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sirius0
2007-Feb-26, 10:26 PM
What causes expansion? I have been having a lot of thoughts lately and I don't want to be reinventing the wheel!

(Those thoughts have and will on their maturity occur in an appropiate place on this forum)

Some one posted to me recently that the accelerating recession of distant galaxies is caused by dark energy infering that the recession itself might be from something else.
Is this correct wrt the standard model/s

Tim Thompson
2007-Feb-26, 11:21 PM
What causes expansion? I have been having a lot of thoughts lately and I don't want to be reinventing the wheel!
Don't worry; you can't re-invent a wheel that was never invented in the first place. Nobody knows what causes expansion. Nobody knows why the big bang banged; there are as many answers as there are people to supply one.


Some one posted to me recently that the accelerating recession of distant galaxies is caused by dark energy infering that the recession itself might be from something else. Is this correct wrt the standard model/s
It is correct that observations appear to show that the expansion of the universe has accelerated. The words "dark energy" are only a place-holder, a name for something which remains otherwise inscrutable & unknown. Nobody knows what causes the expansion in the first place, so it's a cinch that the cause of its acceleration is even less well understood.

Jeff Root
2007-Feb-27, 02:50 AM
Tim,

My understanding is that the acceleration of the expansion has
had an apparently constant value for the past few billion years,
and that before that time, it was masked by gravitational slowing
of the expansion. Can you tell me anything about how far back
those rates (deceleration / acceleration) have actually been
measured so far? In particular, I'm wondering if measurements
farther back in time might find that there never was a period of
deceleration, that the expansion has always been accelerating.

What paper would be a good summary of current knowledge?

-- Jeff, in Minneapolis

sirius0
2007-Feb-27, 05:06 AM
Tim,

My understanding is that the acceleration of the expansion has
had an apparently constant value for the past few billion years,
and that before that time, it was masked by gravitational slowing
of the expansion. Can you tell me anything about how far back
those rates (deceleration / acceleration) have actually been
measured so far? In particular, I'm wondering if measurements
farther back in time might find that there never was a period of
deceleration, that the expansion has always been accelerating.

What paper would be a good summary of current knowledge?

-- Jeff, in Minneapolis


Yes Tim, we await your answer and referal to a paper :)
Chris

sirius0
2007-Feb-27, 06:06 AM
Tim; I agree with your statment about a place holder. I think some of this Λ is a bit Ptolemaic (epicircles etc; beautiful maths but not proven).

However I am not denying that there is an accelerating expansion (some who argue against Λ think expansion to be an illusion; I do not).
A lot of my questions are really me gathering enough knowledge to progress in my thoughts and self education. Often I have an agenda of checking validity too. I often have an intuitive inkling of what the answer to my questions is or I am completely wrong and this is all valuable to me as this is the only physics I get to do (sob).

As I progress I am aware too that I have some ideas and these might make me selective in what I hear which if I don't take care could lead me into the la la land side of ATM.

I think I might soon be able to offer a possible explanation of what Λ is but of course I am a baby physicist and a bit scared! As I might be completely wrong and look like a smarty pants idiot!
Still if I have an idea I am obliged to disclose and perhaps learn from any lambasting I might recieve.

Of course I won't be putting my ideas here; they will be ATM until accepted or disproven otherwise.

astromark
2007-Feb-27, 09:13 AM
If you have some thoughts on what might be the driving force of this universes expansion do not go posting it in the ATM. I like so many will not see it. That ATM place is full of strange things and some of them are people.
I would encourage you to post it here as a question. Could this be possible?
I am interested in this fact finding mission regarding the expansion or not. And whether or not the process is accelerating or not, or not do you not think.~)

StupendousMan
2007-Feb-27, 02:33 PM
If you are willing to spend five minutes, you can find good sources of information on these topics yourself. Permit me to demonstrate.

Method I: go to the astro-ph preprint site, which collects copies of papers which (in most cases) will eventually be published in technical journals or proceedings of conferences. In their search page

http://xxx.lanl.gov/find

type the words "expansion acceleration cosmology overview" in the "Abstract words" box. Press "Do search" button. You'll see a list of papers which contain these words in their abstract. You can then read the titles, and the abstracts, to see if the paper is likely to answer your questions. If it looks good, read the entire text. I was given a list of two papers, of which the one by Linder

http://xxx.lanl.gov/abs/astro-ph/0501057

looks like the better bet.

Method II: go to the Astrophysics Data Servce web site. This contains papers which _have_ been published. In some cases, it does not supply the full text of recent publications, but it will allow you to read the abstract, and, in most cases, point you to a copy of the full text on the astro-ph preprint site.

Again, I choose the words "acceleration expansion cosmology overview" and place them into the Abstract words box. This time, I receive a list of over 100 papers, going farther back in time. It will take a while to look at the titles, and then the abstracts, but you can again find a paper which may meet your needs.

Of course, you can modify your exact search terms as necessary.

Why not give it a try?

01101001
2007-Feb-27, 03:12 PM
If you have some thoughts on what might be the driving force of this universes expansion do not go posting it in the ATM. I like so many will not see it. That ATM place is full of strange things and some of them are people.
I would encourage you to post it here as a question. Could this be possible?

sirius0, I am not quite so interested as Astromark in your thoughts, and I think this subforum of Q&A is rightly reserved for questions, not thoughts.

If you can ask about your non-mainstream thoughts, ask. If you feel the need to assert or defend your thoughts, though, please do so in ATM, where they will be, if not welcome, at least expected.

sirius0
2007-Feb-27, 09:07 PM
Thank you everyone. I think I got a little of topic though. In fact I was shuddering as I logged back in as I couldn't remember what i had written! I have seen too many QA be highjacked into an ATM. This has not been my intent although I have, through a need emotionally to disclose if I have an agenda, come dangerously close myself. My sincere apologies to the forum for this. However I think despite being tired and a bit melanholic; I was fairly balanced in what I said.

I think at least I need the practice of writting a paper. Even if it proves that my ideas are duds. Once I have done this I will paste some or all of it into an emryonic ATM I started some time back. i will then hope some will read and give feed back. The ATM I started has no maths or metric or much in the way of predicted observations. I think cause I have alluded to further thoughts I should ask here.

Could Universal expansion be due to background gravity gently curving space-time in a manner that causes say dimension X (X, Y, Z, (ct)) to as a funtion of distance take on a proportional component of (ct)? There are some interesting new predictions that could come from this idea what do you think?

Now if I have actually stepped into ATM here I will be more than happy to edit this all away should a moderator or even a few members be annoyed.

Tim Thompson
2007-Feb-28, 06:33 AM
My understanding is that the acceleration of the expansion has had an apparently constant value for the past few billion years, and that before that time, it was masked by gravitational slowing
of the expansion.
That looks right. As the universe expands, and the distance between galaxy clusters grows, their mutual gravitational attraction weakens. So even a cosmological constant will be able to push them apart faster as time goes by. That appears to be the case. Gong & Wang, 2007 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006astro.ph.12196G&db_key=PRE&d ata_type=HTML&format=&high=4366fa465126228) show that the universe made its transition from deceleration to acceleration at a redshift of about 0.36, which looks like about 3.9 billion years ago (according to Ned Wright's Cosmology Calculator (http://www.astro.ucla.edu/~wright/CosmoCalc.html)).

There is a huge literature on dark energy, and not everyone agrees on just what the current state of knowledge really is. I will simply show a short, arbitrary list of what look to me like good reviews. Select the arXiv eprint links to find PDF to download. I always prefer to link to the ADS abstract page because it links to papers that cite the selected papers.


Dark Energy, A Cosmological Constant, and Type Ia Supernovae (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2007astro.ph..1692K&db_key=PRE&d ata_type=HTML&format=&high=4366fa465131927), Krauss, et al., 2007
Dark Energy: Mystery of the Millennium (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006AIPC..861..179P&db_key=PHY&d ata_type=HTML&format=&high=4366fa465131927), T. Padmanabhan, 2006
Reconstructing Dark Energy (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006astro.ph.10026S&db_key=PRE&d ata_type=HTML&format=&high=4366fa465131927), Sahni & Starobinsky, 2006
The issue of Dark Energy in String Theory (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006hep.th....7006M&db_key=PRE&d ata_type=HTML&format=&high=4366fa465131927), Mavromatos, 2006
Dynamics of dark energy (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006hep.th....3057C&db_key=PRE&d ata_type=HTML&format=&high=4366fa465131927), Copeland, Sami & Tsujikawa, 2006

RussT
2007-Feb-28, 11:57 AM
Tim, you are probably one of the best people to ask this question.

When Hubble first found the galaxies to be expamding away in all directions there was no concept of "Expansion in the Voids" between the galaxies, right?

So, when was this really found to be the case and who were the pioneers and then the subsequent confirmationists?

Tim Thompson
2007-Feb-28, 04:35 PM
When Hubble first found the galaxies to be expanding away in all directions there was no concept of "Expansion in the Voids" between the galaxies, right?
Correct. In fact, Hubble himself never accepted big bang cosmology, and never accepted the idea of an expanding universe. He accepted only what he had observed, namely a redshift - distance relationship. But an expanding universe necessarily leads to the conclusion that visible galaxies show recession velocities greater than the speed of light, which Hubble and others believed was an unacceptable violation of special relativity. We now know that this is not the case, and recession velocities greater than the speed of light are quite acceptable (i.e., Davis & Lineweaver, 2004 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PASA...21...97D&db_key=AST&d ata_type=HTML&format=&high=4366fa465103261); Lineweaver & Davis, 2005 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005SciAm.292c..36L&db_key=AST&d ata_type=HTML&format=&high=4366fa465103261)).

The big bang idea at the time owes its origin primarily to the Belgian Jesuit cleric Georges Lemaitre (Lemaitre, 1931a (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1931MNRAS..91..483L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531); Lemaitre, 1931b (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1931MNRAS..91..490L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531); Lemaitre, 1934 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1934PNAS...20...12L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531)). Simply put, the universe "banged" into existence (no reason or explanation known or guessed), and was coasting to an eventual stop, expanding ever more slowly with time. And so the idea remained until well after the big bang became the mainstream leader in the 1960s & 1970s. See the book Genesis of the Big Bang (http://www.amazon.com/Genesis-Big-Bang-Ralph-Alpher/dp/0195111826/sr=1-1/qid=1172678716/ref=sr_1_1/104-0514921-8991127?ie=UTF8&s=books) by Ralph Alpher & Robert Hermann (Oxford University Press, 2001) for an authoritative history of big bang cosmology by two or its chief architects.


So, when was this really found to be the case and who were the pioneers and then the subsequent confirmationists?
It's a brand new idea. I don't think anybody thought about it before 1998, when the first assertions of accelerated expansion came forward (Reiss, et al., 1998 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.1009R&db_key=AST&d ata_type=HTML&format=&high=4366fa465119104)). The confirmationists, if there are any, must be Adam Reiss (http://www.jhu.edu/news_info/news/home06/nov06/energy.html) and his group, including Alex Filipenko (http://astro.berkeley.edu/people/faculty/filippenko.html). There are still plenty of claims that we can do without both dark energy & dark matter, so I wouldn't jump on the "confirmed" bandwagon just yet. But the idea does seem to be the mainstream leader at this time.

Kwalish Kid
2007-Feb-28, 05:00 PM
The discovery of the redshift (or possibly blueshift)-distance relation was predicted by Hermann Weyl before its discovery, and perhaps by others.

RussT
2007-Mar-02, 08:53 AM
Correct. In fact, Hubble himself never accepted big bang cosmology, and never accepted the idea of an expanding universe. He accepted only what he had observed, namely a redshift - distance relationship. But an expanding universe necessarily leads to the conclusion that visible galaxies show recession velocities greater than the speed of light, which Hubble and others believed was an unacceptable violation of special relativity. We now know that this is not the case, and recession velocities greater than the speed of light are quite acceptable (i.e., Davis & Lineweaver, 2004 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004PASA...21...97D&db_key=AST&d ata_type=HTML&format=&high=4366fa465103261); Lineweaver & Davis, 2005 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005SciAm.292c..36L&db_key=AST&d ata_type=HTML&format=&high=4366fa465103261)).

The big bang idea at the time owes its origin primarily to the Belgian Jesuit cleric Georges Lemaitre (Lemaitre, 1931a (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1931MNRAS..91..483L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531); Lemaitre, 1931b (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1931MNRAS..91..490L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531); Lemaitre, 1934 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1934PNAS...20...12L&db_key=AST&d ata_type=HTML&format=&high=4366fa465106531)). Simply put, the universe "banged" into existence (no reason or explanation known or guessed), and was coasting to an eventual stop, expanding ever more slowly with time. And so the idea remained until well after the big bang became the mainstream leader in the 1960s & 1970s. See the book Genesis of the Big Bang (http://www.amazon.com/Genesis-Big-Bang-Ralph-Alpher/dp/0195111826/sr=1-1/qid=1172678716/ref=sr_1_1/104-0514921-8991127?ie=UTF8&s=books) by Ralph Alpher & Robert Hermann (Oxford University Press, 2001) for an authoritative history of big bang cosmology by two or its chief architects.


It's a brand new idea. I don't think anybody thought about it before 1998, when the first assertions of accelerated expansion came forward (Reiss, et al., 1998 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998AJ....116.1009R&db_key=AST&d ata_type=HTML&format=&high=4366fa465119104)). The confirmationists, if there are any, must be Adam Reiss (http://www.jhu.edu/news_info/news/home06/nov06/energy.html) and his group, including Alex Filipenko (http://astro.berkeley.edu/people/faculty/filippenko.html). There are still plenty of claims that we can do without both dark energy & dark matter, so I wouldn't jump on the "confirmed" bandwagon just yet. But the idea does seem to be the mainstream leader at this time.

Thanks for the links and explanation Tim, but I was specifically asking about the Voids...
[When Hubble first found the galaxies to be expanding away in all directions there was no concept of "Expansion in the Voids" between the galaxies, right?

So, 'when' was this (that it was actually determined that the 'space' in the Voids "Between the galaxy clusters" was what was expanding) really found to be the case and 'who' were the pioneers and then the subsequent confirmationists?]