It is not even disputable: Karpov would DEFINITELY WIN in 1975

#58
Yes, but you should discount something for inactivity and ageing. Taking his last rating and his rating perfromance in 1992 and assuming linear degradation leads to 2760.

#60
Here Karpov 2800 August 1974.
http://www.chessmetrics.com/cm/CM2/SingleMonth.asp?Params=199510SSSSS3S062745197408111000000000000010100 

Those are not real ratings...you know that, right?

#63
Those are improved calculations by the statistician Sonas. At that time there were only 1 or 2 ratings per year, released with a huge delay. Calculation was even done manually with tables.

Those are adjusted ratings trying to correct for inflation using a completely non-official method, not "improved calculations".  The fact that they were also massaged manually makes it even worse, not better.

As I said, Karpov never reached 2800.

A follow-up to my own reply since the current WC match provided a perfect example:

Nepo after game 4:

"I guess it was more or less the first line of the giants until the very end," [where giants means chess engines] "My goal was simple: try not to mix up my prep."

At the press conference, he elaborated, specifically about 18.Nh4: "Fortunately, I knew the idea, and more or less I could remember what to do. Of course, I was kind of surprised, because it's one of the sidelines but at the same time it's very principled. It's better to remember your moves than to find them over the board."

Note the phrase "your moves" when he means "engine moves".

...and Carlsen:

"What can I say. I tried something concrete and it didn't work. But that's, I think, a normal result. I didn't expect him, obviously, to have missed the line that I played completely, but in some other iterations, there can be a lot of difficult decisions to make for Black. I think the way that he played, there are some different tries but there is just nothing and... the state of modern chess, not much else to say."

By "the state of modern chess", Magnus is clearly talking about the need to rely on engine prep.  Human players are really just playing the analyzed engine line as long as they can manage to, and only doing their own calculations when they forget the line and mess up the move order or face a non-optimal move they did not research.

So, far harder in Fischer's day.  People like to say that modern super GMs know a lot more about chess than the older champions, but...do they?  They know more about riding engine analysis, that is certain.

You won't see the likes of Fischer and Kasparov again (or, somewhere down a tier, Karpov).  Tournament chess is a different animal now.

I agree 1000%. Chess has changed... whether for better, worse or just different depends, I imagine, on one's personal point of view.  

BTW, after an 18 month hiatus from tournament chess, Fischer returned and sliced through the known hierarchy like a hot knife through butter.   For anyone to think he suddenly forgot how to play chess during the interval between Aug. 1972 and 1975 is rather presumptuous (as well as unprovable either way).   Even in their 1978 match, Karpov would have lost to Korchnoi had it not been for all the off-the-board machinations and Korchnoi freely admitted that neither he nor Karpov were at Fischer's level.

NOT "Fischer would have FORGOTTEN".  but he would have been too handicapped.

Coming to 1975, Karpov was the most dominant of the last 3 years, most energetic, youngest and most importantly, the most hardworking. Winner of the candidates.

And unless you are a Stockfish or something like that, taking on someone like Karpov 75 after 3 years of lack of practice and interest in chess?

Also, Karpov was just the top of the iceberg. Entire Soviet chess system would support him. Even if Fischer acknowedlged his participation in April, he would at most have 2 months to prepare

Handicapped,  as he was in 1970 after 1.5 years of inactivity?
That was the point, not that he forgot anything which was being facetious.

As mentioned, Karpov needed off-the-board machinations (i.e. with the entire Soviet system working for him) to (barely) defeat Korchnoi in 1978. That's 3 years after 1975.  As later as 1981, GM Peter Biyiasas, who was at his peak, played a series of 17 games (5/0) with Fischer who was staying with him and lost every game, coming away with the feeling that Fischer was as sharp as ever....that was after a 9 year hiatus.  Maybe he was, maybe he wasn't.  I don't know and neither does anyone else.  Karpov seems to be given some generous overreach while Fischer seems to be give a short shrift concerning his resilience.  Fischer may not have even wanted to play at that point, but if he decided to play, he most likely would have been ready. 

”Human players are really just playing the analyzed engine line as long as they can manage to, and only doing their own calculations when they forget the line and mess up the move order or face a non-optimal move they did not research.

So, far harder in Fischer's day”

I don’t agree about that one. Players don’t just repeat engine lines, but they need to know much more than the players 50+ years ago not to lose in the opening. There are no new novelties at move 6 anymore. But as players like Dubov, who Carlsen has been inspired by quite a lot, has shown there is certainly a very human touch in finding lines that create difficulties for the opponents. Which is easy to see by looking at for example Carlsen’s very engine disapproved sacrifices. He was even down 1.5 pawns according to the engines in one game. But I think many don’t even bother actually looking at these games, but prefer to go on about Fischer :-)

what you neglect is that when Fischer semi-retired in 1968, he was still working on chess: he was following chess, he was working on chess, publishing analysis and annotating. but after 72 he was just reading history books, experiencing new adventures and travelling. That was all. It is well known by his contemporaries, you can read more here: "Dis-covering Bobby Fischer: His life in 1970s after the Spassky match."

But yes, the Korchnoi 1978 case is a worthy case as a rebuttal to my position: Korchnoi in 1978 was barely practiced. All he played was those candidates matches. Karpov barely defeated that Korchnoi despite enjoying so much advantage, one of them being Korchnoi's advanced age. Given that, Korchnoi was still working on chess, he did not lose his form like Fischer would have in 1975.

As an additional note to my last previous response to you, in 1977 Korchnoi too stated that Fischer is still sharp and familiar with the latest chess theory developments.

here are some notes from contemporary actors:

Looking at an earlier news report, June 1973, it was already being discussed whether Fischer would ever play chess again, with some of his friends saying he does not follow chess tournaments anymore. Source: New york Times, 04/06/1973 Fischer's Friends Wonder if He'll Play Chess Again.

According to another The New York times article, October 7th, 1974 , American Grandmaster Robert Byrne similarly thought “Bobby would rather retire undefeated than risk the possibility of losing”. A week later, Bobby Fischer’s biographer Frank Brady rebutted Robert Byrne on the same newspaper, stating:

“His remarks are at the very least extravagant and certainly unkind.” … “Fischer is clearly obsessional about not compromising his principles even though he lost a minimum of $1,800,000 —the loser's share of the purse—by not giving in and probably as much as $3,200,000 since he undoubtedly would have defeated Karpov. It is the monomanical dedication to what he believes in that has forged him into the iron‐willed chessplayer that he is. Fischer has no fear of failing. He has fear of being forced into what are clearly concessions.”

You can read the whole article here: LETTER

Then here is the one with Gligorich:

A local newspaper from New York, Rochester, named Democrat and Chronicle, 14th of May 1979 reports that a match between Fischer and Gligorich that was scheduled to take place in that years spring (1979) is unlikely to materialise. The news includes the following:

The Yugoslav grandmaster confessed privately at the Lone Pine International Tournament a few weeks ago, that a million dollars in prize money is available, but Fischer is not.

20/10/1978 edition of the The evening sun, a Baltimore based newspaper, reports the following about this possible match:

Belgrade, Yugoslavia (AP)—Chances are good that 37-year-old American chess ace Bobby Fischer will stage a comeback soon, a Yugoslav chess official predicts. If he gets a crack at the title, many believe he'd clobber 27-year-old world champion Anatoly Karpov, a Russian.
Fischer arrived in Yugoslavia Monday after six years in retirement to discuss his comeback, meet with his old friend Svetozar Gligoric and consider playing Gligoric or taking part in a tournament, Milos Milovanovic, president of the Serbian Chess Federation, said.
He said that Fischer was shown Belgrade's new convention center as a possible site for a match, that talks with the American are expected to end Monday and that full details will be published by the Yugoslav Chess Federation.

So, it means In 1978 Fischer travelled to Yugoslavia and discussed joining a chess tournament, as well as playing a match with Gligorich.

Same day issue of the News-Press Fort Myers, a Florida based newspaper, has a report reporting the same things.

So, how did this event go Gligorich narrated this event and how this match broke down. Gligorich gave interview in Antwerp in 1989. Here is what he said in that interview:

'There were many psychological mistakes, also by the Yugoslavs, although they were very well-intentioned. But he is very sensitive. And some other things happened in Europe. He was on a private visit in Berlin, with a chess player and organizer, who afterwards published an interview with him with photos which had been taken for his family album. Fischer saw this interview on the airplane and was disgusted. The match wasn't cancelled immediately, but hechanged his conditions and they were impossible to meet.

Also, Gligorich narrates Fischer had beard in his visit to Belgrade in 1978. He says Fischer was treated like a statesman, he did not go through passport control, he was catered with Mercedes Bens, upon landing the Yugoslav officials took Fischer directly to the villa arranged for him, only Gligorich knew the place of the villa and spent some time there.

You're basically saying that the skills have moved off the chessboard to line selection during engine prep...which was my point.  Carlsen does well in this environment because he understands engine prep, but he also understands how to present difficult choices to human players without giving up the draw.  Many GMs today do *not* have this skill, which gives Carlsen a big boost...about a 50 point boost as it has turned out over time .

"You're basically saying that the skills have moved off the chessboard to line selection during engine prep...which was my point.  Carlsen does well in this environment because he understands engine prep"

People tend to think that Carlsen is having an easier time than Fischer because the skills allegedly have moved off the chess board and that his strength supposedly is engine prep and memorization while Fischer et al had chess understanding on another level. This might be a bit of wishful thinking. I think Carlsen's main strength is his chess understanding, while the deep engine prep more is what levels the field than the thing that gives Carlsen the advantage.

Chessmetrics is more accurate than the elo rating in 1974 for 2 reasons:
1) Chessmetrics processed all game chronologically one by one instead of a batch of 6 months assuming all ratings constant during those 6 months
2) Chessmetrics used a more suitable K-factor

Chessmetrics also degraded Fischer for non activity to 2793 with 2800 for Karpov in August 1974.
The prediction with these ratings would be a tie 9-9 with many draws and Fischer retaining his title. Then Karpov was right saying:
"With those rules I can play the match with Fischer for all my life."

There is some venom in Korchnoi saying both he and Karpov would have lost against Fischer.
In 1971 Korchnoi was bitter that the Soviet Chess Federation issued team orders for Korchnoi to lose the Candidates' semifinals against Petrosian, while the federation believed Petrosian had a better chance to stop Fischer in the Candidates' finals and thus keep the World Championship title in the USSR. Korchnoi argued in vain he had a better chance than Petrosian to defeat Fischer.
Korchnoi was also bitter when in 1974 the Soviet Chess Federation issued team orders for Korchnoi to lose against Karpov in the Candidates' Finals, as the Federation believed Karpov had a better chance to dethrone Fischer than Korchnoi. Korchnoi was bitter enough to defect to the West, abandoning his wife and son.
So when Korchnoi later said both he and Karpov would have lost to Fischer he means that his arch enemy Karpov was an unworthy World Champion undeservedly gaining the title by default where he would have lost a title match against Fischer. Moreover without team orders he, Korchnoi would have won the Candidates' Finals against Karpov and thus he Korchnoi would have been the righteous World Champion after Fischer defaulted.
The very close World Championship match between Karpov with all Soviet support and Korchnoi largely on his own supports the view of Korchnoi.

If Korchnoi was forced to throw the 1974 Candidates' Final match against Karpov, then the rating of Karpov was higher than justified as Karpov unduly gained some rating from the thrown game(s).

Yes, Carlsen's chess understanding *is* an advantage...relative to his current peers.

"Not even disputable!"

I love that! It gives me a chuckle every time I imagine the OP waving his little hands around and yelling "Not even disputable!" at the top of his voice. So cute!

Korchnoi being ordered to throw the 71 match to Petrosian is an assertion by Karpov, not by Korchnoi himself. In his 1977 book Chess is my life, Korchnoi states it was a hard fought match. He does not mention anything about being ordered to throw the match to Petrosian.

As for 1974, again Korchnoi does not say anything about being ordered to throw the match to Karpov. However, he DOES state that the government did everything to make him lose and Karpov win. He lists several actions alleging it was done deliberately so that Korchnoi may not win. Nor does Karpov mention something about like this. I am afraid all of these are your fabrications. what is next? "in 1977, Korchnoi found an envelope in his room right after the 31st game. There was a photo of his wife and son, their head being under a gun. Then, Korchnoi threw the 32nd match" ?

While I do believe if it was a fair fight Korchnoi would have defeated Karpov in both 74 and 77, no need to make up things.

Right there is the refutation of your assertion.  Ratings measure actual performance.  Subtracting rating for no measurable public activity is ridiculous.  All prior evidence actually points to Fischer retaining and/or increasing his playing strength during his sojourns from the public eye.

"I can't measure this pound of beef that was weighed last month and frozen, so I am just going to assume it's 0.85 pounds now..."

In the first 3 games of the 71 Petrosian match, Petrosian outplayed Bobby in the opening but in two of them failed to win in the endgame or middlegame.

Even Taimanov outplayed Bobby due to home prep but failed to convert it into a win.

Spassky similarly outplayed Bobby several times but similarly failed to convert. The most notable of them being the 4th game of the match, in which he outplayed Bobby in Bobby's favourite opening, Fischer-Sozin.