What Are the Origins of the Universe?

[Ads the devil]

TL;DR Summary

Why do we talk about the universe beginning at the big bang, instead of the big bang occurring in the universe?

I see much confusion about the "origin" of the universe.

When discussing what caused the big bang, we need to describe the conditions of the universe before the big bang.

For me, the big bang occurred in the universe. The universe existed prior to the big bang and provided the energy to fuel the big bang.

For me the word universe , means everything. It is universal. Encompassing everything. Nothing is outside of the universe.

Multiverses occur with the universe etc.

Need clarity of the term.

The big bang is expanding into the universe.

Did all the fields already exist before the big bang.

 

[DiracPool]

No, the big bang did not occur in an already existing universe. As far as we know there was nothing before the big bang. There were no preconditions as nothing existed. The big bang is understood as commencing the origin of the universe. So, no confusion there as far as the vastly agreed upon understanding among conventional cosmologists.

 

[PeroK]

Summary:: Why do we talk about the universe beginning at the big bang, instead of the big bang occurring in the universe?

I see much confusion about the "origin" of the universe.

When discussing what caused the big bang, we need to describe the conditions of the universe before the big bang.

For me, the big bang occurred in the universe. The universe existed prior to the big bang and provided the energy to fuel the big bang.

For me the word universe , means everything. It is universal. Encompassing everything. Nothing is outside of the universe.

Multiverses occur with the universe etc.

Need clarity of the term.

The big bang is expanding into the universe.

Did all the fields already exist before the big bang.

Even the Wikipedia page makes this clear:

The Big Bang theory is the prevailing cosmological model explaining the existence of the observable universe from the earliest known periods through its subsequent large-scale evolution.

In other words, the Big Bang theory is the evolution of the universe from its earliest known state. It's neither the creation nor origin of the universe; nor is it a one-off event that happened somewhere in the universe.

https://en.wikipedia.org/wiki/Big_Bang

 

[martinbn]

My question stands.

Why do people kerp talking about the big bang being the universe, when it is something 8nside the universe.

No one says that the big bang is the universe. This makes no sense. It is also not something inside the universe. This also makes no sense. You need to clear up for yourself some of the notions you are using.

 

[PeroK]

I am talking about what the big bang is expanding into.
What existed before the big bang.

The Big Bang is not expanding; it's the universe that is expanding. The universe is not expanding into anything; it's simply expanding. The best way to understand this, perhaps, is that the universe has a "scale factor" that increases over time. That means that the measured distance between distant points in the universe increases over time. There is no edge of the universe that is moving out into something else - that is a common misconception.

There are lots of threads on this. here's the most recent one:

https://www.physicsforums.com/threads/what-is-the-universe-expanding-into.1005858/

 

[PeroK]

The big bang theory describes events after the first matter.

This is false. From Wikipedia:

Detailed measurements of the expansion rate of the universe place the Big Bang singularity at around 13.8 billion years ago, which is thus considered the age of the universe.[6]

After its initial expansion, an event that is by itself often called "the Big Bang", the universe cooled sufficiently to allow the formation of subatomic particles, and later atoms.

 

[Nugatory]

Mentors' note: A confused discussion based on initial misunderstandings have been removed from this thread.

 

[elcaro]

No, the big bang did not occur in an already existing universe. As far as we know there was nothing before the big bang. There were no preconditions as nothing existed. The big bang is understood as commencing the origin of the universe. So, no confusion there as far as the vastly agreed upon understanding among conventional cosmologists.

There is NOTHING in the big bang model that says that. A universe emerging from literally nothing is not even physics anymore, as you can not get something from nothing (no space, no time, no energy, no fields, no nothing).

 

[phinds]

A universe emerging from literally nothing is not even physics anymore, as you can not get something from nothing

Lawrence Krauss wrote a whole book disagreeing w/ you (I doubt he's right, but just sayin' ... )

 

[Bandersnatch]

Lawrence Krauss wrote a whole book disagreeing w/ you (I doubt he's right, but just sayin' ... )

IIRC, when pressed during some panel discussion (with Filipenko, I think?) he did clarify that he does not really mean literal non-existence when he says nothing. His meaning seems to be closer to how abiogenesis could be construed as life arising from nothing, even though there would clearly be a pre-existing substrate.

 

[elcaro]

IIRC, when pressed during some panel discussion (with Filipenko, I think?) he did clarify that he does not really mean literal non-existence when he says nothing. His meaning seems to be closer to how abiogenesis could be construed as life arising from nothing, even though there would clearly be a pre-existing substrate.

Exactly.

The only physical theory or speculation I know of is the idea of Vilenkin at al about the emergence of the universe from literally nothing - or, a small space with radius r, and letting r go to zero - In this case in and during the vanishing of space, there is still spacetime, but after the vanishing we are left with nothing. Just why don't we see that everywhere, if a "nothing" can produce a universe, just anything could appear from literal nothing...

 

[PeterDonis]

This is false. From Wikipedia:

Detailed measurements of the expansion rate of the universe place the Big Bang singularity at around 13.8 billion years ago, which is thus considered the age of the universe.[6]

After its initial expansion, an event that is by itself often called "the Big Bang", the universe cooled sufficiently to allow the formation of subatomic particles, and later atoms.

You should know better than to cite Wikipedia as an authoritative source.

Our best current model of our actual universe, the Lambda CDM model, says nothing about any "initial singularity". Yes, such a thing occurs in idealized FRW spacetimes, but that portion of idealized FRW spacetimes is not claimed to apply to our actual universe. The proper referent of the term "Big Bang" in the Lambda CDM model is the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. What came before that state is still an open question, although the current front runner seems to be some version of inflation; in inflation models, the Big Bang occurs at the end of inflation. Some inflation models have an initial singularity before inflation and some do not.

The "age of the universe" that is routinely quoted by cosmologists (and which is referenced in the Wikipedia article) is actually a "notional" age that is obtained by taking the actual Big Bang state and extrapolating it backwards in time on the (false) assumption that the spacetime from that time backwards was a standard radiation dominated FRW spacetime (i.e., no inflation) with temperature, density, and expansion rate at the "Big Bang" time corresponding to our best current values for those parameters in the Lambda CDM model. The extrapolation backwards in time gives "notional" times for events prior to the Big Bang, including a notional "initial singularity", but those times don't actually correspond to anything we know or anything in an actual model like inflation. They are just times that cosmologists find convenient to quote even though they cause much confusion among lay people, who think they mean something they don't.

 

[PeterDonis]

The only physical theory or speculation I know of is the idea of Vilenkin at al about the emergence of the universe from literally nothing - or, a small space with radius r, and letting r go to zero - In this case in and during the vanishing of space, there is still spacetime, but after the vanishing we are left with nothing.

Please give a reference for this idea of Vilenkin.

 

[elcaro]

Please give a reference for this idea of Vilenkin.

Vilenkin - creation of universes from nothing

 

[PeterDonis]

Vilenkin - creation of universes from nothing

As I commented in the other thread where this paper was referenced, it is unfortunately behind a paywall and it does not look like there is a preprint on arxiv. So we can't use this paper as a basis for discussion.

 

[elcaro]

As I commented in the other thread where this paper was referenced, it is unfortunately behind a paywall and it does not look like there is a preprint on arxiv. So we can't use this paper as a basis for discussion.

There are other references to this paper, like this one:
https://inspirehep.net/literature/12227

 

[PeterDonis]

There are other references to this paper, like this one:
https://inspirehep.net/literature/12227

Where's the paper? I only see the abstract.

 

[elcaro]

Related to the idea of Vilenkin, this paper is on Arxiv,

Before spacetime: A proposal of a framework for multiverse quantum cosmologybased on three cosmological conjectures