Time travel

Reading Time: 5 minutes

Time travel is commonly defined by David Lewis’ definition: An object time travels if and only if the difference between its departure and arrival times as measured in the surrounding world does not equal the duration of the journey undergone by the object.

People ask is time travel a philosophical structure or hypothetical or mathematically shown? The answer is that it is the combination of them all!!

Can we travel in time?

Yes, we can! Even we are traveling in time at a steady rate of one second per second or one hour per hour. Most commonly we are taught that there are only three dimensions and there is no similarity in traveling between 2 spatial dimensions. But according to Einstein’s theory of relativity we live in a four-dimensional continuum i.e. space-time in which space and time are interchangeable.

Many of you may have heard about the novel “The Time Machine” by H.G. Wells published in 1895. One of the earliest works in this genre, where Well talked about the concept of time travel by using a device or machine to travel purposely backward or forward in time.

Time travel

In today’s date, Wikipedia lists over 400 titles in the category, ‘Movies about time travel’ In documentaries like “Back to future”, “Doctor Who”, and “Star Trek” characters climb into some wild vehicle to blast into the past or spin into the future.

Many of us are fascinated by the idea of changing the past or looking into the future, but no person has ever demonstrated the kind of back-and-forth time travel depicted in science fiction. Neither of them has proposed any method of sending a person through time without destroying them.

 But that also doesn’t mean that time travel is not happening. We know that according to Einstein’s theory of relativity, the faster we move the slower we experience time. A clock on a jet airplane will run slightly behind the clock on the ground.

But what we don’t know is that we are using the fundamentals of time travel in many day-to-day activities.

Time travel

Time Travel Applications

We use GPS technology to search for varied locations across the globe. NASA also uses high accuracy version of GPS to keep track of where satellites are in space.

To our surprise, this whole system relies on time travel calculations. We and the satellites are traveling into the future at very slightly different rates.GPS satellites orbit around Earth very quickly at about 8,700 miles per hour. This slows down GPS satellite clocks by a small fraction of a second (as demonstrated in 2 clocks example above).

Time travel

However, the satellites are also orbiting Earth about 12,550 miles above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here’s how: Gravity is much weaker at the height where these satellites orbit.

Einstein’s theory also says that gravity slows down the passage of time. So the clocks will run at a faster pace where the gravity is comparatively less.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

If all these corrections are being ignored, GPS maps might think your home is nowhere near where it actually is!

Time travel into future

If you want to advance through the years a little faster than the next person, you’ll need to exploit space-time. As we see above Global positioning satellites (GPS) pull this off every day, accruing an extra third-of-a-billionth of a second daily.

You wouldn’t be able to notice minute changes in the flow of time, but a sufficiently massive object would make a huge difference — say, like the supermassive black hole at the center of our galaxy. Here, the mass of 4 million suns exists as a single, infinitely dense point, known as a “Singularity”. Circle this black hole for a while (without falling in) and you’d experience time at half the Earth rate. In other words, due to time dilation you’d round out a five-year journey to discover an entire decade had passed on Earth.

Quite a similar thing was shown in movie the “Interstellar” directed by Christopher Nolan.

In the movie, the crew spends a few hours on a planet orbiting a supermassive black hole, but because of time dilation, observers on Earth experience those hours as a matter of decades.

Thinking in this way we are traveling into the future. But what about the past? Could the fastest starship imaginable turn back the clock?

Time travel

Time Travel into the past (Changing history!)

A big question in all of our minds. Can we change our history? Can engineers take their decision back of pursuing engineering?

A glance into the night sky should supply an answer. The Milky Way galaxy is roughly 100,000 light-years wide, so the light from its more distant stars can take thousands upon thousands of years to reach Earth. Glimpse that light, and you’re essentially looking back in time.

But can we do better than this?

There’s nothing in Einstein’s theory that precludes time travel into the past, but the very premise of pushing a button and going back to yesterday violates the law of causality. One event happens in our universe, and it leads to yet another in an endless one-way string of events. In every instance, the cause occurs before the effect.

What happens if you go back in time and kill your parents before you are born. How can you be born?

To travel back in time, some scientists proposed the idea of traveling at a speed greater than the speed of light. After all, if the time slows down for the object approaching the speed of light, then exceeding that limit might cause the time to flow backward. But as an object nears the speed of light its relative mass increases until it becomes infinite at light speed.

Accelerating an infinite mass any faster than that is impossible. Maybe that’s the reason we can’t move backward in time.

Time travel


We may reach to the conclusion that time travel is possible but probably not in the way we see it in science fiction and movies. There are still many cards unturned and a lot more to know about this vast topic. Hopefully, this blog gave you a headstart!

THE FERMI PARADOX: Are we alone in the Universe?

Reading Time: 5 minutesBy Sahil Makwana (2nd year)

     Are we the only living things in the entire universe? The observable universe is about 90 billion light years in diameter. There are at least one hundred billion galaxies, each with one hundred to one thousand billion stars. Recently, we’ve learned that planets are very common too. And, there are probably trillions and trillions of habitable planets in the universe, that revolve in the Goldilocks zone of their own stars. Which means, there should be lots of opportunities for life to develop and exist. But where is it? Shouldn’t the universe be teaming with spaceships?

   Even if there are alien civilizations in other galaxies, there’s no way we’ll ever know about them. Basically, everything outside our direct galactic neighborhood, so called “Local Group”, is pretty much out of our reach forever, because of the expansion of the universe. Even if we had really fast spaceships, it would literally take billions of years to reach these places, travelling through the emptiest areas in the universe. So, let’s focus on the Milky Way.

THE FERMI PARADOX: Are we alone in the Universe?

Milky Way

The Milky Way is our home galaxy. It consists of up to four hundred billion stars. That’s a lot of stars, roughly ten thousand for every grain of sand on earth. There are about twenty billion sun-like stars in the Milky Way, and estimates suggest that a fifth of them, have an earth sized planet in its habitable zone “i.e the Goldilocks zone”, the area with conditions that enable life to exist. If only zero point one percent of those planets harbor life, there would be one million planets with life in the milky way. But wait, there’s more. The Milky Way is about thirteen billion years old. In the beginning, it would not have been a good place for life, because things exploded a lot. But after one to two billion years, the first habitable planet was born. Earth is only four billion years old, so there have probably been trillions of chances for life to develop on other planets in the past. If only a single one of them had developed into an interstellar civilization, we would have handshakes by now.

What would such a civilization look like?

There are three categories.

  1. A type one civilization would be able to access the whole energy available on its planet. we are currently around zero point seven three on the scale, and we should reach type one sometime in the next couple hundred years.
  2. Type two would be a civilization capable of harnessing all of the energy of its home star. This would require some serious science fiction, but it is doable in principle. Concepts like the Dyson Sphere.

Dyson Sphere is a hypothetical megastructure surrounding the sun and effectively uses the energy of the sun to fulfill the energy requirements of the planet. 

THE FERMI PARADOX: Are we alone in the Universe?

Dyson Sphere

            3. Type three is a civilization that basically controls it’s whole galaxy and its energy. An alien race this advanced would probably be godlike to us.

If we were to build gen operation spaceships that could sustain a population for around one-thousand years, we could colonize the whole galaxy in two million years. Sounds like a long time, but remember, the milky way is huge.

So, if it takes a couple of million years to colonize the entire galaxy, and there are possibly millions, if not billions of planets that sustain life in the Milky Way, and these other life forms have had considerably more time than we’ve had, then, where are all the aliens?

This, is the Fermi Paradox, and nobody has an answer to it. But there are some possible answers.


Let’s talk about Filters,

THE FERMI PARADOX: Are we alone in the Universe?

A filter in this context represents a barrier that is really hard for life to overcome. They come in various degrees of scary.

One: There are Great Filters and we’ve passed them. Maybe it is way harder for complex life to develop then we think. The process, allowing life to begin, hasn’t yet been completely figured out, and the conditions required may be really complicated. Maybe in the past, the Universe was way more hostile, and only recently things have cooled down to make complex life possible. 

THE FERMI PARADOX: Are we alone in the Universe?

This would also mean that we may be unique, or at least one of the first, if not the first civilization in the entire Universe.

Two: There are Great Filters and they are ahead of us. This one, would be really really bad. Maybe life on our level exists everywhere in the Universe but it gets destroyed when it reaches a certain point, a point that lies ahead of us.

THE FERMI PARADOX: Are we alone in the Universe?

For example, awesome future technology exists, but when activated, it destroys the planet.

The last words of every advanced civilization would be:

“This new device will solve all of our problems, once I push this button!”

If this is true, then we are closer to the end than the beginning of human existence.

Or, maybe there is an ancient type three civilization or type three civilization, that can destroy the earth for its resources, for example consider a bird, we humans destroy their home for resources like woods, we can also be like a helpless bird for a type three civilization.

THE FERMI PARADOX: Are we alone in the Universe?

Maybe there is something out there, that it would be better not to discover. There is no way for us to know.

One final thought: maybe we are alone. Right now, we have no evidence that there’s any life besides us. Nothing. The Universe appears to be empty and dead. No ones sending us messages, no one answering our calls. We may be completely alone, trapped on a tiny moist mud ball in an eternal Universe. If we let life on this planet die, perhaps there would be no life left in the Universe. Life would be gone, maybe forever. If this is the case, we just have to venture to the stars and become the first Type Three civilization, To keep the delicate flame of life existing, and to spread it until the universe breathes its final breath, and vanishes into oblivion.

The universe is too beautiful not to be experienced by someone.

Keep reading, keep learning!


CEV - Handout