How long do we have to wait
How long till computers reach 4000 ratings ?

Elo is not entirely a measure of strength. It's a measure of relative strength. The top engines have high ratings not simply because they are strong, but because they are strong compared to other engines.
Therefore, to reach 4000, the top engines will have to increase in strength at a faster pace than the other engines they are being compared to. So far they have managed it. However, if the other engines improve and narrow the gap, the top engines will see their ratings decline even if they continue to improve.

But there must be a maximum achievable rating? I equate it to the 100m race. The record keeps getting faster but there will come a point where it is physically impossible for a human to travel that distance any quicker.

Maximum achievable? You will eventually reach the point where you're so far above other engines that you don't go up any more when you win, but that only happens if the very top engine (or top 2-3 engines) are far and away above the rest of the field. If there's no such huge gap, there's no theoretical upper limit to Elo ratings.
I think they'll reach 4000 ratings in 5 years because they will probably get like 500 points yearly and they be strong as crap bro. Expect them to be stronger than Kasparov and Magnus Carlsen
@TitlesAreTitles Carlsen wasn't even trying to, in fact no body is actually trying to BEAT the computer, they only play against computer to check their opening preparations, tactical variations and such more but not to defeat them. We use them as a source and Carlsen or Kasparov should be able to figure out how to beat engines like Stockfish 8 or Rybka because Kasparov has already done it to Deep Blue before and why not now?

Carlsen has said that he does not play computers, because it is like playing against an idiot who always wins
@IpswichMatt, True bro but computers are pretty good at prophylaxis and counterplay though, they excel almost at every aspect of the game.

Indeed they do @lmaoyo, I just thought I'd share what Magnus said about playing them because I thought it quite amusing

But there must be a maximum achievable rating? I equate it to the 100m race. The record keeps getting faster but there will come a point where it is physically impossible for a human to travel that distance any quicker.
I agree, at some point the engines will play perfectly. I suspect that's still a long way away though. What that "perfect chess" Elo will be is anyone's guess.

Well to human eyes the fish is unbeatable even now. It's disconcertong that in this field a machine built by humans has surpassed us.

@TitlesAreTitles Carlsen wasn't even trying to, in fact no body is actually trying to BEAT the computer, they only play against computer to check their opening preparations, tactical variations and such more but not to defeat them. We use them as a source and Carlsen or Kasparov should be able to figure out how to beat engines like Stockfish 8 or Rybka because Kasparov has already done it to Deep Blue before and why not now?
There have been a number of human-computer matches, and now the computer always comes out on top. There have been a few instances of odds matches between top GMs such as Nakamura and top engines, with very good results for the engine. Engines today are far stronger than Deep Blue was. In a ten-game match with a modern top engine, Carlsen would do very well to get even a single draw.
What you rekon