Theories about our universe in fact being a multiverse, are becoming increasingly well-known.
Science has moved on to such a degree that now the idea that everyone and
thing could be endlessly doubled elsewhere across reality… is becoming more and more
accepted. We still don’t know with absolute certainty that the multiverse (in any form)
is correct… but, according to some physicists, its existence should be
inevitable. All of which means that some have added rules and details to the theory,
to blow our minds just a little bit more. This is Unveiled and today we’re answering
the extraordinary question: What if humanity lives in a level two multiverse?
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The multiverse is a popular subject both in science and science fiction. And,
despite its seemingly outlandish nature, there’s good reason to believe in it according to our
current understanding of the laws of physics. Naturally, then, some scientists take the concept
of the multiverse extremely seriously… including the esteemed physicist Max Tegmark, who has gone
so far as to create a multi-levelled framework of the potential multiverses that we could live in.
Tegmark’s model extends from a level one multiverse, which is generally
the most accepted and considered the least controversial, through to levels two, three,
and finally, four. Each level builds onto the previous ones, allowing for even more diversity
and possibilities than its predecessor. A level one multiverse mainly relies on two
scientific assumptions that govern our current understanding of the universe:
that space is infinite, and that matter is spread evenly throughout. Both assumptions appear to be
supported by modern observations, which is why Tegmark’s level one generally receives the least
resistance from other scientists. The idea is that if this is the case (if space is infinite
and matter is evenly spread) then all particle arrangements, no matter how unlikely, will appear
somewhere in this never-ending expanse. And then they’ll appear again, and again, and again. This
reasoning then leads to a level one multiverse where it’s seen as inevitable for everyone to
have an exact clone of themselves living somewhere else in space, in a universe that’s just like this
one. There are also many universes that are very different to this one, too - remembering, again,
that all particle arrangements are possible - but the fundamental laws of physics do at least remain
the same. We took a deeper dive into level one in a previous video (so be sure to check that out)
but for today, we’re focussing on the next level: level two.
A level two multiverse, according to Max Tegmark, takes the idea further and envisions even more
varied possible universes. In a level one multiverse, space stretches on infinitely
and encompasses everything we know… but it is all at least still contained within the same
infinite structure. A level two multiverse, however, proposes that our universe (or our level
one multiverse) is actually held in a bubble… and that that bubble is surrounded by countless other
bubble universes, some of which are again like our own and some of which are very different.
These bubbles are then separated by vast stretches of spacetime to form the new and overriding
multiverse structure. The gaps between could be so vast, however, that even were you to be travelling
at the speed of light, you wouldn’t be speedy enough to move between them… since the spacetime
itself is expanding faster than even that. Moving between (or communicating with) universes in a
level two multiverse, then, is theoretically even more difficult than it would be in level one.
But, nevertheless, what happens in these other, unreachable bubble universes? Well, according to
the theory, some could have totally different physical and fundamental characteristics. This
is the main difference between level two and level one. As they’re not necessarily guided by the same
fundamental laws, these other, bubble worlds could have different dimensions, different physical
constants, and even different elementary particles from those we see in our own. This creates the
potential for some seriously strange universes where, for example, gravity is weaker, so there’s
no such thing as a home star or star systems… or where atoms are unable to form altogether,
and so there are no stars to speak of. For decades, scientists have puzzled over how
it is that our universe right now appears to have hit a kind of sweet spot with the laws of physics,
enabling things to be the way they are and for life to form. This idea isn’t always all that
popular because it suggests that the universe works due to pure chance and coincidence… which
is frustrating at best, and faintly terrifying at worst. But, here, a level two multiverse
is seemingly able to provide answers. Broadly speaking, the issue of the universe having perfect
values for life is called the fine-tuning problem. Regularly cited examples of it in our world
include the masses of elementary particles and the density of dark energy, both of which have to be
exact. If they weren’t exact, then the chances are that we wouldn’t be here to ponder them… because
none of this universe would be possible. If our universe were the only universe in existence,
the chances of these numbers being so perfect seems frankly impossible...
and that’s the fine-tuning problem in action. In a level two multiverse, however, the problem
is solved because our universe is no longer alone. It’s simply the one that did work while endless
others didn’t. Among the infinite bubbles that a level two multiverse proposes are, then, an untold
number of bubbles that could never support life or form basic elements… which makes it
easier to accept that ours, through sheer cosmic repetition, can. On the other side of the coin, it
also follows that in a level two multiverse there are also other bubbles that can form everything
we know, and more. Physically impossible life forms and structures from our point of view,
but simple and expected in these other worlds. The possibilities here are essentially endless.
There could be alternate bubble universes where the speed of light is significantly
faster, allowing for more stars to be visible… but also ones where light doesn’t move at all,
and darkness reigns. Or so many others where hydrogen and helium weren’t quite so crucial (or,
in fact, never formed) and so the universe grows differently from the outset. Or perhaps carbon
isn’t so abundant, and so life uses something else. Then again, life forms in another bubble
could be living out their lives in two dimensions, all while trying to work out the third dimension…
whilst the inhabitants of another exist in seven dimensions all at once,
making them naturally able to experience things we ourselves can barely comprehend.
And yet, they would think nothing of it. It’s predicted that all these different worlds,
in a level two multiverse, exist inside of an infinitely expanding pattern of bubbles that’s
forever unknowable to us. Were we to somehow observe them from afar, then we’d need a god-like
level of power. This level of the multiverse does share similarities with other theories, though,
as Tegmark himself has variously pointed out. According to the physicist Lee Smolin,
for example, our expanding universe could theoretically create black holes so dense and
endless that other universes could potentially form inside of those. Another theory holds that
multiple universes could instead form out of an infinite series of big bangs across space.
There are of course big differences between these ideas, but they’re all linked by the suggestion of
a multiverse that could hold universes which all have totally different fundamental properties.
Changing dimensions of time and space, a differing number of elements,
or a changing makeup of atoms and matter. One question this might cause scientists to ask,
then, is… which conditions really are ideal for life?
So far, we’re the only example of life we can see in our universe, but does that automatically mean
that our universe is best suited? Or could it be that there are other universes out there,
in different multiverse bubbles, where life flourishes on every planet, and not just one?
Is there, then, a perfect universe in amongst the countless possibilities? And is that a reassuring
thought for us down here, or could it trigger a world-wide (universe-wide) existential crisis??
If nothing else, we can see that a level two multiverse is massive. Both in terms of physical
size and in terms of how much its existence could shatter more traditional universe models.
But, really, we’re still only halfway through Tegmark’s proposed multiverse road map,
with levels three and four soon to feature in upcoming videos. So, look out for those,
but in the meantime… that’s what would happen if humanity lived in a level two multiverse.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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