Like what do you think they do.
Are they just really effective market makers / arbitrageurs? That's a bit boring for the apparent physics level stuff that is going on.
What is your best guess of the strategies that Renaissance tech use?

Win every day matched with a bunch of guys with a deep understanding of esoteric probability theory. At least at the Medallion. Find
It’s no coincidence the dude hires astro physicists.
That said, i bet it’s mostly luck.Hard to believe in luck when they have made 66% average return consistently beating the market
https://www.institutionalinvestor.com/article/b1l98yt4p0bvr4/TheFamedMedallionFundIsCrushingItOtherRenTechFundsNotSoMuchSimons himself has said they rely in very short lived signals.

they can not be so successful if you can guess what they are doing. No.1 rule in hedge fund industry is: don't talk.
Markets are efficient in the long run, but they are locally very inelastic and present patterns all the time. It's not that hard to find 4/5 uncorrelated short term strategies that give you a success ratio of 55/60%. With that you can generate very high Sharpe Ratios.

RenTech is a wellpackaged myth. First, there are more than one funds managed by RenTech. Medallion, the one with alleged superhigh return, is close to outside investors. It might have a few years of very high yield in the beginning, but since then the level of its performance is unknown.
Then, there's the general RenTech fund that's open to the public (mostly institutional investors), such that outside shareholders do receive reports on performance. In recent years, the performance has been ordinary. It even lost money from time to time.

they can not be so successful if you can guess what they are doing. No.1 rule in hedge fund industry is: don't talk.
Markets are efficient in the long run, but they are locally very inelastic and present patterns all the time. It's not that hard to find 4/5 uncorrelated short term strategies that give you a success ratio of 55/60%. With that you can generate very high Sharpe Ratios.
Just to elaborate. Imagine you have 5 uncorrelated bets that win 1% w.p. 0.55 and lose 1% w.p. 0.45. The expected return is 0.1% with standard deviation of 1%. The 1/N portfolio has standard deviation of 0.44%. The annual return is 252*0.1% = 25.2%, the standard devation 7%, the Sharpe ratio (25.20)/7 = 3.6!
If the success ratio is 60% you get annual expected returns of 37.8% and a Sharpe ratio of 5.55! 
RenTech is a wellpackaged myth. First, there are more than one funds managed by RenTech. Medallion, the one with alleged superhigh return, is close to outside investors. It might have a few years of very high yield in the beginning, but since then the level of its performance is unknown.
Then, there's the general RenTech fund that's open to the public (mostly institutional investors), such that outside shareholders do receive reports on performance. In recent years, the performance has been ordinary. It even lost money from time to time.Medallion still made 30%50% in recent years, even after fees, with at least 10B AUM.
Making several billion PnL with only a fraction of the staff of ~300 is still quite impressive. I agree their outside funds are more ordinary, but still above average within the industry.

so why do rentech do so much better than say aqr? given lots of smart people at both.
AQR has been massively expanding in recent years (both in personnel and asset under management). doesnt make sense to compare rentech and AQR currently, until we have another 5 years at least.
these are both examples of success, so far.
If you want examples of bad funds, plenty you can name.

they can not be so successful if you can guess what they are doing. No.1 rule in hedge fund industry is: don't talk.
Markets are efficient in the long run, but they are locally very inelastic and present patterns all the time. It's not that hard to find 4/5 uncorrelated short term strategies that give you a success ratio of 55/60%. With that you can generate very high Sharpe Ratios.
Just to elaborate. Imagine you have 5 uncorrelated bets that win 1% w.p. 0.55 and lose 1% w.p. 0.45. The expected return is 0.1% with standard deviation of 1%. The 1/N portfolio has standard deviation of 0.44%. The annual return is 252*0.1% = 25.2%, the standard devation 7%, the Sharpe ratio (25.20)/7 = 3.6!
If the success ratio is 60% you get annual expected returns of 37.8% and a Sharpe ratio of 5.55!55% hit ratio is hard. especially oos.

Rentech was a loser for a few years at the beginning too, and took some work to get “right.” If they have a secret sauce, it’s a broad series of processes that really effectively matches a trading strategy to probability theory. No one has figured out what those are though.
so why do rentech do so much better than say aqr? given lots of smart people at both.
AQR has been massively expanding in recent years (both in personnel and asset under management). doesnt make sense to compare rentech and AQR currently, until we have another 5 years at least.
these are both examples of success, so far.
If you want examples of bad funds, plenty you can name.