You are a fellow Worldbuilder and while travelling by train, you fall asleep. Next time you wake up you realize you woke up at Grand Central train station. You quickly realize that you traveled not only through space, but also through time.

The date is September 11 2000. Exactly one year prior to the World Trade Center attacks. You (obviously) can speak English well enough to communicate with people around you. You have all your clothes and everything what you carry in the pockets. Namely your cellphone.

It always puzzles me whether one person can prevent the World Trade Center attacks. Would secret agencies believe that person?

Also, you can tell to the agencies only stuff what you remember right now about the attacks


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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Sep 19 '16 at 13:24
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    $\begingroup$ I can't add an answer but the obvious way that comes to mind is to board AA 11, the first plane to depart, and sit near the front of the plane. The plane was hijacked at 8:14, at the same time UA 175 left Boston. Spend a year in hand-to-hand combat training, bring zip ties, and physically subdue the attackers as they go to hijack the first plane. Warn the pilots there are more. With a little luck (or delay at the airport), the latter three planes will be grounded. $\endgroup$ – Azor Ahai Sep 20 '16 at 16:28
  • $\begingroup$ Or, start working for Boston ATC, delay AA 11 and UA 175, fake getting a call from the FBI, and have the planes searched and then disappear into the night ... (early morning). Or, likewise, start working for American, and bump all the hijackers off their flights ("Oh no, I can't find your reservation."), and call in a bomb threat on the United flights. The hijackers will doubtlessly be flustered by the delays and plane searches, giving them away. $\endgroup$ – Azor Ahai Sep 20 '16 at 16:33
  • $\begingroup$ @Azor-Ahai You are focusing on the wrong thing. It may have happened that the planes were just the first to be taken into consideration, etc. Resolving the effect wouldn't help; rather resolve the cause. $\endgroup$ – cst1992 Oct 1 '16 at 13:13
  • $\begingroup$ Violent way: Kill al-Qaeda. 16 years ago. $\endgroup$ – EKons Oct 2 '16 at 6:35

14 Answers 14


There are two ways to do this, the easy (selfless) way and the hard (selfish) way

The Hard Way

Call the local police station and tell them about crimes that you know happened in New York past said date of Sept 11 2000. If you predict them accurately enough, then when you say that Muslim Extremists are going to attack the World Trade Center, they in turn can set up Anti-Aircraft Artillery, (The much cooler Triple A) but this is difficult as it requires too much foreknowledge, all this does is save yourself if you are a selfish pig. The better choice is option B.

The Easy Way

When 9/11 occurred, it changed security on planes forever. Before the attacks, there were many things you could carry that are now out of the picture, ranging from toothpaste to can openers, to even Durex™ (I am legally bound to say Durex™ is not, nor has it ever been affiliated with TrEs-2b).

Assuming that you are willing to go to any lengths to prevent this attack, the answer is as simple as it is ethically questionable; hijack an airplane. Buy an easily concealable weapon, such as a plastic butterfly knife or ceramic cane sword, the weapon matters not, the attack does. You need to instil fear into the Americans so that it becomes much more difficult to hijack planes. Name the last famous plane hijacking in America, post 9/11? Yeah. While it does suck, by hijacking a plane and committing a terrorist act, you can drastically decrease the odds of 9/11 happening.

You can even go a step further and claim you are doing this for Allah, the one true god; making it even more difficult for the crisis to occur. Remember, the needs of the many....

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Tim B Sep 18 '16 at 22:52
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    $\begingroup$ As in "the easy way" but at the end you reveal that the story protagonists are committing the 9/11 attack to prevent something even worse that happened in their timeline. $\endgroup$ – Ben Jackson Aug 8 '17 at 6:49

It may be difficult to prevent the attacks from happening. It is quite far-fetched a story to tell the pre-9/11 world. Also your seat-of-the pants knowledge can have gaps and inaccuracies, making an iron-cast plan difficult.

However, what is really important here? Do you want to save the building, or do you want to save the people?

The last is really easy. Find out how quickly the building can be evacuated. Then phone in a bomb scare ahead of time.

You have a year to set this up, phoning in self-induced fires in abandoned buildings and seeding the police at large to ensure they will take it very seriously indeed by the time you need to be believed.

And better have a file on you about 9/11 plans for the police to find in case you are caught out too early. Nice and cryptic with just enough hints.

You may even spread out yourself to try and help all the 9/11 attack victims this way.

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    $\begingroup$ From that point of view would it not be better to phone in some bomb scares to the airports the planes left from and prevent the passengers and crew dying as well as the Twin Towers victims. $\endgroup$ – Sarriesfan Sep 17 '16 at 12:04
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    $\begingroup$ This might stop attacks that happened, but it wouldn't stop terrorist (or government agents, depending on where you stand) that wanted to do it. They just might try again later with even worse (better?) results $\endgroup$ – Lope Sep 17 '16 at 12:15
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    $\begingroup$ @Lope If you time it right (ignoring butterfly effect), you can start the evacuation after the planes are in the air and the hijackers have no idea the buildings are empty. $\endgroup$ – Bob Sep 17 '16 at 13:34
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    $\begingroup$ Bomb scare? Nah, place a real cutting charge against one of the girders in a reasonably accessible location so it can be quickly verified, it has a 6 hour timer on it. "To prove the threat is real there is a bomb at location <x>. Many more are better hidden. Pay me $1 billion in cash to get the location of the rest of them." Then FedEx them an envelope explaining there never were any more bombs, the true purpose was to get the buildings evacuated before the kamikazes hit. $\endgroup$ – Loren Pechtel Sep 17 '16 at 19:45
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    $\begingroup$ Bookeater: This graphic novel about a time traveler trying to prevent 9/11 takes a similar approach. (The resolution is poor for the first couple of frames, but it gets better.) Note: This is a work of fiction and I do not claim that everything presented in this novel is historically accurate. Yet, it may be useful in some regards. What do you think? @Sarriesfan $\endgroup$ – Revetahw Sep 18 '16 at 10:22

If you can make the agencies believe you don't depend at all on how you plan your attempts to stop it, it depends on how the time continuum works. The success of the timetraveller is already determined by how he knows the world and he can't ever change that timeline, unless he did not travel both in time and into a different universe. Why? Causality!

Setting the stage

Let's assume our Timetraveller starts 2016 and manages to get a time machine for reasons directly or indirectly related to 9/11. He uses it to get to 2000 and somehow manages to prevent 9/11 the next year through some method, one or another. Now, how does the future unfurl? Here it comes into play how time is handled!

Case A: Instable Time Loop

This is also called the "grandfather Paradoxon" at times. Now, he has prevented 9/11. As he was directly motivated by 9/11 happening just how it happened, his younger self will never have reason to get a time machine and prevent 9/11. So he doesn't enter the time machine, which leads to him never going back in time to prevent 9/11. As he didn't go back to prevent 9/11, he is again motivated to go back in time to prevent 9/11. And we are back to the start of the loop.

It is easy to see, that either, our protagonist has no chance of succeeding or getting out of the loop: If time travel removes the reason for the time travel, you can't get a stable situation as it flickers between the two alternatives! It is like a Schrödinger's Cat parable, where the box can't be opened ever again once it is closed.... However, there is a solution:

Case B: Stable Time Loop

The Novikov self-consistency principle tells that any time travel is only possible if the time travel has only results that have been part of the history already. You can't go back in time to change it, but there might be an alternative universe (many worlds theory!), where somebody from the future of 9/11 did go back in time and did prevent 9/11 in a way that would make sure, that somebody in the future did discover that the evidence that was needed to prevent 9/11 did come from his time and then went back to become this person. This Logical Loop that is created must be a self-fulfilling prophecy: in this AU 9/11 never happened, in no way. Just one person has to undergo the stable loop.

However, this is not the only way, time travel can go on, there are other variants... (original text: here)

Case C: Doctor Who

Now, Dr. Who is clearly not a non-stable or a stable time loop all the times, but somehow manages to have a roughly linear personal timestream (that the timeline of the world around him is an entangled yarn ball doesn't matter, he has personal timeline superiority!). He does adhere to some of the Novikov rules but breaks them at other points. Still, for him the Blinovitch Limitation Effect is governing (most of the time):

  • You can't redo or fix anything you did yourself
  • You can't have any contact with any of your earlier selves or face some heavy energy discharge

On itself, this would not prevent the time traveler from going back, but he can't go back to fix his own mistakes. So he can't just "try again", and if he doesn't manage to prevent 9/11, he can't try again. He could, however (under the paradigm), try to prevent some other thing, as long as it wouldn't void any of his prior time travels.

Conclusion: Causality needs to be maintained!

No matter how time travel is achieved or what method is taken to ensure the success, one has to adhere to the principles of 4D Logic, that is one has to advert time paradoxes at any cost. Maintaining the Causal Loops is essential!

In a world without 9/11, there wouldn't have been a War on Terror. Iraq wouldn't have been invaded. Possibly the Arabian Spring wouldn't have risen. Maybe there wouldn't have been the ISIS either.

Now, any reason that springs from these can't be a reason for the time travel or the result is a non-stable time loop, casual instability and time paradox. Our time travel reason needs to be something that ensures the time travel is being taken to fulfil Case B. If we add Case C, it is just a complication, that makes sure that the time traveler has to try his best to succeed - if he would not, nobody would be able to fix his mess, as those others wouldn't remember it any differently (and neither he), and at the same time he has still to ensure he did the time travel in the first place.

Way out

Now, If he remains in the same universe, the one he came from, then he can't change the path it will run down until the time he started his time travel - either because he would create a non-stable time loop and would end in the Schroedinger state of probable success and failure at the same time, or because he adheres to Novikov and ends up being ignored. However, there is a way out that I mentioned earlier: Many worlds Theory.

Instead of just going back in time, our "time traveller" ends in a branching universe that differs in at least one point from the one he came from, he is there. It might have more differences (Schwarzenegger was President?!), it might be otherwise identical - but this opens up the whole area: It is no longer creating causality errors to prevent or fail at preventing, as you don't try to change the system with the results of it. Instead, you know how system A played out and then alter the conditions in system B, that is the same in most but not all details.

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    $\begingroup$ -1 Not enough "wibbly wobbly timey wimey" in the Doctor Who part $\endgroup$ – LukeG Sep 17 '16 at 14:18
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    $\begingroup$ While a nice commentary on time travel, it does not even approach answering the question as stated. $\endgroup$ – WGroleau Sep 17 '16 at 14:39
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    $\begingroup$ my point is: Either he can't change the timeline due to it being his history that it happened already, he creates an instable time-loop, or his history is already that 9/11 never happened and he (or some other timetraveller) has to become the reason that will happen, no matter how hard he tries not to prevent it. Causality governs it all $\endgroup$ – Trish Sep 17 '16 at 15:06
  • $\begingroup$ This answer is questioning premises of the question which were already assumed to be given. $\endgroup$ – Michael Sep 17 '16 at 20:13
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    $\begingroup$ Well, maybe create a stable time loop by (a) preventing 9/11, and (b) brainwashing your younger self into believing that 9/11 actually happened. $\endgroup$ – celtschk Sep 18 '16 at 5:41

Kick the hornet's nest

At around 0600 to 0700 Eastern Time, September 11, 2001, you call 911, you call news agencies, you call TV stations. You tell them that there are bombs placed on American Airlines's flights 11 and 77, and United Airlines flights 175 and 93. And that there are vans loaded with explosives will drive into World Trade Center Towers, the Pentagon, the White House and the Capitol. You have spent the year reading the manifestos of Osama bin Laden and knows his arguments. So you add suitable passages from these in the calls.

Then you sit around and wait for the police to show up. Accompanying you are former Washington Post reporters Bob Woodward and Carl Bernstein. This is because you have previously called them and said "William Mark Feldt Sr is Deep Throat". And you have shown them your phone.

At around 2001, cameras on phones was next to unheard of. Digital cameras were at about 1 Megapxel at the very most. My Samsung Galaxy S6 can do great pictures in near darkness, at 16 Megapixels. The biggest problem you will have with it is trying to charge it since micro-USB is still a few years away.

There will be some huge confusion but unless people are phenomenal idiots they will be rattled and intrigued enough to look closer at the passenger manifests of those flights, even more so if you say "19 guys will board with box cutters and other such tools".

What happens there-after is anyone's guess... but you have at least cleared out the WTC, the White House and Capitol. You will have made people look closely at who was scheduled to fly of those flights. This may perhaps prevent the attack. But whether this actually catches the baddies or if they escape and try again is anyone's best guess.

  • $\begingroup$ Not so sure about this one. Law enforcement agencies get crank calls all the time where people warn that things will happen. People do it because they have dreams, hear voices, just want to get a kick out of setting off a hoax reaction. FBI would need some credible intelligence to back these claims up. $\endgroup$ – Snow Sep 17 '16 at 15:56
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    $\begingroup$ @Pete Bomb scares and no laughing matter, especially not if the person is directly quoting a known enemy of the state. Crank callers do not do that. $\endgroup$ – MichaelK Sep 17 '16 at 15:58
  • $\begingroup$ I agree that they should be taken seriously. However, if the emergency services reacted fully to every single call they had, they wouldn't be able to function (or have to recruit a lot more personnel to chase those wild gooses). I wouldn't say that someone calling in with a specific multiple target scenario would be immediately believed. They'd probably send a squad car out, but not much more than that. I don't think the twin towers would be evacuated on the basis of one call, especially considering the loss of revenue that would result in for the companies involved $\endgroup$ – Snow Sep 17 '16 at 16:13
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    $\begingroup$ @Pete Heh... try it some time and see is "a squad car" is all you get. :D $\endgroup$ – MichaelK Sep 17 '16 at 16:17
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    $\begingroup$ @MichaelKarnerfors During "the Troubles" in Northern Ireland, the paramilitaries pre-arranged code words with law enforcement and media to confirm bomb threats and claims of responsibility. It is certainly possible to create a credible bomb hoax and get a building evacuated, but it is definitely not a given that your word would be believed. $\endgroup$ – IMSoP Sep 17 '16 at 17:21

Recruit your younger self. Take:

a) Your smartphone from the future

b) Your younger self, genetically identical yet sixteen years younger.

Then head into a major news outlet, the New York Times would do, and tell the whole truth, in as much detail as you can. Then make yourself available for clarifications and testing.

Even if you're not believed, you will make enough of a splash to derail the WTC attack plans.

Don't forget to warn about Fukushima while you're at it!

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    $\begingroup$ Warn them of the Tsunami in 2004 also, please $\endgroup$ – axsvl77 Sep 18 '16 at 3:24
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    $\begingroup$ Sadly, revealing yourself as a time traveler will get you detained and studied for the foreseeable future. $\endgroup$ – Dronz Sep 18 '16 at 4:44
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    $\begingroup$ Yes, you'd be sacrificing yourself to stop the attacks. Arguably worth it. $\endgroup$ – Edward Falk Sep 22 '16 at 20:37
  • $\begingroup$ Relevant XCKD: 2009 called $\endgroup$ – Edward Falk Sep 22 '16 at 20:38

Bear in mind that actual FBI agents who saw what was coming were unable to prevent the attack. Now granted, you have specific information such as date and who and where, but you're also much more likely to be regarded as a crank call.

I think your best approach would be to call the security office at Logan airport from a payphone and tell them that you know that Arab terrorists are going to try to hijack multiple planes that morning using box cutters as weapons. Hopefully they'll take extra screening precautions that day. They may figure you're a crank call, but it still might make them paranoid enough.

I think your cell phone is basically useless. You won't be able to find a charger for it, it won't connect to any networks. You might be able to connect to WiFi, but what would you connect to that could be any help? You might be able to show it to people to prove you're from the future, but do it quickly before the battery dies. And be prepared to be thrown into a cell while they study you to find out how you travelled through time.

Also: as an aside, when the FBI tracks the call to that payphone, and checks the coins for fingerprints, imagine their surprise when they find a dime with a date in the future.

One more comment: a lot of other comments and answers sort of assumed that you had a chance to plan your trip in advance, e.g. by memorizing key facts or putting data into your cell phone. But the original scenario was that you, unprepared for what was about to happen, find yourself in the past.

I certainly haven't memorized the flight numbers or even the airlines involved. I might be able to remember a hijacker's name or two.

Could I name any major events between 2000 and 2001 to convince people I was from the future? That might be a little easier. IIRC, that was the year that Bush won by 500 votes in Florida. Tell people that "hanging chads" was going to become a popular term, and Dan Rather's "pregnant with possibility" quote would be misquoted as "pregnant chads". Mention "butterfly ballot" and you're in. Also mention Arabs taking flight lessons in Arizona. If the FBI follows up on it, then the agent there who tried to warn of the attacks might be taken more seriously.

References: In the book Replay, the protagonist finds himself sent back to 1963. One of the first things he tries is to stop the Kennedy assassination.

In the web series Red vs Blue a main character repeatedly goes back in time to stop previous disasters from happening, only to wind up being the cause of each of those disasters.

In Outlander, the main character tries to stop the massacre at Culloden, but everything happens exactly according to history no matter what she does.

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    $\begingroup$ Hmmm, here's a fun plot complication: the FBI tracks you down from the fingerprints on that dime and arrest the younger you who has no idea what's going on. This changes the future enough so that you never get onto that train. $\endgroup$ – Edward Falk Sep 17 '16 at 21:54
  • $\begingroup$ About the charger issue, that is less of a problem. After all, you can open the phone, take out the battery and charge it "offline", since building a charger of the specified voltage and amperage is trivial in 2000. $\endgroup$ – SJuan76 Sep 17 '16 at 22:50
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    $\begingroup$ Maybe, maybe not. First, not all phones come apart easily and have batteries that are removable. Second, I used to work on battery charging logic for a living, and you'd be surprised what's involved. Many (most?) batteries have their own microprocessor and the main processor has to talk to it via I²C or 1-Wire protocol to negotiate charging parameters. You usually can't just hook them up to 5V power supplies. It would be much easier to somehow build a micro-usb plug and hook that up to a power supply. $\endgroup$ – Edward Falk Sep 18 '16 at 0:24
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    $\begingroup$ EdwardFalk: This graphic novel about a time traveler trying to prevent 9/11 takes a similar approach. (The resolution is poor for the first couple of frames, but it gets better.) Note: This is a work of fiction and I do not claim that everything presented in this novel is historically accurate. Yet, it may be useful in some regards. What do you think? @SJuan76 $\endgroup$ – Revetahw Sep 18 '16 at 10:28
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    $\begingroup$ On the other hand I happen to carry a charger. $\endgroup$ – Joshua Sep 30 '16 at 17:44

Buy an Aviation Band Radio

Park under the departure path of the airplane. Tune to the relevant Tower or ATC frequency the plane will be using when overhead. Call the pilot and tell them that there are hijackers onboard with box knives. Explain that they mean to use the plane as a weapon, and not just as a negotiation tactic.

That's really all anyone needed to know. You wouldn't save the planes, necessarily, but they wouldn't hit the WTC or the Pentagon. That information was enough to stop the 4th plane on 9/11 already.

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    $\begingroup$ Simple, elegant. I like it. Assuming you know which planes to notify. I wouldn't. $\endgroup$ – Edward Falk Sep 20 '16 at 1:12

As long as your goal is only to prevent this particular attack, this is not as hard as it sounds. You do not need to prove or even reveal that you are a time traveler or have knowledge of future events. There was already one attempt made in 1993 to take down the World Trade Center. A plot to destroy the Holland and Lincoln tunnels and attack other New York City landmarks was foiled the same year. Any plausible information about specific new attacks is sure to be investigated.

So, the simplest thing to do is a month or two before the attacks send a the FBI a letter which says something like this:

Over a dozen men from the Middle East are studying at US flight schools (maybe in Florida). They are learning to fly jumbo jets. They do not care about learning to land because they want to fly them into buildings. They hope to hijack several planes on the same day. They think the crews will cooperate if they threaten the passengers with small knives and do not tell them what they intend to do. They will probably hijack long-distance flights leaving the East Coast so that there will be plenty of fuel to cause the most damage. The World Trade center is definitely a target, but there may be others. They hope to do this on September 11th so that the date will be 9/11 (911).

I have included only information which I am pretty sure the conspirators knew before the attack. The FBI will assume that this information comes from inside the conspiracy, perhaps because one of the conspirators blabbed.

The information which I have included describes a novel but plausible attack. It does not matter whether the FBI thinks it would work, they will follow it up because it is a highjacking. The FBI in Arizona already wonders why students from the Middle East are studying at US flight schools. Once they find out that some of them have taken tickets for September 11th, they will give them their full attention.

  • $\begingroup$ Dunno why this got down voted, I think it's the best approach. Although you got the location wrong; they trained in Arizona. $\endgroup$ – Edward Falk Sep 17 '16 at 21:10
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    $\begingroup$ DavidC: This graphic novel about a time traveler trying to prevent 9/11 takes a similar approach. (The resolution is poor for the first couple of frames, but it gets better.) Note: This is a work of fiction and I do not claim that everything presented in this novel is historically accurate. Yet, it may be useful in some regards. What do you think? $\endgroup$ – Revetahw Sep 18 '16 at 10:29
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    $\begingroup$ @EdwardFalk Our time traveler has to go with what he remembers, so I did the same. Since I was not sure, I wrote "probably". It turns out some trained in Arizona while three trained in Florida. I am relying on the FBI to sort it out now that I have told them how to connect the dots. $\endgroup$ – David42 Sep 19 '16 at 14:28
  • $\begingroup$ @Fiksdal My solution is intended to avoid the kinds of problems encountered by the time traveler in that graphic novel. She makes too many truthful but extrordinary claims. Her identity as a time traveler, her iPad, the "movie", the surprising success of the attack, and the discussion of 9/11 conspiracy theories are distractions. The more information she gives, the less credible her story becomes. In contrast, I give the FBI some simple easy-to-verify information about a hijacking plan. Even if they do not think the plan will work, they are still going to try to stop it. $\endgroup$ – David42 Sep 19 '16 at 14:49
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    $\begingroup$ DavidC: Totally agree. The time traveler made a great many mistakes. The thing is, she planned to arrive a week before the attacks. She had probably planned another approach. In her panic, the probably lost the ability think reasonably. It's an understandable reaction to such an emergency of a situation. @EdwardFalk $\endgroup$ – Revetahw Sep 19 '16 at 14:52

Yes, a single person can prevent the 9/11 attacks. One year prior is plenty of time to change outcomes significantly.

Sensitive Dependence on Initial Conditions

The event of 9/11 was the culmination of every single preceding event. Change one tiny little thing and you have most probably (in fact, in all probability), drastically changed the odds on 9/11 occurring.

Personally, I maintain that if I wasn't so slow to learn to tie my shoelaces as a child, then 9/11 wouldn't have happened. But it would be irrational to blame myself (or Velcro, for that matter).

  • $\begingroup$ You may drastically change the odds on 9/11 occurring as it did, but humans are more resilient to changes in the timeline than the weather, and you might find that you merely caused it to happen a day early, or a change in plans caused the attack to unfold differently. $\endgroup$ – Michael Sep 17 '16 at 20:16
  • $\begingroup$ It's possible that something similar might manifest, but not as we'd know it. $\endgroup$ – PCARR Sep 17 '16 at 20:25
  • $\begingroup$ @Michael "Humans are more resilient to changes in the timeline than the weather". I swallowed this statement whole but it's really causing me indigestion! It may be considered somewhat naive of me to think that a single person can burp at 0903 instead of 0904 back in 87' and affect the entire world's future outcome - but yet this is much easier to fathom for me. As each of us are characters 'playing a part' how could anything not completely change things? 9/11 easily preventable I say! $\endgroup$ – PCARR Sep 24 '16 at 11:11

Technology has improved so drastically and continues to do so at a faster rate all the time. One person by itself would find it very difficult to prevent the attacks...so I would find allies...with your cellphone you can show technology understandable but not possible to produce 16 years ago...find technologists in the private sector that would understand this, it will be proof of your assertion of future origin, once they believe that, they will believe the rest, then involve the government (FBI). By the way, guard your six...you do not know who might bring you harm...after all the enemy is committed and with ample financial resources.

  • $\begingroup$ The only problem with this is it buys credibility for your task of delaying these attacks, but it also makes you even more interesting as a time traveler. You care likely to "disappear" and be studied because of this and your knowledge of the future etc., by government and/or corporate agencies. $\endgroup$ – Dronz Sep 18 '16 at 4:42
  • $\begingroup$ David: This graphic novel about a time travler trying to prevent 9/11 takes a similar approach. She shows them her iPad. (The resolution is poor for the first couple of frames, but it gets better.) Note: This is a work of fiction and I do not claim that everything presented in this novel is historically accurate. Yet, it may be useful in some regards. What do you think? @Dronz $\endgroup$ – Revetahw Sep 18 '16 at 10:31
  • $\begingroup$ @Fiksdal I think only people with knowledge of that part of the computer industry would see a laptop without a keyboard in 2000 and think it must be from the future. The right future data on it could be convincing, but would be almost as convincing on a thumb drive. The problem remains that convincing people you are from the future is far more significant than the terror attacks, and will likely get you detained and interrogated for years by power-oriented elements. Sucks for you, but also you need to tell people who will do something about it - the FBI tried to warn people, with no effect... $\endgroup$ – Dronz Sep 18 '16 at 16:02
  • $\begingroup$ @Dronz Yeah. Like in that graphic novel. They thought her iPad was awesome, but they still didn't believe she was from the future. $\endgroup$ – Revetahw Sep 18 '16 at 16:10
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    $\begingroup$ @Fiksdal I liked the graphic novel...it has a painfully sense of realism...1 hour to stop the attacks...she might as well activated the fire alarms an effect evacuation policies...however, 1 year in advance presents interesting scennarios $\endgroup$ – David Sep 18 '16 at 17:06

It should be pretty easy to prevent the attacks as you have one critical piece of evidence in this scenario.

Head to the Pentagon. Explain that you are a time traveler and that you are attempting to bring warning of the 9/11 attacks. Think I'm a kook? Explain where I got this (smartphone). Nothing of the sort existed in 2000, they'll have to take you seriously.

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    $\begingroup$ Bonus points if you can remember the score of Super Bowl XXXV, or other notable events between September 2000 and 2001. But agreed, to someone who understands the technology the only way they'll think you're not a time traveller is if they find the very concept of time travel so absurd that they prefer to conclude you have secret chip fabs, access to unique battery and screen technology, etc. Butterfly-effect permitting, a few correctly predicted news events will ensure the skeptics lose the argument. $\endgroup$ – Steve Jessop Sep 17 '16 at 21:03
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    $\begingroup$ This just results in the Terminator scenario, where you get locked up and tortured as some psycho agent tries to make you tell them where you stole the new tech from, and writes reports about your fantasies about the future. $\endgroup$ – GreenAsJade Sep 18 '16 at 0:35
  • $\begingroup$ Loren Pechtel: This graphic novel about a time travler trying to prevent 9/11 takes a similar approach. She shows them her iPad. Note: This is a work of fiction and I do not claim that everything presented in this novel is historically accurate. Yet, it may be useful in some regards. What do you think? @Dronz $\endgroup$ – Revetahw Sep 18 '16 at 9:57
  • $\begingroup$ I debate still if the best strategy is to contact the military or the private sector. I believe access to key individuals in the private sector would be easier that on the military. Of course the military would be contacted, but you are in such vulnerable spot...if you loose access to the contents of your pockets, you could loose your edge. The military have to follow orders...civilians have freedom that the military do not. $\endgroup$ – David Sep 19 '16 at 12:34

If you prepare a detailed "schedule" of major events that happened that year and send copies to many news agencies and law enforcement agencies, most will throw it away and not be able to evaluate it. But maybe some will keep it and realize along the way that it has been "accurate so far."

A problem however: the less information on it, the less convincing it will be, but the more events listed, the more likely someone will take action on them, thereby changing what will happen, making your list less accurate!

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    $\begingroup$ Right now, from memory only, what major events do you remember between 9/11/2000 and 9/11/2001? $\endgroup$ – Edward Falk Sep 17 '16 at 21:10
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    $\begingroup$ Hey, I'm young enough to run my mouth and old enough to claim "senior moment" $\endgroup$ – WGroleau Sep 17 '16 at 21:57
  • $\begingroup$ Well, you probably do remember the election that year, and how close it was. There's a lot of detail there. There was also a stock market crash, but the worst of that came after 9/11 $\endgroup$ – Edward Falk Sep 17 '16 at 21:59

One year before the attacks, you have the opportunity to attack the attackers, or at least prevent them from being able to set the project up.

They learned how to fly in the USA. Through some concerted effort, you should be able to track them down and take some pre-emptive action.

There might well have been some back-up plan, but if you take out enough of the key players or do something to interfere with their plans, then the attacks would be prevented.

You don't have to take them all out, just one or two of the key players and the whole plan falls apart.

If you woke up on that day without knowing who the attackers were or where they were training, then you'd do what you could to affect how airline pilots were trained.


Yes. Just breathe. Or even don't; just be there. One year is a huge amount of time relative to the scales at which the dynamical systems behind the world are chaotic. A single change now in a single air molecule will yield a one-year-out future that looks nothing like "before" the change.

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    $\begingroup$ Which just means they will be the September 10 attacks... or October 20 attacks... or the attacks that actually succeeded in taking out the Capitol or the White House. Changing history does not necessarily mean "changing history for the better". The Butterfly Effect just says that some things will probably play out very differently. But it does not mean that a person that is very determined to do something will not succeed in one way or another. $\endgroup$ – MichaelK Sep 18 '16 at 6:58
  • $\begingroup$ All sorts of things had to go "exactly right" for such a coordinated attack to actually work out. You're right that "changing history does not necessarily mean 'changing history for the better'", but this applies to any solution whether it relies on naive time travel cliches that ignore chaos or something more sophisticated. $\endgroup$ – R.. Sep 18 '16 at 15:24

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