbow you see depends on where you’re standing. Move a little, and it’s a different set of raindrops creating the effect.

2. The order of colors is always the same—red, orange, yellow, green, blue, indigo, violet, because of how light bends at different wavelengths.

3. A rainbow formed by light of the Moon, is called moonbow. The amount of light available even from the brightest full moon is far less than that produced by the sun so moonbows are incredibly faint and very rarely seen.

How Squirrels Use Physice In Daily Life?

I was sitting in a park nearby my house, bored, having listened to all the trending songs in one go, when I saw a couple of Squirrels jumping from tree to tree. They reminded me of Toby Maguire and Andrew Garfield as Spiderman. More importantly, I was astonished at how they were using the principles of physics to go about their daily lives... 

Although squirrels or any other animal for that matter are not consciously aware of physics, they certainly interact with physical laws in fascinating ways. I am sure you, the reader, must have come across these 10 ways in which squirrels use physics in their everyday lives:

1. Parabolic Jumping: When squirrels jump from one branch to another, they follow a parabolic ttrajectory. Not only that, they spread their arms and legs as if they were birds to increase the surface area and lift force. I wonder if squirrels calculate the optimal angle and velocity needed to reach their destination.

2. Gravitational Potential Energy: When squirrels climb trees, they increase their potential energy. As they descend, they convert this energy into kinetic energy. I have seen them speed up and down the tree like it was nothing. Their bodies are also very elastic, which helps them in their daily chores. I wish I could climb a tree like that.

3. Friction for Grip: Have you noticed how Squirrels have sharp claws? Tiny but still firm. These claws allow them to grip surfaces with high friction. This friction is essential for climbing vertical tree trunks, allowing them to move quickly and stay stable while navigating tricky terrain. No wonder I can't climb with ease as my hands are always sweaty.

4. Elastic Potential Energy: Squirrels' tails act like a rudder and balance aid, but they also store and release elastic potential energy from their tail when the squirrel jumps or changes direction mid-air. This helps them land more precisely or correct their movement in mid-flight. The tail makes up and significant portion of their body weight and acts like a mechanism to (almost) fly.

5. Rotational Motion: When squirrels leap or fall, they can twist their bodies in mid-air, adjusting their orientation using their limbs and tail. This rotational motion allows them to land feet-first and avoid injury.

6. Energy Conservation: Squirrels run very fast, but for shorter periods of time. Like a Cheetah. This combination of high-speed running and short bursts of activity allows them to conserve energy while traveling long distances or evading predators.

7. Bouncing: When squirrels jump off hard surfaces or onto bouncy objects (such as a trampoline-like surface in a tree), their bodies absorb and release energy through elasticity, softening the landing and reducing the risk of injury.

8. Inertia and Momentum: When a squirrel is running at high speed and suddenly changes direction, its body mass and velocity create inertia, making it harder to stop. But with enough friction, it can quickly change direction without sliding, maintaining its momentum.

9. Gliding: There is a species of squirrels which flies, aptly called the flying squirrel. They have a fluffy membrane between their fore and hind legs, helping them to glide. The physics of air resistance helps them stay in the air longer and glide to distant points safely. Not all squirrels can glide long distances though, which is disappointing.

10. Balance and Center of Mass: Squirrels constantly adjust their center of mass as they move along narrow branches or leap across gaps. By shifting their body position and adjusting their posture, they maintain balance and stability to prevent falling. Have you noticed how they pose like Spiderman when they land? That's them adjusting their center of mass to make a safe fall.

In all these (and possibly more) ways, squirrels engage with the principles of physics in daily life, allowing them to thrive in their harsh environments.

5 Predictions of Nikola Tesla That Came True (And 5 That Didn't)

Nikola Tesla was a genius Serbian American inventor who laid the foundations of alternate current power system. Tesla was an advocate of modern technology and made many convincing predictions about the future. Some of Tesla's predictions were proven correct in the 21st century and some have gone wrong, as you shall see in this post.

1. (Right) Alternating current

Nikola Tesla pioneered the generation, transmission and use of alternating current electricity. Tesla believed that one day in the future the entire world would use his power system over direct current.

Thomas Edison famously tried to show with experiment that alternating current was deadly. However, Tesla overcame that fear mongering by showing that AC was safe, inexpensive and usable over large distances.

2. (Wrong) Interplanetary energy exchange

One can see that Tesla and his ideas were on another level when he said that he would be able to complete interplanetary communication. In 1931, Tesla proposed a way in the future that would allow planets to transmit energy, from one planet to another, in large amounts of horsepower - regardless of distance.

3. (Right) Smartphone

In 1908, Tesla said - An inexpensive instrument, not bigger than a watch, will enable one to call up, from one's desk, and talk to any telephone subscriber on the globe. Any picture, character, drawing, or print can be transferred from one to another place.

4. (Wrong) Unlimited free energy

Tesla envisioned a future in which humans are able to harness the energy of ionosphere and distribute it wirelessly to anyone anywhere on the planet. This concept, while inspiring, has not been realized because of practical reasons.

5. (Right) Thought images, MRI

Tesla: I expect to photograph thoughts. In 1893, while engaged in certain investigations, I became convinced that a definite image formed in thought must produce a corresponding image on the retina, which might be read by a suitable apparatus.

The closest machine able to do as Tesla suggested is MRI scan. An fMRI scan can tell you something about what a person is thinking. Tesla predicted - "Our minds would then, indeed, be like open books."

6. (Wrong) Wireless electricity

One notable incorrect prediction of Nikola Tesla is transmission of wireless electricity through the air. There would be no need for wires in the future for long distance transfer using his Wardenclyffe tower. This idea of Tesla was impractical on many levels and was not realized on large scale.

7. (Right) Wi-fi

While wireless electricity did not succeed, wireless transfer of files - documents, photos, music, video worked. His prediction of the internet came true in the 1980s and wireless file transfer in the 1990s.

8. (Wrong) Anti gravity tech

Tesla predicted an anti-gravity technology which would allow levitation in day to day life. Despite ongoing research in this field, anti gravity remains impractical and still quite far from reality.

9. (Right) Robotics and automation

Tesla predicted that robots will replace humans in many fields. He predicted driverless cars. He predicted robots would do menial labor like lifting and loading. Today, not only this, but automation via artificial intelligence is putting human creativity at risk, as they create art and music.

10. (Wrong) Weather control

While modern science has explored temporary weather modification techniques like cloud seeding, a complete control of weather and climate as Tesla had envisioned has not come to fruition.

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?