Big Bang theory

[beecee]

1 hour ago, Phi for All said:

but I wanted the OP to understand that BBT has nothing to do with "the origin of everything", nor is it considered to be a theory of everything. 

Yep, I also on a now defunct forum, remember an Astronomer, saying that in the event of a validated QGT, it will more then likely encompass also that which we know as the BB.

[mistermack]

On the subject of infinities, by coincidence there was a documentary about the cosmos on the tv earlier, in which they were saying that the latest measurements are indicating that the universe is probably perfectly flat, meaning that is probably infinite in extent. 

So you have an infinite universe, preceded by a singularity, which itself throws up infinities all over the place, such as infinite densities, and infinite curvature. Since BBT describes an increasingly concentrated cosmos preceded by a singularity, the terms vague and incomplete are not so wide of the mark. 

Quote wikipedia : "Neither general relativity nor quantum mechanics can currently describe the earliest moments of the Big Bang,^[7]"

[swansont]

6 hours ago, beecee said:

Yep, I also on a now defunct forum, remember an Astronomer, saying that in the event of a validated QGT, it will more then likely encompass also that which we know as the BB.

Much like GR encompasses Newtonian gravity. Quantum gravity might take us back a tiny slice of time earlier in describing the hot dense state. But probably without addressing the origin.

[beecee]

13 hours ago, mistermack said:

So you have an infinite universe, preceded by a singularity, which itself throws up infinities all over the place, such as infinite densities, and infinite curvature. Since BBT describes an increasingly concentrated cosmos preceded by a singularity, the terms vague and incomplete are not so wide of the mark. 

Quote wikipedia : "Neither general relativity nor quantum mechanics can currently describe the earliest moments of the Big Bang,^[7]"

But a singularity need not throw up infinities such as infinite densities and curvature, simply the region where our known laws of physics and GR break down or are not applicable.

13 hours ago, mistermack said:

On the subject of infinities, by coincidence there was a documentary about the cosmos on the tv earlier, in which they were saying that the latest measurements are indicating that the universe is probably perfectly flat, meaning that is probably infinite in extent. 

Perfectly flat would indicate no error bars. Is that even possible? Remembering that any straight line ( say out to the limits of our observable universe) could still be just the arc of a much much larger curvature. I still don't believe the question has yet been entirely settled.

8 hours ago, swansont said:

Much like GR encompasses Newtonian gravity. Quantum gravity might take us back a tiny slice of time earlier in describing the hot dense state. But probably without addressing the origin.

Yes, to the highlighted part. Like confirming the GUT, or a TOE? and whether GR or QT will reign supreme?

Edited October 18, 2021 by beecee

[Markus Hanke]

22 hours ago, beecee said:

Not arguing Marcus, and perhaps I have mistunderstood.......What I think I do understand well, is that the further we go back, approaching that Planck/quantum era, the less certain we can be...

That’s right...nonetheless there is a clear conceptual cut at the end of the inflationary epoch. Inflation itself is a bit speculative; we don’t have a GUT, just a bunch of candidate models; and we don’t have a model of quantum gravity that would describe physics at the Planck epoch either (again just some candidate models). So everything prior to the electroweak epoch is either speculative, or unknown.

[MigL]

16 hours ago, mistermack said:

they were saying that the latest measurements are indicating that the universe is probably perfectly flat

If you went in your back yard, and made some measurements, you would probably come to the conclusion that the Earth was flat.
The extremely large radius oof the curvature makes it 'appear' so.

[geordief]

2 hours ago, MigL said:

If you went in your back yard, and made some measurements, you would probably come to the conclusion that the Earth was flat.
The extremely large radius oof the curvature makes it 'appear' so.

I have been told that the consensus  has for some time been that the universe should be flat (because it should be infinite)

This measurement of a lack of observable curvature in the triangle drawn between us and the edge of the observable universe is just a confirmation of this "bias".

 

We think the universe should be infinite and this measurement apparently lends real credence ,though not proof to this view.

Edited October 19, 2021 by geordief

[mistermack]

12 hours ago, beecee said:

Perfectly flat would indicate no error bars. Is that even possible? Remembering that any straight line ( say out to the limits of our observable universe) could still be just the arc of a much much larger curvature. I still don't believe the question has yet been entirely settled.

Quite right. I think I paraphrased the interview fairly well by saying "indicating that", and "probably", but I can't remember the guy's exact words. But he was clear that they were looking very hard for curvature, using the latest techniques, but found none. 

But it's in the nature of infinity that you can never measure it, you can only report that something tends towards it, so the uncertainty will never go away, if it is flat. 

This seems to be the most relevant passage, in wikipedia : 

 

The latest research shows that even the most powerful future experiments (like the SKA) will not be able to distinguish between flat, open and closed universe if the true value of cosmological curvature parameter is smaller than 10⁻⁴. If the true value of the cosmological curvature parameter is larger than 10⁻³ we will be able to distinguish between these three models even now.^[16]

Results of the Planck mission released in 2015 show the cosmological curvature parameter, Ω_K, to be 0.000±0.005, consistent with a flat universe.^[17]

Edited October 19, 2021 by mistermack

[Beeze]

So, there had to be something there for the big bang to happen. But where did it come from? How did it get there? People are always saying you have to be a creationist or an evolutionist, but what if they are both wrong. Atoms don't just appear out of nowhere. Maybe God created them and let the big bang happen. Maybe there was a different higher power to cause it and it got wiped out when the big bang happened,

[Phi for All]

36 minutes ago, Beeze said:

So, there had to be something there for the big bang to happen. But where did it come from?

The model doesn't go back that far, but the maths suggest even greater density than that of a black hole, where the matter has overcome both electron and neutron degeneracy. That doesn't suggest there was nothing there before that.

43 minutes ago, Beeze said:

People are always saying you have to be a creationist or an evolutionist, but what if they are both wrong.

You can believe what you like, but evolution is a fact. The theory of evolution is what creationists deny in favor of their religion. If one group is wrong, I'd say it's the ones without the mountains of evidence in support of them.

47 minutes ago, Beeze said:

Atoms don't just appear out of nowhere.

Not what happened. Stick around, learn some science, and welcome.

47 minutes ago, Beeze said:

Maybe God created them and let the big bang happen.

This doesn't contradict observation. If only you could get this god to allow us to observe them....

49 minutes ago, Beeze said:

Maybe there was a different higher power to cause it and it got wiped out when the big bang happened,

Omnipotent but drops the grenade at His own feet?! I like this one. Sounds like Loki.

[Markus Hanke]

12 hours ago, Beeze said:

So, there had to be something there for the big bang to happen.

The problem with this is that the Big Bang represents a boundary to spacetime itself. Without space or time, there is no causal structure, so speaking about “before” or asking “what caused” the BB is entirely meaningless.

[Airbrush]

Did cosmic inflation happen before the force of gravity existed?

[joigus]

58 minutes ago, Airbrush said:

Did cosmic inflation happen before the force of gravity existed?

Gravity would exist, but only as a continual bubbling of virtual states. Gravitons would pop up from the vacuum and die down without having found any real particle in their way. In terms of QFT, it would be only loop Feynman diagrams. Assuming a cogent theory of quantum gravity is found some day.

[MigL]

I would agree that gravity was present before inflation, but the inflationary period is believed to be between 10^-35 sec and  10^-32 sec ( electroweak unification energies ).
Gravity would have been the first to split off, at times much closer to Planck time, because it is at close to Planck energies that the four fundamental 'forces' seem to have equivalent strengths.
This assumes, of course, that gravity is a 'force' which can be unified with the other forces.
GR, although incomplete, seems to suggest it is not

[Airbrush]

5 hours ago, MigL said:

I would agree that gravity was present before inflation, but the inflationary period is believed to be between 10^-35 sec and  10^-32 sec ( electroweak unification energies ).
Gravity would have been the first to split off, at times much closer to Planck time, because it is at close to Planck energies that the four fundamental 'forces' seem to have equivalent strengths.
This assumes, of course, that gravity is a 'force' which can be unified with the other forces.
GR, although incomplete, seems to suggest it is not

This confirms your assertion that gravity was a force before the inflationary period.  It would seem to me that the big bang would have been enabled if it inflated before gravity became a force, thereby allowing the explansion unimpeded.  It appears counterintuitive that gravity appeared before the inflationary expansion.  So the big bang was expanding against the force of its' own gravity.

 

"It is believed gravity split from the primordial 'superforce' almost simultaneously with the big bang. See Neil Tyson's discussion here http://www.haydenplanetarium.org/tyson/category/subjects/bigbang"

Reference: https://www.physicsforums.com/threads/big-bang-gravity-split.320140/

Edited June 25, 2022 by Airbrush

[dimreepr]

On 6/25/2022 at 3:06 AM, Airbrush said:

This confirms your assertion that gravity was a force before the inflationary period.  It would seem to me that the big bang would have been enabled if it inflated before gravity became a force, thereby allowing the explansion unimpeded.  It appears counterintuitive that gravity appeared before the inflationary expansion.  So the big bang was expanding against the force of its' own gravity.

Gravity was a force potential before the inflationary period and that potential has been realised ever since.

[Mitcher]

The inflation is based on the handy existence of inflatons that nobody has ever seen. And there are no known mechanism  explaining how inflation was seriously slowed down and, conversely, how it could start again recently.

[MigL]

The first proposed mechanism, was by Alan Guth in the 80s, who postulated the Electro-weak symmetry break allowed the universe to drop down to a lower energy state from a previous false zero state.
This released energy ( of the drop ) powered the inflationary phase from 10^-35 to 10^-32 sec.
The residual energy of the drop may still be active as the Cosmological Constant, or Dark Energy.

There have been many inflationary models proposed since then, as they solve many problems such as isotropy, homogeneity, apparent flatness, and even the scarcity of magnetic monopoles.

The inflaton is a mathematical construct which simplifies the theory/calculations; whether real, or not, is not important as it's a 'model'.

[Mitcher]

On 8/17/2022 at 3:36 PM, MigL said:

The first proposed mechanism, was by Alan Guth in the 80s, who postulated the Electro-weak symmetry break allowed the universe to drop down to a lower energy state from a previous false zero state.
This released energy ( of the drop ) powered the inflationary phase from 10^-35 to 10^-32 sec.
The residual energy of the drop may still be active as the Cosmological Constant, or Dark Energy.

There have been many inflationary models proposed since then, as they solve many problems such as isotropy, homogeneity, apparent flatness, and even the scarcity of magnetic monopoles.

The inflaton is a mathematical construct which simplifies the theory/calculations; whether real, or not, is not important as it's a 'model'.

ok but I was speaking about a braking mechanism(s), capable of stopping the inflation which pushed everything away at many times over the speed of light, then later identically able to seemingly re-accelerate everything.

[MigL]

3 hours ago, Mitcher said:

ok but I was speaking about a braking mechanism(s), capable of stopping the inflation which pushed everything away at many times over the speed of light, then later identically able to seemingly re-accelerate everything.

As the energy supplied by the universe's drop ( slow roll ) from false zero vacuum energy, to true zero level, after the E-W symmeetry break becomes less and less, the exponential inflation also decreases. That is simple enough to understand.

Much less understood is the mechanism for the recently detected accelerating expansion of the last few billion years.
Perhaps oscillations about the true zero vacuum energy level ?

[Markus Hanke]

The current accelerated expansion of the universe is not related to inflation - these are physically different circumstances.

[Mitcher]

3 hours ago, MigL said:

As the energy supplied by the universe's drop ( slow roll ) from false zero vacuum energy, to true zero level, after the E-W symmeetry break becomes less and less, the exponential inflation also decreases. That is simple enough to understand.

Much less understood is the mechanism for the recently detected accelerating expansion of the last few billion years.
Perhaps oscillations about the true zero vacuum energy level ?

A process decreasing the inflationist power can be understood but slowing down all the matter in the Universe from thousands of times c to a relative standstill is a different thing. Maybe gravity at works ? I like the idea the Universe might be critically oscillating.

2 hours ago, Markus Hanke said:

The current accelerated expansion of the universe is not related to inflation - these are physically different circumstances.

I read some authors contest the accelerated expansion measurments. Maybe we should really ascertain it's real first, mostly because it's so weird. And if it's real we should stop talking about the Hubble constant then, it should be the Hubble variable.

[Markus Hanke]

10 hours ago, Mitcher said:

Maybe we should really ascertain it's real first

I don’t know exactly where the confidence level for this stands at the moment, but I think it’s pretty likely that this is real.

10 hours ago, Mitcher said:

mostly because it's so weird

Not really. It straightforwardly corresponds to having a positive cosmological constant in the Einstein equations. To me, it would actually be much weirder should it turn out that this constant is somehow exactly zero, because there is no a priori reason (that we know of) for that to be the case.

[Mitcher]

7 hours ago, Markus Hanke said:

I don’t know exactly where the confidence level for this stands at the moment, but I think it’s pretty likely that this is real.

Not really. It straightforwardly corresponds to having a positive cosmological constant in the Einstein equations. To me, it would actually be much weirder should it turn out that this constant is somehow exactly zero, because there is no a priori reason (that we know of) for that to be the case.

Why not, afer all it was not an obligation for this constant to exist in the first place, the Universe could have decided to quietly slow down and turn back to the future, and to a big crunch. Who are we to decide ?

[MigL]

On 8/18/2022 at 3:47 PM, Markus Hanke said:

The current accelerated expansion of the universe is not related to inflation - these are physically different circumstances.

Circumstances may be different, but the argument can be made that vacuum energy  is the impetus for both.

That is if the accelerating expansion turns out to be real, and not a figment of error, or the accuracy of our type !a  supernova 'yardstick'.

Edited August 19, 2022 by MigL