Imagine you’re leading a game of 20 questions but halfway through you forgot the thing you chose You have to keep answering yesses and nos  and hope that you think of something that’s   consistent with all your previous questions before  the game is done.

Well it could be that’s what the   entire universe is doing as it creates our reality.

I hope it thinks of something good before we run out of questions.

Scientists are fairly attached to the idea that  the universe is real.

We’re fond of the realist   viewpoint: that there’s an objective reality  out there that’s entirely independent of our   subjective experience of it.

That seems innocent  enough, and it served physics awfully well.

But   take this viewpoint to the extreme and we imagine  the scientist as this perfectly detached observer   of the world, capable of monitoring and modeling  physical reality without ever disturbing it.

But then came the 20th century, and quantum  mechanics.

In quantum mechanics, not only does the   act of measurement profoundly influence the thing  being measured, but it seems we can’t even assign   physicality to the world between measurements.

As  Niels Bohr put it “no phenomenon is a phenomenon,   until it is an observed phenomenon”.

Bohr led  the charge with this observer-dependent view,   encapsulated in his Copenhagen interpretation of  quantum mechanics, which insisted that the world   only became meaningfully defined through the act  of measurement.

Others were desperate to maintain   a physical and realist universe, including  Albert Einstein himself.

We’ve talked about   this debate between the founders of quantum theory  before, and of some of the supposed resolutions,   which I’ll come back to.

Today I want to begin a  discussion of a family of quantum interpretations   which say that the universe exists not so  much in physical particles and quantum fields,   nor solely in the mind of the observer,  but rather in the interaction of the two.

To give a better sense of why we need to go to  these crazy lengths to explain the universe,   let’s review some quantum weirdness.

We’ll  start with the good ol’ Schrodinger’s cat   thought experiment, devised by ardent realist  Erwin Schrodinger to highlight the absurdity   of the Copenhagen viewpoints.

We have a cat in a closed box that is either killed or not killed   by a random quantum process.

For a scientist  running the experiment, the cat is in a twin state   of both alive and dead until the box is open - a  superposition of states.

Or so quantum mechanics   seems to suggest.

This seems even more absurd  when you add the so-called Wigner’s friend   extension, where a second scientist  waits on the report from the first,   rendering both cat and first scientist into a  superposition of states.

And doesn’t the cat get   to observe its own state?

Perhaps to the cat,  the scientists are in a similar superposition, The heart of the problem was a simple question:  in a world where observation plays a role in   defining reality, how is it possible for separate  observers to share a single, consistent reality?

Solutions to this seeming paradox spanned the  spectrum.

For example, the Hungarian physicists   John von Neumann and Eugene Wigner  doubled down on the observer-centric view,   in which the act of observation in some  way creates reality.

Others found schemes   by which a real, physical universe could be  interpreted in the behavior of the wavefunction,   such as de Broglie-Bohm pilot wave theory or  objective collapse interpretations.

Still others   sought to explain the observer’s influence  as a sort of selection bias - for example,   Hugh Everett’s many worlds interpretation and  the ideas of quantum decoherence.

And then we   have Richard Feynmann’s “no interpretation”  interpretation of quantum mechanics,   in which he suggested that his colleagues quit  philosophizing and to “shut up and calculate”.

In the end, most physicists took that  advice.

They were eager to put the   whole mess behind them and get on with the  job of actually using quantum mechanics to   invent the modern world.

But  a very select few physicists   refused to let it go.

One of those was John Archibald Wheeler, a prolific physicist   whose students included Feymnann, Everett, Jacob  Bekenstein, and Kip Thorn among others.

Wheeler   was never completely satisfied with any of the  proposed quantum interpretations.

Although he   started out as a pure realist, he came to believe  that the observer must in some way be fundamental.

And yet he couldn’t accept what he saw as the  solipsistic view of von Neumann and Wigner,   in which the observer was in a sense the  primary causal agent and center of its own   reality.

After decades of thought, Wheeler came  to a view that is summarized in his expression   “it from bit.” In his words, “Every it — every  particle, every field of force, even the spacetime   continuum itself — derives its function,  its meaning, its very existence entirely…   from the apparatus-elicited answers to yes or no  questions, binary choices, bits.” In other words,   he came to believe that the universe  is fundamentally informational.

Wheeler felt that reality must have its primary existence not in the observer nor in the   subject of observation, but rather in  the connection between the two.

One of   the thought experiments that led Wheeler to  his view is his delayed-choice experiment,   which is an analogy to the double-slit  experiment.

Here’s one example of this.

Imagine a single photon hitting a beam splitter -  a semi-reflective mirror that has a 50-50 chance   of transmitting or reflecting the photon.

If we  add a pair of detectors we see that each photon   randomly arrives in detector 1 or detector 2, revealing whether it was transmitted or reflected by the beamsplitter.

But remember I said that the quantum world  appears to live in a state of uncertainty until   it’s observed?

In this case, quantum mechanics  states that the photon is in a state of having   been both transmitted and reflected until we  make an observation to check which happened.

We can see this if we add a second  beamsplitter to scramble the beams   so that we don’t know which path brings the photon  to detectors 1 versus 2.

Now detector 1 always   registers a photon and detector 2 never does.

Why?

Well if the photon was traveling both paths at the same time, then the combination of phase shifts in   the beamsplitters causes the photons wavefunction  to perfectly line up in detector 1 - constructive   interference, and to perfectly cancel out  in detector 2 - destructive interference leaving no signal .

For that to work this pair of “possible  photons” had to travel both paths.

This was called the delayed choice  experiment because, in principle,   the second beamsplitter could be put in place  only after the photons passed through the first.

After they’d made their decision  of a path to take.

This experiment,   and many clever variations of it, have now been  performed.

They seem to verify that the universe   really does exist in a superposition of all  possible states until the measurement is made,   and the choice of that measurement can be  made after the superposition is formed.

That   means that the reality that emerges depends in  a profound way on the choice of measurement.

Here’s another experiment.

If we measure the  spin of one member of a pair of entangled   particles - the choice of the direction of the  spin measurement seems to have an instantaneous   influence on its partner, even if that partner is on the other side of the lab - or on the other side of the galaxy.

We’ve talked about this entanglement stuff in  a previous episode.

So it seems that when you   interrogate the universe, the answers that  you get depend on the questions you ask.

Wheeler became convinced that that process of interrogation in some way creates reality.

To help explain what he meant, Wheeler invented a  pathological version of the game 20 questions.

In   the usual game, someone, let’s say Alice,  thinks of an object, and another person,   Bob, asks yes/no questions to narrow down  the possibilities until he arrives at   only one possible answer: the object that  Alice had in her mind from the beginning.

But Wheeler’s version is a little different.

He called it “negative 20 questions,”   and it works like this.

Unbeknownst to Bob,  Alice never thought of an object to begin with.

Instead, she answers the quest ions as they come,   maybe completely randomly, maybe according  to some secret pattern.

Every answer narrows   the space of possible correct answer, even if  Alice still doesn’t know what the object is.

Let’s say the rule is that  Alice will answer yes and no   alternately no matter what the question.

So Bob  asks, “is it smaller than a bread box?” “yes.”   Then “is it living?” “no.” This line of  questioning has narrowed Bob to the realm of   papercl ips and pebbles.

But had Bob  reversed the order of the questions   he’d have interrogated his way towards tigers,  trees and T-rexes.

And depending on Alice’s rules,   you can imagine scenarios where it looks like  Bob’s choice of question influence the past.

But it doesn’t, his questions are  helping reality define itself on the fly.

Wheeler came to the view that the universe  was one giant game of negative 20 questions,   in which the reality we observe is  the only reality that is consistent   with the questions asked of it by all observers.

The universe, according to Wheeler, was a giant,  closed, “self-excited circuit.” The relationship   between the observer (us) and the observed  (the universe) brought *both* into existence.

Take this yet further and you have a version of  the Strong Anthropic Principle: The only reality   that can exist is one that can have observers  whose questions can make that reality real.

Wheeler called this the “participatory universe.”  He symbolized his idea with a sketch of a giant   “U”.

On one side of the U is the big bang.

As the  universe expands, the line of the U gets thicker,   until we reach the present day, the other side of  the U.

An eyeball here symbolizes the observer.

All the astronomers with their telescopes and  observatories are aimed back at the Big Bang.

Their observations *now* cause the Big Bang  *then*.

Well, sort of.

As Wheeler once wrote,   “the past has no existence except  as it is recorded in the present.”   Only the self-consistent now  can have a real existence.

As I warned, this all sounds very mystical.

Let me be clear: Wheeler wasn’t saying that conscious   minds have direct power over reality, as claimed  by some of the worst practitioners of quantum woo.

But the role of consciousness was something  Wheeler really struggled with.

He said   “About no feature of “It from Bit’ do I feel  less comfortable than whose bit.” After all,   information implies a thing to KNOW that  information.

But non-conscious entities can,   in a sense, know something if information of that something is recorded inside their being somehow.

He also once wrote that it was “Not consciousness but the distinction between the probe and the probed”   that was central to the act of observation.

So “Observation” could well be code for   “interaction”, in which every time two particles  bump together and become entangled we have an   act of measurement.

If this all  seems a little vague and wishy washy,   it’s because it is.

Wheeler was  still obsessively thinking and   writing about and trying to solidify  these ideas until his death in 2008.

In John Archibald Wheeler’s version  of an informational universe,   he felt that the information - the bits - resided  in the answers elicited by acts of observation.

It appears to pull the comforting  ground of realism from under our feet.

But others have taken Wheeler’s ideas  and put them back on firm ground.

It’s possible to think of the universe as being  “informational” without altogether giving up on   realism.

In the broad category of “participatory  realism” we have things like quantum bayesianism   and relational quantum mechanics, in which  the universe emerges from the information   that some set of real entities have about  each other.

Crucially, these acknowledge   the importance of the observer in defining the  observed, while still allowing that there’s some   kind of substrate to reality.

We’ll talk about  these ideas soon, in our long quest to find that   substrate.

And do that we just need to keep asking the right questions of a participatory space time.