Time travel works...just invented, by you. The tests prove it! Now for the human tests.

It works by poking the residual timey-wimey weebley-woobley stuff just enough for you to move yourself and your time machine to the point specified. For some strange reason, your time machine is restricted to destinations on Earth. Annoying, but that's a feature coming in Time Machine 2.0! Flying is also on the product backlog.

Your significant other works as an epidemiologist and has implored you in the design of your time machine to include a measure that prevents you from bringing back any nasty diseases (their job is hard enough with the current world diseases, thank you very much). You choose to implement this by having the time machine test your vitals and a quick blood test for any signs of infection. If any signs are found, you may not travel to a different time but you may travel to a different location within your current time. This feature may not be overriden because of several layers of interlocks and protection mechanisms that you cannot get around.

You have access to all of 2015 medicine (being with an epidemiologist has its perks) and can take an extensive medical kit with you.

For your first long distance trip, do you go back in time or do you forward in time? Why?

You don't have to worry about the Grandfather Paradox or causality or any of the other nasty time travel problems. Physical security of the time machine itself is also taken care of, so no worries of theft or breaking & entering. This question only addresses the relative medical merits/demerits of doing your explorations before your own time or after your own time.

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    $\begingroup$ I would travel into the future to seek longevity! I'll be celebrating my 736361st birthday hooray! $\endgroup$
    – user6760
    Commented Aug 9, 2015 at 6:17
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    $\begingroup$ For what motivations are you time travelling? It sounds like the sane thing to do is to leave the time machine in the back garden to rot. $\endgroup$
    – Aron
    Commented Aug 9, 2015 at 14:04
  • $\begingroup$ @Aron, is a lack of motivation in the OP making it difficult to answer? I figured that anything learned while time traveling would be worth the risk, just really careful about the dangers. $\endgroup$
    – Green
    Commented Aug 9, 2015 at 14:57
  • $\begingroup$ @Green my point is that what you want to learn determines where you go... $\endgroup$
    – Aron
    Commented Aug 9, 2015 at 15:05
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    $\begingroup$ Great job taking all the fun out of time travel! (and by that, I mean great job slicing away all the usual excuses for time travel posts, and forcing us to ACTUALLY answer your question!) $\endgroup$
    – Cort Ammon
    Commented Aug 9, 2015 at 19:10

5 Answers 5


It's best to treat time travel missions the same way space travel missions are planned and executed. Both are extremely risky (going up in the space shuttle had a 1 in 39 chance of death). Each mission would be planned meticulously with specific science goals in mind and an array of extra, nice-to-have goals as well.

It's likely that most early time travel missions would be conducted specifically to answer your question. Time travelers would rarely leave their time machine until several missions had been conducted to that time-space to evaluate the risks thoroughly. Sterile probes would be sent in advance and returned to a sterile environment to be thoroughly checked for microbial life and infectious agents. The probes would also carry cameras and other scientific instruments, just like a space probe.

Once it is deemed safe and necessary for mission objectives, time travelers would be sent. Just like astronauts, your time travelers would endure a 2-week quarantine before each mission to ensure that he or she won't get sick during the mission. The time machine would be sterilized completely before departure. On most missions, time travelers would not be allowed to leave their time machine unless mission control deems it safe and necessary to do so. Most likely they would be required to wear hazmat suits or some other protective equipment, just in case.

However, it's likely that time travelers will interact with other humans. Wearing obvious protective equipment could be a risk if the locals are likely to attack or arrest you for it. The risk assessment might show that it's actually safer to wear no protection rather than stand out.

It will generally be safer to travel to the past because it is better understood. There are few or no serious infectious diseases that have been wiped out by 2015 (though we are so, so very close to eradicating a few through vaccinations). As such, a traveler with the full range of modern vaccinations ought to do very well in the past.

Most of the things that killed people in the past were due to poor sanitation, not viruses. Sanitation risk would still be an issue for vaccinated time travelers because a lot of those things have no vaccines. Time travelers would have to use modern sanitation practices to stay healthy and only ever drink water they treated themselves (or alcoholic drinks) and eat food they prepared themselves. (This too could be a problem with the locals, in terms of cultural faux-pas.)

Sanitation problems could affect the future as well, so water purification and sanitation is a given for any time travel mission. The future is more mysterious, but the scientific payoff would be greater. The future could have new diseases that we have no vaccines or treatments for. Chances are that it would never be deemed safe to send a time traveler to the future.

In any case, a time traveler and their time machine would be quarantined for some period of time upon return.


The future, where you would pickup self-pre-prepared drops of information in completely sterilized bunkers that would include thousands of years of research on how to eliminate current problems while the population still numbers in the low billions. You place the information there as soon as you get it from the time machine (no paradox rule!)/or once you've researched it (however long that takes).

Once you've released the engineered anti-disease virals, telepathy genes, plans for zero-point energy generators, anti-aging treatments and nano-assembly replicator bots... you can start sending back probes to document the past, and to download/preserve every human/animal/plant in history, just prior to their deaths, working your way backwards until there's no more life to preserve, sequence, or save.


Other answers are based either on not yet avaiable technology, or like the most voted answer, the time traveler being extremely careful about interacting. Well, to that I say, screw it. I'm going to touch the wenches at the tavern because I can.

Let's analyze:

  • Access to time traveling? Check.
  • Access to medication/sanitarization? Check.
  • Access to strong materials and technology? (you have a time machine) Check.

How do diseases spread?

  • Being transported (eg: Surface of objects/skin, or air particles)
  • Infecting Someone (eg: Blood, airways, Urinary Tract or rectum)

What do we need to ensure?

  • There's not any viruses/bacterias/particles (henceforth boogers) that are dangerous brought home on clothes and items
  • The time traveler doesn't inhale boogers
  • The time traveler doesn't have boogers in his bloodstream
  • Boogers do not get brought in by air

How do we do that?

We use an Airlock of course. The time traveler is subject to desinfectation to ensure that there are no boogers on his clothes or any items he brings. At the desinfectation room (The airlock) he should also have Period clothes (I assume that him/her going into her Highness the Queen's throne room wouldn't go too well in an AC/DC's Highway to Hell T-Shirt).

Secondly, the desinfectation station (the airlock - yes I do like this word) should also be a test-bay. Meaning: He can do blood/hair tests to confirm that he wasn't infected by anything (and thus he's not bringing any epidemic with him). Downside is, if he is infected, he can't get out of the TARDIS, sorry I mean Time Travel Machine.

Thirdly, the machine should only be able to "take off" and "land" at designated desinfectation areas. Those areas should be merged in a desinfectation liquid which would keep any boogers that could be attatched to the outer walls of the Machine.

And there you go, a realistic, and 2015 viable way to create a safe method for time traveling. Minus the time part.


There is a FAR GRAVER concern here:

Traveling to the future or the past can have severe impacts primarily because of conjugation and other similar processes.

Simple quarantine is moronic and primitive potentially resulting in HUGE repercussions.

Quarantining for space missions and epidemics are effective because their mission is simply to prove the absence of their existence. That the immune system has done its job and no harmful pathogens exist.

Time Travel is a whole different beast when you consider pharmacological and bacteriological history.

Today, both good and bad bacteria are evolving resistance to antibiotics. Bacteria through processes like conjugation can pass traits like antibiotic resistance to completely different bacteria.

Why is this a HUGE threat to time travel?

If your time traveler contained antibiotic resistant good bacteria, there is no amount of quarantine that can be performed to eliminate it. If they go back to the 1920s and spread their bacteria they could potentially destroy the onset/proliferation of penicillin which would have huge historical ramifications including a major set back to medical technological advancement.

If you go forward in time you run the inverse which is bring back a bug that contains resistance to all modern and future drugs resulting in an equivalent blow to technological advancement.

Make no mistake, we are currently in a endless arms race against the microbial world and the microbial world advances with every act of ignorance with this being the potential equivalent of giving the Egyptians Google.

The only way I can see avoiding walking around in a full fledged hazmat suit is if you had a nanomachine enhanced immune system that can identify and eliminate all undesirable microbes.


Travelling to the past will actually make you a extremely high toxic hazardous being for several reasons

Immune system development, vaccines and radiation

Our immune system is a lot more developed than how it was hundreds of years ago. Adding the vaccines that made us immune to other killing viruses. And finally our radiation level is higher than it was in the past - we are pretty much radioactive.

As the Article says, we are radioactive as we live under a radioactive environment; earth and the sun constantly produces radiation that accumulates through the passage of ages, this makes the present naturally more radioactive than the past, and the future even more radioactive, and due the latest abuse of nuclear energy the amount of radiation on earth has greatly increased more than in the past (nuclear bombs, nuclear plants, and even Chernobyl disaster).

Going back to the past and coming back to the present would not really be a problem for the present, but it would be a problem for the past. A lot of people dying from unknown diseases and a lot of cancer around the people that got in contact with you.

But travelling to the future would be the polar opposite. Without a better developed immune system or a body capable of handling the radiation levels of the future, you would be doomed a few minutes after arriving.

So, to not destroy the nature balance, and not making you vulnerable to the conditions, then I would use for any travel, specials hermetic travel suits that will not be only hermetic to the elements, but also hermetic to radiation.

(And you'll end up looking like a visitor from another planet.)

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    $\begingroup$ Welcome to WorldBuilding Mike! Do you have any citations for us being "pretty much radioactive"? That's the first time I hear this. It would be nice if you could edit your question accordingly. If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Commented Nov 27, 2017 at 9:31
  • $\begingroup$ Added some source with that information, but yes. life and even the planet is radioactive, with the passage of time the future generations gets more radioactive than the past and also our bodies become more tolerant to radiation, the problem in current ages is that the levels of radiation have becoming a lot higher before our bodies can adapt, making cancer more common than in the past (most cancer is provoked mostly by DNA degeneration provoked by... guess what: radiation) $\endgroup$
    – Mike
    Commented Nov 27, 2017 at 17:25
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    $\begingroup$ I see nothing here that supports this claim that we are somehow more radioactive than we were in the past $\endgroup$
    – anon
    Commented Nov 27, 2017 at 17:45
  • $\begingroup$ Radiation from the Earth would only increase if there were more radioisotopes being produced, but, on the contrary, these are constantly decaying. Radiation from the Sun is almost certainly constant on the timescales of human evolution. Just exposing something to radiation does not make it radioactive. You've just bombarded it with alpha/beta/gamma particles; the exposed object doesn't start producing it's own alpha/beta/gamma particles. Fall out on the other hand is different, since you are dispersing radioisotopes (radioactive dust). $\endgroup$
    – Snyder005
    Commented Nov 28, 2017 at 0:43

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