Deeply sorry that i havent been around much in the past month and a half. way too long of a vacation.
anyways, i havent read the last oh 200ish posts because of time, so forgive me if i have revived older info.
ok, i have read a post earlier somewhere about anti matter as power. several problems: the cost of making anti matter is around $1,000 trillion per ounce
(currently), and when matter and anti matter annialate, most of the energy is either lost as high energy gamma ray radiation (which you need heavy shielding from that), doing little to propell the ship, or as neutrinos, that escape from the system without doing anything what so ever. and then the magnetic field used to channel the exaust is leaky, so more losses are taken. even so, it is possible to obtain 30% light speed because of this after taking in the losses and stuff.
a better idea would be a photon rocket, using the same anti matter ideas, except you only use the light energy generated, instead of the actuall explosive force of matter and anti matter being turned into pure energy. like anti matter, the magnetic field is also leaky, so using this, 50% light speed is possible.
for magnetic sails, devised reletivly early (forgot the date) uses a magnetic field to catch hydrogen in the intersteller wind and use fusion to generate power. in theory at the time, it was capable of going to nearly light speed, but in practice, bad. the reason is that proton proton fusion is about 10 fold more difficult that the tirtnium deturnium fusion that humanity is struggling with, and the magnetic field provides more as a brake than a way to get fuel. but it makes the best brake avalible.
to improve on the solar sail idea i had earlier, we can build a big laser, point it at a star that we want to go to, and unfold the solar sail. with an out put of the equivilent of the sun at .45 AU, the laser would need something around 240 Terrawatts for 6 months. or about 20 times electricity humanity generates in a year. so with this, assuming the sail is .001 microns thick (about 4 atoms) with a radius of 343 km, and with a 1,000 tonne space ship, 30% speed of light is obtainable. one problem: you must use a magnetic sail to stop.
also ideas for tech age 4, we can use picotechnology, which is something like nanotechnology, except it is thousands of times smaller, and gets it's energy from nuclear instead of chemical power. what it can possibly do is considered magic from our perspective (something like showing a gun to a neanderthal).
from what info i managed to deprive from my friend, we can possibly use the 10th dimension to help us travel faster. an example is: say a sheet of fabric is shaped like a dounut, and a person living on the 2 dimensional fabric wants to get to the other side. he/she must go around the inside to do it. but if they can travel into the 3rd dimension, the trip would me much faster. so for the tenth dimension, every single point in space time is at the same point, so traveling from point a to point a requires zero time. but the entire dimension is smaller than an electron, but acording to my friend, it is possible to use the 10th dimensional forces to shrink the ship, get it into the 10th dimension, pick your destination in 3rd dimensional space, and use the 10th dimensional forces to enlarge your ship, and falling out of the 10th dimension back into the 3rd dimension.
more information: for the best energy mass ratios possible, and the best exaust efficient space craft possible
anti matter: 30% light speed.
fusion: 10%
fission: 2%
chemical: .2%
EDIT: since of the high energies involved with all of these types of transportation, a space ship's engines count as weapons of mass destruction.
and ring worlds and dyson spheres are just too hard to build to ever become possible. (you need to melt venus to get enough material for a ring world and you need about 300 years of the sun's out put to get enough energy) and dyson spheres, there just isnt enough solid material in the solar system to work it with the requirement of 240 earths worth of material (try building it out of hydrogen)