The denial of the superluminal speed (and with this the backward time) has lead to the idea that the travelling twin brother, who has made a loop in the space and come back to Earth, will in the end turn out to be younger than his staying at home twin.
Einstein's Twin Paradox is considered unsolved until this day. But acknowledging negative time's existence can effectively solve this puzzle.
The human eye registers photons only at the moment when they hit the retina.
Any flash of light always occurs earlier than it is seen, because the photons need a certain amount of time to reach the observer. This means that photons, as well as any other object approaching the observer, travel from "earlier to later," from the past into the future - in the usual positive time, with its absolute values increasing.
On the contrary, photons and other objects travelling away from the observer seem to be moving backwards, from the future into the past, the past getting more and more distant as they keep moving further and further away.
In other words, by changing his direction in space, the traveller changes his direction in time as well.
So during one of the twin brother's round trip, the difference in clock values between the traveller and his brother at home will duly appear and will keep increasing as the travelling brother moves away from Earth. However, this difference will start to decrease on his way back and will disappear completely at the precise moment when the two brothers meet again.
As we can see, the logical mistake that has resulted in the Twin Paradox seems to originate from the fact that the vector of motion was ignored in the puzzle, with only the module of speed being taken into consideration.
Unfortunately, backward-flowing (from the future into the past) negative time has so far only been recognized by a handful of researchers.
For the subluminal speeds, the time shrinks, but it remains positive.
For a light object, cause and effect is one and the same thing, as it by acquiring the qualities of wave begin to move and reach their target synchronously. It is as if it "multiplies" and is therefore able to be in several places at the same time.
As for superluminal objects, they seem to exist exclusively in negative time, always leaving behind the light wave, with which they may initially have shared the same start line.
These objects elude visual perception and can only be identified through indirect indications.
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Yin, J., Cao, Y., Yong,H.L. et al. (2013) Bounding the speed of 'spooky action at a distance'. ArXiv:1303.0614v1.