Fair warning: this post leans to the nerdy side of me 🙂

I just got done (re-)watching Marvel’s Agents of S.H.I.E.L.D. and was delighted to see that–due to life happening–I had completely missed not one, but four seasons. So much to see here!

Needless to say, Joss Whedon has always been one of my favorite writers and film directors, mostly because of his innovative genius and truly diverse casts. Add in time travels and you’ve got me hooked! I l-o-v-e time travel stories, especially those that involve traveling into the past. The opportunities for messing with implications and consequences are countless!

It’s a topic hard to dismiss by almost any audience. I mean, who has never dreamed of being able to change the past? Of taking back one’s own mistakes, of bringing back good times or even preventing evil? Of course, what has always fascinated me most was the idea of time paradoxes: if and how they could be prevented. How “different histories” might be interwoven and in the end still make sense.

A while back I wrote a novel during NaNoWriMo revolving around that idea (it hasn’t been published to date), and I assure you, that stuff makes for a good headache. Things get really complicated really fast when cause and effect become corrupted.

Why is that so?

Cause and effect

Well, for one thing it raises all kinds of questions. If you have ever wondered about time traveling, you probably came across the grandfather paradox. That is, if we accidentally killed our grandfather at a time before our respective parent was conceived, would we even exist? If not, who was the person traveling in time? Would the journey even take place? And if not, would then not the grandfather not be killed, and thus we do exist and get to time travel after all? Did we just create a time loop? An alternating one at that?

On the other hand, if we did succeed in avoiding time paradoxes would the resulting new reality still be within our own universe at all? In other words, have we changed history for everyone? Or have we—that is our little band of time-travelers—created a whole new universe and left everyone else behind in the old one? Have we taken the easy way out while everyone else is stuck with the same old, same old?

Or maybe does that mean past events can not be changed at all and everything we tried would lead to the same outcome? Because we came back and did what we did? Does that mean our present would be different if we never traveled back in the first place? Which then comes first? The chicken or the egg?

What is time?

We experience time through change. In any given setting, if nothing ever changed we would perceive that as time standing still. Think of a painting or a sculpture. They’re fixed, timeless. On the other hand, when things do change we perceive that as time passing because while our surroundings change we do, too. We grow older.

Now why is it that time only moves in one direction—which is forward? That’s because the very existence of our universe depends on the principles of cause and effect. If things happened randomly, laws of nature could not persist. Just imagine physical elements combining or not combining by pure chance: our air could become unbreathable one moment and poisonous the next, or it might incinerate us in a flash. That should illustrate quite vividly, why cause must come before effect and therefore time must always move forward.

Which leads to the most obvious question of all: do physics allow time travel at all?

In a way, Albert Einstein (1879-1955) himself answered part of this question by way of his special theory of relativity: due to time dilatation, if one twin were to travel nearly at the speed of light to a planet, say, four light years from Earth while the other twin stays home, the travelling twin would be four years younger upon their return than the twin who never left the Earth. In other words, the astronaut twin not only travelled through space, but also into the future.

What sounds like a magician’s trick is the result of the so-called Twin Paradox thought experiment and actual physics, as has been proven in experiments again and again.

Missing the point

Albert Einstein taught us in his special theory of relativity that space and time can not reasonably be separated. Time without a space to measure it in makes not much sense because nothing is there that changes. As it is, the universe is not empty and as a matter of fact it is ever-changing. Everything moves, spins and interacts. The universe itself expands faster than light can travel!

So, if travelling back in time were possible, we’d have a heck of a lot of details to consider. Because everything is constantly on the move, our time machine needs to consider not only the point in time we want to go to, but also the point in 3D space! What good does travelling back to the day when you botched that math test do when instead of in your old classroom you end up in a black hole?

After all of this, I still very much enjoy a good time travel story. After all, fiction is all about make-believe and about the willing suspension of disbelief on the part of the audience. If circumventing the obstacles and pit-falls of paradoxes is well-executed that sure makes for a fun, mind-boggling ride.

Count me in!