The Entropic Brain: Psychedelic Neuroscience's Most Influential Theory — Put to the Test

When you take a psychedelic, your brain becomes more chaotic. More disordered. More entropic. That is the claim at the heart of the Entropic Brain Hypothesis, and for a decade the evidence seemed to be stacking up. A wave of research in 2025 and 2026 put it to the test. A replication study in Copenhagen tested fourteen entropy measures at once, and most of them failed. A major review identified four fundamental problems with it. And Karl Popper, that great old philosopher of science, has something to say about all of it. We cover what the hypothesis claims, what the data shows, how Prof. Dr. Robin Carhart-Harris has answered his critics, and where the field goes from here. ⏱️ CHAPTERS 0:00 Introduction 0:39 Section 1 – What Is the Entropic Brain Hypothesis? 2:10 Section 2 – What Does "Entropy" Actually Mean for a Brain? 8:03 Section 3 – The Copenhagen Study 11:51 Section 4 – Four Problems With the Theory 22:56 Section 5 – Carhart-Harris Responds 27:04 Bridge - The Falsifiability Problem 29:52 Section 6 – What Should We Do? 34:11 Conclusion 🔬 ADDITIONAL RESOURCES Drummond McCulloch's ALPS lecture on brain entropy:    • Evaluating Psilocybin Effects on Multiple ...   The Copenhagen Brain Entropy Toolbox (CopBET): https://github.com/anders-s-olsen/CopBET Karl Popper clip, from "Karl Popper & John Eccles in Discussion (1971)" by Philosophy Overdose:    • Karl Popper & John Eccles in Discussion (1...   🔍 A NOTE FOR THE ATTENTIVE VIEWER In Section 5, Carhart-Harris argues that fMRI was never the right tool for the kind of entropy the theory cares about, and that EEG and MEG are where the effect shows up reliably. The wrinkle: the 2014 paper that launched the hypothesis was built almost entirely on fMRI, and its own entropy measure was one the Copenhagen team could not replicate. The first EEG/MEG entropy finding came in 2017. In fairness, the shift was already proposed in the 2018 revision, years before Copenhagen. But it is exactly the kind of move Popper would want you to notice. 📚 REFERENCES 1. Carhart-Harris et al. (2014), Frontiers in Human Neuroscience https://doi.org/10.3389/fnhum.2014.00020 2. McCulloch et al. (2026), Nature Communications https://doi.org/10.1038/s41467-026-74... 3. Moses et al. (2026), Neuroscience & Biobehavioral Reviews https://doi.org/10.1016/j.neubiorev.2... 4. Chang et al. (2018), Scientific Reports https://doi.org/10.1038/s41598-018-21... 5. Brito et al. (2022), Anesthesia & Analgesia https://doi.org/10.1213/ANE.000000000... 6. Schartner et al. (2017), Scientific Reports https://doi.org/10.1038/srep46421 7. Larsen et al. (2026), medRxiv preprint https://doi.org/10.64898/2026.01.15.2... 8. Murray et al. (2024), Neuropsychopharmacology https://doi.org/10.1038/s41386-024-01... 9. Mediano et al. (2024), ACS Chemical Neuroscience https://doi.org/10.1021/acschemneuro.... 10. McCulloch et al. (2024), medRxiv preprint https://doi.org/10.1101/2023.07.03.23... 11. Mateos et al. (2018), Cognitive Neurodynamics https://doi.org/10.1007/s11571-017-94... 12. Siegel et al. (2024), Nature https://doi.org/10.1038/s41586-024-07... 13. Du et al. (2025), Molecular Psychiatry https://doi.org/10.1038/s41380-025-03... 14. Costa (2023), Journal of Psychoactive Drugs https://doi.org/10.1080/02791072.2022... 15. Bayne & Carter (2018), Neuroscience of Consciousness https://doi.org/10.1093/nc/niy008 16. Cardone et al. (2025), Clinical Neurophysiology https://doi.org/10.1016/j.clinph.2025... 17. Carhart-Harris (2026), Brain https://doi.org/10.1093/brain/awag206 18. Carhart-Harris (2018), Neuropharmacology https://doi.org/10.1016/j.neuropharm.... 19. Lyons et al. (2026), Nature Communications https://doi.org/10.1038/s41467-026-71... 20. Nature Editorial (2026), Nature https://www.nature.com/articles/d4158... 21. Nature Editorial (2025), Nature https://www.nature.com/articles/d4158... 22. Cogitate Consortium et al. (2025), Nature https://doi.org/10.1038/s41586-025-08... 23. Avram et al. (2021), Frontiers in Psychiatry https://doi.org/10.3389/fpsyt.2021.70... 24. Koch et al. (2016), Nature Reviews Neuroscience https://doi.org/10.1038/nrn.2016.22 25. Tagliazucchi et al. (2014), Human Brain Mapping https://doi.org/10.1002/hbm.22562 26. Vollenweider & Preller (2020), Nature Reviews Neuroscience https://doi.org/10.1038/s41583-020-03... 27. Logothetis (2008), Nature https://doi.org/10.1038/nature06976 🔗 FOLLOW PSYCHEDELICSNOW 📰 Weekly newsletter: https://substack.com/@psychedelicsnow ☕ Support on Ko-Fi: https://ko-fi.com/psychedelicsnow1943 🚫 ADS There will be zero advertisements on this channel, for the following reason:    • Bill Hicks on Marketing   ⚠️ DISCLAIMER The content on this channel is for educational and informational purposes only. Nothing in this video constitutes medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making decisions about your health or treatment.