Two Doors puzzle.

A thought came to me the other day, and I couldn't really wrap my head around it fully, but it went something like this:

A person finds themselves in possession of two doors, both of which are connected in that when you enter one, you exit the other (with attention to facing) so that your back will be facing the second door when you step out of it. These doors are contained within their frames, only open outwards, are easily moved, and it doesn't matter which door you enter first; you can enter either door and you'll step out of the other door with your back facing it.

If a person were to set the two doors next to one another, but have one set upside-down, so that the front of the first door and the back of the second door were touching, what would happen if a person were to walk through the door?

First, I'm going to make the assumption that when you walk through the door, your blood and other bodily components aren't going to spill out when you're split.

It'd be impossible. Two masses can't occupy the same space at the same time, so it'd be like walking into yourself, except the points of contact are exactly lined up. (Ex. Your head would hit your head, if you tried to kick through, you'd be kicking your own foot, etc.)

That's only assuming that the doors have no width. If the door frames have a finite width, then you'd just appear in the space in between, which should be pretty easy for you to visualize.

The closer you moved the doors, the closer you'd be to bumping into yourself. If someone applied force to the door, it'd be like being in a hydraulic press - you'd just get squished flat.

Of course you'd also probably tumble as you stepped through the door, since half your body would be being pulled up by gravity and the other half would be being pulled down. Since the halves would be separated by the 'portal', the centres of mass would be offset and it would probably give you severe dizzyness.


Unless I'm confused about the setup. You might just end up stepping through a transparent doorway as if nothing unusual happened, except a bit of queasiness depending how far apart they were.

[video=youtube;3L-rrkyvApU]http://www.youtube.com/watch?v=3L-rrkyvApU[/video]

If Joe's setup were the case, assuming the doors occupy no space, you'd just end up on the other side as you'd walk through a normal door. The reason is that there is no way for you to fit between the two doors, and you emerge from the second door in the same orientation as you enter the first door.

You'd have to specify what happens when you enter from behind the door.

The only way this would work wrt to gravity would be if the doors were connected by opposing corners, and the connection point were exactly at the core of the earth, so that somehow gravity was "negative" (pulling towards said core) on both sides. It would be similar in theory to as if one door was in Canada, and the other was on the complete opposite side of the earth.

Came in seeing two doors one puzzle. o-o

Assuming that when you enter from the front, you will exit from the front of the other door (and vice versa), then if you entered the front, you'd exit out the back of the other door. I'll draw a diagram to show this in a while (if I remember).