As of today we have no engine or rocket that would be able to traverse our own solar system, much less our galaxy. 1 light year is a speed of 180k and change MILE per SECOND. That being said, your own galaxy, the Milky Way would take approximately 120,000 light years to cross. So, as we stand we are stuck travel wise speaking in terms of interstellar or intergalactic in a lifetime. The most feasible and probable concept out there is being able to accelerate to 1 G, 9.8 m/s, same as you know it here. Your destination say if going 10 light years away, would consist of accelerating to 1 G for the first 5 and then decelerating for the second half to arrive at your destination. In our first fact we will use a distance of say going to Jupiter:
**The difference between if you decelerate or not is if this is your destination or a just a beautiful view in passing.
Closest to Earth: 588 million km
Travel time (at 9.80665 m/s2, no deceleration): 4d 0h 11m 2s
Travel time (at 9.80665 m/s2, decelerating halfway): 5d 16h 2m 2s
Credits: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt
But, here’s where the catch 22 so to speak comes in. If we are to truely want to do interstellar vs just inter planetary, you will be giving up your life in just about all occasions. That’s becuase you now are going to be apart of whats known as time under the Theory of Special Relitivity. So, interstellar travel at 1G would take approximately 1 year + the distance in lightyears to our closest star, Alpha Centauri.
First, assume 1g acceleration from Earth halfway to Alpha Centauri and then 1g deceleration from there to the target. Total distance: 4.3 light-years. Due to time falling under the laws of special relativity the difference in time measured aboard the space craft vs home on earth is this:
Ship time: 3.6 years
Earth time: 5.9 years
Image credit: NASA/Penn State University
http://www.eso.org/public/images/colosimo-130704-011
As you may think and problably are, the longer the ship travels round trip, the longer the time gap grows between those traveling and those at home. Lets take another example, this time, a 20-year round trip for the space craft (5 years accelerating, 5 decelerating, to the destination and then back home) will land the ship back on Earth having travelled for 335 Earth years and a distance of 331 light years............a difference of 315 years people. You are not even guaranteed to return to an Earth that habitable, or even still there. Even society itself could have collapsed and found Earth in almost a dark ages again if you will. That’s neither here nor there tough, there are infinite what ifs, but one thing stands constant, your life you left behind, will no longer exhist. Your family, your friends even the enviroment in which you departed from will most certainly be gone and will be different. So you may travel and safely return, but whether you return or not, you still have lost a life once had. This is just interstellar travel may I add, not galactic travel.....As humans, if we find ourselves holding such technology in the future, we will again become a nomadic species. Traveling to great distances to expand our reach. We as humans, all of us, come from nomadic people, its just where and when we laid down roots if you will. We could actually reach another galaxy traveling at 1G within a human life time, our closest neighbor, The Andromeda Galaxy. To reach it going 1G would take about 60 years aboard the space craft, but as time on Earth ticks, 5 million years will have surpassed..........5. million. years. Those who chose this path will be the ones who carry on our species. The ones who not only represent it, but maintain, nurture and grow it, because Im really not thinking the Earth, or at least our species on Earth will be all aces. Mostly likely, our species we will cease to exist anywhere except for those traveling abroad. So I will leave your with this, if we do indeed find ourselves confronted with this situation during humans time on Earth, the crafts that we sent out abroad to the explore unknown and answer timeless questions, ships first launched interstellar starting mans adventure and exploration of such may actually be carrying out two missions. The first is certainly whats aforementioned, but throughout the exploration of interstellar travel, thanks to what physics allows us to do such, Special Relativity, actually is a double edged sword an these exploration ships may and will transition also into a life rafts of sorts. The last of our species, hurdling through space and time, hopefully on course with a destiny that will allow us to, well exhist.
A table below will further show you the time vs travel examples.
