What if we can travel between distinct galaxies?
Updated: Feb 15
Firstly it seems like a very hypothetical concept. Due to the enormous distances between our own galaxy the Milky Way and even its closest neighbours—tens of thousands to millions of light-years—any such venture would be far more technologically demanding than even interstellar travel. Intergalactic distances are roughly a hundred-thousandfold (five orders of magnitude) greater than their interstellar counterparts.
The technology required to travel between galaxies is far beyond humanity's present capabilities, and currently only the subject of speculation, hypothesis, and science fiction. However, theoretically speaking, there is nothing to conclusively indicate that intergalactic travel is impossible. There are several hypothesized methods of carrying out such a journey, and to date, several academics have studied intergalactic travel in a serious manner.
According to the current understanding of physics, an object within space-time cannot exceed the speed of light, which means an attempt to travel to any other galaxy would be a journey of millions of earth years via a conventional flight. Due to the distances involved, any serious attempt to travel between galaxies would require methods of propulsion far beyond what is currently thought possible in order to bring a large craft close to the speed of light. Manned travel at a speed not close to the speed of light, would require either that we overcome our own mortality with technologies like radical life extension or travelling by a generation ship. If travelling at a speed closer to the speed of light, time dilation would allow this kind of travel in a timespan of decades of on-ship time.
Even though there are certain theoretical and hypothetical ways to travel through galaxies.
Time dilation: A slowing of time in accordance with the theory of relativity that occurs in a system in motion relative to an outside observer and that becomes apparent especially as the speed of the system approaches that of light. While it takes light approximately 2.54 million years to traverse the gulf of space between Earth and, for instance, the Andromeda Galaxy, it would take a much shorter amount of time from the point of view of a traveller at close to the speed of light due to the effects of time dilation; the time experienced by the traveller depending both on velocity (anything less than the speed of light) and distance travelled (length contraction). This travel for humans is therefore possible, in theory, from the point of view of the traveller.
Hypervelocity stars: A hypervelocity star is a star that is ejected at very high velocity (on the order of 1,000 kilometres per second) from the centre of a galaxy due to interaction with a massive central black hole. The existence of hypervelocity stars was first proposed in 1988. Computer models indicated that hypervelocity stars ought to be a natural consequence of binary stars coming close to the supermassive black hole known to exist at the heart of our own Milky Way Galaxy. When a binary swings too close to the central black hole, the intense gravity can tear the binary apart, capturing one star while violently flinging the other outward at enormous speed. These could be used by entering into an orbit around them and waiting. But, it would be a very difficult job to catch their speed and entering in their orbit.
Artificially propelling a star: Stellar engines are a class of hypothetical megastructures which use a star's radiation to create usable energy. The concept has been introduced by Badescu and Cathcart. Some variants use this energy to produce thrust and thus accelerate a star, and anything orbiting it, in a given direction. The creation of such a system would make its builders a Type-II civilization on the Kardashev scale. To built around a Sun-like star. It consists of a partial Dyson swarm composed of 5 Dyson Rings of solar collectors (the Class B component), and a large statite Shkadov thruster (the Class A component). Perspective is from below the system's ecliptic at a distance of ~2.8 AU. The system's direction of acceleration is on a vector which passes from the centre of the star through the centre of the Shkadov thruster, which is hovering over the star's north pole (with regards to the ecliptic), at a distance of 1 AU.
Propulsion which can catch the speed of light: The Alcubierre drive is a hypothetical concept that is able to impulse a spacecraft to speeds faster than light (the spaceship itself would not move faster than light, but the space around it would). This could, in theory, allow practical intergalactic travel. There is no known way to create the space-distorting wave this concept needs to work, but the metrics of the equations comply with relativity and the limit of light speed.