This is one of those requests for references and reflections post. Iâ€™d be grateful for thoughts and recommendations concerning the following questions: Which spatial properties are Twinearthable and which are not? Which temporal properties are Twinearthable and which are not?
Regarding â€œTwinearthability,â€? Iâ€™m following the usage of John Hawthorneâ€™s â€œDirect Reference and Dancing Qualia.â€? The way Hawthorne puts it, a concept like â€œwaterâ€? is twinearthable because we can easily imagine an epistemic counterpart that is epistemically just like us but locks onto a different property by â€œwaterâ€? than we do (XYZ instead of H2O). A concept is not Twinearthable when beings epistemically just like us would lock onto the same properties that we do. Non-twinearthable properties are so fully present to the mind that epistemic possibility is a guide to metaphysical possibility.
Properties broadly describable as spatial may differ with respect to their Twinearthability. I consider as relevant the following reflections by Roy Sorensen
The volume of a two inch cube is eight times
the volume of a one inch cube. But the surface of the two inch cube
is only four times as large as the surface of the one inch cube. The
ratio of surface to volume further decreases when the cube achieves
a size of three inches. Now all six sides must be dedicated to
maintaining the organism. Thus the geometry of the cubical
organism imposes a limit on its growth. Since the volume of the
organism is cubed while surface area is squared, the animal must
eventually exhaust its ability to feed. The ratio of an organism’s
surface area to its volume is an internal relation. Hence, the size of
an organism is an intrinsic property.
Size is also an intrinsic property of environments. Doubling
everything would not create a duplicate environment. Although the
increase would not be detectable by linear measurements (for our
rulers would have expanded), the increase would make a difference
to planetary orbits and other phenomena governed by geometrical
Any purely spatial property of an organism is an extrinsic
property. Identical twins can be duplicates even though they stand a
meter apart. Nor is their duplicate status threatened by rotation. If
one spins clockwise while the other spins counter-clockwise, they
remain duplicates. If one twin sleeps with his head to the east while
the other sleeps with his head to the west, they still wake up as
twins. Given this indifference to space, we see that the twins are
duplicates even if they are mirror images of each other.
(From Mirror Imagery and Biological Selection, Biology and Philosophy 17/3 (June 2002) 409-422)
I wonder if temporal properties are similarly split with regards to Twinearthability. I wrestled with this a bit in the puzzle raised in â€œThe Slow Switching Slowdown Showdownâ€? wherein I wondered out loud about how long slow switching would take on a demonically slowed Twinearth. I wonder now about which properties broadly describable as temporal would be Twinearthable and which would not.
Further pointers on space as well as time are welcome.