The Big Bang Theory

This book is dated, but it is a great book, and really lays out the evolution of cosmology in the 20th century:
Lonely Hearts of the Cosmos by Dennis Overbye

Also, if you have an MP3 player, the weekly podcast "AstronomyCast" It is led by a physics professor and it spans a wider spectrum than does most "intro" cosomology sources.
 
I'll try to hit a quick timeline of the modern big bang theory...13.7 billion years ago - Every point in the universe occupies the same location which is smaller than an atom and almost infinately hot. The strong/weak nuclear, electromagnetic, and gravitational forces are unified into a single "force". At this point something happens, and theoretical physics is still trying to work out what it could be, but within a billionth of a second, gravity splits off from the unified force... and things start to expand uniformly through the universe (not explode, but expand).inflation - During this time period where the unified force is starting to break down, the "rules" of physics are in flux, and the universe expands from its atomic size to about the size of our solar system faster than the speed of light. This locks in the uniformity of the universe from its primordial state.

1 second post BB - Things have begun to cool and the electromagnetic (light/magnetism) force splits from the unified force and finally the nuclear splits into the weak nuclear and strong nuclear. The universe is filled with a mixture of energy and sub atomic particles.

3 minutes post BB - The universe has cooled to about 1 billion degrees kelvin, which allows the subatomic particles to "freeze" into atomic nuclea. At this point the universe begins "freezing" into hydrogen, some helium and trace elements. This continues for a good long while.

400,000 years post BB - There is a blinding flash of radiation throughout the universe, radiating through all spectrums. This flash is so great that 13.7 billion years later it is still visible. the temperature has cooled to about 2-3K and the distance it has travelled has stretched the wavelength to the point it only exists in the microwave band... but this is the cosmic microwave background radiation.

500 million years post BB - since the CMBR stars have begun to form. Because the only elements are extremely light, every star in the universe is super massive and extremely energetic, burning all of their fuel in a matter of million years. These "Generation 3" stars burn so hot that they begin to create the universes first round of heavy metals.

1 billion years post BB - To this point, even though there have been stars for millions of years, there is not much light in the universe. The reason for this is the substance of the universe (hydrogen, helium, etc) is opaque, and blocks all of the light. At 1 billion years, the combined light from all of these new stars going through their cycle ionizes the floating gases, making them transparent and for the first time there is a star field.

9 billion years post BB - generations of stars have created enough heavy metals that we been to see what we would define as typical star systems. There are planets and moons, and things which would be familiar to us. Also at this point, universe is so dispursed that dark energy starts to get a toe hold, insuring that the universe will continue to expand and cool.

This description is not complete, but does hit the high points of the modern model.

cmb_timeline75.jpg
 
mia, that example of the Big Bang time line made me think of another question.

So we've been able to peer back in time to just after the BB...13+ billion years. Does that mean that on "the other side" of the Big Bang (as shown in that pic...i don't really know how to phrase that) there's 13.7 billion years worth of "space/stars" that we haven't seen? I'm giving myself tiredhead.
 
I'm not sure what you mean by "the other side of the big bang".

If you are asking if there is more universe beyond our visible horizon... then yeah, there could be. We can only see things which were inside of 4200 Megaparsecs from our current position (how far light can travel in 13.7 billion years), when they began emitting light. Anything which was further than than when the dark ages ended hasn't had a chance to show us its light.

RayDog, understanding that my timeline is biased toward BB... can you provide the mechanisms and broad strokes for SS?
 
I'm not sure I know what I mean by "the other side". The illustration you posted seems to travel in one direction. I have always assumed that the "bang" went in all directions.

Never mind, I think it was probably a dumb question.
 
I think I get it. The picture DOES describe the "bang" flowing in one direction, but that direction is not spacial, it is time.

Which is to say the point in the middle of the cone represent how we see the universe. As you travel from left to right down the cone, the picture describes what you would see at various ages of the universe. The angle of the cone describes the "size" of the universe.

Does that help?
 
The question of "before the big bang" comes up often, and amounts to "whats outside this space time universe". The standard answer is we can't know, or, worse, its "not the right question".

Carl Sagan used to use the example of if we were 2D flat earth people living on an expanding ball, we could deduce what was happening mathmatically, understand it intellectually, but not be able to semantically or pictorially represent it in our minds. Such is the case with our 4D space time universe. There are lignuistic slots for "before" and our 3D representation abilities, both built in via evolution. But these don't adequately construe this question or answer. It can be construed in mathmatics, and "appreciated" or understood via those relations. But we just can't see it in our minds, and we can't satisfy that innate concept slot of "before".
 
Do you have something against fancy charts? It is the graphic representation of the timeline I laid out.

I love this stuff.
 
I've always wondered about this stuff too. I just always thought it was fun to imagen what might be on the "edge" of the universe and if there is an "edge" what's on the other side? I guess I now believe that there is no edge, that there will always be something on the other side cause even nothingness is still something, ya know?

It's mind boggling to think about. Personally thinking about that kind of stuff makes me realize how small I am and how vast the universe is and that for me, for whatever reason, makes me believe in God because only God could be on the other side. What I'm saying is God is the unexplainable, the unknownable. Ya know like the burning bush, the Great I AM. That kinda sums it up for me. "I am that I am" - God. It's as if he's saying, "Dude, seriously? You are trying to figure me out? Really? Awe, that's cute. If I were to actually reveal to you who I was your brain would explode. Just know that I am that I am and we'll leave it at that." Kinda like a parent with they kid. I know that probably seems real stupid to most of the folks on this board but it's the best way I can explain how I feel and what I believe. Anyway, I still love talking about space, time travel, the universe and stuff like that. I always have.
 
Looks like Galactus's big brother is feasting on a few galaxies.

wink.gif


Serious question though, are all of the galaxies/space matter believed to be on the outside of a 'baloon' of expansion?
 
Another problem with the big bang is the Copernican problem. Why are we in the dead center of the universe. Is it just due to our limited (by speed of light and brightness) view of the universe, or are we really dead center.

Given the size of the universe the chance that we are at the center or even remotely close to it is infinitesimally small. We are almost certainly not in the center. But if we were off center the edges of the universe would be different distances in different directions.

Hence the probability that the big bang hypothesis is correct is infinitesimally small, equivalent to the probability that we are at the center of it.
 
For the sake of those who aren't aware of the history of cosmology, it is worth pointing out that Steady State is not an evolution from the Big Bang theory, it is a progenitor theory. The theory was offered by Fred Hoyle in the late 40s and was more or less the standard model until the 60s. It has been reoffered a few times since then, but has not yet returned into favor within the scientific community. This does not mean that the model is necessarily invalid, but it is relevent too point out it is not a generally well regarded theory. It's failings usually come down to two problems. First, that we see different things the further away we look. CMBR, Quasars, abundance of Generation 2 stars.... there is a whole bunch of stuff that we only see really far away from us (which is to say, a really long time ago). If the universe is infinately old, then why do different time periods yield different stellar bodies? The second problem is if new stuff has to pop out of a vaccum, how can you possibly get enough new stuff created in proximity to account for the massive structures which seem to dominate the universe. Why don't you see countless rouge star systems, free from galactic structures? There are other issues brought up with steady state (cosmic voids, galactic clusters, etc), but by in large arguments against come down to those to points.

I say this to balance out some of the very real problems that RayDog has offered with Big Bang theory. There is an awful lot of leaning on Inflation, the antimatter issue is tough to ignore. If these things can't be resolved, then the BB isn't a valid theory. Many of the other issues he points out aren't so much about Big Bang, as they are about problems with our understanding of physics. But regardless of which cosmological theory you subscribe to, it must rest on a cohesive construct of physics to pass the smell test.

RayDog, I'm not at all suggesting that scientific theories get to "role with the data". That said, not all new or even conflicting data invalidates a model. If the requirement of a theory was that it gets everything right the first time... well, then it wouldn't be a theory would it? The standard isn't "its 100% accurate" the standard is "does it conflict with what is observed, can you make predictions from it". Big Bang does meet that critera rather well... not completely... but certainly to the point that it is more than just a fanciful notion. It has been used to predict a number of phenomena, not the least of which is the CMBR and galaxy formation.

more later...
 
RayDog, the Copernican problem is not a problem in BB... not even a little bit. The speed of light means that we can only see things when its light reaches us. If there was no light 14 billion years ago, then every point in the universe would have a 13.7 billion light year light bubble around it. This IS a problem with SS, this is NOT a problem with BB.

Are you trying to identify an isotropy issue (what does the edge "see")? This is still not a problem, but you have to use GR field equations to map why... and I'm not very good at those, so we'll have to find another source.
 
whenever i think about the universe i always think about the ming the merciless quote,"If you knew anything about the true nature of the universe, anything at all, you would have hidden from it in terror...pathetic earthlings..."

fyi, after reading this thread my head exploded.
 
BB/SS aside, RayDog, a good portion of your problems are with the standard models, seperate from cosmology. Do you point those out as an aside, or as a rejection of those models.

My feeling has always been that they weren't wrong, they were just incomplete. Which is to say, GR predicts phenomena of the universe correctly (time dilation, black holes, gravitational lensing, orbital paths, etc). I would expect GR to be a theory which gets refined, but not to be rejected... do you feel differently?
 
mia,

Thanks for the explaination...got it!

netslave, thanks for the link, I'm going to check it out later on.

And I agree that this subject blows my mind but I love reading and thinking about it.
 
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