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by wolram
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wolram
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Nov25-04, 10:16 AM
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I came across this in the AandC reference library posted by Marcus
http://www.astrosociety.org/pubs/mer...2/nothing.html
My question is,Why do we seem to want a universe that started from
"almost", nothing, or reduce our existence and our Us existence
to as close to 0 as possible?
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Chronos
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Nov25-04, 07:23 PM
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Personal preference is not an issue. Observation shows we live in an expanding universe [at least according to most theorists]. If you run the movie backwards, the opening scene is a dimensionless point. Once Hubble discovered the universe was expanding, theorists pretty much jumped straight to such a scenario and proposed a radical theory - that the universe began in a Big Bang [which is an admittedly poor choice of words - the Big Unfolding would have been better but marketing felt BB was sexier]. They then, like all good scientists, began pondering the consequences of such a theory and came up with some startling predictions - notably primordial elemental abundance and a thing called background radiation. Years later, these predictions were confirmed, which explains the current popularity of the theory.
wolram
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Nov26-04, 05:52 AM
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By Cronos
Personal preference is not an issue. Observation shows we live in an expanding universe [at least according to most theorists]. If you run the movie backwards, the opening scene is a dimensionless point. Once Hubble discovered the universe was expanding, theorists pretty much jumped straight to such a scenario and proposed a radical theory - that the universe began in a Big Bang [which is an admittedly poor choice of words - the Big Unfolding would have been better but marketing felt BB was sexier]. They then, like all good scientists, began pondering the consequences of such a theory and came up with some startling predictions - notably primordial elemental abundance and a thing called background radiation. Years later, these predictions were confirmed, which explains the current popularity of the theory.
All the above is understood, but now the singularity is is on the limb of popular
science, and other universe theories are marginal, it seems to me that
some form of energy, matter, has always been in existence in our" vicinity",
and to go beyond that statement is unprovable to date, and may stay
that way until we can send a probe to the edge of a black hole to gather
real data. This is not a dig at popular science, it is just a search for a
fruitful way forward.

NeutronStar
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Nov26-04, 08:44 AM
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starting from 0


Quote Quote by From the article in question
Quantum theory, and specifically Heisenberg’s uncertainty principle, provide a natural explanation for how that energy may have come out of nothing. Throughout the universe, particles and antiparticles spontaneously form and quickly annihilate each other without violating the law of energy conservation. These spontaneous births and deaths of so-called "virtual particle" pairs are known as "quantum fluctuations."
Where these people get off using the word "nothing" is beyond me!

Let's say that the universe did start from a "quantum fluctuation" as the theory goes. That's hardly starting from "nothing".

I mean, you can't have a quantum fluctuation if you don't have a quantum field to begin with. The quantum field with all of its properties (i.e. what we see as mathematical rules and regulations) must have been there to "fluctuate" in the first place.

Field theory are not merely human abstractions, fields are necessarily "real" properties of the universe. In other words, the properties and behavior of a field is just as real as the particles or other phenomena that it gives rise to. In fact, it may very well be (and it's my personal opinion) that the universe and everything in it is nothing more the fluctuating fields.

We can hardly claim that "Quantum theory, and specifically Heisenberg's uncertainty principle, provide a natural explanation for how energy may have come out of nothing." If we are using quantum theory and Heisenberg's uncertainty principle, then we are already talking about the properties of a quantum field. So the quantum field must have then existed prior to any "fluctuations".

Why people insist on calling a quantum field "nothing" is beyond me. It obviously has very specific behavioral properties, and even if that's all that it has, at least it has "something". That's more than "nothing".

In other words, some type of "information" must have existed prior to the fluctuation. Or to look at it another way,… there simply must have been "something" there to fluctuate in the first place!

So this conclusion that things are starting from "nothing" is just a little bit absurd to me. But then the mere fact that anything exists at all is quite absurd to me too, so I guess it really doesn’t matter one way or the other.
turbo
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Nov26-04, 10:15 AM
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Quote Quote by NeutronStar
Where these people get off using the word "nothing" is beyond me!

Let's say that the universe did start from a "quantum fluctuation" as the theory goes. That's hardly starting from "nothing".

I mean, you can't have a quantum fluctuation if you don't have a quantum field to begin with. The quantum field with all of its properties (i.e. what we see as mathematical rules and regulations) must have been there to "fluctuate" in the first place.

Field theory are not merely human abstractions, fields are necessarily "real" properties of the universe. In other words, the properties and behavior of a field is just as real as the particles or other phenomena that it gives rise to. In fact, it may very well be (and it's my personal opinion) that the universe and everything in it is nothing more the fluctuating fields.
Shh! You'll scare the children! The pre-existence of a field in which such a fluctuation could have arisen seems essential, doesn't it? A field with real (or at least potential) properties. Hardly nothing.

Going back to Wolram's initial question and Chronos' follow-up: I believe that we humans are hard-wired to prefer absolute answers and closure over open questions. It is comforting to have a sense of certainty over something, and I believe the psychological appeal of a "beginning of it all" is a major factor in the popularity of the Big Bang theory. Not a reasoned "personal choice" perhaps but a deeply ingrained preference for closure.

Einstein, Hubble, Hoyle and others (both theorists and observational astronomers) were comfortable with the concept of a steady-state universe - in fact Einstein inserted the cosmological constant into GR to ensure that the universe did not expand or collapse. It was not until the concepts of "constant speed of light in a vacuum" and "redshift/distance relationship" were combined to produce the idea of "cosmological expansion" that the Big Bang theory evolved. Yes, some of the predictions of the theory have been borne out, but there are a lot of fudge factors required to keep BB viable in the face of discordant observations. Still, it is an attractive theory to many because it gives us a "nailed down" beginning.

The constancy of the speed of light in a vacuum is a fundamental concept to standard cosmology. One significant problem with this is that according to quantum theory, a vacuum cannot exist in our universe. Instead the "vacuum" through which light waves propagate in space is a seething, frothy sea of virtual EM particles and anti-particles. It is a real field, and we must expect it to behave like one, susceptible to polarizing influences and capable of existing at a range of energy densities. Given the absolute theoretical energy of the ZPE field (summed over all wavelengths), this range could be very large, depending on the degree to which the field can be polarized. If EM waves interact with this field to any degree, we must be prepared to expect some measurable effects, like perhaps seeing the light refracted by the field and/or perhaps being redshifted as it traverses great distances.

Hubble "found" the redshift/distance relationship (actually, he demonstrated its linearity), but he was not comfortable with the idea that redshift was caused by the expansion of the universe. It may be that the proponents of a "tired light" concept are correct, since there is no true vacuum in space. Time will tell.
marcus
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#6
Nov26-04, 04:49 PM
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Quote Quote by wolram
I came across this in the AandC reference library posted by Marcus
http://www.astrosociety.org/pubs/mer...2/nothing.html
My question is,Why do we seem to want a universe that started from
"almost", nothing, or reduce our existence and our Us existence
to as close to 0 as possible?
Hi wolram, about that statement (by Filippenko and Pasachoff) of the
"universe is the ultimate free lunch" idea...

Alex is an acquaintance and both he and Ray pasachoff are great teachers and textbook writers---they know how to communicate to undergrad non-majors. So I thought their account of the idea might be a good one to have even tho it is just pedagogical exposition for general audience.

but I dont want to hold it up as an authority!

the universe that bootstraps itself into existence
or begins with a comparatively small fluctuation
is a common idea. Alan Guth also has a good exposition of it IIRC.

but ideas change with time and no one can say This Is It.

It is worth knowing about but maybe it's wrong.

==============
you ask a provocative question about it.
you say, Why are people so drawn to this idea? what is so attractive about free lunch, or getting something from nothing?
========
one thing is it is catchy, it gets your attention because of the paradoxical character. we all know energy conservation and that you DONT get all the matter and energy in the universe from comparatively small beginnings.
but the idea is that it really can happen that way

so the surprise and paradox appeals to people
=========

another appeal is the fact that it takes off some of the constraints and frees the theory up

It is really hard to picture how the universe got started and it makes it easier to come up with descriptions if they dont have to explain where all the huge amount of energy came from.

I guess I'm just saying the obvious here
========

My own personal take: I think everybody should read the latest
Ambjorn Jurkiewicz Loll
Semiclassical Universe from First Principles
because it that paper they have the universe come into existence by itself IN THE COMPUTER, that is, in a computer simulation.

in every one of their runs, there is this long "stalk" of time when the universe has essentially zero size and when growth hasnt started.

and then at some unpredictable moment the thing begins to expand and burgeon out.

they say their model recovers the equation that hawking etc. postulated about the scale factor. and they say they get out of their computer model the business that Villenkin was promoting about the universe coming into existence from littler or nothing.

the AJL paper does bear looking at. I'll be back after lunch.
turbo
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#7
Nov26-04, 06:22 PM
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Quote Quote by marcus
I think everybody should read the latest
Ambjorn Jurkiewicz Loll
Semiclassical Universe from First Principles
because it that paper they have the universe come into existence by itself IN THE COMPUTER, that is, in a computer simulation.

in every one of their runs, there is this long "stalk" of time when the universe has essentially zero size and when growth hasnt started.

and then at some unpredictable moment the thing begins to expand and burgeon out.

they say their model recovers the equation that hawking etc. postulated about the scale factor. and they say they get out of their computer model the business that Villenkin was promoting about the universe coming into existence from littler or nothing.

the AJL paper does bear looking at. I'll be back after lunch.
After your free lunch. In the final reckoning, does not there have to be a field or ground state in which this universe suddenly comes into being? We are back to defining initial conditions.

Indeed, it's turtles all the way down.
Chronos
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Nov26-04, 08:31 PM
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Quote Quote by wolram
All the above is understood, but now the singularity is is on the limb of popular science, and other universe theories are marginal, it seems to me that some form of energy, matter, has always been in existence in our" vicinity", and to go beyond that statement is unprovable to date, and may stay that way until we can send a probe to the edge of a black hole to gather real data. This is not a dig at popular science, it is just a search for a fruitful way forward.
The singularity has always been out on a limb. It has always been generally recognized as the point where the mathematical model breaks down, not reality. The pre-BB state is hidden from view by the planck wall [the first tick of planck time] and we may never penetrate that veil. So yes, it is purely speculative to predict or describe the nature of the pre-emergent state. To call it nothing is as good as any other description. It certainly has no known counterpart in the post emergent universe, save perhaps a black hole as you suggested. Of course we can't see inside those either. Just another one of nature's tantalizing little practical jokes.

But was it 'nothing' in the purest philosophical sense? That's not very appealing and gives rise to the most intractable paradox of all. By the strictest logical standard, nothing is omnipotent. How can nothing be destabilized? By what? When you take this into consideration, it is easy to see why the quantum fluctuation proposal is attractive. What do we know about nothing? In this universe nothing is a pure vacuum state. But even a pure vacuum state does not just lay there doing nothing. It continuously churns out stuff [virtual particles] from literally nothing. How can that be? It uses no energy, no matter, but keeps itself amused by popping out little somethings then promptly destroying them. Has that always been the nature of nothing, or did nothing get bored after something crashed the party and decided to take up a hobby?
marcus
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#9
Nov26-04, 09:01 PM
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Quote Quote by wolram
My question is,Why do we seem to want a universe that started from
"almost", nothing, ...
Turbo, read the original post on the thread.
we are not talking about U arising from nothing
but from a comparatively little something

the turtles-all-the-way-down business is of no concern

what apparently concerns a lot of us is our deeprooted notion of Conservation of Energy.

People find it strange that the mass of a billion billion stars could come from, say, a black hole with a mass of no more than few solar masses.

How could the mass-energy of the universe multiply itself a quintillion-fold?

this question needs addressing no matter whatever and however you imagine the original fluctuation or original field or original turtle.

This is why I hope that at least a few people will actually READ the
new AJL article Semiclassical Universe from First Principles

the universe in their simulation, running by their model, bootstraps itself into existence (not from nothing but) from NEARLY nothing, and does so at an unpredicatble time.

and in the process follows a semiclassical equation that was not put into the model, but just happens to be followed.

and the beginnings, in their model, are NOT A FIELD and have no pre-existing spacetime! The kernel from which it begins and burgeons out is purely combinatorial

Indeed the whole model is combinatorial and consists of bunches of n-tuples of natural numbers----space and time and geometry are just
things that emerge at largescale.

And, impressively enough, for the first 10 years or so they were trying to do this stuff, macroscopic space and time did not emerge. what emerged was too fractal-branchy or else too crumpled. In other words they finally got it to work right.

What I am saying is, it matters what kind of turtle.
marcus
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Nov26-04, 09:14 PM
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Semiclassical Universe from First Principles
http://arxiv.org/hep-th/0411152
turbo
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Nov26-04, 10:31 PM
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I did read it. The BB universe cannot have arisen out of nothing in a field devoid of rules or potentials. "Essentially nothing", "almost nothing", "really close to nothing", etc are all equivalent to SOMETHING. Where did the "tiny little something" come from?

This cannot be addressed logically, any more than the creationists' God can be addressed. If you need a prime mover, a creator, or an initial fluctuation to jump-start your cosmos, you are all in the same boat.
turbo
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Nov26-04, 10:44 PM
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Quote Quote by Chronos
What do we know about nothing? In this universe nothing is a pure vacuum state. But even a pure vacuum state does not just lay there doing nothing. It continuously churns out stuff [virtual particles] from literally nothing. How can that be? It uses no energy, no matter, but keeps itself amused by popping out little somethings then promptly destroying them. Has that always been the nature of nothing, or did nothing get bored after something crashed the party and decided to take up a hobby?
Indeed! And the energy level that our universe maintains as its ground state seems to be very high indeed, if quantum field theorists can be believed. Everything that we see, feel, experience, etc, etc, is a fluctuation relative to that ground state. Ain't existance fun?
wolram
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Nov27-04, 03:49 AM
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Marcus
This is something i have not read yet but it sounds interesting

My own personal take: I think everybody should read the latest
Ambjorn Jurkiewicz Loll
Semiclassical Universe from First Principles
because it that paper they have the universe come into existence by itself IN THE COMPUTER, that is, in a computer simulation.
wolram
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Nov27-04, 04:00 AM
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By Tubo1


Indeed! And the energy level that our universe maintains as its ground state seems to be very high indeed, if quantum field theorists can be believed. Everything that we see, feel, experience, etc, etc, is a fluctuation relative to that ground state. Ain't existance fun?

NO its the most perplexing enigmatic itchy subject i have ever stuck my foot in
Maybe an eternal ZPE field is the answer, i can think of nothing better, but what
about the special turtles Marcus mentions?
wolram
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Nov27-04, 05:00 AM
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Marcus.
Semiclassical Universe from First Principles
http://arxiv.org/hep-th/0411152
I may be missing something, but to run this simulation," computer power", is used
is this not cheating?
turbo
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Nov27-04, 09:29 AM
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Quote Quote by wolram
Marcus.
Semiclassical Universe from First Principles
http://arxiv.org/hep-th/0411152
I may be missing something, but to run this simulation," computer power", is used is this not cheating?
Well, it's not as if they just turned on the computer and watched model universes spontaneously arise. They modeled a minisuperspace "stage" that conformed to some very specific laws, as explained in this earlier paper:

http://arxiv.org/PS_cache/hep-th/pdf/0105/0105267.pdf

Unlike previous approaches, we use a space of piecewise linear Lorentzian space-times as our starting point. That this procedure is in general inequivalent to path integrals over bona fide Euclidean geometries has already been demonstrated in two dimensions [7, 8].
The reason why previous discrete path-integral approaches have been formulated for Euclidean gravity 3 is often a technical one, rather than the conviction that Euclidean space-times are more fundamental physical quantities than Lorentzian.
There is a preferred notion of a discrete “time”, namely, the parameter labelling successive spatial slices. Note that this has nothing to do with a gauge choice, since we were not using coordinates in the first place. This “proper time” is simply part of the invariant geometric data common to each of the Lorentzian geometries. We choose particular sets of simplicial building blocks in three and four dimensions. Unlike in the Euclidean case, we cannot make the simplest possible choice of making all d -simplices equilateral. Instead, we fix all spatial (squared) link lengths to 1, l 2 space = 1, and all time-like links to have a squared length l 2 time = −α , α >0. Keeping α variable allows for a relative scaling of space- and time-like lengths and is convenient when discussing the Wick rotation later. As usual, the simplices are taken to be pieces of at Minkowski space, and a simplicial manifold acquires non-trivial curvature through the way the individual building blocks are glued together.
The initial conditions for these simulations were set rather stringently, with lots of decision-making along the way. An analogy to this would seem to favor the "intelligent design" folks and the creationists, for how did our universe arise in the absence of similar initial conditions?
marcus
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Nov27-04, 10:26 AM
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Quote Quote by turbo-1
... They modeled a minisuperspace "stage" that conformed to some very specific laws, as explained in this earlier paper:

http://arxiv.org/PS_cache/hep-th/pdf/0105/0105267.pdf
Hi turbo. It is really helpful to see relevant passages quoted from the paper, as in your post.
The 2001 paper you give a link for, and quote from, is
hep-th/0105267 "Dynamically Triangulating Lorentzian Q. G."

I agree that this is a really basic paper, and when you read later ones you need to refer back to it for specific detail---so I printed it out.

But I can't find any mention of "minisuperspace" in the paper.
Maybe my eyesight is poor. Do you have a quote from the paper talking about this?

Could you perhaps be mistaken that, in fact:
"They modeled a minisuperspace "stage" that conformed to some very specific laws, as explained in this earlier paper..."

A minisuperspace model----something with a very small number of degrees of freedom, like in the classic Friedmann model where there are just a couple of parameters that evolve and a lot of symmetry is assumed----is different from a full model cosmology.

I would rather say that AJL programmed a FULL model cosmology than that they did a minisuperspace.

However in their recent paper "Semiclassical Universe..." they GOT RESULTS which, if you integrate out other information, BOIL DOWN to a wave function for some other people's earlier minisuperspace.

So they do a full model, but it runs right, and so in gross outlines it reproduces the largescale behavior of an earlier simpler minisuperspace model. But that part was precisely what they DID NOT BUILD IN.

At any rate that is my take on it---maybe you can find some passage that contradicts this. And I think it is a really important distinction.
they start with a comparatively simple and general model. they get results by running it that they did not put in. some evidence of verisimilitude.

For sure there's more to do. They can hopefully make their model
more simple, more general, and more true-to-life in the features that come out of running it.

BTW Martin Bojowald, in Loop Quantum Cosmology, DOES use minisuperspace models derived by simplifying down the full LQG model.
But that is something different---it is Loop, and not Dynamical Triangulations.

You probably are well aware, but i want to emphasize the distinction for clarity, between Loop and CDT.
marcus
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Nov27-04, 10:46 AM
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Quote Quote by turbo-1
... conformed to some very specific laws, as explained in...

... initial conditions for these simulations were set rather stringently, with lots of decision-making along the way.
specific laws: the question is not how specific the laws, but whether the laws are the right laws.

this is an ontology discussion----bout what is there---and there is a chance that some laws are the right laws because they generate realistic behavior
(given limited computing, like they only had at most 360 thousand 4D blocks to play with, and no matterfields as yet, etc)

stringent initial conditions: I am not sure I would agree.
the initial condition is about as unimposing as I can imaging----just start out with essentially zero volume and wait for something to happen

the initial conditons were so un-demanding that for 10 years or so they couldnt even get a 4D spacetime to emerge---kept getting feathery 2D fractal-like things, or heavily ingrown compacted infinite dimensional crunches.

just because the building block you use is 4D doesnt guarantee the macro assemblage will be 4D----because it is not built in any surrounding space,
the assembly of blocks can happen any way allowed by the model and it IS space

so I would say the initial conditions are rather MINIMAL and UNconstraining, 'cause they dont even guarantee familiar 4D results till you get the evolution rules right

lots of decision-making along the way I think you may be mistaken here also. My impression is that there was no human intervention during runs.
The rules of geometric evolution were set, the minimal initial conditions imposed, and the thing was run repeatedly-----to let an idea of typical geometric evolution emerge.

they accumulated statistics of various types, from hundreds of different runs, which would have been meaningless had they been making decisions by hand---or otherwise interfering

if they had been inclined to put stuff in by hand they could have published (I would say much less valuable) results 10 years ago


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