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Original location of the Big Bang

by Jack Bauer
Tags: bang, location, original
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Jack Bauer
#1
Jul22-06, 02:20 PM
P: 11
Would it be possible by comparison of expansion rates and directions at various points to back-extrapolate the location of the original Big Bang? Certainly in a local part of the universe, everything is expanding away from everything else with rates and directions as if the whole expansion were homogenous but if the universe arose at one point, I would think analysis of vastly separated points would show subtle differences that would point to the location of that one point. Just as with sufficient data points within an expanding sponge that had been squeezed into a tiny wad we should be able to deduce the center of compression of the sponge before it was allowed to expand -- or is this too unknowable?
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marcus
#2
Jul22-06, 02:56 PM
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Quote Quote by Jack Bauer
Would it be possible by comparison of expansion rates and directions at various points to back-extrapolate the location of the original Big Bang?
Not in any meaningful way.

any point in today's space that you pick
has an equal claim with all other points to being the "location of the original Bang"

the Bang event was not an explosion of stuff "in" some pre-existing space, so it cannot be traced back to a point in space.

typically astronomers do not picture the Bang event as an explosion IN space but as the beginning of the observed expansion OF space.
(they do not suppose there was some surrounding other kind of space in which our space began expanding---perhaps there is or was some surrounding space, possibly higher dimensional, but I know of no way to ascertain this)

there is a Scientific American article available online which deals with several misconceptions people often have about the expansion of space and its beginning. Would you like the URL so you can read it?

Anyway, the answer to your question is that in the usual model of cosmology that astronomers have, ALL POINTS ARE EQUALLY the location of the beginning of expansion.

(or else you could say that there is no "location" of the onset of expansion---the idea is not well-defined because there are no relevant coordinates)

the Sci Am article is by Charles Lineweaver. You might like it. ask if you want the URL.
Jack Bauer
#3
Jul22-06, 03:15 PM
P: 11
Thanks, yes I would like the URL for that article, if you get a chance.

marcus
#4
Jul22-06, 06:16 PM
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Original location of the Big Bang

Quote Quote by Jack Bauer
Thanks, yes I would like the URL for that article, if you get a chance.
http://www.physicsforums.com/showthr...299#post482299

should be several active links in that post,
please tell me if you have any trouble.
the article was by Lineweaver and Davis
marcus
#5
Jul22-06, 06:18 PM
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to facilitate, I just copied that whole post


http://www.sciam.com/article.cfm?cha...2383414B7F0147

Popular written feature article "Misconceptions about BigBang"
Here are some sample "sidebars" of the article. Each has one or more visual diagrams with a wrong answer discussed and a right answer explained.


http://www.sciam.com/media/inline/00...7F0147_p39.gif
What kind of explosion was the big bang?

http://www.sciam.com/media/inline/00...7F0147_p40.gif
Can galaxies recede faster than light?

http://www.sciam.com/media/inline/00...7F0147_p42.gif
Can we see galaxies receding faster than light?

http://www.sciam.com/media/inline/00...7F0147_p43.gif
Why is there a cosmic redshift?

http://www.sciam.com/media/inline/00...7F0147_p44.gif
How large is the observable universe?

http://www.sciam.com/media/inline/00...7F0147_p45.gif
Do objects inside the universe expand, too?
Jack Bauer
#6
Jul23-06, 12:59 PM
P: 11
Marcus, thanks for the links. I just read the whole article -- really helpful.

Some things occured to me. If some objects are "receding" from us faster than the speed of light because of expansion of space, could this be a way of travelling faster than light? If we could somehow cause such expansion (by using whatever force or process is causing the universe to expand) locally, along a particular path, could we "expand" a spaceship over to a certain part of the universe? Or conversely could we "pull in" a particular part of the universe by reversing expansion along a particular path? An analogy would be a frog bringing an insect back on its tongue :)

Also although I understand the current BB theory posits that expansion was "from everywhere", not from a particular point, why? Has the alternative of expansion from a particular point been disproven? It seems to me there is a lot of variation in the velocities of expansion when you look around -- do these really not point to a particular part of the universe as the "oldest"/least expanded?
marcus
#7
Jul23-06, 03:20 PM
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Quote Quote by Jack Bauer
Some things occured to me. If some objects are "receding" from us faster than the speed of light because of expansion of space, could this be a way of travelling faster than light?
cute idea
but personally, I think not:
"travelling" involves the idea of "getting somewhere"
and recession speed doesnt get you closer to any destination


imagine someone in a galaxy X that is 27 billion LY from us.
We see galaxy X receding at speed = 2c

he sees us receding from HIM at speed 2c, but he doesnt see us catching up with light, or getting closer to anything

we see him receding from US at speed 2c, but we dont see him catching up with anything, or approaching anything. All the space around him in his local neighborhood is also receding from us at about the same 2c speed.

recession speed doesnt "do any good" to anybody in a transportation locomotion sense-----as animals we have this instinctive urge to go somewhere so it's natural to ask what you can do with the expansion of space: can you save on gasoline bills, hitch a ride, etc.?

Most likely not.

But it does a lot of good for us in other ways. If space were not expanding we would be getting cooked by the accumulated light. If it hadnt expanded 1000-fold since the time the CMB light was released we would be like standing in front of a 3000 Kelvin heat lamp turning crisp and then getting vaporized
the expansion is nature's way of COOLING the light that is coming to us from all directions. So it is a nice cold 3 Kelvin. think of it as air conditioning for the universe
BoTemp
#8
Jul23-06, 04:10 PM
P: 92
Remember warp drive, on star trek? It's not theoretically impossible. "Gravity" by Hartle has a box about it in chapter 20. Basically, you need to be able to shrink space in a region surrounding you. It's impossible to travel faster than light locally, but the distance you're covering is shorter so you can cover a distance in a shorter amount of time than a light ray would.

This would require negative energy to create, which may exist, but has never been observed. So don't hold your breath.
EL
#9
Jul24-06, 02:57 AM
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Marcus, this is a really nice text! It should be a sticky or something like that.
russ_watters
#10
Jul24-06, 11:34 AM
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Quote Quote by BoTemp
Remember warp drive, on star trek? It's not theoretically impossible. "Gravity" by Hartle has a box about it in chapter 20. Basically, you need to be able to shrink space in a region surrounding you. It's impossible to travel faster than light locally, but the distance you're covering is shorter so you can cover a distance in a shorter amount of time than a light ray would.
Unfortunately, though it would work, that would only be useful for tunnels, not for spaceships, because the field that "warps" local space to allow shorter travel distances is itself constrained by Relativity to propagate at C. If, for example, you were going to travel to Alpha Centuari, you'd need to let the field propagate for 4.5 years before you could enter the tunnel and travel there. There is a benefit, though - you'd save on fuel.
XanPaul
#11
Mar15-09, 01:45 PM
P: 4
So then could it be, or has it been, said that everywhere in the obsevable universe is the sight of the Big Bang? Because of expansion, the Big Bang not only occured but is still occuring in some way? Like being inside a giant "explosion" as it's happening? The point it occured at just expanded to create the empty space between all the matter that was there from the start?
marcus
#12
Mar15-09, 04:38 PM
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Quote Quote by XanPaul View Post
... Like being inside a giant "explosion" as it's happening? The point it occured at just expanded to create the empty space between all the matter that was there from the start?
That's pretty decent as an initial description. You might enjoy these two articles
Lineweaver SciAm article "Misconceptions about the Big Bang"
http://www.astro.princeton.edu/~aes/...onsBigBang.pdf

And "A Tale of Two Big Bangs" at Einstein Online (a research institute's outreach website)
http://www.einstein-online.info/en/s...ogy/index.html

These articles will help your refine your picture quite a bit. They are both aimed at eliminating common misunderstandings about the standard cosmo model.

Be careful not to rely too much on the "explosion" picture. The standard big bang model is not like an actual explosion with stuff flying out into empty space---from some central location. I think from what you say you understand this though---there is no surrounding empty space, distances simply increase.

In a figurative sense, the pattern of increasing distance as you say "creates the empty space" between galaxies etc. But space is not a substance that needs to be created, at least as far as the general relativistic models in cosmology are concerned. The main thing is simply that the distances increase and if you figuratively say that creates space OK.
Judycrayton
#13
Oct10-10, 06:25 PM
P: 3
Marcus, thank you so much for all this information. My mind isn't really grasping it but at least I know what it is I'm not grasping :) That is much better than before.
mrspeedybob
#14
Oct10-10, 08:17 PM
P: 700
Quote Quote by Judycrayton View Post
My mind isn't really grasping it but at least I know what it is I'm not grasping :) That is much better than before.
That's going to be an immortal quote.
Judycrayton
#15
Oct11-10, 01:32 PM
P: 3
Why thank you ms speedybob. What a nice welcome :)
Kevin_Axion
#16
Oct11-10, 01:48 PM
P: 921
I'm not sure if you're being sarcastic but his reasoning isn't different from many other scientists, the current state of physics has no grasp on these questions although we are approaching them through String Theory and LQG.
marcus
#17
Oct11-10, 02:22 PM
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Quote Quote by Judycrayton View Post
Marcus, thank you so much for all this information. My mind isn't really grasping it but at least I know what it is I'm not grasping :) That is much better than before.
I'm glad you brought back this thread, Judy. I still think the factual content is up to date and useful. I know what you mean about getting a handle on what puzzles you. It can help just to be able to narrow down and say more definitely what it is you find hard to understand.

The Lineweaver SciAm link in the 2009 post needs to be replaced. The old one at princeton.edu doesn't work anymore but there's a new one:
http://www.mso.anu.edu.au/~charley/p...DavisSciAm.pdf
When you go there, the file has one blank page at the beginning, so just scroll down. Don't think it isn't working because you just see a blank page.

Quote Quote by Kevin_Axion View Post
I'm not sure if you're being sarcastic but his reasoning isn't different from many other scientists, the current state of physics has no grasp on these questions although we are approaching them through String Theory and LQG.
Kevin, thanks for the supportive comment. I tend to look at it from the "half full" perspective---personal perspectives differ: I tend to think that physicists have made significant progress in grasping "these questions". Depends on what you mean, but I think Judy is puzzling over some things that came to light in 1915-1935.

What is space and how can it expand without some other kind of space for it to expand into?

Answer (Einstein, Friedmann, Hubble...1915-1935): In the most primitive sense, space is not a thing or substance but rather space is just the distances between things. All expanding means is that distances between things increase---by a certain percentage every million years, the percentage can change over longer periods of time. And that is only distances between things far enough separated so that gravity doesn't bind them to each other and interfere with their separation growing.

The current rate is about 1/140 of one percent per million years. It's not something you'd notice except with distances that are already very very large, because it is such a small percentage. And the number 1/140 is very very slowly diminishing

So space is not a thing, it doesn't need to have some other kind of space to live in, it is simply the catalogue of distances between things, and it is "expanding" in the sense that there is this regular pattern of percentage increase---which is actually governed, we think, by a certain simple equation first written down by Alex Friedmann around 1923-1925

And because it is simply the distances between things, it doesn't need to have a boundary. It is too simple an idea to need a boundary or some other kind of "space" to live in. It can expand in a pure simple way without any of the usual accessories.

Judy, admittedly that still leaves huge awesome questions to wonder about!
But it is already a great achievement for people to be proud of. Kevin talked about grasp. Alex Friedmann gave us a terrific grasp of this process by discovering an equation that seems to spell out how that percentage rate changes over time! And there was a bonus, in that his equation was derived from, and explained by, Einstein's 1915 equation (which is something we can test in earth orbit, and within the confines of the solar system, an equation describing the relation of gravity and geometry.) So that put Friedmann's cosmology formula, which on very large scales describes expansion, on an empirical footing---connected it to something testable.

So on the one hand it's great, and there is a real grasp---and on the other hand there are still huge mysteries.

Yes the 1925 Friedmann equation is very good, and agrees with tons of evidence, millions of observations, but if you follow it back and back and back in time eventually it stops making sense---it says infinite density. A singularity is, by definition, something unphysical, a failure of theory. It is the breakdown of a model that has been pushed too far.

So, with this wonderful grasp that Einstein Friedmann Hubble and others gave us, we also get this problem of what, in reality, replaces the bang singularity?
My "half full" view is I am very glad we have come as far as we have and I am not worried by this problem. I see progress, I see it being addressed. The research area that deals with this is called "quantum cosmology". It is cosmology around the time of big bang, when the concentration of energy was so high that quantum effects make a difference (and may even reverse the effect of gravity and make it repel instead of attract.)

The first textbooks and popularizations dealing with what is currently mainstream quantum cosmology (QC) are beginning to appear. But what is mostly available is stuff laypersons will NOT want to read. You might look to see who the main authors are though.
Here are the technical research papers keyword "quantum cosmology" date > 2005 (i.e. last five years) ranked by number of citations (most cited papers listed first).
http://www.slac.stanford.edu/spires/...tecount%28d%29

Looking at the authors of the first 20 or so papers (the 20 most cited) will give an idea who the main authors are and what names to look for when QC books begin to appear.
ViewsofMars
#18
Oct11-10, 03:00 PM
P: 463
Quote Quote by marcus View Post
That's pretty decent as an initial description. You might enjoy these two articles
Lineweaver SciAm article "Misconceptions about the Big Bang"
http://www.astro.princeton.edu/~aes/...onsBigBang.pdf
Hi marcus. The pdf isn't working for me. Test it out. Please. Thanks.


Quote Quote by marcus View Post
Be careful not to rely too much on the "explosion" picture.
Yep, you are correct. From NASA, NASA Official: Dr. Gary F. Hinshaw, Page Updated: Monday, 05-24-2010

Please keep in mind the following important points to avoid misconceptions about the Big Bang and expansion:

- The Big Bang did not occur at a single point in space as an "explosion." It is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite. If it is closed and finite, then it was born with zero volume and grew from that. In neither case is there a "center of expansion" - a point from which the universe is expanding away from. In the ball analogy, the radius of the ball grows as the universe expands, but all points on the surface of the ball (the universe) recede from each other in an identical fashion. The interior of the ball should not be regarded as part of the universe in this analogy.

- By definition, the universe encompasses all of space and time as we know it, so it is beyond the realm of the Big Bang model to postulate what the universe is expanding into. In either the open or closed universe, the only "edge" to space-time occurs at the Big Bang (and perhaps its counterpart the Big Crunch), so it is not logically necessary (or sensible) to consider this question.

- It is beyond the realm of the Big Bang Model to say what gave rise to the Big Bang. There are a number of speculative theories about this topic, but none of them make realistically testable predictions as of yet.
http://map.gsfc.nasa.gov/universe/bb_concepts.html


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