"[...] the ship that made the Kessel Run in less than 12 parsecs." - Han Solo about the Millenium Falcon, Star Wars Episode IV.
You may now already know that a Parsec is unit of distance, not time, in astrophysics, derived from Parallax and Arc-second, is the distance a star needs to be from the Sun so it's measured parallax is 1 arc-second across, which is roughly 3,26 light-years.
I bet you may be pretty well fondled with the idea of pulling a lever and the background stars starts to trace and blue-shift in front of your eyes like on Star Wars...
Or even Startrek...
That blue-shift is wrongly placed xP
...AND HERE WE GO!
There is always something those movies and games depict right and horribly wrong about FTL or Faster-Than-Light travel.
1. Blue-shift/Red-shift
As a police car rushes near you with the sirens on you may notice that the sound have a higher pitch than when the car is running away, or the more common case, when a plane crosses the sky it is more noticeable. That is the Doppler effect, any waves from a moving source get compressed on the front and stretched on the back, sound-waves gain pitch when the object is approaching and lose pitch when it is going away.
Stars suffer the same with light waves, but we perceive the difference in the wavelength as a shift in the star's hue. Moving towards us, blue-shift, moving away, red-shift.
If you are moving pretty fast among the stars, they would blue-shift in front of you and red-shift as they go behind you. And you can calculate the amount of shift with a given velocity by:
(λ-λ0) / λ0 = v / C
λ - Is the wavelength you measured.
λ0 - Is the natural wavelength.
v - Is the source speed.
C - is the speed of light.
For example, if a green-painted ship at 550nm is photographed by a stellar speed-trap as being 450nm, then the ship is blue-shifted (smaller wavelength) by 100nm (|450 - 550| = 100), given the system knows the ship is originally 550nm colored, the speed at what the ship is going is 0,18C (100 / 550 = 0,1818), ie, ~54.540km/s.
Or if you want to know what color your green ship looks when running away at 0,5C, multiply the original hue by the speed in C, 550*0,5 = +275nm, since we are considering the ship is red-shifting away from us, then the apparent color is black at 850nm infrared (550+275=850), if other colors are available like white hull, it's overall color-temperature would be similar to an object at 3.132ºC.
By the way... Cover your eyes!
It is not just a visual depction, the crew of any starship close to the speed of light shouldn't be allowed to peek over a window, naturally unharmful red-light can be shifted into harmful UV light, and UV light into Xray and Gamma Rays, any light coming from outside might be deadly ionizing and should not be appreciated.
2. Methods
WARPDRIVE
Although it is impossible to surpass light in a race, it is virtually possible to change the space rules to favor you, like bending space-time so you can surf around with ease, Warpdrive, like the difference between pushing a block in the rough street, and then pushing a block in a soaped board, you didn't change any physics in the system, you didn't changed the force so the block slides more, or the mass of the block, you just reduced friction between the block and the surface.
SLIPSTREAM
A great idea in the Halo series is the Slipstream realm, a section of space-time with different "friction" than our normal space, if with 100GJ you can only accelerate your ship up to 0,0001C (30km/s) in normal space, in Slippy-stream (maybe an internal pun) you can use that same amount of energy to move at 0,01C, and yet exit in a very distant point of space, like 10Ly away by only moving 1AU in the slipstream space, distances in the slipstream realm are not changed at all. This kind of concept works well, if we compare normal space with running in a water tank, and slipstream space travel with running in the beach where the air offers way less resistance to running yet under the same physics like gravity and friction, how you would achieve it, it is up to you.
EINSTEIN-ROSEN BRIDGES
Using worm-holes is a great idea as well, in fact many authors may opt by using a mix of wormhole tech to access a kind of slipstream dimension, wormholes or Einstein–Rosen bridges, are in a few words, tunnels that connect two points in space and time, like a tunnel leading from the Moon's orbit to Saturn, ~76 light-minutes away in the past from Earth's perspective. The only problem is that gravity tends to always close the wormhole, traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them, somehow you need a way to get it.
BLACK HOLE STARSHIP
Creating a series of super massive Kügelblitzes in a controlled ambient ahead of the ship may work, such a tiny black hole may not warp you lightyears ahead, but making them with a tenth of your ship's mass and in a sequence may do, given that when you are already in movement it takes less acceleration to add the same kinectic energy as before in the same direction (Oberth Effect), project the kügelblitz behind your ship to reduce velocity.
EXTREME GRAVITY ASSIST
I personally like Hohmann Transfers and Lagrange isles, not FTL but also not an outlandishly complicated topic, is just using the way gravity works in order to save fuel.
Imagine any given orbit around a body as a staircase, you need to make a first step, you achieve orbital speed 400km above the ground at 28.000km, but your goal is to orbit at 10.000km from the ground. According to Newton's cannon and Kepler, if I push a little further my orbit trajectory will become more elliptical, I will push the ship's aphelion further away while maintaining my perihelion, once at the aphelion of my orbit I can turn the thrusters on again, and lift my former perihelion so it matches my new orbit 10.000km away from Earth, or keep it on so it orbits the Sun instead, using the Lagrange points between the Sun and the planets as gravity-free highway you ignore the sun's pull on your ship what saves lots of effort, you can correct courses using marked asteroids which serves as street signs for "turn around to Jupiter this way".
If you are asking yourself where does interstellar travel goes here, imagine dropping your ship freefall into the Sun right from Mercury's orbit, now, that wouldn't be actually possible but very hard given you need to lose velocity to fall into the sun, but it is not true at all, Hohmann transfers outwards can give your ship an elliptical orbit that you can sideway thrust towards the sun every turn, two or three turns may be enough to approach your ship as close as 1/10th that of Mercury's orbit, and use the Oberth Effect to slingshot out of the Solar System.
And you can extrapolate the method to orbit black holes, by dropping an asteroid payload and receiving kinectic energy and slingshot out of it.
Or either accept it will always take centuries to go the next star and back to Earth like in the Alien series...
- M.O. Valent, 11/07/2019
