I’d like to discuss what seems to me to be a fundamental problem with various forms of wormhole/ portal based travel in either space or time as represented in various forms of science fiction. It occurred to me some time ago, and in fact I started writing this post back in November 2012. I was reminded of it today while reflecting a little on the last five seasons of Fringe, which led to me thinking about The Observers and the way they can travel through time.
Science fiction frequently treats the Earth as if it was fixed in space relative to all other points and objects in space when we know this is not the case. Consider, if you will, Back to the Future when the DeLorean hits 88 mph and jumps through time to arrive in the exact same place on Earth, but at a different time.
The Earth rotates on its axis at a speed of about 465 m/s. In other words, if the Earth was otherwise fixed in space, after standing in place on the surface of the Earth for one second, you’d be about 465 meters from the point in space where you were the previous second.*
However, the Earth is not otherwise fixed in space. While it rotates about its axis, the Earth orbits the sun at roughly 30 km/s. So after that one second, you’d be about 30 km from your previous point in space regardless of whether the Earth was rotating on its axis or not.
But wait, there’s more. The sun and the entire solar system orbit the center of the Milky Way galaxy at around 220 km/s. This means that after one second, you would have traveled 220 km from the point in space you were at just one second prior, give or take 30 km depending on where the Earth was in its solar orbit and what direction it was traveling relative to the motion of the Solar System.
As the sun orbits the center of the Milky Way, the Milky Way is also not fixed in space. Our galaxy moves in and with an expanding universe, and is influenced in that motion by various factors, such as the gravitational pulls of the Great Attractor and the Shapley Supercluster. The Sun and Solar System move with a resultant velocity of about 370 km/s relative to the Cosmic Microwave Background radiation.
So by jumping just one second forwards or backwards in time and arriving in the exact same location in space, you would be several hundred kilometers from the surface of the Earth in space because the Earth, the Solar System, and The Milky Way are all in constant motion in a celestial ballet.
This problem would apply to most wormholes and portals in space (technically space-time) as well unless such portals were gravitationally bound to the locations of the endpoints so that they traveled through space with the planets/ locations of the entry points. The Stargate franchise gets around this problem nicely by making the wormholes connections generated between two gates rather than two regions of the fabric of space-time itself.
Back to the Delorean- after jumping through time to arrive in the same location in space, it would be stranded in the (near) vacuum of space and the drive doomed to death. (There’s no way to drive back.)
Interestingly, this brings up another interesting conundrum: What’s so significant about traveling at 88 mph (or any speed) relative to the surface of the Earth in the first place, and should it matter what direction you are driving relative to the motion(s) of the Earth? Velocity is relative to some reference frame and not absolute. The Delorean might be traveling at 88 mph relative to a bystander standing on the ground, but it would be traveling less than that relative to a tailwind and more than that relative to oncoming traffic, to say nothing about its velocity relative to something like the Moon or the Voyager 1 probe. That DeLorean in free space would be traveling at least 88 mph relative to something; what would or wouldn’t cause it to time travel? In fact, since there would be no air resistance or friction with the ground, it would likely still be traveling at 88 mph relative to the Earth** as its momentum carried on in space.
I don’t really have a good conclusion or summary here other than to say that traveling in time without also traveling in space may not such a good idea. Sorry, Doc.
* Note that the net distance from the previous point will be less that the arc distance traveled, but the difference over the time interval used would be minimal. I’m also ignoring the motion of the Earth as a result of the Earth-Moon gravitational interactions as they co-orbit each other and other similar factors.
** I suppose things gets even trickier here. No longer being on the surface of the Earth, the Delorean would no longer be rotating with the Earth’s surface as it revolves about its axis, but would continue on a tangent from where the Earth was before the DeLorean hit 88 mph and jumped through time. This would be further complicated the change in gravitational forces exerted on the Delorean by the various actors due to their changed locations relative to the Delorean, which will be greater the further it has jumped in time. There are also other complicating factors involved here, but I think I’ve made my point.