One thing that seems to be almost completely overlooked when time travel is discussed, or used within a work of fiction, is location (the only example I can find that mentions it is this Dilbert cartoon strip).
This is a critical omission.
If someone was to go backwards or forwards in time just one minute they would not find themselves standing in the same place on Earth in relation to their original surroundings. They would most likely find themselves many kilometres up in the air, or embedded in rock deep underground. This is because the Earth is rotating and moving through space at many thousands of kilometres per hour as it orbits the sun, which is also moving in relation to the center of our galaxy, and so on.
To put it simply, we are constantly moving, and so travelling in time will mean we travel to a time before the Earth was in its current location, or to a time after it has moved on. If someone travels in time just a few days they will find themselves millions of miles from Earth in deep space. If they time-travel a couple of decades they will find themselves far beyond the Solar-System in interstellar space.
But the issue of location should not be viewed as a problem. Far from it, in fact. It should be viewed as a major advantage. If we can eventually master time travel in some form it could well be the easiest and fastest way to travel interstellar distances, if only along the path the Earth will take, or has taken.
It's an incredible prospect. But can it ever be possible?
Travel into the future can be achieved, in principle, using the time dilation effect described in Einstein's theory of relativity by travelling close to the speed of light. Travelling to the past would require velocities that exceed the speed of light. This is theoretically possible using cosmic strings, wormholes, or an Alcubierre drive. A huge amount of energy would be required, which would need exotic matter, particularly matter with negative mass. It's all very complicated, and not well understood. But our understanding will improve in this area, as it always does. Sometime over the next few centuries the generation and control of such vast amounts of energy may well be harnessed, and then a device that would enable time travel could be constructed.
Assuming such a device could be built, perhaps in the form of a large orbiting facility that could transport large spacecraft across time, what would be the best way to use it?
|An orbiting time portal, capable of transporting large spacecraft to other times|
Sending a human crew through such a portal would be an immense undertaking.
Such an expedition would essentially be a one way trip to an unknown destination, with no possibility of return or help once the journey had begun. The spacecraft would need to be interstellar in nature, with the ability to sustain its crew and passengers for decades if necessary, as there would be no way of knowing how close a viable planet would be at the time of arrival. At best we could target the vicinity of an appropriately aged star system that we think has a good chance of hosting an Earth-like planet. And due to the impossibility of knowing the conditions of any planet found for colonisation, the ship would need to contain all the resources required to land and set up a colony in a variety of climate conditions.
However successful the mission is, no one left on Earth is likely to ever know about what happened.
If we just want to ensure the continuation of Earth life we could simply send thousands of probes to different times along the Earth's journey path and have them 'seed' the most Earth-like planets they find with the building blocks of Earth life. One day, a billion years later, perhaps a technologically advanced species would evolve on some of those worlds, an incredibly distant relative of our species.
|A probe, sent through time to seed suitable planets with Earth life, arrives and begins observations|
I use term 'simply' in a relative sense as this kind mission would still be difficult and complex. The probe's would have to be smart, with artificial intelligence beyond what is currently possible. They would need to observe and detect the most suitable planets or moons within their range, plot and execute a suitable trajectory, and despatch their payloads without any help from scientists on Earth.
Perhaps there are civilisations out there right now based on Earth life, evolved from simple life forms sent back through time by our descendants. If we do eventually master time travel then perhaps we go on to seed worlds a billion or more years ago, when other galaxies occupied our location. Perhaps a bipedal species, reptilian, mammalian or avian (or something extraordinarily different), will one day build a time portal to send explorers to our galaxy.
Perhaps they will find Earth and the ultimate origin of their species.
Or perhaps they will seed Earth and be the origin of ours.