At the end of ‘Post Traumatic Slide Syndrome’, there’s a tussle between the two Professor Arturos – the original one from Earth Prime and the local double. One of them slides and the other doesn’t. However, it’s never made clear which one slid. Which one was it? Was it the original or the local double?
It was the original Professor from Earth Prime.
The production order for the episodes for Season 2 of ‘Sliders’ shows that ‘Post Traumatic Slide Syndrome’ was the 10th episode of the season. The 11th episode – the one immediately following ‘PTSS’ – was ‘In Dino Veritas’. Their production numbers confirm this:
Why do I mention this? Because this shows that the events in ‘In Dino Veritas’ happened after the events of ‘Post Traumatic Slide Syndrome’. Therefore, the Professor who lands on Dinosaur World is post-‘Post Traumatic Slide Syndrome’ –the Professor who left Earth Double Prime is the Professor on Dinosaur World.
And, in this episode, our sliders are all wearing truth collars. The episode starts with them on a world where these lie-detecting collars are compulsory, they’re wearing the collars when they slide to Dinosaur World, and they’re stuck with the collars for a great deal of the episode.
Therefore, we can look to what Professor Arturo says while he’s wearing the truth collar to determine the... umm... truth of the matter.
Some of the Professor’s lines in this episode include:
On our earth, man and dinosaur lived millions of years apart. [To Wade.]
In the world where we come from, dinosaurs are long extinct, and this area here is the great city of San Francisco. [To the holographic scientist.]
We have certainly seen the best and worst of each other. [To Wade.]
First up, let’s note “On our Earth” and “On the world we come from”. Singular “Earth”, singular “world”. Arturo is saying that all the sliders come from a single Earth, a single world. In other words: he comes from the same Earth, the same world, as the other sliders. If he was the Professor from Earth Double Prime, he would have been forced by the truth collar to say “Our Earths” and “on the worlds” – plural. The truth collar didn’t react; ergo, he’s telling the truth when he implies they all come from the same single world. And, he’s not just talking about the previous world they came from: he’s talking about “our Earth”. The Earth they all share; their home Earth.
Second, that comment that “We have seen the best and worst of each other.” is quite telling. If he’s the replacement Arturo, he can’t have seen the best and worst of the other sliders, nor can they have seen the best or worst of him. To have seen the best and worst of each other, this Arturo must have been sliding with them for a while – before their recent visit to Earth Double Prime. Again, the truth collar doesn’t correct him on this statement.
I know that Tracy Tormé has said in an interview that “I believe the wrong Arturo slid”, but that’s just one of many ideas which didn’t make it on to the screen: witness the other discussions about a five-episode story arc involving Ryan (from Lottery World), and the return of Bennish in the fifth season, and Quinn and Colin Mallory appearing for the first half of the fifth season – all ideas which didn’t make it to the screen. That interview covered a lot of “maybes” and “if onlys”. But, if it’s not on-screen, it’s not canon.
These comments by Professor Arturo in ‘In Dino Veritas’, told under the restrictions of a truth collar that doesn’t permit lies, prove that this is their original and beloved Arturo from Earth Prime, the one who’s been with them all along.
It was the imposter. In the episode Summer of Love Arturo is shown to have some knowledge about football, but in the episode The Guardian Arturo is shown to have no understanding of football and didn’t know what a team was.
Also, in the pilot, when Quinn got home from his first slide he went to Arturo to explain it and named the Einstein-Rosen-Podolski bridge, as if Arturo knew what it was. But in the episode Double Cross, Arturo claimed that he had never talked to anyone about sliding.
I realise Word of God isn't necessarily canon. However, Tracy Tormé has stated his intention that it should be the 'impostor' Arturo.
Completely canon-wise, it appears to have been intentional that the viewer can't tell. The camera does switch away during their final fight, which makes it impossible to fully determine.
The imposter slid. I have to address the points made by Algernon_Asimov in his answer.
As Tracy Tormé himself remarked the intention was that the imposter slid. He also states that this idea did not make it to the screen. By that however is (most likely) meant that it was never revealed on screen that the imposter slid. It was clearly intended that such a reveal should have taken place at some point in the future.
The episode Dino Veritas does not provide sufficient evidence to conclude that the correct Professor slid. First of all, the imposter is very smart. He knows in the very moment that the Sliders arrive in the world of truth collars that he has to think on his feet in order to trick the lie detector. If the collar works in any way similar to the lie detectors that we know, then this is not too difficult for him. He has only to be convinced by the truth of what he is saying in order for his heart rate and vital signs not to indicate to the device that he is lying. Even if there is some kind of AI technology parsing the sentences uttered, it can still be tricked by sentence disambiguation issues. Of course the sliders could have asked him a straight, direct question regarding this matter. But this at least is never shown on screen, therefore we should not assume they did. What is shown however, is them meeting up for the slide. This implies that the imposter had some alone-time to figure out all the quirks of the truth collars and prepare himself. The following statements in question can thus be explained easily:
(1) On our earth, man and dinosaur lived millions of years apart. [To Wade.]
(2) In the world where we come from, dinosaurs are long extinct, and this area here is the great city of San Francisco. [To the holographic scientist.]
(3) We have certainly seen the best and worst of each other. [To Wade.]
(1): If the (EDP) Professor thinks at the moment of utterance of this statement that 'our earth' refers to the people that live on Earth Double Prime (including the Professor himself), then he can make the statement without triggering the collar. Of course Wade, and anyone listening, can interpret the sentence differently, i.e. such that the possessive pronoun 'our' refers to the earth of the Professor AND Wade, but that is merely a possible interpretation. Earth Double Prime is so similar to Earth Prime, that part of the statement, that the dinosaurs are long extinct (on EDP), itself is clearly true.
(2): This is a true statement on the face of it. They all come from earth double prime. Sometime before landing on truth collar world, they indeed all came from EDP. They do not all 'originally stem from' EDP, but that is not the intended meaning of the sentence.
(3): Again a true statement. The Professor from EDP has read Wade's diary. So he indeed has 'seen' (in his mind, while reading the diary) the best and worst of the other sliders. On the other hand, the sliders have seen the worst of him on EDP (he stole the timer and tried to take all the credit for sliding etc.). They presumably also have seen the 'best' of this version of the Professor. He actually mutters to himself 'foolish old man' in this episode, indicating that he thinks rather lowly of himself. So perhaps he thinks the way he is acting now is probably the best they have seen of him. Altogether, the statement is the TRUTH, also if the EDP Professor utters it.
Come to think of it, (3) is a particularly curious statement to make, if this was the Professor from Earth Prime. It seems much more plausible for the EDP Professor to make such a statement. What is the worst they could possibly have seen of the Earth Prime Professor afterall? On the other hand the statement fits in well with the whole attitude of the Professor in this episode, somehow blaming himself for tripping over a rock ('foolish old man'). It is plausible that he is probably feeling remorse or at least regret for his deeds in Post Traumatic Slide Syndrome.
Other evidence for the Earth Double Prime Professor have already been stated in this thread. I think one of the most compelling is the football remark made in 'The Guardian', in an episode directed by Tracy Tormé, making it much more Canon that the wrong Professor slid than not in my view.
Taking the above disproof of Algernon_Asimov's answer, together with the positive evidence stated in 1. and 3., I think there is a slight surplus of evidence for the notion that indeed the imposter slid. In other words, the Professor is still alive and well on Earth Double Prime! In fact there has been some talk about a potential sliders reboot in recent years, which if ever made would most likely prove me right in that (most of) the original cast will return, including the Professor. Link: https://screenrant.com/sliders-reboot-release-date-cast-story/
They are both the wrong Arturo.
Both Arturos arrived from separate slides around the same time, saw the real Arturo enter the home of the wrong Earth, then they all fought, and one remained triumphant, who then imprisoned the real Arturo off-site from the world's Arturo home so they could ensure no one found him imprisoning the other fake Arturo in that dimension's Arturo home - so if someone did come then they would be led astray by another Arturo who also wanted the slider fame.
So finally, when the sliders arrived at that dimension's Arturo home, they found both fake Arturos and couldn't tell the difference, and it didn't matter because they were both fake.
Also, by this time the real Arturo of that world arrived back with the sliders of that world and found the Arturo we have been following in the serialized episodes chained up in one of the lab equipment rooms in the university he works at.
He was then released and the serialized Arturo thought this other Arturo who just returned to his true home world was of the Arturos he fought with in this dimension's Arturo home and so then fought with this Arturo, was victorious, and convinced the other sliders this was not their world, though in fact it was, causing that dimension's sliders to all leave their true home world, with only the real Arturo left behind plus the other Arturo who was defeated on the front lawn after that other Arturo fight before the serialized sliders slid off that dimension's earth. Then another set of sliders came in to that world yet again....