Home > Open Letters > An open letter to future time travellers

An open letter to future time travellers

Dear hopeful time travellers,

Have you thought about disease?

Do you know how many bacteria are crawling across your beloved time machine right now? Billions. Do you know how many bacteria they can make in one hour? Let’s say once per hour, I’ve seen things about them being every 10mins, but those are particularly quickly dividing bacteria in optimum conditions. You know how many people in ancient Rome have immunity to diseases that arose AFTER the Western Roman Empire collapsed? None, so how many will die from the ensuing epidemic that occurs after you shake hands with Julius Caesar? Millions! 

Of course, time travel hasn’t been invented yet, but these are serious concerns if time travel were ever possible. If a capsule which transmitted people (or any living matter for that… matter) through time (more rapidly than conventional time travel of forwards at 1sps), then there becomes a very real danger off cross contamination. Disease transfer from direct contact with people could not only transfer disease to populations from the time travellers, but it can happen in reverse.

What if someone came into contact with smallpox (Which killed approximately 300-500 MILLION people in the 20th century, imagine the United States being emptied of all people, that’s the lower band for that estimate) and brought it back. This scenario isn’t entirely ridiculous if you leave out the assumption of impossibility of time travel (Which as I’m writing this letter to time travellers, you wouldn’t assume anyway). No one is vaccinated* against smallpox today, because the only samples left are with World Health Organisation laboratories in the United States and Russia. Millions would die before we could get the epidemic under control and it would take several more decades before we would be able to exterminate it.

So, future time travellers, sterilise your hulls, clean yourselves, before and after every jump or you may just kill us all.

This problem does not exist only for travelling through time. This is an issue addressed for missions of exploration to other bodies in space.


There is an issue that has been raised many times regarding time travel, that is, the earth is not a stationary object, hell, the solar system nor the galaxy is. The universe itself is in a state of expansion. Often, people will write about the problems of time travel as if the time machine would become a truly immovable rod and so would fly off into interplanetary space.

This view of time machines often omits the fact that the sun is orbiting the centre of the galaxy and so it would fly off into interstellar space if it were truly immovable and of course, the galaxy is moving relative to other galaxies and so the time machine would be lost to intergalactic void in a few thousand years.

But of course, this doesn’t make sense, why? Because movement is always relative to something else (Re: Einstein) and the time machine will have inertia acting upon it still (assuming it doesn’t just break current understanding of physics beyond being able to move in either direction along the time dimension (assuming time is a dimension)). So it depends on how the time machine works as to what happens, so if you do make a time machine, don’t make it work like an immovable rod. There may be some problems if tha- *CLANG*

Ageing in time

Suppose you are a time traveller and you are thirty years old and go back in time 20 years. How old are you? Well the one that did the travelling is still 30 (Assuming instantaneous travel) but there is also one which is 10 but is *you*. How do you count years when time travelling? Any time traveller must keep track of their own time scale or they risk losing themselves to time. Try this:

Hop into your time machine and go to a week ago and spend the week doing something, then go back in time a week and spend the week doing something, then go to the point in space and time where you left for your first week long trip. You are now two weeks older than you would have been but you have not missed any time in the universal scale, that is, you’ve had two weeks *more* time than everyone else.

But then who cares if you’re 20 or 21, or even 25 or 35 for that matter? It’s not like your health and well-being requires differential treatment of people of differing ages- wait, shit.

I went to the shops tomorrow.

This sentence makes no sense really, how can you have gone to a place before the time you say you did it? With time travel, that’s easy! You go forward in time 24hrs, go to the shops, then go back in time 24hrs and go home. You technically have been to the shops and it did happen tomorrow. This creates a very difficult problem for grammar specifically, how to use tense for time travel. You could always use your personal time frame for when events occur, but how do you say that it happened tomorrow? That still seems nonsensical. Alternatively, you could always use the universal time frame and say:

“I’m going to the shops tomorrow.”

But then that doesn’t differentiate between what you will do and what you have done in the future. I think that in order to talk about time travel, we need some ground rules for tenses. I would come up with them myself but I don’t think that rules made up by some nerd on the internet are likely to be useful to the majority of time travellers (It’s likely that time travellers make up exactly 0% of my readership) so I’ll leave it up to the time travellers to develop words themselves and grammar will evolve as it naturally does.

Finally, I’m sure people who aren’t time travellers are reading this and thinking “Where’s all the physics stuff about how to travel through time?!” Well, unfortunately, I’m not a physicist and so I thought I’d write about some of the more “mundane” problems of time travel and only hint at the others. If you want to learn about time travel and physics click here.

*Note on Vaccination: Anyone who argues against vaccination should read up on how we got rid of smallpox and also try to think to themselves what each of these diseases does and what it looks like if someone is infected:

  • Measles
  • Mumps
  • Rubella
  • Tuberculosis
  • Smallpox
  • Diphtheria
  • Polio
  • Whooping cough
  • Cholera
  • Typhoid
  • Hepatitis.

Also, try to understand this as clearly as possible, CORRELATION DOES NOT EQUAL CAUSATION. Google that shit, seriously, vaccinations are one of the greatest things science has done for humanity. The technology to prevent diseases like those listed above has done more for us than anything, ever. Take a look at the probabilities of a human child to survive to adulthood from 1910 and 2010, take a look at probabilities of a baby elephant surviving to adulthood in the same time periods. You’ll see a baby elephant had a BETTER chance to make it to adulthood than a child in 1910.

  1. September 23, 2012 at 11:57 pm

    I was wondering if you ever considered changing the structure of your blog?
    Its very well written; I love what youve got to say.
    But maybe you could a little more in the way of content so people could connect with it better.

    Youve got an awful lot of text for only having one or two images.
    Maybe you could space it out better?

    • October 7, 2012 at 2:46 pm

      I was told off by my supervisor for my dissertation about not having enough pictures in my presentation. I struggle to think of decent ways to incorporate images. I agree, thanks for the tips.

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