I have a question about the big bang

[Vysero]

I know the mathematics and physics behind all this stuff is currently beyond my comprehension but maybe someone can explain it in relative terms that I can understand. Does the problem of unification effect the probability of the Big Bang Theory? What I mean is, since we are having trouble unifying quantum mechanics and relativity (aside from string theorists), and since the Big Bang theory relies on relativity, does that mean that the Big Bang might not be a very good explanation for our origins. Or, if someone has, can someone explain (to some degree) how quantum mechanics would work in a singularity, do the laws change when things are that dense and hot?

[Watson]

I'm not an expert on this but it seems to me that the unification question is independent of the BBT. QM, relativity and the BBT are all good theories on their own. Just because the first two can't be explained in a single theory doesn't mean the BBT is wrong? (I thought strings were out of fashion?) As for QM working in a singularity, I think that when you are that far outside the envelope of human knowledge you don't even ask the question, as it is pointless.

[Marshall]

Somehow I missed this post. Watson thanks for calling it to everyone's attention. I don't know if Vysero is still around and interested in getting an answer. Maybe we will hear from him which would motivate more discussion.

The most important thing to realize is that "BBT" means two different things. This causes no end of confusion. there is an essay about this. Google "einstein online two big bangs"
and you will get http://www.einstein-online.info/spotlights/big_bangs

Basically on the one hand there is the speculation about the FIRST SECOND of expansion, where known and tested physics breaks down ("singularity" means breakdown and is a symptom that the usual theory doesn't extend to extreme conditions)

And on the other hand there is fairly solid understanding AFTER THE FIRST SECOND of expansion. that is covered by known physics and there is a good mathematical model that is confirmed by lots of observational data.
=======================

What a lot of people don't realize, because it has not gotten into popular books, is that there is an active field of research called Quantum Cosmology where researchers are developing new physics according to which the universe did NOT BEGIN at the start of expansion but GOES BACK EARLIER. So there are models of the "Big Bang" which do NOT suffer from "singularity" problems but go back before where the failure occurred in the old model. The new models are run as computer simulation and they make testable predictions.

In fact there is a series of talks about this titled "experimental signature of quantum gravity" which is being given at NORDITA in Stockholm Sweden just this month. The talks are organized to bring young researchers in---PhD students and postdocs.

There was a conference on the same topic at NORDITA last year. It's an exciting and growing research area.

So it is probably not a very good idea to think of the start of expansion as the beginning of the universe.
Keep an open mind, about what is the beginning. Our ideas about that can change.
========================

To sum up BBT AFTER THE FIRST SECOND of expansion is probably OK and not likely to change, but

BBT BEFORE THAT especially WHAT CAME BEFORE THE START OF EXPANSION is an active research area and models are being worked on that don't have a breakdown---they need to be tested and they will be.
We don't know how this will turn out! Stay tuned.

[Watson]

Is this the Big Crunch, then the Big Bang senario?

[Marshall]

Is this the Big Crunch, then the Big Bang senario?

Never heard the term "Big Crunch then Big Bang" used. But there are various quantum gravity models and in some gravity turns repellent at very high density so you get a bounce. You may be talking about one of those lines of research.

There's not just one scenario. Several being studied. Several models have a bounce at start of expansion. So they go back further in time. If you are interested here are some papers. This is not the only approach and these are not the only papers, but you can get an idea. It could be what you are asking about.

LOOP QUANTUM COSMOLOGY RESEARCH BY YEAR
keyword "quantum cosmology: loop space"
2006 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (21 found)
2007 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (39 found)
2008 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (45 found)
2009 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (45 found)
2010 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (56 found)
2011 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=&f1=keyword&op1=a&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=50&sc=0&of=hb (47 found)

[Watson]

Well it was from the thought the Universe was open or closed and was going to expand forever, or expand to a point and then contract to a big crunch, and then perhaps spring back to expansion, from the big crunch? I think it was determined the Universe is open? If I recall correctly, reading about it some time ago.

[Marshall]

You and I seem to have come to essentially similar ideas from different directions. If you look at the summaries of the papers in those links they are almost all about bounce cosmology.
(not necessarily cyclic, may just be one bounce)

For example look at 2010 list and scroll down to #20
Click on "detailed record" to see the summary:
http://inspirehep.net/record/875842
"Observing the Big Bounce with Tensor Modes in the Cosmic Microwave Background: Phenomenology and Fundamental LQC Parameters."
It is a paper by four european theory-testing specialists--so-called "phenomenologists" whose job is to see how quantumcosmology models can be tested by observed phenomena.
You can see the full paper PDF if you want, the link is at the bottom of the page.

If you look at the 2010 list, just to take an example, most of the first 20 or 30 papers are about bounce cosmology. It is studied a lot. Maybe all are.

A search like that lets you poke around and look at titles and summaries---form your own impression of where the current research is going.

[Watson]

You and I seem to have come to essentially similar ideas from different directions. If you look at the summaries of the papers in those links they are almost all about bounce cosmology.
(not necessarily cyclic, may just be one bounce)

I thought the whole premise of the bounce, or bang/crunch was to give a degree of explaination to the expanding Universe? So the bounce you are referencing is a low energy, (low relative to the energy of the singularity, and explainable in theory) pop of energy which becomes the Universe at the moment of the Big Bang?
The term bounce seems to imply hitting something, or change of direction. I'm not sure how the term bounce is applied non-cyclic way. Where does it bounce from?
The article you provided says:
In this case we require not only that the features of the bouncing+inflationary model dif-
fer from that standard prediction but also that they can be detected by themselves.

I thought the bounce was another way of explaining inflation, but this model has both, unless bounce is the intitial inflation and then the Guth inflation?

I'm pretty sure I'm way off here?

[Marshall]

You and I seem to have come to essentially similar ideas from different directions. If you look at the summaries of the papers in those links they are almost all about bounce cosmology.
(not necessarily cyclic, may just be one bounce)

I thought the whole premise of the bounce, or bang/crunch was to give a degree of explaination to the expanding Universe? So the bounce you are referencing is a low energy, (low relative to the energy of the singularity, and explainable in theory)...

The "Loop" approach (LQG) is one of several competing attempts to formulate a quantum theory of spacetime geometry that reproduces classical GR in the limit.
That name was appropriate in the 1990s, when it was formulated using the idea of tiny loops which sense and express spatial geometry. By the mid-1990s they no longer used loops---there were more general ways to express and calculate quantum states of geometry (mixtures of uncertain shapes, so to speak). But they kept on calling it LQG.


The bounce was not a premise but rather an unexpected thing that came out of the math during the struggle to quantize GR, around 2001.

When you apply classic (i.e. non-quantum, deterministic) GR to cosmology the Einstein field equation boils down to a simpler equation called the FRIEDMANN EQUATION that governs the evolution of the broad outlines of the universe's expansion and spatial curvature as it relates to overall matter and energy density.

In 2001 the LQG method was applied to cosmology to obtain a QUANTUM FRIEDMANN EQUATION, at low density it reproduced the classic expanding geometry we know and love. But at very high density there were "quantum corrections" that made it behave differently.

In 2005 some problems were pointed out with that original version of LQG cosmology (LQC for short) and in 2006 it was re-derived and reformulated, primarily by an Indian guy named Abhay Ashtekar. Then you got a very clear quantum Friedmann equation, with clear quantum correction terms. The quantum effects were small at low density and could be ignored. At very high density the correction terms became large and became dominant in the equation. In effect gravity became repellent!

After 2006 the universe's geometric behavior was studied in many different cases, both using computer simulation methods and analytical "solvable equation" methods. In every case they always got a bounce.

Ashtekar and friends are still checking this, relaxing restrictive assumptions made at first, generalizing etc.
The bounce seems to be "robust" in the sense that it keeps on recurring in whatever variation they try.

It tends in many cases to happen when the energy density reaches about 40% of the socalled "Planck" density. That energy is very hard to imagine. Think of the gamma-ray light in the core of a star. Very short wavelength photons. Think of light that is a trillion trillion times hotter and brighter than that starcore light.
Very short wavelength photons, many many packed together. Each photon with enough energy to drive your car 100 miles. Unbelievable energy in each photon and unbelievably many crowded together. That is the energy density at Planck-like scales where the LQC quantum corrections become dominant and bounce happens.

It is high but it is not infinite. So there is no singularity. A singularity is where a theory breaks down and gives infinite answers---answers that therefore do not mean anything. No definite number. No physics.

The bounce naturally triggers a period of inflation, or actually socalled superinflation. Ordinary Alan Guth inflation was only exponential expansion that gradually slid down from initial the exponential rate. In superinflation the exponential rate actually increases---you get faster than exponential inflation for a while after bounce but then it quickly slows down to ordinary (if you have usual Guth-type assumptions).

This does not predict a cyclic pattern. You can get that under certain assumptions but the only robust conclusion from the theory is that OUR start of OUR expansion was a bounce. There was an immediately preceding contraction phase. Where that prior contracting universe came from the theory does not say.

Also the theory has to be tested and it predicts some features of the ancient light, the microwave background, which may or may not be observed. So it is not something to believe, it is something to be tested by observation and possibly discarded or improved-on.

I have to go. haven't finished answering, but no more time for now.

[Watson]

I have to go. haven't finished answering, but no more time for now.

Thanks,
In the mean time, does the bounce not give an indication of what came before? The singularity hides the truth about what happened in the first faction of a second after the big bang with extreme energies. It sounds like the bounce has a certain energy at the moment of the big bang, predictable by the equations. If this is correct then wouldn't that energy and the change in that enegry over time indicated a trend that could be extrapolated back to a time milli-moments before the BB. I don't want to get back to a singularity and I am aware that by asking such a question I may as well count fairies on a pin. I just seems there should be a theory that starts with nothing and pop, bounce or bang, we have something, like energy.
Are time and energy conjunctive variables?

I look forward to the rest of your answer above.

[Marshall]

I have to go. haven't finished answering, but no more time for now.

Thanks,
In the mean time, does the bounce not give an indication of what came before? ...

Your question makes it easier for me to continue. First keep in mind that we are just looking at one of several research programs. there are several parties trying different ways to get up the mountain. This is the "Loop" researchers' approach and they no longer use the small mathematical loops that gave them their name. the loops have been replaced by networks that feel and describe the uncertain changing geometry of space.
Quantum states of geometry are described by networks charged with information like that resulting from measuring geometric quantities (angle, area, volume...)

Their Quantum Cosmology modeling is called LQC. And they don't try to say where the universe came from or if it was always there or if not always then how it arose. They act as if they think it might be premature to ask such questions and they seem to want to focus on something much simpler:

approximately what was going on around the start of our expansion process, that we see?

what really happened (instead of the "singularity")?

This is a much more accessible tractable question to address because we can SEE the result in the form of the ancient light from a few hundred thousand years after the start. You know the figure of about 380,000 years after start of expansion---for the microwave background light. Redshifted by a factor of about 1100.

A magnified image of what was, at the time, a much smaller volume of space.

So there is practical investigation to do, Watson, which is not more philosophical speculation about the origin of existence.

So that is what the Loop people do. There are however other groups of researchers who are thinking more along the lines of Being "popping" out of a Vacuum state. I steer clear of that because the terms are so confusing and there seem to be no really solid observational tests. You hear plenty of HYPE but hardly anybody is running computer models case by case and pointing out features in the CMB to look for. It is not a question of who's right. Anybody can be right or wrong. It is a question of comparative maturity of research programs.

I'm more interested in the programs that are more completely worked out and closer to testing. So I avoid the "popping out of the vacuum by a quantum fluctuation" stuff.;;;;;

[Watson]

Yes I didn't mean to go in that direction. As for the particles popping out of the vacuum of space, don't they arrive in pairs then quickly anielate unless one gets dragged off by gravity of some sort, like an event horizon? It seems like a pretty inefficient way to build a Universe? At the lower energies of the bounce theories, relative to a singularity,are they any where near what the LHC deals with?

[Marshall]

Nowhere near. Lincoln is the expert---he goes to CERN and is part of one of their experimental collaborations. But even as a dyed-in-the-wool non-expert I can say that.

LHC falls many orders of magnitude short of Planck scale

You might want to google "Planck units". I understand Wikipedia is going to temporarily shut down to protest some proposed Internet rules, but when it comes back on, you could check what they say about Planck quantities of energy, temperature, energy density. Planck quantities are extreme de la extreme.

Just to take one example you know the LHC collision energy is on the order of arouind TeV = 10¹⁵ eV.
Building to around 10 TeV. (order of magnitude) So call it 10¹⁶ eV.

Planck energy is around 10²⁸ eV

So LHC energy is only a trillionth of that. There has to be a different way to study physics at Planck scale.
The cosmic background radiation might afford one window on it. Conceivably gammaray bursts (GRB) could provide another if they represent something collapsing to form a black hole. Not sure about that.

[legosbulock]

Got a quick one for you.
If the majority of the expansion happened in 15 minutes (as it has been suggested to have done), what slowed it down?

[Marshall]

Got a quick one for you.
If the majority of the expansion happened in 15 minutes (as it has been suggested to have done), what slowed it down?

That's an unsolved problem. Inflation scenarios contain unjustified assumptions and fine tuned parameters that are tweaked to get enough inflation (to explain the flatness and uniformity it was invented to explain) and then, after enough has occurred, to get it to stop. They refer to the latter problem as how the universe can make a "graceful exit" from inflation.

Paul Steinhardt is a highly respected Princeton cosmologist who was a major contributor to Inflation early on. But he is now skeptical of the whole thing and had a piece in the Sci Am in 2011 about this. Airing his doubts.

That doesn't mean its wrong.

If you aren't talking about Inflation then the easy answer is GRAVITY. That"s simple. Expansion gets a good start, say from a bounce. The Einstein law of gravity (the GR equation) says that once started expansion will tend to continue but will be slowed down by the gravity of the matter which is assumed to be approxmiately uniformly distributed throughout all space. If the density is high enough expansion will actually come to a halt.

Have to go. Probably more can be said about this on a quantitative level.

[legosbulock]

my gf is snoring. I cant think. I will get back t.
o you

[Watson]

So bounce, big bang, inflation over the first milli-second, Then? Matter at high energies is energy. So big bang energy cooling during inflation becomes matter. Is matter spewing from the inflation what gives us expansion?

[legosbulock]

I guess my question is: How can Gravity be an influence during expansion unless Gravitational influence is essentially immune to time? That is to say that can the influence of object A be felt by object B even if the two objects are moving apart from each other relatively faster than the speed of light?

[Lincoln]

Your problem is that you are not adequately distinguishing between the nature of space and its associated expansion/deformation/etc. and the behavior of forces that are constrained to operate within space.

In essence, space can move at any speed. Forces within space can move no faster than the speed of light .

[Marshall]

I think Lincoln's post provides a response to this question as well

... Is matter spewing from the inflation what gives us expansion?

Matter can move through space only at speeds < c. As Lincoln indicates, space is different.

By space, I mean geometry---basically the web of distance relationships (but also angles areas etc.)

The expansion of space (i.e. of geometry) is something different from motion of matter through space. This was realized a long time ago, probably in 1915 and definitely by 1930, but still isn't widely assimilated. The expansion of distances (if it is according to the 1915 Einstein field equation) can occur at any rate, including > c. I would not even say occur an any speed because the word "speed" suggests that it is motion.

According to the 1915 GR equation, geometry itself can change dynamically and the change (which can for instance be a pattern of expansion of distances) has something analogous to momentum. It is not literally the momentums we associate with a spinning wheel or tossed ball. But the GR equation is a differential equation governing rates of change of geometry and it tells us that certain kinds of changes in geometry (not ordinary motion of particles, something different) will tend to persist once they get started, and may only gradually slow down or speed up due to other influence (the righthand side driving terms of the equation).

So the presentday pattern of expansion of distances should be understood essentially a natural persistence of expansion at much higher rates that got started at bang time.

It does not require the influence of "spewing" matter. The matter could only move thru space at speed <c and the distances in early universe were expanding at rates much > c.
Indeed the distances to many if not most of the galaxies we now observe were, according to the proper distance measure used by cosmologists to state the Hubble Law expansion pattern, expanding > c when the light from them started traveling towards us. (There is a trick to understanding how the light got here.)

What I'm telling you is that superluminal expansion of geometry is still going on (on very largescale) and was not limited to the early universe or to some special "inflation" scenario. It's just a fact of life.
So it can't be confused with the ordinary motion of matter thru space which we are used to and which has a speed limit from 1905 special rel.

[Watson]

Marshal wrote: [The matter could only move thru space at speed <c and the distances in early universe were expanding at rates much > c.]

The geometry of space is traveling at >c, and matter is traveling <c, then what is >c minus <c? The extent of the geometry less the matter, not there yet because of slower travel is what, an region of nothing, or no matter, yet?

[Marshall]

Marshal wrote: [The matter could only move thru space at speed <c and the distances in early universe were expanding at rates much > c.]

The geometry of space is traveling at >c, and matter is traveling <c, then what is >c minus <c? The extent of the geometry less the matter, not there yet because of slower travel is what, an region of nothing, or no matter, yet?

I did not say the geometry of space was traveling, Watson.

Here's what I suggest you try---which may bring us into closer understanding:
google "misconceptions big bang charley"
that will get you http://www.mso.anu.edu.au/~charley/pape ... sSciAm.pdf
as the first hit.
Read the whole article. It is from the March 2005 Scientific American, by a worldclass cosmology expert who knows how to write well for general audience.

the first page is blank so scroll down. If you have any trouble, ask me.

Charley explains how light can get to us from a galaxy the distance to which is increasing at 2c when it emits the light.

Of course the flash of light aimed in our direction will begin by being dragged back. The distance to it will increase at rate c (even though it is moving thru space towards us at speed c.) But there is a special trick which allows from such galaxies to have reached us, and to be reaching us even now today.

I suggest you read Charley's article fairly carefully and then ask more questions here.

Remember how to get the article, it is the first hit (or was when I tried) when you google the words
"misconceptions big bang charley" (without the quote signs of course)

It is also the first hit if you google the words "baffled expansion charley" (again wihout the " signs)

[LouisB]

What is called Big Bang Theory (BBT) is a meta theoretical framework for the whole of physics and the whole of the cosmos. BBT is constantly evolving since the 1920's in order to integrated new observations and new physics. BBT first originated with the solution of the general relativity field equations which predicted an expanding universe from a state of infinite density. They are still a large number of features of the cosmos which are not explained within this theoretical framework and there are a large number of mathematical problems within the framework.

BBT’s domain of validity break down at the plank scale. The framework will either be replaced or be fundamentally revised when a quantum gravity theory will be established.

BBT is not a theory of the origin of the Universe. It describes a lot of aspects of the expanding Universe from the time when its density was low enough.

[gerhard]

I have a third grade education, and I think the universe came into existance through a progressive sublimation of energy. This may not help you, but big bang ideas depend on outgoing energy, whereas an ancient idea was that everything was simmered down to what it is. We only measure what seems to impact on our perceptions, but whatever we cannot perceive can be just as powerful. What are those little gaps inbetween packages of energy? Does the wave of matter dip below the line of equilibrium? Do we have to invent black holes when every particle oscillates with an emptiness equal and opposite to its presence? Does space time bend or are we dealing with aspects of inperceptible forms of energy that balance what we see? I think the universe is an allowance by powers infinitely stronger than matter itself, and that the path of least resistance is how it exists, not a red faced, vein popping explosion out of nothing.