Don’t forget the issue of galactic drift.  10,000 years ago the Earth would have been several light-years away from its present location.  So to travel through time you also have to travel through space or there’s not too much point in it.  But the faster you travel through space the slower time moves.  Since time is mathematically the same forward and backwards (why it isn’t with regards to entropy is one of the Big Unknowns) it’s possible that as you traveled to the point in space that you wanted to be at your travel backwards in time would necessarily slow down.  In other words, you could either travel to your spatial location or travel to your time location, but never both together.

Okay Charybdis, this is getting sucky.  I don’t want to have to make a decision like that….

Also, this guy is proposing creating a “closed loop”—wouldn’t that be sort of like Groundhog’s Day (or part of an episode of Doctor Who)?

Could be a nightmare.

Well if the loop was created at the right moment I would be in heaven forever without knowing it. 

Charybdis - 30 August 2007 08:21 PM

Since time is mathematically the same forward and backwards (why it isn’t with regards to entropy is one of the Big Unknowns)

This is true of the continuous systems of classical mechanics. If treated as a system of discrete particles, as it was by Ludwig Boltzmann at the end of the 19th century, entropy can be defined as

s = k log Ω   (Arguably a more profound formula than E = mc².)

The ‘directional’ property of entropy with respect to time becomes a natural consequence of the statistical properties of the system. Nothing prevents a system significantly decreasing in entropy other than the sheer unlikelyhood of its doing so.

This time machine is like the one in the movie ‘Primer’. The machine makes a loop, and you can only come out when the machine was turned on if you enter it when it was turned off.

http://en.wikipedia.org/wiki/Primer_(film)
BTW, VERY complicated movie. Dont watch it unless you are a nerd.

In the movie, they also make multiple versions of themselves by taking a disassembled time machine back through the time machine and setting it up again. In the end, most of the clones decide that time travel isnt such a good thing.

David, I’m as confused (as usual) as I’m impressed.  I have absolutely NO idea what the equation means even after you’ve spelled it out.  I have a great deal of trust that you understand it though so I’m secure in your assessments (as usual). 

AussieBruce I’m wondering though if having all those geeky nerds might be a good thing for others anyway, if their collective minds were all put to good use.  Sucky for them but Lucky for everyone else?

[*maybe?]

David B. - 31 August 2007 11:51 AM

Charybdis - 30 August 2007 08:21 PM

Since time is mathematically the same forward and backwards (why it isn’t with regards to entropy is one of the Big Unknowns)

This is true of the continuous systems of classical mechanics. If treated as a system of discrete particles, as it was by Ludwig Boltzmann at the end of the 19th century, entropy can be defined as

s = k log Ω   (Arguably a more profound formula than E = mc².)

The ‘directional’ property of entropy with respect to time becomes a natural consequence of the statistical properties of the system. Nothing prevents a system significantly decreasing in entropy other than the sheer unlikelyhood of its doing so.

But entropy should also increase when going backward in time, the statistical properties should be identical when moving from any point in time in any direction.  The fact that they aren’t gives time its direction, but just why this is so remains a mystery.