What Parts of the Big Bang Do Scientists Dispute?

[PdotdQ]

@Patrick

Fred Hoyle died in 2001. Just the Planck final results (2018) alone is enough to confirm the Big Bang to 1% precision in most parameters of the Lambda- CDM model of the universe. @dga471 chime in here please.

@dga471

Reading the Planck final results that you mentioned, I see that they have measured 5 of the 6 parameters of the Lambda-CDM to at least 1% precision (see page 18 of the paper), which is probably what you meant. However, that’s not exactly the same as a test of Lambda-CDM to 1% right? That would only be the case if Lambda-CDM can calculate and predict these values from first principles and they found that they match up to observation. But while I’m sure the ability to measure the parameters to such high precision depends on part on the effectiveness of the model, the precision is more a vindication of the observational power of the Planck spacecraft than of the theory. Am I right, @PdotdQ?

@dga471 got it right. Just because I can fit my datapoints with 13 parameters to 1% precision does not mean that the data cannot be fit by 13 other parameters.

I will take this opportunity to share some causes of concerns for Lambda-CDM. These issues are not deal-breakers in the sense that there might be a way to reconcile them with LCDM, but notably all of these issues can be dealt with by modifying LCDM. This is what I meant when I said previously that most astronomers (including myself) believe in LCDM with a little bit of modifications.

Issues with CDM (Cold Dark Matter):

1. CDM predicts too many small galaxies
2. CDM predicts that galactic centers have densities that rise sharply - in contrast to observational evidence.
3. Recently, McGaugh et al.'s paper which we discussed previously in this forum suggests that either there is no dark matter or that there is a coupling between dark matter and baryonic (normal) matter. This is in violation of LCDM.
4. Recently, the EDGES experiment that aims to detect neutral hydrogen in the cosmological scale produces a controversial finding that either there is an extra source of cooling of hydrogen gas or there is an extra source of low frequency photons than the Cosmic Microwave Background. Both of these can be solved by coupling the dark matter with either baryons (normal matter) or electromagnetic fields (~photons). These are in violation of LCDM.

Issues with inflation (all of these are exacerbated by the Planck results):

1. The inflationary potential which governs dynamics during inflation is extremely fine tuned
2. It is extremely unlikely for inflation to produce our observable Universe - this requires very specific initial conditions that probability-wise is exponentially suppressed.
3. In light of quantum mechanics, inflation produces a multiverse resulting in the theory becoming unfalsifiable. The common adage is “anything can happen and will happen an infinite number of times". Comically, this is considered a problem by some and a feature by others.

@pevaquark

Yes but Georges Lemaitre got the idea from playing around with Einstein’s equations of GR and the Friedmann equations

A small historical correction: Georges Lemaitre did not fiddle with the Friedmann equations. Instead he independently reproduced it.