It’s all about information
When, in a single photon or electron double-slit experiment, the act of looking at the slit – doing a measurement – always completely removes the interference pattern even though we look at only one of the two slits when we know also that the photon or electron was fired. This well established fact tells us quantum effects are strongly correlated with the information we have about the world. However, this cannot be considered as a proof that this information must be processed by a conscious observer.
Verily beautiful and sophisticated double-slit experiments have been done, see https://www.synchrotron-soleil.fr.
Shooting photons at a conventional double-slit was replaced by shooting röntgen photons at O2 molecules to see if the normal interference pattern of the deflected photons depended on availability of the information about which O atom was hit by the photon. When hit an electron would break free and be captured for information. The interference indeed disappeared as soon as information about the selected slit, in this case actually which atom of the oxygen molecule O2 was hit by the photon, became available. That information was obtained through the capture and smart interpretation of released electrons, without actually touching the quantum objects – the O2 molecules – by a measuring instrument. This information only became available when de energy of the röntgen photon was enough to make the O atoms break loose and fly apart so the atom which was hit could be deduced from the captured electron. If the molecule stayed intact the electron capture could not reveal information about which atom was hit.
Also ingenious is the delayed choice quantum eraser experiment. There have been intense discussions about that quantum eraser experiment and valid comments have been made. Read Quora. But the author of that article also immediately suggests a better implementation of this experiment (download pdf) that is less likely to be criticized and that the conclusion merely confirms that information about the chosen slit makes the interference disappear. The experimental result is displayed on the top of this page. Black squares represent detection when information about which slit was passed by the photons, blue circles when this information was irretrievable erased.
Unfortunately, the above experiments did not investigate whether a conscious observer should also be involved. By the way, that is no easy task if it is indeed the case that a conscious observer causes the entangled quantum wave chain to collapse and thus ends the entire entanglement chain from the measured photon to the neural information entering the brain of the observer. Even if the measurements are fully automatically carried out, an observation by a human observer will ultimately have to be done, in which case the observer will cause the entire entangled chain to collapse.
But the above experiments surely give the impression that the quantum collapse is connected to information and that the way in which that information is obtained and stored apparently does not matter. That is an extremely strong argument for the hypothesis that an observer must be involved. And what is it that distinguishes an observer from any measuring instrument? Exactly, consciousness.
Experiments showing explicitly the role of consciousness
That is why I mention here two other experiments where the role of consciousness can no longer be denied without questioning the quality and sincerity of the experimenters. Between 1976 and 1985, Helmut Schmidt did experiments on whether test subjects could consciously influence the outcome of quantum processes. A quantum random number generator producing zeros and ones in completely random sequences was connected to a panel with a red and a green light, 0 -> red, 1 -> green. The test subjects were instructed to try with their mind to produce more green than red lights by just concentrating. The outcome, 2% more green than red, turned out to be statistically significant. Even more interesting is that Schmidt also recorded the output of the quantum generator on tape, stored the tape away, and then later played that tape which controlled the same lights giving the test subject identical instructions getting identical results. This outcome can only be explained by entanglement. The tape had become entangled with the quantum generator and the viewer caused the total quantum wave chain to collapse. If true that should also work with copies of tapes. The information retrieval of only one of the copies would also collapse the total quantum wave chain that now extended across multiple tapes so that all tapes now contain the same set while only one is used for the experiment. And it indeed did come out that way. A small caveat that Schmidt himself posted in his publication is that quantum mechanics is based on uncontrollable coincidence and his experiment showed controlled coincidence.
Dean Radin conducted experiments (download pdf) with 31 test subjects in 51 sessions in 2012 to determine whether conscious attention could influence the interference pattern of a classic double-slit setup. With extremely high statistical reliability, the results show that awareness does indeed that, experienced meditators performed significantly better than non-meditators.
Has the role of consciousness with quantum effects now been established beyond doubt? Certainly not, but that applies to almost everything from relativity to Higgs particles. But there is more than enough reason to justify more and better research, preferably carried out by people and institutions with a neutral attitude to metaphysical issues.