After all, they do beautiful, incredibly precise experiments that lead to, at least so far… null results.

Now, null results are important and interesting in themselves, especially when they are sufficiently precise to exclude promising fundamental theories. But it requires a certain kind of abstract mind to get excited by them.

Thanks for the clarification. I hate having my mental analogies taken from me. I’ll try to come up with something new.

And space can definitely be warped without being embedded in something bigger. It’s hard to visualize, I know. If the whole universe were the surface of a two-dimensional sphere, we could still tell (even if we couldn’t step outside to an extra dimension), for example because initially parallel lines would eventually come together.

I understand the rationale behind positing extra dimensions in small scales to explain anomalies in gravity. Mostly. But if those dimensions disappear at the observable level, what are cosmologists talking about when they discuss the “shape” of the universe?

E.g., the soccer ball shape, or the horn shape? I always picture the “shapes” as a three dimensional analog in a higher-dimensional space. Or, more accurately, I picture a two-dimensional world on a piece of paper, wrapped into a horn shape, or whatever, where the “shape” exists only in a higher dimension than what the 2D paper dwellers are aware of. Then I try to do the same thing +1 dimension, so our 3D universe wrapped into a 4D horn or soccer ball. Is that not an accurate analogy?

If not, how can 3D space be warped or shaped, without a higher spacial dimension to warp in?

It includes a good anecdote about how melting snow on the surrounding mountains upset the calibration of their equipment between summer and winter. I think this gives a good idea of the incredible sensitivity of their experiment.

I think it should very apparent to an educated layman with a passing interest in quantum gravity that this is serious and important work and one of the very few experiments that is directly probing the predictions of and putting constraints on some quantum gravity models.

For the record, I am also very interested in following recent tabletop results that hint at axion-photon mixing and I am looking forward to following up some of the other links in the posts above from Christine Dantas and others.

Thanks for another interesting post.

Simon — I haven’t read the paper, but the abstract refers to the AdS curvature radius in warped models, which isn’t exactly the same as the radius of the extra dimensions in ADD models (where the compactification is flat). Maybe it would also apply.