Instigator / Pro
12
1649
rating
29
debates
72.41%
won
Topic

The Big Bang Probably Happened

Status
Finished

All stages have been completed. The voting points distribution and the result are presented below.

Arguments points
6
3
Sources points
2
4
Spelling and grammar points
2
2
Conduct points
2
2

With 2 votes and 1 point ahead, the winner is ...

Sum1hugme
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Science
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Two weeks
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Contender / Con
11
1632
rating
20
debates
72.5%
won
Description
~ 268 / 5,000

The Big Bang Theory - the theory that the universe expanded from a hot, dense state to a cool and sparse one.

Universe - spacetime and its contents

BOP is shared:

Pro : The Big Bang Probably Happened
Con : The Big Bang Probably did not Happen

I hope this is fun.

Round 1
Pro
  Thank you Fruit_Inspector for accepting this debate. This won't be a terribly long opening.

  DEFINITIONS

Scientific Theory - a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and repeatedly confirmed through experiment or observation[1]
Proof -  Evidence or argument establishing a fact or the truth of a statement [2].

  QUALITIES OF A SCIENTIFIC THEORY

    A scientific theory is an attempt to construct a model of some aspect of reality. A scientific theory must have three qualities:

1. It must be independently verifiable, preferably by making novel predictions about future data.
2. It must be potentially falsifiable, otherwise it can be discarded into the category of pseudoscience.
3. It must make as few assumptions as possible, the idea of Parsimony in Science.

  If a theory is not verifiable, or it's predictions fail, that is indicative that it is not a reliable model of reality. If a theory is not falsifiable, then it cannot be tested with the scientific method, and therefore is probably pseudoscience. And a theory that is not parsimonious will contain extraneous elements that limit the scope of its explanatory power, liable to be disregarded in favor of a model with less assumptions (Occam's Razor).

  I will demonstrate that the theory put forth satisfies all of these qualities, indicating it is the best current model to fit the data.

THE BIG BANG THEORY

  The Big Bang Theory claims the following:
  1. The Universe expanded from a hot, dense state to a cool and sparse one and,
  2. The Universe is still expanding.

  The theory has been vindicated many times, but I will focus on three specific ones here: Hubble’s Law, the Universe’s temperature, and the Cosmic Microwave Background Radiation.

HUBBLE’S LAW

  In 1922, Alexander Friedmann published his Friedmann Equations[3] based on General Relativity, predicting that the Universe is expanding. In 1929, Edwin Hubble observed that Galaxies were moving away from us at a uniform rate[4]; Galaxies that are twice as far away are moving twice as fast, Galaxies that are three times as far are moving three times as fast, etc. This is indicative that the Universe itself is expanding, uniformly, in all directions. This is an observational confirmation of a prediction of the model, lending credence to its explanatory power.

THE UNIVERSE’S TEMPERATURE

  If the Universe was smaller and hotter, and is expanding uniformly in all directions, then the model predicts it should have a relatively uniform temperature distribution. Even though their calculations were slightly off, Alpher and Herman (1948) used the model to predict the temperature of the universe to be around 5K [5]. This is very close to what was later observed to be closer to 2.7K [6]. This is a prediction made using the model, that was confirmed with observation later. This is another clear example of why the model is an accurate description of reality.

COSMIC MICROWAVE BACKGROUND RADIATION (CMBr)

   If the Big Bang Theory were true, then there should be a radiation afterglow spread throughout the Universe as a result of the extremely high temperatures in the early Universe.  The existence of the CMBr was first predicted in 1948, and was observationally confirmed in 1965 on accident by Penzias and Wilson [7]. Today, we have a clearer picture than ever of the CMBr [8] thanks to experiments like WMAP and Planck Satellite. Again, the model accurately predicted future data, which we are now observing.

CONCLUSION

  In conclusion, the Big Bang probably happened. The model makes novel, testable predictions about future data, and has been vindicated repeatedly against this rigorous standard. It is the best model to fit the available data. It fits all the criteria of what a good Scientific Theory should be, and its predictions lead to novel observations and novel data. There is no greater qualifier for a theory than to make successful predictions. I look forward to my opponent’s response.

Con
Given the debate topic, I will go directly into a response to my opponent's claims about the Big Bang. The opening statements were fairly straightforward and I think they will provide a good start to this discussion.

Response: "HUBBLE'S LAW"
I don't think there are many who disagree with the claim that the universe is currently expanding. The disagreement is about whether the universe has been expanding for billions of years as the Big Bang Theory posits. However, I think it would be misleading to say that Friedmann predicted the Big Bang. The reason is that predicting the universe is currently expanding and predicting the universe has previously been expanding for billions of years are two very different claims. That doesn't mean that the Friedmann Equations and the Big Bang Theory are unrelated. It just means that Friedmann should not be used as an example of a novel prediction of the Big Bang Theory. I would be happy to be shown direct evidence to the contrary though.

A similar statement can be made for Edwin Hubble's findings. Concluding that the universe is currently expanding does not automatically prove the Big Bang. It just shows that the universe is currently expanding. The generic concept of the Big Bang being deduced from such a conclusion certainly does not defy basic logic. If we can observe the current expansion of the universe, then it is not illogical to say that it has previously been expanding. But science is not merely based on logical deductions. It also requires empirical evidence.

The problem I see with this particular argument by PRO is that I don't see any evidence that Hubble's law was an "observational confirmation of a prediction of the model." That would be putting the cart before the horse. It seems that the concept of the Big Bang is a conclusion based on the established premise of a currently expanding universe. As far as I can tell, even Georges Lemaître's early idea of a primeval atom was not seriously proposed until 1931, two years after Hubble's observations. So unless PRO can provide specific timelines and direct evidence, I think it is erroneous to say that the Big Bang Theory predicted that the universe is expanding.

Response: "THE UNIVERSE'S TEMPERATURE" and "COSMIC MICROWAVE BACKGROUND RADIATION (CMBr)"
The Horizon Problem has been raised by many about this particular aspect of the Big Bang Theory. I think Wikipedia offers a succinct, albeit unscholarly, summary of the issue:

"The horizon problem (also known as the homogeneity problem) is a cosmological fine-tuning problem within the Big Bang model of the universe. It arises due to the difficulty in explaining the observed homogeneity of causally disconnected regions of space in the absence of a mechanism that sets the same initial conditions everywhere. It was first pointed out by Wolfgang Rindler in 1956...If the universe started with even slightly different temperatures in different places, the CMB should not be isotropic unless there is a mechanism that evens out the temperature by the time of decoupling. In reality, the CMB has the same temperature in the entire sky, 2.726 ± 0.001 K."
So even though there was a prediction of the Cosmic Microwave Background, the isotropic nature of the CMB does not actually support the Big Bang model that predicted it. In other words, the theory is not supported by the evidence.


The Flatness Problem
NASA provides a short summary of the Flatness Problem:

"WMAP has determined the geometry of the universe to be nearly flat. However, under Big Bang cosmology, curvature grows with time. A universe as flat as we see it today would require an extreme fine-tuning of conditions in the past, which would be an unbelievable coincidence."


To provide a bit more context, here is another unscholarly statement from Wikipedia:

"In the case of the flatness problem, the parameter which appears fine-tuned is the density of matter and energy in the universe. This value affects the curvature of space-time, with a very specific critical value being required for a flat universe. The current density of the universe is observed to be very close to this critical value. Since any departure of the total density from the critical value would increase rapidly over cosmic time, the early universe must have had a density even closer to the critical density, departing from it by one part in 10^62 or less. This leads cosmologists to question how the initial density came to be so closely fine-tuned to this 'special' value."


Now I chose to use these citations because I think they do a good job of briefly laying out the issue in an easy-to-understand way. The Horizon Problem and the Flatness Problem are not new issues by any means. However, I am interested to hear how my opponent addresses them. I would suggest that unless the Big Bang model can account for these problems - or an alternative scientific theory supported by empirical evidence can account for them in a consistent way - it would be irresponsible to say that the Big Bang probably happened from a scientific perspective.

Round 2
Pro
  Thank you Fruit_Inspector for your response. There were two main objections brought up in the last round:
  1. The horizon problem
  2. The flatness problem 

  Fortunately, these haven't been problems for the theory since 1979. In 1979, Alan Guth (with others) extended the theory to include a new element that solves these problems: cosmic inflation [1]. Cosmic inflation states that there was an exponential expansion of the Universe in the first fraction of a second. 

  I will use the same source my opponent used to explain how this solves the above mentioned problems. 

"The Flatness Problem:
Imagine living on the surface of a soccer ball (a 2-dimensional world). It might be obvious to you that this surface was curved and that you were living in a closed universe. However, if that ball expanded to the size of the Earth, it would appear flat to you, even though it is still a sphere on larger scales. Now imagine increasing the size of that ball to astronomical scales. To you, it would appear to be flat as far as you could see, even though it might have been very curved to start with. Inflation stretches any initial curvature of the 3-dimensional universe to near flatness.
The Horizon Problem:
Since Inflation supposes a burst of exponential expansion in the early universe, it follows that distant regions were actually much closer together prior to Inflation than they would have been with only standard Big Bang expansion. Thus, such regions could have been in causal contact prior to Inflation and could have attained a uniform temperature. [2]"

  Plainly, even in my opponent's own source, the Big Bang Inflationary model (as it's called nowadays) does account for the objections my opponent has raised.

CLARITY OF TIMELINE

  Georges Lemaître had derived the same equations as Friedmann, and published his paper in French, linking those equations to the idea that the Universe is expanding, in 1927 [3]. The translated version didn't come out until 1931.  

  Therefore, Hubble's observation, in 1929, was observational confirmation of a prediction of the earliest form of the Theory. I hope that clarifies the timeline.

MISC. REBUTTALS

"Concluding that the universe is currently expanding does not automatically prove the Big Bang. It just shows that the universe is currently expanding...But science is not merely based on logical deductions. It also requires empirical evidence."

  Science is inductive, and therefore will never deal in epistemic certainty. Science proposes models, which try to describe reality. In this case, the model predicted that the Universe is expanding, based on General Relativity (Friedmann and Georges). The observation of uniform expansion confirms a novel prediction made by the model. That's the hardest form of empirical evidence: novel, testable predictions of future data. If that prediction is confirmed, that is a solid inductive reason to accept the model as a provisionally true descriptor of reality. Even more so if that model can predict multiple things correctly.

  I'm not going to pretend the Theory hasn't been patched together over the years, but it, like so many other theories, typically have to be updated to account for the known data, or discarded. In this case, the Theory has been extended to include Cosmic Inflation as part of the model, and therefore resolves it's former problems. 

  If the model states that the Universe is expanding, and has been for a while; and, if that theory is vindicated observationally, like the Big Bang has been, then it is reasonable to accept that model as an accurate descriptor of reality.

"The disagreement is about whether the universe has been expanding for billions of years as the Big Bang Theory posits."

"Astronomers estimate the age of the universe in two ways: 1) by looking for the oldest stars; and 2) by measuring the rate of expansion of the universe and extrapolating back to the Big Bang; just as crime detectives can trace the origin of a bullet from the holes in a wall.[4]"

  We can dive deeper into these methods if my opponent wishes, But I only touch upon them here since the age of the universe is not the topic of the discussion; the accuracy of the Big Bang inflationary model is.

CONCLUSION

  In conclusion, the Big Bang Probably happened. The Big Bang model has met the highest standard of scientific rigor: successful predictions of novel future data. In every case I have offered, the predictions of the theory were validated observationally. The objections my opponent has proposed, are well accounted for by the Theory. If the model can make accurate predictions about future data, and accounts for the known facts, then it is reasonable to say it is probably a true descriptor of reality. I look forward to my opponent's response and I hope I didn't miss anything.
Con
Continued Response: "HUBBLE'S LAW"
Let me start by addressing the timeline issue. Friedmann had already predicted a currently expanding universe in 1922 before Georges Lemaître published his paper in 1927. From what I understand, the paper published in 1927 only dealt with the current expansion of the universe based on observing redshift. The paper that was published in 1931 was not only translated into English, but was also edited and expanded to include the proposal that the universe started from a primeval atom - the earliest form of the Big Bang Theory [1].

I will summarize my objection. The earliest forms of the Big Bang model were not meaningfully proposed until AFTER the discovery of an expanding universe. The predictions of Friedmann and Lemaître were that the universe is currently expanding. That is a completely different claim than predicting that the universe has been expanding for billions of years from a single point, and it requires a different method of confirmation.

My opponent has claimed that the Big Bang model predicted the expansion of the universe. I see no evidence of this claim. Friedmann did not present a Big Bang model to predict an expanding universe in 1922. Lemaître did not present a Big Bang model that predicted his calculations regarding redshift and an expanding universe in 1927. And Hubble did not use a Big Bang model to predict his redshift observations in 1929. It was not until 1931 - after the discovery of an expanding universe - that a hypothesis resembling a Big Bang model was presented. Therefore, the Big Bang model did not predict an expanding universe. The discovery of an expanding universe was used to predict a Big Bang.

For my opponent's argument to be substantiated, I believe we need to see two things:

  • A citation in which a meaningful Big Bang model is clearly presented prior to the discovery of an expanding universe. And since Lemaître's 1931 paper was edited and expanded, we would need to see a citation specifically from his 1927 paper that shows him presenting a Big Bang model making this prediction.
  • Clear evidence that this Big Bang model was used to predict an expanding universe (and not the other way around). If someone like Lemaître used the concept of an expanding universe to deduce that the universe began from a small dense state, PRO's claim is unsubstantiated and the Big Bang Theory did not predict an expanding universe.
If no specific citation is provided that clearly identifies a Big Bang model predicting an expanding universe, PRO's claim should be dismissed.


Continued Response: "THE UNIVERSE'S TEMPERATURE" and "COSMIC MICROWAVE BACKGROUND RADIATION (CMBr)"

"I'm not going to pretend the Theory hasn't been patched together over the years, but it, like so many other theories, typically have to be updated to account for the known data, or discarded. In this case, the Theory has been extended to include Cosmic Inflation as part of the model, and therefore resolves it's former problems."

I find it interesting that a model that has supposedly been vindicated repeatedly in its predictive power would need to be consistently updated to account for existing data, lest it be discarded. Shouldn't the model be predicting the data before it is observed rather than being significantly adjusted to fit the observations? The only actual prediction that I have seen with some justification is the prediction of a Cosmic Microwave Background.

But allow me to reiterate that even though a previous version of the Big Bang model was used to predict the existence of a CMB, the observation of the actual CMB did not really support the model that predicted it. The model alluded to by my opponent in Round 1 that predicted a CMB required an entirely new theory to be added to work with this new data. Cosmic inflation had to be inserted after the CMB was observed, so the model was fundamentally changed in order to fit the previously observed data. Therefore, I find it hard to substantiate the claim that the Big Bang model accurately predicted data regarding a CMB because the observed CMB data was incongruent with the model that predicted it. Without the theory of cosmic inflation, the Big Bang model can't solve the Horizon problem. But since the Big Bang Inflationary model has been presented, we will deal with that in a moment.

I will also point out that cosmic inflation is required to explain the inadequacy of the previous Big Bang model in accounting for the Flatness Problem. I am reiterating these issues because unless PRO can resolve these two problems another way, cosmic inflation becomes the hinge upon which his argument rests that the Big Bang - as a scientific theory - probably happened.


Cosmic Inflation
Let's test the theory of cosmic inflation according to PRO's qualifications for a scientific theory from Round 1.

1.  Inflation has made no novel predictions about future data.

It is a highly arbitrary model that is adjusted to fit existing data, but it cannot meaningfully predict anything. In an article critiquing the validity of cosmic inflation, three authors (including Paul Steinhardt who was a contributor to inflationary theory) explained how the theory does not meaningfully predict anything because "inflation is not a precise theory but a highly flexible framework that encompasses many possibilities" [2]. And since Steinhardt shared the 2002 Dirac Medal with Guth and Linde for his contributions to develop the concept of cosmic inflation [3], I think his analysis has at least a little credibility.

2. Inflation is unfalsifiable.

Let's see what Alan Guth himself thinks about whether inflation is falsifiable [4]:

Interviewer: "Is [inflation] falsifiable?"

Guth: "I think that's kind of a silly question...Inflation is really an ingredient of theories and someday we'll pin down the right theory and then we can decide whether we want to call it inflationary or not."

When the question was asked again a moment later:

Interviewer: "Is it possible to do an experiment that would falsify [inflation]?

Guth: "Well I think inflation is a little bit too flexible an idea for that to make sense."

I believe PRO must show us in specific detail how cosmic inflation is falsifiable for it to fulfill this trait of a scientific theory.

3. Inflation lacks parsimony and is reliant on assumptions.

Physicist Neil Turok said this in an interview about cosmic inflation [5]:

"It's a theory which doesn't explain the Big Bang. It doesn't explain the moment of the emergence of the universe. It just assumes that for some reason we can't explain, the universe sprang into existence dominated by a strange repulsive form of matter, the like of which we don't see today. But you can put this matter into Einstein's equations. It's like a spring. It's like a compressed spring and it causes space to expand like an expanding spring. And that is the inflationary explanation for the Big Bang. The reason I don't find it convincing is that it assumes this spring was compressed in the beginning. Who compressed the spring? Why was it compressed? So it turns out if you calculate what is the likelihood of the universe to have emerged full of this strange inflationary energy, it's exponentially tiny. It's absolutely negligible."

The three authors quoted previously that included Paul Steinhardt published a follow-up article [6], in which they referenced a paper by Alan Guth:

"As Guth has put it, 'In an eternally inflating universe, anything that can happen will happen; in fact, it will happen an infinite number of times. Thus, the question of what is possible becomes trivial—anything is possible […] The fraction of universes with any particular property is therefore equal to infinity divided by infinity—a meaningless ratio.' See, highlighted text in the Conclusion section of Guth's paper published in J.Phys. A40, 2007 [7]"

Paul Steinhart also said this about inflation in an interview [8]:

"But my concerns really grew when I discovered that, due to quantum fluctuation effects, inflation is generically eternal and (as others soon emphasized) this would lead to a multiverse...Since 1983, it has become clear that inflation is very flexible (parameters can be adjusted to give any result) and generically leads to a multiverse consisting of patches in which any outcome is possible. Imagine a scientific theory that was designed to explain and predict but ends up allowing literally any conceivable possibility without any rule about what is more likely. What good is it? It rules out nothing and can never be put to a real test."

So the theory of inflation literally assumes an infinite number of possibilities will happen an infinite number of times. That hardly seems to fit the principle of parsimony. And, as these critics have noted, the theory of inflation has not predicted future data; rather, the highly flexible model was adjusted to fit previously observed data. And the theory of inflation is unfalsifiable which, by PRO's definition, shows that we ought to place it in the category of pseudoscience. This conclusion is also not unique to me. Paul Steinhardt feels that way, and even Alan Guth admits there are problems with inflation being unfalsifiable.


Conclusion
The argument presented to us so far by PRO is that the Big Bang Theory, with the necessary addition of the theory of cosmic inflation, probably happened. While inflation can theoretically account for the two problems I presented in Round 1, it becomes a major problem when placed under further scrutiny. If the Big Bang model requires the theory of cosmic inflation be added to fit the observed data, and if my analysis of inflation is correct according to PRO's qualities of a scientific theory, then the Big Bang requires inflationary pseudoscience in order to be validated. Is it scientifically responsible to base our claims in such a way? Steinhardt doesn't seem to think so:

"Some scientists accept that inflation is untestable but refuse to abandon it. They have proposed that, instead, science must change by discarding one of its defining properties: empirical testability. This notion has triggered a roller coaster of discussions about the nature of science and its possible redefinition, promoting the idea of some kind of nonempirical science" [9]

Round 3
Pro
  Thank you for this debate Fruit_Inspector, it was a lot of fun and I hope I've been able to sway you personally on this topic. Even if you remain unconvinced, perhaps this will at least challenge your personal beliefs regarding the matter. Science works by creating models, and then testing those models and comparing them against the available data. In most cases, the models must be updated to be more precise, but that doesn’t mean that the predictions they made, or the problems they solved were not accurate. 

Let me reiterate what the BB model claims:
  1. The Universe expanded from a hot, dense state to a cool and sparse one and,
  2. The Universe is still expanding.
"... cosmic inflation becomes the hinge upon which his argument rests that the Big Bang - as a scientific theory - probably happened."
  Cosmic inflation is a tool for solving the problems the earlier forms of the theory had. If it turned out to be wrong, that would not, in any way, invalidate the predictions and confirmations I laid out in my R1. But as we will see, it's actually well substantiated.

DEVELOPING A THEORY


"From what I understand, the paper published in 1927 only dealt with the current expansion of the universe based on observing redshift. The paper that was published in 1931 was not only translated into English, but was also edited and expanded to include the proposal that the universe started from a primeval atom - the earliest form of the Big Bang Theory [1]."
  Georges 1927 paper was a solution to Einstein's equations of general relativity for the case of an expanding Universe. His model proposed a linear relationship between a galaxy's distance and it's redshift, and that this shift was caused by the expansion of space itself [1]. This is a proposal of the second point of the theory as it stands today. This prediction of his model was observationally confirmed by Edwin Hubble in 1929. So that prediction was confirmed by the earliest form of the model.

  The 1931 revision proposed a finite beginning to the universe from a single quantum. This was a further development of the theory, which can be derived from extrapolating back the expansion of the universe that we observe today until time equals zero. If the Universe is expanding uniformly in all directions, then it was closer together in the past. Eventually, you reach a state where all energy is compressed into a single point of infinite curvature (a singularity).


"I find it interesting that a model that has supposedly been vindicated repeatedly in its predictive power would need to be consistently updated to account for existing data, lest it be discarded. Shouldn't the model be predicting the data before it is observed rather than being significantly adjusted to fit the observations?"
  As our understanding increases, our models become more precise. That doesn't mean it didn't predict the data that it predicted, But as time goes on the model gets updated to be more precise. A more precise model better describes reality. Does the fact that we discover new elements mean that the model of the periodic table and the predictions that it's earlier forms made is somehow unscientific? Of course not. While the older model (Mendeleev's) was not incorrect, it was incomplete, and new observations have to be incorporated to extend the model to better describe reality.

  It's the same thing here. The model started incomplete and has been updated to account for new data so that it better describes reality. Every form of the theory has made predictions, and solutions have been found for its problems, resulting in an updated model.

CMBr AND TEMPERATURE


"Cosmic inflation had to be inserted after the CMB was observed, so the model was fundamentally changed in order to fit the previously observed data. Therefore, I find it hard to substantiate the claim that the Big Bang model accurately predicted data regarding a CMB because the observed CMB data was incongruent with the model that predicted it."
  The CMBr was predicted by Alpher and Herman in 1948, along with the prediction of what its temperature should be. This prediction was predicated on the expanding universe model that had already been developed by that time, thanks to the derivations of Friedmann and Georges. They predicted that there would be a cosmic microwave background radiation, and that its temperature would be around 5K. The prediction of the CMBr was not a prediction of Cosmic Inflation (which hadn’t been developed at that time), it was based on a uniformly expanding Universe (which had already been observed in 1929). So, if the Universe is expanding uniformly, and it expanded from a hot, dense state, then there should be a radiation afterglow spread uniformly throughout the Universe. This was observed in 1965 by Penzias and Wilson. The temperature prediction was incredibly close too: predicted at 5K (-450.67 F); discovered to be  2.7 K (-454.81 F). That's remarkably close to what was observed.  Again, we have earlier forms of the model,  making novel predictions, while being itself incomplete. Even without Cosmic Inflation yet developed, the earlier forms of the model made accurate predictions about novel future data.

"...the observation of the actual CMB did not really support the model that predicted it. "
  The model that predicted it, was an earlier form of the current model. The observation of the CMBr confirmed the predictions made by the model. So yes, it did support the Big Bang model that the Universe was once smaller and hotter. 

COSMIC INFLATION

  When we vindicated the idea that the Universe was once smaller and hotter,  then we are left with the fact that we have to provide some explanation to account for the Flatness problem and such. This solution was proposed in the form of Cosmic Inflation. It is the best current explanation, specifically because it solves every problem of the Big Bang Theory.

1.  Inflation has made no novel predictions about future data.
According to astrophysicist Ethan Siegel:
"In brief, the six most generic predictions were:
  1. There should be an upper-limit to the maximum temperature the Universe achieves post-inflation; it cannot approach the Planck scale of ~1019 GeV.
  2. Super-horizon fluctuations, or fluctuations on scales larger than light could have traversed since the Big Bang, should exist.
  3. The quantum fluctuations during inflation should produce the seeds of density fluctuations, and they should be 100% adiabatic and 0% isocurvature. (Where adiabatic and isocurvature are the two allowed classes.)
  4. These fluctuations should be almost perfectly scale-invariant, but should have slightly greater magnitudes on larger scales than smaller ones.
  5. The Universe should be nearly, but not quite, perfectly flat, with quantum effects producing curvature only at the 0.01% level or below.
  6. And the Universe should be filled with primordial gravitational waves, which should imprint on the cosmic microwave background as B-modes.
It's now 2019, and the first four predictions have been observationally confirmed. The fifth has been tested down to the ~0.4% level and is consistent with inflation, but we haven't reached the critical level. Only the sixth point has not been tested at all, with a famous false-positive detection appearing earlier this decade owing to the BICEP2 collaboration.
The maximum temperature has been verified, by looking at the cosmic microwave background, to be no greater than about 1016 GeV.
Super-horizon fluctuations have been seen from the polarization data provided by both WMAP and Planck, and are in perfect agreement with what inflation predicts.
The latest data from structure formation indicates that these early, seed fluctuations are at least 98.7% adiabatic and no more than 1.3% isocurvature, consistent with inflation's predictions.
But the best test — and what I'd call the most significant confirmation of inflation — has come from measuring the spectrum of the initial fluctuations. Inflation is very particular when it comes to what sorts of structure should form on different scales. We have a quantity that we use to describe how much structure forms on large cosmic scales versus smaller ones: ns. If you formed the same amount of structure on all scales, ns would equal 1 exactly, with no variations.
What inflation generically predicts, however, is that we will have an ns that's almost, but slightly less than, 1. The amount we depart from 1 by is determined by the specific inflationary model. When inflation was first proposed, the standard assumption was that ns would be exactly equal to 1. It wouldn't be until the 2000s that we became capable of testing this, through both the fluctuations in the cosmic microwave background and the signature of baryon acoustic oscillations.
As of today, ns is approximately 0.965 or so, with an uncertainty of around 0.008. This means there's about a 4-to-5 sigma certainty that ns is truly less than 1, a remarkable confirmation of inflation." [2]

"2. Inflation is unfalsifiable."
  Inflation is falsifiable if its predictions fail.

"3. Inflation lacks parsimony and is reliant on assumptions."
  It's actually both the simplest and the most comprehensive explanation for the proposed problems for the Big Bang model. It solves every problem of the Big Bang model, and several of its predictions have been verified observationally.

CONCLUSION

  In conclusion, the Big Bang probably happened. For a century, a model has developed that describes the structure and origin of the Universe. It has made consistent predictions about novel future data, and been vindicated repeatedly. It has, in every case, withstood the strain of scientific rigor and is the best model that describes reality as we observe it. In every form of its development, it was making these predictions, advancing it as an accurate model. And the Big Bang Inflationary model as it stands today, is extremely compelling. 
Con
I would like to also thank my opponent for what has been an engaging debate. I always enjoy digging into particular subjects like these.

I will start by summarizing my main position to frame my concluding arguments. In response to the resolution "The Big Bang Probably Happened" under discussion, I do not believe it is scientifically responsible to make such a statement until the seemingly irreconcilable problems have been resolved. The two I have brought up are the Horizon and Flatness problems. These are not minor details to be explored later after assuming the conclusion is true. The uniform temperature and the curvature of the universe we currently observe are impossible outcomes of the Big Bang Theory without fundamentally changing the theory altogether. In this case, the theory has been altered with the addition of Cosmic Inflation. My assertion is that, according to PRO's own definition of a scientific theory, inflation falls under the category of pseudoscience.

We were given 3 reasons in Round 1 why PRO believes the Big Bang Theory has been vindicated, or shown to be true. I will summarize my arguments against each one.

1. "HUBBLE'S LAW"
PRO stated in Round 1 that the observation of an expanding universe "is an observational confirmation of a prediction of the model, lending credence to its explanatory power." I cannot state this emphatically enough: the Big Bang model was not used to predict an expanding universe. I will cite my opponent's own logic in his Round 3 argument under the "CMBr AND TEMPERATURE" heading:

"The prediction of the CMBr was not a prediction of Cosmic Inflation (which hadn’t been developed at that time), it was based on a uniformly expanding Universe (which had already been observed in 1929)."


PRO clearly understands there is a chronological aspect in which the prediction itself must precede the observation that is being predicted. It violates PRO's own logic then to say that an observation made in 1929 was predicted by a theory that did not exist in its earliest form until 1931. PRO's own source from Round 3 demonstrates this very point:

"In 1927, Belgian priest and physicist Georges Lemaître made what is perhaps the greatest discovery in modern cosmology — our universe is expanding. Four years later, he proposed that the universe began with a “single quantum” — what we now call the big bang."


So, my opponent's argument is that the Big Bang model predicted an expanding universe. As I said in Round 2, I believe for this to be substantiated, we need to see two things:

  • A citation in which a meaningful Big Bang model is clearly presented prior to the discovery of an expanding universe. And since Lemaître's 1931 paper was edited and expanded, we would need to see a citation specifically from his 1927 paper that shows him presenting a Big Bang model making this prediction.
  • Clear evidence that this Big Bang model was used to predict an expanding universe (and not the other way around). If someone like Lemaître used the concept of an expanding universe to deduce that the universe began from a small dense state, PRO's claim is unsubstantiated and the Big Bang Theory did not predict an expanding universe.

No citation has been provided to prove such a claim. It would be more accurate to say that the Big Bang model was a hypothesis created in an attempt to explain the previously discovered expanding universe. Therefore, the Big Bang model did not predict an expanding universe.

2. "THE UNIVERSE'S TEMPERATURE"
My opponent is correct in asserting that Alpher and Herman made a prediction about the temperature of the CMB. Does this vindicate the Big Bang Theory though? While this prediction was significant, it also led to a major problem that the Big Bang Theory cannot solve by itself - the Horizon Problem. Remember, the Horizon Problem arises due to the uniform temperature throughout the universe of 2.726 ± 0.001 K. The reason this is a problem is that it would essentially be impossible for this uniformity to exist if the universe simply expanded from a hot, dense state as my opponent's description of the Big Bang Theory states. I alluded to this at the end of Round 1 because that means the Big Bang Theory without the addition of Cosmic Inflation (or some other plausible alternative theory) cannot account for the uniform temperature of the CMB.

To put it more simply, the temperatures we have observed show us a universe that could not have come about if it simply "expanded from a hot, dense state to a cool and sparse one" as my opponent asserts. Now my opponent has claimed that we can say the Big Bang model is proven to be true even if Cosmic Inflation turns out to be wrong. But the Horizon Problem - as well as the Flatness Problem - shows that it is impossible for our current observable universe to be a product of the Big Bang without some addition to the model. Can we really say the model has been vindicated then? This is why Cosmic Inflation becomes the crux of the debate, without which it would be unreasonable to say that the Big Bang probably happened.

3. "COSMIC MICROWAVE BACKGROUND RADIATION (CMBr)"

PRO's argument about the temperature of the universe is directly tied to the CMB, which I have just dealt with in the last section. I will just reiterate that the CMB is the only observation that can be said to have been a prediction of the Big Bang model given our discussion of chronological events. However, I will refer the reader to my argument "Continued Response: "THE UNIVERSE'S TEMPERATURE" and "COSMIC MICROWAVE BACKGROUND RADIATION (CMBr)" from Round 2 for my arguments against the CMB as a valid prediction of the Big Bang model without Cosmic Inflation.



Cosmic Inflation
I will summarize my assertion that Cosmic Inflation should be considered pseudoscience according to PRO's argument "QUALITIES OF A SCIENTIFIC THEORY" from Round 1.

1.  Inflation has made no novel predictions about future data.
We were given a quotation from an article that simply made claims about "predictions" that Cosmic Inflation has gotten correct. We were given no citations as to where to find those specific predictions, nor when those particular observations were made. Remember, even my opponent recognizes how important the chronological aspect of predictions is. But notice the author cited previous observations leading to the Horizon and Flatness problems as successful "predictions." This goes back to my earlier point. If an observation was made prior to the existence of the theory of Cosmic Inflation, then it cannot be said that it was a prediction of the model. Both observations leading to the Horizon and Flatness problems were made before the existence of the theory of Cosmic Inflation. But as the original contributor Paul Steinhardt said, "inflation is not a precise theory but a highly flexible framework that encompasses many possibilities" (https://physics.princeton.edu//~cosmo/sciam/assets/pdfs/SciAm.pdf).

2. Inflation is unfalsifiable.
Alan Guth, the main person associated with developing Cosmic Inflation has recognized the difficulty in falsifying the theory as my citations from Round 2 showed. I also cited that Paul Steinhardt, a contributor to Cosmic Inflation with Guth, has claimed the theory is unfalsifiable. But these citations went unaddressed, with the only response being, "Inflation is falsifiable if its predictions fail." Here was my request from PRO in Round 2:

"I believe PRO must show us in specific detail how cosmic inflation is falsifiable for it to fulfill this trait of a scientific theory."

We have been given no such example.

3. Inflation lacks parsimony and is reliant on assumptions.
If you go back and read through my Round 2 citations under the "Cosmic Inflation" heading, you will see that Guth, Steinhardt, and Turok all agree that inflation is an extremely complex framework that includes an infinite number of possibilities, making the theory essentially unfalsifiable. PRO has not provided any actual arguments other than to claim - on his own authority with no evidence - that Cosmic Inflation is "both the simplest and the most comprehensive explanation for the proposed problems for the Big Bang model."


Therefore, I hold to my assertion, backed by unaddressed citations from Guth, Steinhardt, and Turok, that Cosmic Inflation should be placed in the category of pseudoscience according to PRO's Round 1 argument.

Conclusion
The Big Bang Theory has at least two seemingly irreconcilable problems: the Horizon and Flatness Problem. PRO has not argued the validity of these two problems, and the only explanation given to reconcile them is Cosmic Inflation. Given that no specific test was provided on how one would falsify Cosmic Inflation, the only way to reasonably assert that "The Big Bang Probably Happened" is to base the whole theory on the pseudoscience known as Cosmic Inflation. If we do not have a scientific explanation based on empirical evidence and testability to account for the observable conditions of the universe, then it seems irresponsible to make the scientific claim that the Big Bang probably happened.