Steampunk Patashu
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- Posted: Thu, 14 Jun 2007 07:06:26 +0000
Noting that opposition to and resentment to the big bang theory is not often due to sound, scientific reasons but due to a lack of knowledge and misconceptions on the subject, I decided to compile this reference topic. Enjoy! You can discuss/debate here if you want, but please read this post before posting.
Why a big bang?
Back in the 1900s, the view of the universe was that it was a 'steady state' universe; ie, it was eternal, more or less static and possibly infinite. Even Einstein subscribed to this idea! However, as more and more inquiry was made into the universe's makeup and more and more observations were made, things were about to change.
The movement of a celestial body relative to our own can be measured by looking at how red-shifted its light is; that is, measure the frequency spectrum of the light emitted from a celestial body, overlay it onto the frequency spectrum of the atoms we know it is made up of and see if the overall shape has been shifted to the red or blue end; if it's red-shifted it's moving away from us, if it's blue-shifted it's moving towards us and by how much is how fast it's going. Basically, it's the well known doppler effect only applying to light; if you're traveling away while emitting sound your sound waves are of a higher wavelength and vice versa.
In addition, we can even measure the distance away from us a certain cluster or galaxy is; there is a certain kind of star, a Cephid variable star, who's luminosity is tightly related to its period. Once we know the period we can calculate the expected luminosity then figure out how far away it must be.
Read more here since I don't think I can explain it well enough: http://en.wikipedia.org/wiki/Cepheid_variable
Anyway, a pair of astronomers, Edwin Hubble and Milton Humason, were looking at the red-shiftedness of things in the universe compared to their distance away from us and, after excessive study, found a pattern; basically, the further away things were, the faster away they were moving for us. This was all in the 1920s.
This can be formulated as: v = (H0)D, where v is the recessional velocity, D is the distance away from us and H0 is hubble's constant. This is not a relativistic formula; v can be bigger than c, that will be explained later however.
If we take this principle and 'rewind' time, moving all the stars and galaxies in the opposite directions, it is predicted that they all come together about 13.7 billion years ago. And this is how the big bang theory was first conceived.
What is the big bang?
The big bang theory states that the beginning of the observable universe (that is, the one we live in) started off as an ultra-dense, slightly heterogenous pocket of energy that underwent a period of rapid inflation that continues to this day. Note that is not the matter and energy that is moving outward, but the spacetime on which it lies; imagine it as sticking objects to a balloon then inflating it. This is how the expansion seems to violate special relativity; matter and energy cannot travel faster than the speed of light, but it's okay if it's due to spacetime itself moving.
As the early universe expanded its energy spreaded out and thus it became cooler and cooler steadily. From the ultra-hot sea of free energy, leptons (ie electrons) and baryons (ie protons) formed in processes known as leptogenesis and baryogenesis respectively; we know this could have happened since we've witnessed it in high-energy particle accelerators. Note that these processes happen simultaneously so as to not violate the conservation of electric charge.
At first the remaining energy in the form of photons was interacting with the protons and electrons constantly, but as the energy and matter grew sparser and sparser the first atoms were able to form, hydrogen and helium, and the photons were no longer attracted strongly and were able to travel out into open space; this is known as the universe becoming transparent, and the cosmic background radiation is the leftovers from when this happened.
As mentioned earlier, the energy density of the big bang was slightly heterogenous. That means that some parts were slightly denser then others. Once matter had formed from this energy it was also arranged in this heterogenous fashion, and where matter clumped it was drawn closer and closer via the process of gravity over millions and billions of years, forming protogalaxies. This is a process known as accretion, and in a similar fashion, individual clusters and solar systems also accrued together from lumps of matter on a smaller scale, and stars and planets on a smaller scale still.
Hopefully you can see from this that the big bang is not an 'explosion' at all; it's hardly comparable! If you detonate a bomb, you don't stick around for 10 billion years and watch the debris slowly pull itself together via gravity, and that's why analogies between the big bang and dynamite fail. Neither did the big bang create the Earth or life fully formed; that took billions of years as well, and life arose by a process known as abiogenesis which is completely different anyway.
If you're interested in the full timeline of the big bang, then read:
http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang
So, what's the evidence for it?
Glad you asked! Well, the biggest piece of evidence is the cosmic background microwave radiation; it has a certain distribution and temperature to it which the big bang theory's prediction matches perfectly, and I do mean more or less perfectly; the big bang model predicts that the CBMR should match that of an almost perfect black body, and it does! This is one of the main arguements for the big bang theory, as no other cosmological model was able to explain why the CBMR was exactly like this.
Other pieces of evidence:
•Hubble's law, that everything in space is moving away from us, the further away the faster it's regressing
•The abundances of primorial elements; the big bang predicts that the universe started out as mostly hydrogen and helium with certain ratios between elements and their isotopes, and these are closely matched by observational evidence.
•When we look at galaxies that are far away (ie into the past) we see that they are always less formed and less aged, implying that all protogalaxies started at more or less the same time.
What caused the big bang?
Short answer: We don't know, and we can't find out directly since the state of the big bang before atoms formed was opaque and couldn't leave any traces.
Slightly longer answer: But that doesn't stop us from hypothesizing! We can think up situations that conform to the known laws of physics and see if they lead to a big bang like our own starting. One such model is the cyclic model, which states that the universe has been undergoing a constant cycle of big crunches and big bangs for all eternity. It doesn't have much credibility any more, since we discovered the universe's acceleration is increasing and not decreasing; it's more likely that this universe will end by pulling itself apart after it starts inflating too fast.
There are other models, though; I don't remember them off the top of my head, but it is one of the open questions of science that we hope to have an answer for one day.
If it's not an explosion, why is it called the big bang?
It's the name given to the theory by an opponent of the theory, Fred Hoyle, back in the 1920s during a radio show. It wasn't an accurate name by any stretch of the definition, but it was catchy so it stuck.
Further notes
•The big bang, abiogenesis and evolution are unrelated theories; that is, finding problems in one does not imply there are problems in the others.
•Neither the big bang nor abiogenesis nor evolution precludes the existence of God, and you can be a theist while accepting the big bang/abiogenesis/evolution.
•While the big bang theory is not complete, its premise is considered correct by all of the scientific community, and work is done in the details only.
•There is a fallacy you should take note of and try to avoid; that is, the straw man. It's where you present a false or twisted view of a concept and falisfy it and then claim that the real view is also falsified. For example, "The big bang is just a bomb going off, and bombs never make anything happen, therefore the big bang theory is false!" This is using a straw man, as the big bang is not an explosion in the conventional sense.
•The expanding universe is not expanding into anything, not even empty space. It's an isolated system. There's no possibility of running into a extra-universal wall one day or anything.
Why a big bang?
Back in the 1900s, the view of the universe was that it was a 'steady state' universe; ie, it was eternal, more or less static and possibly infinite. Even Einstein subscribed to this idea! However, as more and more inquiry was made into the universe's makeup and more and more observations were made, things were about to change.
The movement of a celestial body relative to our own can be measured by looking at how red-shifted its light is; that is, measure the frequency spectrum of the light emitted from a celestial body, overlay it onto the frequency spectrum of the atoms we know it is made up of and see if the overall shape has been shifted to the red or blue end; if it's red-shifted it's moving away from us, if it's blue-shifted it's moving towards us and by how much is how fast it's going. Basically, it's the well known doppler effect only applying to light; if you're traveling away while emitting sound your sound waves are of a higher wavelength and vice versa.
In addition, we can even measure the distance away from us a certain cluster or galaxy is; there is a certain kind of star, a Cephid variable star, who's luminosity is tightly related to its period. Once we know the period we can calculate the expected luminosity then figure out how far away it must be.
Read more here since I don't think I can explain it well enough: http://en.wikipedia.org/wiki/Cepheid_variable
Anyway, a pair of astronomers, Edwin Hubble and Milton Humason, were looking at the red-shiftedness of things in the universe compared to their distance away from us and, after excessive study, found a pattern; basically, the further away things were, the faster away they were moving for us. This was all in the 1920s.
This can be formulated as: v = (H0)D, where v is the recessional velocity, D is the distance away from us and H0 is hubble's constant. This is not a relativistic formula; v can be bigger than c, that will be explained later however.
If we take this principle and 'rewind' time, moving all the stars and galaxies in the opposite directions, it is predicted that they all come together about 13.7 billion years ago. And this is how the big bang theory was first conceived.
What is the big bang?
The big bang theory states that the beginning of the observable universe (that is, the one we live in) started off as an ultra-dense, slightly heterogenous pocket of energy that underwent a period of rapid inflation that continues to this day. Note that is not the matter and energy that is moving outward, but the spacetime on which it lies; imagine it as sticking objects to a balloon then inflating it. This is how the expansion seems to violate special relativity; matter and energy cannot travel faster than the speed of light, but it's okay if it's due to spacetime itself moving.
As the early universe expanded its energy spreaded out and thus it became cooler and cooler steadily. From the ultra-hot sea of free energy, leptons (ie electrons) and baryons (ie protons) formed in processes known as leptogenesis and baryogenesis respectively; we know this could have happened since we've witnessed it in high-energy particle accelerators. Note that these processes happen simultaneously so as to not violate the conservation of electric charge.
At first the remaining energy in the form of photons was interacting with the protons and electrons constantly, but as the energy and matter grew sparser and sparser the first atoms were able to form, hydrogen and helium, and the photons were no longer attracted strongly and were able to travel out into open space; this is known as the universe becoming transparent, and the cosmic background radiation is the leftovers from when this happened.
As mentioned earlier, the energy density of the big bang was slightly heterogenous. That means that some parts were slightly denser then others. Once matter had formed from this energy it was also arranged in this heterogenous fashion, and where matter clumped it was drawn closer and closer via the process of gravity over millions and billions of years, forming protogalaxies. This is a process known as accretion, and in a similar fashion, individual clusters and solar systems also accrued together from lumps of matter on a smaller scale, and stars and planets on a smaller scale still.
Hopefully you can see from this that the big bang is not an 'explosion' at all; it's hardly comparable! If you detonate a bomb, you don't stick around for 10 billion years and watch the debris slowly pull itself together via gravity, and that's why analogies between the big bang and dynamite fail. Neither did the big bang create the Earth or life fully formed; that took billions of years as well, and life arose by a process known as abiogenesis which is completely different anyway.
If you're interested in the full timeline of the big bang, then read:
http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang
So, what's the evidence for it?
Glad you asked! Well, the biggest piece of evidence is the cosmic background microwave radiation; it has a certain distribution and temperature to it which the big bang theory's prediction matches perfectly, and I do mean more or less perfectly; the big bang model predicts that the CBMR should match that of an almost perfect black body, and it does! This is one of the main arguements for the big bang theory, as no other cosmological model was able to explain why the CBMR was exactly like this.
Other pieces of evidence:
•Hubble's law, that everything in space is moving away from us, the further away the faster it's regressing
•The abundances of primorial elements; the big bang predicts that the universe started out as mostly hydrogen and helium with certain ratios between elements and their isotopes, and these are closely matched by observational evidence.
•When we look at galaxies that are far away (ie into the past) we see that they are always less formed and less aged, implying that all protogalaxies started at more or less the same time.
What caused the big bang?
Short answer: We don't know, and we can't find out directly since the state of the big bang before atoms formed was opaque and couldn't leave any traces.
Slightly longer answer: But that doesn't stop us from hypothesizing! We can think up situations that conform to the known laws of physics and see if they lead to a big bang like our own starting. One such model is the cyclic model, which states that the universe has been undergoing a constant cycle of big crunches and big bangs for all eternity. It doesn't have much credibility any more, since we discovered the universe's acceleration is increasing and not decreasing; it's more likely that this universe will end by pulling itself apart after it starts inflating too fast.
There are other models, though; I don't remember them off the top of my head, but it is one of the open questions of science that we hope to have an answer for one day.
If it's not an explosion, why is it called the big bang?
It's the name given to the theory by an opponent of the theory, Fred Hoyle, back in the 1920s during a radio show. It wasn't an accurate name by any stretch of the definition, but it was catchy so it stuck.
Further notes
•The big bang, abiogenesis and evolution are unrelated theories; that is, finding problems in one does not imply there are problems in the others.
•Neither the big bang nor abiogenesis nor evolution precludes the existence of God, and you can be a theist while accepting the big bang/abiogenesis/evolution.
•While the big bang theory is not complete, its premise is considered correct by all of the scientific community, and work is done in the details only.
•There is a fallacy you should take note of and try to avoid; that is, the straw man. It's where you present a false or twisted view of a concept and falisfy it and then claim that the real view is also falsified. For example, "The big bang is just a bomb going off, and bombs never make anything happen, therefore the big bang theory is false!" This is using a straw man, as the big bang is not an explosion in the conventional sense.
•The expanding universe is not expanding into anything, not even empty space. It's an isolated system. There's no possibility of running into a extra-universal wall one day or anything.
