Today’s guest article is by Chris Kentlea of Ennead Games, designer of kits and guides to help players and GMs alike. Thanks, Chris!

Time travel, forward and backwards, is a subject that can cause many problems for GMs and players alike.

The main problem that most people are aware of is the so-called “Grandfather Paradox.” In case you don’t know it, it runs like this:

  • You travel back in time
  • Meet your paternal grandfather (or even your direct parents or another ancestor) and, by accident, kill him before your father is born
  • As your father no longer exists, neither do you
  • As you don’t exist, you can’t go back and cause your Gramps’ death, which means you do live, so you do go back, so he dies, so you don’t exist…

This can cause people to go cross eyed. There are many ways around this problem — the movie Back to the Future perfectly illustrates what can happen when time is changed.

Let’s assume you found a way to solve the paradox and that time can be changed if you travel through it in ways you were not meant to. The temporal paradox is not the only issue you may have to deal with. There are other, often overlooked dangers of time travel include (but not limited to) the following — the key ingredient in all of them being that they make games interesting.


When you materialise at your temporal destination, you have a chance of there being something already there. The method of time travel may replace what is at the destination point with the traveler. If you have the wrong temporal/spatial co-ordinates you may materialise inside a mountain, at the bottom of the ocean, or even inside the planet! Or the tree that would inspire a nation to rise up against its oppressors might be knocked down on arrival.

Technological & Economical

For many people, the biggest lure of time travel is acquiring knowledge. This can range from seeing the birth of a famous figure in your world’s history or finding out next week’s Mega-Lotto numbers with triple rollover. This at first glance is the safest method of time travel. You are not moving, you not going to squash a bug in the past that prevents your species from evolving, and you negate the risk of the grandfather paradox.

The major issue with looking into the past is that sometimes the information you discover is not what the history books record. Your famous leader might have be born normally and not under an eclipse like the legends tell. The slayer of the mighty beast may have been in fact been their servant and they took the credit and fame that went along with it.

Looking into the future, though, is actually much more dangerous than it first appears. Let’s assume time in your world can be changed. What happens if, upon looking through the time window, you spy your own death as you go to buy a lotto ticket?

Social & Linguistic Problems

Language and social customs change over time. A word that means one thing now may have had a different meaning 100 years ago and will mean something else in another 100 years’ time. Not know the correct terms and customs for the time period can at best cause embarrassment or confusion. At worst you commit a faux pas or insult an important person by accidently making a comparison between their mother and a garden implement.


Everything in the multiverse moves. The planet moves around its parent star. The star moves in the galaxy it resides within. The galaxy moves away from other galaxies. It is even suspected that the universe moves. Which is why making sure that your destination is where you think it is, or having some way of compensating for this movement, is so critical when traveling through time.

Diseases, Microbes, and Bacteria

In many ways this is the most overlooked and most dangerous aspect of time travel (after the risk of possible paradox). The destination point (future or past) may have diseases, microbes, and bacteria you don’t have immunity to. Traveling into the past (or returning from the future) runs the risk of introducing a disease or microbe into a time period that doesn’t have the resources to handle it.

Picture this, you take a short expedition to the future and take every precaution you can think of. Sadly a small microbe hitches a ride back with you. Over the years it had developed immunities to many of the most powerful cures. Congratulations: You’ve just introduced a super-virus into a population that can’t handle it.

Going into the past can cause the same problem, taking along microbes that wipe out a developing settlement or creature that is essential for a major hero to be born and kill the mega-demon from the 12th plane of the abyss. A rigorous form of quarantine and cleaning, before and after the time jump is highly recommended.

Hopefully these considerations have given you some ideas for incorporating time travel — and its attendant dangers — into your own campaigns. If you’ve used time travel in a game, I hope you’ll share your experiences in the comments.