Is Time Travel Possible

Is Time Travel Possible — And What Would It Take?

10 min read

Can humans time travel? It’s a question that countless science fiction authors have asked, and have created answers to. Two of the most famous examples of this are Doctor Who and Back to the Future, as both have characters who find themselves able to time travel. However, the easiest one to take a deeper look at is probably Back to the Future, given that Doc Brown lived on Earth in the 80s and built his time machine out of an DeLorean.

The question still stands today: are we able to time travel? But first, in order to understand time travel and break down the DeLorean, we have to understand two big concepts:

The physics behind time travel, and what it takes to warp spacetime. If we approach the question with the belief that spacetime is something which is linear, or a fabric (although it could take multiple shapes, perhaps being fluid and constantly changing), then we have to understand what it would take to rupture spacetime and travel to a different point in it. However, there are also spatial phenomena which could be contenders for time travel.
Theories which already encompass time travel and our understanding of it. The biggest problem with understanding time travel is that no one’s ever managed to do it before. The closest we’ve come as of now are theories and science fiction ideas, both of which we can analyze for validity and see if they can explain more of how time travel could work.

Despite having these big categories in mind, time travel is still a very large unknown, making all theories about it mere speculation. However, could we use these speculative theories and a hearty spoonful of physics to actually determine whether we could build our own DeLorean time machines? Maybe! Here’s a good question to ask: before deciding if time travel is possible, what is time?

Defining Time

That’s probably the vaguest title for a section, especially since it’s defining one of the biggest immaterial ideas humans have had. But what is it?

Well, time fits into its own dimension. People always describe there being three dimensions, length, width, and depth — in this case, defining a definition as a measurable extent of some kind. The universe is considered to have around nine or ten dimensions, leaving spacetime with only three or four.

So if “time” is a measurable extent (which it is) then logically in the same way you should be able to move “up” the length of the universe, you should also be able to move into a different point in time.

Even in our experience, the phenomena of special relativity occurs, in which time can speed up or slow down depending upon how close to the speed of light you go.

Astronauts and other space farers are affected by this, often slightly younger than twins or people born the same time who had remained on Earth due to the speeds at which they had been moving and living at.

So that’s a breakdown of what exactly time is, although it’s still a relatively abstract concept.

However, assuming we can travel it, we have to address the next steps, which involves seeing how designing a time travel device could possibly work — and debunk the DeLorean. So what are the main questions to ask to figure out if it’s possible or not?

What are the physical undertakings of an object time travelling? From human knowledge of travelling from one place to another at fast speeds or through dangerous environments usually requires physical protection. If you did try to rip a DeLorean through the fabric of spacetime, what physical protection would be required to keep the DeLorean intact for the entire journey?
How much speed/force would you have to have to rupture the fabric of spacetime? In order to break the sound barrier, an object must travel at least 767 miles per hour. Although we haven’t been able to actually break the fabric of spacetime yet (assuming that spacetime is a fabric), which means the amount of force is also an unknown value.

A jet makes it through the sonic boom, breaking the sound barrier.

What would the displacement be like for anyone experiencing time travel? We probably wouldn’t just send a machine through time, so let’s assume that this trip involves a human. How would the spacetime displacement affect the person? And how long would the trip from one time to another take?
How would space displacement occur and affect the landing of the time machine? So, let’s say that you did successfully launch your DeLorean, then what? If your goal is to travel back three months, the Earth is revolving around the sun.
This means that three months ago, the Earth was in a different place, leaving you in empty space in your DeLorean. So would you have to modulate your precise space coordinates for the landing date? Or is there actually universe movement which would bring you to a complete different location (since the universe is constantly expanding)?

Despite all these questions (and many more), there’s still the question of if we can actually turn a car into an epic time machine. So back to the basics: let’s tackle each question, deem if it works with theories and physics, and then evaluate if the DeLorean time machine is actually possible.

The best place to start is looking at what we already know about physics and how this could affect our capabilities of time travel.

Going Down The Wormhole: Physics And Wormholes

The first question to ask here is how spacetime is shaped, because this will affect travel first. It’s like figuring out the layout of the road before a street race: you want to know if it’s curved, flat, has many hills, is paved, etc. That way you can prepare. The same goes with the shape of spacetime and time travel.

Right now, spacetime is considered a fabric, in a flat, non-curved universe. Of course, we can’t prove this, but right now that’s what modern physics leans more towards. Time travelling would be leaving one point in spacetime and entering another (likely instantly, although it could take a lot longer). From our current knowledge here, spacetime can be warped by dense objects with a lot of gravity — like black holes. But at what point does this become officially “ripping” the fabric of spacetime?

Most physicists agree that there isn’t exactly a point in which the spacetime is “ripped”. On the assumption that spacetime is continuous, then it can’t necessarily be ripped, a term which is mostly used only in science fiction. However, if it’s a fabric, two points can fold in on one another, creating a pathway from one point in spacetime to another.

This could include (but isn’t limited to) change of location, time, universe, or a combination of all three. This theory, known more commonly as “The Wormhole Theory”, is consistent with Einstein’s theory of general relativity.

However, no one has actually seen a wormhole, although there is speculation on whether or not black holes could actually provide a similar connection to wormholes.

So the easiest way for the DeLorean to get from point A to point B in time might seem like just creating a wormhole, but it probably can’t.

That’s because wormhole would likely be formed by creating two entangled black holes and then pulling them apart, making a pathway between the two black holes. At least that’s the way that would actually work in the universe.

There’s also the possibility of having a white hole and a black hole connect, forming a wormhole, which would work except for the fact that white holes don’t exist.

They’re the theoretical stark opposite of black holes, being a point in space where nothing could enter (unlike black holes, from which nothing can escape).

So this means in order to create a mini wormhole and travel back in time, the DeLorean would have to harness two black holes, entangle them, and then separate them again.

However, there’s another possibility for making wormholes, except this one involves ties between quantum mechanics and classical mechanics.

Applying Quantum Mechanics To Wormholes And Time Travel

Applying Quantum Mechanics to Wormhole and Time Travel

So we’ve already established that setting up a regular wormhole would be pretty difficult, but as it turns out, maybe there are answers when we look more at the details.

Going into the tiny world of quanta, scientists have started to see ties between the theoretical wormholes and spooky action at a distance.

One possibility involves string theory, in which tiny strings could snap and cause energy flow which could result in the creation of two black holes intertwined in the way necessary for a wormhole.

However, the energy would overpower the black holes, causing them to spiral off in separate directions and straight up collapse the wormhole.

Another analysis of this possibility resulted in the idea that the curvature of spacetime could possibly counteract the acceleration of the black holes, even though the whole idea is pretty unlikely.

On top of that, this wormhole wouldn’t permit time travel, meaning that even if you could create it and keep it stable, there wouldn’t be any time travel happening.

So it doesn’t look like quantum mechanics is a huge help in designing a wormhole, either, especially not one which could be created by a time-machine DeLorean.

So what other options do we have?

Well, time travel isn’t just narrowed down to a wormhole option — in fact, there are a lot of connections between quantum mechanics and time travel paradoxes and theories.

Deutsch’s Prescription — The Quantum Mechanics Of Time Travel Logic

So although we’re still disputing the idea of whether or not someone would be able to travel back in time, there are still the long running theories on what would happen if someone travelled back in time, and how the science would look at that. In 1991, a physicist named David Deutsch proposed a solution for time evolution equations, specifically ones which suggested resolution for both the grandfather paradox and nondeterminism.

The grandfather paradox is the idea that a time traveller goes back in time and kills their grandfather before their father is born, thus rendering it impossible for them to return to the present time.

Essentially a loop through which the grandfather is both lives and doesn’t, creating timelines in which the grandson exists and therefore creates the time machine and kills the grandfather as well as timelines in which the grandfather is dead, meaning the grandson is never born and can’t build the time machine to kill him, so he lives.

Nondeterminism is the term for when a computer algorithm which will provide different output for the same input.
This is like going to a soda fountain and pushing on the button marked ‘Sprite’ but getting Sprite, Coke, Santa Fe, and Root Beer once each of the four times you try to get Sprite.

Some people don’t agree with the solution provided with Deutsch’s Prescription, because it involves the time traveller entering a parallel universe in which the quantum state is quantum superposition, meaning the time traveller both does and doesn’t exist at the same time — something with also technically can’t happen.

So in the Deutsch Prescription, the quantum system is split into two categories, state A and the CTC (closed time-like curves).

There is a tensor product which is a result of the combine states of both systems. He assumes that the density isn’t necessarily the same in both categories, but that the density state of the CTC is restricted to a fixed point.

This is how a CTC would work/is designed, as it’s basically the rotation which exists to create a timelike curve.

From there, he suggested that fixed points like this always exist, due to the fact that after a repeated trials with the CTC value, the expectation value will match. This just means that the percentage of potential outcomes will come out the same if tried again and again. To some extent, though, this implies that there must also be parallel universes in order for the prescription to be filled.

So You Want To Build A Time Machine?

But of course, in Back to the Future, Doc Emmett Brown is able to traverse spacetime in his souped-up car and a case of plutonium.

This, too, isn’t very likely — although most people consider time machines to require some exotic matter called “negative energy density”, the machine would have to work without it.

That’s because this matter is theoretical — and even if it did exist, it would likely exist in too-small quantities to be used in an actual time machine.

Thankfully, there’s a potential alternative: if you start within a doughnut shaped vacuum inside a normal sphere of matter, you could use focused gravitational fields to create a closed time-like curve (CTC).

To go back into the past, the traveller would have to loop around and around in the doughnut, constantly moving faster, until he/she moved sufficiently back in time.

However, the gravitational fields would have to be very precise and directed at certain locations.

A Final Breakdown — Is Time Travel Possible

The short answer is yes, by all means, theories allow time travel to be very possible and an option. Although it’s not something we as humans in our current development are capable of experiencing, perhaps time travel will have a bigger chance to occur in the distant future.

Right now, there are still many aspects of the world we have to understand, and whether that’s breaking down paradoxes with quantum computers, exploring the theoretics of science and understanding how string theory connects classic mechanics and quantum mechanics, and understanding the fabric of the universe better…

well, it’s clear we’ve got our work cut out for us.

So the next time you think about tooling around the decades in a plutonium-loaded car, remember that getting there might be the hardest part!

Thank you so much for reading my article! I hope you enjoyed reading it, and maybe learned a little about time travel! If you’d like to talk more, give feedback, or just comment, feel free to connect with me on LinkedIn, follow this Medium account, or even email me at amesett@gmail.com!

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