[FoRK] Inertial Mass != Gravitational Mass?

silky michaelslists at gmail.com
Sat Jun 19 06:30:37 PDT 2010

On Sat, Jun 19, 2010 at 10:35 PM, Jeff Bone <jbone at place.org> wrote:
> > Obviously, you're assuming that time travellers go back into our time.
> > Which may not be the case.
> This is actually a reasonable point worth addressing.
> There is a whole class of speculative "time machines" that have the following property:  they permit travel to the "past" but only to
> points in the historical light-cone subsequent to the initial construction / operation of the device. An even more plausible subclass
> of these creates a closed time-like loop of fixed length or anchored origin / endpoint, meaning at any future point subsequent to
> their own creation they only permit travel a fixed distance into the past, or (slight variation, different 4-geometry) to a particular
> arbitrary point in the past, probably the first operation of the device.

Probably the funniest argument I've come up with relating to time
travel is this: If you assume one can be built at some point in the
future, and you assume that they do come back to our time, then you
must ask yourself why they haven't prevented anything we consider bad.
Say, global warming, or hitlers birth, or some invasion of some
country, or the starting of a war.

Maybe you could claim that they've *already* stopped *worse*
incidents. That would be convenient, and hard to disprove. But I
happen to think that time travel into our "existing" time is not
possible. I think that we don't see time travellers now, not because
they can't stop these events (or that they aren't worthwhile stopping)
but because they can't.

I don't know much about the Physics of time, so I can't really comment
on what would happen if you did find a way to go back in time, but it
seems to me that it could be even just a passive process. I.e. time
travel may consist of a box. You stand in the box, and are able to
stop all the "things" around you (via some liquid). You can then,
perhaps, replay it in reverse, watch things happen, but not interact.

At least, maybe that will be the first steps. Anyway, my uneducated
speculations are fairly useless. It's an interesting thing to think
about though.



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