Let’s say you are blindfolded and taken across the universe. You wake up in your sophisticated spaceship in some unknown corner of the cosmos…where are you? Is there any way to tell? Perhaps more realistically, if you are navigating your craft through the galaxy, how don’t you get lost?
The first thing to do when trying to figure out where you are in the universe is to figure out which way is North. Well, not North in the Earth sense, but more generally figuring out which direction is what. If we want, we can define a unique Universal coordinate system. Whatever we pick is arbitrary, but that’s okay as long as we’re consistent! Lets say we are suitably advanced and have access to a huge database of astronomical information. What one could do is take photographs of distant galaxies and compare them to known maps. With a big enough database and good enough photographs one could actually determine our orientation to an arbitrary coordinate system! It’s a little like spinning a map around until it makes sense with what you can see out of your window.
Better than that, we can actually guess where we are by looking at those galaxies, or at least guess what galaxy we are in or near. If our database maps of space are 3D, meaning we actually know where most every galaxy is, we can make a theoretical map of space from any arbitrary location. All that’s left to do is make enough measurements from the lost spacecraft that you can compare to the database in 3D until the theoretical map looks the same as your measurements. This, however, is a very rough technique. It only gives you a guess that gets you to the nearest galaxy. In other words, say, plus or minus 100,000 parsecs (1.9 × 1018 miles). Not exactly GPS. But now, assuming your vast database has stars listed in it too (information is power in the modern galactic world) you can do the same trick with the close-by stars of the nearest galaxy. This might get you a guess down to a few dozen to a thousand parsecs, depending on where you are. At the very least you have gone from having no idea where you are to having a pretty good idea where you are.
What would be far better would be to have a magic GPS that works everywhere in the universe. The GPS system we use on Earth actually works in space too, but not nearly as well. In order to have a good position guess, you need to have a many different GPS satellites in many different parts of the sky—one overhead, one on the horizon, etc. Once you get further away than say, the Moon, all of the satillites orbiting Earth look more or less to be in the same spot (and that spot is the now tiny, distant Earth).
Recently it has been suggested that we can use pulsars to do the same work as GPS satillites. Pulsars are small dead stars with strong magnetic fields that are spinning. As they spin they emit a radio pulse (hense, pulsar) once per revolution. This shows up in radio telescopes as a constant ping ping ping ping….Many pulsars are well known and have very stable, very constant pulsing. In many ways they act just the same as the atomic clocks on the GPS sats. It’s not quite the same though; they wont give you a position, just changes in position. But if you know where you are starting you can track how far you have moved by carefully timing the signals of several distant pulsars. All you need are some radio telescopes on the outside of your craft and you can constantly track your position anywhere in the solar system.
Maser’s are even more exotic than pulsars. A maser is essentially a giant radio laser. Surprisingly they are formed naturally all over the universe in certain nebula where the conditions are just right. Just like lasers, masers produce a very stable light at very specific wavelengths. Tracking the light from them, we can look for tiny Doppler shifts which tells us how fast we are moving towards or away from them. Again, if we start knowing where we are, we can track our movements, constantly updating our position.
Both masers and pulsars have the potential to track the position of a a spacecraft down to a couple of meters! Even neater, the technology to do this already exists, but I can imagine it being even better in the future.
With a really good database of masers, pulsars, galaxies and stars, you can never be lost!