Time travel is possible. You are traveling forward in time as you read this. We are so used to traveling forward that we forget this. We travel forward in time from the moment we are born until the moment we die. We are moving forward in time, but are limited to traveling in one direction.
 Simulated movement of the sun in one year. The sun actually moves over 1/2 it's diameter every hour. |
 Path of the Earth around the Sun after one and a half years. This is very compressed. The crests and valleys represent 93 million miles from the Solstice line. The same date one year apart has moved 4.25 Quadrillion miles. |
Some people are obsessed with travelling back in time. In popular fiction a person just pops back and find themselves in the past. In the Mechanics of time travel, the Earth has moved from it's past location. You need to step outside our solar system and view it as a part of the Milky Way to see how the Earth of moving in space.
We move in spirals and waves. The Earth rotates at 1100 mph. Each minute the Earth moves 0.25 degrees. We orbit the Sun at 67,000 mph. In a 24 hour cycle, around the Sun. The sun revolves around the center of the Milky Way once every 226,000,000 years at 486,000 mph. The Milky Way galaxy is moving toward the Andromeda galaxy. The Milky Way and Andromeda galaxy are approaching each other with a speed of about 81 miles per second. Our galaxy and neighbors are moving at 370 mps in the direction of the constellation Hydra. The Milky Way moves through space within the cluster of galaxies it is a member of. This cluster in turn moves through space towards yet another larger cluster of galaxies off in the direction of the constellation Virgo at approximately 185 mps. Therefore, the speed of the Milky Way galaxy is not a single number, its value is relative to the speed of other objects.
If you imagine the Milky Way Galaxy as a piece of circular graph paper, then stack one photo copy of each sheet on top of the last one for each hour that passed, you would wind up with a leaning spiraling cylinder of time. Our solar system has moved over 4,850,000,000 miles from where it was previous year.
If you had a method for traveling back in time, you need to calculate the location of where the Earth was on the date you want to go. Not taking into account any of the delta's, you would have to calculate over to 550,000 miles for every hour you wanted to go back in time. You would need to step outside our Galaxy to really picture how complicated the mathematics would be. A flattened out Slinky stretched into a circle with 226 million loops would represent our travel around the Milky Way. The ends would not meet though, since the Milky way itself had moved during that time. Three dimensions is enough to tell you where you are within the Galaxy, but you would need to add additional points to show where you will be above or below the plane of the galaxy at it's current location.
Current Milky Way coordinates would be three points; X0, Y0, Z0. A point where you would want to go in the past would be; X-1, Y-1, Z-1. A point in the future would be; X1, Y1, Z1. For example, to move back one day using Earth as the center coordinate, you would need to calculate the difference in the position of earth 24 hours ago.