A Beautiful 2D Embedding Is Not Quantitative Evidence, Warns AI-for-Science Researcher

bravo_abad · x · 2026-10-05

An AI-for-Science researcher cautions that t-SNE and UMAP plots — used across crystal structures, molecules, spectra, single-cell profiles and more — should never be treated as quantitative evidence. These methods mainly preserve local neighborhoods and necessarily distort global geometry when squeezing data into 2D: distant-looking clusters in t-SNE aren't necessarily very different, cluster sizes and densities are unreliable, low perplexity can reveal pure noise, and much of UMAP's apparent global structure comes from initialization. Plots shift with perplexity, nneighbors, mindist and the random seed.

The recommended workflow: use 2D maps to explore neighborhoods, subpopulations, outliers and mislabeled entries — then validate in the original space via neighbor computations, cross-seed checks, PCA comparison, and physical ground truth like composition, symmetry, DFT energies and experiments. Principle: generate hypotheses with t-SNE/UMAP, don't turn visual distances into scientific measurements.

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