So, there I was, in the library basement, looking through a dusty copy of the 1768 Encyclopedia Britannica, and out slips this sheet of paper dated October 6th, 2001. Of course, nobody had been down here in years....
Perhaps you've been tinkering with palladium reactors and tesla coils and you've finally put together your time machine. Or maybe you bought one, whatever. You're ready to become a time traveller and embark on an exciting journey through history, but you're not quite where sure where to start, what to bring, and how to get back alive. Well, you've come to the right place.
A Few Words on the Nature of Time
I'm not a quantum physicist, and chances are that you're not either, so I won't go into details on those matters. There are a few things that you really need to know, however. There are multiple timelines. Imagine history as a tree, with new timelines branching off at different points. When you go back in time and change something, you don't affect your home history at all, but rather create a new one which diverges from the old at the point where you enter.
It should be noted that any timeline which you create will eventually diverge from the original. A minor change in the present can result in a major change in a century. The upshot of all this is that if you travel a century into the past and back, you won't be in the same place as you were when you started. This also means that if you travel into the future and come home, you won't be able to visit the same future again.*
This problem can be avoided if you use recall boxes.
Your First Trip
You should not start out by travelling into the past, unless you never want to come back. You can try to win the lottery, but you can't count on it - the most digits I've ever been able to win this way is four. The first thing you should do is travel into the future and purchase a more advanced time machine. You'll need radiation shielding, and something to trade. Time-travelling civilizations won't pay much for antiques. Precious elements are ideal.
Send yourself to about 2200 CE. This is really the ideal time for purchasing time machines. If you go much earlier than this, you're not likely to be able to find a time machine, and if you show up much later, you'll discover that nobody wants your trade goods.**
About two times out of three, you'll arrive to find barren wastelands and glassy craters. This is what the aftermath of a nuclear war looks like. Chances are it happened about a hundred years ago, so you're safe if you remembered your radiation shielding. You should go home and try again.
There are two main types of time machine: machines that you carry, and machines that carry you. Each has its advantages. A machine that you carry is small and inconspicuous, so you can walk around with it wherever you go, but a machine that will carry you can fit a great deal of supplies. You are likely to get into trouble if you drive around in a shiny hovercraft during the middle ages, so unless you are planning to field an army, you'll want to hide it somewhere. The problem with this is that if you get into trouble, you won't have a panic button to bring you back. I use a backpack. I once met a man who had a time machine built into a stylish platinum bracer, but I could never afford such a device, and it's unlikely that you could either, unless you're J.P. Morgan.
Your time machine should come with several pairs of recall boxes, or whatever the people there call them. Recall boxes come in pairs which are attached. Boxes from 2200 CE vary from about 6 to 15 centimeters on a side, and smaller boxes will be more expensive. Boxes from the far future can be as small as a single centimeter, but are difficult to purchase. Your time machine should have a number of places to attach or insert them. Find a safe place and break apart one of the pairs. Leave one box there, and attach the other to your machine. You really need to be careful when deciding where to leave it. If somebody throws it away, you might hit your panic button and materialize in a dump somewhere, beneath tonnes of garbage. Of course, you can rent a booth if you have the money, and leave it there.
It's important to leave a recall box in the period where you purchased your time machine, because it's the only place anywhere to buy boxes of the right dimensions for your machine.
Supplies
You can keep making trips into the future if you want, but most travellers prefer to explore and alter the past. There are certain supplies that you'll need.
You need a gun. A pistol will probably be enough, but an assault rifle is better if you can acquire one and you're willing to carry it. If you're going to periods that already have guns, you'll also want kevlar. Some people prefer to carry weapons indigenous to the times and locales they are visiting. Don't do it. That is a sure-fire recipe for disaster. If you get into a fight, you need to win. A samurai warrior will be more skilled with his katana then you will ever be. Line him up and pull the trigger, and he'll go down.
You need a first-aid kit, and make sure to get all your shots before you go, even if it hurts really bad.
You need a Swiss army knife or some similar product. You should also have duct tape.
You should bring a small book about the culture you're visiting. Try to learn a significant portion of their language before you go, but bring a dictionary anyway. Also, hold onto the manual that came with your time machine.
Some people like to bring calculators, scales, rulers, and similar implements. If you want introduce science to primitive folk, you can try, but it won't be easy.
Where not to Go
Don't go anywhere where you won't be able to speak to the natives. If you really want to go to Sumer, first try a slightly more recent period and see if the scholars there can teach you the older language.
Don't go more than a billion years in either direction without proper protection. If you're not certain about conditions at your destination, assume the worst. You can always take off your pressure suit when you get there.
Well, that's about it. You're ready to go zooming through time. Don't forget to floss.
* Clever readers will notice that this explains the question of why, although time travel is possible, we don't see folks from the future popping up everywhere. As soon as a traveller from the future enters the present day, he will create a branching timeline which will not contain his society. In most futures, nuclear war occurs before such a society can evolve.
** Note that advanced civilizations can't manufacture gold economically, but simply tend to place less value on it.
All your base are belong to us.