Antiearth

This principle states that, if we could somehow replace every particle on earth with its antiparticle—thus creating a sort of antiearth—no one would be able to tell the difference.

Each extends what would be called, on antiearth, a right hand.

But actually, CPT only tells you that if you drop an apple to the earth it will fall exactly as if you drop an antiapple to an antiearth.

Antiapples would still fall to antiearth, radioactive antielements would still decay, and antisugar would taste sweet

The old imaginary antiearth (άγτιχϑωγ) of the Pythagoreans does not belong to the sphere of these conjectures. It and the Earth were supposed to have a parallel concentric movement; it was an idea devised to spare the Earth, which was supposed to perform around the central fire a planetary revolution in 24 hours, from having also to execute a movement of rotation, and, indead, represented no doubt the opposite hemisphere, or the antipodal half of our planet.

For the later Pythagoreans the world was made up of four elements: earth, water, air, and fire; the universe had a spherical earth traveling around in a circle once every 24 hours (instead of rotating); there was an invisible central fire, with the sun reflecting light from it; and in order to have exactly 10 major bodies in the universe, there was stipulated an antiearth, visible only from the back of the earth.

As for the planet high up to the right in the sky, I have not managed to ascertain whether it is a product of the Pythagorean Antiearth, or of the sentiment laid in my soul by the radiation of Planck's 'Black Body'

Directly opposite the oikoumene was the "antichthones," or "opposite land," or "antiearth," also called the "periocci." It corresponded to the quarter of the globe North America occupies, and its night and day were the reverse of the oikoumene.