Big Bang Hypothesis

[LaurieAG]

Hi IrishRover,

 

Amazing hubris.

 

Good point.

 

http://www.britannica.com/EBchecked/topic/274625/hubris

 

Hubris fit into the shame culture of archaic and Classical Greece, in which people’s actions were guided by avoiding shame and seeking honour. It did not fit into the culture of internalized guilt, which became important in later antiquity and characterizes the modern West.

 

Are we missing the real point in the modern west?

[Eclogite]

Irish Rover, your observations were interesting, but not exactly relevant to the thrread. Perhaps that's why you had no responses. If you return I woul be interested to hear what you think about the Big Bang.

 

My two penniesworth: I don't get why people don't get the idea once it is explained. In particular I am at a complete loss as to what Laurie is trying to say and I applaud Modest for patiently asking the same questions and still not getting an answer. Any chance you could change that pattern Laurie?

[CarlNGraham]

What confuses me about the big bang view of things, is thinking about space exploding out from the singularity.

It implies in some way that the singularity was small, but small compared to what?

It was the only thing that existed, so the singularity was already as big as the universe, so how can it expand?

[CraigD]

What confuses me about the big bang view of things, is thinking about space exploding out from the singularity.

It implies in some way that the singularity was small, but small compared to what?

It was the only thing that existed, so the singularity was already as big as the universe, so how can it expand?

According to the Big Bang theory, the very early universe was very small compared to the slightly (about 10^-23 seconds) later universe as measured by physical constants like the range of interaction such as the strong interaction that now binds quarks into protons and neutrons, so you could say as measured by the size of these particles, though such a comparison must be made with care, as according the BB, these particles didn’t exist at this time, and some of the present day fundamental forces were combined. The point is, not everything expanded in the same way – essentially, small bodies and interactions, like massive particles and the particles that carry their interaction, expanded less or not at all, while the whole universe expanded much more.

 

Your question’s a good one, though. In many ways, it doesn’t make sense to speak of the very early BB universe having size in the usual sense, but rather to speak of it as a collection of mathematical concepts – symmetry groups, etc. It’s hard to have a good intuitive sense of what this kind of speaking really means, or even understand the terms and concepts of this kind of speaking, though, so I expect the question will always be a perplexing one.

 

There are a lot of good books and websites on the subject, including the Wikipedia article Timeline of the Big Bang.

[CarlNGraham]

I am not sure it make sense but, I think of it as the universe is not expanding into space, but expanding by creating space inside itself.

Otherwise topics like inflation just blow your mind.

 

Thanks, but I have been doing a lot of reading on Wikipedia for research into a science fiction I am working on, where the aliens say the universe is not expanding. They needed to say something major at first contact:)

But I am now having problems finding a fault with their argument, which is a bit of an oops for finishing the book.

[Robert Angstrom]

What confuses me about the big bang view of things, is thinking about space exploding out from the singularity.

It implies in some way that the singularity was small, but small compared to what?

It was the only thing that existed, so the singularity was already as big as the universe, so how can it expand?

The singularity may have been "small" but it contained the same space that it does now. The compacted space of long ago took up less space than space does now in its expanded form.

We could also ask, relative to 'What?' is the universe expanding? Relative to my point of view the universe may be expanding but, relative to the radius of the universe, the entire material world is growing smaller. Perhaps the universe was always the enormous thing we see now while the material world within is growing smaller. Is the universe growing larger or is everything within growing smaller?

[CarlNGraham]

According to the Big Bang theory, the very early universe was very small compared to the slightly (about 10^-23 seconds) later universe as measured by physical constants like the range of interaction such as the strong interaction that now binds quarks into protons and neutrons, so you could say as measured by the size of these particles, though such a comparison must be made with care, as according the BB, these particles didn’t exist at this time, and some of the present day fundamental forces were combined.

 

According to the Wikipedia on Helium-4 the early universe started with a 6:1 ratio of protons neutron, but I can't find the explanation for this. Is this based on the expected abundance of more fundamental component particles?

[CraigD]

According to the Wikipedia on Helium-4 the early universe started with a 6:1 ratio of protons neutron, but I can't find the explanation for this. Is this based on the expected abundance of more fundamental component particles?

My particle physics is too weak to have worked this out on my own (I’m a Math major who took all the elective Physics I could manage, then soon after graduation into a rather dissolute junior faculty job, was gobbled up by the computer programming profession, where I use only a fraction of my old academic core knowledge), but as I understand it, the primordial proton:neutron ratio doesn’t depend on the abundance of their component particles, but on the statistics of how those particles combined.

 

The concept of protons and neutrons – collectively called nucleons – being made of component particles doesn’t work very well, because their component particles – U and D quarks and a “sea” of gluons which ... well, “glue” 3 quarks into each nucleon, and also constitute about 99% of the nucleons’ mass – can’t exist except within nucleons or strange, high-energy density environments such as the early Big Bang universe’s quark-gluon sea, and maybe some kinds of huge, gravitationally bound degenerate matter bodies like neutron and quark stars that exist near and now. Gluons are virtual bosons – you can’t really say that individual ones exist, only that some effectively infinite number of possibilities of paths followed by one or more of them have, all explaining the interaction of their constituent quarks, have probabilities of existing. Quarks themselves are virtual most of the time: you have to do some exotic stuff along the lines of deep inelastic scattering experiments, to distinctly measure their position and momentum, and until you do, they too are really a collection of probabilities.

 

Once past the issue of thinking of quarks and gluons as probabilistic, quantum particles, rather than familiar classical ones like bullets and planets, the roughly 6:1 proton:neutron ratio can be calculated by considering the probability of protons (UUD quark triples) or neutrons (UDD) forming from the primordial quark-gluon sea, given the expected lifetime of a free neutron – recall that, if not “managed” inside an nucleus, a neutron decays into a proton and an electron. The real calculation is complicated, as UUD and UDD triples have slightly different probabilities of forming, but here’s a simplified calculation:

• Assume equal starting numbers of free protons and neutrons (the early universe is too hot for neutrons to be bound into nuclei yet). If we call the total number of protons and neutrons at the beginning of this hot period [imath]n[/imath], we start with [imath]x_0=\frac{n}{2}[/imath]
  
• Assume this hot state last about 1020 seconds
  
• Assume the observed half-life of a free neutron of about 614 s.
  
• The number of neutrons after 1020 s is [math]x_1= \frac{n}{2} \left( \frac12 \right)^{\frac{1020}{614}} \dot= \frac{1}{6.326} n[/math]
  - pretty close to the [imath]\frac17[/imath] we were shooting for. :)
  

 

So the key factors that give us the roughly 1:6 proton:neutron ratio are:

• The half-life of a free neutron (614 s)
  
• The duration that the universe was cool enough to have nucleons, but too hot to bind them into nuclei (1020 s)
  

 

Cool, huh?

[CarlNGraham]

Nice :)

 

I wish I had read it before posting http://scienceforums.com/topic/23559-condensing-universe/

As the above does not fit at all

[modest]

Brilliant reply, Craig.

 

Here is a good synopsis supporting Craig's explanation and showing how it fits in the rest of the nucleosynthesis time line: http://www.astro.ucla.edu/~wright/BBNS.html

 

I think the confluence between big bang nucleosynthesis and particle physics is one of the most impressive scientific predictions of the 20th century.

 

~modest

[CarlNGraham]

What are the current ideas on natural sorting processes affecting the observed relative abundances of the elements?

 

Off the top of my head, examples of these processes could be:

• 
   
  
• The first stars forming around Lithium hydride cores?
  
• Most early stars forming near the centres of early galaxies, and then evaporating under radiation pressure from the active centre of the galaxy.
  
• Heavy elements trapped it white dwarfs or black holes.
   
  

The possibility being these would increase the relative levels of helium while hiding away other heavier element by-products at the centres of galaxies or in dense objects.

 

I suspect there has been processes similar to these at work, but are they significant in the big scheme of things?