# Historical time and place paradox

1. Jun 5, 2014

### Mr. Speck

So, I have an idea to write a (sort of) "time travel" story in which future historians are able to transport a non-intrusive (possibly mass-less) viewport to various important events in history (and then accidentally incinerate Mohenjo-Daro with this technology, thus explaining certain Vedic myths and fused glass found at archaeological sites :-).

I try to keep my stories as accurate as possible to the laws of physics, but I am having a tough time reconciling where these events actually took place in the past (in reference to where the Earth is now in space), since special relativity states that there is no "absolute" time or space reference. I do understand very basic quantum physics and relativity, and can calculate "calibrations" for this hypothetical time machine, but only in reference to other fixed places in the Universe such as the center of our galaxy or the Virgo super-cluster, etc. I even read one thread that stated that the earth is moving at something like 677 +/- 22 kps from the cosmic background radiation, but it did not give a three dimensional vector direction.

My instinct tells me that since that every point in the Universe can be considered the "center" since if you travel far enough back in time from any point, you will arrive at the same exact point of the Big Bang singularity. Einstein's equations and Lorentz transformations will confirm this when you compensate for time dilation and length contraction, assuming the Universe is expanding (post inflation period) at a rate where the Limit of V → C. This is where my brain hits the brick wall of absurdity and counter-intuitiveness since surely solid matter such as the Earth IS moving through three dimensional Cartesian space relative to two arbitrary times in its history, right?

I guess my main question is: what would be the best way to reconcile this "past position paradox": Using that background radiation relative motion, or having scientists figure it out empirically beforehand using very short periods of time to establish some sort of "universal velocity" constant or equation? Hmmm... I think I may have just answered my own question, but I am still curious how one would calculate displacement through time without a relative reference frame.

Last edited by a moderator: Jun 6, 2014
2. Jun 6, 2014

Staff Emeritus
Don't bring it up.

3. Jun 7, 2014

### Mr. Speck

Gee, that's what every single sci-fi writer since Jules Verne has done when dealing with the subject. Excuse me for attempting to bring the slightest bit if creative intelligence to the genre...

4. Jun 7, 2014

Staff Emeritus
Well technically, you were trying to bring our creative intelligence to the genre. And Jules Verne did not write about time travel.

But what H.G. Wells and others recognized is that either this not relevant to the story, or if it is, what is required is a description, not an explanation. Which is why they came to the same conclusion I posted - don't bring it up.

5. Jun 7, 2014

### DrStupid

The dipole anisotropy of the background radiation provides a three dimensional velocity vector.

If I understand you problem correctly than it is limited to a universe with perfect homogeneous energy distribution. In such a case you wouldn't need any references at all. But our universe is full of reference objects that could be used to locate specific points in time-space.

6. Jun 9, 2014

### Mr. Speck

Fair enough. in hindsight my original post is somewhat rambling and unclear. Sorry for the sarcasm...

7. Jun 9, 2014

### Matterwave

Maybe think more 4 dimensionally. Don't go back to a place and time go back to an event. Track where you want to go by going to events. So, instead of going back to 1865, go back to the assassination of Lincoln.

Last edited: Jun 9, 2014
8. Jun 9, 2014

### Mr. Speck

DrStupid,

This is exactly what I was looking for - CMBR dipole anisotropy:

"From the CMB data it is seen that our local group of galaxies (the galactic cluster that includes the Solar System's Milky Way Galaxy) appears to be moving at 369±0.9 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 263.99±0.14°, b = 48.26±0.03°."

Add to that the angular velocity orbits of the sun and Earth, and Earth's rotation, and I should be able calculate a velocity relative to this "CMB rest frame". It may not be valid or even meaningful, but is at least original "techno-babble" as far as time travel fiction goes, IMO.

Thanks!

9. Jun 10, 2014

### Bandersnatch

A correction: the ~370 km/s is not the velocity of the Local Group w/r to CMBR, but the heliocentric velocity in that frame. It's what an observer on the Sun would deduce from the anisotropy.

The LG velocity needs to be calculated by adding Sun's orbital and proper velocities, and the velocity of Milky Way w/r to the LG's centre of mass.

Have a look here:
http://pl.scribd.com/doc/76798330/T...strophysics-Volume-III-Galaxies-and-Cosmology
page 379

The chapter goes through all those steps. It's got some numbers that you may use if you really want to go that way.
Although I don't know why would your time machine care about this particular reference frame, and not for example, perhaps more in tune with the curving of the space-time theme, the frame of the nearest major gravity well(i.e., Earth). But I suppose time machines are weird like that.