How did the universe start and evolve into what it is today?

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In summary: Peter says that we don't know how the universe blew out from a very small space in a big bang, and he suggests that it could be due to inflation. He also suggests that the pre-BB condition might have been one of energy, which has zero mass.
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HomesliceMMA
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Why did it happen? What force would make the universe, which is contracted into a very, very small space, blow outward and expand?

Another random question: I've heard that, at least in the inflationary model, the universe started in an amount of space like the size of an atom, or less. How is that possible? How would all the atoms in the universe fit into that small space? I know there is a lot of space in atoms (like the proton/neutron nucleus is like waaaaay way from where the electrons are orbiting), but given the number of atoms and particles in our universe? How can alllllll that mass an energy fit into something as small as an [atom]?

Thanks!
 
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  • #2
HomesliceMMA said:
Why did it happen?
We don't know. This is an open area of research.

HomesliceMMA said:
What force would make the universe, which is contracted into a very, very small space, blow outward and expand?
That's not what happened in the Big Bang. The Big Bang was not an explosion of a tiny universe into a larger, pre-existing space.

In our best current model, the universe is and always has been spatially infinite; at the Big Bang, it was simply much, much denser, and the scale factor was increasing much, much more rapidly than it is increasing today.

HomesliceMMA said:
Another random question: I've heard that, at least in the inflationary model, the universe started in an amount of space like the size of an atom, or less.
Our observable universe did. But our observable universe is not the same as the entire universe.

HomesliceMMA said:
How would all the atoms in the universe fit into that small space?
No atoms existed at the Big Bang; atoms did not form until a few hundred thousand years later, when the temperature dropped low enough for them to exist.

The state of the universe right after the Big Bang was a very, very hot, dense, rapidly expanding plasma in which all of the Standard Model quantum fields were in very high energy states, very, very different from the states we are familiar with. So your intuitions about how things "occupy space" do not work for that state.
 
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Thanks Peter! On my main question, so its sounds like know one knows - are there any ideas that people have floated? I watched some pop-sic where a guy said we found something in quantum fields or what not that would lead to huge outward expansion. That was the genesis of my question - I was aware of no such thing, having watched and read much pop-sci in my life! I figured he was probably BSing or at least playing very fast and loose with what we know.

On my second question, I follow you, but is another way to answer my question there being a simple possibility that: "There was issue regarding all matter in the universe being in too-small a place before the big bang, because it was then all effectively energy, which has zero mass." That sort of thing.

Thanks so much!
 
  • #4
HomesliceMMA said:
I watched some pop-sic where a guy said we found something in quantum fields or what not that would lead to huge outward expansion.
No one knows the ultimate cause of the Big Bang. The only sensible thing your pop-sic [sic] could be talking about is inflation, which is a theory of the early universe that does involve rapid expansion. Or it could be talking absolute nonsense with some quantum fairy dust sprinkled on it. It's difficult to tell from your description, which is why we need better references than "I read this somewhere".
HomesliceMMA said:
On my second question, I follow you, but is another way to answer my question there being a simple possibility that: "There was issue regarding all matter in the universe being in too-small a place before the big bang, because it was then all effectively energy, which has zero mass." That sort of thing.
I'm afraid that makes no sense at all.
 
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  • #5
The question can be restarted as "how did the pre-BB condition transition into the post-BB condition". Thing is, we have no idea what was before the BB or even whether this question makes any sense.
 
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  • #6
Another take on this question is that it is a required consequence of our best theories based on what we see around us. That is, given current observations plus general relativity and the standard model, then evolve time backwards, you are led to the big bang state. This is not a necessary consequence of GR and standard model per se, only when combined with what we see. We could instead see galaxies with blueshift instead of redshift, in which case GR would suggest (depending on details) that we are in the collapsing phase of cyclic universe, rather than in a universe that will always expand (the model that best fits current observations). In this way of looking at it, there is no 'reason why' our universe is one way rather than one of many other possible ways.
 
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  • #7
PAllen said:
collapsing phase of cyclic universe
Not knowing if there would be such a thing in a collapsing universe, a civilization might rather conclude that the universe started from a vacuum state, which somehow had a phase change producing the energy and matter. They might wonder, as we do now, from where did all the matter and energy come.
 
  • #8
HomesliceMMA said:
There was issue regarding all matter in the universe being in too-small a place before the big bang, because it was then all effectively energy, which has zero mass.
I have no idea what you are trying to say here. If you are asking whether there is some theoretical issue with the density and temperature being as high as they were at the Big Bang, the answer is no, there isn't.
 
  • #9
256bits said:
Not knowing if there would be such a thing in a collapsing universe, a civilization might rather conclude that the universe started from a vacuum state, which somehow had a phase change producing the energy and matter. They might wonder, as we do now, from where did all the matter and energy come.
Note my phrase "depending on details". For a range of observations, running back in time via GR would mandate a prior expanding phase, and cyclic overall state. There are also sets of observations that would not correspond to cyclic models. The point is, given current observations and best theory, you can extrapolate back in time as well as forward in time. However, you may reach a limit of such extrapolation, beyond which asking "why' is meaningless within current theory.

Also, in BB cosmology, one thing not a mystery is where the matter and energy came from - the pre-BB state. There need never have been a state of nothingness.
 
  • #10
Ibix said:
No one knows the ultimate cause of the Big Bang. The only sensible thing your pop-sic [sic] could be talking about is inflation, which is a theory of the early universe that does involve rapid expansion. Or it could be talking absolute nonsense with some quantum fairy dust sprinkled on it. It's difficult to tell from your description, which is why we need better references than "I read this somewhere".

I'm afraid that makes no sense at all.
Thanks ibix! Why you say that makes no sense at all, what exactly? Would not, prior to the big bang, when all matter (and energy) is (supposedly) concentrated in a size of space of an atom (or smaller), everything not be so hot that any matter was converted to energy (or something like it)? I'm just trying to figure out how the matter that makes up our universe could ever be concentrated into a space so small - is not the answer "hey dude, it ain't matter then, its energy, and energy can be infinite in a single point of space"?

Thanks!
 
  • #11
HomesliceMMA said:
prior to the big bang, when all matter (and energy) is (supposedly) concentrated in a size of space of an atom (or smaller)
This isn't accurate. We believe that the universe is infinite in size and always was, and was always filled with stuff everywhere. The "smaller than an atom" thing is talking about the finite region of the universe that we can see, the observable universe. It's important to distinguish which you're talking about.
HomesliceMMA said:
I'm just trying to figure out how the matter that makes up our universe could ever be concentrated into a space so small
It isn't matter in the ordinary sense. That doesn't mean "matter was energy", which is sci fi technobabble and not meaningful. The theory is that there was a thing called the inflaton field, so named because its presence drives very rapid inflation, and all the energy was carried in that field. At some point all the energy condensed out of that field and is picked up by the normal matter fields, and we're on the road to the universe we see today.
 
  • #12
HomesliceMMA said:
Would not, prior to the big bang, when all matter (and energy) is (supposedly) concentrated in a size of space of an atom (or smaller), everything not be so hot that any matter was converted to energy (or something like it)?
Energy is not a 'thing'. Energy is a property of 'things'. It does not exist on its own. There are various forms of energy, but they are all associated with the movement and configuration of objects, fields, and systems of objects and fields.

HomesliceMMA said:
I'm just trying to figure out how the matter that makes up our universe could ever be concentrated into a space so small - is not the answer "hey dude, it ain't matter then, its energy, and energy can be infinite in a single point of space"?
No, as energy is not found by itself.

Quantum objects are not like normal, macroscopic objects that you're used to. Your misunderstand likely lies in a few key things:

1. They can, when appropriate, 'overlap' each other in some sense. For example, the proton and neutron found in a deuterium nucleus are not two spheres nudged up against one another. They literally occupy the same space.

2. Extreme energy densities create a sort of plasma where particles and very high-energy radiation are being created and destroyed all the time.

3. Extremely high energy densities result in the sustained creation of very massive, very high energy particles that don't exist usually. Things like top quarks, which are about 180 times more massive than a proton and don't exist outside of particle colliders, are very common once you have a super high energy plasma. This means that there are fewer numbers of particles than you might otherwise think since there are a lot of very massive particles that all have very high kinetic energies.

4. At these extreme energies and densities, the distance scales of interactions change. Instead of having atoms, molecules, and electrons who normally interact mostly through long-range EM and gravitational forces, you have high-mass, high-energy particles that are normally found in things like atomic nuclei and interact through short-range forces like the strong force. Everything is MUCH more compact. Think white dwarf or neutron star levels of compactness.

5. At high energies, particles don't stay far apart from each other (far meaning atomic/inter-atomic distances). They get very, very close without being repelled since they have so much energy. Think nuclear fusion, where nuclei get thousands of times closer than they usually do thanks to their kinetic energies, but orders of magnitude higher energy.

The combination of all these let all this matter occupy small volumes. High-mass, high-energy particles interacting with short-range forces, that can get very, very close to each other and aren't set into (relatively) large structures through inter-atomic bonds like normal matter often is.

At even higher energy scales we may have a complete breakdown of known physics. All these particles and radiation that I'm talking about might not even exist. Instead there may be an unknown type of field (with a corresponding particle to that field) that behaves very differently that contains all of this energy. Such a field might be something like the inflaton field/particle found in inflation models.
 
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  • #13
Ibix said:
This isn't accurate. We believe that the universe is infinite in size and always was, and was always filled with stuff everywhere. The "smaller than an atom" thing is talking about the finite region of the universe that we can see, the observable universe. It's important to distinguish which you're talking about.

It isn't matter in the ordinary sense. That doesn't mean "matter was energy", which is sci fi technobabble and not meaningful. The theory is that there was a thing called the inflaton field, so named because its presence drives very rapid inflation, and all the energy was carried in that field. At some point all the energy condensed out of that field and is picked up by the normal matter fields, and we're on the road to the universe we see today.
So wait a second Ibix, in that second paragraph, you said "matter was energy" is sci fi technobabble, but later on in that same paragraph you said "At some point all the energy condensed out of that field and is picked up by the normal matter fields, and we're on the road to the universe we see today." Those seem pretty damned close to me. :)
 
  • #14
"Energy is not a 'thing'. Energy is a property of 'things'. It does not exist on its own. There are various forms of energy, but they are all associated with the movement and configuration of objects, fields, and systems of objects and fields."Ohhhh, I got it Drakkith, thanks. Ibix, you can disregard my reply to you immediately above, got it now. Energy is not a thing, but properties of a thing. So whatever was there at the big bang had high energy, but it was not energy itself.

Thanks so much!
 
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  • #15
rakkith, reading through the rest of your awesome post, had questions on a couple of them:

"2. Extreme energy densities create a sort of plasma where particles and very high-energy radiation are being created and destroyed all the time."

When you say "extreme energy densities", because, as you explained, energy is not a separate thing, but properties of other things, I guess you mean "objects/fields with extreme energy densities"?

"4. At these extreme energies and densities, the distance scales of interactions change. Instead of having atoms, molecules, and electrons who normally interact mostly through long-range EM and gravitational forces, you have high-mass, high-energy particles that are normally found in things like atomic nuclei and interact through short-range forces like the strong force. Everything is MUCH more compact. Think white dwarf or neutron star levels of compactness."

Yea, this is directly addressing what I, as a layman, see as a "WTF, does that make sense?" problem. For someone to say, all the matter we see today was compacted into a space smaller than an atom right before the big bang, my natural reaction is to question that. I mean, I know atoms are like 99.99% space, but even then could you really compact all matter in the universe into that space? There is a LOT of matter in the universe, and an atom is pretty darned small in relation. So I'm trying to get at the simplest explanation for that that I can understand, it sounds like that is something like "immediately before the big bang there was not matter (at least not matter per se), but only fields with an extremely high energy, out of which all the matter we can see today coalesced after the big bang", something like that!?

Everything else I follow, loud and clear!

Thanks!!!
 
  • #16
@HomesliceMMA, please learn to use the Quote feature to include direct quotes in your posts from posts you are replying to, instead of just cutting and pasting the quotes and putting them in quotation marks. If you highlight the text you want to respond to, you will see a little popup with "Quote" and "Reply" options; clicking "Reply" puts the highlighted text in quotes in the nearest post editing window.
 
  • #17
HomesliceMMA said:
For someone to say, all the matter we see today was compacted into a space smaller than an atom right before the big bang, my natural reaction is to question that.
Why is that your natural reaction? What model of matter are you using that predicts something different?

HomesliceMMA said:
immediately before the big bang there was not matter (at least not matter per se), but only fields with an extremely high energy
What you are calling "matter" is still "fields" (quantum fields), just with much lower energy density. They are not different things. They are just different states of the same underlying thing (the same quantum fields).
 
  • #18
PeterDonis said:
@HomesliceMMA, please learn to use the Quote feature to include direct quotes in your posts from posts you are replying to, instead of just cutting and pasting the quotes and putting them in quotation marks. If you highlight the text you want to respond to, you will see a little popup with "Quote" and "Reply" options; clicking "Reply" puts the highlighted text in quotes in the nearest post editing window.

Thank you. I think I follow, will do!
 
  • #19
PeterDonis said:
Why is that your natural reaction? What model of matter are you using that predicts something different?What you are calling "matter" is still "fields" (quantum fields), just with much lower energy density. They are not different things. They are just different states of the same underlying thing (the same quantum fields).

Yea, I've modeled it out and come up with inconsistent results. No modeling or model, LOL.

It may be a simple notion, but it should be a simple notion to follow, as well. I've stated it a few times now, but I'll state it again. I know an atom has a lots of "space" in it, I.E. electrons are far, far away from protons/neutrons, but it seems a little funny to say all the matter of this universe, include all the millions, billions, or even infinite (based on the thread you closed LOL) black holes, and all the other matter in the universe, could fit inside the space of an atom. I'm just looking for a simple explanation of that. Plain English. Can matter just "compress" indefinitely? Is there no limit at all? Is there no minimum threshold into which things can compress? No like "plank distance" or "plank unit" or something similar below which things cannot compress? The answer I THINK I'm hearing, and which makes sense to me, is that back then it (or at least a lot of it), was not matter, but really just fields with a very, very high energy level (temperature). After the big bang happened the matter we see coalesced out of that. And there is no limit to energy levels fields can have. Does that not sound right?
 
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  • #20
HomesliceMMA said:
When you say "extreme energy densities", because, as you explained, energy is not a separate thing, but properties of other things, I guess you mean "objects/fields with extreme energy densities"?
Yes, 'high energies' or 'high energy densities' is shorthand for 'stuff with high energy' or 'extremely high density of objects that themselves have extremely high energies'.
HomesliceMMA said:
I mean, I know atoms are like 99.99% space, but even then could you really compact all matter in the universe into that space? There is a LOT of matter in the universe, and an atom is pretty darned small in relation.
It wouldn't be matter as you know it, if at all. It would either be extremely high energy exotic particles that you only find in particle colliders, or it would be something we've never seen before.

And while an atom is indeed a very small space, remember that normal matter is rather spread out in the universe. First, there's a whole lot of empty space between stuff on average. We have millions of lightyears between galaxies that are virtually empty. So get rid of all that empty space. Now get rid of all the empty space inside of galaxies between the stars. Now get rid of all the empty space between all objects in all solar systems. Now compress all of that matter into itself so it's about as dense as a neutron star, which is about 10^17 times more dense than ordinary matter.

Just doing that we've taken the matter in the entire visible universe and reduced it from occupying a region that's about 100 billion lightyears across, with billions of galaxies inside it, into a region that's more comparable to the size of a few galaxies (note: very handwavy estimate on that size). And this is still within a density scale that we understand fairly well, that of nuclear material (the stuff inside atomic nuclei).

Also, understand that the 'size of an atom' estimate is a VERY rough estimate that's not based on particle physics, but on a much simpler model that only looks at the energy density of space. As we run the cosmological clock backwards, we see that the energy density increases as everything contracts and gets closer together. There's a certain point in this process that the energy density gets so high that our gravitational equations start to spit out infinities, letting us know we've likely screwed up and don't understand physics well enough at this scale to make accurate predictions. The size of the observable universe at this point where our math breaks down is somewhere around the size of an atom.

But given our lack of knowledge about physics at this point in time, it's likely that our size estimate is off by a lot as well.
 
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  • #21
HomesliceMMA said:
I know an atom has a lots of "space" in it, I.E. electrons are far, far away from protons/neutrons, but it seems a little funny to say all the matter of this universe, include all the millions, billions, or even infinite (based on the thread you closed LOL) black holes, and all the other matter in the universe, could fit inside the space of an atom.
Remember that we're talking about the size of the observable universe, not the whole thing. So there's no infinities to worry about.
 
  • #22
HomesliceMMA said:
On my main question, so its sounds like know one knows - are there any ideas that people have floated?
No one knows, but sure there are ideas. One idea for example is brane cosmology, which states that our universe is restricted to a 4D brane existing in a higher dimensional space, like the setting you have in type II string theories. This higher dimensional space could contain more than one brane, and the collision of two such branes could have caused the Big Bang. This model has some issues though.

However, there are many other models, although none of them is well-established for the time being.

For the brane model, see for example:

P. J. Steinhardt, N. Turok (2002). "Cosmic Evolution in a Cyclic Universe"
P. J. Steinhardt, N. Turok (2001). "A Cyclic Model of the Universe"
P. J. Steinhardt, N. Turok (2005). "The Cyclic Model Simplified"
 
  • #23
HomesliceMMA said:
I've modeled it out and come up with inconsistent results.
Um, what? Why don't you just read a textbook on quantum field theory? Why are you trying to invent your own models? Even leaving aside the fact that personal theories are off limits here at PF, you would be much better served by learning the theories that already exist and have been shown to make accurate predictions.

HomesliceMMA said:
all the other matter in the universe, could fit inside the space of an atom. I'm just looking for a simple explanation of that. Plain English.
There is no explanation that you would call "simple" and "Plain English" because you are insisting on interpreting things using your intuition, and your intuition is wrong.

HomesliceMMA said:
Can matter just "compress" indefinitely?
Yes. But note that in the very early universe, matter was expanding very rapidly; it was not just sitting there at very high density.

HomesliceMMA said:
Is there no limit at all? Is there no minimum threshold into which things can compress? No like "plank distance" or "plank unit" or something similar below which things cannot compress?
There are speculations that the Planck density might be some kind of limit. But the Planck density is still many orders of magnitude denser than the densest states we have evidence for. So it does not impose any kind of limit that comes into play in our best current model.

HomesliceMMA said:
The answer I THINK I'm hearing, and which makes sense to me, is that back then it (or at least a lot of it), was not matter, but really just fields with a very, very high energy level (temperature).
No. Go read the last paragraph of my post #17.
 
  • #24
Drakkith said:
And while an atom is indeed a very small space, remember that normal matter is rather spread out in the universe. First, there's a whole lot of empty space between stuff on average. We have millions of lightyears between galaxies that are virtually empty. So get rid of all that empty space. Now get rid of all the empty space inside of galaxies between the stars. Now get rid of all the empty space between all objects in all solar systems. Now compress all of that matter into itself so it's about as dense as a neutron star, which is about 10^17 times more dense than ordinary matter.

Just doing that we've taken the matter in the entire visible universe and reduced it from occupying a region that's about 100 billion lightyears across, with billions of galaxies inside it, into a region that's more comparable to the size of a few galaxies (note: very handwavy estimate on that size). And this is still within a density scale that we understand fairly well, that of nuclear material (the stuff inside atomic nuclei).

Never thought of it that way - thanks for a new perspective.
 
  • #25
Nobody has yet linked to the Family Guy clip? Really?

Ok, here goes:



Now you understand evolution too.
 
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Related to How did the universe start and evolve into what it is today?

1. What caused the Big Bang?

The exact cause of the Big Bang is still unknown and is a topic of ongoing scientific research. Some theories suggest that it was triggered by a quantum fluctuation, while others propose the existence of a "multiverse" where our universe is just one of many. Ultimately, the cause of the Big Bang is still a mystery.

2. Was the Big Bang a one-time event?

According to current scientific understanding, the Big Bang was a one-time event that marked the beginning of our universe. However, some theories suggest that there may have been multiple Big Bangs, leading to the creation of multiple universes.

3. How long ago did the Big Bang happen?

The current estimate for the age of the universe is about 13.8 billion years. This is based on observations of the cosmic microwave background radiation, which is the leftover energy from the Big Bang. However, the exact timing of the Big Bang is still a subject of ongoing research and debate.

4. Did the Big Bang create everything in the universe?

The Big Bang is believed to have created the basic building blocks of our universe, such as protons, neutrons, and electrons. However, it did not create everything in the universe. For example, elements like carbon and oxygen were formed later through the processes of nuclear fusion in stars.

5. Will the universe eventually stop expanding?

Current evidence suggests that the universe is expanding at an accelerating rate, meaning it will continue to expand indefinitely. However, this is also an area of ongoing research and there are some theories that suggest the expansion could eventually slow down or even reverse.

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