What does the BGV theorem say?

Then you cannot say anything about the beginning of the Universe with the BGV theorem, as the beginning of the Universe concerns ~Planck time.

Well this definitely is true:

But this statement seems to be true to me as well:

The BGV theorem is not evidence for the beginning of the Universe, as in general theorems in classical physics cannot be extended to the quantum regime. In fact, now that I think about it, it is hard to think of a theorem in classical physics that survives in the quantum regime. Here are some examples of classical theorems that fail in the quantum regime:

  1. Conservation of energy: fails in the quantum regime
  2. Conservation of momentum: fails in the quantum regime
  3. Conservation of number of particles: fails in the quantum regime
  4. Continuum of energy states for particles in bounded potentials: fails in the quantum regime
  5. etc

Most classical theorems become invalid in the quantum regime, so why would I think that the BGV theorem (which is classical) remains valid in the quantum regime?

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I guess my response to all of the above, outside of the constraints of methodological naturalism, is that BGV, which accounts for all of past physical reality except for the last moment of plank time, seems to seriously infer a beginning of physical reality.

The fact that there seems to be many philosophers and scientists who seem to agree with that inference, I think would suggest that it is a reasonable inference. The fact that all physical reality that is empirically confirmed has a beginning and a cause is further evidence to support that inference.

Since, as I understand it, we don’t even have a theory of quantum gravity due to the problems that arise when applying quantum field theory to the force of gravity, I would say it’s premature to suggest with any significant degree of confidence what is or isn’t possible at the quantum level in regards to a beginning of physical existence.

So from the perspective of an abductive argument, I would say it’s perfectly warranted to argue that the best explanation of the evidence we currently do understand is that physical existence had a beginning.

“Seriously” why? As of now, I can’t say that it “seriously infer a beginning of physical reality”. I can as non-rigorously say the fact that conservation of energy breaks down in the quantum regime seriously imply that the BGV theorem will also break down in the quantum regime.

Again, this is appeal to authority towards personal beliefs of people. This is non-rigorous. Show me the math.

That is my point. It is premature to suggest with any significant degree of confidence that the BGV theorem survives in the quantum regime. So don’t use it in these arguments.

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How confident can we be that conservation of energy breaks down in the quantum regime is true? There’s no way to empirically confirm that, is there?

What I’ve stated is that from all confirmed empirical evidence and from other evidence that we do understand, like BGV in the context of classical GR that says that in the past direction physical reality heads towards a boundary point, it is warranted to infer a beginning to the universe. Can you demonstrate to me from evidence that is empirically confirmed and well understood that what I’m inferring is unwarranted?

As close to 100% as is possible in the sciences. It’s baked into the uncertainty principle, which is at the heart of quantum mechanics. If it turns out that the conservation of energy is always preserved at the quantum scale, then all of quantum mechanics comes tumbling down. Any empirical confirmation of quantum theory (which is the most well tested theory of physics) is essentially a confirmation of this fact.

Remember, my entire point is not to say that the universe has no beginning, but that we do not know whether the universe has a beginning. It’s easy to support my argument: Because we don’t have a theory of quantum gravity, then it is premature to suggest that the BGV theorem survives in the quantum regime. Our knowledge of this limitation of contemporary physics is well understood and non-controversial. So your inferring, which requires that the BGV theorem survives in the quantum regime is unwarranted.

What about the other way? You now need to show me that, given that the BGV theorem is a classical theorem, and given that in general classical theorems are invalid in the quantum regime, that it is warranted to use it to infer the beginning of the universe, which is necessarily quantum.

Also note:

This “boundary point” is just a point where GR breaks down, nothing more. It says surprisingly little about the beginning of the real Universe, which can be either at that point or even beyond that point - if that can even be well-defined. For example, what happens if the Universe balloons on the other side of that boundary?

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I was about to answer this way, but was beat by the astrophysicist!

Even in GR the conservation of energy is not absolute: I.e. to start:
https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

@Jim

  • The BGV theorem applies to classical GR
  • The universe at the beginning was not classical
  • The BGV theorem is a useful guideline to where the classical description breaks down
  • Thus the BGV theorem is not as a great of apologetic for the Christian worldview as some apologists might like to imagine
  • And I would add in agreement with @PdotdQ, while Yahweh was the ultimate source of the universe… things like the BGV theorem aren’t part of this belief

For example, Dr. Hugh Ross dubiously (in light of this thread and my conclusion) uses this argument for Yahweh in particular. @PdotdQ, was I accurately understanding a Christian apologists/astrophsicsts use of the BGV theorem:

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Thank you for this post. I really like what you said here:

@Jim, to be clear, I am a Christian, just like you (and so is @pevaquark). I would like it if the BGV theorem supports the assertion that the Universe has a beginning, but it is simply not true. Let us defend Christianity with good science, not misunderstandings of scientific results.

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Correct me if I’m wrong, but from a laypersons perspective how I see it is that there are varying degrees of certainty in science. The empirical, i.e., observational and experimental, is objective and when confirmed is pretty much considered as fact and accepted without debate. The theoretical is subjective and can be and should be disputed until confirmed by direct observation of some kind, or it can be shown that almost all the evidence that can be available is, and that it is decidedly on the side of the theory.

If I’m not mistaken deductive inferences are based on direct evidence and are objective in nature. Inductive inferences are based on an overwhelming amount of indirect evidence in favor of a claim that, though subjective, leaves very little, if any, room for doubt about its truth.

Abductive inferences are based on limited evidence where there is still a substantial amount of information that isn’t available either because a way has yet to be devised for further exploration, or due to it being beyond human limitations, which leaves considerable room for debate as to the best explanation of the limited evidence, and is therefore the most subjective type of reasoning.

Now when you say “as close to 100% as is possible in the sciences,” I find that too ambiguous of a statement to deal with. My limited understanding is that the uncertainty principal and the observation of oscillation patterns of energy fields are involved in positing the temporary violation of the law of conservation of energy.

What I would like to know first is, what other evidence is there besides a principal, i.e., confirmed mathematical formula, and oscillation patterns of energy fields? And correct me if I’m wrong, but I’m assuming besides indirectly, e.g., through oscillation patterns, there is no direct observation of an actual occurrence of the proposed violation, but that it is wholly theoretical at this point in time.

(This may be getting a bit off topic?)

@Jim, it is getting off topic. Regardless, I think you have the wrong view of how scientists operate. Either that or we are using very different languages, so much so that we are talking past each other.

You seem to think that scientists rank the certainty of their theories based on whether they used deductive, inductive, or abductive inference. In reality, what scientists do is use Bayesian inference, which is a mathematically rigorous way to determine the probability of a theory being true given the evidence at hand. The probability that is outputted from Bayesian inference is what I refer to when I say stuff like “as close to 100% as is possible in the sciences”.

Second, the idea of “direct” evidence is somewhat ill-defined in physics. I did not appreciate this fact, but @dga471 and others corrected me in this thread, and I became convinced that this is the case.

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I largely agree but would point out Bayesian reasoning has severe limits. I more understand science as a type of hypothesis testing process.

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I assume that you’re referring to virtual particles here? Since conservation of energy does hold in “standard” (non-relativistic) QM if we’re talking about a time-independent Hamiltonian, see e.g. this review here. Even in the case of virtual particles, this is one way people make sense of this, although it sounds a bit hand-wavy:

In many decays and annihilations, a particle decays into a very high-energy force-carrier particle, which almost immediately decays into low-energy particle. These high-energy, short-lived particles are virtual particles.

The conservation of energy seems to be violated by the apparent existence of these very energetic particles for a very short time. However, according to the above principle, if the time of a process is exceedingly short, then the uncertainty in energy can be very large. Thus, due to the Heisenberg Uncertainty principle, these high-energy force-carrier particles may exist if they are short lived. In a sense, they escape reality’s notice [emphasis mine].

The bottom line is that energy is conserved. The energy of the initial decaying particle and the final decay products is equal. The virtual particles exist for such a short time that they can never be observed.

Correct. But I want to add:

It’s true that at the end energy is conserved, but this statement is not true for short timescale. And also they said:

But, while it’s true that we cannot observe virtual particles like we do other particles, the reality of their existence is corroborated by their effects on other observables, such as the Lamb Shift.

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Yes, we can calculate the Lamb shift by summing the relevant Feynman diagrams. But it’s not clear to me whether physicists regard virtual particles in these diagrams as “real” in the same respect as the observables. One could say that they are just a calculational tool. Famously, before Feynman diagrams became popular, Oppenheimer and others tried to calculate the Lamb shift with traditional perturbation theory techniques and found them to be divergent (as detailed in Chapter 4 of Schwartz’s QFT textbook). However, Feynman’s method was able to get over this, essentially by canceling infinities with other infinities. Even today, this aspect of QFT (renormalization) makes people uneasy. Most people don’t think much about it as QFT can give such accurate predictions. But it seems to me that one could regard this as a placeholder, heuristic theory for a more fundamental one. Which is why I’m not sure if we should regard the virtual particles as existing in the same way as the actual experimental observables.

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I suppose this goes to what one consider to be “Real”. Maybe you would be interested in reading Gordon Kane’s opinion of the matter here.

Before going off too far off tangent, @dga471, I wanted to know what you think of the charge that the BGV theorem is not evidence for the beginning of the Universe. I think the clearest formulation of it is @pevaquark’s:

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Fair enough, although I wonder if it may be a matter of different scientists’ preferences. But as I understand it, Bayesian inferences are not fundamentally different from other types of inferences, just a way of putting a figure on an inference to provide a bit more clarity, and possibly a more practical way to be able to update once new info is at hand.

But whatever the type of inference, as far as I can tell, they’re all based on background knowledge and evidence. So in order to defend a position, the background knowledge, which would include any assumptions, and evidence should be made available. I don’t know if it’s just me, but I still don’t know whether or not that’s been done yet.

I have to say I’m still not convinced about the BGV not being useful in arguing for a beginning. It certainly isn’t evidence against it. And to point out that there are both philosophers and scientists, including Vilenkin himself, who seem to think it infers a beginning is not, as I understand it, appealing to authority, simply pointing out that as experts their opinions need to be considered as to whether or not they add any additional weight to the validity of the inference.

And considering the amount of uncertainty surrounding the quantum realm I would say using it to argue against the inference is weak at best considering the weight of the evidence in favor of the inference, i.e., all empirically confirmed physical entities with beginnings, expansion of the universe, 2nd law of thermodynamics, and BGV, i.e., all of history involving physical existence heading towards a singularity only possibly excluding the first moment of planck time, not to mention the philosophical reasons for a beginning.

I don’t know how else to convince you. This is the time when you have to answer the question:

Give me something rigorous to sink my teeth into, not just claims like the BGV theorem “strongly indicates” or “seriously infer” a beginning. You need to explain why “strongly indicates”? Why "seriously infer? What are your priors? How do you update your probabilities? If you do this in a convincing enough manner, this is a serious topic that can be published in a physics journal, so I am really looking forward to it.

Also, this:

Is definitely an appeal to authority. Saying that an expert’s opinion needs to be considered is the definition of appeal to authority. This is not really good reasoning. I can also cite many other experts that disagree with your experts.

Note that I do not claim that the “uncertainty” of quantum gravity means that the BGV theorem does not survive in the quantum regime. I argue that this very uncertainty is the reason that it is premature to say that the BGV theorem survives in the quantum regime.

I think this is the fundamental difference in our reasoning. I’m starting from what is known and arguing from that position. You’re starting from what isn’t known and arguing from that position. So it seems like the old Aristotelian vs Plato debate. Are ideas primary and experience secondary? Or is it the other way around? I think until we agree on that we’ll have to agree to disagree. :slight_smile:

Unfortunately I disagree even with that. I start with what are known:

  1. General Relativity is a theory that is classical
  2. In general, theorems in classical physics cannot be used in the quantum regime
  3. BVG theorem is a theorem in General Relativity
  4. The beginning of the Universe is in the quantum regime

These four things are knowns, and I argue from there.

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Jim, I think what @PdotdQ is saying, is that using the BGV theorem to conclude anything about the beginning of the universe is not correct, as you are misapplying the theory. It is no different than saying, “Because many people in America drive gas guzzling cars, it must be the case that many people all over the world drive gas guzzling cars!” Such an inference is illegitimate because what is true in America might not be true elsewhere in the world.

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So, based on similar reasons as what you, @pevaquark, Aron Wall and others have pointed out, I agree that using the BGV theorem alone is not a good argument for arguing that the Universe had a beginning. This could be the impression left by many Christian apologists including Craig himself in some of his debates. However, Craig’s advocacy of the Kalam Cosmological Argument (KCA) goes back much further than the BGV theorem, and his contemporary version of it goes far wider than simply citing the BGV theorem. I think Matthew is not representing it fully. It is certainly not a naive argument for the existence of God.

The most recent version of Craig’s KCA is (I think) the essay in The Blackwell Companion to Natural Theology, coauthored with James Sinclair. Here, they marshall a wide set of arguments to argue for the finitude of the past. The first two are philosophical arguments: 1) Arguing that the existence an actual infinite is impossible, and 2) Arguing that the formation of an actual infinite through successive addition is impossible. I think these philosophical arguments have been developed by Craig since the 80s.

The third argument is the scientific one. Here, Craig & Sinclair’s argument is quite comprehensive, starting from the history of Big Bang theory. (Perhaps it would be interesting for you to read this complete article, as someone trained in GR and cosmology.) Before the 1920s, most physicists assumed that the universe was eternal and static. After Big Bang theory caught on, this no longer was the case - we can say that the universe is about 13 billion years old, and it included a singularity in the past, as C&S argue, due to the Hawking-Penrose theorems. C&S then talk about the exceptions to the H-P theorems, including eternal inflation, for which BVG is relevant. However, they also talk (with considerable technical detail) about quantum gravity models, including Pre-Big Bang inflation (Veneziano & Gasperini), ekpyrotic/cycling (Steinhardt & Turok), loop quantum gravity models, and Hartle-Hawking. For each of these models they argue that a beginning is required.

After C&S establish that a beginning is required, and that things which begin to exist have to be caused, they also talk about what kind of causal agent could have caused that. They argue that the First Cause must be beginningless, changeless, immaterial, timeless, spaceless, personal and enormously powerful. It is not merely saying “God did it”.

What do I think about all of these arguments? I think that C&S have done almost as much as is possible with current cosmological knowledge to argue that the universe must have had a beginning. BVG is spoken of a lot, but it is far from being the only thing they utilize. From an experimentalist point of view, none of these quantum gravity models have experimental corroboration yet, so I think that general scientific caution and skepticism is warranted. However, I think making a philosophical argument for the existence of God based on these comprehensive arguments is legitimate, even if I think they are not very strong arguments because we have very little knowledge about quantum gravity. (Assuming what C&S say about the science is correct. I am not sufficiently trained in GR & cosmology to judge that.)

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