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FEB 4, 2013 11:31 AM 95,037 488 Share
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What is the purpose of the Universe? Here is
one possible answer.
George
Dvorsky
The more we learn about the universe, the more
we discover just how diverse all its planets, stars, nebulae and unexplained
chunks of matter really are. So what is all this matter doing in our universe,
other than just floating in space?
Well, it just so happens that there is a theory
that gives a kind of raison d'etre to our universe and all the objects flying
through it. If true, it would mean that our universe is nothing more than a
black hole generator, or a means to produce as many baby universes as possible.
To learn more, we spoke to the man who came up with the idea.
It's called the theory of Cosmological Natural
Selection and it was conjured by Lee Smolin, a researcher at the Perimeter
Institute for Theoretical Physics and and an adjunct professor of physics at
the University of Waterloo.
In his book, The Life of the Cosmos, Smolin
proposed that Darwinian processes still apply at the extreme macro-scale and to
non-biological entities. Because the universe is a potentially replicative
unit, he suggests that it's subject to selectional pressures. Consequently,
nearly everything the universe does is geared toward replication.
"It's a scenario that explains how the
laws of nature are chosen," Smolin told io9, "and if true, these
parameters are geared to maximize the number of black holes made in the
universe."
Of cosmological singularities and baby
universes
Indeed, black holes — and the cosmological
singularities they produce — are central to Smolin's theory. These are regions
of space-time where the quantities used to measure gravitational fields or
temperature become infinite. It's also where general relativity stops being useful,
making any kind of prediction impossible. Classical general relativity says
that a singularity exists inside each black hole. But both string theory and
loop quantum gravity suggest that black hole singularities can be eliminated —
and when this happens, it may be possible to describe the future evolution of
the space-time region within it.
"Everything that falls into a black hole
doesn't just hit the cosmological singularity and just stop evolving so that
time simply comes to an end," he says, "Time continues and everything
that fell into the black hole would have a future where the singularity was,
and that region is what we call a baby universe."
Moreover, Smolin says these baby universes are
immune to whatever happens in the parent universe, including eternal inflation
and its ultimate heat death.
"Black holes are predicted to evaporate by
making radiation — what's called the Hawking Process," he says, "but
only until they get down to an equilibrium with the temperature of the cosmic
microwave background." This process, says Smolin, has to do with the
properties of the horizon — and it's only the horizon that evaporates.
"The baby universe may come into a kind of
contact with the original universe in a way it didn't before, but whether this
happens or not depends on the details of the quantum gravity theory," he
says.
A Darwinian model
And like Darwin's theory of variation and
selection, Smolin also surmises that baby universes are slightly different than
the parent who spawned them. In turn, this cosmological "mutation" —
in which the parameters of nature have been slightly modified — may result in a
new universe that's either better or worse in terms of its replicative ability.
Full size
For example, if the cosmological constant and speed
of light were slightly tweaked, or if the law of gravity became too weak or
strong, the new universe could be suboptimal in its ability to make massive
quantities of massive stars. In such a universe, matter might not be able to
coalesce into stars, or galaxies might be unable to form.
In this model, a "fit" universe,
therefore, is one that has evolved such that its ability to produce black holes
has been optimized. And this may explain why we observe a universe that
produces large swaths of giant stars — each one an attempt to make a baby.
The idea of cosmological variation, however, is
one of pure conjecture. "It's an hypothesis," Smolin concedes.
But that said, Smolin points to string theory
as a potential mechanism. "There could be a connection there," he
told us, "it describes a landscape of different cosmological parameters —
different phase transitions between them — and this is almost exactly the kind
of example I had in mind when trying to explain the variation of the constants."
Smolin is also unsure how many baby universes
each black hole is able to produce — though he suspects that it's one per black
hole. "The answer," he says, "will ultimately depend on quantum
gravity theory."
Life as epiphenomenon?
We asked Smolin if life in the universe is
therefore an accident — that humans and all other organisms are mere
epiphenomenon, a sideshow to a much larger process.
"If the hypothesis of Cosmological Natural
Selection is true, then life — and the universe being biofriendly — is a
consequence of the universe being finely-tuned to produce black holes by
producing many, many massive stars."
But he added: "Those if statements are
important."
Other scientists have conversely argued that
the universe is freakishly biophilic — that the laws of nature appear to be
geared towards making life. Some even suggest that this is the ultimate purpose
of the universe — that it's fine-tuned to spawn biological organisms (the
so-called biocosm hypothesis).
Full size
Similarly, philosophers like to talk about the
Anthropic Principle — the notion that any analysis of the universe and what
happens within it must must take into account the presence of observers (i.e.
intelligent life). We're subject to an observational selection effect, they
argue, which means we can only ever observe a universe that's friendly to life.
Smolin, on the other hand, brushes these lines
of argumentation aside, saying that cosmologists should study and understand
the properties of the universe in a way that doesn't connect it to life. The
Anthropic Principle, he says, is simply incapable of making a falsifiable
prediction for any kind of testable experiment.
At the same time, however, "Cosmological
Natural Selection," he says, "is very capable of doing just
that."
Moreover, the laws of the universe — and all
the stuff that's within it — can all be explained without referencing it to
life.
"It's not a coincidence," he says,
"that we live in a world which has lots of carbon and oxygen in it, along
with long list of suitable stars, and so on." The presence of these
apparent life-friendly elements — like carbon and oxygen — has a perfectly good
explanation outside of the biophilic paradigm. These elements, says Smolin,
creates the conditions necessary for the efficient formation of sufficiently
massive stars that form black holes.
The claims made as evidence by Anthropic
Principle supporters, he says, can be explained in an alternative way.
The critics
Needless to say, Smolin's Big Idea has received
its fair share of criticism. It's an extraordinary idea, after all, and
extraordinary ideas often undergo extraordinary levels of scrutiny.
Cosmologist Joe Silk, for example, says the
universe we observe is far from being an optimal producer of black holes. He
speculates that other "versions" of the universe could do a much
better job.
Similarly, Alexander Vilenkin argues that the
rate of black hole formation can be improved by increasing the value of the
cosmological constant. Smolin is wrong, he says, to hypothesize that the
current values of all the constants of nature are perfectly adjusted to
maximize black hole production.
Ruediger Vaas complains that Smolin's first
mistake was to start making analogies to Darwinian processes. The fitness of
Smolin's universes, he says, aren't constrained by their environments, but by
the numbers of black holes. Moreover, although Smolin's universes have
different replication rates, they aren't competing against each other — what he
feels is a crucial component of any Darwinian process.
Writing in the Edge, Leonard Susskind — Felix
Bloch Professor in theoretical physics at Stanford University — had this to
say:
Smolin...believes that the constants of nature
are determined by survival of the fittest: the fittest to reproduce that is.
Those properties which lead to the largest rate of reproduction will dominate
the population of universes and the overwhelming likelihood is that we live in
such a universe. At least that's the argument.
But this logic can lead to ridiculous
conclusions. In the case of eternal inflation it would lead to the prediction
that our universe has the maximum possible cosmological constant, since the
reproduction rate is nothing but the inflation rate.
When we asked Smolin about these objections, he
said that many of these concerns were addressed in his book, The Life of the
Cosmos, and that his upcoming book, Time Reborn: From the Crisis in Physics to
the Future of the Universe, will also tackle many of these questions (the book
also dispels the idea that time is a kind of illusion). And when possible,
Smolin has addressed individual concerns (for example, the entire Smolin-Susskind
debate can be read here; and his retort to Vilenkin can be seen here).
Ultimately, however, the objections leave him
unfazed.
"My impression is the idea has not been
refuted even though several people have tried," he told us. "It doesn't
mean the idea is true, but the idea has stood up to attempts to falsify
it."
Pausing for a moment, and speaking more quickly
now, he continued:
"Look, for me, the important part of the
claim is that it is a scientific argument. The idea itself is not the most
important thing — it's a very interesting idea, sure — but it instantiates a
general claim that — if you want to explain the universe — one of the things
you're going to have to explain is why we see certain laws of nature and not
others. And the claim I'm making is that this question can in fact be answered
scientifically — one that will lead toward a way for us to make predictions to
see if the laws of nature are not fixed for all time, but evolved. That is the
key point for me."
As for the exact mechanism of cosmological
evolution, he says that a certain model or scenario might be right, or it might
be wrong. The important point, says Smolin, is that science can only be
completed to the extent of our ability to explain why the laws of nature are
they way they are if they evolved over time.
"As far as the scenario of Cosmological
Natural Selection is concerned," he says, "it's just an hypothesis
just as much as it was for Darwin and Mendel — two scientists who figured out
how natural selection worked before knowing anything about DNA or the molecular
instantiation of genes."
Images: NASA/JPL-Caltech; Smolin pic:
ideacityonline; galaxy/dna: physics.sfsu.edu.
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