Relativity is easy

 Einstein did it the hard way, but there's a much easier approach to relativity.

Additional text is in italics.         ... = text etc omitted.  See more via source at foot of page.

Could space-time or just space have existed before the Big Bang inflationary period? 

The Inflation Theory proposes a period of extremely rapid ...  expansion of the universe during its first few moments. It was developed around 1980 to explain several puzzles within the standard Big Bang theory, in which the universe expands relatively gradually throughout its history. source

Or could space-time be created like a wave far ahead of inflationary region past matter/energy? Is it possible space-time extends so far beyond any BB matter/energy?

1. The thing is that we intuitively feel time should be linear, so with that mental image of time in mind, there should also be a “before the Big Bang”.
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3. But spacetime is a 4D continuum, 
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5. While 4D spacetime is usually considered to consist of three dimensions of space and one dimension of time, the researchers' view suggests that it's more correct to imagine spacetime as four dimensions of space. In other words, as they say, the universe is “timeless.”  source
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7. which relativity has shown that what can be 100% pure simultaneous space for one observer can actually contain time for another observer ...
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9. Only when we take space and time together, do we find invariant intervals that every observer agrees to:
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11. ...
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13. But since our minds can’t comprehend four dimensions, we tend to imagine spacetime in 3D, by removing one dimension of space.
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15. Unfortunately, this idea is commonly represented in this way:
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19. With this kind of representation, we tend to become curious to what’s on the “left side” of that.
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21. But this is misleading as the future direction of time is not a fundamental direction like that at all. In this 4D continuum, everything pointing away from the Big Bang is always higher in entropy 
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23.  often interpreted as the degree of disorder or randomness in the system. source
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25. and therefore considered a future direction:
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29. So, there’s no counting down to the Big Bang, only a counting up from it.
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31. This is analogous to the 2D surface of Earth, where you can't go north of the North Pole. If you started a bit away from it, you could point north towards the North Pole, but just when you think you're going further north than the North Pole itself, you're really just going south again.
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33. So just like “north of the North Pole” has no meaning to us, “before the Big Bang” has no meaning either, besides it just being more “after the Big Bang” within our own (not necessarily observable) universe.
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35. So, think of our 4D spacetime and its earliest point in time to be analogous to our 2D surface of Earth having a most northern point on its surface.
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37. Time is a property of 4D spacetime itself and does not exist outside of it.
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39. Similar to going up in space at the North Pole isn’t going further north on that 2D surface, either, but just adding extra dimensions.
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41. source
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43. Return to 17 and see Dark Energy Accelerated Expansion at top right.
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45. Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart. One explanation for dark energy is that it is a property of space. ... As a result, this form of energy would cause the universe to expand faster and faster.  source
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47. A more simple but similar version of the graphic at 17 is for children via   "2   From the Big Bang to now" here
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49. Return to 9.   “Einstein said, 
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51. 'Time has no independent existence apart from the order of events by which we measure it,'”      source 

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