[LibWhacker]

is that it takes a huge amount of energy (because you're changing the fabric of space-time to a much greater degree when you time travel than when you space travel)

Never considered that before, but it's true... Whether you're going very far into the future, or the past according to some theories, the energy expenditure is enormous, thanks! I won't forget; it says something about the nature of the temporal dimension.

[woofie]

(Julian Barbour)in his spare time, tirelessly investigating the idea that time does not exist, constructing theoretical models of classical and quantum gravity in which time plays no fundamental role.

He has lots of spare time?

[MUDDOG]

Time travel is analogous to ordinary space travel as follows:

To do other than inertial space travel, you apply force to an object’s ordinary matter. (F = ma.)

To do other than inertial time travel, you apply force to an object’s “time-matter.” (Inertial time travel is the usual past-present-future time flow.)

The problem is, “time-matter,” unlike ordinary matter, is an enormous number.

That’s why you only see inertial time travel.

Possibly for a subatomic particle like a photon, the measure of “time-matter” is small enough that we might send one on noninertial time travel.