快猫短视频

LAST century鈥檚 cartoonists had it made. All they had to do was draw Charles
Darwin鈥檚 head, attach it to an ape鈥檚 body and, hey presto, they had lampooned
the most controversial scientific theory of their era.

If Lee Smolin鈥檚 ideas had been around at that time, they would have proved
more of a challenge. Smolin is a theoretical physicist from the University of
Pennsylvania. And when he thinks about Darwinian adaptation, his mind turns not
to the physiognomy of apes or the necks of giraffes, but to the fundamental
constants of particle physics and cosmology. For Smolin, the biggest and most
impressive product of natural selection is none other than the Universe itself.
Galaxies, stars, subatomic particles鈥攁ll are the way they are, Smolin
believes, because the physical laws that control them have evolved to maximise
the fitness of the Universe.

Smolin鈥檚 book, The Life of the Cosmos, is published next week. It is
a dizzying attempt to cross Darwinism with cosmology and produce a new, hybrid
explanation of the Universe and, in particular, why its physical constants are
so perfectly adjusted for stars and carbon-based life. The result is Stephen
Hawking-meets-Richard Dawkins minus the philosophical arrogance for which those
two authors are renowned. And if that alone doesn鈥檛 guarantee success, something
else will: those tried and tested crowd-pullers, black holes.

When physicists discovered that stars implode to form these dense specks of
matter with their famously large gravitational fields, they threw away the rule
book. All sorts of things became possible鈥攊ncluding the emergence of new
regions of space and time. Such 鈥渂aby鈥� universes are entirely hypothetical, and
even if they existed, we could never observe them. But suspend your disbelief,
says Smolin. Suppose black holes really can give birth to new universes.
Suppose, too, that with each birth the masses and charges of the fundamental
particles, and the forces between them, come out looking slightly
different. Suppose physics itself mutates.

Indulge Smolin, and your reward is a new outlook on why the laws of physics
seem so fortuitously compatible with our existence: the Universe has evolved to
maximise its production of black holes, and hence its production of offspring.
And, luckily for us, the kind of ingredients鈥攕tars, carbon and
oxygen鈥攖hat are good for making black holes are also good for making
life.

Inner confidence

Imaginative, yes; but is it proper, testable science? For someone who clearly
thrives on impossibly big questions, Smolin displays none of the pushy
showmanship you might expect. He stresses that he actually spends most of his
time doing 鈥渧ery mainstream鈥� mathematical physics, attempting to apply the
principles of quantum mechanics to general relativity. He goes to great lengths
to explain how his idea of 鈥渃osmological selection鈥濃�攚hich he developed in
his 鈥渟pare time鈥濃�攃ould be tested and disproved. And yet behind this Woody
Allen-like self-deprecation one senses a wellspring of inner confidence.
Smolin鈥檚 linking of black holes with life is just one of many hotly contested
aspects of his theory. But courting controversy is not what motivates him. It
seems he genuinely believes that theoretical physics is ailing and that the
remedy is a dose of Darwinism.

Ironically, diagnosis begins with that great success story of physics, the
Standard Model. Its equations successfully predict many of the properties of
fundamental particles. But there鈥檚 a core of some seventeen constants whose
values have to be set by hand. Nobody, for example, can say why the quarks from
which neutrons and protons are made have the masses they have. The values of
these things just 鈥渁re鈥�.

It鈥檚 the kind of arbitrariness that makes determinists break out in a rash.
If neutrons were just a tiny bit heavier or electrons carried a tad more charge
or the strong nuclear force was different, you could kiss goodbye to stable
carbon atomic nuclei, stars, galaxies and, of course, life. 鈥淎ll the variety and
complexity we see in the world would simply vanish,鈥� says Smolin.

Physicists have different ways of coping with this conundrum. Some take
refuge in an idea known as the anthropic principle, the mildest form of which
says we inhabit only one of an infinite number of universes, each having
randomly chosen physical constants. Because our Universe contains us, it follows
that its randomly chosen constants might be just right for galaxies, stars and
carbon-based life. In other words, our Universe is the way it is because we
exist in it.

Smolin is quite happy with the idea that we inhabit one of many universes.
But the anthropic principle depresses him. It gives, he says, the illusion of
explaining everything but offers no testable predictions. 鈥淭o argue this way is
not to reason, it is simply to give up looking for a rational explanation.鈥� It
is, Smolin adds in a rare moment of dismissiveness, 鈥渃artoon鈥� science.

Not that the alternatives impress him much either. The idea that something
(or someone) fixed things so that we could evolve is . . . well, fine if you
like that sort of thing, but it isn鈥檛 really physics. And Smolin also parts
company with the likes of Hawking and other optimists who think the problem of
the hand-set constants will vanish into the night once physicists discover how
to unite quantum theory with general relativity. Smolin agrees that physicists
need a unified theory. But he doubts the result will be a 鈥淭heory of
Everything鈥�, a one-off formula free of hand-set constants that is capable of
predicting all the properties of the Universe.

Mystical maths

Smolin鈥檚 objections are partly philosophical. Physicists calculate that the
probability of our Universe having the ingredients of life purely by chance is
about 1 in 10²²⁹. To argue that mathematics alone can win us that miniscule
chance is, in the end, no less mystical than invoking a divine creator.
Mathematics becomes the creator.

And there other, more down-to-earth reasons why Smolin doubts whether
mathematics will tell us why we鈥檙e here. Though he has spent much of the past
decade trying to apply quantum theory to gravity, Smolin sees fundamental limits
in his own and other people鈥檚 equations: 鈥淲e鈥檝e been successful, but only
partially.鈥� Here he points to string theory, in which particles are represented
as vibrating strands or surfaces.

鈥淚n the 1980s, there was this naive idea that you just had to solve string
theory and you would understand every question about the physical world,鈥� he
says. Everything would be specified uniquely. All parameters would be
determined by virtue of their relationships with each other. Alas, says Smolin,
it just didn鈥檛 work out. By the end of the decade, no version of string theory
had succeeded in curing physics of its dependence on hand-set parameters. 鈥淚t
was quite a shock. Physicist friends of mine got depressed. I mean, if none of
the theories worked, just what was determining all these parameters?鈥�

Smolin started to think about an old idea to do with black holes. As long ago
as the 1960s, John Wheeler at Princeton University suggested that as massive
stars collapse to form black holes, quantum effects might trigger a 鈥渞ebound鈥�
expansion resulting in a new region in space and time, concealed from us behind
the black hole鈥檚 event horizon. And when this happens, Wheeler suggested, the
parameters of particle physics and cosmology might change.

Eureka moment

Smolin was also reading some evolutionary biology 鈥渢he ideas of Lynn Margulis
and Richard Dawkins . . . all these things were stirring around in my mind.鈥�

A short mental leap took him to the idea at the heart of his book鈥攖hat
the Universe is the way it is because it has been selected to replicate via
black holes. Universes with the most black holes, he reasoned, would produce the
most 鈥渙ffspring鈥� and would quickly come to dominate their competitors.

The problem was turning that into a testable hypothesis鈥攕omething
which, unlike the anthropic principle, would make firm predictions. Smolin
recalls that he was out sailing, in the spring of 1990, when the penny dropped.
鈥淚t was a eureka moment. I had this idea that you could use the parameters of
the Standard Model to predict how many black holes would be made in a region of
space and time.鈥�

How does this help? Well, if Smolin is right, the Universe we inhabit should
make the maximum number of black holes that is theoretically possible. One way
to test the idea is to see if any of the parameters of particle physics can be
varied to produce a hypothetical world with more black holes. If they can,
cosmological selection is dead. If they can鈥檛, it lives on. So far, claims
Smolin, nobody has delivered a fatal blow.

That might seem surprising. After all, the Universe scarcely looks stuffed to
the gills with black holes. Black holes are formed when a massive star reaches
the end of its life, and its central nuclear engine switches off. Some of the
stellar material is blown away in a dramatic explosion known as a supernova,
while the core of the star collapses under its own weight to form a black
hole.

But physicists estimate that only a few per cent of stars are massive enough
to collapse into black holes, the rest ending up as white dwarfs or, if they鈥檙e
too massive for that but not quite in the black hole league, as neutron stars.
So why not 鈥渕ake鈥� more black holes by simply varying the parameters of physics
to produce a bigger crop of massive stars?

One tactic would be to tweak the parameters so that stars don鈥檛 shed so much
of their mass during their supernova phase. But Smolin doubts this would have
the desired effect. Yes, he says, hypothetically speaking, you could make the
nuclear reactions that trigger supernovae less violent by reducing the strength
of the weak nuclear force. But that would also slow down some of the processes
that help stars to form in the first place: supernovae explosions send out shock
waves that compress nearby clouds of gas, helping them to condense into stars.
So the result would be a world with fewer, not more, black holes.

In fact, shutting down supernovae might be doubly unhelpful, says Smolin. To
maximise the total number of black holes in the Universe, you want each one to
have as little mass as possible. The mass ejected by supernovae is recycled into
other stars and black holes. So, far from suppressing black holes, supernovae
may actually help to keep their numbers up.

Of course, keeping up numbers of black holes doesn鈥檛 in itself explain why we
are here. For Smolin鈥檚 theory to achieve this, black holes and life must thrive
under exactly the same conditions. That means carbon must have a vital role in
maximising the Universe鈥檚 output of black holes.

Critics see this as the weakest link in his argument. Cosmological selection
would lead to universes adapted to making black holes but not necessarily life,
says Edward Harrison of the University of Massachusetts. In fact, some
physicists speculate that a world without carbon would produce even more black
holes than a world with carbon.

Smolin will have none of that. He believes that such criticisms overlook the
important role carbon monoxide plays in transferring heat from the centre of the
giant molecular clouds from which stars condense. Without carbon monoxide, stars
and black holes would still form鈥攂ut at a slower overall rate.

If Smolin is right about carbon鈥檚 role in maximising black holes, it severely
limits the options for varying the parameters to make more black holes. That鈥檚
because carbon nuclei are so delicately balanced. The tiniest variations in the
masses of the proton or neutron would destroy any possibility of making any
carbon.

None of this cuts much ice with fans of the anthropic principle. They
attack the idea of cosmological selection by turning Smolin鈥檚 logic on its head.
Life does not exist courtesy of black holes, they say, black holes exist
courtesy of life. If the Universe produces lots of black holes, it鈥檚 because
that鈥檚 what universes with carbon and stars in them are equipped to do.

Strange matter

It amounts to a weird cause-and-effect dilemma: what comes first, conditions
for life, or black holes? Smolin, however, believes there is a solution, based
on the science of neutron stars and a peculiar particle called the kaon. Kaons
can be produced in particle accelerators but don鈥檛 normally exist in nature.
What鈥檚 more, they contain a quark that is not found in ordinary matter. By
changing the mass of this strange quark, you can alter the mass of the kaon
without producing sweeping side effects, such as destroying all hope of stars
and life. This allows the possibility of testing the idea of cosmological
selection free from any complications to do with the anthropic principle. All
you have to do is see how the mass of the kaon affects the predicted number of
black holes. And this, explains Smolin, is where neutron stars enter the
picture.

In the textbook theory of how neutron stars are formed, electrons combine
with protons at the centre of a dying star to make neutrons and neutrinos. The
neutrinos fly away, and only neutrons are left in the central core. But Hans
Bethe at Cornell University and Gerald Brown at the State University of New York
have forged an alternative model in which the electrons decay into kaons and
neutrinos. This time the star ends up with a core made of kaons, protons and
neutrons. Which model is right depends on the mass of the kaon in the very dense
environment of a neutron star. Only if the kaon is light enough will the
electrons 鈥減refer鈥� to decay into kaons.

If cosmological selection is right, the kaon must be so light that all
neutron stars choose the kaon scenario. This is because the kaon model limits
neutron stars to a mass no greater than 1.5 times the mass of the Sun. By
contrast, the textbook model allows neutron stars to have masses between three
and four times higher than the mass of the Sun. And the lower the mass set for
neutron stars, the more stars will be left to form black holes. So, if kaons are
light, there is a chance of maximising the number of black holes without
altering the prospects for life in the Universe. For Smolin to be right, nature
must seize that chance. Kaons really must exist in neutron stars. Do they?

What little evidence there is looks good. All of the masses known for neutron
stars lie in a narrow range between about 1.3 and 1.45 times the mass of the
Sun, supporting the kaon model. 鈥淏ut if someone tomorrow discovers a neutron
star of three solar masses, then the kaon is not light enough and it鈥檚 a strong
mark against cosmological selection,鈥� says Smolin. 鈥淚t鈥檚 a beautiful, clean
迟别蝉迟.鈥�

Still, even if cosmological selection passes on this kind of test, there are
other important questions. Can black holes really produce new regions of space
and time? 鈥淥bviously this isn鈥檛 experimentally testable,鈥� says Smolin. The best
we could hope for is that physicists are one day able to produce a detailed
quantum theory of gravity that predicts this would happen. In the meantime,
however, some people are using approximate models鈥攁nd getting worrying
answers.

Overly pessimistic

Claude Barrabes from the University of Paris and Valerie Frolov at the
University of Alberta in Canada have produced theoretical evidence indicating
that black holes may actually be capable of producing not one but many new
regions of space and time. And the number of such regions should increase, they
say, with the mass of the collapsing star.

If that鈥檚 true, it鈥檚 a problem for Smolin鈥檚 theory. The fittest universes
would be under evolutionary pressure to produce ever more massive black holes,
instead of ever greater numbers. 鈥淚 don鈥檛 like the assumptions their
calculations use. But if they got the same result with a quantum theory of
gravity that everyone believed in, this would count against the idea,鈥� he
concedes.

And, of course, it鈥檚 always possible that Smolin is being overly pessimistic
about the chances of discovering a 鈥渢heory of everything鈥�. Tomorrow, or next
week, or next year, physicists could prove him wrong by coming up with a perfect
version of, say, string theory 鈥攁 set of equations that defined everything
without the need for any hand-set parameters.

But if this happens Smolin will at least be well rehearsed. Six years ago an
abstract of such a paper appeared on the Internet, endorsed by an impressive
cast list of scientists. 鈥淭he theory was unique and specified only four
dimensions and predicted everything exactly. I thought, OK, if they鈥檝e done
that, this theory of mine is off.鈥�

So Smolin requested the whole paper. A minute later he received an electronic
message reminding him of the date. It was 1 April.