Ever since the idea of a time machine was proposed by H. G. Wells, in his 1895 novel with the same title, there is no end to the series of books, movies, novels and comics featuring protagonists sent back and forth in time. Since traveling forward is perfectly possible (in theory at least (1)) and thus comes with little controversion, allow me to focus on the idea of jumping back into a prior era. Who knows? We might as well learn something about our present predicament in the process...
Rarely anyone, who has ever seen a movie involving time travel, has to be introduced to the grandfather paradox. The riddle can be summed up like this: what would happen to me if I prevented my own birth? (Or what would happen if I accidentally caused the death of my ancestor(s) before my conception.) You see, if I were not born, then it would not be possible for me to undertake such an act in the first place… Would I disappear immediately, then? In order to understand the consequences of such an act, and thereby resolve this seeming contradiction, we need to put things into perspective first.
Traveling back in time presumes that there is physically a place somewhere in the “past” to visit… Where people eat, poop and die, just like in any other country in the present. As to where is that ‘somewhere’, one can come up with two distinct answers: a) it is right here, just “back in time”, or b) it is in a “parallel universe”. Let’s start with option a), in which case you would somehow have to force time to flow in reverse while you stay in place. ‘Wait, you said force time to flow in reverse?’ Well, you see, there is no such thing as “the past”, or “the future”. We are living in the present which bears the marks of past events. The future hasn’t happened (yet) either, so there is nothing to visit there also. This leaves us with the only logical conclusion that we must physically turn back conditions into their prior states in order to relive past events or have a chance at altering them. But before we can do that, we must talk about what is time actually, and what gives its direction.
As long time readers of this blog might have already guessed, the flow of time has more than a thing or two to do with energy. Energy, be it in the form of heat, electricity or motion, tends to flow from a high density source towards the environment where it can dissipate. In the meantime it goes through a number of transformations, and if we inserted a machine into this flow we might actually derive some useful work in the process. Let’s take electricity for example: by turning on your toaster you first convert electricity into heat, which, after crisping your bread, gets dissipated into the air (heating up the kitchen by a fraction of a degree). According to the first law of thermodynamics, energy is neither created nor destroyed in the process of dissipation: the amount of energy going into your toaster thus always equals the amount of heat leaving it (plus the amount of energy needed to perform the desired chemical / physical transformation of bread).
Now, what does this has to do with time? Well, imagine visiting a place where there is absolutely no energy. First, it is pitch dark. Second, it is cold: the temperature is 0 Kelvin, or -273.15°C or -459.7°F — with the only heat source being you. If you light a torch and look around you, you would see nothing but dead rocks. No life, no movement, no sound, no nothing. Everything is in standstill. An hour later you would see the same thing: nothing has changed. A year later? Ditto. A million years later? Nah, not a single dust particle has moved.
Time has no meaning without energy. In fact this is why we use energy to measure time; be it in the form of mechanical energy stored in a spring of a wristwatch, or measuring electrons changing energy levels in an atomic clock. Time is thus nothing more than a measure of energy dissipation — from a dense form into waste heat or background radiation. Sure, in the meantime all sorts of interesting things happen: energy might find itself locked up in dense clots (like a seam of coal, or a battery charged to the rim), not to mention all the motion and life it is converted into on its way to being dissipated as waste heat. One thing doesn’t change, however: you will always have less concentrated energy by the end of the day, compared to what you had in the morning. You’ve burnt fuel, spent electricity, put things in motion — and ultimately — dissipated a lot of energy. The Sun did just the same: it has spent a tiny fraction of its vast hydrogen storage and converted it into helium, and thereby released an immense amount of heat, light and particles. In the grand scheme of things, one day all dense energy in the Universe will be dissipated into background radiation. From the Big Bang, through the formation of stars and to their eventual demise, all concentrated energy will be converted into waste heat. This is the process what gives time a direction and meaning. And this is why time is so precious to us: because it’s finite.
Now, should we want to go back in time while staying in place, we would have to reverse this entire process. Remember, it is the dissipation of energy which gives time a direction. Trouble is, that you would have to do this across the entire Universe. Yes, you have read that right: since everything is connected, from the sunlight hitting an apple tree, to the bacteria turning soil into plant nutrients, or from the wind blowing over the Atlantic to the storm hitting your town, in order to accurately go back the causal chain of events, the entire Universe must be returned to a prior state. Sorry to be so blunt, but the world either goes back in time in one piece, or it doesn’t.
Since it is the dissipation of energy which defines the arrow of time, all previously dispersed power would thus need to be returned into its concentrated form, and all material and chemical processes would need to be replayed in reverse. From your metabolism to cars running on the street and burning fuel, everything would have to go through this massive reversal in order to return to the past while you stay in place and watch. All the material what you have left behind in the morning (all prior mornings) as a result would be flying back to you at breakneck speed, you would be forced to un-digest it, then… Perhaps I need not to continue explaining the process at this point. Enough to say it wouldn’t be a pleasant experience, but at least you would become a lot younger. Obeying the laws of physics, however, this time reversal would require more energy than what was dissipated during the period you wish to cover. (2) (Oh those damn losses at every corner.) Thereby you would not only raise the temperature of the entire Universe as a side effect, but would need an external power source larger than our cosmos. Good luck finding that.
After understanding the physics behind option a) time travel in place, one can easily resolve the grandfather paradox set out above. Since everything would be moving back in time, you would first unborn and thus had no chance at preventing your own conception. Should you be able to cast a protective sphere around you — preventing you from getting younger and protecting you from all the matter flying in your direction — you could do what you want in the past. In that case if you removed your parents, a clone eerily resembling you would not be born later (3). If you changed some important historic event, the future — which is now your future as well — would of course unfold somewhat differently, but you could not go back into the future to tell anyone how you removed the man who started WWII, as the old future was already destroyed and undone by your act of traveling back in time. The new future has not yet come, and if it arrived it would be just as new to you as to anyone else.
What about the other option then? How about traveling back in time by visiting a parallel universe where the calendar shows a much earlier date? There is a theory according to which every decision creates a bifurcation in time and creates a parallel universe. (I’m a bit skeptical as to that, but let’s say it’s true for now.) In this case, and presuming we have found a loophole between these worlds, we would have a practically infinite number of parallel realities to choose from. And since the future has not happened in any of them yet, changing a thing there would only affect the world in question, and not this one. So go ahead, remove “your” grandfather in that parallel universe: you would not disappear. The only difference would be a clone eerily resembling you not being born down the line there.
In summary, should time travel ever become possible it would be either extremely energy intensive to perform (sending back the Universe into an earlier version of itself), or it would have no effect whatsoever on this world (traveling to a parallel universe and changing something there). In both cases the future would still need to be written, and killing your ancestor could only prevent a clone of you not being born.
This little thought experiment has much more to teach us, though. It highlights the role of energy in the passage of time. Remember: it is the dissipation of energy which gives time a direction and a meaning. Viewed from the perspective of human civilization, from the first agrarian settlements to metropolises, history — and the apparent speed with which time has passed — was defined by the amount and quality of energy consumed. Hunter gatherer tribes used only a tiny portion of the surplus energy locked up in fruits, roots and prey animals. For them time was slow and circular. Ten thousand years here and there didn’t make a difference: life was just the same, kept in motion by the flow of gentle solar energy through the ecosystem. Things sped up somewhat with the advent of agriculture and the foundation of the first city states in Mesopotamia, still a thousand years plus or minus didn’t meant much back then.
Compare this to the oil age. For starters, just take a look at the history of the 20th century: two world wars, nuclear bombs, the birth of the Internet; not to mention the explosion of world population from 1.6 billion in 1900 to 6.1 in 2000. All this was the courtesy of an incredibly dense energy resource: fossil fuels; for which we still haven’t found any replacement, even as the accelerating phase of their depletion looms. (Forget nuclear, solar panels or wind turbines. These are all products of the oil age, and none of it could be produced, delivered and maintained without burning carbon. Sorry.) Thus once we burn through the easy to get part of this massive accumulation of dead matter (mostly algae and trees), we will be forced to return to a much slower life.
Problem is, Earth would still need millions of years to regenerate from the damage we have done to it. Deforestation, the strip mining of its best mineral reserves, our disastrous agricultural practices — just to name a few — have all left their marks on the face of this planet, making a return to pre-industrial life all but impossible in many places. Civilization, both in an ecological and thermodynamic sense, it seems, is a one-way street with a beginning and an end. And the higher the octane of the fuel we pour into its gas tank, the faster it depletes its resources and destroys its environment. By “choosing” agriculture eight thousand years ago, then starting an industrial revolution a couple of centuries back, we have stepped off the path of our ancestors, and gradually became a totally different species: a self-domesticated hypersocial creature colonizing the entire planet. And, boy, we have become terribly successful at that.
Hence humanity has fulfilled its destiny — not by becoming a wise steward of this planet — but by turning into a superorganism: seeking out and burning through all the energy it could lay its hands on. Once the dense, easy to get part is burned, though, we will experience something akin to the death of a star. After having burned all of its lighter elements, it’s fate is sealed. At this point — so late in the game — the only question remaining is thus whether we go out in a blinding white flash and drag most other species with us into a black hole, or become a tiny white dwarf in the wider community of life, after experiencing an ejection of all the accumulated material.
We are so deep into ecological overshoot, and have become so much dependent on finite reserves of dead matter, that once the party is over, there will be no easy way left for us to deflate this massive bubble bloated by our unconstrained energy use. It’s no use dreaming about traveling back in time either. We have consumed most of the high density energy resources already, and there is no way putting that Genie back into the bottle (4).
Until next time,
B
Thank you for reading The Honest Sorcerer. If you would like to support my work, please subscribe for free and consider leaving a tip. Every donation helps, no matter how small. Thank you in advance!
Notes:
(1) According to the theory of special relativity, proposed by Einstein, time flows more slowly for you if you happen to move very fast compared to a “stationary” observer on planet Earth. For example: if you would take a round trip to Proxima Centauri — the nearest star to Earth after the Sun, located 4.25 light-years away — at a high enough speed, you would be only a few years older, while your friends will have aged decades by the time you returned. Thereby, according to your own observations, you have “jumped” forward in time.
(2) Remember energy always flows from a higher state to a lower state, from a concentrated, dense form into a sparse, diluted form. In the meantime, it can be used to concentrate energy into a tiny space (like compressing a spring, or charging a capacitor) but the amount of energy which goes into concentrating it into a dense form will be always higher than the amount of power derived from using up that stored energy. As a result, springs, batteries, capacitors always heat up when charged, and dissipate some of the energy going into them.
(3) This act of excluding yourself from time-reversal would not be without its own side effects. It either means that you create a copy of yourself at the instant you press the start button on your time machine, and you are forced to watch the birth of your original in reverse, or you would be excluded from the process entirely, making it impossible to play back things in reverse exactly as they happened.
(4) If we tried to squeeze back all that released CO2 into the ground for example, we would have to spend considerable amount of our finite energy stocks on doing so. Even if we used solar panels to do so, we would heat up the planet considerably. The amount of heat trapped by those black panels, together with the waste heat released by the pumps (not to mention the heat released during the manufacturing of the necessary steel pipes) would certainly cause another bout of heating. This act, together with the many side-effects of continuing civilization (agriculture, mining, deforestation etc.) would still guarantee a climate and ecological disaster… When do we accept, finally, that the party is over? I guess never… but hence collapse.
