Time travel

When someone travels through time, they are able to screw their grandmother before they were even born. A phenomonen known as Doing the nasty in the pasty.
This happened to Julian Bashir when he traveled backwards in time to meet his grandmother. He did not screw her, and when he returned, he found out he was never born. But because he was never born, he could not have not screwed her, and thus could not be born. therefore he was born so he could go back in time to not screw her.
:We're not sure if this is what Wells had in mind; Heinlein, perhaps.
== Throughout the Series ==
Every. Single. Person. That has been a recurring cast member on any Star Trek series has traveled in time. Time travel can be accomplished several ways, some much easier than others.
*Go warp lots, then make a quick u-turn around a star or something with a sufficient gravitational pull. Any ship better than a shuttlecraft can accomplish this, but you need good math skills to arrive in your desired timeframe. Doing this all willy-nilly will result you crashing into a field in 12th centruy Japan when you were aiming for 19th century Michigan.
*Go take a visit to the Guardian of Forever. He's a nice, sentient time portal and he's always perfectly willing to send you to any year you want. You just have to do a dramatic "leap" when going through him, 'cuz he's theatrical like that.
*Wait for another time-traveler from the future to show up. Trust me, this is common enough. Everyone after the 25th century can get their hands on time machines like they were toasters, so you can just ask them for a lift once they arrive. Or you can steal their time machine, either way.
*Get a ship with a cloaking device and make your starship invisible. Once it is, lob a bunch of dangerous or unstable particles at it and eventually a build up will alter transporters and you'll be able to beam people through time. Just remember to cover up your crewmen's funky alien noses with bandages!
*Ask Q or any of the dozens of the other omnipotent, non-corporeal lifeforms on file in virtually any galactic database. They might make you learn a valuable moral lesson on your journey, but consider that as cab fare.
*Contact Dr. Sam Beckett of the NX-01 Enterprise. Tell him Al sent you.
*Steal the all-powerful relic of an advanced race of aliens that are so far beyond us they don't even understand time. You'll be free to plant all the bombs in all the Tribbles you want then. Be obligated to laugh at the irony that the Cardassians had this thing in their possession for years (YEARS!) and were too dumb to use it. Stupid spoonheads!
*Go park your starship in a normally empty area of space. Within two weeks a funny Spatial anomaly or anomaly will open and there's a better-than-average chance it will allow travel through time. Seriously. Happens to that Janeway all the time.
*Ask that Klingon from Star Trek III to borrow his DeLorean. Once you get that thing to warp 8.8, you're gonna see some serious shit.
*Wait for the Borg to open a portal in time and just follow them through it. You lazy fuck.
*If you are too lazy to even do that, you can just sit on your ass to travel forwards in time. While rather slow, you will actually be able to watch events as they unfold, preferably with a nice glass of romulan ale in hand.