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The LCDM is the standard model of cosmology and is well validated by experiments. If we go back to the Big Bang, the energy density diverges. Therefore, my question is "How far back can experiments confirm the LCDM model and what is the experiment which can look furthest back into the past?"

user185188
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    $\Lambda\text{CDM}$, as its name suggests, mismatches the observed amount of matter in the universe by 95% and cannot survive without inventing unphysical "dark energy" or unobserved "dark matter". No surprise it is breaking apart. Search for "crisis in cosmology", "axis of evil", "Hubble tension". "Today's space telescopes provide no direct view of anything-they produce measurements through an interplay of theoretical predictions and pliable parameters, in which the model is involved every step of the way." - https://blogs.scientificamerican.com/observations/cosmology-has-some-big-problems/ – safesphere Dec 19 '19 at 16:48
  • Unfortunately, this does not answer my question. Of course, the LCDM doesn't explain the physical background of dark matter and dark energy but there are a lot of experiments which confirms that the scale factor of the universe can be modeled with the Friedmann equations. – user185188 Dec 19 '19 at 18:36
  • There is no direct evidence that the scale factor follows Friedmann. For example, according to FLRW, more distant galaxies should appear larger in the sky, but nothing like this is observed: https://physics.stackexchange.com/questions/422644/ – safesphere Dec 19 '19 at 20:43
  • I don't understand the question. Everything diverges at the Big Bang, because it's a singularity. Everything up until the Planck time is relatively well understood. Is "Planck time" the answer you're looking for? – Allure Dec 20 '19 at 00:35
  • Yes, if ‚relatively well understood‘ means that it can be explained by LCDM and is validated by observations. Is that the case? – user185188 Dec 20 '19 at 06:51
  • It's all part of the world's richest (not per capita, but richest nonetheless) country, and one of its most populous, having a higher educational system whose substantial socialist component is tolerated only thru pandering to the imaginary joy of finding a universe magically attached to one's crib. A different subcontinent did much better, very long ago, with a reversed attitude and almost no resources. – Edouard Jan 20 '20 at 20:04

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I think the right word should be observations rather than experiments. You cannot make experiments on the universe. $\Lambda CDM$ model can work pretty well in some cases but it has also some problems. I mean you can explain the BBN with $\Lambda CDM$ model but there's Lithium problem. One of the fundamental parameter in the cosmological model $H_0$ gives different results for different measurements.

There's also $\sigma_8$ discrepancy. However it also explains lots of things. It really depends on your perspective of "success"

what is the experiment which can look furthest back into the past?

If we forget about inflation, I would say the BBN and the abundance of the light elements.

seVenVo1d
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