[tt] NS: Hawking 'close' to explaining universe's inflation

Thu Jul 3 20:57:39 UTC 2008

Hawking 'close' to explaining universe's inflation
http://space.newscientist.com/article/mg19826624.300-hawking-close-to-explaining-universes-inflation.html

* 28 June 2008
* Zeeya Merali

WHY was the big bang so very big? It has been a struggle to explain
why the infant universe expanded so rapidly. But now Stephen Hawking
at the University of Cambridge, and colleagues, think they are close
to perfecting an answer - by treating the early cosmos as a quantum
object with a multitude of alternative universes that gradually
blend into ours.

The idea that the universe expanded at a blistering rate in the
first 10^-34 seconds after the big bang was proposed to explain why
regions of the universe separated by vast distances have such a
similar background temperature: before inflation occurred, these
regions would have been close together with similar properties. But
just why the universe inflated in the first place remains a mystery.

"There's no fundamental theory that can explain why inflation
happened in our universe - it's just proposed as an ad hoc solution
that explains some particular observations," says Thomas Hertog of
Denis Diderot University (DDU) in Paris, France.

What's worse, one of the best attempts to explain how the universe
came to be - string theory - has arguably complicated matters. It
suggests that more than 10^500 variations of the universe, each with
different physical parameters, could exist side by side in a vast
"landscape". "You will have all kinds of universes, some with no
inflation, and others where there is a long period of inflation -
and our universe could be any one of those," says Hertog.

In 2006, Hawking and Hertog floated an idea that they hoped might
explain why inflation happened and embrace all of string theory's
alternative universes. They did this by treating the early universe
as a quantum object. According to quantum mechanics, when a particle
travels between two points, it doesn't simply take one path - it
takes every possible path between the two locations simultaneously,
although some paths contribute more than others.

The pair suggested that, in a similar manner, there was no unique
beginning to the universe. Instead, the wave function of the
universe encompassed a multitude of alternative paths up to today
(New Scientist, 20 April 2006, p 28).

Instead of starting with a set of initial conditions and calculating
how the universe evolves, Hawking and Hertog started with current
observations and worked back to narrow down what the initial set of
possibilities might have been.
"Instead of starting with a set of initial conditions, they took
today's observable universe and worked backwards"

They began by choosing the most fundamental characteristic that they
believe defines our present universe - that we largely experience
the world classically. In other words, Newtonian physical laws hold
sway over our everyday lives rather than weird quantum effects. The
pair then calculated all possible early histories that would produce
a classical universe.

Here they encountered a problem: their calculations predicted that
the early universe would have experienced only a tiny amount of
inflation. This conflicted with observations of the pattern of
temperature variations in the cosmic microwave background (CMB) -
the radiation left behind by the big bang - which suggest that
inflation lasted for a significantly longer period. "This has been
recognised to be a problem for some time," says Hawking.

Now, though, they claim to have solved it. Working with James Hartle
at the University of California, Santa Barbara, their solution
involves the fact that we can only observe a finite portion of the
whole universe. This observable region is called the "Hubble
volume". First time around, they had assumed that the Hubble volume
could only fit within the universe in one way, like a jigsaw piece.

Their original model predicted only a tiny minority of universes
that could have inflated enough to fit the Hubble volume, so they
discounted those universes as improbable. In fact, there are
potentially millions of ways that our observable patch could sit
within each of the universes in that minority of possibilities.
Taking this "volume weighting" into account massively increases the
probability that our universe developed from one of that minority
(Physical Review Letters, vol 100, p 201301).

"We have shown that this proposal, with volume weighting, can
explain why the universe inflated," says Hawking, who presented the
work at a cosmology meeting at DDU last month. "We found that you
cannot have a classical universe without inflation," adds Hertog.
What's more, the theory explains what "path" through string theory's
predicted universes we took to get where we are today, he says.
"That's a striking and powerful result."

Alex Vilenkin, a cosmologist at Tufts University in Medford,
Massachusetts, is impressed that the theory now matches observations
of the CMB. "This is interesting work, by a talented group. They are
finding intriguing connections with inflation," he says. However, he
adds that "for now, this is a theory that is still under
construction".

Cosmology - Keep up with the latest ideas in our special report.

There are 8 comments on 1 page

Piffle
By Stephen Rhodes
Fri Jun 27 21:04:19 BST 2008
"According to quantum mechanics, when a particle travels between two
points, it doesn't simply take one path - it takes every possible
path between the two locations simultaneously, although some paths
contribute more than others."
Come off it, who cuts and pastes this stuff?
This is not what quantum mechanics says.
The whole point of quantum mechanics is that it is just that a
mechanistic process that "very" accurately predicts the behaviour of
single interactions by adding together the probabilities of all the
possible ways in which the interaction can occur. (cf R Feynman).
The answer to this protracted mechanistic process is the very
accurate prediction, provided you can anticipate all the possible
ways, of course.
This is not the same as piffle printed in your article and it is
disingenuous to purvey this sort of mumbo jumbo in a journal that is
- I hope - intending to inform the public in matters of science.
Whether or not Stephen Hawking is close to an answer I do not know,
although I doubt that it will be an end to debate, but I expect his
theory is based on an understanding of the universe that does not
involve magical explanations like this.

Piffle
By Windy
Mon Jun 30 04:35:36 BST 2008
I am not so sure that statement in the article is "piffle" ...
You are talking about "wave function" of adding up all the
probabilities...and yes, qunatum mechanics is indeed very accurate
in predicting the behaviour of the particles using those
probabilities .... But WHY do you use probabilities in the first
place?
I mean, if particles acted like soccer balls or baseballs ...
Objects that you could track on a trajectory, then you wouldn't need
to add up all the different probablities ... You would just measure
the precise location of particle and its speed, on this path or that
path and make the prediction about where it will be next.
But you just CAN'T do that with particles. Why not? Because they are
weird. As far as we can tell, the particle seems to actually be in a
state of being all of those paths simultaneously and so, the only
way you can make prediction (albeit an accurate one) about the
particle's behaviour is to use the probabilities of all the
different ways that the interaction can occur ,,, and come up with
the prediction that way.
The article then goes on to say:
"The pair suggested that, in a similar manner, there was no unique
beginning to the universe. Instead, the wave function of the
universe encompassed a multitude of alternative paths up to today."
It's weird, I know, but in quantum mechanics terms, if you assume
the beginning universe as a quantum object with quantum
mechanics-type behaviour, and if you accept that weird aspects of
quantum mechanics are real and that there is no underlying "other"
hidden explanation ... Then what they are saying makes sense.

Piffle
By Stephen Rhodes
Mon Jun 30 17:15:32 BST 2008
I have two issues with the article as printed.
Firstly it perpetuates the myth that particles are weird - as you
put it - and that we should just accept this. This despite the fact
that we are left with two mutually exclusive - albeit highly
successful - decsriptions of reality operating at very different
scales, Einstein's relativity and quantum mechanics. Blind faith in
any system is tantamount to religious belief and has no place in
science - making Einstein's remark that 'God doesn't play dice'
doubly significant.
Secondly, the suggestion in the article [no doubt to be clarified in
the paper shortly to be published] that the 'unique beginning' of
the universe will be determined when its 'wave function' 'collapses'
begs two questions "when?" and "how?"
I am with Einstein on this one - 'God doesn't play dice' she/he has
just made it look like that to the intellectually uninquisitive.
Just because a tool - quantum mechanics - works in its own back yard
doesn't mean we should worship it, as in the Wizard of Oz we need to
pull back the curtain and find out what is really pulling the
strings of reality.

Emergence
By Stephen Rhodes
Sat Jun 28 15:23:29 BST 2008
"...that we largely experience the world classically. In other
words, Newtonian physical laws hold sway over our everyday lives
rather than weird quantum effects."
This relationship between 'underlying' quantum behaviour and the
physical laws governing the universe we experience is now becoming
understood as 'emergence' - see the highly readable book 'A
Different Universe' by physics Nobel Laureate R. Laughlin.
Proponents of 'emergence' - as I understand it - consider that
because of the failure of the quantum behaviour of matter
(established by mainstream reductionism) to predict the behaviour of
materials in the world we experience, the physical laws must
'emerge' from the 'collective' behaviour of quantum interactions --
by analogy, the erratic behaviour of single Starlings becomes highly
ordered synchronised mass flight when interacting as flocks of many
tens of thousands of birds, but must at root result from the same
erratic behaviours of the individual birds.
In this context it seems unlikely that it will be possible to
determine the Universe's initial quantum conditions from a
consideration of the emergent behaviours it now exhibits.
This is, in fact, yet another an attempt to apply failed
reductionist logic to a problem that will probably remain
intractable absent a better understanding of the symmetry breaking
that results in the various state of matter and energy by which we
perceive our Universe.

Emergence
By Derek
Sun Jun 29 02:54:05 BST 2008
While you seem to have a good understanding of these theories, I
would suggest not jumping to conclusions about their logic until you
actually go through their proof once it's made public.

Emergence
By Stephen Rhodes
Mon Jun 30 17:31:48 BST 2008
Are you not concerned that peerless logic was used by theologians to
determine the number of angels that would fit on a pin's head.
Two mutually incompatible belief systems - quantum mechanics and
relativity - smack of religiosity. Better to find out the underlying
realities and combine the two before speculating on the origins of
the universe based on either or both uncombined.

Where Have All The Comments Gone
By Observor Clark

Sun Jun 29 19:14:54 BST 2008
Surprisingly , there were 44 comments on Mr Hawkins ideas a couple
of days ago Now there are only three. Did they dissapear into a
black hole at New Scientist. Remember , no democracy without the
vote being counted properly!

Where Have All The Comments Gone
By Stephen Rhodes
Mon Jun 30 18:34:58 BST 2008
There are 174 on the Hawking and colonies on Moon and Mars article.
This is a really quiet thread since Friday evening when I started
commenting.