Delicately manipulating his thrusters and making continual microadjustments of the jets, the astronaut drew within half a meter of the mirror. He stared straight into his reflection, amazed once again at its fidelity: a perfect copy, one perhaps even more finely wrought than the original. He extended a hand toward it until he and his reflected hand were practically touching, separated by less than a centimeter. His earpiece was silent—the commander did not order him to stop—so he pushed forward, and his hand disappeared into the mirror. He and his image were joined at the wrist. There had been no sensation of contact. He retracted his hand and looked at it carefully. The suit glove was perfectly unharmed. No marks whatsoever.

Below the astronaut, the shuttle was gradually drawing away from the mirror and had to constantly run its engines and thrusters to maintain proximity. However, due to its trajectory its drift was accelerating, and before long such adjustments would be impossible. A second encounter would require waiting an entire orbit, but would the mirror still be there? With this in mind, the astronaut made a decision. He switched on his thrusters and headed straight into the mirror.

His reflection loomed large, filling his field of vision with the quicksilver bubble of his helmet’s one-way reflective faceplate. He fought to keep from closing his eyes as his head touched the mirror. At contact he felt nothing, but in that very moment everything vanished before his eyes, replaced by the darkness of space and the familiar Milky Way. He jerked around, and below him was the same view of the galaxy, with one addition: his own reflection receding into the distance, the maneuvering units he and his reflection wore linked by streams of thruster jet fog.

He had crossed the mirror, and the other side of it was a mirror, too.

His earpiece had been chirping with the commander’s voice when he was approaching the mirror, but it had cut out. The mirror blocked radio waves. Worse, the Earth wasn’t visible from this side. Surrounded entirely by stars gave the astronaut the feeling of being isolated in a different world, and he began to panic. He adjusted the jets and arrested his outward motion. He had passed through the first time with his body parallel to the mirror, but now he oriented himself perpendicular, as if diving headfirst into it. Just before contact, he cut his speed. Then the top of his head touched the top of his reflection, and then he passed through and saw with relief the blue Earth below him, and heard the commander’s voice in his ear.