455

Stop one ship from either sailing into a storm or (later) being taken over by pirates. In 1793, Thomas Jefferson ordered a set of instruments from France that would let the US calibrate to SI units, but the ship hit a storm at sea, blowing his ship into the Caribbean. There it was attacked by pirates (British privateers). The materials never arrived. By the ...


130

Go back to the cold war era and start a "Russians are trying to warm the planet" scare. You will need a lot of money to fund some big advertising campaigns. You also want to seed a few specific technologies like nuclear and solar power to try and push them along. Let ignorance and paranoia work towards the betterment of mankind for a change. It's ...


129

There's an old fashioned option You can't travel back in time to a point before the invention of the first time machine. That means of course that the first person to invent a time machine couldn't travel back in time to point before his own invention, and possibly initially thought it didn't work, which is true for a given value of true.


117

If they are just bringing the drives, and not the attached computer, this is pretty much impossible. The infrastructure simple isn't there in 1300 to refine anything to the necessary purities to even begin manufacturing microprocessors. See this answer to get an idea of how hard this is to do: How long would it take to create a Windows 1.0 capable machine ...


108

A previous time machine crashed and exploded on August 12th 1941 during a test flight. Maybe sabotage or a design fault. The explosion and shockwave will exist forever at that point in time. The explosion acts like a reverse black hole. The closer you get to the point of time of the explosion, the more power you need to bypass the shockwave emanating from ...


67

The printing press is not what Gutenberg invented. The printing press itself was known in Europe since the High Middle Ages at least, and in China even earlier. He did not invent movable type, which was also known. As for the "mechanization skills" needed -- printing was the last of the basic industries to be mechanized. Printing remained extremely labor-...


58

Hard Drugs Never Hit the Streets The beginning of the end for the mafia was when drugs came involved in mafia business. The mafia made a pretty tidy racket doing some rather laughably mundane things prior to the hard drug trade. One such racket was stealing tanker trucks full of gas and using them to refill mafia owned gas stations. The gas stations would ...


56

You need to know where the Earth is. If you think about it, the Earth is spinning around the sun, in a spinning galaxy in an expanding universe. If you just headed back in time, you'd appear in the void of space. Not only do you need to know when to send someone, you also need to know where. To have a limit on how far you can go back, your time machine has ...


56

Pre-emption is the best prevention There is no way to do it with 15th century technology. But. The best course of action is to pre-empt the epidemics by running them early. Use your time traveling saucer to kidnap some flea-infested bug-ridden mangy European and Chinese serfs in the 5th century, and drop them in the Americas. The epidemics will start, lots ...


53

It's hard to come with a single method that both works when you have 5 minutes in a dense forest, and 5 days in a city. But here are some ideas: Find out who the current pope is. Locate a graveyard (or a church with in-church burial), search for the most recent date on a tomb stone. Search through church records (weddings, burials, baptism) for the most ...


51

There are no paradox concerns. Your system prevents modification of the past, so there is no way to cause changes which would lead you to not go back in time, or go back in time differently. Your system cannot see into the future, so you cannot see the effects of your actions and act differently. Really, it's more of a VCR than time travel. You can go ...


51

But we do all run on steam All (non-renewable) power plants are steam driven. Even nuclear power is a glorified steam engine. What we don't do so much any more is drive directly using the steam, it's now a stage removed from the effect. The steam drives the turbines to generate electricity that drives your machines. As soon as you swap to an electric car, ...


42

I think there is a major flaw: Since there is no fast forward, you could never catch up with the present. For everyone else, time moves forward and you are always behind. Unless triggering the time travel freezes time for everyone else.


40

Euler Euler was a brilliant astronomer, but unfortunately he probably wouldn't be able to get a job in modern astronomy without a college diploma, much less without a high school diploma. He was also an excellent mathematician, though, and I think that is his best bet in the modern world. It seems likely that Euler would find a job as a programmer (once ...


38

The thing is the massive amount of energy. Sure you could go back and collect iron, coal, oil, etc but is it worth the expense? Raw materials can be collected from space by asteroid harvesting and the energy to rip a hole in the fabric of time/space just to mine I suspect will be far greater than asteroid mining. Now where you make your money is collecting ...


37

If you're willing to accept that the machine (as in this specific apparatus for time travel; not as in any apparatus capable of time travel in your universe) cannot travel further back in time than some specific amount of time, rather than to some arbitrarily selected date, then there's an easy option that might even make a modicum of sense scientifically (...


36

Bring the Tools, not the Weapons The hard part here is getting the precision tooling you will need done right. Rifling a barrel and pressing ammunition is pretty darn hard without the right equipment, but all the tools needed to set up a fire-arms and munitions workshop take up surprisingly little space. Since he has enough wealth in the 21st century to ...


35

Search for some money: coins were made according to the reigning king, they might give a fair estimate for the period you are in. If you are in a major city, take a look at the most recent churches or religious building. Their architectural style can hint to the period. Search for potatoes, corn and tomatoes. At least you can tell if you are before or after ...


34

Quite obviously, the only way to read SSDs in the 14th century is to bring a computer. Or, actually, several computers. With great care, the computers will last for some twenty years, in which time one could hope, with an extraordinary amount of good luck, to push technological progress up to the 17th century -- you know, printing presses, telescopes, ...


33

I think the knowledge would simply be lost in time unless they actually have use for it. A tribe of post-neolithic settlers have very little use for differential equations and stuff of that level. And even simpler stuff like linear algebra would not be helpful to them. Basic math is easily applicable in everyday life. Even in simple non-currency-based ...


33

The mad scientist sledgehammer option for this particular nut. Kill a very large slice of the world population. It worked when Europe colonised the Americas, so many natives were killed it actually changed the global climate. America colonisation ‘cooled Earth's climate’ He travels back in time to the height of the cold war at its most unstable & ...


33

Antoine Lavoisier should not have been executed Lavoisier's importance to science was expressed by Lagrange who lamented the beheading by saying: "Il ne leur a fallu qu’un moment pour faire tomber cette tête, et cent années peut-être ne suffiront pas pour en reproduire une semblable." ("It took them only an instant to cut off this head, and one ...


32

The simplest way would be to limit the machine's range (see Asimov's classic Chronoscope). But this way you wouldn't have a "precise start date", as the start date would move forward in time. You could have some strange mechanism by which the range extends gradually backwards - each day, you can reach exactly one day farther in the past. So the farthest ...


30

You have a whomping big paradox You stipulate that the traveller "cannot change anything that happened to [he/she]." That's a problem. You can jump back and relive time, but you can't change the fact that you jumped back to relive time. You'll never live another second of free will at all. Let's investigate this. Assumption Let's ignore the entire is-...


29

Had the Metric Conversion Act of 1975 been drafted differently, with concrete milestones and requirements, and an intent not just of adoption of metric units, but adoption of existing international standards based on metric, it might well have been the turning point. Having lived through that period, I believe the most significant factor was that it ...


29

First people need to understand how relativity works. There's a thing called proper time which we regard as an interval between two events or points in spacetime. In "ordinary common sense" space you define the distance (the interval) like this : $$s^2 = (x_2-x_1)^2+(y_2-y_1)^2+(z_2-z_1)^2$$ That's the square of the distance between two point. Time (and ...


29

Unless he's an expert metallurgist the biggest issue you're going to have isn't in terms of producing the parts; anyone with a drill and a hand file (or some rocks that will serve the purpose) and enough patience can make a gun from a solid block of appropriate metal and therein lies the problem. Modern weapons require modern alloys, many of which are ...


28

Euler Euler's interest in stellar paths would transfer well into being a bus driver. "I've charted paths through the heavens! I can certainly memorize the rout of your carriage." Newton Newton's expertise in Newtonian physics would make him well suited to building demolition. He was kinda scrawny, so he'd perform well as the guy operating the wrecking ...


25

I know too little of the internal US affairs, but let's take a wide swing. Help Napoleon A paramount thing in making Napoleon I lose the war was the attack on Russia 1812 that eventually lead to the first defeat of Napoleon's forces by the allied forces. Notice UK being part of the coalition. Some time before, however, Napoleon was seeking alliance with ...


24

They cannot "just bring SSDs" - they need something to read it with. The simpler, the sturdier, the less energy-hungry, the better. Actually they don't need SSDs, they need memory. The main things they have to worry about are, roughly in order: theft and confiscation. They have no guild, no home, no patron. They have no servants or guards. For the ...


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