Mechanics of Time Travel

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Time travel only works if you plot the movement of planets, stars and galaxies. For a time machine to stay in one spot on Earth as it travels through time, it must also follow the Earth's trajectory through space.
This instructable lists a few, but not all of the mathematical projections you will need to take into account before you set off on your trip across time.

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Step 1: First, You Need to Know Where You Are Going.

For instance, it's May 9th 2008, you want to go back to Nov 4 2007.

If you just pop back in time, without moving in space, you'll wind up on the other side of the sun from where you want to be. Due to the Earth being in a different place on Nov 14th

The Earth spins counterclockwise at approximately 1675km per hour, looking down from the north pole.
The distance from the Earth to the Sun changes due to it being in an Elliptical orbit. The Average distance is 149.6 million km with the Perihelion (shortest distance) being on January 3rd 147,300,000 Km, and the Aphelion (longest distance) being 152,100,000 km on July 4th.

You'll need to find a way to move through the Suns gravity well to the point where the Earth was before.

Step 2: Then You Need to Know Where Our Solar System Has Moved.

Then the difficulty increases when you look into how the solar system moves in our galaxy.
As our solar system orbits the galaxy at a speed of almost 220km per second, it moves in a sine wave that has a 64 million year cycle.

So the entire solar system on November 14th 2007 would be over 3,364,416,000 Kilometers from where it was on May 9, 2008.

Step 3: Where Has the Galaxy Gone?

To further complicate things, The Milky Way Galaxy is even moving.
From Wikipedia;
Many astronomers believe the Milky Way is moving at approximately 600 km per second relative to the observed locations of other nearby galaxies. Most recent estimates range from 130 km/s to 1,000 km/s. If the Galaxy is moving at 600 km/s, Earth travels 51.84 million km per day, or more than 18.9 billion km per year, about 4.5 times its closest distance from Pluto. The Galaxy is thought to be moving towards the constellation Hydra, and may someday become a close-knit member of the Virgo cluster of galaxies.

Another reference frame is provided by the Cosmic microwave background (CMB). The Milky Way is moving at around 552 km/s[33] with respect to the photons of the CMB. This can be observed by satellites such as COBE and WMAP as a dipole contribution to the CMB, as photons in equilibrium at the CMB frame get blue-shifted in the direction of the motion and red-shifted in the opposite direction.

Step 4: So Before You Set the Date in Your De Loren and Take Off.

So in order to land on the same spot on Earth at any time in the future or past you would have to be able to map the movements of the Earth while taking into account all this spatial movement from the rest of the universe. Otherwise you will pop up in the right time, but in empty space, the sun, or in solid rock.

These calculations would show you where you need to move to, but you'd still have to find a way to move through the time barrier so that you and the Earth would meet up.

If you think of how this would actually work, you would actually be able to move anywhere in the Universe, in time. Only if you can do the calculations.

To all your budding time travelers, good luck!

Update: I changed the title to Mechanics of Time Travel from your suggestions. Thanks!

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64 Discussions

i like this very much, it will aid me in building my time machine- however my thery is that i would place a sort of beacon deep in the antartic, then when travelling through time it can be used as a sort of locater, so the time machine can lock onto it and place the machine any where on the earth.

2 replies

I think last time a beacon was buried in the Antarctic James Arness wound up running around and infecting the scientists, while Kurt Russell went around torching things with a flame thrower.  It may be better to place the the beacon on the Moon, perhaps in a simple geometric shape so it won't attract any attention.

OK first of all if you were to travel through time you would have to move at a speed close to the speed of light. the closer you get to the speed of light the further you would go in a shorter amount of time. nothing is faster than the speed of light so trying to go faster than it is not in the picture. second, what you are saying is good food for thought if you were trying to time travel in space. I like where you are going with that, keep up the thoughts. reply and we will continue the conversation.

3 replies

Actually, you don't need to travel even close to the speed of light to time travel. The point is that we are already moving forward in time right now. But some scientists have managed to slow down light to about 80% of it's speed. So I wonder what nifty things that experiment will bring us.

the speed of light varies with the medium that it travels through. but say if you were also able to travel though a transparent block glass with the light, you wouldn't be able to travel faster than the light in the glass. Neat.

i like the way you think. i didn't know that about the slowingof light. my want is to move back through time, now that is going to be an interresting thing to do. i'm in the works at this time to figure out the mechanics, and the math.