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:
* Post Traumatic Slide Syndrome = Production Code K0812
* In Dino Veritas = Production Code K0813
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 <PERSON> 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 <PERSON>.]
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 <PERSON>.]
First up, let’s note “On our Earth” and “On the world we come from”. Singular “Earth”, singular “world”. 117
<PERSON> 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 <PERSON>, 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 <PERSON> 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 <PERSON> has said in an interview that “I believe the wrong <PERSON> 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 <PERSON> (from Lottery World), and the return of <PERSON> in the fifth season, and <PERSON> and <PERSON> 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 <PERSON> 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 <PERSON> from Earth Prime, the one who’s been with them all along. 663