[lutusp]

> The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either.

Yes, that's true, but if the paper's thesis is correct, then there aren't any black holes or singularities at all, at any time. If the thesis is false, then there can be black holes at the universe's beginning, and they can form today, given the right conditions.

> Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now.

Not so different, and from a theoretical standpoint, they lie on a continuum from the present to the past. The condition of the universe as a whole has changed over time, but from the present we can mimic earlier conditions using high energies.

It is often said that one goal of accelerator technology is to move backward in time toward the Big Bang. As technology advances, as accelerator energies increase, we create conditions more like the conditions in the early universe. The ultimate hope is to create conditions as much as possible like the first few seconds of the universe's existence, to be able to see the genesis of present conditions and refine physical theory.

> Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario.

A physicist would immediately see the inconsistency in that. If the conditions of the Big Bang theory can exist in reality, then given the same conditions of temperature and pressure, we should be able to imitate an earlier reality on a small scale. That's what an accelerator is designed to be -- an imitation of nature at an earlier time.

[kijin]

No, the article only claims that a singularity cannot arise from a collapsing blob of matter.

We have no evidence that the singularity that existed at the moment of the Big Bang was the result of a collapsing blob of matter. Therefore, we have no reason to think that it could not have occurred.

In fact, it might not even make sense to think of that initial singularity as the result of anything at all, since causality requires time and there was no time before the Big Bang. Time is asymmetric, and this is especially important when we're talking about t = 0. You cannot simply imitate it from the other direction.

[lutusp]

> No, the article only claims that a singularity cannot arise from a collapsing blob of matter.

If true, it calls into question the existence of the initial singularity thought to precede the Big Bang. The alternative -- that the working of physical theories depends on circumstances -- isn't a very good one.

People sometimes hypothesize that this universe arose as a fluctuation in some other universe. For this kind of speculation to have any credibility, we have to assume that any singularity can be explained by physical theory, not just present-day singularities.

My point is that a theory whose workings depend on the circumstances isn't a very powerful one.

> We have no evidence that the singularity that existed at the moment of the Big Bang was the result of a collapsing blob of matter.

Look at this logically. If there was a singularity at the moment of the Big Bang, then it arose from the same physical theory that creates them in the present, but on a bigger scale. The alternative is to argue that physical theory is inconsistent, depending on circumstances. That sort of condition undermines physical theory, makes it more like a soap opera than science.

> In fact, it might not even make sense to think of that initial singularity as the result of anything at all, since causality requires time and there was no time before the Big Bang.

Yes, true, but once time exists, then we can start describing phenomena as having causes and effects. So physical theory only applies after time zero, not before. But if, at time zero, there was a singularity, we can try to apply physical theory to it. I'm not saying we will be successful, but it would be a mistake not to try.

[kijin]

I'm not advocating the idea that the laws of physics depend on circumstances. I'm just pointing out that similar processes may have vastly different consequences, even according to the same theory, given vastly different environment variables (as evidenced by the ongoing Bash fiasco).

For example, we know that things tend to behave weirdly at quantum scales. It that because the usual laws of physics do not apply at quantum scales? No, our best theories should be able to explain why the scale makes such differences, and therefore accurately predict phenomena at every scale, both large and small.

Likewise, there would be nothing wrong with singularities occurring under some circumstances and not under others, as long as we can come up with a compelling theory to explain how the different circumstances affect the outcome.

That's the kind of theory we should try to come up with. Not hasty generalizations based only on limited observation of familiar circumstances. I'm not saying we will be successful, but it would be a mistake not to try.