The Photon Magazine #4 July 2021

JULY 2021 · ISSUE 4

photon

YOU CAN'T OUTRUN LIGHT: NOTHING MAKES SENSE ANYMORE PAGE

15

THE PARTICLE THAT BROKE TIME SYMMETRY PAGE

IT'S ABOUT TIME

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ALBERT EINSTEIN

THE ONLY REASON FOR TIME IS SO THAT EVERYTHING DOESN'T HAPPEN AT ONCE.

ON THE EXPERIENCE OF TIME

PAGE 2 GALILEO GALILEI AND THE FLOW OF TIME PAGE 10

en THE BOOTSTRAP PARADOX

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co COMPLEXITY INTERTWINES WITH MYSTERY PAGE 14 YOU CAN'T OUTRUN LIGHT

PAGE 15 WEIRD THEORIES OF TIME

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TIME TRAVEL IN SCIENCE FICTION

TIME TRAVEL, SPECIAL RELATIVITY AND THE BELL INEQUALITY PAGE 5

nt THE PARTICLE THAT BROKE TIME SYMMETRY PAGE 18

ts TIMELESS HUMOUR

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PAGE 31

LETTER FROM THE

EDITORS

Hello readers!

Welcome to the first Photon issue of 2021!

One of the most talked about topics in Physics is that of spacetime. Well, we did 50% of it already, so we decided to go the full way and present an issue on time. This issue contains articles from every nook and cranny of time theories, ranging from imaginary time to time travel. We hope you can make the time to read it - we promise you will not be disappointed.

Time is the most underappreciated thing ever. It either goes too fast or too slow depending on whether we’re having fun or we’re bored, but what is it? How do we experience the passage of time? Why can’t we move in any direction apart from forward (as far as we know)? You’ll find answers (of sorts) to these and more as you turn the hallowed pages of this issue, so dive right in.

It’s about time.

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The Editorial, Shrishti, Siddhant, Aanya

On the Experience of Time - Rishabh Jain

Time is an integral part of the human experience and, thus, it is not surprising to note our fascination with it. Physicists, philosophers and thinkers have pondered the origins and implications of time for millenia, and countless works about time have been created, from the H. G. Wells classic, “The Time Machine” to the more recent Christopher Nolan film, “Interstellar”.

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As for physics, there is the promise of time travel with tachyons – hypothetical faster than light particles – and relativistic wormholes. Tachyons may never be detected and passing through a wormhole may be impossible, but even so, real particles moving backwards in time isn’t an extraordinary concept: Richard Feynman visualized them through

his Feynman Diagrams to demystify interactions between elementary particles.

But, for all these exotic particles and fantastical notions, physicists still have not come close to producing a full theory of time.

Nonetheless, physicists have long incorporated and tackled unique concepts of time in their attempts to explain the universe. Early in Isaac Newton’s seminal Principia (1687), which laid the foundations of modern physics, he defined “absolute, true and mathematical time” that “from its own nature flows equably without regard to anything external”. Time was a fixed entity. However, this notion was re-examined and abandoned with Einstein’s revolutionary theory of relativity. We now know that time varies with a moving

General relativity has also shifted the spotlight towards time. Time is now its own dimension and the distance light travels in time t (this distance is ct, as the speed of light is c) yields a 4-dimensional spacetime manifold that precisely describes gravity and the universe. This has now elevated time to the importance of space.

Other features of physics aid us in our quest to perceive time.

Entropy, the randomness inherent to a system that can never decrease, has led to a forward arrow of time: unlike the reversible processes of classical mechanics, time always moves forward. Even so, the human mind seems to perceive time differently: miserable experiences drag on while fun experiences are fleeting! This discrepancy is because of the disparity between how the human conscience subjectively deals with time and how we objectively measure time through the use of atomic clocks.

In Consciousness Explained (1991), cognitive scientist and

philosopher Daniel Dennet suggests that our consciousness operates under “multiple drafts”.

Instead of a central place in the brain that interprets sensory information, consciousness emerges from various functions occurring at different times in different parts of the brain. To bring together these neural events distributed in space and time, Dennett maintains we create a coherent internal narrative that is the “I” of a person, with personality, memory and so on. The scattered behaviour behind consciousness guarantees that “the temporal order of subjective events is a product of the brain’s interpretative processes, not a direct reflection of events making up those processes”.

Our bodies, too, experience time.

Behind our moment-to-moment responses to external events is the circadian rhythm – the approximately 24-hour cycle of physiological activity built into much of life on Earth, from people and animals to plants. In humans, it defines the periods of lowest body temperature, greatest alertness, sharpest rise in blood pressure and deepest sleep. The circadian rhythm is of great benefit to us: enabling us to

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observer and in a gravitational field; if time is a flow, its flow rate can be altered.

utilise light to its best extent. Our perception of time has, thus, been linked to us since time immemorial.

Time affects us most through aging. Would there be any way to slow down this process, now that we know that time is a variable?

From measurements aboard aircraft and space satellites in the global positioning system, relativity correctly predicts how time dilates with speed and gravitational field to make a traveller age more slowly. The famous twin paradox is not really a paradox and is actually true. But at the comparatively low speeds and gravitational variation we can reach with today’s technology, the changes are tiny compared to human lifetimes. NASA astronaut Scott Kelly spent over 11 months aboard the International Space Station starting in March 2015, but returned to Earth barely a few milliseconds younger than his identical twin brother astronaut Mark, who remained on our planet.

This multidisciplinary look into time, specifically our mental and physical perceptions of time, may seem strange for a physics-oriented magazine, but it is harder to imagine a more interdisciplinary field than time itself. Time affects our senses, our relations, our studies and, as made evident through this article, our perceptions. Feynman himself recognized this when he spoke at Cornell of “remorse and regret and hope” that “distinguish perfectly obviously the past and the future”. So, as we march on in our quest to understand time, we must utilise every measure of human understanding available to us and examine the true impact time has, not only on the physical universe, but also the human universe.

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Rohan Doddavaram

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Time Travel, Special Relativity and the Bell Inequality

Time travel is possible – and I can prove it. Now, now, I know what this sounds like. But it’s true – and easily verifiable as well. You’ll have to set all things but a wristwatch aside, and observe it for a minute or so.

Let’s say you start at 12:01 p.m.

A minute later, your watch should read 12:02 – if it doesn’t, I feel like there may be more serious issues at play.

Although it does sound like a scam, you have in fact travelled in time: you’ve travelled forward 1 minute at the rate of 1 second per second. This seems inane and in fact rather irritating given the hype of the previous paragraph, but unglamorous as it sounds, this is as close any of us is ever going to get to time travel: for a very simple reason – causality.

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A bit more than a hundred years ago, a certain German man with a certain famous moustache (no, not that one) came up with a radical new idea. So radical, in fact, that most people at the time dismissed it as mere conjecture.

This man was Albert Einstein, and the idea was his theory of special relativity.

Special relativity does not appear too

complex at first: it simply states that the faster someone travels in space, the slower they travel in time.

Sounds simple enough, right? So what’s all the talk about it being some nefariously complex concept? Well, the devil, as they say, is in the details – or in this case the absurdly complex mathematics, which arguably is as close to Satan as I personally want to get.

This seems like a good time (pun very much intended) to introduce the concept of frames of reference – in simple terms, a frame of reference is the perspective from which someone measures the rate of passage of time. A key takeaway before we explain the postulates of special relativity is this: an observer who has no relative velocity or delta-V to a clock will always measure the rate of passage of time by that clock as 1 second per second.

When we introduce that delta-V though, things start to get a tad more complex. Let’s introduce two spaceships to explain – presumably the budget available to the Indian space agency has increased drastically allowing

Spaceship 1 enters orbit, and thus circles the planet at a fixed speed, V1.

Spaceship 2 continues to circle the planet at a suborbital altitude, at a speed of V2 such that V2 > V1, allowing it to remain out of orbit. Once both spaceships are established in their paths, both pilots go to examine the clocks on their respective ships closely and broadcast a video feed of their clock faces to the outside of the spaceship, so that the third individual, a stationary observer on the planet’s surface, can see both clocks in real time. Don’t worry, they made sure to engage the autopilot before leaving their seats: no chance of them getting arrested by the alien traffic cops.

Our stationary observer – let’s call him Chuck – on the planet’s surface, has a clock next to him as well. Now since Chuck and

the clock are both stationary with respect to the planet, there is no net velocity or delta-V between the two of them. So of course, Chuck perceives his own clock as ticking at a positively brisk one second per second.

Similarly, both of our intrepid spacemen perceive their own clocks as travelling at one second per second, since although both of them are moving relative to the Earth, their absolute velocities are identical, leading to a delta-V of 0. So both perceive their own clocks at 1 second per second.

But here’s where it gets interesting (I promise this part is interesting, please don’t skip to the next article). Where we do have a delta-V – for example, between Chuck and either of the spaceships, Chuck’s frame of reference leads to the clock appearing to tick slower than 1 second per second. In other words, in the frame of reference of their respective humans, all clocks go at one second per second. But when frames of reference are introduced, the greater the speed of a clock through space, the slower its relative speed through time.

Hence – relativity.

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the construction of a new ship.

Ships 1 and 2 are crewed by a single pilot each, and have on board one identical table clock each. They both take off from a hypothetical small planet, sufficiently sized so that the spaceships can cover several circuits of it a minute.

Now if you envision it as a sort of graph where the rate of passage through time gets slower as speed increases, it follows that as you increase the speed beyond a certain point, time might start to flow backwards. So does that mean time travel is possible by going fast enough? This, unfortunately, is where the time travel fantasy ends. You see, travelling backwards in time leads to all sorts of nasty issues with causality: where one event causes another.

Our world tends to follow a nice, neat order to things: you hit a bell and it makes a sound, you drop a glass and it shatters, and you order Taco Bell and get indigestion. These things are dependent on causality – imagine a shattered glass reassembling itself and floating upwards! Aside from the sheer absurdness of such an action, this would also violate the rules of entropy: you couldn’t have reversed causality since it would lead to things like broken vases magically reassembling themselves, and supernova-d stars returning to red giant form, reducing entropy or the state of disorder. In case you were wondering, this is why faster-than-light travel is not something that can conceivably be a reality: because it violates causality and thus entropy, therefore violating the second law of thermodynamics and making us rethink everything we've ever thought of.

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Except it isn’t that simple. You see, what I explained above used to be the universally held notion until 2017, when something interesting happened. A group of researchers headed by Gonzalo Carvacho found a way to violate bilocal causality. Now the concept of local causality is one that I probably should’ve introduced earlier on, but I am fairly lax in my organisational skills so I will do it now. Remember not to put me in charge of any nuclear programmes.

Local causality is simple: it states that for an object to influence or otherwise affect another object, something – either a particle or a wave – must travel from the first object to the second. Seems simple enough, right? This is the foundation of the famous Bell inequality, which gives a series of conditions that must be fulfilled for some data to have been obtained from a joint data distribution. However, these aren’t always true: in fact, they are frequently violated in quantum mechanics, usually because of the violation of statistical independence or ‘free will’: for example with two entangled particles. But when the sources of data used are independent, the system possesses bilocal causality – since there are two independent probability pools that we’re drawing from.

These researchers have devised a way to violate this bilocal causality – but only bilocal causality, and not local causality (since that would lead to several problems with the coherence of the universe).

So while I hate to be the bearer of bad news, none of you reading this right now are ever going to be the real-life Marty McFly. But perhaps that’s for the best – I’ve always thought that film was tremendously overrated anyway.

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So what’s the big deal? Well, these violations of causality aren’t time travel, and it’s impossible that we’ll ever have Back to the Future-style linear time travel ever become reality. But that doesn’t mean that causality can’t prove important for other applications – quantum computing, for example, could benefit greatly from the secure communication channels violations of bilocal causality could create.

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He didn’t stop himself at Physics however. Galileo is often called the father of modern science as he made major contributions to the field of Mathematics (created a new type of balance, which finds the mass of substances in water), Astronomy (credited to have invented the telescope), and Philosophy (famous for having defied the Church by saying the Earth revolved around the Sun, and not the Sun around the Earth). He died in Arcetri on January 8th, 1642 at the age of seventy-seven.

Returning to Physics however, a bored seventeen-year-old Galileo Galilei felt his eyes wander around the room during a long, long lecture (after all, one could not just whip out a mobile phone then!). His eyes continued to wander before resting on something rather trivial... a swinging lamp.

Suddenly, he noticed something: this lamp was moving with no change in its speed, and it took the same time for each oscillation.

This intrigued Galileo. How is it that it moves at a uniform speed?

Why did it do this? Was there a reason to suggest why its speed did not change? Was time a controlling factor of why this object moves so? Thus began Galileo’s interest in time.

So now that you have a brief idea about who this man was, let's delve into one of his greatest discoveries– the discovery of the flow of time. Galileo realized that the lamp had a harmonic motion with a constant period, which means the time it took to repeatedly swing back and forth around a central equilibrium point was the same. However, he was not entirely sure and therefore decided to test if other objects also had the same harmonic and periodic flow. He tested his pulse, a pendulum and then decided to check how an object rolled down an inclined plane using a water clock to keep time.

To his delight, he found that the speed increased linearly the longer the object rolled down the ramp.

He realized that the acceleration of all objects was very similar, with minor differences due to forces such as friction.

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Galileo Galilei was a phenomenal scientist and a rebel. The eldest son of musician and scholar, Vincenzo Galilei, he was born in Pisa in 1564.

In the year 1581, he joined the University of Pisa where he developed a love for mathematics, but he never earned a degree (yes, that’s right, Galileo Galilei was a college dropout!). However, he developed a fascination for Physics early on, making his first discovery when he was just eighteen! More on that later.

Thus, he formed a universal law: that force causes acceleration. He also went on to make new discoveries using this, such as acceleration due to gravity, and how it applies not just to the Earth (just thought I would let you know – the acceleration due to gravity on Earth is around 9.8 m/s2) and to all the known planets in the Solar System. He also inspired many scientists to come, such as Sir Isaac Newton (remember that man and the apple?) who, using Galileo Galilei’s work, devised the notion of linear time. Later on, Albert Einstein would devise the concept of spacetime using Galileo’s work on it. One of Isaac Newton’s famous quotes is: “If I have seen further, it is by standing on the shoulders of giants”. No doubt, Galileo would have been one of the giants he was referring to. Now onto some fun facts about him!

FUN FACT Galileo was also an accomplished astronomer, and discovered that the Earth revolves around the Sun. The Church was very angered by his work and accused him of heresy. They put him on trial and Galileo was placed under house arrest. After being forced by the Church to recant his findings and admit that the Earth was the stationary center of the universe, Galileo allegedly muttered, "Eppur si muove!" ("Yet it moves!") during his trial (I told you he was a rebel).

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Over 350 years passed before the Catholic Church finally forgave Galileo in 1992 (thus showing that sometimes one has to be a rebel for the sake of truth!). Galileo was personally nonrepentant, however, and is said to have written “the purpose of Science is to determine how the heavens go; while the purpose of religion is to determine how to go to Heaven”.

FUN FACT Galileo was said to have dropped two cannon balls of different masses from the leaning tower of Pisa to demonstrate that their speed of descent was independent of their mass. Many people believe this story to be untrue since its only source was Galileo’s secretary. However, what you believe is up to you!

KEY TERMS Harmonic Motion: Repetitive movement back and forth through a central point (equilibrium), where the maximum displacement on each side is equal.

Oscillation: Movement back and forth at a consistent pattern.

Central Equilibrium Point: A center point during an oscillation where the net force acting upon an object is 0.

Inclined plane: A flat surface tilted at an angle.

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Spacetime: The concept by which the three dimensions of space combine with the fourth dimension, time. This is called a spacetime continuum.

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Relative to the layman, often appeased by the erudite.

Extravagant to those who preach it’s very existence.

Like honestly, the Egyptians have perplexed the very minds Associated with the foundations of the assumed universe.

Tick-Tock– the sound of their nightmares. Fundamentally fallaciousness Instigate their agitation further.

Appallingly amusing.

Vicious, exclaims the layman. Beautiful, claims the edifice.

Extravagant? It scorches the minds, as one fails to understand.

On the other hand, well, one cannot claim. As Relative as it may be, it is ironically universal.

Now entities differ. She herself was one.

Overwhelming. Agitating.

Trouble taunts her, for the layman still fails to understand.

Questions pile on.

For, Is tomorrow really a mystery?

And can the past really be history?

Devarya Singhania

1905, popularly known as Einstein’s miracle year.

It was then that he published a plethora of research papers on different topics in physics, redefining each in its own way.

One such paper was that of special relativity. In the paper, he postulated that both the laws of nature and the speed of light were absolute and the same for all inertial onlookers.

The first part is kind of intuitive for many people, making the entire theory seem like a veiled platitude. The second part is where the problems arise, and that’s where the consequence of time dilation comes into the picture.

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Time was forever thought to be an absolute, just like mass or length. People took it for granted that the passage of time would be the same for everyone, no matter where they were or what they were doing. Whether one was in the middle of a boring history lecture or enjoying a fun day with their best friends, time flowed the same. Newton, when he conceived the theory of linear time, established this concept of time as axiomatic. However, Einstein came along and - as he did in countless other realms of physics - disproved this theory.

Let me take you on a thought experiment. You are in a spaceship, floating with no gravitational acceleration.

Another friend of yours, let’s call him Al, is floating on another spaceship nearby.

You have two parallel mirrors attached to your floor and ceiling, with a photon laser in between the two pointed at the ceiling. The two of you also have clocks which are perfectly synced to one another. Now imagine that Al is travelling at a near-light speed, while you remain stationary. Since all motion is relative, according to him, you’re the one who’s moving, while he is stationary.

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Next, imagine that you shoot the photon laser at the pair of mirrors and it takes the total round trip back to where it started. From your point of view, everything’s normal - Al is speeding past you, while the photon travels at exactly c (the speed of light) to return to the laser. All is well. When you look at this from Al’s point of view, intuition seems to break down and chaos takes over. According to him, you’re the one who’s speeding

past him at a high velocity, and due to this lateral motion, the photon has to take a diagonal path to return to its original position.

Remember, the speed of light is absolute for everyone, including you and Al. We’ve learnt in school that with a constant speed and a larger distance, the object takes a larger time to traverse the distance. In effect, the photon takes a longer time to return from Al’s point of view when compared to yours. Thus, time flows slower in Al’s moving clock as compared to your inertial counterpart.

When people first hear of time dilation as a concept, their minds are totally boggled and their first thoughts are always ‘No, that can’t be possible at all!’ If you’re not having such thoughts, that’s when something’s wrong. Quite frequently, people tend to wheedle out seeming paradoxes from within the folds of relativity in an attempt to disregard such a blasphemous notion. Here's one of the famous ones.

Let’s go back to the thought experiment from earlier. Al is speeding past your spaceship at a high speed. Conversely, Al thinks you’re the one who’s speeding past him.

According to special relativity, they say, from your point of view, Al is the one whose clock is slowing down, since he is the one at a higher speed. From his point of view, you’re the one whose clock is slowing down, since you’re at a higher speed than him. So who is correct? And that’s where you can truly marvel at the beauty of relativity. The answer? Both of you are correct – in your own way.

-Devansh Mishra

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When Einstein conceptualised his theory of general relativity, even he was perplexed looking at all the consequences that arise from such a deceivingly simple theory. Yet, all these consequences have withstood the battle against time and rigorous experiment to be proven correct. He left us with one phrase – ‘Time is an illusion’, and we haven’t been able to figure out anything more ever since.

The Particle That Broke Time Symmetry - Dev Sahu

A brief introduction to symmetry:

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When we hear the word ‘symmetry’, our minds are taken back to our early geometry classes, where we marveled at shapes that could be divided into perfect halves or folded over themselves over and over. This concept of symmetry, though easily understandable, is simplistic.

A more rigorous definition of symmetry, in the mathematical and geometrical sense, is ‘invariance under various transformations, such as rotation, reflection, translation etc.’

Physicists have extended this concept to the study of the nature of reality, in order to reveal

fundamental laws and obtain a deeper understanding of the universe around us.

Symmetry in the universe manifests in many forms, such as invariance under translation in space or time, rotation about a fixed angle, reflection in space, etc. Many fundamental principles of physics are derived from these symmetries.

For example, applying quantum mechanical principles to space translation invariance gives conservation of momentum, while doing the same to time translation invariance gives conservation of energy.

1. Charge conjugation (C): This meant that the laws of physics would remain the same if every particle of matter in the universe were to be replaced with its antimatter counterpart (opposite charge) 2. Parity (P): This meant that physical laws remained invariant if every particle, interaction and decay were replaced with its mirrorimage counterpart.

3. Time symmetry (T): This implied that physical laws were invariant forwards or backwards in time.

Each of these symmetries were thought to be fundamental on their own until 1956, when an experiment performed by physicist Chein-Shiung Wu demonstrated that the weak interaction violated parity-symmetry, thereby providing an operational definition of left and right without referencing the human body.

Subsequent experiments demonstrated the violation of the other two symmetries as well.

The Experiment: Experiments performed through the 1960s revealed that interactions with the weak force violated charge, parity, and CP symmetry (charged and parity applied together). Hence, it was expected that these systems would show asymmetries in time reversal as well. A straightforward method is measuring the differences in transformation rate of one quantum state to another with the time reversed. Any significant difference in the rates would indicate T-symmetry violation.

One such observation was made at the BaBar detector at the PEP-II facility at SLAC in Southern California. This detector made use of electron-positron collisions to generate Y(4S) mesons. These mesons proceeded to instantly decay into B and anti-B meson pairs. Since these pairs originate from the same Y meson, they were ‘entangled’ in a way. The state of the first meson to decay dictated the state of the other meson, which itself underwent decay after some time. The violation of time symmetry was studied by analysing these decay processes.

The interaction chosen was the decay of the first B-meson from a ‘flavour’ state to a ‘linear combination’ state and the time

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Three fundamental symmetries have been (or rather, were thought to have been) identified in physics:

reversed process from the linear combination state to the flavour state. By comparing the time taken for these transformations, physicists could determine if there was any difference, as predicted by T-symmetry violation. They succeeded in doing so, with their results achieving a significance of 14σ, well above the 5σ threshold required for a hypothesis to be considered probable enough to be accepted.

CPT Symmetry: Many experiments conducted over the past have demonstrated violations of all the three symmetries individually, as well as in pairs, such as CP, PT or CT. However, it was also observed that in all of these experiments, interactions remained invariant when they underwent C, P and T transformations simultaneously. This new symmetry is called CPT symmetry and has held true for all interactions observed and experiments conducted so far, indicating that it must be a fundamental symmetry. In fact, a theorem first proved by Julian Schwinger in 1951, postulates that this symmetry must not be violated. CPT is also intricately connected with Lorentz invariance, which states that all physical laws must be the same for all observers in all inertial (non-accelerating) frames, a fundamental principle of relativity.

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Given the record of extensive experimentation, it remains unlikely that CPT symmetry will be proven false. However, only time will tell whether or not a new kind of interaction is observed which violates this symmetry, throwing away most of modern physics along with it.

-Arushi Kolluru

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THE BOOTSTRAP PARADOX

The Bootstrap Paradox is a theoretical paradox of time travel. This paradox states that when an object or piece of information sent back in time becomes trapped within an infinite cause-effect loop, the item no longer has a discernible point of origin. Therefore, it is said to be “uncaused” or “selfcreated”.

It is also known as an Ontological Paradox, in reference to ontology, a branch of metaphysics dealing with the study of being and existence.

All these new words together might not make a whole lot of sense yet, but perhaps an example would help clear things up.

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Let's assume a time-traveller goes back in time to teach Isaac Newton The Laws of Motion before he discovers them.

Newton publishes the information as part of his own findings. The time-traveller then learns about the laws in the future through Newton's works.

Now, where did the information come from in the first place? It couldn't have come from Newton, as he learnt it from the

time-traveller.

It couldn't have come from the timetraveller, as he read it from Newton's books. Thus a paradox is formed. When an object or piece of information no longer has a source, it is said to be “uncaused” or “selfcreated”.

The Bootstrap Paradox has been referenced in several literary works since the 1940s.

The term was popularized by science fiction writer Robert A. Heinlein. His book 'By His Bootstraps', revolves around time travel and time paradoxes, including the Bootstrap Paradox.

The famous British TV show Doctor Who also features several time travel-related paradoxes.

The films ‘Somewhere in Time’ (1980) and the Terminator movies both feature this ontological paradox.

The Bootstrap Paradox, unfortunately, breaches several fundamental laws of Physics.

This paradox is yet another fascinating problem that has emerged with further exploration of the theoretical possibilities and limitations of time travel. While we do not have any concrete answers or solutions to this paradox, it is an incredibly interesting perspective to consider when researching the implications of time travel.

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Thanks to this paradox, we cannot say that a past event leads to a future one since the opposite could also be possible. This is a violation of the Law of Causality, as the effect cannot come before the cause. Moreover, with this paradox, the past, present and future will all be ever-changing.

This breaks down the concept of linear time as we know it. If the Bootstrap Paradox is real, the past will not be set in stone and the future will be able to mould the past. An origin, as a concept in time, will be meaningless.

Weird Theories Of Time -Krisha Kothari

When referring to time, we often use spatial metaphors like ‘flowing’, ‘running’ or ‘passing’.

However, time is not space. It is intricate, intangible and too many of us, incomprehensible at its most fundamental level. For centuries, scientists and philosophers have pondered upon its very nature, devising theories to explain its complexities. These often eccentric theories make an appearance in popular and widely accepted theories like the Mtheory.

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M-theory is a theory that combines the compatible versions of superstring theory.

While it seems to be able to unify General Relativity and Quantum Mechanics, it’s original formulation consists of 10 dimensions of space and 1 time dimension. This idea may seem counterintuitive since we can only see 3 spatial dimensions, but it can be explained by allowing the extra 7 spatial dimensions to be curled up into themselves in an extremely tiny space. This way, we only perceive 3 spatial dimensions. A well rounded correlation to this idea is the ant on a wire analogy that goes something like this: if a distant observer was to view an ant moving helically on a wire, it would seem as though it is moving along a straight line in one dimension. This is because the observer perceives the wire to be a one-dimensional line having only length and the ant

Another lesser known version of the M-theory is its two-time module. This suggests that there could, alongside 11 dimensions of space, exist two time dimensions. This would result in a combined total of 13 dimensions as opposed to the three spatial ones and one time dimension we are familiar with.

Imaginary time is a mathematical representation of time having undergone a Wick rotation, which is a rotation by 90º on an Argand diagram or complex coordinate system. The time is essentially having its coordinates multiplied by the square root of -1 or the imaginary number ‘i’. Similar to the algebraic concept in which when a real number is multiplied by an imaginary one, the real number becomes imaginary, the coordinates of real time (T) when multiplied by i, become imaginary (Ti).

This imaginary time axis mathematically is perpendicular to the real time axis, thus creating a two-dimensional plane consisting of an x and y axis.

The two-dimensional time plane consists of two axes, one depicting real time and the other, imaginary time. Real time is what we already know as linear time consisting of a past, present and future. It is extremely useful in describing motion as motion is usually described as a function of time i.e., 10 km/hr, 5m/s etc. It is not absolute as was believed prior to the publication and acceptance of Einstein’s theory of relativity, but varies depending on the relative speed and position of an observer.

While widely considered a theoretical concept, one of the many implications of imaginary time is that it could help smooth out gravitational singularities, areas where all known laws of physics break down. As a consequence of the unravelling of singularities, imaginary time could go on to prove Stephen Hawking’s no boundary condition that states that the universe has no boundary, as a boundary in spacetime is simply a singularity.

The unproven relationship between imaginary time and its

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can therefore move only forward or backward. The ant however, being smaller, is theoretically able to scout all three dimensions of the wire i.e., its length, width, and height.

manifestations in real time has raised criticisms to the likes of physicists like Roger Penrose. If a tangible relationship is found, however, it could enable us to gain insight into the question of ‘what’s before the Big Bang?’ since time as we know it - i.e., real time - did not exist. Imaginary time also opens up the possibility of time travel as it forms a plane that when inwoven can loop back over itself.

McTaggart’s argument John McTaggart was an English metaphysician, recognised most widely for his philosophical work ‘The Unreality of Time’ and the argument that went on to be dubbed ‘McTaggart’s paradox’. This argument is highlighted below.

The positioning of events in time can be explained in terms of the A-series and the Bseries.

The A-series takes on a temporal order of events, flowing from future to present and ultimately, past. For example, the publication of Einstein's paper on special relativity was once a future event, became the present in 1905, and is now in the past. Thus, the A-series describes events changing in position.

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The B-series describes relations between events in terms of earlier, later or simultaneous. These events are understood to be at a fixed position in time but are relative to each other.

For example, the publication of Einstein's paper in 1905 is always after the publication on Newton’s principia mathematica in 1687 and before Stephen Hawking’s singularity theorems in the 1960s. While these events are relative to each other, they are fixed in time, which is described by dates.

However, McTaggart claims in‘The Unreality of Time’ that both theories are false. His argument against the A-series is that “nothing that exists can be temporal”. That means that for an event to change in tense time, it cannot exist in all three tenses since every event must have every position in the A-series, making them “jointly incompatible” and thus creating a paradox. This argument, however, is a false dilemma since tenses are an issue of language. Another argument against the passage of time is the rate at which it passes. If we perceive the rate between two events to be one second per second, we must also agree that this ratio is arbitrary. A clock therefore does not measure time, but durations between events.

So, our ideas of time have progressed with - well, time - and these have only served to enhance our understanding of this dimension (or dimensions) that we understand so little about. The question now arises from whether we can have time that is applicable in all equations and all scenarios - a super time, in a sense. And who knows? Maybe the time is finally ripe.

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The B-series on the other hand, does not account for change. It fails to explain the transitional nature of time. Therefore, while A-series explains the transitional nature of time, the B-series talks about its fixedness.

Time Travel In Science Fiction -Mayas Kumble and Varun Satish The concept of time travel is widely seen throughout science fiction. From movies to TV shows, this fantastical facet of theoretical physics has spawned the creation of many plotlines, captivating audiences for generations. While some writers reference time travel in realistic ways in fictional works, others include explanations that are quite literally out of this world.

However, these fictional depictions of time travel can be generalised to an extent, and that is what we aim to do through this article.

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The most realistic time travel movie is perhaps Interstellar (2014). Vetted by physicist Kip Thorne, the movie involves actual physical concepts such as time dilation and supermassive black holes to bring us probably the closest thing we’ll get to time travel in the foreseeable future.

Other, less realistic movies use a

similar concept. For instance, in movies like Ender’s Game (2010) and Planet of the Apes (2001), the time travel is somewhat realistic, with the characters experiencing a slower passage of time with interstellar travel, defined by Einstein to be time dilation. The regular world is unaffected by their adventures, and progresses in normal time, which would imply that this sort of time travel cannot change the past or lead to timealtering decisions.

However, movies and shows like Avengers: Endgame (2019), Star Trek (2001), X-Men: Days of Future Past (2014), and Agents of S.H.I.E.L.D. (2013-20) have a slightly weirder concept of time travel. In all these movies, visiting the past becomes extremely twisted and often confusing, and any plot holes are generally brushed off with the excuse that ‘time travel is strange’. Many of these movies

Some movies forego the explanation entirely and just use time travel to move the plot forward.

Movies like the Terminator series (1984-2019), Men in Black 3 (2012), or the Bill and Ted trilogy (1989-2020) merely acknowledge the existence of time travel to explain events taking place.

Other movies and TV shows revolve around the fact that time travel is possible by using a particular vehicle. The most popular of these are the Back to the Future trilogy (1985-90) and the TV show Doctor Who (1964-89 and 2005-present). In both cases, time travel is possible using a certain vehicle and in these cases in particular, there’s always something that goes wrong when time travel is attempted.

Even though most time travel movies generally follow the aforementioned examples, there are still some outstanding movies and shows that manage to exceed expectations and come up with extremely confusing time travel rationales. Tenet (2020) is a prime example, where time is “inverted” through the ability to reverse entropy, allowing the characters to move backwards in time. They see the world normally, while the world around them moves in reverse. It is extremely confusing, so we suggest watching the movies in order to better grasp the concept. The German show Dark (2017) explores time travel that is possible only between certain points in time. These points are each 33 years apart, and the

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introduce the concept of a ‘branch reality’ when discussing time travel. Essentially, when characters meddle with past events, they create a separate timeline or a branch reality, an alternate version of the world we are in where events might be playing out differently. This is clearly the case with all these movies, where the characters wish to fix past mistakes, and hence end up creating alternate versions of themselves. Taking the most popular example out of the lot, when the Avengers went on their “Time Heist” and Nebula was compromised, Thanos led his army into the future to battle it out with them in the year 2023.

But by doing so, he created an issue of continuity since now, the Guardians of the Galaxy did not have any strong opposition after Peter Quill stole the Orb. Hence, this becomes a branch reality.

show explores the explanation representation of time travel.

behind

this

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All in all, it must be kept in mind that sci-fi movies are generally entertainment-centric and less likely to try to maintain any sort of continuity or scientific accuracy. However, this does not stop physics enthusiasts like us from dissecting these movies and attempting to understand their explanations of time travel.

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Compiled by Rishabh Menon

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PHOTON JULY 2021

04 Editors-in-Chief Shrishti Kulkarni / Siddhant Doshi / Aanya Pratapneni Correspondents Rishabh Jain / Rohan Doddavaram / Agastya NH / Devansh Mishra / Devarya Singhania / Dev Sahu / Arushi Kolluru / Krisha Kothari / Mayas Kumble / Varun Satish / Rishabh Menon Design Head Akshara Polavarapu Visit our website at: thephotonmagazine.com Follow us on Instagram: @thephotonmag Email us at: thephotonmag@gmail.com