Could someone please explain....

[damocles]

http://www.ligo.org/pdf_public/techpapers_mandic.pdf

or;

http://www.google.com/search?q=cache...dic.pdf+&hl=en
--------------------------------------------------------------------------------

Accessibility of the Pre-Big-Bang Models to LIGO

Vuk Mandic

California Institute of Technology,

MS 18-34, Pasadena, CA 91125

(Dated: July 8, 2005)

Abstract;

A recent search for a stochastic background of gravitational waves using LIGO interferometershas produced a new upper bound on the amplitude of this background in the 100 Hz region. We investigate the implications of the LIGO result on pre-Big-Bang models of the early Universe. We find that LIGO is already begining to explore the interesting region of the parameter space of thesemodels, although its reach is still weaker than the indirect bound from Big-Bang nucleosynthesis.We estimate that the future searches by LIGO and by Advanced LIGO should significantly constrain the parameter space, and in some parts even surpass the nucleosynthesis bound.

I'm following the mathematics in the article with great difficulty. I think I uinderstand what the authors are saying(limits on the possible theoretical pre-big-bang models of space; but how does LIGO measure a stochastic beckground of gravitational waves before gravitation existed as a discrete binding force? Is this some part of string theory that I don't understand?

Help!

First of all, the concept of gravity is of yet not even clost to being completely understood, and has not yet been reconciled with the laws of energy conservation. I believe what the people you are referring to are talking about is how gravity was/is pivotal in the creation/development of the universe. Considering the possible fact that a black hole can be caused by a "gravity rip" in the space/time continuum, gravity is a force requiring much more study and can truly turn out to be pivotal to the creation and demise of the universe.

[maddog]

Originally Posted by damocles

I'm following the mathematics in the article with great difficulty. I think I uinderstand what the authors are saying(limits on the possible theoretical pre-big-bang models of space; but how does LIGO measure a stochastic beckground of gravitational waves before gravitation existed as a discrete binding force? Is this some part of string theory that I don't understand?

Your link mentioned seem no longer to work. I might look on Cal Tech's site or do an
abstract search on the author. However, reading the abstract seems to be implying
that LIGO can measure a background distribution of Gravity Wave (about 100 Hz) that
appear to be pre-big bang according to some models not mentioned. Also mentioned
this was found by looking at pre-nucleosyntethis (pre star period of universe). The
mention of "Stochastic background" implies this distribution is probabilistic. Mind you
only going off the abstract, I didn't get to read the papers. Hope this helps.

maddog

[CraigD]

The paper (http://www.ligo.org/pdf_public/mandic.pdf – note filename change) is light on explaining the theoretical background on which it’s built. As you note, the math in it is difficult for non-specialists, so I just skimmed the article, attempting to get a general sense of it. Since I lack the technical background of the authors and their intended audience, the assumptions I was required to make have a higher than normal chance of being incorrect, so please consider my interpretations tentative.

Originally Posted by damocles

but how does LIGO measure a stochastic beckground of gravitational waves before gravitation existed as a discrete binding force?

It doesn’t.

The “gravitational background radiation (GBR)” (my phrase) they’re describing, would, like the better known Comic Microwave Background (CMB), have occurred post-Big-Band, when the universe became transparent to gravitons. I am unsure if this would have occurred at the same time, around the same time, or before it became transparent to photons at the beginning of the “radiation phase” (Deionization Epoch, ~379,000 y ABB)

In short, measuring the GBR should provide a datum similar to the CMB and the relative abundance of elements due to nucleosynthesis, which can be used to further constrain the parameters of the pre-Bib-Bang model under consideration, which involves a “string phase” beginning some time before the Big Bang, and ending at it.

This is really some extreme experimental Physics, testing some very tentative theories. I believe Kip Thorne said that the problem with String Theory is that there’s no one yet alive mathematically smart enough to grasp it well, and suggested that it might be necessary to wait a century for Math to catch up. I don’t even understand it enough to have an informed opinion about comments like Thorne’s, but enjoy the nibbles of understanding I get from threads like this.

[C1ay]

Originally Posted by CraigD

This is really some extreme experimental Physics, testing some very tentative theories. I believe Kip Thorne said that the problem with String Theory is that there’s no one yet alive mathematically smart enough to grasp it well, and suggested that it might be necessary to wait a century for Math to catch up. I don’t even understand it enough to have an informed opinion about comments like Thorne’s, but enjoy the nibbles of understanding I get from threads like this.

I noticed near the end of the paper it stated,

Finally, we note that the string phase in the PBB models is not well understood yet. Hence, many modifications to the PBB model are possible and have been proposed.

IOW, they're still guessing at some of it.

[damocles]

Thanks to all! I knew that I got most of it wrong at the first reading, and the folks' generous help clarified to me what I mis-interpreted in the article.(especially about background gravitational ripple effects.). Now if some Feynmann could come bombing in here and supply the simple illustration that clears everything up in the mathematics for a schmuck(me) that would be wonderful.

Again thanks to all!

Best wishes;

[Turtle]

Originally Posted by damocles

... supply the simple illustration that clears everything up in the mathematics for a schmuck(me) that would be wonderful.

___I agree with Craig's observation; if & when someone understands intuitively the super symmetric forms of string theory, it won't have a shmuckian isomorphism inspite of its wonderfulositudinality.

[maddog]

Originally Posted by CraigD

The “gravitational background radiation (GBR)” (my phrase) they’re describing, would, like the better known Comic Microwave Background (CMB), have occurred post-Big-Band, when the universe became transparent to gravitons. I am unsure if this would have occurred at the same time, around the same time, or before it became transparent to photons at the beginning of the “radiation phase” (Deionization Epoch, ~379,000 y ABB)

In short, measuring the GBR should provide a datum similar to the CMB and the relative abundance of elements due to nucleosynthesis, which can be used to further constrain the parameters of the pre-Bib-Bang model under consideration, which involves a “string phase” beginning some time before the Big Bang, and ending at it.

This is really some extreme experimental Physics, testing some very tentative theories. I believe Kip Thorne said that the problem with String Theory is that there’s no one yet alive mathematically smart enough to grasp it well, and suggested that it might be necessary to wait a century for Math to catch up. I don’t even understand it enough to have an informed opinion about comments like Thorne’s, but enjoy the nibbles of understanding I get from threads like this.

CraigD,

Thanks for link update, I was able to receive the actual paper that way. I didn't have
time to read all of it, I just skimmed it also. What was stumbling me though was my
lack of knowledge in Probability - forgetting what "stochastic" means. I got from the
http://en.wikipedia.org/wiki/Stochastics the Stochastic
just means "random function". So I was right in guessing the author meant in
describing a random background distribution.

He alluded to three sources for such a distribution as to why fairly clearly:

1) Closely spinning binary pulsars (causing a gravitational wake). This model would
create a GW spectrum that might vary in frequency and amplitude yet would not really
decay. Also he mentioned this was a more local phenominae

2) Inflation Models (even though this is after the BB, Inflationary period is Pre-CMB.
I suppose this is model that would get my vote. For more on Inflation read Alan Guth's
book or Brian Greene's book, "The fabric of the Cosmos".

3) His third example seems to be his favorite as a "Pre-Big Bang" set of models. This
is actually based on the examples by John Archibald Wheeler on Bubble Universes that
can be generated. This birthing would create a huge wake that would decay since the
beginning, just like CMB. Though I am not sure that if an Inflation model is accurate,
that Inflation itself would negatively attenuate the amplitude of the GW signal. When I
get a free moment, maybe I will study this paper in more depth.

Thanks again for the details.

maddog

[Qfwfq]

Originally Posted by CraigD

would, like the better known Comic Microwave Background (CMB), have occurred post-Big-Band,

Typos? Or intended satire?