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> It does not have a great predictive record; it is good at explaining obervations after the fact (the CMB notwithstanding).

Can you elaborate on what you mean? LCDM hasn't been "tweaked" since \Lambda was established in the 90s (at least, not for large-scale cosmological observations). The current discrepancies are all at the precision level (<10%) rather than a qualitative O(1) difference. An important (but not dispositive) nuance is that LCDM well explains all observations individually; the percent-level tensions arise only between fits to datasets, meaning unknown systematics remain a viable explanation.

The unknown fundamental nature of CDM (as important a problem as it is) seems irrelevant to arguments about LCDM's predictivity (as a cosmological model).

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A couple of examples:

1. LCDM predicted hierarchical formation of large galaxies through aggregation. JWST seems to show this is not what happens (large galaxies at early times). I am sure it can be made to work, but it was not a prediction.

2. Constant Lambda - recent obervations seem to show it may be changing (OK - that is more built into the theory rather than being a prediction).

By the way, I am not saying LCDM is not massively successful. It can clearly be used to explain a lot of things. I am saying that I am not aware of many things it successfully predicted ahead of observations being made.

> I am saying that I am not aware of many things it successfully predicted ahead of observations being made.

CDM successfully predicted the CMB features that COBE could measure. LCDM certainly was a known model before supernova data in the 90s first provided evidence for it. CMB data shortly after detected a consistent fraction of \Lambda and have since provided evidence of multiple kinds (structure growth in addition to the original, the distance to the last scattering surface). Distances from baryon acoustic oscillations are another subsequent, independent test that corroborated the LCDM model.

2 and (especially) 1 are to me too speculative to place much weight on. I would also draw analogy to the Standard Model of particle physics: its predictivity and past success are not refuted by any deficiencies beyond the regimes we've been able to probe thusfar. (Of course, in the SM we fully expect those deficiencies.) Just to say that not every failed prediction falsifies a model's success in previously established regimes of energy/scale/dynamics.

> By the way, I am not saying LCDM is not massively successful. It can clearly be used to explain a lot of things.

Sure, I didn't think so.

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