Where is the edge of the universe

[timmdeeg]

It is assumed that the big bang wasn't a pointlike singularity, rather the size which represented the observable universe at that time was in the order of the Planck scale.
Now, going back in time things get closer together and each point in today's observable universe will be represented by its respective worldline. However, arriving at Planck scale the density of the worldlines would be << Planck length. Do we thus have to think of an "no worldline epoch"? Sorry for this weird question.

 

[Boy@n]

I think it is possible to see the birth of the unvierse in the futre, but it won't be via light or by the universe's expansion for the reason phinds pointed out. But there are two types of radiation that can penetrate the surface of last scattering.
1 neutrinos , these could take us back to about 2 seconds after the big bang.
2 gravity waves, these could go even earlier and some have suggested even before the big bang itself.

The technology needed for this is not going to happen in the next fw years in my opiion, it's somewhat scifi but it is not impossible.

Sounds probable to be true...

Phinds, Mordred?

 

[phinds]

Sounds probable to be true...

Phinds, Mordred?

Yes, there have been several proposed ways that we will be able to see past the surface of last scattering and those are two of them. I'm sure there are others but I don't recall what.

 

[Mordred]

The neutrino measutements holds the best promise of seeing further. However the second option is also viable. Technology still has a ways to go however.

 

[Mordred]

That's mostly fair, and I CERTAINLY won't argue the bubble universe, but I believe that the 11- dimensions come from the mathematical models from the string theory? Again, I know very little about this topic and I apologize for the pseudo-science

thats essentially correct. String theory isn't something I am too familiar with however

 

[Adrian07]

phinds re post 80. I am not hanging onto misconceptions only repeating what others have written, if what is written is incorrect then that is not my fault but the fault of the academics that have come up with these ideas, I have no personal preference and do not actually think the BB theory is correct.
Perhaps you could give a short explanation of what you believe to be true, including where inflation fits in and how things could have started from a quantum fluctuation and which does not include starting from a point.

 

[phinds]

phinds re post 80. I am not hanging onto misconceptions only repeating what others have written, if what is written is incorrect then that is not my fault but the fault of the academics that have come up with these ideas, I have no personal preference and do not actually think the BB theory is correct.
Perhaps you could give a short explanation of what you believe to be true, including where inflation fits in and how things could have started from a quantum fluctuation and which does not include starting from a point.

No serious academic promotes the idea of everything starting from a point. For one thing it would imply a lack of the isotropy which is so clearly evidenced. If you think the BB theory is incorrect, I'd say that's likely because you don't understand it. The BB theory says NOTHING about how everything started, quantum fluctuation or otherwise. It is about everything that has happened from about one Plank time after the singularity (whatever THAT was) and NOT about how it started.

Early inflation is a contentious subject and not proven. It does solve some problems but still is not proven or totally accepted.

 

[Mordred]

First let's clarify the BB model.

The BB model does not start from a point. The singularity described as mentioned numerous times is simply where the math no longer works.
The early inflationary models utilize the quantum fluctuations. False vacuum is now called old inflation.
There are over 100 models dealing just with the inflationary era. Some use the Higgs field. Some the inflaton field. Some use other mechanisms.
The inflationary era is still poorly understood.
The BB model has its sucesses however its also important to realize that in actuality its a collective of good fit to observational data models.
The current concordance model. Which is a term for the standard model (not necessarily the most popular) is tha lamddaCDM model.

Inflation era is sometime in the first second. Depending on which inflationary model your using. Commonly though its at the beginning of the ekectroweak epoch

 

[Mordred]

If you truly want to understand the LCDM or \LambdaCDM model and what we have learned compared to observational data I would suggest reading this review. Its written in an easy to understand format that doesn't require a lot of previous knowledge.

http://arxiv.org/abs/1304.4446

however its not designed to teach the model, its only designed to provide a descriptive and comparison to observational data

 

[Adrian07]

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.

 

[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) &amp; R_{\infty} (Gly) &amp; S_{eq} &amp; H_{0} &amp; \Omega_\Lambda &amp; \Omega_m\\ \hline 14.4&amp;17.3&amp;3400&amp;67.92&amp;0.693&amp;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&amp;S&amp;T (Gy)&amp;R (Gly)&amp;D (Gly)&amp;D_{then}(Gly)&amp;D_{hor}(Gly)&amp;V_{now} (c)&amp;V_{then} (c) \\ \hline 0.000&amp;20000.000&amp;0.0000&amp;0.0000&amp;46.177&amp;0.002&amp;0.003&amp;3.21&amp;659.18\\ \hline 0.000&amp;4859.562&amp;0.0000&amp;0.0000&amp;45.979&amp;0.009&amp;0.013&amp;3.19&amp;192.23\\ \hline 0.001&amp;1180.767&amp;0.0003&amp;0.0006&amp;45.385&amp;0.038&amp;0.052&amp;3.15&amp;69.66\\ \hline 0.003&amp;286.901&amp;0.0033&amp;0.0051&amp;43.945&amp;0.153&amp;0.211&amp;3.05&amp;29.83\\ \hline 0.014&amp;69.711&amp;0.0290&amp;0.0442&amp;40.852&amp;0.586&amp;0.823&amp;2.84&amp;13.26\\ \hline 0.059&amp;16.938&amp;0.2468&amp;0.3718&amp;34.481&amp;2.036&amp;3.009&amp;2.39&amp;5.48\\ \hline 0.243&amp;4.116&amp;2.0604&amp;3.0614&amp;21.565&amp;5.240&amp;9.246&amp;1.50&amp;1.71\\ \hline 1.000&amp;1.000&amp;13.7872&amp;14.3999&amp;0.000&amp;0.000&amp;16.472&amp;0.00&amp;0.00\\ \hline 4.116&amp;0.243&amp;37.1746&amp;17.2451&amp;12.301&amp;50.627&amp;17.245&amp;0.85&amp;2.94\\ \hline 11.920&amp;0.084&amp;55.5546&amp;17.2977&amp;15.050&amp;179.403&amp;17.298&amp;1.05&amp;10.37\\ \hline 34.526&amp;0.029&amp;73.9517&amp;17.2999&amp;16.000&amp;552.424&amp;17.300&amp;1.11&amp;31.93\\ \hline 100.000&amp;0.010&amp;92.3494&amp;17.2999&amp;16.328&amp;1632.838&amp;17.300&amp;1.13&amp;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) &amp; R_{\infty} (Gly) &amp; S_{eq} &amp; H_{0} &amp; \Omega_\Lambda &amp; \Omega_m\\ \hline 14.4&amp;17.3&amp;3400&amp;67.92&amp;0.693&amp;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&amp;S&amp;T (Gy)&amp;R (Gly)&amp;D (Gly)&amp;D_{then}(Gly)&amp;D_{hor}(Gly)&amp;V_{now} (c)&amp;V_{then} (c) \\ \hline 0.000&amp;20000.000&amp;0.000002&amp;0.000004&amp;46.177&amp;0.002&amp;0.003&amp;3.21&amp;659.18\\ \hline 0.000&amp;4859.562&amp;0.000027&amp;0.000049&amp;45.979&amp;0.009&amp;0.013&amp;3.19&amp;192.23\\ \hline 0.001&amp;1180.767&amp;0.000326&amp;0.000552&amp;45.385&amp;0.038&amp;0.052&amp;3.15&amp;69.66\\ \hline 0.003&amp;286.901&amp;0.003261&amp;0.005135&amp;43.945&amp;0.153&amp;0.211&amp;3.05&amp;29.83\\ \hline 0.014&amp;69.711&amp;0.029011&amp;0.044197&amp;40.852&amp;0.586&amp;0.823&amp;2.84&amp;13.26\\ \hline 0.059&amp;16.938&amp;0.246808&amp;0.371763&amp;34.481&amp;2.036&amp;3.009&amp;2.39&amp;5.48\\ \hline 0.243&amp;4.116&amp;2.060351&amp;3.061435&amp;21.565&amp;5.240&amp;9.246&amp;1.50&amp;1.71\\ \hline 1.000&amp;1.000&amp;13.787206&amp;14.399932&amp;0.000&amp;0.000&amp;16.472&amp;0.00&amp;0.00\\ \hline 4.116&amp;0.243&amp;37.174602&amp;17.245130&amp;12.301&amp;50.627&amp;17.245&amp;0.85&amp;2.94\\ \hline 11.920&amp;0.084&amp;55.554650&amp;17.297731&amp;15.050&amp;179.403&amp;17.298&amp;1.05&amp;10.37\\ \hline 34.526&amp;0.029&amp;73.951682&amp;17.299856&amp;16.000&amp;552.424&amp;17.300&amp;1.11&amp;31.93\\ \hline 100.000&amp;0.010&amp;92.349407&amp;17.299900&amp;16.328&amp;1632.838&amp;17.300&amp;1.13&amp;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