Everything about Big Bang theory

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Lisa!
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I want to know everything about Big Bang theory. For example what were the clues which led scientists to this theory and how much they are certain of this theory.
Big Bang theory says how this universe came to existence and started its expansion, now I want to know what will happen to the universe at last? Does it cotinue its expansion forever?


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SpaceTiger
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Lisa! said:
I want to know everything about Big Bang theory. For example what were the clues which led scientists to this theory and how much they are certain of this theory.
Describing all of the details of the Big Bang Theory is an undertaking far too vast for a single thread. For an overview, I suggest you search the web. Here's a sample website:

The Big Bang Theory

I would also suggest my Review of Mainstream Cosmology. It sums up many of the relevant points about the state of the theory in a few paragraphs.


Big Bang theory says how this universe came to existence and started its expansion, now I want to know what will happen to the universe at last?
Does it cotinue its expansion forever?
The most popular current theories say yes, but I would not put much faith in this conclusion. We can say a lot more about what has already happened than we can about what will.
 
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Lisa!
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SpaceTiger said:
Describing all of the details of the Big Bang Theory is an undertaking far too vast for a single thread. For an overview, I suggest you search the web. Here's a sample website:

The Big Bang Theory
I searched the web before starting this thread and I visited the site you've introduced. But I want to have PFer's ideas about this theory too. I even searched this forum for that but I didn't find any particular thread about Big Bang. But I think the thread you've linked here, could help me alot. Thank you very much.
 
Chronos
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Here is the Reader's Digest version, Lisa. Big Bang theory has its roots in the unexpected 1929 discovery by Hubble that distant galaxies are moving away from Earth. And the more distant they are, the faster away they move. This suggested galaxies were much closer together in the past. Crude calculation based on the velocities and directions of their motions showed all galaxies would have been in the same place about 14 billion years ago - meaning the universe must have been fantastically dense back then. This hypothesis is strongly supported by two forms of evidence.
1 - Abundance of chemical elements in the universe.
George Gamow realized in the 1940's that the early universe must have been extremely hot as well as dense. He estimated in such a hot, dense, and expanding universe about one-quarter of the simplest chemical element - hydrogen - would be converted into helium. Astronomers subsequently measured proportions of hydrogen and helium in the universe [and certain other elements], and found it matches the prediction almost perfectly.
2. The cosmic microwave background radiation [CMBR]
According to the Big Bang model, the Big Bang took place everywhere in space [not at a point embedded in some sort of preexisting 'space']. For hundreds of thousands of years after the Big Bang, all matter in the universe was so hot it glowed. The afterglow from this phase in the history of the universe should still be detectable. In 1964, radio astronomers Penzias and Wilson became the first to detect this relic radiation. Several scientific studies of the CMB have since been conducted - WMAP most recently. These studies are regarded as compelling evidence of the validity of Big Bang theory, and deemed one of the greatest discoveries of the 20th century..
 
EnumaElish
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Chronos said:
Crude calculation based on the velocities and directions of their motions showed all galaxies would have been in the same place about 14 billion years ago
Simply substitute the expression "same point" for the expression "same place" in the above quote, and it seems like you'd get a contradiction with:
Chronos said:
the Big Bang took place everywhere in space [not at a point embedded in some sort of preexisting 'space'].
I know that's the Reader's Digest version, but still...:uhh:

P.S. As a non-physicist, my sense of wonder and awe with respect to the Big Bang theory is because it proves that the initial conditions for the universe correspond to an incredible degree of disorder, which in turn lends support to either of these two hypotheses: either (1) BB was not a random event (the "what are the chances?" question); and/or (2) the universe is not a closed system. Unless, that is, I misunderstood it all... :redface:
 
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SpaceTiger
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EnumaElish said:
I know that's the Reader's Digest version, but still...:uhh:
Unfortunately, that's one of the consequences of translating an abstract theory into layman's terms. Space itself has expanded, so at the beginning, the entire universe was a single point (or so the theory says), containing all of the energy of the universe. The space we now see "grew" from it. It's analogous (in a very crude sense) to a plant growing from a seed. Asking where the big bang occurred is sort of like asking which part of the plant was the seed.
 
Lisa!
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Chronos said:
Here is the Reader's Digest version, Lisa. Big Bang theory has its roots in the unexpected 1929 discovery by Hubble that distant galaxies are moving away from Earth. And the more distant they are, the faster away they move. This suggested galaxies were much closer together in the past. Crude calculation based on the velocities and directions of their motions showed all galaxies would have been in the same place about 14 billion years ago - meaning the universe must have been fantastically dense back then. This hypothesis is strongly supported by two forms of evidence.
1 - Abundance of chemical elements in the universe.
George Gamow realized in the 1940's that the early universe must have been extremely hot as well as dense. He estimated in such a hot, dense, and expanding universe about one-quarter of the simplest chemical element - hydrogen - would be converted into helium. Astronomers subsequently measured proportions of hydrogen and helium in the universe [and certain other elements], and found it matches the prediction almost perfectly.
2. The cosmic microwave background radiation [CMBR]
According to the Big Bang model, the Big Bang took place everywhere in space [not at a point embedded in some sort of preexisting 'space']. For hundreds of thousands of years after the Big Bang, all matter in the universe was so hot it glowed. The afterglow from this phase in the history of the universe should still be detectable. In 1964, radio astronomers Penzias and Wilson became the first to detect this relic radiation. Several scientific studies of the CMB have since been conducted - WMAP most recently. These studies are regarded as compelling evidence of the validity of Big Bang theory, and deemed one of the greatest discoveries of the 20th century..
Thank you very much. Now I want to ask a silly question: :redface:
How do these 2 Forms of evidence tell us it happened 14/15 billion years ago?
 
Chronos
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First, let me say that Space Tiger is the expert here. Ignore everything I have said and follow what he says. Second, the model is conceptually simple. When you compress space and time backwards, you get a very dense, and hot universe at T ~ -14 billion years ago, by our clocks. The reason these models are so well respected is because observational evidence supports them to a very high degree.
 
SpaceTiger
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Chronos said:
First, let me say that Space Tiger is the expert here. Ignore everything I have said and follow what he says.
I didn't mean to imply that what you said or quoted was wrong, just that it was written in layman's terms, so there was some ambiguity in the literal meaning. The same was true of my response, but I was trying to give a different point of view in the hopes that it would clarify things a bit for EnumaElish.
 
Chronos
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I'm not offended, and I don't claim any expertise. I have a sincere desire to learn. Thanks for being patient with me.
 
SpaceTiger
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Lisa! said:
How do these 2 Forms of evidence tell us it happened 14/15 billion years ago?
Actually, the two things quoted there are the best evidence that there was a big bang, but our constraint on the age of the universe is most closely tied to our measurement of Hubble's constant. Hubble's constant is the fractional rate of expansion of the universe -- in other words, it tells us roughly how quickly the universe is expanding relative to its size. The inverse of this quantity will give an approximate age of the universe. More details can be found here:

Age of the Universe
 
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DrChinese
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EnumaElish said:
... either (1) BB was not a random event (the "what are the chances?" question); or ...
Keep in mind that the odds are 100% that it has happened at least once!

Without knowing more, we cannot be sure if the BB is a "rare" event or a common one. Ditto for whether the BB is a test tube creation of a god-like creature or a random quantum fluctuation (another popular hypothesis).

The best guess of current science is that we will never be able to see outside of our universe, meaning that the answers to the above are not likely to ever be learned. So for now, you are free to imagine your own preferred scenario.
 
Chronos
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See Lisa! I told you SpaceTiger could explain it better. We are fortunate to have a resident, qualified expert. I'm just a librarian. Dr. Chinese is also a very bright fellow who makes high quality posts.
 
SpaceTiger
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Chronos said:
See Lisa! I told you SpaceTiger could explain it better. We are fortunate to have a resident, qualified expert.
Partially qualified...I don't yet have my Ph.D. Besides, you're the one with the ribbon. :wink:
 
Lisa!
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Chronos said:
See Lisa! I told you SpaceTiger could explain it better. We are fortunate to have a resident, qualified expert. I'm just a librarian. Dr. Chinese is also a very bright fellow who makes high quality posts.
Thanks all of you. I think all of you are experts in this area and we're fortunate that you help others and answer their questions.
 
Lisa!
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SpaceTiger said:
Partially qualified...I don't yet have my Ph.D. Besides, you're the one with the ribbon. :wink:
I'm sure you'll get the ribbon too.:smile:
 
Chronos
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Partially qualified? To anyone paying attention, SpaceTiger, while not yet having earned his PhD, has vast knowledge of astronomy and cosmology. I am a layman, and my ribbon [while flattering] is a joke. It only means PF had a bad year recruiting experts who understand astronomy and cosmology. I welcome and greatly respect ST's contributions to our forums.
 
SpaceTiger
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Chronos said:
I am a layman, and my ribbon [while flattering] is a joke. It only means PF had a bad year recruiting experts who understand astronomy and cosmology.
Don't be modest. You're a clever fellow and much more grounded than the majority here (including myself), but let's not continue to litter Lisa's thread with back-scratching.

Did you have anymore questions, Lisa?
 
Lisa!
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Not now. Thank you very much. Actually I was enjoying your conversation.:blushing:
 
Phobos
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Daminc - please use the PM system for such questions
 
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Sorry about that (I've deleted that question and PM'ed Chronos)
 
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