[Serious] Is the Past Real?

[BrianSoddingBoru4]

If one could, even hypothetically, travel back to the past, then, the past must be real:

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time. This creates a natural time machine. If you could somehow get onto the loop, which physicists call a closed timelike curve, you would find yourself on a trajectory through space that starts in the future and ends in the past.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!

EarthSky -- Black holes are time machines, with a catch

Also seems to argue for the Many Worlds interpretation of Quantum Mechanics.

Big whoop. Sleep is a time machine that gets me to breakfast. No catch.

Boru

[polymath257]

If one could, even hypothetically, travel back to the past, then, the past must be real:

EarthSky -- Black holes are time machines, with a catch

Also seems to argue for the Many Worlds interpretation of Quantum Mechanics.

Causal loops are compatible with General Relativity, but I'm unaware of how they would generated in a Black Hole.  This article gives no reference to any theory.

I haven't worked through the details, but I have seen it claimed that causal loops can be created by toroidal black holes.

Now, whether such black holes can actually be made is another question.

[HappySkeptic]

I haven't worked through the details, but I have seen it claimed that causal loops can be created by toroidal black holes.

Now, whether such black holes can actually be made is another question.

The solution for causal loops in General Relativity involves a rotating universe.  Inside a fast rotating black hole, spacetime is rotating because of frame dragging, and perhaps such loops can exist.

A google search finds that if the rotation happens fast enough, and you get a naked singularity, you could traverse a causal loop outside an event horizon.  However, such black holes may be impossible.