A new book explores how the concept of the multiverse has evolved

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The Number of the Heavens
Tom Siegfried
Harvard Univ., $29.95

There is no bigger question than whether the universe is all there is.

Scientists are
juggling several ideas for what a multiverse, if one exists, might be like. Our
universe could be one bubble in a vast cosmic fizz. Or one of many 3-D domains
stacked, like pages of a book, in higher dimensional space. Or one series of
events that continually branches off from other histories in a tree of
alternate realities. All these possibilities, while tantalizing, remain
unconfirmed.

The prospect of many universes has
intrigued scholars for millennia — and has evolved to mean different things, as
humankind’s concept of the universe has zoomed out from a single solar system
to a galaxy to a great cosmic web.

“The multiverse debate is like a
long-running TV series with new characters replacing the old ones,” science
journalist Tom Siegfried, a former editor in chief of Science News and
current contributing correspondent, writes in The Number of the Heavens.
His new book is a recap of that age-old discourse.

Each rendition of the multiverse debate
has revisited common themes, including whether science has any business
speculating about unobservable realms. Each iteration has had its believers and
its naysayers. But those curious minds have been united in their common
fascination with one of the most profound mysteries of all time: What is the
entirety of existence?

Science News spoke with Siegfried about what we can learn from
past generations of multiverse debates and how scientists might determine
whether a multiverse exists. The following conversation has been edited for
length and clarity.

Tom Siegfried
Science journalist Tom Siegfried is the author of The Number of the HeavensCourtesy of T. Siegfried

SN: Were there any historical details that caught you by surprise?

Siegfried: I
hadn’t appreciated the extent to which the multiverse had been an issue in
ancient Greece. The atomists were the ancient Greeks known for suggesting the
existence of atoms, which was contrary to what the prevailing views were. I
wasn’t aware that the atomists had also been such advocates for the
multiplicity of universes. Their belief that the universe had been made of
atoms required an infinite number of atoms, and if there were an infinite
number of atoms that you needed to make that structure, then there would be an
infinite number of atoms left to make other universes.

SN: Are there ways to test any of the modern conceptions of the multiverse?

Siegfried: They might be long
shots, but it’s not impossible. If there are other [bubble universes] out there,
it is conceivable that one of those bubbles could collide with our bubble and
imprint on the cosmic microwave background radiation in space to reveal that.

But the main point that people overlook
is, the multiverse is not a theory. The multiverse is a prediction of other
theories [such as superstring theory] that can be tested in other ways. If you
have a theory that makes many testable predictions that turn out to be right,
that implies the existence of other things the theory predicts. Atoms could not
be observed directly for [about] 2,500 years. But they were nevertheless
inferred to exist by things that could be observed. The multiverse could be the
same way.

SN: You recount how, in 1277, the bishop of Paris declared it heresy to teach the Aristotelian view that God couldn’t make multiple worlds, granting medieval scholars new freedom to contemplate the multiverse. Have there been similar paradigm-shifting moments for the multiverse question in the modern era?

Siegfried: The underlying belief
among physicists for a long time has been that there is a theory out there that
could specify everything there is to specify about the universe. In 1998, when
the discovery of the acceleration of the expansion of the universe was announced,
that changed the game. Now you had this apparent force called dark energy
driving the universe to expand faster and faster, which had to be of a
magnitude that the fundamental physical theories we had could not explain.

That freed up physicists to explore issues
outside the prevailing view that there was one specification for all the forces
and properties of the universe. It led to this idea that there could be
multiple universes, and that dark energy is the amount that it is in our
universe because that amount produces a universe that’s hospitable for life.

SN: What can people contemplating the multiverse today learn from people who have asked similar questions in the past?

Siegfried: Two things. One is, every time this issue has come up, of whether there’s one universe — as was conceived at that time — or many, the answer has always been many. That doesn’t mean that it’s going to be the case this time for sure. But it is an instructive point. Second is that history shows that [contemplating the multiverse] is a scientific question. It is not a
metaphysical question or a meaningless question. It is a legitimate scientific
question that warrants further investigation — and scientific research might
someday provide the answer.

SN: You write that you believe “it makes much more sense for a multiverse to exist than not.” What would you be willing to bet that we live in a multiverse?

Siegfried: [Laughs.] I would not wager on this, because I only bet on sure things. I like the idea. It’s got great explanatory power, and I find it pleasing. But that doesn’t translate, in my mind, to mean it has to be true. I have to just wait as the evidence comes in, and the evidence hasn’t definitely answered the question yet.


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Originally posted by: Maria Temming

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