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dgh64
2010-Jun-21, 05:31 PM
My dad asked me the other day, "Where did the Big Bang happen?"

Knowing almost nothing on the subject, I made something up. I said "It happened right here." and I pointed at my left knee.

Since stars and galaxies are pretty much all moving away from each other (at least on a large scale) and there is no "edge" to the known universe, it's impossible to tell where the big bang happened, right? That's what I said after he stopped laughing.

He also wants to know what there was before the big bang, and I said something like "They think that the mass of the whole universe was concentrated in a single, infinitely dense point, but there's no way to know that, either."

BigDon
2010-Jun-21, 07:15 PM
As time began with the BB there was no before...

dgh64
2010-Jun-21, 07:22 PM
Really? Wow... you just boggled my mind.

Swift
2010-Jun-21, 07:32 PM
My dad asked me the other day, "Where did the Big Bang happen?"

Knowing almost nothing on the subject, I made something up. I said "It happened right here." and I pointed at my left knee.

Since stars and galaxies are pretty much all moving away from each other (at least on a large scale) and there is no "edge" to the known universe, it's impossible to tell where the big bang happened, right? That's what I said after he stopped laughing.

Yes, your left knee is as good a spot as anywhere else. The Big Bang happened everywhere in the Universe at once. And, as BigDon said, it is impossible to define "before".

Ken G
2010-Jun-21, 07:38 PM
Yes, I think your answers are fine. You might try a related tack, by asking in return, "where did 2009 happen?" The Big Bang is a story about time, not a story about place-- the "cosmological principle" says that the story plays out the same everywhere.

George
2010-Jun-21, 07:55 PM
Yes, your left knee is as good a spot as anywhere else. Agreed, I like that since a good place to start has been kneeded. ;)

forrest noble
2010-Jun-22, 04:34 AM
Question about the Big Bang...

My dad asked me the other day, "Where did the Big Bang happen?"

Knowing almost nothing on the subject, I made something up. I said "It happened right here." and I pointed at my left knee.

Since stars and galaxies are pretty much all moving away from each other (at least on a large scale) and there is no "edge" to the known universe, it's impossible to tell where the big bang happened, right? That's what I said after he stopped laughing.

He also wants to know what there was before the big bang, and I said something like "They think that the mass of the whole universe was concentrated in a single, infinitely dense point, but there's no way to know that, either."


Whether or not the BB is the correct cosmological model or not, for your dad's two questions I think the answers to his questions are properly explained by this model.

"Where did the Big Bang happen?" This model asserts that all of space was created by the expansion of the original matter meaning that all of space is a part of the original space meaning that the space that your knee occupies and the space surrounding it, is accordingly a part of the beginning location of the universe however big or small that beginning might have been.


He also wants to know what there was before the big bang

Again the standard BB explanation is that not only space but time is matter dependent, meaning that there was no such a thing as time before the beginning of matter, space, and the first changes. There was accordingly no time or changes that occurred before the first change(s).

Cougar
2010-Jun-22, 02:06 PM
They think that the mass of the whole universe was concentrated in a single, infinitely dense point...

Well, not literally. "Infinitely dense" makes no sense. Basically, our observations, experiments, logic, and math can take us back only so far. When the math starts giving answers involving infinity (which it does), that means the math and the theory are just not powerful enough to give a meaningful answer.

Remarkably, most physicists, astrophysicists, and cosmologists are in agreement as to the state of the universe just 1 second after the "beginning," and they actually have evidence to support that position.


...but there's no way to know that, either.

We don't know if the conditions/state of the very "beginning" can be known. There may be a way. But we certainly don't know now.

dgh64
2010-Jun-22, 02:19 PM
Well, thank you all for your answers. I'll now go baffle him with knowledge now :)

George
2010-Jun-22, 09:15 PM
Well, thank you all for your answers. I'll now go baffle him with knowledge now :) It is usually helpful to back into the answers that you now have. There is solid evidence from many different types of observations that has led theorists to where they are today. If you highlight some of the steps and explain them then the BBT just falls into place, but that takes time and many are too impatient to hear these details even though it is one of the greatest scientific stories of all time.

Some steps to BBT include:
1) Einstein's Gen. Rel. theory which states that the mass of the universe should cause our universe to collapse due to gravity. [Einstein had to quickly add a fudge factor (ie cosmological constant) to give it the balance it needed to prevent collapse.]
2) Lemaitre and Freidman both independently recognized that GR suggests the universe must be expanding if it isn't collapsing. Lemaitre introduced his "Primordial Atom" based on the idea that if you rewind the clock of an expanding universe you end up with a beginning all at one small space.
3) Like many today, and perhaps your father is one, this idea was silly and Einstein called Lemaitre's model (physics) abominable, though he admired the math. :)
4) Vesto Slipher discovered Doppler redshift in galaxies, which was our first clue that things were moving away from each other.
5) Edwin Hubble discovered that galaxies were indeed moving away from each other at a rate that increased with distance (Hubble Constant). This meant that the universe is expanding.
6) Soon a great deal of supporting evidence came along and BBT bumped the old Static Theory off its small throne.

There is a list of these supporting lines of evidence found in the Big Bang Bullets (http://www.bautforum.com/showthread.php/8241-Big-Bang-Bullets-gt?p=148135#post148135) thread.

The Big Kahuna evidence comes from the CMBR, which was predicted by the theory.

Swift
2010-Jun-22, 09:25 PM
The Big Kahuna evidence comes from the CMBR, which was predicted by the theory.
CMBR = Cosmic Microwave Background Radiation. If you "look" in any direction in the Universe, you see a "glow" of microwaves that seems to fill the Universe. This is the signature leftover from the Big Bang. (look and glow are in quotes as one usually thinks of those terms for visible light, not microwaves, at least in everyday use).

George
2010-Jun-22, 10:14 PM
CMBR = Cosmic Microwave Background Radiation. If you "look" in any direction in the Universe, you see a "glow" of microwaves that seems to fill the Universe. This is the signature leftover from the Big Bang. (look and glow are in quotes as one usually thinks of those terms for visible light, not microwaves, at least in everyday use). Thanks, I tend to take shortcuts by using acronyms, but they ain't very short if I have to spell them out. :) A few acronyms should be required prerequisites for everyone: BBT, GR, QM, CMB, CMBR, BAUT, GUT, TOE, IIRC and BYOB. :)

Argos
2010-Jun-22, 10:20 PM
Thanks, I tend to take shortcuts by using acronyms, but they ain't very short if I have to spell them out. :) A few acronyms should be required prerequisites for everyone: BBT, GR, QM, CMB, CMBR, BAUT, GUT, TOE, IIRC and BYOB. :)

ToSeek is your friend (http://www.bautforum.com/showthread.php/72891-Frequently-asked-questions?p=1229337#post1229337).

George
2010-Jun-23, 02:43 AM
ToSeek is your friend (http://www.bautforum.com/showthread.php/72891-Frequently-asked-questions?p=1229337#post1229337).
Ah ha! But no CMBR? :)

Gomar
2010-Jun-23, 03:21 AM
Newton: "An item at rest shall remain at rest unless acted upon by an extarnal force" right?

ok, so what force caused the matter to go big bang? this beginning matter had to have come from somewhere. It couldnt just have materialised from empty space. If there was no universe before the BB, then in what did this matter exist in?

01101001
2010-Jun-23, 03:29 AM
ok, so what force caused the matter to go big bang? this beginning matter had to have come from somewhere. It couldnt just have materialised from empty space. If there was no universe before the BB, then in what did this matter exist in?

OK, so, Misconceptions about the Big Bang by Lineweaver and Davis (http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf) (half-megabyte PDF)


Baffled by the expansion of the universe? You're not alone. Even astronomers frequently get it wrong

(From BAUT topic ** FAQs ** Resources On The Web (http://www.bautforum.com/showthread.php/22865-**-FAQs-**-Resources-On-The-Web), still worth reading.)

Geo Kaplan
2010-Jun-23, 03:35 AM
Newton: "An item at rest shall remain at rest unless acted upon by an extarnal force" right?

ok, so what force caused the matter to go big bang? this beginning matter had to have come from somewhere. It couldnt just have materialised from empty space. If there was no universe before the BB, then in what did this matter exist in?

A couple of things: The big bang more properly describes a sudden expansion of space itself. The popular picture of an explosion of matter into an implicitly pre-existing space is unfortunate, for it is grossly misleading.

As to what caused the big bang, no one knows, although there's no shortage of ideas. One that has gained some adherents recently is the "ekpyrotic universe" hypothesis. Google that term, and I'm sure you'll enjoy reading about collisions of branes, etc. However, you will see that the hypothesis says nothing about where the initial universes came from...

As to your assertion that the universe could not have materialised from empty space, recognize that it is just that -- an assertion. Unless you are privy to some deeper knowledge than the rest of us, you have to keep your mind open to possibilities that may just be beyond your imagination.

Argos
2010-Jun-23, 01:13 PM
Ah ha! But no CMBR? :)

Just submit it to him. IŽm sure heŽll be glad to add it. :)

dreadpirateemily
2010-Jun-23, 01:39 PM
I like Timothy Ferris' answer to both questions:
"The big bang happened everywhere. At Time Zero, all places were the same place."
"Nobody knows, but one possibility is that "our" universe began as a bubble arising from a bit of space in a previously-existing universe."

Cougar
2010-Jun-23, 04:38 PM
I like Timothy Ferris' answer to both questions...

Welcome to the board, dreadpirateemily. I agree - Timothy Ferris's early works are quite good. I always liked this quote of his:






"Making a model of the universe is like trying to pitch a tent on a moonless night in a howling Arctic wind. The tent is theory. The wind is experiment. When one gets to the precipice, where the secure lands of the known have been left behind and the dark canyons of the unknown fill one's field of view, it becomes very difficult to guess just where to set the tent pegs and to predict which ones will hold once the wind comes up."


"Nobody knows, but one possibility is that "our" universe began as a bubble arising from a bit of space in a previously-existing universe."

Lots of people, even well-known scientists, are doing a lot of speculating these days. They're putting "tents" all over the place, specifically where there is no "wind" to test how secure they are. And they're not using tent pegs!

Click Ticker
2010-Jun-23, 04:42 PM
5) Edwin Hubble discovered that galaxies were indeed moving away from each other at a rate that increased with distance (Hubble Constant). This meant that the universe is expanding.

Every once in a while a light goes on in my head. Of course, that doesn't mean I actually understand things better.

Galaxy's moving faster at increased distance. Is this because we are looking farther back in time, closer to the big bang and thus closer to the time when acceleration started?

Galaxy's closer are moving slower because more time has elapsed for them since the big bang and they are losing momentum?

Or am I way off?

Shaula
2010-Jun-23, 05:06 PM
Way off I am afraid. Galaxies are moving faster the further away they are because space is expanding. In fact current best estimates put the rate of this expansion as getting faster with time - so looking back in the universe galaxies are actually moving more slowly than expected (if you had assumed that the current rate of expansion was the same as it had always been).

Galaxies are not losing momentum (I guess they might lose a minute amount due to friction from the ISM) - the Big Bang was not like a physical explosion that threw them all out. They are being swept along as space expands.

George
2010-Jun-23, 05:08 PM
Galaxy's moving faster at increased distance. Is this because we are looking farther back in time, closer to the big bang and thus closer to the time when acceleration started? It can be a bit mind boggling, but this is a good question and the answer is understandable, but I always have to stop and think about it since it is unnatural.

Contrary to what I orginally thought was true some time ago -- I am still just and amateur -- it is held that the receeding radial speed galaxies have relative to us will be the same today and a billion years from now.... more or less. [This is no longer true since the discovery that our universe is now in an acceleration mode for expansion, but it isn't a huge factor, so let's ignore it for now.]

This means that the ~ 71 kps/Mpc Hubble Constant tells us that a galaxy that is, say, 1 billion lightyears (~ 300 million parsecs; 300 Mpc) away from us will have a radial velocity (motion that is directly away from us) of about 21,00 kps (kilometers per sec.). But a million years from now, though it will be further from us, it will still have about the same speed, ignoring the acceleration fator I mentioned. [For this reason, if you like mind-boggling, galaxies that are traveling faster than the speed of light away from us can still be observed by us, and we have some threads on this if you're interested.]

So, surprsingly, time is not a big deal in this case.

blueshift
2010-Jun-24, 02:16 AM
Newton: "An item at rest shall remain at rest unless acted upon by an extarnal force" right?

ok, so what force caused the matter to go big bang? this beginning matter had to have come from somewhere. It couldnt just have materialised from empty space. If there was no universe before the BB, then in what did this matter exist in?The problem with this view is that it breaks down at the quantum level, which was the size of the universe in the beginning. At the quantum level, cause and effect does not exist. Probability does.

whimsyfree
2010-Jun-24, 03:23 AM
he Big Bang happened everywhere in the Universe at once. And, as BigDon said, it is impossible to define "before".

Does that work for theists too?

George
2010-Jun-24, 03:56 AM
Does that work for theists too? Sure, for most anyway. BBT began from a Belgian priest (Lemaitre) and the Catholic Church saw it as a likely Genesis event. Fortunately, Lemaitre and others convinced them to chill and let science be science.

pzkpfw
2010-Jun-24, 04:38 AM
whimsyfree (and everyone), let's not take this thread down that path. See rule 12.

Jens
2010-Jun-24, 05:27 AM
Newton: "An item at rest shall remain at rest unless acted upon by an extarnal force" right?

ok, so what force caused the matter to go big bang? this beginning matter had to have come from somewhere. It couldnt just have materialised from empty space. If there was no universe before the BB, then in what did this matter exist in?

Thankfully, Newton hadn't been born at the time of the big bang, so it wasn't necessary to obey his laws.

whimsyfree
2010-Jun-24, 09:44 PM
whimsyfree (and everyone), let's not take this thread down that path. See rule 12.

Rule 12 is not relevant to my post.

Infinitenight2093
2010-Jun-24, 11:48 PM
He also wants to know what there was before the big bang, and I said something like "They think that the mass of the whole universe was concentrated in a single, infinitely dense point, but there's no way to know that, either."

That was only a single point in time. The point just before the universe inflated to cosmic proportions. There are many theories trying to explain what really happened before our universe was here. One such theory called Chaotic Inflation (first proposed by Andrei Linde) says that maybe our universe came from a previous universe that suddenly inflated, giving rise to our existence. Others say that maybe two parallel universe came into contact with one another and birthed our universe out of the impact. I believe that time did not suddenly start at the BB, rather it has been flowing from, and into eternity. In other words, there have been an infinite number of universes before ours, and an infinite number of universes after ours. These universes, including ours, can be thought of as branches of a tree that make up something called the Multi-verse.

Cougar
2010-Jun-25, 12:38 AM
One such theory called Chaotic Inflation (first proposed by Andrei Linde) says that maybe our universe came from a previous universe...

Others say that maybe two parallel universes...

I believe that...

Of course, none of these has a shred of evidence. Our own inflationary epoch has some modest observational support, but that implies nothing about any "other universes."

WayneFrancis
2010-Jun-25, 12:47 AM
Rule 12 is not relevant to my post.

Do you not understand that "theists" in your quote below is a discussion of religious views?


Does that work for theists too?

WayneFrancis
2010-Jun-25, 12:49 AM
Of course, none of these has a shred of evidence. Our own inflationary epoch has some modest observational support, but that implies nothing about any "other universes."

Well put.
We have a good understanding of what our early universe was like. What caused it may never be known. What was before it...well if there was a "beginning" to space time then that question has no meaning the way it is worded. Much like asking what the first positive whole number before zero is. It is undefined.

George
2010-Jun-25, 02:16 AM
Rule 12 is not relevant to my post. The cautionary note is not inappropriate. Notice that the warning wasn't that we were on the wrong path, but that it was lying before us. In the past, it wasn't surprising to see posters jump in and derail a thread with unfriendly religious mud-throwing, which is why the rule exists.

There are a number of important threads that address religion in the context of science, but the OP is another direction from religious viewpoints. Parallel universes "theories" are close behind them. Get 'em Cougar! :)

pzkpfw
2010-Jun-25, 09:27 AM
I'd like to point out that replying to an off-topic or rule-breaking/bending post is almost as off-topic or rule-breaking/bending.

kevin1981
2010-Jun-25, 12:47 PM
That was only a single point in time. The point just before the universe inflated to cosmic proportions. There are many theories trying to explain what really happened before our universe was here. One such theory called Chaotic Inflation (first proposed by Andrei Linde) says that maybe our universe came from a previous universe that suddenly inflated, giving rise to our existence. Others say that maybe two parallel universe came into contact with one another and birthed our universe out of the impact. I believe that time did not suddenly start at the BB, rather it has been flowing from, and into eternity. In other words, there have been an infinite number of universes before ours, and an infinite number of universes after ours. These universes, including ours, can be thought of as branches of a tree that make up something called the Multi-verse.


Of course, none of these has a shred of evidence.

When i first learnt about those ideas, i thought to myself, it all makes sense now because there was an answer to why it happened, how it happened and they validate the fine tuning problem. These days i have come to except that, up till around a second after the initial expansion (bang) we have absolutely no idea what was going on. There may have been a "before" the big bang, there may have not, but truth be told, we have no idea.

It is however, still fun to speculate :)

AriAstronomer
2010-Jun-25, 01:39 PM
The idea is correct to say that the big bang happened everywhere. Think of the big bang occurring on a single pixel. As time goes on, we are zooming in on that pixel, but the co-ordinates of the entire square are still (1,1). As for galaxy expansion, the most popular example for explaining how the farther a galaxy is away, the faster it seems to be receding is to put evenly spaced dots on a balloon. If we choose 3 dots, labeled a, b, and c (with b in the middle, and a and c on either side of it), as the balloon expands, even though a,b and c are all traveling the same speed, c will appear to be moving faster than b w.r.t. a, even though b (in the middle) will see a and c moving away at the same speed.

George
2010-Jun-25, 01:49 PM
It is however, still fun to speculate :) Speculation is both fun and the earliest stage for something that may prove very fruitful. Those that claim the multiuniverse theory explain the origin for the Big Bang are putting their imagined fruit way ahead of any plant that can bear it. I see it as speculation that deserves genuine attention.

kevin1981
2010-Jun-27, 11:43 AM
I see it as speculation that deserves genuine attention.
That is a fair point. I like the idea of eternal inflation, that there are universes bubbling off, of each other. All i am saying is that, there are lots of ideas floating about but we have no evidence for them.(yet) So if someone wants a straight answer to why and where the universe came from, i would say we do not know.

George
2010-Jun-27, 01:49 PM
That is a fair point. I like the idea of eternal inflation, that there are universes bubbling off, of each other. All i am saying is that, there are lots of ideas floating about but we have no evidence for them.(yet) So if someone wants a straight answer to why and where the universe came from, i would say we do not know. Yes, but it is incredible to me just how close we have come. Often this gets ignored in the wake of the big question of the origin itself

Gomar
2010-Aug-02, 02:30 PM
The problem with this view is that it breaks down at the quantum level, which was the size of the universe in the beginning. At the quantum level, cause and effect does not exist. Probability does.

Fine... whatever that may mean. However, the BB did occur at some point in time, and did not occur at another. What I mean is _why_ didnt it happen 1,000years or 10 days or 10 hours before it did? How long did it exist in that (unexploded) state, and where did it originally come from?
If there was no universe, then matter cannot exist inside of or within nothing.
If the BB created the universe, then something created the BB and the matter which exploded inside the universe which became stars, planets, etc.
Some external force(s) caused the matter to finally explode, and that's what we call the BB.

caveman1917
2010-Aug-02, 02:46 PM
Fine... whatever that may mean. However, the BB did occur at some point in time, and did not occur at another. What I mean is _why_ didnt it happen 1,000years or 10 days or 10 hours before it did? How long did it exist in that (unexploded) state, and where did it originally come from?

The main problem is that the equations 'blow up' at the point of the Big Bang. At this t=0 point a singularity is reached. Wether that singularity is something 'real' or a sign that our current theory is lacking, we simply can't tell. There is no theory at all that describes this t=0 point, only t>0 is described (and even then quite shaky at the very first moments). Granted, some theories do exist which attempt to describe this moment, but as they stand now there is no way to tell them apart from eachother. And they all provide different explanations.



If there was no universe, then matter cannot exist inside of or within nothing.

Matter only formed much later after the Big Bang.


If the BB created the universe, then something created the BB

The BB is an event which describes the process of a system (the universe), it is not correct to say the BB created the universe, the BB happened to the universe. Or more strictly, the BB is a property of the universe. Not an entity existing outside of it.


and the matter which exploded inside the universe which became stars, planets, etc.

The BB is about the 'explosion' of space, it is the explosion of the (fabric of) the universe. Not any explosion of matter (or energy) inside the universe.


Some external force(s) caused the matter to finally explode, and that's what we call the BB.

Why should this be so? Disregarding the fact previously pointed out re matter.
Take for example the collapse of a cloud of H into a star. At some point the star will begin to fuse stuff. Does this mean it has to be an external force that sets of the process of fusion? Of course not, it is the dynamics of the system which at some moment comes to a 'tipping point' where something will happen, all by itself.

George
2010-Aug-02, 02:48 PM
Fine... whatever that may mean. However, the BB did occur at some point in time, and did not occur at another. What I mean is _why_ didnt it happen 1,000years or 10 days or 10 hours before it did? How long did it exist in that (unexploded) state, and where did it originally come from?

If there was no universe, then matter cannot exist inside of or within nothing.
You are asking great questions that, unfortunately, are outside the realm of science. At this point, one can only speculate about the true origin of our universe including all that come from it: energy, matter and all else.


If the BB created the universe, then something created the BB and the matter which exploded inside the universe which became stars, planets, etc. It is better to say BBT is our best model that seems to match both the observations we see today and what we would expect to find if we reversed the clock. However, this model flys apart when we attempt to go all the way back to t=0.

I like the Darwin "Orign of the Species" analogy because his theory did not address how life first started, but does a nice job at informing us how species likely change and become new species.


Some external force(s) caused the matter to finally explode, and that's what we call the BB. Matter would have been way too hot to even exist. Energy, and maybe something more exotic perhaps, came first; matter formed as soon it was cool enough.

[I see caveman1917 already has mentioned much of this. He beat me to the post. :)]

kevin1981
2010-Aug-02, 03:26 PM
However, the BB did occur at some point in time, and did not occur at another. What I mean is _why_ didnt it happen 1,000years or 10 days or 10 hours before it did?
The Big Bang did not happen at some point in time. Time as we know it, came into existance when space started to expand from some initial state that we don't understand. It did not happen 10 days before or 10 minutes before because there was no time before the expansion of space.

Matter, like stars and planets were not created at the big bang. Energy was created which formed simple atomic elements like Hydrogen and Helium.

These Elements over time got pulled together by gravity, as they formed into bigger clumps they attracted even more Helium and mostly Hydrogen- turning into gigantic clouds of gas.

As these gigantic clouds of gas got so big they started to implode inwards, collapsing under there own weight. This creates massive pressure and heat, then it gets to a point where those atomic Elements start to fuse together to create the first stars.

These first stars burn and create heavier Elements due to the massive heat and pressures.

The stars have rather short lives because they are so big and use up all there fuel quickly- the fuel being mostly hydrogen.

Then after they use up all there fuel they explode, creating new stars and also other debris like rocks.

These rocks bump into each other and get bigger and bigger, again due to gravity. And sometimes these rocks are so big that they can crash into each other and become the size of a planet like ours.

So solid matter like planets and stars did not form at the big bang but tiny atomic elements did, mainly Hydrogen which is the main fuel for stars.

This is a basic model of how stars and planets come into being, i hope it helps you understand a little more.

caveman1917
2010-Aug-02, 08:16 PM
So solid matter like planets and stars did not form at the big bang but tiny atomic elements did, mainly Hydrogen which is the main fuel for stars.

I wanted to point out that H (and He) formed only ~400.000 years after the Big Bang. The nuclei formed earlier (starting around 3 minutes after BB), however they were unable to capture electrons until recombination, so we'd only have H+ and He(2+) for a very long time. Incidentally, this is why we have the CMB emitted at recombination, the universe becoming transparent due to its matter content becoming neutral.

BadTrip
2010-Aug-05, 02:32 AM
You are asking great questions that, unfortunately, are outside the realm of science. At this point, one can only speculate about the true origin of our universe including all that come from it: energy, matter and all else.

It is better to say BBT is our best model that seems to match both the observations we see today and what we would expect to find if we reversed the clock. However, this model flys apart when we attempt to go all the way back to t=0.


Why are these questions outside the realm of science? Not arguing... simply wondering... why is it that attempting to work things out mathematically all the way back to the BB is within the realm of science, but at the point where we recognize, without a doubt, that either the theory is incomplete/lacking or the math is erroneous we then claim that we have reached an impasse because further progression is outside the realm of science?
It's certainly outside of our current theory...outside of our current math...or outside of our ability to comprehend, for one reason or another.... but why would it be outside the bounds of science simply because we don't understand it?

Also...when you "reversing the clock"....are you implying that there is a global/universal clock?

Not trying to argue... just questions.

BadTrip
2010-Aug-05, 02:38 AM
I wanted to point out that H (and He) formed only ~400.000 years after the Big Bang. The nuclei formed earlier (starting around 3 minutes after BB), however they were unable to capture electrons until recombination, so we'd only have H+ and He(2+) for a very long time. Incidentally, this is why we have the CMB emitted at recombination, the universe becoming transparent due to its matter content becoming neutral.

When did photons form?

Shaula
2010-Aug-05, 03:01 AM
When did photons form?
The electroweak unification happens at about 10^15K - which corresponds to somthing like 10^-30 seconds. Well before 10^-12s anyway. Before that there was no EM force as we know it - so I guess strictly speaking photons didn't exist.

Sam5
2010-Aug-05, 04:01 AM
Some steps to BBT include:
1) Einstein's Gen. Rel. theory which states that the mass of the universe should cause our universe to collapse due to gravity.





This was common knowledge among early physicists, after Newton developed his theory of gravity. The universe seemed “static”, but due to all the gravity in the universe, it should be collapsing in on itself. This mystery puzzled Newton and others.

In letters to various other physicists and friends of his, he proposed four ideas about the whole universe: 1) it could be collapsing but there was no way to tell it at that time, 2) the universe could be expanding, caused by some kind of initial “projectile force”, 3) the universe could be rotating, keeping it from collapsing, and 4) the universe could be infinite.

Many of Newton’s letters were published in books after his death, and scientists after Newton studied them and wrote about some of his ideas. Here is his “big bang” idea as outlined or mentioned by writers in the 18th and 19th Centuries:

Here are the comments of Jean Jacques Rousseau (1712–1778), re: Newton’s “projectile force”, which was also sometimes called a “projectile impulse”:
http://www.bartleby.com/34/4/1.html
“Newton discovered the law of attraction; but attraction alone would soon have reduced the universe into one solid mass: to this law, therefore, he found it necessary to add a projectile force, in order to account for the revolution of the heavenly bodies.”

In William Paley’s 1803 astronomy book, Paley mentioned Newton’s expansion and “projectile impulse” ideas. This is a copy of a page from my 1803 copy of his book:
http://i28.tinypic.com/2cp26om.jpg

“But many of the heavenly bodies, as the sun and fixed stars are stationary. Their rest must be the effect of an absence or of an equilibrium of attractions. It proves also that a projectile impulse was originally given to some of the heavenly bodies, and not to others. But further; if attraction act at all distances, there can be only one quiescent center of gravity in the universe: and all bodies whatever must be approaching this center, or revolving around it. According to the first of these suppositions, if the duration of the world had been long enough to allow it, all its parts, all the great bodies of which it is composed, must have been gathered together in a heap round this point.”

This is what Ralph Waldo Emerson said about it in 1844:
”What shall we say of this omnipresent appearance of that first projectile impulse,”
http://www.bartleby.com/5/114.html

Alexander von Humboldt’s “Cosmos” series (4 or 5 volumes), published early in the 19th Century and re-printed many times during that Century, discussed the possibility of an expansion cause by some kind of initial “projectile” force.

Edgar Allen Poe read Humboldt’s books and was fascinated with the idea of an expanding and a possible later contraction of the universe. In 1848 he wrote a highly philosophical and speculative essay about it titled “Eureka”:
http://xroads.virginia.edu/~HYPER/POE/eureka.html
”The assumption of absolute Unity in the primordial Particle includes that of infinite divisibility. Let us conceive the Particle, then, to be only not totally exhausted by diffusion into Space. From the one Particle, as a centre, let us suppose to be irradiated spherically -- in all directions -- to immeasurable but still to definite distances in the previously vacant space -- a certain inexpressibly great yet limited number of unimaginably yet not infinitely minute atoms.

------------

But even in the merely general equability of distribution, as regards the atoms, there appears a difficulty which, no doubt, has already suggested itself to those among my readers who have borne in mind that I suppose this equability of distribution effected through irradiation from a centre. The very first glance at the idea, irradiation, forces us to the entertainment of the hitherto unseparated and seemingly inseparable idea of agglomeration about a centre, with dispersion as we recede from it -- the idea, in a word, of in equability of distribution in respect to the matter irradiated.”

So the first “big bang” idea came from Newton.

mugaliens
2010-Aug-05, 06:55 AM
When did photons form?

Here's a timeline (http://en.wikipedia.org/wiki/History_of_the_universe)of what happened and when. :)

Strange
2010-Aug-05, 08:17 AM
Why are these questions outside the realm of science? Not arguing... simply wondering... why is it that attempting to work things out mathematically all the way back to the BB is within the realm of science, but at the point where we recognize, without a doubt, that either the theory is incomplete/lacking or the math is erroneous we then claim that we have reached an impasse because further progression is outside the realm of science?
It's certainly outside of our current theory...outside of our current math...or outside of our ability to comprehend, for one reason or another.... but why would it be outside the bounds of science simply because we don't understand it?

Because that is the definition of science. If there are no observations or measurements and our current mathematical theories don't apply (because of singularities) then it isn't science. It is simply speculation. It may be informed speculation based on what we currently know, but it isn't science.

That doesn't necessarily mean it will always be beyond science. New data, or an improved version of GR, might allow us to extend our knowledge further. But "why" the big bang happened or what happened "before" are likely to be always outside the domain of science.

George
2010-Aug-05, 02:48 PM
Why are these questions outside the realm of science? Not arguing... simply wondering... why is it that attempting to work things out mathematically all the way back to the BB is within the realm of science, but at the point where we recognize, without a doubt, that either the theory is incomplete/lacking or the math is erroneous we then claim that we have reached an impasse because further progression is outside the realm of science? There is no guarantee of a permanent fixed boundary for science. Either science can address something or it can't. If it can't, then we have a boundary that may or may not be a temporary one. The boundary exists for BBT, though BBT was never about how it all got started. Lemaitre's earliest model (Primeval Atom) started with a something and expanded from there. The tremendous improvements to this model has taken us back almost to a zero moment in time, but physics flys apart just before it gets there. If QM and GR do get unified, this should move the boundary even closer to t=0.


It's certainly outside of our current theory...outside of our current math...or outside of our ability to comprehend, for one reason or another.... but why would it be outside the bounds of science simply because we don't understand it? One of the problems in our society is the lack of understanding as to what science is and what it isn't. Science is founded upon objectivity. This means others must be able to conduct tests that produce equivalent measurements. If any view comes along and it is beyond any form of measurement, then how can science behave like science? It can't. But there are those who imply that it can, and this is a rub since it is a path that would take science and make it meta-science instead. Philosophy and religion would now have some control over it. If so, then the claim that a "theory is just be a theory" could be better argued, but, today, such a statement is completely unfair to science.


Also...when you "reversing the clock"....are you implying that there is a global/universal clock?I suspect so because of the isotropy of space seen in the CMBR. Physics is far more successful, however, with their models of local space.


Not trying to argue... just questions. These are good and importnat questions to ask.

BadTrip
2010-Aug-05, 04:39 PM
Here's a timeline (http://en.wikipedia.org/wiki/History_of_the_universe)of what happened and when. :)

Thank you!

BadTrip
2010-Aug-05, 05:34 PM
Thank you Strange and George, for your replies and responses.

George - I especially appreciate your explanation of there being a boundary for science, which may be temporary or permanent. It would seem to me that we should optimistically view many of these boundaries as temporary and should recognize and classify them as such. It just seems much more reasonable and logical to say that our model is simply not sufficient at this time....or that our math is not sufficiently advanced yet to provide scientific foundation for explanation of singularities, rather than to say that the singularity is outside the bounds of science.
A statement such as that smacks of throwing up one's hands saying we'll never know, never understand it, and we should just drop it. That's not science as I understand it. Perhaps saying that our technology and techniques have not progressed to the necessary levels to be able to explain these things to a proper level of detail.... that sounds like a more scientific statement.

I suspect I'll receive the "whatever floats your boat" treatment here. LOL ....but thank you both for your time!

George
2010-Aug-05, 06:28 PM
George - I especially appreciate your explanation of there being a boundary for science, which may be temporary or permanent. It would seem to me that we should optimistically view many of these boundaries as temporary and should recognize and classify them as such. It just seems much more reasonable and logical to say that our model is simply not sufficient at this time....or that our math is not sufficiently advanced yet to provide scientific foundation for explanation of singularities, rather than to say that the singularity is outside the bounds of science.

A statement such as that smacks of throwing up one's hands saying we'll never know, never understand it, and we should just drop it. That's not science as I understand it. That's a good point since it can be misleading to confuse courrent boundaries with future ones. The great success story of science is its track record of pushing boundaries back.

However, being a little more blunt regarding any clear demarcation for science can be helpful whenever the erroneous view that science is more unbounded pops-up (e.g. multiuniverses). There is no requirement that the boundaries will always be pushed-back anymore than the requirement that any one is forever fixed.


Perhaps saying that our technology and techniques have not progressed to the necessary levels to be able to explain these things to a proper level of detail.... that sounds like a more scientific statement. Yes it is more scientific, though technology and techniques are more tools of science. But such statements can become the fine print, if at all, for some popular science shows. I enjoy those shows, but not as much if I see science being used in any area where it has no purview... at this time.:)

mugaliens
2010-Aug-06, 05:46 AM
There is no guarantee of a permanent fixed boundary for science.

I'm sorry, but I see science as having an asymptotic boundary, in that while there are finite levels of "deeper" knowlege," there are infinate variations thereof with respect to how they might intertwine with that which we already know.

More specifically, if we do discover deeper boundaries into quantum physics, it will likely be more along of the lines of those between chemistry and atomic science, and that of quarks i.e. ever-increasing but more minute levels of of the same, yet, ever-energetic twists thereof.

Meanwhile, the intricate nature of how those interactions manifest themselves at our macroscopic level I feel will (nearly) infinitately about.

I'm excited!

Strange
2010-Aug-06, 09:31 AM
George - I especially appreciate your explanation of there being a boundary for science, which may be temporary or permanent. It would seem to me that we should optimistically view many of these boundaries as temporary and should recognize and classify them as such. It just seems much more reasonable and logical to say that our model is simply not sufficient at this time....or that our math is not sufficiently advanced yet to provide scientific foundation for explanation of singularities, rather than to say that the singularity is outside the bounds of science.

I think scientists are generally very aware that the best understanding we have today is provisional and could change based on new discoveries and/or understanding. Not: could change. It isn't certain that everything we know today is "right" in some absolute sense but, equally, it isn't true that everything we think we know will turn out to be "wrong". Very few scientific theories are completely overthrown; mostly they are just extended. For example, Netonian gravity is still "right" we just know that it is an approximation that needs to be modifed in some situations.


A statement such as that smacks of throwing up one's hands saying we'll never know, never understand it, and we should just drop it. That's not science as I understand it. Perhaps saying that our technology and techniques have not progressed to the necessary levels to be able to explain these things to a proper level of detail.... that sounds like a more scientific statement.

That is not unreasonable. But remember, until we have that technology or more data or better theories, those topics will still be outside the realm of science and anything we say about them will still just be speculation (including the idea that we might one day be able to say something more scientific!)

speedfreek
2010-Aug-06, 05:24 PM
However, the BB did occur at some point in time, and did not occur at another. What I mean is _why_ didnt it happen 1,000 years or 10 days or 10 hours before it did?
How do you know it didn't? ;)

All we can do is estimate the time that has elapsed since it happened. We cannot compare when it happened with anything but what has happened since.

Sir Knots A Lot
2010-Aug-06, 06:15 PM
Would a white hole from the Kruskal-Szekeres coordinate system look like the Big Bang in a localized area of space?

George
2010-Aug-06, 06:17 PM
I'm sorry, but I see science as having an asymptotic boundary, in that while there are finite levels of "deeper" knowlege," there are infinate variations thereof with respect to how they might intertwine with that which we already know.

More specifically, if we do discover deeper boundaries into quantum physics, it will likely be more along of the lines of those between chemistry and atomic science, and that of quarks i.e. ever-increasing but more minute levels of of the same, yet, ever-energetic twists thereof.

Meanwhile, the intricate nature of how those interactions manifest themselves at our macroscopic level I feel will (nearly) infinitately about. I am unclear what you are saying. Are you saying there are some boundaries that are forever fixed?

BadTrip
2010-Aug-07, 02:25 AM
.....But remember, until we have that technology or more data or better theories, those topics will still be outside the realm of science and anything we say about them will still just be speculation (including the idea that we might one day be able to say something more scientific!)

Well stated Strange.... I suppose I'm just having issues with the semantics. I believe there are things that are outside the boundaries of science. ...such as: "why did one lie on that resume", or "prove that you loved your father."
So just for clarity, I'm not presuming science can answer everything. I just don't "feel" that it's correct to state that things are outside the realm of science simply because we don't understand them yet.

Not trying to pick a fight or anything of that nature... just my own views, etc. And I appreciate you offering yours and explaining things.

heusdens
2010-Aug-07, 03:21 PM
As time began with the BB there was no before...

Time does not "begin". To begin something it already is presupposed that time exists, else the phrase "begin" is meaningless.

Nereid
2010-Aug-07, 05:25 PM
Time does not "begin". To begin something it already is presupposed that time exists, else the phrase "begin" is meaningless.
It's just a shorthand; the underlying concept is not easy to express in ordinary, everyday words.

forrest noble
2010-Aug-07, 07:30 PM
heusdens,


Time does not "begin". To begin something it already is presupposed that time exists, else the phrase "begin" is meaningless.

In the Big Bang model, as well as other finite universe models, time and space start/ were created at the inception of the universe. To get a handle on this concept consider the following analogies/ definitions. Consider time as equivalent to change. It would not be possible logically for there to have been any change(s) to have occurred before the first change such as a big bang beginning (a logical contradiction to the word beginning). Consider space as equivalent to the volume which matter occupies. In the BB model this initial volume has been proposed to have been roughly the size of a proton. So accordingly space did not exist outside this volume. Following a BB type beginning (or any other conceivable finite beginning at one point for that matter) matter or energy would expand outwardly whereby matter energy would then occupy a much larger volume which would then include distances between matter. Space would continue to accordingly be defined as the volume matter occupies (collectively). These definitions may be considered as analogous concepts if one prefers. According to most versions of the standard cosmological model, there were no changes or time before the beginning BB, and the only space that accordingly initially existed was the volume that the beginning BB entity occupied. So accordingly both space and time would be functions of matter.

Einstein put it this way: "When forced to summarize the general theory of relativity in one sentence:
Time and space and gravitation have no separate existence from matter."
(Albert Einstein)

Nereid
2010-Aug-07, 08:39 PM
heusdens,


Time does not "begin". To begin something it already is presupposed that time exists, else the phrase "begin" is meaningless.
In the Big Bang model, as well as other finite universe models, time and space start/ were created at the inception of the universe.
This is oft repeated, especially in popular level material; however, it is not true.

If by "the Big Bang model" one means "LCDM-based cosmological models", then they apply no earlier than the Planck time. In particular, all these models are silent on what occurred in the Planck regime ... and for very good reason!

LCDM models are based on the two most successful theories in physics, today; namely, General Relativity (GR) and the Standard Model of particle physics (based on quantum theory). These are mutually incompatible, in a particularly fundamental way, in the Planck regime. Ergo, no models based on both can have any internal consistency in this regime.


To get a handle on this concept consider the following analogies/ definitions. Consider time as equivalent to change. It would not be possible logically for there to have been any change(s) to have occurred before the first change such as a big bang beginning (a logical contradiction to the word beginning). Consider space as equivalent to the volume which matter occupies. In the BB model this initial volume has been proposed to have been roughly the size of a proton. So accordingly space did not exist outside this volume.
This, too, is oft found in popular accounts; however, what is referred to is the size of today's observable universe (or something similar). LCDM models (most of them anyway) do not say anything about the size (space) of the universe as a whole at the first tick of the Planck clock.


Following a BB type beginning (or any other conceivable finite beginning at one point for that matter) matter or energy would expand outwardly whereby matter energy would then occupy a much larger volume which would then include distances between matter. Space would continue to accordingly be defined as the volume matter occupies (collectively). These definitions may be considered as analogous concepts if one prefers.
This, too, is a common explanation. It's OK as far as it goes, but it is very important to recognise that the actual LCDM models contain all the subtleties and counter-intuitives of GR.


According to most versions of the standard cosmological model, there were no changes or time before the beginning BB, and the only space that accordingly initially existed was the volume that the beginning BB entity occupied. So accordingly both space and time would be functions of matter.
Sorry fn, but this is pure nonsense; standard cosmological models say nothing about conditions during the first Planck second.


Einstein put it this way: "When forced to summarize the general theory of relativity in one sentence:
Time and space and gravitation have no separate existence from matter."
(Albert Einstein)
While that may be so, the key thing to recognise is that no one knows what physics is, in the Planck regime. It may be that GR rules, or that a modest extension of it rules; equally, it may be that something as radically different from GR as GR is different from Newtonian mechanics and gravitation rules.

forrest noble
2010-Aug-07, 09:01 PM
Hi again Nereid,


LCDM models are based on the two most successful theories in physics, today; namely, General Relativity (GR) and the Standard Model of particle physics (based on quantum theory). These are mutually incompatible, in a particularly fundamental way, in the Planck regime. Ergo, no models based on both can have any internal consistency in this regime.

Maybe the Big Bang model in general has its basis in GR and possibly particle physics, but the LCDM version of it has its basis in dark energy and dark matter.


Sorry fn, but this is pure nonsense; standard cosmological models say nothing about conditions during the first Planck second.


This is a quote from Wiki


The Big Bang is the prevailing cosmological theory of the early development of the universe. Cosmologists use the term Big Bang to refer to the idea that the universe was originally extremely hot and dense at some finite time in the past and has since cooled by expanding to the present diluted state and continues to expand today.


(bold added)
http://en.wikipedia.org/wiki/Big_Bang

Many theorists today distance themselves from Plank times concerning beginning events, considering the sequences leading up to a hot dense field, as a concern for competing models. Instead many hold to the above embolden quote concerning beginning times as just being extremely hot and dense, and "......say nothing about conditions during the first Planck second" or Plank times in general.


.......the key thing to recognise is that no one knows what physics is Whether or not this statement is valid, doesn't mean however that no one knows or understands what time and space, or spacetime really are. The understandings of the word Physics, like other words, is based upon its one or more definitions. If your meaning for this statement was that no one knows for sure the validity of theories or "laws" in physics, or that all equations in Physics are solely theoretical, then I totally agree will you. Realize that definitions and related concepts such as space and time, do not necessarily have to involve theory; like other words they just have different meanings, definitions and usages. The definitions that I was explaining for these words were given above. I did not suggest that other definitions, explanations, or theoretical understandings of these words have less merit, instead I was suggesting that the best word definition/ explanation for a particular usage should be based upon the ideas which are trying to be conveyed.

Your statement in the quote immediately above, may or may not have validity depending on the definitions and considerations involved. It concerns the word "knowing," which can be ambiguous considering its different possible meanings and related epistemology, as you have questioned before concerning astronomy: "Astronomy: what can we know?"

Ken G
2010-Aug-09, 03:46 AM
Maybe the Big Bang model in general has its basis in GR and possibly particle physics, but the LCDM version of it has its basis in dark energy and dark matter.
LCDM still has its basis in GR and particle physics-- DM and DE are merely parameters that can be added within those basic paradigms. It's true that they are very fundamental and important parameters, and there is not wide agreement on just how to include them, all of which is troubling, but they don't require any deviations from GR or quantum mechanics. That's actually the sole reason we have those added parameters.


This is a quote from Wiki
And that very standard quote neither refuted Nereid's objections, nor supported what you said that she objected to. What you said about the BB was simply not an accurate description of that model, it was more the way it is often talked about when precision is not important. And that's usually fine, but in this thread it seems we are trying to get past the imprecise language and get to what the model is really saying that we can actually test.


Many theorists today distance themselves from Plank times concerning beginning events, considering the sequences leading up to a hot dense field, as a concern for competing models. Instead many hold to the above embolden quote concerning beginning times as just being extremely hot and dense, and "......say nothing about conditions during the first Planck second" or Plank times in general.That just means they are being even more conservative than Nereid was, which was already more conservative than what you said. It all comes down to, are we going to assert only what we can demonstrate, or will we say much more, if we think it helps get a certain useful picture across? The inescapable fact is that the closer we get to the Beginning with our language, the more uncertain we become that we are not speaking nonsense. We don't know there was a Beginning, and we don't know at what point the physics we now use breaks down, which means we don't know that our current language is up to the task. That's why the safest thing is to start the Big Bang model at the place that our modern accelerators have already probed, and proceed with great caution going any earlier. There's just a big lure to talk about a Beginning, since the Big Bang model suggests its presence, but nothing about the Big Bang model requires it in literal terms.

The definitions that I was explaining for these words were given above. I did not suggest that other definitions, explanations, or theoretical understandings of these words have less merit, instead I was suggesting that the best word definition/ explanation for a particular usage should be based upon the ideas which are trying to be conveyed.I believe Nereid's point is that there are absolutely no definitions of space and time that make any sense earlier than the Planck era. Operational or observational definitions don't approach anywhere close to the Planck scale, and theoretical definitions are known to break down there. That exhausts the meaningful definitions.

forrest noble
2010-Aug-10, 02:30 AM
Ken G,


I believe Nereid's point is that there are absolutely no definitions of space and time that make any sense earlier than the Planck era. Operational or observational definitions don't approach anywhere close to the Planck scale, and theoretical definitions are known to break down there. That exhausts the meaningful definitions.

I have seen the argument that I stated for the standard model concerning space and time for many years now which can be seen in the link below.

http://curious.astro.cornell.edu/question.php?number=364

In my opinion space and time, as well as spacetime are very simple entities regardless of the time frame considered based upon the definitions given above, which I think better support the BB model and any finite model concerning its beginning, space and time. I can think of no better definitions than these very simple ones that give as much insight into reality. I think these definitions both can explain the very beginning times and space of the universe as well as the questions of what existed outside the universe (nothing). But certainly your statement and Nereid's concerning "not knowing" is one of the more common perspectives of theorists concerning the BB model but it does not seem to me that this perspective contradicts the possibility of the definitions above, the same as I probably cannot dispute your opinion or possible preferred definitions relating to space and time. btw -- you always have postings that are well-considered and interesting to read, cheers!

Ken G
2010-Aug-10, 05:27 AM
I have seen the argument that I stated for the standard model concerning space and time for many years now which can be seen in the link below. Yes, I mentioned that one sees this kind of language in a lot of places, and it is quite imprecise and not intended to be taken very literally. For popularized dogmatic responses that shut off certain lines of questioning where the responder does not want to go, it suffices, but for more probing analyses, it's pretty close to downright wrong. For example, it says we can define time as beginning with the Big Bang, but definitions don't work that way-- if we define time like that, then we can't use some other definition, say one that is actually used for time. Alternatively, if we want to use a definition like physicists really use for the concept of time, we cannot say it began at the Big Bang, because we already know it won't make any sense prior to the Planck time. The popularized answer you linked to has simply made the choice not to get into the "Planck scale" issues, because that would require a more complicated answer. That's a fine decision for them to make, but it limits how literally you can take their answer-- it's a limitation on the kinds of questions that answer is relevant to.

But certainly your statement and Nereid's concerning "not knowing" is one of the more common perspectives of theorists concerning the BB model but it does not seem to me that this perspective contradicts the possibility of the definitions above, the same as I probably cannot dispute your opinion or possible preferred definitions relating to space and time. btw -- you always have postings that are well-considered and interesting to read, cheers!And I'm not trying to make a big deal out of whether time starts at the Big Bang, or if it starts at the Planck time, or even some later time that we actually can test. It really all depends on the question being asked. I'm just saying that we are not free to define things about the Beginning, because we already have definitions for things like time and space, and using those definitions forces us to run into a big ? before we ever get to The Beginning. Indeed, I view it as a feature of the Big Bang model, not a problem with it, that it starts in a ?-- physics does not do beginnings, it does evolution, so starting with a ? is the perfect place for a physical theory about the history of the universe to start.

forrest noble
2010-Aug-10, 06:44 PM
Ken G,


.......And I'm not trying to make a big deal out of whether time starts at the Big Bang, or if it starts at the Planck time, or even some later time that we actually can test. It really all depends on the question being asked. I'm just saying that we are not free to define things about the Beginning, because we already have definitions for things like time and space, and using those definitions forces us to run into a big ? before we ever get to The Beginning. Indeed, I view it as a feature of the Big Bang model, not a problem with it, that it starts in a ?-- physics does not do beginnings, it does evolution, so starting with a ? is the perfect place for a physical theory about the history of the universe to start.


I agree that the Q & A section is meant for the best considered mainstream answers and your answers always seem to be good representations of current theoretical thinking, besides giving indications that you also can think outside the box.

AKONI
2010-Aug-29, 11:10 PM
Perhaps I watch a bit too much Science channel, but I was always under the impression the Big Bang started at a single point which suddenly went BANG! BOOM! and all that jazz, which is why the Universe is expanding equally on all "sides." Would that not mean there is a single point in space where we can locate the origin of the Big Bang?

On the other hand, I'm reading here that it might have happened everywhere at once, but doesn't that somehow go against the even expansion of the Universe? If it happened everywhere wouldn't there be "bubbles" in our universe, or to put it another way, wouldn't our universe be more potato shaped with some areas expanding faster and further than others like a series of explosions that detonate at the same time, sending air pressure waves in different directions at varying speeds - some even colliding with one another?

caveman1917
2010-Aug-29, 11:28 PM
I was always under the impression the Big Bang started at a single point which suddenly went BANG! BOOM!

Interestingly enough, the big bang wasn't big, and it didn't bang.


which is why the Universe is expanding equally on all "sides."

It is space itself which is expanding, every tiny cube of it, it is not added to the "sides".


Would that not mean there is a single point in space where we can locate the origin of the Big Bang?

No. Though it will look like that from every single point in space. How could you tell which one is the 'real' one?

kevin1981
2010-Aug-30, 12:00 AM
Perhaps I watch a bit too much Science channel, but I was always under the impression the Big Bang started at a single point which suddenly went BANG! BOOM! and all that jazz, which is why the Universe is expanding equally on all "sides."

From what i have read, It did'nt start at a single point. It was a single point. There was nothing outside or around this point.

Space and time came into existence from this point and expanded. So there are no sides to the universe as there is no 'outside' of it. The mainstream view is, the universe is all there is.


Would that not mean there is a single point in space where we can locate the origin of the Big Bang?

No, because it happened everywhere. The initial expansion was a small piece of space that has now expanded billions of light years.


doesn't that somehow go against the even expansion of the Universe

The universe is not expanding evenly. The further out we look, the faster the universe is expanding. The universe is getting bigger. Is the expansion getting quicker with time, i do not know?


sending air pressure waves in different directions at varying speeds - some even colliding with one another?

There are no air pressure waves in space. Space is a vacuum with no air molecules.

George
2010-Aug-30, 12:23 AM
Perhaps I watch a bit too much Science channel, but I was always under the impression the Big Bang started at a single point which suddenly went BANG! BOOM! and all that jazz, which is why the Universe is expanding equally on all "sides." Would that not mean there is a single point in space where we can locate the origin of the Big Bang? It is easier to understand the Big Bang theory when you see that they are rewinding the clock and noticing everything, including space, compacts tighter and tigher. Physics holds together nicely but when it starts getting smaller than a grapefruit -- I'm not sure the size -- then the number crunching of physics runs off into infinity, which means things like unification of general relativity and quantum mechancs will be necessary to get closer to the possible point you suggest.

Ken G
2010-Aug-30, 01:53 AM
The two most common misconceptions about the Big Bang theory are that it is a theory of the origin of the universe, and that it starts from a point. The first part is wrong because there is no such thing as a physics theory of a fundamental origin of anything-- physics strictly does one thing, which is track evolution. So any origin in physics must be seen as an evolution (a process that unfolds with time, starting from pre-specified conditions that are outside the theory). No exceptions, all physical theories are just like that, and the Big Bang is also not an exception-- if something is originating as a result of a physical theory, then it can only be the result of some other initial condition that is not explained.

The second part is wrong because we have no physics for the evolution of a point-- our laws simply don't work there. Since the Big Bang model does use our current laws of physics, with a few tweaks (like the cosmological principle, the inflationary epoch if that is included, dark matter and dark energy if they are included, etc.), we know that it cannot be an evolution that starts at a point. Instead, the best way to think of the Big Bang model is the way George explained it-- with time running backward, starting with what we see now. If you start with "now", and run time backward, you can take the reverse-evolutionary model as far back as you like, as long as the laws are still working. Then you just stop when you lose confidence that the laws still mean anything, put a big "?" right there, call whatever you have at that point the "initial condition" of your evolutionary model-- and then you retrace time in the normal way. That's the Big Bang model.

George
2010-Aug-30, 04:11 PM
... we have no physics for the evolution of a point. That's a dandy! I don't recall hearing it before, though there are about 3 million hits of "evolution of a point" by Google, though they may all be unrelated to the origin of our universe.

kevin1981
2010-Aug-30, 05:14 PM
Maybe Ken is talking about the standard big bang model, without all the inflationary epoch business.

Because, from what i have read, the universe starts from an initial 'patch' many times smaller than the size of a proton.

From there, it gets bigger, but still has time to reach a very nearly uniform temperature, tiny quantum fluctuations do appear though, which gives rise to the seeds of galaxy formation at a later date.

We are still at a stupidly small scale here. Then once it has had time to reach this nearly uniform temperature, inflation takes over and the universe expands at a rate of about 22 times the speed of light for a fraction of a second, taking the size up to that of a grapefruit.

Now, that is the basics of the inflationary theory of the big bang model. But to be completely honest, it is pretty much all i know about it. Well i do understand about the decaying scalar field and a few other details too, but i am keeping it simple.

If people would like to correct me or tell me i am right about anything, then carry on, as offence will not be taken.

But this inflationary epoch i am talking about is not testable yet, or if it is, there have not been any observations to back it up. So for now, at least, this is just speculation backed up by fancy mathematics.

I think, this is why Ken G and George say it is better to go backwards in time until the numbers and physics breakdown. Because, we have observable and tested evidence of what happened up till the universe become the size of a grapefruit. Anything in the realms smaller than that we do not have tested evidence to back up what was happening.

Is this about right?

Nereid
2010-Aug-30, 06:16 PM
Maybe Ken is talking about the standard big bang model, without all the inflationary epoch business.

Because, from what i have read, the universe starts from an initial 'patch' many times smaller than the size of a proton.

From there, it gets bigger, but still has time to reach a very nearly uniform temperature, tiny quantum fluctuations do appear though, which gives rise to the seeds of galaxy formation at a later date.

We are still at a stupidly small scale here. Then once it has had time to reach this nearly uniform temperature, inflation takes over and the universe expands at a rate of about 22 times the speed of light for a fraction of a second, taking the size up to that of a grapefruit.

Now, that is the basics of the inflationary theory of the big bang model. But to be completely honest, it is pretty much all i know about it. Well i do understand about the decaying scalar field and a few other details too, but i am keeping it simple.

If people would like to correct me or tell me i am right about anything, then carry on, as offence will not be taken.

But this inflationary epoch i am talking about is not testable yet, or if it is, there have not been any observations to back it up. So for now, at least, this is just speculation backed up by fancy mathematics.

I think, this is why Ken G and George say it is better to go backwards in time until the numbers and physics breakdown. Because, we have observable and tested evidence of what happened up till the universe become the size of a grapefruit. Anything in the realms smaller than that we do not have tested evidence to back up what was happening.

Is this about right?
Is this about right?

Sorta.

First, what your post is about is, most likely, the observable universe, not the universe as a whole (esp. wrt its size - there is currently nothing to constrain that; it could be infinite, and may well have always been infinite).

Second, using today's physics, we cannot say anything about the behaviour of the universe during its 'first' Planck second, as has been mentioned in many posts in this thread already (so the observable universe does not 'start' with anything; the best cosmological models we have today start at no earlier than a Planck second).

Third, at about this Planck second, the observable universe seems to have been homogeneous in its distribution of mass-energy (i.e. the best cosmological models we have today start with a uniform 'temperature').

Fourth, the tiny quantum fluctuations seem to be scale invariant (a term we need, perhaps, to spend some time understanding), and the relationship between these and the formation of galaxies is very poorly understood.

Fifth, the 'inflationary epoch' is exactly one of the things which detailed observations of the CMB allow us to model, and constrain. For example, any deviation from scale invariance tells us a lot about the nature of the inflation; so it is very far indeed from being "just speculation"!

(There's more, but I'll stop now)

kevin1981
2010-Aug-30, 08:39 PM
First, what your post is about is, most likely, the observable universe, not the universe as a whole (esp. wrt its size - there is currently nothing to constrain that; it could be infinite, and may well have always been infinite).

What makes you think i am only talking about the observable universe. I was just talking about the universe in general.

Though how can space be infinite, if it has only been expanding for 14 billion years ?



Second, using today's physics, we cannot say anything about the behaviour of the universe during its 'first' Planck second, as has been mentioned in many posts in this thread already (so the observable universe does not 'start' with anything; the best cosmological models we have today start at no earlier than a Planck second).

Ok, so are you saying that, because we know nothing about the very first instant initial conditions, we can't say it started, because we don't know? All we know is 'something' happened?


Third, at about this Planck second, the observable universe seems to have been homogeneous in its distribution of mass-energy (i.e. the best cosmological models we have today start with a uniform 'temperature').

So the temperature very early on was completely uniform. Same as the mass-energy and this is why no black holes were created?


Fourth, the tiny quantum fluctuations seem to be scale invariant (a term we need, perhaps, to spend some time understanding), and the relationship between these and the formation of galaxies is very poorly understood.

Fair comment, i thought the inflation 'stretched' these tiny fluctuations and that gave rise to density irregularities that we see in the CMBR. These irregularities were a little denser, so attracted more mass- thus, starting of galaxy formation.

I thought this was fairly well understood and an accepted theory of how galaxy's first formed.

Is the start of galaxy formation not well understood ATM then?

Maybe you could expand my current thinking in galaxy formation if you don't mind.


scale invariant

You are correct ! I have no idea what scale invariant means : )




Fifth, the 'inflationary epoch' is exactly one of the things which detailed observations of the CMB allow us to model, and constrain. For example, any deviation from scale invariance tells us a lot about the nature of the inflation; so it is very far indeed from being "just speculation"!

Before we go any further with this, i would like to understand the questions above please.

I am just getting used to deconstructing peoples posts, but it is a great way to learn. Cheers

Ken G
2010-Aug-30, 09:02 PM
Maybe Ken is talking about the standard big bang model, without all the inflationary epoch business.

Because, from what i have read, the universe starts from an initial 'patch' many times smaller than the size of a proton. That still isn't a "point"-- our physics works on scales like that.

But this inflationary epoch i am talking about is not testable yet, or if it is, there have not been any observations to back it up. So for now, at least, this is just speculation backed up by fancy mathematics.Yes, the "Big Bang model" has to be flexible enough to either handle inflation, if we want it, or start after it's over, or not have it at all-- that's the beauty of the model, you get to "start it" whenever you are comfortable. Since the initial condition is alway ad hoc, it doesn't matter much if you have to change it. What matters is the evolution afterward, and what laws it follows.

Though how can space be infinite, if it has only been expanding for 14 billion years ?
You are thinking about the expansion from a point, but when the observable universe was any finite size you care to mention, say smaller than a grapefruit, we still can let the total universe be any size we want. What observation would say we are wrong? Occam's Razor is no help either-- which is "simpler", simply asserting the universe is only what we see, on the grounds that we can't say anything about the rest, or just extrapolating what we see so that it has no arbitrary boundary? Sometimes infinity is simpler than finity-- when finity needs either an arbitrary boundary or an arbitrary curvature.

kevin1981
2010-Aug-30, 09:31 PM
Oh i get it now. We can say the universe is infinite because there is a cosmic boundary. There is the observable universe, but then because the expansion of space at the furthest distances is quicker than c, we are cut of from those parts. So there is nothing to stop us from saying that it is expanding at speeds we could never imagine and it goes on forever. We can't see past our observable part, so we can not say what is or is not happening.

George
2010-Aug-31, 04:01 AM
Oh i get it now. We can say the universe is infinite because there is a cosmic boundary. Boundaries are not very helpful for the infinite, though I want to say there are bound to be areas I am unbounded, but I won't say it, of course. :)

One of the reasons Einstein intially trashed Lemaitre's view of an expanding universe -- though the view came out of Einstein's equations -- was because he, like almost all the scientists of his day, favored an infinite universe - one that just sorta sat there described by the Static Theory. Once Edwin Hubble revealed the evidence for the expansion, Einstein was quick to applaud Lemaitre.


There is the observable universe, but then because the expansion of space at the furthest distances is quicker than c, we are cut of from those parts. You are pretty close with that although light can, surprisingly, come from regions that were and are traveling faster than light and still reach us, so the observable universe is bigger than otherwise.


So there is nothing to stop us from saying that it is expanding at speeds we could never imagine and it goes on forever. Yes, but it is all those darn fleeing turtles that once held up our planet that are pulling space along with them. In other words, if it is beyond the purview of science, we can say whatever we want but it won't be science.


We can't see past our observable part, so we can not say what is or is not happening. Yep. Metaphysics may address it, perhaps.

AKONI
2010-Sep-01, 12:33 AM
From what i have read, It did'nt start at a single point. It was a single point. There was nothing outside or around this point.

Space and time came into existence from this point and expanded. So there are no sides to the universe as there is no 'outside' of it. The mainstream view is, the universe is all there is.

See, now this is where it gets interesting. If there are no sides, or end to it, then how can it be expanding? If something expands there must be an end to it in order for it to grow larger or further away.




No, because it happened everywhere. The initial expansion was a small piece of space that has now expanded billions of light years.

Right, a small piece of space. So this small piece of space was everywhere when it went bang? I understand that the universe is expanding everywhere now, but wouldn't this small piece of space indicate it at least started at one point?




There are no air pressure waves in space. Space is a vacuum with no air molecules.

Err, read what I wrote again. I wasn't saying there are air pressure waves in space. I was using the example of explosions with pressure waves to highlight the point behind my question so there would be no confusion as to what I was asking.

Ken G
2010-Sep-01, 01:08 AM
See, now this is where it gets interesting. If there are no sides, or end to it, then how can it be expanding? If something expands there must be an end to it in order for it to grow larger or further away.

Then just imagine the bound systems are shrinking, it's the same thing and it avoids your objection completely.

kevin1981
2010-Sep-01, 12:36 PM
See, now this is where it gets interesting. If there are no sides, or end to it, then how can it be expanding? If something expands there must be an end to it in order for it to grow larger or further away.

Firstly, i am no expert, i just have an interest in space and nature as a whole. But i do not see why space has to have an 'end' to it. And i do not see why it has to have 'sides' either. In both cases to me, that would imply that the universe is expanding into 'something'. AFAIK the universe is all there is, so it does'nt make sense to say it has 'sides to it'.

The same goes for space having an 'end'. That would imply there is an edge, where you could just jump off, to me that makes no sense. When people say the universe in infinite, that does confuse me a bit i must admit.


Right, a small piece of space. So this small piece of space was everywhere when it went bang? I understand that the universe is expanding everywhere now, but wouldn't this small piece of space indicate it at least started at one point?

I am not saying it did'nt start at a point. All i was saying is where the initial "point" of origin came from, there was nothing 'outside' of it. The initial "point" was all there was and that initial 'point' of origin has now expanded billions of light years- Thus the big bang happened everywhere.

My personal view on space is that it is a gigantic sphere, but with no 'inside'. And it has expanded to such a great size that the part we observe seems to be flat.


Err, read what I wrote again. I wasn't saying there are air pressure waves in space. I was using the example of explosions with pressure waves to highlight the point behind my question so there would be no confusion as to what I was asking.

Sorry if i miss read your question, it was probably late at night !

Strange
2010-Sep-01, 12:53 PM
See, now this is where it gets interesting. If there are no sides, or end to it, then how can it be expanding? If something expands there must be an end to it in order for it to grow larger or further away.

I don't see the logical connection there. Something that is infinite can expand. Take the (infinite) set of integers on an infinite number line. Now double all of them so you have the (infinite) set of even numbers spread out twice as much.


Right, a small piece of space. So this small piece of space was everywhere when it went bang? I understand that the universe is expanding everywhere now, but wouldn't this small piece of space indicate it at least started at one point?

That small piece was "everywhere". It was the universe (not in the universe). There was nowhere else but that small patch. It got bigger and so the origin was still everywhere.

Note that that description is not inconsistent with the universe being infinite, either. That small piece of space (which became the observable universe) could have been surrounded by (an infinite number of) other pieces which also expanded.