I've worked on the same problem and came up with the same solution. My password was "Teapot Dome" from 2016-2018, and it's been "Cottage Cheese" since then. I have just come up with a new password, which I obviously won't share.

This solution doesn't actually work. Maybe the people are mind readers rather than time travelers. Maybe they beat the password out of you and then wiped your memory. Maybe they are time travelers, but it's like Groundhog's Day rather than Back to the Future and they've guessed ten billion passwords until getting it right. Maybe they have an Infinite Improbability Drive and just got really lucky.

Your test can prove that something funky is going on. It can't prove that the something funky is time travel.

Also, let's presume that some dinosaurs in the past were really smart, and evolved some thinking skills before the asteroid wiped them all out.

They just so happened to evolve the same scheme. How do you prove to them that you're from the future?

I climb back into my cardboard box (with "time machine" scrawled on the side); jump forward 1 year, ask them what last year's temporal password was; go back one year and tell them.

Did it work?

This has a big flaw. If the future visitors copy all passwords to a usb stick and take it with them then anyone in the present time that gets a copy can pretend to be from the future. Worse still, everyone would believe the phoney future visitors without question.

It would be good enough to know that there is at least one person somewhere who is actually from the future.

Yes but on that case the earlier suggestion of just asking them for a stock market prediction would be good enough without implementing the password system.

But then you have to wait for the stock market prediction to come true. Instead, since you already know your temporal password for the year, the proof would be immediately available.

Tomorrow's close should be good enough. Preferably for a mix of stocks or indices.

Yes tomorrow is okay

I'm pretty sure no-one from the future will have a way to plug his/hers mini-USB-XC or whatever the usb name will be at the time in the future (USB standards are just a mess).

I would expect a future that still has a copy of these passwords to be highly likely to have copies of the relevant standards.

I think you just found yourself a business opportunity :)

True. They would need to burn to a CD :-D

Do you think they'd still be using USB drives and bothering to keep track of antique passwords in the future?

If it can happen, it will happen, all you need is a sample (in this case: number of people who know about the time traveler) large enough.

There's a few reasons for that, including avoiding anachronisms for aesthetic purposes.

Time machines could be invented in the near future. In fact I am wholly unable to say one hasn't been invented already.

You may need to get an old usb stick from eBay. The good news is that they probably would be selling for quite cheap.

Unless they're priceless antiques of an age long gone and sell for millions of inflation and future currency exchange rate adjusted dollars

That’s a very good point.

Time travel and democratic governance are mutually incompatible.

Also lotteries.

If the time Travelers came from the past instead of the future, the password sharing is useless.

maybe they have jump [1] from the past after doing a change that alter your present (their future) trying to fix the future (your present).

[1] https://visual.ly/community/Infographics/entertainment/back-...

But we know that is very possible to do already, via relativistic effects.

Why commit passwords to memory and build Temporal Password Registries if we can throw parties which no one attends?

https://vinepair.com/articles/stephen-hawking-time-travel-pa...

Didn't we conclude time travel is unlikely?

With the knowledge of the current pandemic situation, perhaps the concept of 'party' and/or 'invite' is a wholly alien concept to the people of the future with access to time-machines. And assuming a similar reaction to current archeology for things they can't explain better than 'artifact was used during religious or reproductive practises' and didn't consider attending.

Exactly. Luckily a solution has long been found. Simply take a log of the stock market back and then pay me a billion dollars to convince me.

(also you could predict variations in the rotation rate of galactic pulsars. That would be pretty convincing for scientists. But who cares about those guys ?)

How do you know they are not just good mind readers instead of time travelers?

Maybe you could use a tamper-evident security token along with the password. Could be as simple as a fortune cookie. Keep it safe and crack it open at the end of the year to write the fortune next to your password. In the case of a probable time traveler who tells you your password, challenge them to tell you your fortune and open it afterwards to verify.

Need passwords greater than 4095 characters :)

What if the visitors are from November of this year?

Unfortunately they wouldn’t have access to the registry. But with enough determination, they could still brute force your password by returning repeatedly

Couldn’t they just tell you tomorrow’s stock prices? Or a future sports score.

As the PROBLEM statement says:

> it would be difficult for them to quickly prove their authenticity

Yes, you could tell them something that happens tomorrow or the next day. But if time is of the essence and you can't wait until tomorrow, then the Temporal Password helps you _immediately_ demonstrate your authenticity.

They have a time machine. How can time be of the essence?

No more Pym particles.

What if we generate a random number every, say, 5 minutes and maintain a log of them along with their timestamp. Then the time traveler could just look up a few entries immediately after their destination time and convince people by predicting them in advance. Not immediate but pretty quick.

The hash of the next bitcoin block can already be used for this. Easy tamper resistant random number every 10 minutes.

Wouldn’t the butterfly effect change the numbers? If not then the numbers need more entropy and less pseudo.

That would probably break the rules. With the password solution, they're not telling you anything you didn't already know.

What rules? They’re telling you time travel is possible and happens. That’ll be news for me.

Somehow all time travellers seem to guess that my codephrase is password[current year].

Could just bring along a future copy of the bitcoin blockchain, though as a downside that would potentially give away other information about the future (what people become rich, etc) they may not wish to divulge.

What if the time traveler arrives today and tells you - as gently as possible - that he doesn't know your 2020 password because you didn't (technically couldn't) communicate it on Dec. 31 2020?

I guarantee you I'm going to forget a password in 12 months if I never have to type it in anywhere or use it on any regular basis.

Can I please come up with my password and submit it to the Temporal Password Registry immediately -- and just have it "go public" on December 31 of that year? It'd also be a nice way for me to check back in throughout the year, logged in as me (the only person who should be able to see my password for this year), just to verify what I thought was the password was correct... in the event of needing it.

That makes hacking the registry an obvious step to convince someone you're a time traveler. I wouldn't trust a scheme with that weakness.

There's also password managers. But with all this Apple clipboard non-sense, I don't know if it is safe to use one.

Time travelers would need to be time and space travelers as earth and solar system move perpetually and their location would be different between time spots in space.

The space-time continuum stays the same. So the time travelling device (if it’s a decent one) should automatically compensate for this.

Hmm. Couldn’t they use isotopic analysis to determine where and when someone grew up? Would this also be robust across different planets (if that becomes a thing)?

There could still be the possibility that the person claiming to be the time traveler is just someone who managed to hack into your computer memory.

I mean if this happened to me, my first thought would "who is this person and how did I got hacked?" which seems way more likely than being visited by someone from the future. Would prefer to wait for a confirmation such as telling me about what would happen on the next day.

Wouldn't it be easier for them to just tell you what the Dow Jones Industrial Average will close at the day of their visit. If that's not convincing enough, they could do it for two or three days in a row.

Their arrival may change it!

I thin it would be better to generate every day a new random password, and publish it automatically (no wait). So no one can "hack" your memory or the system you use to generate it.

The typical plot device is that they predict published events for you. News, horse races, weather, stock prices, direct quotes, etc.

The technology used to time travel would be present in any situation, right? Seems like that's your clear and instant evidence.

Isn't it enough if they predict (know) the next lottery numbers?

It wouldn't work provided that how vulnerable passwords is nowadays.

I would instead tap into blockchain technology. For instance, to generate blocks for each passing seconds/minutes which randomly ties your UID to a random user. A decryption will be provided to you in 1 years period, i.e. in 2021, you will receive a hash key that will help you decrypt your blocks in 2020. You will get the exact time now if you decrypt the block. That way, by the time you get the keys, the locks will already be deprecated, unless of course you time traveled.