There are two main issues that make us think these theories and their equations may be unrealistic.

The first issue is a practical one: Building a time machine seems to require exotic matter...

• This physics theory essentially states that you can travel to the past, but you cannot change it.
• If I tried to destroy my time machine five minutes in the past, I would find that it is impossible to do so. The laws of physics would somehow conspire to preserve consistency.

Allowing for multiple histories (or in more familiar terms, parallel timelines) can resolve the paradoxes that are eclipsing all the other theories. In fact, it can resolve any paradox you throw at it.

The idea is very simple. When I exit the time machine, I exit into a different timeli...

Consider a scenario where I enter my time machine, use it to go back in time five minutes, and destroy the machine as soon as I get to the past. Now that I destroyed the time machine, it would be impossible for me to use it five minutes later.

But if I cannot use the time machine, then I c...

There is an observation that time travel seems to contradict logic, in the form of time travel paradoxes. There are several types of such paradoxes, but the most problematic are consistency paradoxes.

A popular trope in science fiction, consistency paradoxes happen whenever there is a certa...

Time travellers are usually warned not to make significant changes to the past and to avoid meeting their past selves to avoid creating a paradox. Examples of this may be found in many time travel movies, such as the Back to the Future trilogy.

But in physics, a pa...