Is Time Travel Scientifically Possible?
By Jon Therkildsen, MSc MBA from University of Århus (2004)
THIS ARTICLE WILL ADDRESS AND ANSWER THE FOLLOWING:
CAN TIME DILATION MOVE US FORWARD IN TIME?
CAN WE TRAVEL BACK IN TIME?
WHAT IS THE SOLUTION TO TIME PARADOXES?
WHAT DO THE LAWS OF THERMODYNAMICS SAY ABOUT TIME TRAVEL?
Yes, absolutely. Time travel is scientifically possible. No rule of science prohibits time travel, and in fact, we have specific theories that tell us how. Often the “Law of Conservation of Energy” is invoked as a counterargument, but this is misunderstanding the very law. More on that later at the end of this article. Other popular notions claim to shoot down the possibility as well. All of which, I will address too.
The short answer is: Yes, it is possible, we know exactly how to do it, we have done it, and it happens all the time around you.
CAN TIME DILATION MOVE US FASTER TO THE FUTURE?
Yes, it can. Einstein’s theories of relativity taught us that time is a function of speed and gravity, meaning we can manipulate relative time so that it ticks differently from different frames of reference. Imagine we put you in a machine; you wait there for a week, and when you get out, the rest of the Earth is 100 years into the future. This is possible. Undoubtedly.
“Special Theory of Relativity” (1905) taught us that time is a function of speed. Anyone speeding relatively to someone not speeding will experience time dilation (aka a different flow of time). And this goes for any speed - be it a stroll in the park or in a spaceship whooshing away. Naturally, the difference is more noticeable the closer to the speed of light one travels, but the effect appears at any speed.
Would you travel at the speed of light, your time would have slowed so much down that it would have stopped entirely. Of course, Einstein also tells us that we can never achieve this speed, but could we, and we could factually travel to any part in the universe - instantly, from our perspective.
Think about that for a moment.
A photon of light travels at the speed of light, which means time does not exist in its frame of reference. It also means that when it leaves a star perhaps a billion of our light-years away, it will instantly hit your telescope - from its perspective. To it, no time has passed at all. A billion years in a moment. How is that for time travel?
On top of this, we also have the “General Theory of Relativity” (1915). It taught us that time, too, is a function of how close something is to a source of gravity. Only by being on Earth, our time ticks a bit slower than if, for example, we were floating in space far away. It also says that since your feet are closer to Earth than your head is, your feet are a tiny bit younger than the rest of you. Crazy, I know. But it is true. You can read more about it here.
Anyway, all objects experience time quicker or slower, depending on how fast they relatively move or how close to a source of gravity they are. The speed you experience on earth (like when you are taking the bus, or flying in an airplane, or running down the stairs) affect your time a tiny bit. The effect is so tiny it really does not matter for any of us - even that the difference is real.
But look at our GPS satellites: They tick faster than our clocks on Earth. They tick precisely 38 microseconds faster. To use them, we need to compensate for this difference in experienced time. The 38-microsecond difference is perfectly corresponding with the predictions of both the “Special” and “General Theory of Relativity”.
Those satellites are constantly traveling a little bit further into the future, than we are — a proven fact.
HOW DO WE TRAVEL BACK IN TIME?
While time dilation permits traveling faster into our future, it does not permit traveling back in an already experienced time. It is a one-way ticket.
As we learned above, the effect of time dilation increases the closer we travel to the speed of light. The faster we move, the slower our own time will tick. Geometrically, you cannot move faster than the cosmic speed limit of light. It is physically impossible. You can read more about why here. But were we to keep “all else equal” in the equations, and only increase speeds above what is possible (to faster than the speed of light); then ”time” will consequently become negative.
What “negative time” means is impossible to say. Some interpret it as ”back in time,” others as merely nonsensical. However, in my view, it is unfair to the equations, as reality is not meant for an “all else equal” manipulation, and so whatever the results, such fiddling cannot be above mere academic insights into the dynamics of these equations.
Add more degrees to a circle, if you wish. The end conclusion will be that you can’t. A circle has 360 degrees, no matter how creative you are. The maximum achievable speed is 300 000 km/s. Adding more in the equations does not change the fact.
But, look past time dilation for a moment, and “The General Theory of Relativity” has another way to travel back in time. Or at least back to the moment in time, where we invent this “way.” This method is messier and much more complex than the time dilations mentioned above and would require its own set of articles to properly explain. First time explained by the famous Professor Kip Thorne in 1988. The abridged version is something like this: Let us say we create two connected traversable wormholes in 2025. Then we speed up one of the wormholes or keep it near a strong source of gravity. Because of time dilation, the time surrounding this wormhole will slow down or even freeze, while the other wormhole continues normally through time - yet, they are still connected, they are still traversable. This means we create a gateway to 2025. The gateway is from whenever this other hole may be, but it always leads back to the year 2025. For this method, we first need to create traversable wormholes. We know how to, just not technically how.
Once this device is created, it will allow us to travel back to the point it was first turned on, but not further back. It does not help us now, but it gives comfort knowing it might someday.
So in conclusion, we know how to travel in time-future either faster or slower than our normal time. And it is very easy. Your car is such a machine. Unfortunately, the gain is yet very tiny. Eating your vegetables is still the better option to gain a few more ticks on the clock.
HOW DO WE AVOID REALITY SCATTERING PARADOXES?
A time paradox will happen when you travel back in time and change something that would prevent you from ever traveling back. And if you never travel back, you could not prevent this something from preventing you, and thusly you can travel back changing it again. We have a paradox.
The famous “grandfather paradox” asks the question; “what if you went back and prevented your grandfather from meeting (how dare you) your grandmother?”
In this case, you would never be born and never be able to travel back and block your grandfather. Meaning you would again be born etc. And so we are back to the beginning.
The answer is either that the universe will collapse, that the timeline simply won't allow for such a change, or that you will be erased from both past and future history. A bit like how Marty McFly started to dematerialize in “Back to The Future” (1985).
In truth, we do not know if it is possible to change the present by going to the past, and we do not know what will happen if we try. Nonetheless, “Quantum Mechanics” offer an interpretation that will prevent any time paradoxes ever to happen.
The so-called “many world interpretation” of “Quantum Mechanics” says that other branches of the wave-function split parallel universes constantly and near infinitely. For every subatomic interaction, in our reality, a parallel world split from our world, in which the opposite action is made.
You go left today, and a parallel world splits off, in which you go right. This is a crazy idea, but it is not a crazy rationale. This interpretation can explain many of the challenges with our understandings of the quantum realm. And it is one of the most accepted models in current quantum mechanical science.
The tree illustrates your life, your timeline. For every action, there is another world where you perform the opposite action, etc. When you travel in time, you are setting off new branches in your tree of life.
If the interpretation is correct - and much suggests that it may very well be - going back in time and, for example, killing your grandfather, will then create a parallel world where he is dead, and you are never born. This will, however, not affect your history (your world), where your grandfather continues to live. You are safe from oblivion, even in the worst thinkable time travel scenario.
Any conceivable time travel paradox is solved this way. Any consequences created by meddling with the timeline will be in parallel worlds, not yours.
There are paradoxes no more.
HOW CAN A TIME TRAVEL MACHINE AVOID ENDING SOMEWHERE IN SPACE, BECAUSE EARTH CONSTANTLY MOVES THROUGH SPACE?
This is a rather widespread question. Since the Earth moves through space, using a time machine to jump to another time, it means the Earth was in a completely different region of space at this moment.
Wouldn’t a time machine just strand someone somewhere out there in space?
I know this as a “clever” observation. At first, there seems to be a bit of an aha thing about it. But in truth, it is an absurd wonder as it forgets how basic navigation works.
Any travel in our reality - if in time or just in space - requires coordinates to work: Trains, cars, GPS, a walk to the local diner, and time machines need this to function.
Our reality consists of 4 dimensions, and so in turn also 4 coordinates to define any point in our vast universe. Be it at the diner, on top of the Eiffel Tower, or somewhere on Mars. 3 coordinates are spatial, and 1 is time, and we need all 4 when navigating.
Imagine inviting on a date, but only tell where (the 3 spatial coordinates) but not when (the time coordinate) - you will never meet.
Imagine inviting on a date and only tell when, but not where - you will never meet.
Imagine sending a probe to Mars, without the inclusion of time in its navigational path - it would never land… at least not on Mars.
All travel in our world relies on 4 coordinates. So with these 4 coordinates, any time machine will know where and when exactly to put you.
Since space has no fixed points to navigate by, it would likely work by estimating any relative position to the Sun, faraway star constellations, and similar - we used such tricks in our maritime history, and it works. In any case, do not buy a time machine from IKEA, and you should be perfectly fine.
THE LAWS OF THERMODYNAMICS
There are no laws or theories in science that prohibit time travel. And I hope this article has shed some light on several theories that actually support the mechanics of time travel. The Law of Thermodynamics does, however, provide a concern:
The First Law of Thermodynamics (aka the Law of Conservation of Energy): Energy and matter cannot be created or destroyed in a closed system.
The Second Law of Thermodynamics: All isolated systems tend toward an equilibrium state where entropy is at a total maximum, and where no energy will be available to be used in any form.
The third law of thermodynamics: The entropy of a system approaches a constant value when its temperature approaches absolute zero..
By traveling to another time - you are adding matter to this time - you are violating the first law?
By traveling to another time - you reverse the flow of entropy by your presence - you are violating the second law?
By traveling to another time - you add temperature by your presence - you are violating the third law?
Although the above mentioned thermodynamic consequences are correct, none of them violate the laws.
All the laws of thermodynamics are based upon “closed-” or “isolated systems”. This is a fact often ignored by those who quote them. If you combine systems, you can add matter, lessen entropy, or increase temperatures and violate no laws.
A future timeline must be considered another system. Thusly; “The Laws of Thermodynamics” do not apply here.
Your time travel will combine two systems, making any meddling possible - at least from a thermodynamic point of view. Once connected, these two systems become one system, reestating the laws henceforth. However, from then on, your meddling will change nothing as it is one system now, and so violates no laws.
If we were to consider a future timeline and a past timeline as one system instead of two systems - time-travel still does not violate the first law of thermodynamics. In such a case, you leaving your present and landing in your past, will have affected the total matter and energy in the system by exactly nothing: “2019 minus you” vs. “1975 plus you”, equals still one you. No change. No violation.
However, unlike the first law of thermodynamics, the second and third law includes vague references of time in their statute. Entropy will decrease, and temperature will increase in the past when you arrive. So were we to consider the past and present as one system, it seems to invite violations? It doesn’t. Both the second and third laws used phrases like this; “... tend towards/approaches… total/absolute…” and this trend in the direction of time is not obstructed or contradicted “totally” or “absolutely” by your arrival. The laws remain in effect because the direction of the dynamics does not fundamentally change.
Regardless of this healthy exercise in the laws, past and present are not the same system, and cannot be considered as one.
In conclusion, “The Laws of Thermodynamics” are a cornerstone in our science. The laws are guiding the mechanics within a system. They do not, however, obstruct the idea of traveling across systems.
EPILOGUE
The above article is not indirectly representing my view on time travel. I have no idea if it ever will be possible in any remarkable sense. Likely, I think it won't. But, my article aims to show how our science supports the possibility, as I believe this fact is generally and unfairly ridiculed a bit.
Attribution: I am often asked if Time Dilation has been confirmed? As expressed, in the article: yes it has, beyond any reasonable doubt. For reference, see, for example, these experiments: Pound–Rebka experiment (1959), Hafele–Keating experiment (1971), Gravity Probe A experiment (1976), Iijima et al. experiments (1975 - 1977), Chou et al. experiments (2010), Via our Particle Accelerators; fx (2014), van Baak et al. experiments (2005 - 2016) & Wayward Satellite Experiments (2019), etc.
Photos via Google