time travel

Wormholes: theoretical tunnels through spacetime. Einstein-Rosen bridges, exotic matter, traversability, ER=EPR, and time travel paradoxes explained.

Forward time travel already happens. This is what it would actually cost a person who chose to use it — a one-way ticket, physically real.

Say a working time machine turns up tomorrow, an artifact and not a theory. Before anyone uses it, scientists would have to prove it is real, governments would fight over who owns it, and the first people through the door would run into the causality wall that makes time travel physics so strange.

Time travel forward already happens — astronauts do it, in tiny amounts. Time travel backward is much harder, but Einstein's equations don't strictly forbid it. Here's what physics actually says.