black hole vs big bang

tia89

And here you come again in the realm of theories, which by the way can't be put aside as you would like to do... and this because we do not have any idea of what really happened. There are only theories and sometimes they don't even agree.
Anyway as for the question about the size of the universe, it all depends on inflation (again a theory) http://en.wikipedia.org/wiki/Inflation_(cosmology). And I do not think there is a way (at least by now) to answer your question, as we can not observe anything beyond the Hubble horizon (you can visualize it as a sphere around us with the radius given by the time passed from Big Bang till today).
And again, aside knowing that the Big Bang is the most probable "beginning" of the Universe (also here there are theories which avoid the Big Bang, but they are not in agreement with observations most of times), what is actually Big Bang is unknown, and will probably be unknown for many years... giving a size to the Universe is then clearly impossible, at least to my knowledge.

jety89

I wasn't implying a similarity between a black hole singularity and the singularity "at the beginning".

@tia89
I think what we can know about the BB, is that it was the singular origin of the universe.

The fact that, for example, photons coming from opposite ends of the observable universe report about a remarkably self-similar universe, talks about that in the past, the predeccessors of those parts of the universe were not simply closer to each other, but were, in fact, the results of the same process, that, as it seems now, happened prior to the planck era. You could call that a singular origin of the universe.
Now, a singular origin implies finiteness, so I think the universe we live in is finite, although very-very big.

bapowell

This is shear speculation. Your assertion that all things emerged from the same singular origin because they are similar is but one possible conclusion. First, as has been painstakingly laid out in this thread -- the big bang singularity is not physical. You can imagine that there was a singularity in the past, and you can call this thing the big bang, but you wouldn't be doing science then. You'd do just as well to call it God.

The uniformity of the CMB to which you refer does not imply a singular origin -- what would that even mean? Again -- we don't have any physical model whatsoever that is operative at the times about which you are speculating, let alone one that describes a physical singularity in any meaningful way. What the uniformity of the CMB tells us is that very early on (after the Planck time, btw), the process that governed the generation of the CMB photons varied little across space. This requires really 2 things: that the laws of physics are the same across the observable universe and that the conditions (the inputs to these laws) were similar across the universe. The former is generally assumed, the latter can be understood by proposing an inflationary epoch, for example.

You also argue that the fact that electrons are identical implies that the universe had a singular beginning, i.e. all electrons came from the same place. But what about those electrons that we create in colliders every day? Or those that result from pair production following high energy cosmic ray collisions in the upper atmosphere? It makes more sense to suppose that it's the laws of physics that are prescribed and uniform -- not that all matter with similar properties necessarily came from the (exact) same (singular) point.

tia89

Which is saying all and nothing...

This is exactly the fact to explain which inflation was introduced... and (as also bapowell pointed out) it happened AFTER the Planck era... about which we do not know anything.

I also DO call that the singular origin of the Universe (read my other posts). But there are interpretations claiming that the Big Bang is a simultaneous "explosion" happening in all the points of an infinite space-time rather than an "explosion" from a localized "single point". But this is all philosophy, not physics, and no one is right or wrong... we simply do NOT know.

bapowell

Nobody doing serious science refers to the big bang as an "explosion". And it is *not* merely philosophy to discuss the nature of the early moments of the expansion -- we have actual data on these points! Observations of the cosmos reveal a uniform, isotropic expansion of space: this is supportive of the notion that even back to the earliest times, expansion was occurring uniformly throughout space and was not localized. So while for sure we don't know the mechanism that started the expansion, we have a pretty good idea that it was not a localized event.

jety89

I might be phrasing misconceptions, and then it is appropriate to strike them down.

I think that what I was challenging here, is the notion that there are no clues as to what happened before the planck era(or the inflation, thereof). Perhaps it is more appropriate, then, to talk about the reality of physical laws. As I understand it, the laws of physics are, as far as we can tell, the same across all of the observable universe, and operate independently in far away regions of spacetime. This implies that there are multiple 'copies' of these laws.

During the planck epoch, as I understand from the previous comments, all that existed, was a very dense sea of "something". So what can we tell with some level of certainty about that "something" that made up this "soup"?

tia89

My apologies... I meant it is philosophy to talk about what happened THE VERY MOMENT of Big Bang... I am perfectly aware that we have data about the early moments of expansion

tia89

That is exactly the point... we have a lot of theories but no sure knowledge of this... as you will know, at those energies gravity becomes (perhaps?) coupled to the other 3 fundamental interactions... but still there is not a clear theory for Quantum Gravity, only possible candidates (main ones being Loop Quantum Gravity and String Theory)... no certainty then

bapowell

During the Planck epoch, we don't know what particles (or more generally "degrees of freedom") are relevant. We do, however, generically expect that there will be quantum mechanical manifestations of gravity that will govern the dynamics in some way -- we need a complete quantum theory of gravity in order to understand the specifics, but much progress has been and we are beginning to get a sense of the broad features of this era. Unfortunately, the particle spectrum is still uncertain and likely depends on the details of this as-yet unknown theory.

That said, as the universe emerged from the Planck time, one expects to see a particle spectrum given by the appropriate particle physics model at the relevant energies. This too is not fully known, but we have a much better picture of what it looks like. For example, if supersymmetry turns out to be a good symmetry of nature, then we expect to see a whole swarm supersymmetric particles in existence along with those from the standard model. As long as the temperatures are high enough, the general rule is that all particles with energies below this temperature can exist.

Inflation happens after the Planck time, and we have a pretty good handle on how it works and what kinds of universe it gives us. Observations of the CMB and large scale structure surveys have imposed some constraints on the physics of inflation, but there's much we still don't know (stay tuned for the ESA Planck surveyor press release in late March for an update!). In order for inflation to get started, there needs to be a sufficiently high density of a certain type of matter in the universe. This matter is unusual in that it has the properties of the vacuum, but it's dynamical in the sense that its energy density changes as the universe expands. Regions in which we find this sufficiently high concentration of vacuum-like matter undergo inflation. So, the challenge is to put a finger on the agent of the inflation -- to find a particle that comes from fundamental particle theory that has the properties of the strange matter needed to drive inflation. It's generically dubbed the "inflaton", but we're still hunting for it.

jety89

Great! Thanks!

typical guy

I've been reading (and asking) about the recent pop science articles on the Higgs mass and the vacuume instability (metastable). If this turns out to accurately describe the universe, does it in some way predict the past as well?

To be specific, in my mind the logical extension of the vacuume instability is that there was an even less stable vacuume in the past and our universe is moving outward annihilating the space in the older universe and at the same time leaving what appears to be a big bang at the edge of the expanding bubble.

This would also imply that most likely the previous spacetime with an even less stable vacuume is out there well beyond the observable universe.

Are there any articles or calculations where our "universe" bubbles out of the vacuume instability of the previous?

Chronos

See chaotic inflation and eternal inflation.