Big Bang & Inflation: Exploring Infinite Inflation

[PantherModern]

"Infinite" inflation

Hello all,

I have a series of questions relating to the Big Bang and Inflation! First, a disclaimer: I am a science/astronomy/cosmology enthusiast, but I have no advanced education in the subjects. My knowledge is gleaned from as many books as I can read and shows I can watch on the subjects, so if I get something wrong, let me know.

Terribly simplified, the laws of physics as they pertain to this question as I understand them are:

1: Energy = Mass, Multiplied by the square of the speed of light
2: Matter/Energy cannot be destroyed, only converted
3: For every action, there is an equal but opposite reaction
4: Thermodynamics disallows infinite or perpetual systems
5: The fundamental forces, follow the inverse square law
(...and a few others)

My question is this:

As I understand it, the violence of the "Big Bang" is responsible for cosmic inflation. The elementary particles that made up this early fireball were expanding at tremendous speeds away from each other. This, as I understand it, is the cause of inflation: the Big Bang produced so much energy that the universe will keep expanding. For the universe to continue to expand and not slow down, that would mean that the products of the Big Bang had reached "escape velocity" and would not slow down due to gravitational influence in the early universe.

If the fundamental forces interact to cause matter to form from the elementary particles (some attracted, some repelled, some annihilated, etc), then does it follow that the fundamental forces would cause sufficient interaction on the elementary particles in sum to eventually cause the "Big Crunch"?

Without the fundamental forces causing matter to coalesce, we wouldn't have stellar/galactic formation in the first place, right? Shouldn't the sum of those interactions over time be enough to act as "drag" to slow everything down to the point that it then begins to collapse again?

Last, but not least... is it even possible for the Big Bang to produce enough energy to send elementary particles into "escape velocity" in the first place? I would expect that regardless of how energetic the Big Bang was, that it must also follow the law of Conservation of Energy; similar to a rocket, the energy that caused the inflation in the first place was finite: therefore, the ability for the particles to expand would be limited over time by their fundamental interactions with each other, unless continually acted upon by an outside force.

Thus, if the energy of the Big Bang was sufficient to send the fundamental particles into escape velocity, wouldn't that mean matter would never coalesce in the first place?

Hopefully some of you can put this in better light for me or tell me if I'm waaaaaaay off. Cheers!

 

[Mark M]

PantherModern, welcome to PF!

Well, a few of your assumptions there are actually incorrect. Let me show why:

1. Rest energy is equal to mass times the speed of light squared. Objects may also gain kinetic energy through motion.

2. The conservation of energy does not apply in an expanding universe. You should read the FAQ on it.

4. Well, if by that you mean perpetual motion then you are correct. But once again, the expanding universe is a precarious situation, it can continue to do so forever.

Inflation occurred after the big bang. Remember, the big bang does not refer to an explosion, it refers to the point in time at which the universe was in a state of singularity, when every point was infinitely dense. Inflation occurred very shortly afterwords. Essentially, a field known as the inflaton field would have permeated the entire universe. It would eventually reach a false vacuum - a state that a field can decay into while trying to reach a true vacuum. While in this false vacuum, the field exerted an enormous negative pressure - and in general relativity, negative pressures can expand space. The pressure caused the universe to undergo incomprehensible amounts of expansion, before the inflaton field finally decayed into a true vacuum, and decayed into a bath of radiation.

Remember, inflation is a different phenomenon than expansion - inflation was one time, rapid event, but expansion is what goes on today. Also, the universe is accelerating due to the fact it has a on-zero cosmological constant (known as 'dark energy')

Because of the cosmological constant, the universe will not undergo a Big Crunch. Instead, it will continue to expand until it becomes a de Sitter space, and uniform cold state with a positive cosmological constant.

Galaxies and other large structure were created because of vacuum fluctuations prior to inflation. If you're familiar with quantum mechanics, then you're aware that fields can take on different values, changing through 'quantum fluctuations'. Inflation would have turned these small fluctuations in spacetime into enormous 'wrinkles' in space. These wrinkles would then accumulate large amounts of matter and dark matter, coalescing into galaxies.

Like I said at the begining, the conservation of energy just doesn't apply on global scales.

 

[clamtrox]

Inflation occurred after the big bang.

You have to be careful with this terminology. In fact, I would claim that most cosmologists would say that inflation happened before big bang.

According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly.

As I understand it, the violence of the "Big Bang" is responsible for cosmic inflation. The elementary particles that made up this early fireball were expanding at tremendous speeds away from each other. This, as I understand it, is the cause of inflation: the Big Bang produced so much energy that the universe will keep expanding. For the universe to continue to expand and not slow down, that would mean that the products of the Big Bang had reached "escape velocity" and would not slow down due to gravitational influence in the early universe.

In fact, it's the other way around! It's exactly the "non-violence" of the initial state that caused inflation. In order for inflation to start, the universe must be in a very very smooth and organized state. After inflation ends, there is a massive amount of energy "stored" in the expansion rate of the universe (just enough to keep it expanding ~ forever), so in fact it's inflation that explains the expansion, not the other way around.

One further note is that this process does not need ANY net energy; as the gravitational energy is negative, you can have inflation from very low initial energy produce all the 10⁸⁰ particles in the observable universe, and this particle creation is balanced by the expansion. That's the coolest thing about inflation, it is the ultimate free lunch.

 

[Drakkith]

1: Energy = Mass, Multiplied by the square of the speed of light
2: Matter/Energy cannot be destroyed, only converted
3: For every action, there is an equal but opposite reaction
4: Thermodynamics disallows infinite or perpetual systems
5: The fundamental forces, follow the inverse square law
(...and a few others)

2. Mass and Energy cannot be created or destroyed, but matter can and is created and destroyed every day in particle colliders.

5. Only electromagnetism and gravitation follow the inverse square law. The strong nuclear force and the weak force are very different.

 

[PantherModern]

Interesting.

To help me understand further, while I type out another reply:

So, the early universe was not so much a "soup" of elementary particles, but an energy field?

 

[phinds]

You have to be careful with this terminology. In fact, I would claim that most cosmologists would say that inflation happened before big bang.

Surely you don't mean that? Inflation happened just after the singularity and is part of the early stages of the Big Bang Theory. Nobody knows WHAT happened BEFORE the big bang or even if there WAS a "before".

 

[PantherModern]

Causality says you can't have an "after" without a "before".

Of course there was a "before" the "Big Bang"; we're just not sure *what*.

The problem I'm trying to wrap my head around is the composition and state of the singularity that existed right before inflation started, combined with the method of inflation.

At the risk of using Wikipedia, I'll do so this time because this is a nice summary:

According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state. According to the most recent measurements and observations, the Big Bang occurred approximately 13.75 billion years ago,[2][3] which is thus considered the age of the Universe.[4][5] After its initial expansion from a singularity, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. While protons and neutrons combined to form the first atomic nuclei only a few minutes after the Big Bang, it would take thousands of years for electrons to combine with them and create electrically neutral atoms. The first element produced was hydrogen, along with traces of helium and lithium. Giant clouds of these primordial elements would coalesce through gravity to form stars and galaxies, and the heavier elements would be synthesized either within stars or during supernovae.

This was precisely how I understood it, however the mechanism for expansion is what is confusing me.

If the mechanism for expansion is not an "explosion", what is it? Interaction of another force on matter/energy that we're not yet aware of?

 

[phinds]

Causality says you can't have an "after" without a "before".

Of course there was a "before" the "Big Bang"; we're just not sure *what*.

That is not supported by cosmology as we know it, which is agnostic about whether or not there was a "before" but definitely has no evidence of one. What you say certainly makes sense from a human experience point of view, BUT ... many things in cosmology and quantum mechanics make no sense at all from a human experience point of view, so you need to be more careful about making categorical statements that you cannot support with science.

If the mechanism for expansion is not an "explosion", what is it? Interaction of another force on matter/energy that we're not yet aware of?

That's a great question. It most emphatically was NOT an "explosion" and if you can figure out what it WAS I see a Nobel Prize in your future.

 

[PantherModern]

Hahaha I wish! That's the $64m question, isn't it?

Currently, the best guess we have for the mechanism of accelerating expansion is "dark energy", right?

Disclaimer: I may be speculating in this next part, but I'm only trying to fully understand.

Just as there is anti-matter, could there also be "anti-energy" and (related) "anti-mass"? Is there any mathematical or observational data to suggest either?

If "anti-energy" or rather, "negative energy" and "negative mass" exist as elementary properties in the same way that positive and negative charges do, would that potentially explain cosmic inflation through the phenomenon of negative pressure?

EDIT: y
Also, "working backwards", the very nature of the fundamental forces and the properties of elementary particles being either attracted to or repelled from each other, would seem to indicate that inflation must be due to influence from another force, right?

As I understand it, nothing, not even the Big Bang, is capable of violating causality: Causality is what disproves things like supernatural events (because by proxy, anything having an observable effect in our visible universe must have a cause that does not violate the laws of physics), because it guarantees that there is always a cause for an event. For the universe to expand seemingly without cause would violate that, therefore it must be acted on by something else, right?

...or am I completely and utterly wrong? :p

 

[phinds]

Certainly "dark energy" (and yes, it IS the name for the unknown thing that causes acceleration of the expansion) can be looked at as an inverse of gravity (the word "anti-gravity" is WAY too loaded to use) in the sense that it has the opposite effect. On the other hand, I think it must be totally unrelated to gravitational effects in that it occurs independant of mass. As far as I am aware, it exists EVERYWHERE uniformly, it just has no effect inside bound systems (gravitationally, or due to strong force, etc). Other more knowledgeable folks will, I hope, jump in on this.

 

[PantherModern]

Interesting. I'm starting to get a clearer picture of the knowledge I'm lacking.

Is there any observational or mathematical data to suggest that "Dark Energy" is actually -E or rather, -M?

I'm also wondering the following:

Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.

Would it also follow that for "most kinds" of energy there is an associated "antienergy", and that for every observable "property" that there is an associated "antiproperty"?

 

[phinds]

Is there any observational or mathematical data to suggest that "Dark Energy" is actually -E or rather, -M?

No. Which part of my term "unknown thing" was not clear? Perhaps I should have said "totally" unknown thing, but that's too much really, because we know the EFFECT, even if not the cause.

Would it also follow that for "most kinds" of energy there is an associated "antienergy", and that for every observable "property" that there is an associated "antiproperty"?

Another question for the experts, but I don't see any reason why that should be the case. Certainly SOME characteristics have anti-'s but I don't thing that leads conclusively to the thought that they ALL do.

 

[PantherModern]

Interesting! The realm of cosmology is fascinating, isn't it?

Thanks a ton for your input. Anyone else?

 

[Mark M]

You have to be careful with this terminology. In fact, I would claim that most cosmologists would say that inflation happened before big bang.

What? The big bang refers to the singularity, which most definitely happened prior to inflation.

 

[phinds]

What? The big bang refers to the singularity, which most definitely happened prior to inflation.

Did you not read post #6 ?

 

[clamtrox]

Surely you don't mean that? Inflation happened just after the singularity and is part of the early stages of the Big Bang Theory. Nobody knows WHAT happened BEFORE the big bang or even if there WAS a "before".

What I mean is that people often use the words big bang in a different way. As you know, in the standard big bang theory, the universe starts out in a hot, dense, rapidly expanding state. Now, having inflation kind of screws this up, as it takes whatever the initial state was, dilutes away all particles and cools the temperature to zero. Then you have this magical event called reheating, which transforms the energy stored in the inflaton to a bath of ultrarelativistic elementary particles.

This is the point where the "cosmological standard model" coincides with the traditional model of a big bang. Now, if you want to talk about a singularity that existed before inflation (if "before inflation" even makes sense!) then that's entirely fine. All I'm saying is that some people may understand these terms in a slightly different way.

 

[phyzguy]

Surely you don't mean that? Inflation happened just after the singularity and is part of the early stages of the Big Bang Theory. Nobody knows WHAT happened BEFORE the big bang or even if there WAS a "before".

I agree with clamtrox. I work directly with a number of cosmologists, and their agreed-upon terminology is that inflation happened before the big bang. By 'Big Bang Theory', it is usually meant the hypothesis that the universe is expanding from a hot, dense, uniform initial state where the current laws of physics apply. By this definition, the start of the big bang was at the era of 'reheating', which was the end of the era of inflation. The evidence of the big bang theory is overwhelming, but the evidence that the big bang was preceded by an era of inflation is much less compelling. And the evidence that there was a singularity before that is non-existent. So lumping it all together and saying, as you did, that "Inflation happened just after the singularity and is part of the early stages of the Big Bang Theory," lumps together well-established theory with much more speculative ideas, and should be avoided.

 

[bapowell]

The "Hot Big Bang", from which the CMB was generated and the nucleosynthesis of light elements proceeded, occurred after inflaiton during the process of reheating. If there is an initial singularity, then it would have been in existence prior to inflation.

 

[phinds]

I agree with clamtrox. I work directly with a number of cosmologists, and their agreed-upon terminology is that inflation happened before the big bang. By 'Big Bang Theory', it is usually meant the hypothesis that the universe is expanding from a hot, dense, uniform initial state where the current laws of physics apply. By this definition, the start of the big bang was at the era of 'reheating', which was the end of the era of inflation. The evidence of the big bang theory is overwhelming, but the evidence that the big bang was preceded by an era of inflation is much less compelling. And the evidence that there was a singularity before that is non-existent. So lumping it all together and saying, as you did, that "Inflation happened just after the singularity and is part of the early stages of the Big Bang Theory," lumps together well-established theory with much more speculative ideas, and should be avoided.

I do understand that inflation is controversial and not understood, but I was still under the impression, and remain so, that "big bang theory" starts at one Plank time after the singularity, and yes, I know that "singularlity" just means "we have no idea what happened"

 

[phinds]

The "Hot Big Bang", from which the CMB was generated and the nucleosynthesis of light elements proceeded, occurred after inflaiton during the process of reheating. If there is an initial singularity, then it would have been in existence prior to inflation.

So then we have:

singularity (maybe ... whatever it is)
inflation then reheating
hot big bang (including expansion and later accelerated expansion)

Yes?

I always thought that "big bang meant two things

singularity
everthing starting 1 Plank time after the singularity

So, I had it wrong?

 

[bapowell]

So then we have:

singularity (maybe ... whatever it is)
inflation then reheating
hot big bang (including expansion and later accelerated expansion)

Yes?

I always thought that "big bang meant two things

singularity
everthing starting 1 Plank time after the singularity

So, I had it wrong?

I really think this is just semantics. Everything that we suppose the "big bang" did -- operationally -- like generate the CMB and synthesize the light elements, happened after inflation. Assuming inflation is not past eternal (there is not full consensus on this though), then there is still an initial singularity (or something, let's say a universe at the Planck energy) and there is still a universe emerging out of this era, describable in terms of the "big bang model". So I think the distinction is mostly operational.

Observationally, when I refer to the Hot Big Bang, together with the associated generation of the CMB and nucleosynthesis, I have in mind the early expansion following inflation. Expansion that happened earlier is not observationally accessible.

 

[phinds]

I really think this is just semantics. Everything that we suppose the "big bang" did -- operationally -- like generate the CMB and synthesize the light elements, happened after inflation. Assuming inflation is not past eternal (there is not full consensus on this though), then there is still an initial singularity (or something, let's say a universe at the Planck energy) and there is still a universe emerging out of this era, describable in terms of the "big bang model". So I think the distinction is mostly operational.

Observationally, when I refer to the Hot Big Bang, together with the associated generation of the CMB and nucleosynthesis, I have in mind the early expansion following inflation. Expansion that happened earlier is not observationally accessible.

OK, thanks.

 

[Drakkith]

This is why I hate the term "Big Bang". It seems to imply a single event that instantly created the universe under the present laws, not the gradual (if quick) change from super hot and dense to cool and expanded.

 

[Ich]

Hi bapowell,

Observationally, when I refer to the Hot Big Bang, together with the associated generation of the CMB and nucleosynthesis, I have in mind the early expansion following inflation. Expansion that happened earlier is not observationally accessible.

I don't agree. There are are some structures in the CMB that date back to that epoch, which is why inflation is so widely accepted, despite its difficulties.
I'm sure that you know the observations better than me, so I'm a bit irritated by your statement. Is there something I am missing?

 

[clamtrox]

So then we have:

singularity (maybe ... whatever it is)
inflation then reheating
hot big bang (including expansion and later accelerated expansion)

Yes?

I always thought that "big bang meant two things

singularity
everthing starting 1 Plank time after the singularity

So, I had it wrong?

I think you will find that there are multiple conventions about this. I would say that people who are on the GR/string theory/etc side of the isle tend to talk about singularities and all that stuff, while more observationally inclined cosmologists never do. The former way of talking is also propagated very efficiently by popular science shows, which seem to be very fixated on the initial bang.

 

[bapowell]

I don't agree. There are are some structures in the CMB that date back to that epoch, which is why inflation is so widely accepted, despite its difficulties.
I'm sure that you know the observations better than me, so I'm a bit irritated by your statement. Is there something I am missing?

Sorry for the misunderstanding. When I say the "expansion that happened earlier is not observationally accessible" I mean pre-inflationary expansion (which is of course not strictly true if the inflationary period was very short, but even then the kinds of things we can measure are limited.) Being generated after inflation via reheating, the CMB remains a key source of data on the details of the inflationary expansion.