"The future ain't what it used to be."

Time travel could be possible, but only with parallel timelines


Temporal Novice
Albert Einstein's theory of general relativity provides an accurate description of the causal structure of our universe. There are two main issues which make us think these equations may be unrealistic. The first is that building a time machine seems to require exotic matter, which is matter with negative energy. The other main issue is that time travel seems to contradict logic, in the form of time travel paradoxes. In science fiction, paradoxes happen whenever there is a certain event that leads to changing the past, but the change itself prevents this event from happening in the first place.

In physics, a paradox is not an event that can actually happen — it is a purely theoretical concept that points towards an inconsistency in the theory itself. Stephen Hawking's chronology protection conjecture states that time travel should be impossible. One attempt at resolving time travel paradoxes is theoretical physicist Igor Dmitriyevich Novikov's self-consistency conjecture, which essentially states that you can travel to the past but cannot change it. Introducing multiple histories When I exit the time machine, I exit into a different timeline. This takes us back to square one, since if even just one paradox cannot be eliminated, time travel remains logically impossible. We showed that allowing for multiple histories (or in more familiar terms, parallel timelines) can resolve the paradoxes that Novikov's conjecture cannot.


What paradoxes are we talking about? Are we talking about changing events such that it conflicts with prior human memories and stating that that violates some physical law thus introducing a paradox? In other words are we stating that human consciousness is a physical law unto itself?

Let's test that hypothesis:

What if instead of sending a human being into the past we send a single high energy neutron and let it bang into some random nuclei? Humans won't remember anything at all about the original state of those neuclei or that they have changed. Now where's the paradox? Does this event need chronology protection? Have we violated Novikov's self-consistency conjecture? Do we need to invent a convoluted many-worlds interpretation to resolve the mystery?

I'm not saying that I actually agree with my argument. I might then again, I might not. The point is that we have to be very careful when we look at a complex question and go for a simple answer. We have to carefully define out terms and parameters.