SCIENTIFIC AND STANDARDS SOURCES
Reviewed November 7, 2026.

Einstein Online: the travelling twins
https://www.einstein-online.info/en/spotlight/twins/

Einstein Online: light clocks and time dilation
https://www.einstein-online.info/en/spotlight/light-clocks-time-dilation/

NIST: atomic-clock tests and the GPS comparison
https://www.nist.gov/atomic-clocks/a-powerful-tool-for-science/putting-einstein-test

MIT 8.962: Schwarzschild clocks, section 6.2.2
https://web.mit.edu/8.962/www/lecnotes/8_962TA-lec-all.pdf

NGSS: high-school science and engineering practices
https://www.nextgenscience.org/sites/default/files/HS%20Practices%20Combined.pdf

NGSS: Appendix G, crosscutting concepts
https://www.nextgenscience.org/resources/ngss-appendices

Common Core: quantities, HSN.Q.A.1
https://www.thecorestandards.org/Math/Content/HSN/Q/

Common Core: rearranging formulas, HSA.CED.A.4
https://www.thecorestandards.org/Math/Content/HSA/CED/

Educational license
https://creativecommons.org/licenses/by-nc/4.0/
