Immediately after the Big Bang, space may have vibrated like a string from quantum effects. As these oscillations faded, they would have left a mark on the expansion of galaxies — a memory effect. The search for this echo in telescope data turned up nothing.
Scientists modeled this memory as a vanishing energy and compared it with distances to supernovae and the sound waves of the early universe (baryon acoustic oscillations). They found no deviations from the standard picture with dark energy and dark matter. Even a faint signal, contributing more than 5% of the dark energy density, would have been noticeable.
So, either quantum gravity doesn't affect expansion, or its traces are thinner than a spider's web. And while Adam Riess and other scientists are building ultra-precise maps of the cosmos, the quantum past remains silent for now. Paradoxically, this very silence strengthens our trust in the standard model, while future instruments might just catch the whisper of the first moments.
To directly detect quantum gravity, you'd need an accelerator the size of the Milky Way: that's why scientists look for its indirect traces.