Where is the edge of the universe

[phinds]

...Are you saying that if the expansion we see was reversed then it would not end up at a single point...

YES ... good, you are finally getting the point (no pun intended)

I am trying to understand expansion that does not expand out from a central point unless the expansion is from many central points i.e. there was more than one starting point. Forget how it started and explain expansion from the one plank time or from where it was say the size of a pea or melon where it would have had an obvious edge at least to an outside observer.

The expansion did not HAVE an "outside edge". The expansion was of everything there is. If there had been something "outside" of it, that would have been part of everything there is and thus would have been part of the expansion. The expansion did not happen INTO something.

 

[timmdeeg]

I thought we were talking about what happened after it started I.e how it got to where it is now from where it started. Either it expanded from a very small space into what we see now or is there another explanation. Are you saying that if the expansion we see was reversed then it would not end up at a single point. I am trying to understand expansion that does not expand out from a central point unless the expansion is from many central points i.e. there was more than one starting point. Forget how it started and explain expansion from the one plank time or from where it was say the size of a pea or melon where it would have had an obvious edge at least to an outside observer.

The universe started at Planck scale, at least according to present mainstream. At that time, as today, it obeyed the cosmological principle which means each point looks the same, there is no center and no edge.

 

[phinds]

The universe started at Planck scale, at least according to present mainstream. At that time, as today, it obeyed the cosmological principle which means each point looks the same, there is no center and no edge.

I would disagree that the universe started at the Plank time. What I would say is that our understanding of the universe, as expressed in the Big Bang Theory, started at the plank time. What happened before the Plank time is what we call the singularity (meaning we don't know WHAT it was) but IT was the start of the universe.

 

[timmdeeg]

I would disagree that the universe started at the Plank time. What I would say is that our understanding of the universe, as expressed in the Big Bang Theory, started at the plank time. What happened before the Plank time is what we call the singularity (meaning we don't know WHAT it was) but IT was the start of the universe.

Well, it depends on what you call universe. The earliest period from which the Lambda-CDM model starts is the Planck epoch. What is the physical meaning of before Planck time? Should there have existed something - a quantum fluctuation perhaps - was is part, just cause or both, related to the universe?

 

[julcab12]

In addition to shy away from enigma of analogy.

In theory(Model), At the very moment of the big bang(not a bang) all the points(let's just say its a point for now) in the universe were at 'infinitesimal distances' from each other; that's what is meant by calling it a "singularity". In mathematical term, immeasurable or its variable limit rest and break @ 0 or in common language, "It doesn't make sense". But on top of it all. It is not really known whether or not the universe started(uncertain/temporal start) from a singularity or not. So what they did. They catalog it as a series of events not mainly the start of the universe but a start of an EVENT.
The cosmos at the start of the big bang are mostly unproved conjecture. And yet we have to deal with it somehow.BTW QP is doing a nice job.^^

 

[Mordred]

Well, it depends on what you call universe. The earliest period from which the Lambda-CDM model starts is the Planck epoch. What is the physical meaning of before Planck time? Should there have existed something - a quantum fluctuation perhaps - was is part, just cause or both, related to the universe?

thats true but they were careful to make the 10^-43 seconds just slightly later than
planck time. (The start of Planck epock)

t_{p}\ =\ 5.3906(40)\ \times\ 10^{-44}\ s

 

[Adrian07]

What I am reading about expansion is not making sense.
How big was it at the plank time and how did it get to the size we see now? If it had no edge how do you measure size.

 

[phinds]

What I am reading about expansion is not making sense.
How big was it at the plank time and how did it get to the size we see now? If it had no edge how do you measure size.

We DON'T "measure size" of the universe. No one has any idea what the size is. It started off as a hot dense plasma of unknown size and expanded from there. It MIGHT have been infinite at the start in which case it is infinite now. If it was finite at the start, the consensus is that it was unbounded and had no center or edge and so STILL has no center and no edge.

EDIT: also, it did NOT start off as a point. "Singularity" doesn't mean a point, it just means that place where the math breaks down.

SECOND EDIT: I see that everything I said in this post is just a repeat of stuff you have already been told earlier in this thread. Your unwillingness to believe it all is not going to get you any different answers.

 

[bapowell]

If it had no edge how do you measure size.

When we talk about size, we are referring to the observable universe. The observable universe is simply that part of the universe that we've had time to observe since the big bang -- all the measurements that cosmologists make pertain to the observable universe only. Even if the universe itself is infinite, the observable universe is finite because there has been a finite amount of time since the big bang, and light can travel only so fast.

 

[Spourk]

What I am reading about expansion is not making sense.
How big was it at the plank time and how did it get to the size we see now? If it had no edge how do you measure size.

Where is the center of infinity? Where is the edge? It's a simple logic argument to try and picture what is going on here. There is no "Point" that infinity starts at. At the BB things were just ALOT closer together, but still infinite. Earth is just "our" spot in infinity, the "observable universe" is just how far out into infinity we can see.

Does that help?

 

[bapowell]

Where is the center of infinity? Where is the edge? It's a simple logic argument to try and picture what is going on here. There is no "Point" that infinity starts at. At the BB things were just ALOT closer together, but still infinite. Earth is just "our" spot in infinity, the "observable universe" is just how far out into infinity we can see.

Does that help?

Except that the universe might not be infinite.

 

[Boy@n]

Except that the universe might not be infinite.

Of course it is, by definition. Universe is all of 'it', it is everything.

If Universe is not infinite what is that beyond Universe?

And if definitions keep changing then we know nothing.The tricky part, at least for me, is not understanding/imagining infinite/whole Universe, but the finite/observable part of whole Universe, which is said to be a nicely defined sphere, yet without center or whatever kind of edge.

 

[George Jones]

Of course it is, by definition. Universe is all of 'it', it is everything.

If Universe is not infinite what is that beyond Universe?

And if definitions keep changing then we know nothing.

No, it is possible that the universe is closed, and, for the standard model, space in a closed universe is like the surface of a sphere, but with one more dimension. The surface of a sphere is finite, not infinite.

The tricky part, at least for me, is not understanding/imagining infinite/whole Universe, but the finite/observable part of whole Universe, which is said to be a nicely defined sphere, yet without center or whatever kind of edge.

We are at the centre of the observable universe.

 

[phinds]

Of course it is, by definition. Universe is all of 'it', it is everything.

If Universe is not infinite what is that beyond Universe?

And if definitions keep changing then we know nothing.


The tricky part, at least for me, is not understanding/imagining infinite/whole Universe, but the finite/observable part of whole Universe, which is said to be a nicely defined sphere, yet without center or whatever kind of edge.

You seem to have either not been reading or not been listening to the previous posts in this thread. ALL of the above (all of which is wrong) has already been addressed in this thread.

 

[Adrian07]

Have re-read this thread including some links to other information. Regarding the balloon analogy, I can see this working in 3d (unlike rubber sheet analogy in gravity), but it only works once the galaxies have formed and become far enough apart to become gravitationaly unbound and if it is reversed so balloon shrinks then all comes together at a single point which as pointed out in a previous post would not happen. If the universe is truly infinite then it must have started not in one place but many widely separated places with space expanding out from each starting place, or many balloons expanding and pushing against each other, if only to produce what we see in the time available.

 

[bapowell]

Have re-read this thread including some links to other information. Regarding the balloon analogy, I can see this working in 3d (unlike rubber sheet analogy in gravity)

The two-dimensional rubber surface of the balloon is an analog of the three-dimensional space of the real universe. Instead of a so-called 2-sphere, we live on the surface of a 3-sphere (assuming that the geometry of the universe is in fact closed so that the balloon analogy is good.)

There are clear limitations of the balloon analogy, one being that the balloon is a 2-dimensional surface embedded in and expanding in 3-dimensional space; the universe is a 3-dimensional surface that needs no higher-dimensional space within which to expand. See phinds' write-up on this for more: http://www.phinds.com/balloonanalogy/

but it only works once the galaxies have formed and become far enough apart to become gravitationaly unbound and if it is reversed so balloon shrinks then all comes together at a single point which as pointed out in a previous post would not happen.

Why? In the early universe when the expansion can be said to have begun, there were no galaxies -- just a smooth hot plasma. By the time galaxies began to form, the initial perturbations in this plasma from which they grew were sufficiently far apart that the universe was close to uniform. A universe with uniform energy density expands uniformly, just like the balloon.

If the universe is truly infinite then it must have started not in one place but many widely separated places with space expanding out from each starting place, or many balloons expanding and pushing against each other, if only to produce what we see in the time available.

The balloon analogy works for a finite, closed universe. In any case, the balloon is the universe, so it makes no sense to talk of many balloons existing together in the same universe.

 

[phinds]

Have re-read this thread including some links to other information. Regarding the balloon analogy, I can see this working in 3d (unlike rubber sheet analogy in gravity), but it only works once the galaxies have formed and become far enough apart to become gravitationaly unbound and if it is reversed so balloon shrinks then all comes together at a single point which as pointed out in a previous post would not happen. If the universe is truly infinite then it must have started not in one place but many widely separated places with space expanding out from each starting place, or many balloons expanding and pushing against each other, if only to produce what we see in the time available.

Once again, I say to you that your persistence in not believing what you have been told is NOT going to get you any different answers. bapowell has summed it up quite nicely, once again telling you what you have already been told.

I KNOW this stuff is hard to get your head around but you might give some consideration to the thought that the folks who have been giving you answers HAVE thought about it some and read about it some and discussed it here before and no one is trying to mislead you.

EDIT: what I mean is, your persistence in making statements that are contrary to the answers you have been given are frustrating to those trying to help you understand. It's not that you are asking questions for clarification about the answers that you've gotten, it's that you are making statements that contradict them.

 

[marcus]

Adrian, according to my information back in year 2000 any two locations as much as 4000 lightyears apart were separating at the speed of light, and larger distances faster in proportion. Matter was approx. uniform hot gas---hadn't begun clumping and falling together---as Brian already indicated.

Phinds, Adrian, maybe conceivably also Brian Powell, you might be interested in glancing at what Jorrie's calculator says about year 2000.
http://www.einsteins-theory-of-relativity-4engineers.com/LightCone6/LightCone.html
It is not designed to go back that far in time so when you open it you have to increase the number of decimal places in the "Time" and the "Hubble radius" columns from 3 to 6. Those columns are in billions of years (Gy) and billions of lightyears (Gly), so that
0.000 002 Gy means 2000 years, and 0.000 004 Gly means 4000 lightyears

Besides opening column selection and changing the number of decimals in those two columns, which only takes a second to do, all you need to do is set S_upper = 20 000 and press "calculate"

The top row of the table will then give you information about the time around year 2000 when distances were 1/20 000 their present size.

Locations a mere 4000 lightyears apart were separating at the speed of light. And larger separations increasing proportionally faster. There were no objects (it was all nearly uniform hot gas that hadn't started clumping and falling together into structures) but if there HAD BEEN two dense objects that were, say, at two locations only as far apart as we are from the center of Milkyway galaxy, then no known force could have held them together. It was impossible for even relatively nearby neighbors to be gravitationally bound, as Adrian imagines. They wouldn't even have to be that far apart, I just picked that as an example.

I'll print the table you get just by changing S_upper from 1090 to 20000 and leaving everything else the same as when it opens. And then I'll show what you get by selecting to have more decimal places shown in the Time and Hubble radius columns.

Here's what you get making no changes except to say top row S = 20000. You can see that it shows Time (T) and Hubble radius (R) as ZERO but that is because it is not showing enough decimal places.

{\scriptsize\begin{array}{|c|c|c|c|c|c|}\hline R_{0} (Gly) & R_{\infty} (Gly) & S_{eq} & H_{0} & \Omega_\Lambda & \Omega_m\\ \hline 14.4&17.3&3400&67.92&0.693&0.307\\ \hline \end{array}} {\scriptsize\begin{array}{|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|} \hline a=1/S&S&T (Gy)&R (Gly)&D (Gly)&D_{then}(Gly)&D_{hor}(Gly)&V_{now} (c)&V_{then} (c) \\ \hline 0.000&20000.000&0.0000&0.0000&46.177&0.002&0.003&3.21&659.18\\ \hline 0.000&4859.562&0.0000&0.0000&45.979&0.009&0.013&3.19&192.23\\ \hline 0.001&1180.767&0.0003&0.0006&45.385&0.038&0.052&3.15&69.66\\ \hline 0.003&286.901&0.0033&0.0051&43.945&0.153&0.211&3.05&29.83\\ \hline 0.014&69.711&0.0290&0.0442&40.852&0.586&0.823&2.84&13.26\\ \hline 0.059&16.938&0.2468&0.3718&34.481&2.036&3.009&2.39&5.48\\ \hline 0.243&4.116&2.0604&3.0614&21.565&5.240&9.246&1.50&1.71\\ \hline 1.000&1.000&13.7872&14.3999&0.000&0.000&16.472&0.00&0.00\\ \hline 4.116&0.243&37.1746&17.2451&12.301&50.627&17.245&0.85&2.94\\ \hline 11.920&0.084&55.5546&17.2977&15.050&179.403&17.298&1.05&10.37\\ \hline 34.526&0.029&73.9517&17.2999&16.000&552.424&17.300&1.11&31.93\\ \hline 100.000&0.010&92.3494&17.2999&16.328&1632.838&17.300&1.13&94.38\\ \hline \end{array}}

And here's what you get when you also allow more digits to show in the T and R columns{\scriptsize\begin{array}{|c|c|c|c|c|c|}\hline R_{0} (Gly) & R_{\infty} (Gly) & S_{eq} & H_{0} & \Omega_\Lambda & \Omega_m\\ \hline 14.4&17.3&3400&67.92&0.693&0.307\\ \hline \end{array}} {\scriptsize\begin{array}{|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|} \hline a=1/S&S&T (Gy)&R (Gly)&D (Gly)&D_{then}(Gly)&D_{hor}(Gly)&V_{now} (c)&V_{then} (c) \\ \hline 0.000&20000.000&0.000002&0.000004&46.177&0.002&0.003&3.21&659.18\\ \hline 0.000&4859.562&0.000027&0.000049&45.979&0.009&0.013&3.19&192.23\\ \hline 0.001&1180.767&0.000326&0.000552&45.385&0.038&0.052&3.15&69.66\\ \hline 0.003&286.901&0.003261&0.005135&43.945&0.153&0.211&3.05&29.83\\ \hline 0.014&69.711&0.029011&0.044197&40.852&0.586&0.823&2.84&13.26\\ \hline 0.059&16.938&0.246808&0.371763&34.481&2.036&3.009&2.39&5.48\\ \hline 0.243&4.116&2.060351&3.061435&21.565&5.240&9.246&1.50&1.71\\ \hline 1.000&1.000&13.787206&14.399932&0.000&0.000&16.472&0.00&0.00\\ \hline 4.116&0.243&37.174602&17.245130&12.301&50.627&17.245&0.85&2.94\\ \hline 11.920&0.084&55.554650&17.297731&15.050&179.403&17.298&1.05&10.37\\ \hline 34.526&0.029&73.951682&17.299856&16.000&552.424&17.300&1.11&31.93\\ \hline 100.000&0.010&92.349407&17.299900&16.328&1632.838&17.300&1.13&94.38\\ \hline \end{array}}

To repeat, the top row of that table is why I said that in year 2000 (which just happens to come when distances are about one twenty-thousandth of present) the size of distance that was then increasing at speed of light was 4000 lightyears.

Because 0.000002 of a billion years is 2000 years
and ).000004 of a billion lightyears is 4000 lightyears.
You could further refine the precision by clicking column select and upping still further the number of decimal places displayed in the T and R columns, but this much precision seems enough to make the simple point (re Adrian's comment) that the approximately uniform hot gas was being expanded very fast. No type of binding (gravitational or otherwise) could have held it in any compact clump or cluster structure.

 

[Naty1]

The earliest period from which the Lambda-CDM model starts is the Planck epoch.

Not that it is critical to the discussion, but the actual model starts AFTER the inflationary epoch which starts just after grand unification at roughly 10^-36 seconds...inflation is a glued on addition to the Lambda CDM model...
In fact various inflation versions were tried and Paul Steinhardt and collaborators created the slow roll model favored today...There is nothing in the EFE nor the lambda CDM model that leads directly to slow roll inflation...

 

[Mordred]

Depending on which inflation model. Most of the ones I am familiar with places it at the beginning stages of the electroweak epoch. Which follows the grand unification epoch

 

[Adrian07]

phinds sorry if you are frustrated with me but I am also frustrated with your answers that don't seem to answer the questions I asked. Basically all I asked for was a simple explanation of where the universe was and how did it get to what we see now. A 3d grid analogy is much easier to understand regarding expansion than a 2d balloon, although this still has severe limitations.
Marcus thanks for input, am I right in thinking that what you are saying at the end of your post is that the rate of expansion should have prevented large scale structures forming, something I have been wondering about re balloon analogy and starting from deflated balloon. Is there a simple explanation anywhere that would make understanding the table you posted easier to understand.

 

[Mordred]

Here is a a wiki article that explains the history of development.
http://en.m.wikipedia.org/wiki/Chronology_of_the_universe

As Marcus pointed out the
calculator can only go so far
back in time. Although his coaxing of it to get back to as far as he did is a handy hidden feature.
During the inflationary epoch the inflation of the universe and high temperatures were too hot for matter to form. The inflation era however only occurred for less than a second.

Matter did not start forming until the universe cooled down the increase is size due to the inflation epoch helped in that cooling down.
Once matter started forming the earliest structures to form were primordial black holes. Wiki referres to these as quasars.

Google universe chronology for more info.

 

[bapowell]

Depending on which inflation model. Most of the ones I am familiar with places it at the beginning stages of the electroweak epoch. Which follows the grand unification epoch

Really? Which ones? Inflation that takes place at the electroweak scale would certainly be considered "low scale" and would be difficult to embed in most extensions to the SM.

 

[Mordred]

Chaotic inflation, false vacuum. Pretty much any QED papers that cover the epochs.

I should have been a little clearer the inflationary epoch is in those models slightly ahead of the electroweak epoch



http://www.nicadd.niu.edu/~bterzic/PHYS652/Lecture_13.pdf



http://physics.uoregon.edu/~jimbrau/astr123/notes/chapter27.html

http://www.fas.org/sgp/othergov/doe/lanl/pubs/00285549.pdf

 

[bapowell]

Chaotic inflation, false vacuum. Pretty much any QED papers that cover the epochs.

Sorry, I'm confused. What QED papers?

The term "chaotic inflation" refers to any inflation model in which the initial field value of the inflaton was highly randomized across the universe. The term "false vacuum" refers to any inflation model in which the field starts out in a region of sufficiently high vacuum energy to drive inflation, with inflation ending when the field evolves to a true vacuum.

These are two very broad categorizations (that are not even necessarily exclusive of each other), so I don't see how these offer examples of electroweak scale inflation. I know it's possible to build a specific model of false vacuum inflation that inflates at the electroweak scale, but there are plenty of models that don't.

I was just wondering if you had any of specific realizations in mind when you made your comment.

 

[Mordred]

http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html

Like I stated false vacuum model and chaotic inflation both place it in that timeline.

Look at lecture 13 in previous post.

I was still gathering papers when your post came in.

the last link of the previous post however shows it later.

I don't know where slow roll
inflation or natural inflation
places it.

This link also shows the early inflation epoch

http://web.njit.edu/~gary/202/Lecture26.html

 

[Mordred]

Took me a bit to find it but Higgs inflation also places at the electroweak epoch

http://arxiv.org/abs/1210.8190

 

[bapowell]

Like chaotic inflation and false vacuum inflation, slow roll inflation is a whole class of models that happen to satisfy the slow roll criteria (e.g. there are chaotic and false vacuum models that are slow roll, so again, these are not exclusive classifications.) It's totally possible to construct slow roll models at virtually any energy scale.

Regarding Higgs inflation, yes, this is what I had in mind as far as specific inflationary scenarios. Since the Higgs is an electroweak degree of freedom, of course Higgs inflation occurs at this scale. You stated that "most" models you know about occurred "at the beginning" of the electroweak epoch, and I'm stating that there is no reason for inflation to preferentially occur here. Inflation works at 10^{16} GeV just as well as it does at the electroweak scale.

The timelines you posted either have inflation occurring at a specific energy scale (which is just wrong) or across a range of scales that is too conservative.

 

[Mordred]

Those articles are based more on particle physics symmetry breaking. More classically the GUT aspects of it. So its natural they would want to refine its energy levels.
Your point is taken in the most models aspect. I should of stated some instead.

 

[bapowell]

More classically the GUT aspects of it.

Right, which is why I'm confused about the emphasis on the electroweak scale. Inflation is generally discussed in the context of particle physics as a GUT-scale phenomenon (the earliest models were based on the SU(5) and SO(10) GUT theories). While these specific approaches didn't pan out, phenomenologically speaking inflation at the GUT scale is still alive well.

 

[Mordred]

You make a good point there, I would be interested in more current papers on GUT. Preference on technical papers.

The particle physics text I'm studying didn't emphasize the timeline of the inflationary epoch. That could explain the "why".

 

[Chronos]

... Once matter started forming the earliest structures to form were primordial black holes. Wiki referres to these as quasars. ...

Evidence for the existence of primordial black holes [PBH] is uncertain [e.g., Primordial Black Holes: Do They Exist and Are They Useful?, http://arxiv.org/abs/astro-ph/0511743] . The evolution of super massive black holes, such as those that power quasars, remains very uncertain. It is fairly evident they were not the earliest structures to form in the universe. CMB studies constrain the number of primordial black holes with masses above 1000 solar to a vanishingly small number [e.g., Effect of Primordial Black Holes on the Cosmic Microwave Background and Cosmological Parameter Estimates, http://arxiv.org/abs/0709.0524] . Contraints on micro PBH's is even tighter [e.g., New cosmological constraints on primordial black holes, http://arxiv.org/abs/0912.5297] . The most distant object yet detected is the galaxy UDFy-38135539 at z=8.6 [re: Ancient giants: on the farthest galaxy at z=8.6, http://arxiv.org/abs/1102.1726] . Other similar candidates include UDFj-39546284 [Photometric Constraints on the Redshift of z~10 candidate UDFj-39546284 from deeper WFC3/IR+ACS+IRAC observations over the HUDF, http://arxiv.org/abs/1211.3105: The Abundance of Star-Forming Galaxies in the Redshift Range 8.5 to 12, http://arxiv.org/abs/1211.6804] The most distant known GRB is GRB 090423 at z=8.1 [GRB 090423 at a redshift of z~8.1, http://arxiv.org/abs/0906.1578] . The most distant quasar yet detected is ULAS J112001.48+064124.3 at z=7.1 [re: A luminous quasar at a redshift of z = 7.085, http://arxiv.org/abs/1106.6088] .

 

[Mordred]

Thanks there is some good articles in that post going to enjoy reading them. In particular the first in regards to PBH'es

 

[Spourk]

http://arxiv.org/abs/1106.6088

"Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang."

Pretty awesome, this is.