We know that the general theory of relativity is compatible with the existence of space-times in which travel to the past or remote future is possible.

NEWYORKER: The Region of Unlikeness

The company will further investigate the possible spread of contamination and its potential impact in the ocean, including the existence of beta radiation that could contain harmful strontium, company spokesman Yoshikazu Nagai said.

WSJ: New Leak at Japan Reactor Threatens Ocean

The simplest form - that which fits neatly into the existing Standard Model of particle physics - would surely shore up the theory, but the possible existence of more "exotic" versions of the particle would open exciting new vistas in science.

BBC: LHC cements Higgs boson identification

President Peres, Prime Minister Netanyahu, friends -- our very existence, our presence here tonight, is a testament that all things are possible, even those things that, in moments of darkness and doubt, may seem elusive.

WHITEHOUSE: President Obama and President Peres of Israel Speak at State Dinner | The White House