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How to map the multiverse
05-08-2009, 01:51 AM,
#1
How to map the multiverse
http://www.newscientist.com/article/mg2022...multiverse.html

How to map the multiverse

* 04 May 2009 by *Anil Ananthaswamy*
<http://www.newscientist.com/search?rbauthors=Anil+Ananthaswa my>

BRIAN GREENE spent a good part of the last decade extolling the virtues
of string theory. He dreamed that one day it would provide physicists
with a theory of everything that would describe our universe - ours and
ours alone. His bestselling book /The Elegant Universe/
<http://www.sparknot es.comt/elegantuniverse/ summary.html> eloquently
captured the quest for this ultimate theory.

"But the fly in the ointment was that string theory allowed for, in
principle, many universes," says Greene, who is a theoretical physicist
at Columbia University in New York. In other words, string theory seems
equally capable of describing universes very different from ours. Greene
hoped that something in the theory would eventually rule out most of the
possibilities and single out one of these universes as the real one: ours.

So far, it hasn't - though not for any lack of trying. As a result,
string theorists are beginning to accept that their ambitions for the
theory may have been misguided. Perhaps our universe is not the only one
after all. Maybe string theory has been right all along.

Greene, certainly, has had a change of heart. "You walk along a number
of pathways in physics far enough and you bang into the possibility that
we are one universe of many," he says. "So what do you do? You smack
yourself in the head and say, 'Ah, maybe the universe is trying to tell
me something.' I have personally undergone a sort of transformation,
where I am very warm to this possibility of there being many universes,
and that we are in the one where we can survive."

We keep banging into the possibility that we are one universe of many.
Maybe that's telling us something

Greene's transformation is emblematic of a profound change among the
majority of physicists. Until recently, many were reluctant to accept
this idea of the "multiverse" , or were even belligerent towards it.
However, recent progress in both cosmology and string theory is bringing
about a major shift in thinking. Gone is the grudging acceptance or
outright loathing of the multiverse. Instead, physicists are starting to
look at ways of working with it, and maybe even trying to prove its
existence.

If such ventures succeed, our universe will go the way of Earth - from
seeming to be the centre of everything to being exposed as just a
backwater in a far vaster cosmos. And just as we are unable to deduce
certain aspects of Earth from first principles - such as its radius or
distance from the sun - we will have to accept that some things about
our universe are a random accident, inexplicable except in the context
of the multiverse.

One of the first to argue for a multiverse was Russian physicist Andrei
Linde, now at Stanford University in California. In the 1980s, Linde
extended and improved upon an idea called inflation, which suggests that
the universe underwent a period of exponential expansion in the first
fractions of a second after the big bang. Inflation successfully
explains why the universe looks pretty much the same in all directions,
and why space-time is "flat", despite Einstein showing that it can just
as easily be curved.

Linde realised that inflation could be ongoing or "eternal", in the
sense that once space-time starts inflating, it can stop in some parts
(such as ours) yet take off with renewed vigour elsewhere. This process
continues ad infinitum, giving rise to a patchwork of regions of space,
each with different properties. When and how inflation ceases in a
particular patch dictates the exact nature and types of fundamental
particles there and the laws of physics that govern their behaviour.
Over time, eternal inflation gives rise to just about every possible
type of universe predicted by string theory. Our universe, argues Linde,
is a part of this multiverse.

It wasn't until 1998, however, that the multiverse gained any traction,
when astronomers studying distant supernovae announced that the
expansion of the universe is accelerating. They put this down to the
vacuum of space having a small energy density, which exerts a repulsive
force to counteract gravity as the universe ages. This became known as
dark energy
<http://www.newscientist.com/article/mg193259 11.700-dark-energy-seeking- the-heart-of-darkness. html>,
or the cosmological constant.

Its discovery was a huge blow. Up till then, physicists had hoped that
some ultimate theory would deduce the values of fundamental constants of
nature from first principles, including the cosmological constant, and
explain why the laws of physics are as they are, just right for the
formation of stars and galaxies and possibly the emergence of life. This
seems not to be the case. Nothing in string theory, or indeed any other
theory in physics, can predict the observed value of the cosmological
constant.

However, if our universe is part of a multiverse then we can ascribe the
value of the cosmological constant to an accident. The same goes for
other aspects of our universe, such as the mass of the electron. The
idea is simply that each universe's laws of physics and fundamental
constants are randomly determined, and we just happen to live in one
where these are suited for life. "If not for the multiverse, you would
have these unsolved problems at every corner," says Linde.

The other compelling argument for a multiverse comes from string theory.
This maintains that all fundamental particles of matter and forces of
nature arise from the vibration of tiny strings in 10 dimensions. For us
not to notice the extra six dimensions of space, they must be curled up,
or compacted, so small as to be undetectable. For decades,
mathematicians toiled over what different forms this compaction could
take, and they found myriad ways of scrunching up space-time - a
staggering 10^500 or more.

Each form gives rise to a different vacuum of space-time, and hence a
different universe - with its own vacuum energy, fundamental particles
and laws of physics. The hope, nurtured by Greene and others, was that
there was some kind of uniqueness principle that would pick out the
particular form of space-time that produces our universe.

That hope has since receded dramatically. In 2004, Michael Douglas of
the State University of New York in Stony Brook, and Leonard Susskind of
Stanford University surveyed the developments in string theory to date
and concluded that all these theoretical varieties of space-time should
be taken seriously as physical realities - that is, they point to a
multiverse. Susskind coined the term "the landscape of string theory"
<http://www.newscientist.com/ article/mg180241 95.400-a- universe- like-no-other. html>
to describe the 10^500 or more different universes. Nothing in string
theory suggests that any one of these universes is preferred over
others. Rather, it appears all are equally likely.

Together, dark energy and string theory are making physicists see the
multiverse anew. "Just about everybody is convinced that the idea of
uniqueness has gone down the drain," says Susskind. So what are we to
do? Throw up our hands and admit that we will never be able to explain
why our universe is the way it is?

Exploring the landscape

Not a bit of it. Susskind argues that we can still ask meaningful
questions within the context of the multiverse, just not the ones we'd
ask if ours were the only universe. Questions such as: can we identify
the exact point in the landscape that corresponds to our universe, or at
least the parts of the landscape that most closely resemble our
universe? Is it possible to tell which of our universe's properties can
be derived from first principles and which ones are random?

We can still ask meaningful questions about the universe, just not the
ones we'd ask if it were unique

Also, can we find parts of the landscape with the right conditions for
eternal inflation to take place? After all, the landscape and eternal
inflation are independent concepts. Confirming that they are compatible
would lend more credence to the multiverse idea.

These are not trivial questions to answer, but string theorists are
rising to the challenge by feverishly exploring the landscape.
Investigating a collection of 10^500 universes is not a matter of
enumerating the properties of each of them, however. "We just can't make
a list of 10^500 things," says Nobel laureate Steven Weinberg of the
University of Texas at Austin. "That's more than the number of atoms in
the observable universe."

The first line of attack has been to develop mathematical models of the
landscape. These describe the landscape as a terrain of hills and
valleys, where each valley represents a place with its own parameters
(such as the mass of the electron) and fields (such as gravity).

How does a universe develop according to this scenario, and what can it
tell us about ours? Imagine the universe as it starts off as a speck of
space-time. This baby universe is filled with fields, whose properties
change due to quantum fluctuations. If the conditions are ripe for
inflation, the speck will grow and this will alter its nature. Depending
on the changing environment inside the emerging universe, the
inflationary process could grind to a halt, continue apace or even spawn
other specks of space-time.

According to the landscape picture, the baby universe starts off in one
valley. Quantum fluctuations can then cause the entire universe to
"tunnel" through an adjoining hill, eventually ending up in another
valley with different properties. This process continues, with the
universe tunnelling from valley to valley, until it reaches a place
stable enough for inflation to run its full course.

Given this scenario, one of the most important tasks is reconciling
eternal inflation with the landscape. "The whole picture can be boiled
down to one issue: is there eternal inflation in the landscape?" says
Henry Tye of Cornell University in Ithaca, New York. In Linde's model of
eternal inflation, the speck of space-time starts off with high energy
density. The energy density slowly falls as space-time inflates. The
quest is to find configurations of space-time among the 10^500 that
match Linde's requirements for eternal inflation.

Until recently, this had seemed impossible. Then, last year, Eva
Silverstein and Alexander Westphal of Stanford University identified two
places within the landscape for Linde's version of eternal inflation to
take place (/Physical Review D/, vol 78, p 106003
<http:/nk.aps.org/doi/ 10.1103/PhysRevD .78.106003>).

It's a promising start, but Tye argues that eternal inflation within
string theory is not a done deal. Physicists could just as well start
with string theory models of the universe with entirely different
initial conditions that would lead to inflation, though not eternal
inflation.

Experiments are the key to answering such concerns, by testing the
predictions of the various alternative theories. For instance, the
energy density in the model proposed by Silverstein is high enough to
create strong gravitational waves, ripples in space-time generated by
the rapid expansion of the universe. Such waves could have polarised the
photons of the cosmic microwave background, the radiation left over from
the big bang, and such an imprint would still be detectable today. The
European Space Agency's Planck satellite, due to launch soon, will look
for any polarisation.

If Planck sees it, then it will lend support to Silverstein' s models and
eternal inflation. But even if experiments like Planck do lend support
for eternal inflation, theorists will need independent confirmation for
the ideas of string theory. Unfortunately no specific predictions of
string theory are yet within experimental reach
<http://www.newscientist.com/ article/mg195261 21.200-string- theory-the- fightback. html>,
but there is one key general property that could be confirmed soon.
String theory requires that the universe has a property known as
supersymmetry, which posits that every particle known to physicists has
a heavier and as yet unseen superpartner. Physicists will be looking for
some of these superpartners at the Large Hadron Collider
<http://www.newscientist.com/ topic/large- hadron-collider>, the new
particle accelerator at CERN, near Geneva, Switzerland.

The scenario of a universe tunnelling through the landscape also makes a
unique prediction. If our universe emerged after tunnelling in this way,
then the theory predicts that space-time today will be ever so slightly
curved. That's because in this scenario, inflation does not last long
enough to make the universe totally flat.

Today's measurements show the universe to be flat, but the uncertainty
in those measurements still leaves room for space-time to be slightly
curved - either like a saddle (negatively curved) or like a sphere
(positively curved). "If we originated from a tunnelling event from an
ancestor vacuum, the bet would be that the universe is negatively
curved," says Susskind. "If it turns out to be positively curved, we'd
be very confused. That would be a setback for these ideas, no question
about it."

Until any such setback the smart money will remain with the multiverse
and string theory. "It has the best chance of anything we know to be
right," Weinberg says of string theory. "There's an old joke about a
gambler playing a game of poker," he adds. "His friend says, 'Don't you
know this game is crooked, and you are bound to lose?' The gambler says,
'Yes, but what can I do, it's the only game in town.' We don't know if
we are bound to lose, but even if we suspect we may, it is the only game
in town."

/Anil Ananthaswamy is a consulting editor for /New Scientist//
Reply
05-11-2009, 11:38 AM,
#2
How to map the multiverse
Quote:"If not for the multiverse, you would
have these unsolved problems at every corner," says Linde.

bullshit. and ill tell you why. he hasn't mentioned the evolution of the subatomic particle. hes basically saying the rules were written AT the big bang. Thats like saying I was created by god. Theres a reason that this universe can support matter. the matter itself can survive more than a fraction of a second. There would of been all kinds of different things going on at this big bang. but in a bat of an eye, the stuff that won out was that that CAN survive. You have to try quite hard to break an atom up. That because it was forged under a massive energetic process.

Im yet to find coherence with this. even looking at the maths and saying "hey great workings out, like the answer", the real principle question is "is it provable?" and the answer is no. If it was so there wouldn't be any debate about it as it would be self evident. I dont need to prove the non-existence of a multiverse.
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