I think that people are misconstruing what a "constant" actually is...
It's not somebody you care about, to the point that you think about them a lot and they "magically break a spell". It's somebody whom completes your equation when trapped in a time loop.
It's a necessity that it's somebody you
are familiar with, so that they will (presumably) be around in your past, present and future. It's somebody whom will release you from the paradox of crossing your own time-line.
Desmond closed his time loop by phoning Penny at an agreed point in time.
Going back in time to tell
somebody else you intend to do something in the future, might not
seem that astounding, but it's two sides of the same coin...
Imagine your future
self coming back to the present, advising you to act a certain way... It couldn't happen, because your future self's advice may dissuade you from acting how you were meant to - and because of this, you might never exist in the future to go back in the past and tell yourself - see
this post for a good example.
Now, imagine a
friend from the future advising you to do (or not do) something...
The idea of a constant is an external force whom can break the paradox of time travel.
There are theoretically four dimensions to reality but I believe there is a fifth. To exist, all matter must have the following constraints:
01. Height
02. Width
03. Depth
04. Time
Even the smallest atom has to have a size and a presence at a certain point in time...
I believe the fifth dimension is perception (or consciousness). If you
don't perceive the other four dimensions then you evidently don't exist - and conversely what you cannot perceive does not exist to you. Einstein referred to "relativity" - but from what I can understand, he assumed relativity was a result of experiencing the other four dimensions in differing circumstances. I don't believe relativity is another variable inside an equation, but part of the math itself. Relativity
is perception - it
is the fifth dimension.