in his popular (pseudo-science) book Biocentrism ch.8 (see here, scroll down to "the most amazing experiment") Biologist Dr.Robert Lanza makes a number of assertions on quantum mechanics based on double slit experiments:
the simplest case, if one passes a beam of photons through a double slit, he will get an interference pattern at the end detector. This one is obvious.
If one adds quarter wave plates before each slit and a polarization detector at the end plate in such a way that he now has "which way" information on which slit each photon passed through, the wave function collapses and he will no longer see an interference pattern at the end plate. (as a side point, he claims that removal of the polarizing detector while keeping the QWPs will bring back the interference pattern. This was pointed out to be incorrect here)
if one repeats step 2 except that he uses entangled photons with photon S going to exactly the same setup as step 2 and photon P towards an end plate but with a coincidence counter and polarization window which garbles photon P's polarization in such a way that erases the "which way" information obtainable for photon S, then here too the interference pattern shows up at the end plate of photon S (even though photon S has the exact same setup as in step 2 except for the entangled photon P). This he claims is because photon P erased the "which way" information obtainable for photon S.
Same as 3 except the length of photon P's path is lengthened so that Photon S hits its detector before Photon P gets garbled. here too the interference pattern is restored despite that photon P's erasing of "which way" information occurs after photon S hit its detector.
Are any of these assertions incorrect? for more details see above link.
From what I understand, they are all basically saying the same thing: if there is no "which way" information obtainable then the interference pattern shows up at the end detector, otherwise the wave function collapses and no interference pattern shows up.
please source with verifiable sources such as actual experiments.