The Multiverse Idea: Could There Be Many Universes?

multiverse idea says that many universes exist, possibly an infinite
number of them. The word “Universe” literally means everything
that there is, but it can also be more narrowly defined as everything
that we can observe. This narrow definition allows for the
possibility that other universes exist beyond this one, it’s just
that we can’t observe them or at least we haven’t received any
evidence that they exist yet. The multiverse idea can be traced all
the way back to the Greek philosopher Democritus (460 BC). Over 2000
years ago philosophers such as Democritus, Leucippus, Heraclitus and
Lucretius were already arguing that everything was made of “atoms”
– little bits of matter. Democritus also talked about there being
“more worlds” and that some of them will be very different to the
one we know.

The Italian astronomer Giordano Bruno wrote in his book
On the Infinite Universe and Worlds
(1584) that he thought since God is infinite, he must’ve made an
infinite universe, with an infinite number of separate “worlds”.
Although in contrast to Democritus’ idea that these worlds would be
hugely different from ours, Bruno writes: “In it [the Universe] are
an infinity of worlds of the same kind as our own”. People have
said that Bruno foreshadowed Hugh Everett’s many-worlds
interpretation of quantum mechanics. But I’ll get to Everett’s theory
later on. Bruno’s claim that many worlds exist would land him in a
lot of trouble. The Roman Inquisition confronted him about these
views, asking him to deny them. He refused to and was eventually put
on trial, imprisoned and finally executed (by being burned at the

idea that many worlds or many universes exist has been, and still is,
a controversial idea. But at least it can be discussed without
threats of execution from the Catholic Church. There are many
variations on the multiverse idea and each one is as interesting as
the next. The idea of “parallel universes” or “alternate
realities” is one of them and is commonly imagined in many science fiction
and fantasy stories. Jorge Luis Borges looks at this theme in his short story
The Garden of Forking Paths
(1941) where each “path” in the story is revealed to be a
separate future. The idea of alternative realities is a common theme
in Philip K Dick’s works, in books such as Ubik and
The Three Stigmata of Palmer Eldritch.
These fictional scenarios might, however, correspond to how
things really are.

reason why the multiverse idea could turn out to be true is because
of something called the fine-tuning problem.
In our universe, there are certain values, such as the strength of
gravity and the mass of the electron, which make life possible. If
gravity was just a tiny bit weaker, the universe would’ve expanded
much faster after the Big Bang and clusters of gas and particles
would not have formed. There would be no planets and therefore
nowhere for life to evolve. If gravity were just a tiny bit stronger,
then expansion would be slower and eventually all the matter that did
expand would soon be compacted together in a kind of Big Crunch. Life
also couldn’t evolve in this kind of scenario since it would be
crushed by the weight of gravity. The gravitational force, like many
other “constants” in nature, appears to be tuned just right to
support the formation of galaxies, stars, planets and life. If many
universes exist, then it could just be that we got “lucky” with
our particular constants – we don’t have to say that our universe
was “designed” (by a god, alien civilisation, computer simulation

The same reasoning applies to the fact that we live in 3
spatial dimensions, not more or less. The anthropic
says that we shouldn’t
be surprised to find ourselves in a universe suitable for life, since
out of all the many universes that exist, at least one (however
unlikely that may be) will have laws which support the existence of life. Furthermore, if there is an infinite array of universes, we should be even less surprised.

equations of general relativity predict that at the centre of each
black hole is a singularity.
The singularity is where space-time curves to become infinite (if you
can imagine that) and it also has infinite density. Since our
universe also came from a singularity, some have argued that inside
each black hole a new “baby” universe is created. So our universe
could be a parent universe or a baby universe.

The physicist Lee
Smolin argues in his book The Life of the Cosmos
that natural selection, which is responsible for biological
evolution, could also be responsible for the universes with a
particular set of laws. For example, natural selection could favour
universes which are the best at reproducing. If universes are born in
black holes, then the best universes for reproducing are ones which
produce black holes. Furthermore, the laws of physics which guarantee black
holes are the laws which we have in our universe. So we really
shouldn’t be surprised to find that we live in a universe where
galaxies and life-forms exist – they are a natural consequence of
the fact that our universe is effective at producing black holes.

Linde has proposed that there could be an “eternal” inflating
Universe, where separate Big Bangs are going on all the time,
inflating to become separate universes with their own region of
space-time. Each universe can be thought of as a soap bubble lying
close to another soap bubble, but being completely cut off from it as

Hugh Everett’s many-worlds interpretation of quantum mechanics follows a principle of quantum mechanics to an interesting
conclusion. In quantum mechanics, a particle can exist in many
different states, but when it is observed it exists in only one of
them. Everett’s interpretation says that the particle exists in all
of these possible states, in a different universe. So every possible
decision you could have made, you will have made, only in a different
universe. We can never know about these “alternate histories”
though because they cannot interact with each other. The outlook of
the many-worlds interpretation can be represented by a many-branched
tree, where each branch is a different universe, unable to touch
another branch that has split off from it.

common criticism of the multiverse idea is that it is unscientific.
If we cannot know about or observe these other universes or alternate
realities, then how can we ever find out if they exist? The point of
any scientific hypothesis is that it has to be testable. If the
hypothesis cannot be tested, then no evidence can be gathered to
either support it or disprove it. Paul Davies in his article A
Brief History of the Multiverse

argues that the multiverse idea is similar to using God to explain
the universe: they both assume the existence of something “unseen”
to explain what we can see. Both explanations, Davies says, are based
on faith. 

However, the physicist Laura Mersini-Houghton and her team
developed a multiverse theory which makes four predictions. Three of
these predictions were confirmed by them, one of them being a “cold
spot” in a universe which was taken to be a sign of “the
unmistakable imprint of another universe beyond the edge of our own.”
These “confirmed predictions” are controversial, but at least
they show how the multiverse idea is not beyond the scope of scientific investigation.

Another criticism of the multiverse idea is that it seems to contradict a rule of thumb known as Occam’s Razor.
This is a principle that comes from William of Ockham (1287-1347) and
it says that you should accept the explanation which is the simplest or makes
the fewest assumptions. Some say that the multiverse idea makes too
many assumptions, since in some cases it assumes that an infinite
number of universes exist. Max Tegmark has replied to this by
emphasising that the simplest and most elegant theories include
parallel universes by default. He says to exclude these parallel
universes would only complicate the theory. Thus, the multiverse idea may
be the simplest way to explain our universe. This seems strange – even
counter-intuitive – but that doesn’t mean it’s not true.


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