There's No Single Objective Reality

Drawing out the implications of one of the weirdest thing I've ever come across in physics

Let’s start with a thought experiment. You put a cat in a box, with a device that measures the spin of some laser-trapped rubidium atom. Is the spin up or down? If its up, the cat gets a treat. If it’s down, the cat gets vaporized in a compact Gen-IV thermonuclear device.

Now, is the cat alive or dead? Who knows! It’s both! It’s neither! That’s quantum mechanics for you - that’s physics. Schrodinger’s cat-box thought experiment was actually conceived by Schrodinger to poke fun at quantum mechanics for being so weird, and rightfully. It’s weird as hell. Since then we usually don’t think of macro-scale objects like cats being in a superposition of both alive and dead, and this only applies to quantum-scale objects like photons or atoms. However, this thought experiment has a spiritual successor known as Wigner’s Friend thought experiment, and it’s rapidly become one of my favorite launching points for exploring the weirdness of modern physics.

The thought experiment is fairly straightforward to begin with - suppose that cat got a PhD in experimental physics and is now operating the device which measures the spin, and there’s no more bomb or treat. The cat has become best friends with Wigner, who runs the laboratory as a whole. Until the cat makes a measurement, Wigner sees the whole room (device + friend + atom) in a superposition of outcomes, and no information can leave the laboratory except when the friend reports the result of the experiment to Wigner. Wigner actually drew out this thought experiment to explore the Mind-Body question and nature of consciousness, arguing that it appears that reality is indeterminate in some sense until it enters conscious awareness, or at the very least conscious perception means we can’t simply apply a straightforward linear time-evolution of the Schrodinger equation to find out an outcome when the system involves a conscious being. For the laboratory measurement there is no privileged observer - both the friend and Wigner have equally valid perspectives, yet Wigner doesn’t know the result of the experiment until the friend communicates. The question arises - when does the experimental outcome become determinate? When the friend measures it, or when they report it to Wigner?

This leads to an apparent paradox in that different observers will perceive different states of affairs depending on the information accessible to their observation. This isn’t so strange, really - I can’t see through a door into another room but it doesn’t mean what goes on there is some “different reality” - in later years Wigner concluded that perhaps the thought experiment doesn’t say much about the influence of consciousness on physical systems, rather that the fundamental theory of quantum mechanics needs to be revised in some way.

This line of reasoning was followed up in 2018 by Frauchiger and Renner in their paper titled “Quantum theory cannot consistently describe the use of itself” to produce what’s come to be known as Extended Wigner’s Friend thought experiment. The net-net from EWF is there’s no avoiding the weirdness anymore - you can’t just interpret this as “I just didn’t know whats going on beyond the door,” rather, people will actually disagree on the objective record of events even after all the information is revealed. The situation is similar as before, but now we start chaining together several rooms with measurement setups where the rooms pass information between each other. The general gist is something like, a random number generator determines whether room 1 prepares a particle in spin state up or down, and then this particle is passed to a following room 2, which then measures the state, and so on, meanwhile there are observers external to the rooms which try to make inferences on the outcome of the original random number generator based on the results reported by rooms downstream. Borrowing the following figures from their papers, Fig 1 illustrates the original Wigner’s Friend thought experiment, and Fig 2 illustrates their Extended Wigner’s Friend thought experiment.

In their original paper they carefully work out a series of possible outcomes with the premise that the observers are all using a straightforward application of quantum mechanics to make inferences about whether original RNG was heads, or tails. Another assumption is that they think all the other people in the experiment are also using the very same theory to make their own reasoned assumptions about whats going on at different points in time.

They find that, in a small fraction of possible sequences of events, you get to some outright contradictions. Not just “oh I don’t know what’s going on behind that door” but rather, two people will disagree about the objective record of events. There’s actually three general statements that can’t all be true at once, or rather, at least one of these has to be false:

1. Local Determinism: An observers measurements aren’t affected by other distant events outside of what we consider that person’s volume of causal interaction.

2. No Superdeterminism: The choice of measurement settings used by an observer isn’t influenced by any pre-existing hidden variable, i.e. there is ‘free will’ on the part of observers.

3. Absoluteness of Observed events: There is a single record of events or ‘what happened’ that all observers agree to, and so facts or outcomes are not strictly observer-dependent.

These set of conditions that we *think* should all hold true at once, but don’t, are summed up in the concept of “Local Friendliness,” as put forward by some interesting follow-up work on this by Bong et al. Bong did some experiments using photons as observers and proved that, indeed, you can’t have all these statement be true at once. At least one has to be wrong. While photons aren’t the same size as ‘observers’ in our usual sense, they do demonstrate that if you want something like free will, and that there is locality in terms of physical interactions (or only things inside your light cone can affect you), then there is no single absolute record of events agreed upon by all observers.

Yep, that’s right. There’s no single objective reality. Will Zeng followed this up with another experiment - after all, what do photons prove about actual observers? A human is clearly a lot different than an observer in our usual sense. To wrangle with this problem Zeng constructs a metric called Branch Factor which measures how ‘classical’ an observing system is compared to a more ‘quantum’ system, and then implements an experiment on a superconducting qubit quantum processor to measure violations of Local Friendliness. As the quantum circuit gets bigger and incorporates more qubits, the branch factor increases, and so the overall system gets closer in size to what we think of as ‘observer scale.’ The interesting finding is that as they increased the size of the quantum circuit, they still found violations of Local Friendliness, with the caveat that noise in the system muddies the water a bit.

What to make of all this?

There are no real paradoxes

Here’s the funny thing about paradoxes - they aren’t actually real, rather they point to faulty world models. The apparent paradox of violations of Local Friendliness doesn’t mean reality is broken in some fundamental sense, just our assumption or conceptions about it. If we want to believe in free will, or locality, then there’s just no room left for a single objective reality in which all observers will agree on what happened.

This isn’t the first time an apparent paradox ends up just blasting apart our world model - special relativity had a similar effect in that two observers moving past each other at relativistic velocities might disagree about the size of an object, or, the timing or order of a sequence of events, or else how much time had elapsed. We thought time was this absolute thing that all people experienced the same way, but it turns out, nope, clocks run faster or slower depending on how fast they’re moving. Not just that, they run faster or slower depending on how far up or down a gravitational well you are, something that provides a necessary correction to GPS satellites that would otherwise drift in accuracy on the order of a few miles per day. Special relativity already has shown us that things like temporal duration, clock rate, physical size, and ordering of events is relative to an observer. EWF just takes this one step further - what events actually occurred or didn’t occur is also relative to the observer. This is certainly true at the scale of photons, and all the available experimental data show this doesn’t stop being true as the system size gets bigger.

This is of course extremely strange, but it actually solves another apparent paradox, time travel into the past. The physical possibility of faster-than-light travel does not violate any well-established physics when you consider the Alcubierre drive, which works by creating a positive curvature region of spacetime behind a craft and a negative curvature region of spacetime in front of the craft, creating a ‘wave’ that the ship surfs on. Locally, the ship never exceeds the speed of light, but relative to a distant observer it absolutely can. After all, the speed of light is always a local speed limit and there is no single universal reference frame. Usually constructing an Alcubierre drive requires some kind of preposterous engineering feat like compressing something the mass of Jupiter into a negative energy density, but more recent work shows this isn’t actually necessary at all. I mean, we’re just getting started here, and perhaps there’s kooky physics out there that might let us do things like polarize the local vacuum and change the effective speed of light and produce anti-gravity, like this paper by Hal Puthoff titled “Spacetime Metric Engineering.”

Lets suppose at some point in the distant future (or the secret past) humanity or other technological civilizations develop faster than light travel. You can get on an FTL ship, blast off into space effectively traveling into the past, and then turn around and head back to Earth, traveling even further into the past.

Now you do something silly like kill your own grandparents. Is there suddenly a paradox? Some kind of timeline shift where where you start disappearing from photographs? As it turns out - no. There is no single objective reality where all observers will agree on all events, rather, the only thing we can say for certain is this:

Every single observer exists in a self-consistent timeline of events.

In your past, you had parents, and grandparents, and so forth. You then went into the past and accidentally killed your own grandparents. You don’t suddenly cease to exist, because in your own timeline you had grandparents that weren’t killed by a time traveler. Rather, your act of homicide exists wholly within your own personal future, long after you were born. If you were to stick around in this new timeline your parents wouldn’t be born, there wouldn’t be a competing you, rather different things would unfold. There’s another funny thing we can piece together here - you entered some kind of different timeline without ever actually ‘leaving’ this universe. What do I mean by that?

There’s this concept floating around of ‘the multiverse’ or some kind of branching of universes on every event, quantum or not, constantly, in some kind of big mess of possible timelines. As if reality is constantly spawning copies of itself with super tiny variations. But here you are, having just clearly entered a new timeline of events that will unfold into the future. Clearly you just traversed the multiverse while maintaining your own self-consistent timeline of events. I’ll rephrase this with another rather outlandish sounding statement;

We live in the multiverse.

The multiverse isn’t some kind of ‘branching’ of realities where there’s infinite copies of yourself spawning every instant and you somehow only experience one of them. Rather the multiverse is composed of all the individual ‘universes’ made by each conscious observer as they go about producing a self-consistent timeline of events via observation. Two people might not agree on past events, but thats okay - they took place in different 'universes' (or really, timelines, since all these timelines exist within the same Hubble volume). There is no single objective reality or sequence of events agreed to by all observers, rather each observer is like the sole inhabitant of their own timeline, their own universe, self-consistent only to themselves.

We can get even weirder because by this point, if you haven’t been paying attention, I now consider it a taken-for-granted fact that alien civilizations have been paying visits to Earth for a long time, certainly at least since the nuclear bomb tests and possibly much longer. Why do I think that? Thousands of eye-witness reports, radar data, photographic evidence, and senior ranking military and intelligence officials from multiple countries all say its true, and I’ve seen things with my own eyes that match all these reports. How do we relate this to all this business about faster-than-light travel, multiple overlapping timelines, and no single objective reality?

What’s the deal with Earth and Aliens?

Is Earth a special planet? The conventional perspective in the scientific mainstream has a bit of an odd contradiction - we should assume that we occupy a fairly representative kind of place in the universe, at the same time, we’re the only conscious or technologically developed species as far as we can tell. The solar system is supposedly both typical, and, extraordinarily special at the same time. Humans are both just another species that evolved, and a once-in-four-hundred-billion fluke of history. We recently developed radios and radio astronomy and when we point these instruments at the night sky we don’t pick up a lot of radio waves, and because I suppose we think radios are the epitome of advanced technology conclude we’re the only ones here.

This should sound obviously dumb for lots of reasons, but the simplest way I can phrase is is a kind of lack of imagination or cultural blandness on our part. Rockets and Dyson Spheres and O’Neill cylinders are all very captivating science fiction from the 1950s through 1970s and we sort of ‘locked in’ to that interpretation of how the future would look, we can’t find any Dyson Spheres, and can’t imagine anything cooler and so conclude there’s no aliens.

But there are aliens and clearly they’re bopping around. What if Earth is somehow special? What if perhaps humanity has some kind of interesting role to play in future events? Perhaps we produce a galaxy spanning tyrannical empire like in Warhammer 40k, or perhaps we just throw the best parties or taste really good.

Or, as many suggest, perhaps some of these alien species are really just offshoots of humanity from the future - or perhaps, all of them are offshoots of humanity from different future timelines. Remember, we live in the multiverse - it’s not some kind of inaccessible parallel dimension that you can’t travel to, rather its just a whole bunch of different timelines that are produced by different collections of conscious observers going about doing their thing.

Now there’s lots of supposed different alien species in the lore and for the curious I’ll just name a few: the Nordics, the Grays, the Reptilians, the Mantids, etc, and according to whichever sources you read they apparently have a pretty diverse set of motivations, everything from eating children to making art in crop circles. The point is, for some reason they’re all visiting Earth in this time, right on the brink of humanity going off into space in a much larger capacity, developing things like artificial intelligence, having this kind of compounding rate of technological advancement and progress that’s going to start accelerating extremely quickly. If humanity spreads to the stars and spawns multiple independent colonies with competing interests, and they've all mastered spacetime metric engineering, why fight each other head-on? Why not just come back in time via FTL travel and subtlely influence things in their favor. In other words...

We see such variety among alien species and motivations because right now is the latest period in history in which all of humanity was on the same planet.

This era is the common ancestor all possible offshoot human civilizations. No matter how things pan out, if you want to tip the scales in your favor, this is perhaps an interesting time to travel to. Does humanity evolve into some kind of tyrannical cannibal cult that over millions of years evolves to look like reptiles? Or do we enter some kind of VR metaverse nightmare and become sexless, featureless, small-bodied Grey-skinned cyborgs? Or do we all take Bryan Johnson immortality potions and become beautiful long-haired peace-loving folks with smooth silky skin? Visitors can come from any possible future timeline and their own recollection of events on Earth can be wholly different from the sequence of events we're experiencing right now.

This is the weird thing with all this “no objective reality” business - it justifies the plot of Terminator fully, because you can just go back in time to influence a key tipping point in the history of the world, and then stick around to live in that universe instead of the one you left behind. Likewise entities from a future timeline that your own world is not leading into can come visit us here and mess around. Again there’s no paradox. In the distant future the human species has somehow inbred itself into a genetic dead-end, and it needs some fresh new blood to replenish the genestocks. So what do you do? Why, you kick up the FTL drive, travel back in time, abduct some genetically compatible ancestors, and there you go. Or even more easily - you just nudge world events a little bit without being too overt about it to prevent that dead-end metaverse outcome anyway. Oddly enough we can actually recover the rather conservative and skeptical view of most scientists today - there’s no aliens out there but us. Now all we have to assume is we make it off the rock and get better at engineering Alcubierre drives over time, and given sufficient incentives future humans start visiting us in the past for their own purposes.

In that sense perhaps Earth is like a battleground, or a melting pot, or just a rich source of novelty that future immortal alien species like to visit, as we do the 1980s to farm out makeovers of IP franchises that should’ve long been retired like Top Gun. There’s something about the 1980’s that is maybe very Earth-like in the Galactic context: full of passion, greed, sex and glamour, where people smoked cigarettes indoors and rode motorbikes without helmets. If the future of humanity is anything like the Nordics, or I should say Scandinavia - clean, functional, modern, egalitarian - you’ll recognize instantly they are somehow lacking this raw passion, this violent questing, and seem subsumed into a droll conformity and complacency. The system works, life is good, why change anything? That’s a pleasant society but its altogether rather boring. Lets go back to the 1980s, let’s go to Earth - where things are dangerous, competitive, passionate, dysfunctional. There’s something for everyone, really: people to help, people to hurt, children to eat, or abduct, or imbue with psychic powers, or whatever your favorite alien races motivation might be.

We’ve all fantasized about this kind of thing anyway. Going back in time to the Roman Empire with a machine gun and taking on the Gauls, or visiting the Battle of Troy and hooking up with Helen. The past has always seemed more passionate, more dangerous, more epic. It’s where we came from, after all. And in that sweet golden era to come, just after we nail down this space-time metric engineering and before they pass laws forbidding timeline manipulation, it can be where we’re going, too.