Welcome to the vast and infinite realm of the multiverse. There’s nothing quite like
it in all of science, physics, space, or theoretical thinking. It’s a concept
that essentially laughs in the face of most mainstream models on how the world works, and
provides us instead with an endless, glittering, constantly regenerating expanse… of potential.
By now, thanks in large part to various works of science fiction,
we of course know that the multiverse is multiple universes. A web of realities
that’s in some way entangled to form the true, wider, total physical structure that we are but
a tiny part of. It’s parallel dimensions and alternate realities; it’s bridges, wormholes,
quantum phenomena and time travel. It’s thrilling and it’s disconcerting.
Thankfully, then, some have at least tried to make even a little bit of sense out of it all. And,
today, we’re moving through the many levels of one explanation of the multiverse, in particular.
This is Unveiled, and today we’re taking an in-depth look at the nine
types of multiverse, according to the theoretical physicist Brian Greene.
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Brian Greene is a US physicist and mathematician. He was born in New York City, graduated Harvard
and Oxford, he’s a professor at Columbia University, and he founded (and chairs) the World
Science Festival. He’s also deeply integrated in the modern history of the multiverse.
In 2012, Greene released his book, “The Hidden Reality: Parallel Universes and the Deep Laws
of the Cosmos”. In it, he outlines one of the most comprehensive attempts to explain the multiverse,
in full, dividing it all into nine more specific categories. While variations
of the categories had been seen (and debated) before, by others,
Greene pools them all together in a bid to finally nail down the true nature of reality.
#1: The Quilted Multiverse
In general, this is the simplest of all Greene’s multiverse types. The quilted multiverse only
really requires this universe to be infinite - which many believe that it is. From there,
all manner of arguably “parallel” worlds are possible. It certainly works in theory because in
an infinite structure, everything should be (and happen) an infinite number of times - including
all possible variations of physical matter. Greene suggests that it’s only due to the
universal speed limit - the speed of light - that we’re wholly unaware of the multiverse we’re in.
If true, one of the implications is that not only do we share this universe with other life forms,
but we share it with other versions of ourselves. Naturally, we know that life the like of which we
find on Earth is possible… because we’re the proof of it. So, in the quilted multiverse,
somewhere beyond the catchment of lightspeed, life as we know it should happen again. And
again. And again, an infinite number of times. On a larger scale, the same should
be true for planets and stars. Meaning that, in this quilted reality, there should be other
instances of Earth and the sun, of our entire solar system, exactly as we know them. And,
in fact, there should be an infinite number of other solar systems, just like this one.
The other implication is that if we could only find a way to travel beyond lightspeed,
then we would eventually discover this multiverse with our own eyes. In simple terms,
it should be only a matter of traveling in any direction for long enough before we inevitably
encounter ourselves, again. As to all of the other variations of life, matter and
energy that we might find along the way… it’s a patchwork of yet more infinite possibilities.
#2: The Inflationary Multiverse
Sometimes referred to as the bubble multiverse, this rendering asks us
to take our first major step away from the conventional cosmos, as we typically know
it. The inflationary multiverse is born out of eternal inflation theory… which says that,
at the highest level, our reality is always expanding, and that an event such
as the big bang could actually be caused by that expansion, rather than being the cause of it.
Along our own timeline, we know that there was a period of extremely rapid expansion
that occurred fractions of a second after our universe began. During this fleeting moment,
space-time grew faster than light speed. A subatomic speck was transformed into a sprawling
expanse teeming with energy and potential. And this initial burst set everything in motion. But,
in the higher, wider inflationary multiverse, it didn't happen just once.
Such inflation wasn’t an isolated event, but was (and is) an ongoing process occurring in
different regions at different times - like popcorn kernels popping endlessly in a vast,
cosmic popper. Each kernel represents potential universes within bubbles that are expanding within
higher-dimensional space. But, no one piece of popcorn pops at exactly the same time, nor in
exactly the same way. Scaled up to multiverse level, this means that every bubble universe
that’s created isn't just separate; but should also have its own unique laws and parameters.
The laws of physics that we know are universal, yes, but perhaps they aren’t multiversal. Every
bubble stands alone. One might have stronger gravity, for example, or no electromagnetism.
Another could be teeming with forms of matter that are fundamentally alien to us.
#3: The Brane Multiverse
With its roots in M-theory - an extension of string theory that requires eleven dimensions
to work - the brane multiverse model also suggests that everything we know exists as just one of many
on another, higher plane. This time, however, the universe is a three-dimensional membrane,
floating in a higher dimensional space - sometimes called the bulk or hyperspace.
Brane cosmologists also suggest that the infinite nature of reality should mean
that there are endless other membranes out there, all also suspended in the same broader structure.
One key implication, however, is that it might be possible for separate membranes
to interact. And for those interactions to then have a profound effect. From our point of view,
perhaps our membrane - our universe - has before collided with another. Or maybe we’ve spent our
entire 13.8 billion years overlapping with a nearby membrane - another reality - which
has then in some way shaped this reality in a fundamental sense.
The brane multiverse also triggers all new considerations when it comes to potentially
moving through the multiverse. Whereas in the quilted and (to some degree) inflationary models,
traveling the multiverse may only ever boil down to reaching (and breaking) light speed…
in the brane, a would-be traveler would need to physically cross over from this world to another.
#4: The Cyclic Multiverse
This grade of multiverse is closely related to the previous brane model,
but it rests on one idea, in particular. In the cyclic multiverse, membrane universes
certainly do interact with each other, and in the most profound way possible…
because collisions between branes are here what double up as big bang events.
Now, the multiverse assumes a more dynamic and even more eternal regenerative trait,
as the membranes in the bulk also become the birthers of other universes, just by being
there. The precise mechanics of how a membrane collision could cause something as dramatic as a
singularity cascading into life… are unknown. But, if true, it’s a model that repaints hyperspace as
being something like an easel, upon which a chain reaction of creation is constantly unfolding.
Of course, this is hardly the only cyclic model in cosmology, in general. The big bounce theory
has fallen in and out of favor over the years, suggesting that universal expansion will one
day halt, and everything will contract back inwards from that point… until such time as
it’s all compacted back down into a singularity, and the big bang happens again. At that moment,
it could be said that the universe will have been bounced back out into space.
The cyclic multiverse, by comparison, employs a similar logic, but on an even grander scale.
#5: The Landscape Multiverse
Next, and we’re heading full tilt into string theory, probably the most well known attempt
at a “theory of everything” there is. It posits that the fundamental constituents
of reality are one-dimensional, vibrating "strings" rather than point-like particles.
And one (of many) things that this would affect is the makeup of the multiverse.
In general, string theory allows for many different ways in which its strings can vibrate,
and each mode of vibration corresponds to a different elementary particle. Meanwhile,
and as a result of that, reality is really divided into many more dimensions than just
the three space plus time that we’re familiar with. There are then many possible shapes that
all of those extra dimensions can take, when they’re compacted down. In fact,
there could be an effectively endless number of shapes possible,
each leading to an all new universe with its own distinct set of physical laws.
The landscape of the “landscape multiverse”, then, pitches these different universes as
though they exist along a never ending series of hills and valleys. Every universe of the
multiverse… appears somewhere along this structure. Some are more stable than others,
but none are identical. All are unique. In this view, our universe just so happens to reside in
one valley within this broader landscape created by the fundamentals of string theory. And our
particular set of physical laws corresponds to just one way in which strings can vibrate.
But, all the while there are infinite other valleys and environments out there,
to represent all other universes with different laws derived from their own
unique vibrational patterns. And their own unique shape, taken as a result.
#6: The Quantum Multiverse
Along with the quilted multiverse, this is probably the most widely known and
discussed of all Greene’s nine types. The quantum multiverse suggests that at
every moment when a choice or diversion is made, a new universe is created along
with the one we inhabit. It works on both the micro and macro levels,
and is best laid out by the famed Many Worlds Interpretation of quantum mechanics.
On the quantum level, due to various phenomena including the observer effect and wavefunction
collapse, we know that particles can be one thing or another - until they
eventually settle down into what they ultimately become. But the quantum multiverse imagines that
nothing is lost as reality takes shape; that all possible outcomes take place,
just along an endless mesh of different timelines. These timelines (or what some
refer to as parallel worlds) are constantly branching off from the one you’re in right
now… which, in itself, has branched off of uncountable others in the past.
It’s perhaps more satisfying to visualize at a larger scale, though. Consider all of
the choices you’ve already made today. What you had for breakfast; what you said to a colleague;
how many YouTube videos you’ve watched; whether or not you scratched behind your left ear,
switched your alarm to snooze, or tripped on your own doorstep. You might think of some
of your actions as being more consequential than others, but in the quantum multiverse
they’re all equally valuable… because they all spawn parallel worlds of what could have been.
Apply the same thinking to every single quantum fluctuation that’s happening all around you,
countless times, during every single second of your existence… and the sheer density of
this particular multiverse becomes clear. Some strands of it will be almost indistinguishable
from the one along which you’re currently living. But, still, take just a short journey through it,
and you could very quickly end up in an entirely alien place.
#7: The Holographic Multiverse
This wouldn’t be a video about the true underlying physics of reality without at
least a passing mention of black holes - and this is that mention! The holographic multiverse builds
on the holographic principle, which says that our three-dimensional reality could be encoded
on a two-dimensional plane. That everything we know - from stars and planets to cars
and sandwiches - is actually projected from that 2D structure, to generate our universe.
It ties back to black holes as a possible solution for the black hole information paradox. This is
the realization that information is seemingly lost in black holes that eventually evaporate away,
despite that apparently being impossible as per the conventional laws of physics.
Grand cosmic holography isn’t the only - or even the most well supported - solution,
but for advocates it could be that the seemingly lost information within a
black hole is actually encoded in 2D along the event horizon.
Apply a similar model to the entirety of the universe, and it could well be a process that
happens time and time and time again. And suddenly the multiverse begins to feel like
a multiplex cinema, with multiple movies (or realities) playing across multiple screens
(or spaces). Perhaps more than any other model up until this point, it could quickly make you
feel quite… inconsequential. Suggesting, as it does, that at your root you’re not
even a three-dimensional being. However, and as with all proposed multiverse types,
it can also easily be argued that, really, it doesn’t matter. That, even if life,
the universe and everything is a hologram, nothing actually changes from our point of view.
#8: The Simulated Multiverse
This is another of the more widely known multiverse possibilities,
given how it’s permeated pop culture in recent times. Born out of the simulation hypothesis,
as proposed by Nick Bostrom, it says that our universe is first and foremost a
product of complex digital code. That everything we know, see and feel is only ever the result of
a program that’s running on some far-off supercomputer, in a higher dimension.
For those in favor, it might even be argued that a simulated multiverse is inevitable so long as
technology progresses. In our own world, we’ve seen how computer simulated games and virtual
reality experiences have become more and more life-like over a relatively short period of
time… to the point that some have predicted it may be impossible to tell the difference between
the real world and a simulated environment, in the future. Ideas on the simulated multiverse
simply approach that line of thinking from a different perspective. Because, what if,
for some other, higher, more advanced civilization or entity, that line has already been passed… and
we’re the ones being convinced (or tricked) by it? What if our world is just a very good sim?
Traditionally - so to speak - it was an idea that led some to envisage one single controller
or player; a supreme, god-like being who’s watching over our every move, because they’ve
designed every single thing about us. But combine all the potential for a simulated reality with
the endless repetition of a multiverse… and you quickly land on something even bigger.
If simulated universes are possible, and if multiple universes are possible,
then all that we know could (even should) be just one variation of cosmic code in amongst
an endless stream. Consider that we, ourselves, have constructed simulated realities, albeit quite
primitive and superficial at present. This would mean that our controller created us to create
and control others. So, why not a creator for our controller, to control them while they control us,
while we control our sims, and so on? Then consider that comparable chains must surely
be erupting an infinite number of times along an infinite number of other chains,
and we again have one of the deepest and densest multiverses imaginable.
#9: The Ultimate Multiverse
Finally, to an effectively unknowable multiverse that represents the most
expansive and all-encompassing of all concepts possible. In this view,
every conceivable universe with every possible set of physical laws and constants exists
within a grand cosmic collection. Imagine that you could lay all of everything we’ve covered
in this video out on the table, and bag it up. The ultimate multiverse is that bag.
Sometimes referred to as the mathematical multiverse,
and directly comparable to Max Tegmark’s level four multiverse,
it transcends all possible constraints that might be placed on any other multiverse version.
In this staggering vision, not only are there universes like ours with slight variations,
or even like ours but with radical differences… there are also universes that are governed by
completely different mathematics. This means that any form of logical or mathematical structure
that can exist does exist as a separate reality somewhere within this overriding,
ultimate landscape. In this way, most of it is impossible for us to even picture,
given the limited view that we inescapably have. It’s a final structure that pushes infinitely
far beyond our understanding of physics because it suggests that our own universe's laws - everything
from quantum mechanics to general relativity - are not uniquely fundamental in any way,
whatsoever. Instead, we’re merely cast adrift in an endless sea of theoretical frameworks.
While highly speculative and abstract, contemplating such a multiverse challenges
us to reconsider what we deem as necessary truths about existence,
in general. It opens up profound questions about reality's true nature and our place
within it. It may be, then, that our universe isn’t just one page in a much longer book,
but that it’s one page in an endless library. For some, the ultimate multiverse could even lead to
a multiverse of multiverses, contained only by the one truth that it cannot be contained.
So, what do you think? Which of Brian Greene’s nine types of multiverse do
you think hits closest to the truth? Or are you unconvinced by the idea of
a multiverse in any form? Let us know your take in the comments!
For now, while the prospect of a multiverse is increasingly covered in contemporary science,
it remains true that - at its heart - there are questions that humankind
has always wrestled with and will always wonder about. Why are we
here? What is our purpose? How real is real? And what does tomorrow hold?
Importantly, the multiverse has yet to be proven. But,
it’s an idea that’s very much alive, and challenging us all to take a higher, wider view.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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