Lots of media (e.g. CNET) bring us the gospel about a survey organized by the Associated Press and GfK among 1,000+ Americans. They were asked about their beliefs in various claims made by the scientists.







Only 4% doubted that smoking causes cancer; over 80% actively claimed it does. Only 8% doubted that cells contain a consequential genetic code; almost 70% actively argued that they did. The reality of the Big Bang 13.8 billion years ago was the least believed proposition, getting about 20%. That's vastly lower than the number of Americans who believed in various religious insights such as the resurrection of Jesus Christ or the claim that the weather patterns get less favorable in the wake of the human sins (the so-called "climate change" religion is bought by nearly 1/3 of Americans).









Natural selection and evolution was actively backed by 31% of the Americans.







It's not pretty but the Big Bang's results were much worse than that. It seems that the percentage for the Big Bang is as low as the percentage of the TV viewers who are watching The Big Bang Theory on CBS. Maybe all believers in the Big Bang Theory are watching the sitcom of the same name! ;-)









Dear 80% Americans, why don't you try to look at the color of some galaxies and see that it's redshifted? This shift towards the lower (redder) frequencies is due to the outward motion, the Doppler effect, that you should have known from Sheldon. Four your convenience, the definition of the Doppler effect is repeated 3+1 times in the video below:







It was enough for Penny!



The reddening shows that the outward velocity of a galaxy at distance \(D\) is equal to \(V = DH\) where \(H\) is an observed constant, Hubble's constant. Just assume that the velocity was always of the same order. How much time did it take for the galaxies to get this far? It's \(T = D / V = 1/H\), the inverse Hubble's constant. It's just of order 10 billion years, stupid. So 10+ billion years ago, the galaxies were very close, unless someone already made them diverge that quickly a long time ago. A good enough explosive to do so only works if the galaxies' matter were extremely compressed. So 10+ billion years ago, the galaxies were just superclose to each other.



Some extra maths you don't want to follow helps you to calculate it a bit more accurately – including the variable speed of the galaxies and the curvature of space and time – and the best measured age of the Universe is 13.8 billion years according to the data from numerous experiments. You know that you need an ancient universe, anyway. 27% of Americans answered that the Earth is 4.5 billion years old. The Big Bang Theory has made other predictions – about the relative abundance of light elements in the cosmos; and the cosmic microwave background, among others – and they were confirmed. They would surely contradict other random ways to get the galaxies in outward motion.







OK, I don't want to try to convince the 80% Americans about the reality of the Big Bang in any deatail because it is a waste of time and most Americans who are visiting this blog are confident that the Big Bang has occurred, anyway. But let me just say that if Christianity is the reason, it is actually bizarre for the Christians not to embrace the sharp beginning – the Big Bang – enthusiastically. The hippie on the picture above is the Christ, Jesus Christ, and he has just said "BANG". Such a "BANG" when the time started needed a creator – it's probably the only activity where the modern science may actively consider a creator helpful.



I have actually listened to parts of various debates and talks by William Lane Craig, a Christian apologist (e.g. one debate with Lawrence Krauss and another one with Sean Carroll). He is not your kind of a dumb obsessed Young Earth Creationist. He is an intelligent man who decided to rationalize Christianity. I don't believe that he enjoys the social and ethical freedom to abandon Christianity and its basic dogmas altogether but given the straitjacket into which he has squeezed his soul, he is doing a good job in defending some traces of God within physics.



Needless to say, I would disagree with most of the other "religiously tainted" insights (including his views on resurrection, a topic that I mentioned because we just celebrated the Easter) – as well as his unjustifiably skeptical attitude towards string theory and other key parts of modern physics – but he's been on the winning side in the question "whether the Universe had a beginning". For some reason, Krauss – and other atheists – would prefer a cosmology without any beginning, the kind of the past-eternal "static Universe" that physicists would believe in the 19th century. Why would atheists favor such a thing? Well, because there would be no room for Jesus to say "BANG". ;-)



The Big Bang Theory has actually been assaulted by the Marxist ideologues for quite some time; that much for the "scientific character" of Marxism. They don't like the idea that the mass/energy conservation law has to be revised in the context of cosmology (modern cosmology is an application of the general theory of relativity) – and essentially becomes invalid or vacuous, depending on your viewpoint.



Even though tons of professional atheists are either overt or covert Marxism sympathizers, they gradually got used to the Big Bang. But most of them would still prefer some past-eternal picture on top of the Big Bang. I would bet that even efforts such as the cyclic/ekpyrotic (or Penrose's cyclic conformal) cosmological models are partly motivated by the authors' fear of the true beginning. Eternal inflation allows new universes to grow all the time – and it produces a future-eternal universe.



But all cosmological models actually prohibit a past-eternal cosmology; they always imply that the world had a beginning. This has been most clearly proven by Arvind Borde, Alan Guth, and Alex Vilenkin ("BGV") in 2003:



Hi Lawrence [Krauss],



Any theorem is only as good as its assumptions. The BGV theorem says that if the universe is on average expanding along a given worldline, this worldline cannot be infinite to the past.



A possible loophole is that there might be an epoch of contraction prior to the expansion. Models of this sort have been discussed by Aguirre & Gratton and by Carroll & Chen. They had to assume though that the minimum of entropy was reached at the bounce and offered no mechanism to enforce this condition. It seems to me that it is essentially equivalent to a beginning.



On the other hand, Jaume Garriga and I are now exploring a picture of the multiverse where the BGV theorem may not apply. In bubbles of negative vacuum energy, expansion is followed by contraction, and it is usually assumed that this ends in a big crunch singularity. However, it is conceivable (and many people think likely) that singularities will be resolved in the theory of quantum gravity, so the internal collapse of the bubbles will be followed by an expansion. In this scenario, a typical worldline will go through a succession of expanding and contracting regions, and it is not at all clear that the BGV assumption (expansion on average) will be satisfied.



I suspect that the theorem can be extended to this case, maybe with some additional assumptions. But of course there is no such thing as absolute certainty in science, especially in matters like the creation of the universe. Note for example that the BGV theorem uses a classical picture of spacetime. In the regime where gravity becomes essentially quantum, we may not even know the right questions to ask.



Alex [Vilenkin]



They showed that the integral of the Hubble parameter is smaller than a finite bound in a cosmology that is mostly expanding – and they didn't even need any energy condition for that (a condition saying that the density of energy or some related quantity can't go negative).William Lane Craig is on a mission – and the beginning of the Universe seems very Christian to him. So the BGV theorem has actually become his pet result and he has understood it rather well. So well, in fact, that – painfully and ironically enough – he's been more correct or more honest about its interpretation than cosmologist Lawrence Krauss with whom Craig has debated.In September 2013, a month after the Craig-Krauss debate, the Christian apologists got very excited about the fact that Krauss has partially censored and misinterpreted an e-mail he got from Vilenkin . Krauss has pretty much cropped some sentences in a way that dramatically changes the overall implications of Vilenkin's e-mail. On the other hand, Vilenkin sent another e-mail to Craig where he acknowledged that Craig has interpreted the BGV theorem "very accurately".(Even if all the people were acting dishonestly and purely in their personal interest, it wouldn't be shocking that Vilenkin has supported Craig and not Krauss: after all, Craig thinks that the work by Vilenkin et al. is important and robust while Krauss treats it as an inconvenient piece of dust that may be blown away.)Craig has later published the full e-mail from Vilenkin to Krauss and you may compare it with Krauss' truncated version , too. Krauss' censorship is pretty scary and his claims that he omitted the "too technical parts" of the e-mail are clearly indefensible. The parts censored by Krauss are written in bold:You see that in the censored parts, Vilenkin essentially says that all the conceivable and proposed loopholes are unlikely or probably wrong and that the BGV theorem may be extended to one that bans these would-be loopholes, anyway. Even if the theorem were formally wrong in some interpretation, it is still morally right, Vilenkin argues.Note that one proposed would-be loophole was due to Carroll and Chen . That paper reflects Carroll's omnipresent misunderstanding of the origin of the second law of thermodynamics. He says that the Universe could have been past-eternal before a certain point but the entropy was decreasing for \(t\lt 0\) which he finds – and, probably, they find – OK. At \(t=0\), the arrow of time was reverted and the entropy had a global minimum. It is not really possible to revert the arrow of time – the thermodynamic arrow of time is a derived one (via the H-theorem) from a more fundamental and unavoidable one, the logical arrow of time – and even if you found a framework in which such a reversal would be formally allowed, the \(t=0\) moment would be so special and catastrophic that it should still be called "the beginning", anyway (both Vilenkin and your humble correspondent say).Because the entropy was decreasing for \(t\lt 0\), it is better to use the entropy itself – and not the coordinate \(t\) – to be a faithful quantification of time since the beginning. And because the entropy was high both for \(t\gt 0\) and \(t\lt 0\), it would be more correct to say that the Carroll-Chen universe had a beginning at \(t=0\) and from that beginning, it was evolving into two futures, one for positive \(t\) and one for negative \(t\). You shouldn't imagine the time as a straight line but rather as a V-shaped manifold that is increasing in the left as well as in the right; it's two (equivalent or inequivalent?) futures evolving from the beginning.Another "not really real" loophole that Vilenkin discusses is the same one that I discussed in March when I disagreed with Matt Strassler's claim that there was probably no Big Bang singularity . (Now I realize, maybe Matt Strassler has voted along with the 80% majority of the Americans – claiming that there has been no Big Bang LOL.) If one adds some quantum-gravity regime that regulates various quantities and protects their finiteness, the "period of time" in which the quantum gravity is existentially needed should have been very short (Planckian short) and it is conceptually right to view it as a part of the object called "singularity" (our right description of the concept of the Big Bang singularity is improved and regulated when we switch from classical GR to quantum gravity but as long as the following – nearly classical – expansion of the Universe is still there, we have no right to say that the singularity as a locus has entirely disappeared).Incidentally, when Craig caught Krauss' censorship of important segments of Vilenkin's e-mail, I was also disappointed by Krauss' foggy suggestion that science hasn't proven that there had to be a beginning, and so on, which – Krauss indicated – meant that Craig was building on sand. However, science never proves things with a strict 100% certainty. But this limitation doesn't prevent science from getting really close to 100% and the "nearly proven" propositions are treated as rather important ones by scientists. That's exactly what Craig was doing – he used the evidence to argue that it was far more likely for the Universe to have a beginning – so it was painful for Krauss to try to weaken Craig's propositions by saying that there exists no 100% rigorous proof. There never exists a 100% rigorous proof of propositions that directly apply to Nature!So I do think that the BGV theorem kills the models that want to extend the cosmological history of the visible Universe in a way that makes it eternal. The real motivation is clearly to make it past-eternal – because the (finite or infinite) future couldn't have affected the present, by causality, so the future's being finite or infinite is inconsequential for us today – but cosmologies can't really be past-eternal. So it is silly to "prefer the past-eternal cosmologies for aesthetic reasons" because the very basic feature of these models makes them impossible, BGV showed.I don't have any doubts that William Lane Craig is also spinning insights and results in ways that depend on the outcomes he wants to defend. But it's disappointing to see that people like Krauss and Carroll are doing the same thing. If both sides of a controversy are doing such a thing, it may happen that each of them is more right. And indeed, it has just happened that the Christian apologist ended up as the man who has more accurately interpreted a theorem, the BGV theorem.(Just to be sure, the proof of the beginning – even if we view the existing evidence as a proof, and we're arguably not far from that – doesn't imply that some God or supernatural forces at the beginning have been established. The initial conditions of the Universe may follow perfectly rational, natural, and scientifically accessible laws.)I should also try to "weaken" my claims that the evolution of the Universe had to have a beginning by saying that I can imagine some room for the pre-Big-Bang cosmological evolution. Perhaps, our visible patch of the Universe had a father, perhaps a grandfather, possibly a few great grandfathers, and a forefather – and the evolution was looking for the right compactification that is so hospitable for us. But it's important to realize that according to the available evidence and calculations, the number of these generations probably had to be finite.