Flow of time is just an illusion | Brian Greene

“Once upon a time” is ………

Many good stories begin with this magical phrase, but have you ever thought that “what is the story of time?” Does time exist? We always say time can be spent, time is money, we waste time, we are trying to save time, but what do we really know about the time? Is time an illusion? According to physicist Brian Greene, “all the time exist at once in spacetime”


time is an illusion



Well, time seems like an unchangeable flow like a river from one moment to the next and we always see the flow of time in one direction only towards the future. But this is not true. From the discoveries of the last century, we find that what we think about time is nothing more than an illusion. Unlike our everyday experiences, time does not flow to anyone at all.

Our past may not be gone and our future may already exist. We know that the speed of time can be fast or slow and all the events that seem to be appearing in only one direction are not true. They can also appear in the past. But how can this be? How can we be so wrong despite being so familiar with time? If time is not what we think it is, then what is time really? What is the beginning of time? Where does it come from?

Columbia University professor and physicist David Albert says what time is. Everyone knows it well, but until you ask them to define time. Professor Ellen Guth of the Massachusetts Institute of Technology says what is the time? It’s really a 64000$  question for the physical.

So now how can we begin to uncover the mystery of this deep and elusive time? One way is to measure time. We have been using different sizes and different types of watches to measure time accurately for thousands of years. Our first watch is our Earth, that is, the rotation of the Earth.

We have always used the repetition of the Earth’s daily rotation to assess time itself. Professor Peter Gallison of Howard University says that we have always been looking for things to measure the time that repeats itself repeatedly. This cycle of repetition itself becomes a clock and this clock is time for us.

After measuring the speed of the Earth with the solarium, we divided the days into hours and then divided the minutes into seconds using the pendulum. Now we are using quantum crystal vibrations to measure time more accurately.

If you really want to know what time it is then you must go to The Colorado-based National Institute of Standards and Technology. Time is measured with great accuracy here. It is the most accurate time measurement center In the whole world.

Most accurate clock

Cesium is a rare metal atom. Atoms have a natural property, that is, their frequency that’s why they always vibrate. This atom vibrator is giving a repeating motion to itself, so it is a natural clock.


cesium Atomic most accurate clock
cesium atomic clock


This frequency of cesium atoms tells us the most accurate time in the world today. When we bombard the cesium atom it becomes easier for us to count this frequency When we count this frequency, the cesium atom vibrates 9,192,631,770 times in one second.

It is a surprising fact that our clock cannot measure time so accurately, so our watch loses a few seconds in a few months. We are also talking about clocks that have been measuring time or losing time for 10 million years. Nevertheless, we have been improving our instruments for accurate measurement of continuous-time for hundreds of years and will continue to do so.

But no matter how accurate or how wrong our watches are, the clocks will always be running, but they have not been able to tell us what time is and what we are measuring. We do not know what time is but the experience of passing time is an important part of our life.

We always think about time, remember the past, plan for the future, and live our lives in constant ticking time. You must have been to a railway station at some time or the other, what do you do by going to the railway station first?… The answer is you find out whether the train is running on time or not.

Do you know? that this train journey has played the most important role in the early searches of time. In the early days of the train journey, a unique problem arose due to time, after that each city had to set its own specific time.


We all know that in the afternoon the sun is just above our head, but in other cities, the time is different because the sun is not above their head at this time, although this does not mean much for most people. When we travel by train, the train can take the time of the city from where it started its journey.

Suppose you are going to Geneva from Paris, then you are completely in the Paris timezone because you started the journey from Paris. If you travel on the opposite then you are in the timezone of Geneva. If the time between the two cities is not differentiated, then you will get confused.

If there is a difference of time in any two cities, if a train starts crossing more and more rail lines, then the people located on that interchange started getting confused due to the separation of time of both the cities.

The need to coordinate the long-distance clocks emerged as a major problem especially when two cities are connected by the same train track. To overcome this problem, the need for synchronized watches was felt. This is where the story of modern times started. This is where the story of modern time’s started.


Einstein’s Revolutionary Idea That Shook the world

Albert Einstein, a young physicist, was working as a clerk in the patent office in Bern, Switzerland. This was the best time to uncover the mystery of time as well as other mysteries related to science.

At the same time, Albert Einstein came to know from a patent that new and exciting ways are being used to synchronize clocks for the exchange of telegraph signals, and clocks will be synchronized by radio waves.

Einstein found the idea very important and exciting and then realized that the attempt to synchronize watches was nothing more than a creative invention, but these mechanical devices were providing him with unexpected inspiration.

Now Einstein was soon going to shake the whole world with his revolutionary theory. He knew that he was going to completely change the current understanding of time for the whole world.

Most people see time in a very simplistic way. Time remains the same for all, Isaac Newton, the father of modern science, also believed in this. According to Newton, time always changes at the same rate for all, that is, time is the constant in the entire universe.

If we look around us, we find this principle of Newton perfectly correct, but Einstein said that this theory is not correct. Time flows at different rates in different places, that is, the time experience for me cannot be equal to the time experience for you.

This discovery of Einstein had demolished Newton’s notion of reality. Einstein did not stop this. He further said that time does not run at the same speed in the whole universe and time is experienced differently in individuals means everyone has their own personal time which runs at their own personal rates.

In fact, the universe does not have a ticking time, it is just your illusion. Other than this Einstein exposed the mysterious relationship between space and time and put many shocking facts in front of the world.

He said that if you are moving in space, then the speed of time will slow down for you but you cannot see this effect in everyday life because the effect of your speed on time will be so small that you cannot experience it. This effect is real and can also be measured but by atomic clocks.


Spacetime: General Relativity and Quantum Physics

Suppose I am moving in the direction of north from my car at a speed of 60.00 km / h. I am moving towards the north direction at a good speed. Now I have diverted my car to another road, this road goes towards the north-west direction. I am still going at the speed of 60.00 km/h but now I am not able to move towards the north at the speed with which I was going a while ago.

You can say that I have divided my speed in both directions, so have I also divided the time in both directions. The answer is… no!! I could not separate time from motion and my motion (with time) was not taking place in any direction but in space.

Because of this unpredictable relationship between time and space. Einstein realized that time and space cannot be thought of separately, so he called it Spacetime because time and space are linked together. When space and time cannot be separated from each other, how can we differentiate time between past, present, and future?

According to Einstein, Time is only our illusion. We experience time as a continuous flow. We can also see it as a series of moments. every location in space and each and every moment in time from the birth of our universe from the big bang some 14 billion years ago to the birth of stars from galaxies to the creation of Earth 4.5 billion years ago to the rise of dinosaurs to events happening on earth today like you’re reading this article.

But it is not just a series of time, it is a series of spacetime. To understand this, we present a simple concept to you. I am thinking something right now, some cat is jumping from my window right now, some train is moving away from me, a pigeon is flying at this very moment, A meteor is still falling on the moon and a distant star is exploding. All these events are happening in the same slice of spacetime but in different regions of our universe. Now we naturally start thinking that what will happen now, we can also portray it by lying on a slice of spacetime that it will happen or that will happen.


Spacetime slices

Common sense says that you and I can agree on that what is happening at this moment or just what exists at the slices of spacetime right now. But Einstein said that when you speed up, this common sense of time is not the picture of spacetime. This is one of the more complex concepts, to understand it well, consider spacetime as a loaf of bread.


spacetime slices


Einstein said that there are different ways to cut this loaf of bread into different pieces. Now there are different ways to cut spacetime into different slices because motion affects space and time. If someone is moving in this spacetime, he will cut this spacetime in a separate slice and the angle of that slice will also be different.

In simple words, the person who is moving in spacetime will be cutting slices of spacetime from different angles with his knife, his spacetime slice will not be parallel to the slice of my spacetime.

To understand this strange effect, imagine that an alien is located 10 million light-years away from us in another galaxy and here a boy is sitting in the Earth’s space station. Both are sitting in the same slice of spacetime and both clocks are also moving at the same rate, so we can say that both are sharing the same slices which can be cut into a straight slice of the loaf of bread.

If that alien starts moving away from Earth with one of its ships, then its speed will slow-down time. Now our astronaut boy and that alien’s clocks will start to differ and both will not be able to share the same slice of spacetime. Now that alien will cut spacetime slice in a completely different way, Now his spacetime slice is about to go past the astronaut boy.

That alien is moving away at a certain speed and the slice it cuts will be cut from a very small angle but that small angle will also make a huge difference in the slice of spacetime on this huge distance. Now, what would that alien get in his spacetime slice in this situation? We believe that the astronaut boy would not be in that slice because just 40 years ago our astronaut friend was a child.

We can imagine that the spacetime slice of the Alien must have recorded only 200 years old history of the earth, that slice would have included only 200 years old events. We believe that the astronaut boy would not be in that slice because just 40 years ago our astronaut friend was a child.

Now let us imagine that if that alien starts coming from his vehicle towards Earth, then even in this situation the alien will cut a completely different spacetime slice, this time its spacetime slice will be in our future. The sliced ​​slice of that alien will record the events of our earth that are going to happen in the future after 200 years of the earth. It is possible that after 200 years, the granddaughter of our great friend’s granddaughter will be teleporting from Paris to New York.


The past and future are intervals of time

We think about our past, make new plans for our future, and also learn from the events of the past. But physicists believe that our past, our present, and our future are all realistically present in this spacetime. If you believe in the laws of physics then the future and the past are as real as the present as a moment.

In simple words, our past, present, and future is not going to be known and is not going to come, everything is present only in slices of spacetime. Einstein said that there is no distinction between past, present, and future, this is only our illusion which is happening continuously.

But if every moment of time already exists, then how do we explain that very real feeling that time is a river which is constantly moving forward? If you believe me, there is really no flow. Time is like a frozen river. There is no flow of time in the law of physics, just from our subjective perspective, it seems that all things are constantly changing, so time is flowing.

This is just as an entire film already exists on celluloid. All the moments of the film already exist on that celluloid, just a projector sheds light on a frame, then on the next moment, and then on the next moment, thus the continuous moment is displayed.

But there is no evidence in our laws of physics that there is something like projector light, which is choosing from one moment to another. This is why our brain makes the impression that in fact we all experience time as a flow, it is really nothing more than an illusion.

But if time is like a frozen river with no current, is it possible to travel past or future? Time travel is theoretically possible but it is not as practical as we think, if time travel is done then it will not be anything according to our imagination.


Arrow of Time

We all see time as an arrow means once left this arrow is not coming back. This arrow always moves in one direction, that is the future direction. Now a general question must be coming to your mind that how do we see all the events in one direction only? Why can’t we see those events in reverse order?

We answer it simply that the laws of physics do not allow to do something like this to happen. But according to the physicist, all events happen in the reverse order same way as it happens in the future. In physical equations, time is not the same as an arrow, this equation of physics is going to seem contrary to your everyday experience.

Let us explain in a little detail. I currently have an egg in my hands. We all know, what will happen if I leave this egg high?… The egg will break. Now the egg is broken. But according to the law of physics, this whole event can be reversed, then the egg can be back in my hand in its perfect state.

The only thing I need to do is just reverse everything, to reverse the velocity of everything. Every piece of egg, every liquid drop of egg, every atom of whole liquid, every atom of the complete shell, even my table, air, every molecule and atom will have to reverse their velocity and then !! That egg will be back in my hands!

This may seem an astonishing fact to you but whether you believe it or not, it is a real physical theory. The laws of physics do not care whether the egg is broken or not broken. Here a question arises that the breaking of eggs is very easy and it is also possible to bring that broken egg back to its previous state, so why are we not able to bring the broken eggs back to normal in everyday life?


Arrow of Time
Credit- BBC Earth


The 19th-century Austrian physicist Ludwig Boltzmann gave the most satisfactory answer to this question. Their equation is (S = K log W) This is an equation known as the entropy equation.

We know that water flows downwards, not upwards because gravity acts like this, gravity is a force and the gravitational attraction behaves in such a way that it is located in the centre of the earth and the water draws downwards.

But we do not have a simple explanation of the fact that why snowflakes melt in a hot water vessel, and why snowflakes are not formed automatically in a cold water vessel? It is related to the distribution of heat and the solution to this problem was the biggest success of the 19th century.

The solution to this problem was found by the Austrian physicist Ludwig Boltzmann, who discovered that there are more ways of heat distribution in hot water with ice cubes than in cold water. Nature’s game runs in probability.

Nature often chooses the highest probable method and this relationship defines the Boltzmann constant. The disorder is more common than order, there are more ways to spoil a room than to clean it. It is easier to create disorganized conditions in the form of melted ice than to make systematic snowflakes.

Boltzmann’s entropy equation that incorporates the Boltzmann constant also explains Murphy’s law:

If anything can go wrong, it will. No evil force is responsible for anything wrong with you, the ways of doing the wrong thing are too many in the number of ways of doing the right thing.

To understand this, we do a simple experiment. I have sorted my 569 pages by marking them. Now I bounce it in the air. Now all my pages are randomly scattered. There is no order of their disintegration and the reason is simple, There are many ways of getting the wrong thing in the number of ways of getting the right thing.

If it is easier to spoil anything than to make it, then the meaning is clear. Perhaps the trend of the arrow of time actually works according to nature’s tendency. But a small problem also comes here because the laws of physics do not differentiate between the future and the past, so the entropy equation should move not only towards the future but also towards the past.

It seems very easy to say, but in which direction should the entropy move. If the entropy had been increasing in the past, my 569 pages would have been chaotic before then my hands would have to rearrange them.


Cosmic Expansion

The history of the universe is like a film. If we go back to this film, we will come to a place where space and time have finally come to a point. There is no existence of space and time before this single moment, on the basis that the last end of the following entropy sequence should start with the big bang.


illusion of time
A graphic representation of the Universe’s evolution since the Big Bang [N.R.Fuller, National Science Foundation]


This is the reason for the increase in entropy that has started since the big bang. Physicists believe that the entropy at the beginning of the universe was low. From our understanding, the big bang must have determined time and space in the universe as an arrow. Then the expansion of our universe started abnormally and it determined the time in one direction.

We only feel that we are moving from past to future. What we are seeing, like the birth of stars, the little events of our lives that are the result of increasing disorder in the universe defining future differences from the past. We are constantly moving in the direction of disorder to date from the event of 13.7 billion years ago, but if the disorder is always increasing from the beginning of time, then can there be an end to spacetime.

The universe has been expanding continuously since the Big bang inflation and the speed of this expansion is getting faster. This expansion is going to show a strange effect in the future, after 100 billion years, all the galaxies will disappear from our vision. A theory for the end of time and space tells us that in the end a supermassive black hole will dominate our universe and everything will disappear in it. After that block holes will evaporate too.

In a far distant future where everything decayed and everything just sort of smoothed out. There’s no change and without any change, we do not have a clear notion of the passage of time, then how can we think about what is the time and what was the time ?? It’s really confusing time itself one day lose its meaning.

About 350 years ago Isaac Newton said that there is no need to define time because we all know time well. Normal people believe that time controls this universe and the flow of time is unchangeable like the flow of rivers. But in reality, is nothing more than an illusion and the past, present and future may all exist on equal footing.

Our everyday experiences of time will always make a powerful influence and we will continue to imagine that time is universal. We have been believing that our past is gone and the future is yet to come. But because of our scientific discoveries, we can also look beyond these experiences and realize that we are in a far richer and far stranger reality.


Also read:

What time really is? an illusion | Time intervals

What are black holes? | Do they follow the laws of physics?

Strange Unsolved Mysteries No One Could Explain

Simultaneity: Does Time Exist? or It is just an illusion



brain greene
Brian Greene


The Fabric of the Cosmos (Brian Greene: Brain Greene) by Brian Greene.

Brian Greene is a Physicist, Columbia University at Columbia University.

In this article, the statements and ideas of the following scientists have also been included.



  • JANNA LEVIN (Barnard College/Columbia University)
  • DAVID ALBERT (Barnard College/Columbia University)
  • ALAN GUTH (Massachusetts Institute of Technology)
  • MAX TEGMARK (Massachusetts Institute of Technology)
  • PETER GALISON (Harvard University)
  • WILLIAM PHILLIPS (National Institute of Standards and Technology)
  • STEVE JEFFERTS (National Institute of Standards and Technology)
  • S. JAMES GATES, JR. (University of Maryland)
  • SEAN CARROLL (California Institute of Technology)
  • DAVID KAISER (Massachusetts Institute of Technology)
  • JOSEPH LYKKEN (Fermi National Accelerator Laboratory)

Rajat Red

Admin and Founder of "UNTOLD SCIENCE | Exploring The World Of Science & Nature". He is a science student pursuing B.Sc in Biology from India. He is a curious being and an explorer, who has an interest in many fields besides science. But, He loves to study and write about science.

This Post Has One Comment

  1. 1
    Joe Rosario

    Brian Greene's "Flow of Time… " is phantastic and lucid. I am very grateful! I'm not a scientist but I understood it reasonably well. Thoroughly enjoyable reading.
    But laws of physics however correct and accurate will never change one's perception of reality on Earth or change our concept of time as experienced here on Earth of course. The magic is that humans can decifre the magic of reality, explain it so well that common people like myself can understand.
    However, as we can never physically travel at the speed of light the physics can only be experienced as wonder at the complexity of creation as observed from here.
    I was very happy to read about the i.agined likely future of the universe in terms of huge black hole (could call it anti-matter)
    Phylosoohically,Taoism, etc. and also by observation all in observation experience is cyclically (oposits). Breath in and out.
    Why should universe be any different. Since lerning about black holes I created the phantasy that the universe must also breath in and breath out. That everything is born and dies and breaths in again….
    I imagined that black holes as they grow forever larger by absorption of celestial bodies will eventually attract each other until a"big bang event" starts a baby Universe again. At least poetic and satisfyes my phylosohical beliefs.
    But of course it seems that the Universe is expanding by ever increasing speed so I'll just have to waite for further discoveries from our scientists which hopefully will satisfy my philosophical beliefs.

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