Bell's Theorem | Breakthrough Junior Challenge 2020

A very brief overview of Bell's Theorem, explaining how researchers used entangled photons to show that fundamental assumptions about our universe were incompatible with quantum mechanics.
This is a dense topic so please pause if you don't understand. If you have a basic understanding of trigonometry and probabilities (Algebra 1 or 2 for US students), you should have all the prerequisites to ignore most of the small text boxes that appear, and the rest are just provided in case you're curious and want to learn more.
My hope is that this video is able to explain both the significance of Bell's Theorem and how we know it's true within 3 minutes, while avoiding diving too deeply into quantum theory or the mathematics behind choosing Bell-type inequalities.

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Footnotes:
³ Astute observers may notice that I seem to contradict this later when talking about Spontaneous Parametric Down-Conversion (SPDC) which does split photons in half. However, SPDC also cuts the frequency of the light in half because the energy of a photon is linearly proportional to the frequency. Observing the polarizer, we see that it does not change the color of the light, so therefore each photon must be either entirely absorbed or entirely allowed through. It is also worth noting that SPDC is very, very rare, occurring only about 4 times for 1,000,000 photons that hit particular crystals (Bock, Lenhard, Chunnilall, & Becher, 2016). If polarizers really were splitting photons, the light coming out would be much more reduced than we observe.

References

Bierhorst, P. (2015, April 17). A Robust Mathematical Model for a Loophole-Free Clauser-Horne Experiment. Journal of Physics A: Mathematical and Theoretical. doi:10.1088/1751-8113/48/19/195302

Bock, M., Lenhard, A., Chunnilall, C., & Becher, C. (2016, October 7). Highly Efficient Heralded Single-Photon Source for Telecom Wavelengths Based on a PPLN Waveguide. Optics Express, pp. 23992-24001.

Clauser, J. F. (1974, July 15). Experimental Consequences of Objective Local Theories. Physical Review D, pp. 526-535.

Eberhard, P. H. (1993, February). Background Level and Counter Efficiences Required for a Loophole-Free Einstein-Podolsky-Rosen Experiment. Physical Review A, pp. R747-R750.

Giustina, M., Versteegh, M. A., Wengerowsky, S., Handsteiner, J., Hochrainer, A., Phelan, K., . . . Zeilinger, A. (2015, December 18). Significant-Loophole-Free Test of Bell’s Theorem with Entangled Photons. Physical Review Letters, pp. 250401-1 - 250401-7.

Giustina, M., Versteegh, M. A., Wengerowsky, S., Handsteiner, J., Hochrainer, A., Phelan, K., . . . Zeilinger, A. (2015, December 14). Supplemental Material: Significant-Loophole-Free Test of Bell’s Theorem with Entangled Photons.

International Baccalaureate Organization. (2016, November). Physics Data Booklet. IB Diploma Programme. Cardiff, Wales, United Kingdom.

Johannes Kofler, M. G.-Å. (2018, October 8). Requirements for a Loophole-Free Photonic Bell Test Using Imperfect Setting Generators. arXiv, pp. 1-11.