Last time, we looked at Max Tegmark’s version of the multiverse theory and its 4 levels.
We briefly discussed what each of these levels of the multiverse would be like under Tegmark’s
interpretation. Today, we will take an in-depth look at what the Level 1 multiverse is all
about.
Around 1980, Alan Guth discovered some serious problems with the earliest stages of Alexander
Friedmann’s version of the Big Bang model. In particular, the horizon problem; which
says that if the Big Bang explosion happened everywhere, at an infinite number of points,
then why is it the case that the temperature of the cosmic microwave–background radiation
is almost identical in different regions of space? And the flatness problem; which simply
asks, why is our universe so flat despite it being a highly unlikely outcome according
to Friedmann’s equation. To answer these fine-tuning problems, Alan Guth proposed a
revolutionary solution that he called inflation. He assumed the existence of an extremely dense
point-like substance that was there before the Big Bang that defies all our everyday
experiences. Meaning, if 1 gram of this substance expanded into twice the volume, its density
would remain the same producing 2 grams of the substance. According to Einstein’s theory
of gravity, such a substance could undergo a most remarkable explosion doubling its size
at an exponential rate. This repeated doubling of the size automatically causes repeated
doubling of the expansion speed. However, this exponential inflation process eventually
slowed down to a much more relaxed pace, at least in our visible universe, as the inflating
material decayed into ordinary matter gradually decelerated by gravity. Now, it should be
noted that inflation generally refuses to stop, forever producing more space, as discovered
for specific models by Andrei Linde and Paul Steinhardt. This is the concept of eternal
inflation, the discovery of which has radically transformed our understanding of what’s
out there in space on the largest scales. Moreover, the observations of Edwin Hubble
and the discovery of dark energy gave a huge credibility boost to the theory of inflation
further solidifying its place in the scientific literature. In summary, inflation has radically
transformed our understanding of our cosmic origins, giving us infinite space with an
infinite number of galaxies, stars, and planets.
Now, assuming inflation really happened and made our space infinite. Then there are infinitely
many Level I parallel universes. Our visible universe is about 93 billion light-years across.
The most distant visible objects are now about 4 ×10^26 meters away, and a sphere of this
radius defines our observable universe, also called our Hubble volume, or our horizon volume
or simply our universe. Moreover, all the infinite space was created full of matter
which, much like here in our own Universe, gradually formed atoms, galaxies, stars and
planets. This means that most of the Level I parallel universes shared our own cosmic
history in general. However, they may differ from our Universe in the details, because
they started out slightly differently due to random quantum seed fluctuations. So, there
are infinitely many other inhabited planets, including not just one but infinitely many
with people with the same appearance, name and memories as you. Actually, there are infinitely
many other regions the size of our observable universe, where every possible cosmic history
is played out. This is the Level I multiverse. In fact, Max Tegmark estimates that if you
traveled in a straight line for about 10^10^118 meters, you would come across an identical
copy of our observable universe. But if you wanted to meet an identical copy of you, then
the distance to that would be relatively less, about 10^10^29 meters away, which is still
beyond astronomical.
Now, our physics description of the world is usually split into two parts: how things
start out and how they change. In other words, we have initial conditions as well as the
laws of physics that specify how these initial conditions evolve over time. For this reason,
observers living in a Level I multiverse observe the exact same laws of physics as we do, but
with different initial conditions than those in our Universe. For example, for different
level 1 parallel universes, some particles may start out in slightly different places,
moving with slightly different speeds. These slight differences ultimately determine what
happens in their universes; like which regions turn into galaxies, which regions become intergalactic
voids, which stars get planets, which planets get dinosaurs, which planets get their dinosaurs
killed by an asteroid collision, and so on. In other words, the quantum-induced differences
between parallel universes get amplified over time into very different histories. So, people
in Level I parallel universes would learn the exact same thing in physics class but
different things in history class.
Now it may seem extremely unlikely that your life turned out exactly as it did, since it
required so many things to happen. For example, Earth had to form, life had to evolve, your
parents had to meet and so on. But the probability of all these outcomes happening clearly isn’t
zero, since it in fact happened right here in our Universe. And if you roll the dice
enough times, even the most unlikely things are guaranteed to happen. With infinitely
many Level I parallel universes created by inflation, quantum fluctuations effectively
rolled the dice infinitely many times, guaranteeing with 100% certainty that your life would occur
in one of them. Indeed, in infinitely many of them, since even a tiny fraction of an
infinite number is still an infinite number.
And an infinite space doesn’t contain only exact copies of you. It contains many more
people who are almost like you, yet slightly different. So, if you were able to go meet
the closest person out there in space who looked like your identical copy, this person
would probably speak an alien language you couldn’t understand and would have experienced
a life quite different from yours. But out of all your infinitely many look-alikes out
there on other planets, there’s also one who speaks English, lives on a planet identical
to Earth, and has experienced a life completely indistinguishable from yours in every way.
This person subjectively feels exactly like you feel, yet there may be some very minor
difference in how the particles move in your identical twin’s brain causing your two
lives to start diverging from this moment onwards.
Nonetheless, in an infinite space created by inflation, everything that can happen according
to the laws of physics does happen. And it happens an infinite number of times. In fact,
for there to be no Level I parallel universes at all, there must be no space whatsoever
beyond the region we can see. And to assume that only what we see can only exist is like
an ostrich with its head in the sand, claiming that only what it can see can exist according
to Tegmark. Thus, the Level 1 Multiverse is a natural consequence of the theory of inflation
and has as much evidence for it as theory of inflation itself. But the Level 1 Multiverse
is just the beginning of what the theory of inflation predicts. Chaotic eternal theory
of inflation predicts an even higher level of the Multiverse, that Tegmark refers to
as the Level 2 Multiverse. But that is a discussion for another time!
If you enjoyed this video, do leave a like, share and subscribe to our channel for more
content ahead. Is our universe truly infinite as predicted by inflation, or just extremely
large and finite? Let us know your thoughts down below! Until then, we’ll see you in
the next one!