The Best Test of General Relativity (by 2 Misplaced Satellites)

The Best Test of General Relativity (by 2 Misplaced Satellites)

A launch mishap led to the best experimental confirmation of gravitational redshift. Get a free audiobook with a 30-day trial of Audible: or text VERITASIUM to 500500

Huge thanks to
Dr. Pacome Delva:
Dr. Sven Herrmann:
Gravitational Redshift Test Using Eccentric Galileo Satellites:

Disclaimer: It is arguable what is THE best test of general relativity because there are different ways to test the theory. This is the best confirmation of gravitational redshift, which is one of the three original tests proposed by Einstein.

Special thanks to Patreon supporters:
Donal Botkin, James M Nicholson, Michael Krugman, Nathan Hansen, Ron Neal, Stan Presolski, Terrance Shepherd

Animations and editing by Alan Chamberlain

Music from “Subtle Substitutes 2” “A sound Foundation 1” “Cell Research 1” “Particle Attraction 1”


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  1. I’d be interested to know your thoughts on this format. Would you like to see more ‘Talking to scientists about their recent publications on Skype’? Maybe not on this channel but on Sciencium perhaps?

  2. I actually saw the launch of Gravity Probe A from Wallops Islanda in June 1976. I didn't understand it properly – I thought it was just about time dilation – but it was really exciting to see the rocket's tail in the night sky from the mid-atlantic.

  3. I thought the satellite would also vary its velocity through its elliptical orbit so the comparison on clock times would need to allow for both gravitational field and also velocity. Would be good to hear about that compensation also.

  4. I have two questions:
    1) could gravity be a physical dimension? One that can't be seen because photons are massless? The Kaluza-Klein hypothesis has never been proven, nor disproven.
    2) could dark energy be the result of light traveling in empty space? To an observer, light slows down next to massive objects, wouldn't it speed up when in mass free space? Therefore appearing to be traveling faster than expected?

  5. Can someone please help me with this question: at around 8 minutes, it is mentioned that the momentum of the photons from the sun is causing errors on the satellites. How can photons be exerting force when they have 0 mass and charge?

  6. Just as a completely irrelevant aside:

    I worked on GPS in the 90s. We had to correct for tiny discrepancies in calendar time compared to real time (the Earth orbits the Sun every 365.25 days, giving us leap years, but for space we have to count the leap seconds). For orbits, it matters that Earth isn't quite round. It's a bottom-heavy oblate sphere. For the clocks on GPS, it matters that the ground is sometimes closer and sometimes more distant in a perfectly circular orbit, because of elevation changes in the ground itself. Large mountains have their own gravity systems that can change the clock times on something as precise as a cesium beam clock and the speed the bird flies at. I wasn't any kind of a scientist in those days, just the guy who ran the coms for satellite contacts. This all blew my mind.

  7. You should do an episode on amateur astrophotography, b/c I think there's a lot of interesting stuff that layman can see and do, and I think it would expose normal people to that amazing world and get it more popular!

  8. The change in (potentially) time dilation is what I would call "a consistent inconsistency". The fact that this phrase is an oxymoron is why I love it so much, and I believe that this is also why it works so well as a (very) brief description. Maybe I'm wrong, maybe I'm not. Who knows, right? And I don't mind not knowing. It's part of science.
    Edit: imagine "Quantum Relativity"…

  9. Is there or will there be a possibility to measure time difference in the EM field between the E and the M amplitudes? Maxwell and QM imply they er instant effects without traditional causality and therefore in perfect phase.

  10. Congratulations! What you have proven is that gravity affects the motion of physical objects, even that of clocks. Every clock is based on a physical substance that has a regular, cyclic motion. If the distance the substance moves over a fixed period changes, then the clock speeds up or slows down. This doesn't require a mystical concept of something called "time" that has some universal global "rate" across some global expanse called space. Because physics imagines that there exists some sort of backdrop framework called "space/time" that holds all the physical stuff in place, it comes up with the fallacy that this "space/time" substance has to change in order to accommodate the change in the actual physical materials within it. You are simply witnessing a change in the motion of a physical object being observed alongside the measurement of change of another physical, cyclic motion.

  11. what if atom clock speed up because of the higher gravity not because time is faster?
    did they used different types of watches? all i have seen was atom watches

  12. GM describes the universe of the very large extremely well. But we know it can't be completely accurate because it can only describe the world of the very large and breaks down when applied to the quantum world. I don't know what the tweak will be but it will be fascinating to find out. Maybe it will help us understand what dark energy and dark matter really are.

  13. Mass and gravity are related. Relativity. And orbit are related. Why isnt valency considered, afterall the earth is weightless in space and can be moved around by celestrial effects.

  14. It’s a ridiculous conceit to pretend that Einstein predicted that The resonant frequencies of atoms changes under different gravitational potentials. He didn’t.
    He predicted TIME would speed up and slow down. Not that atomic resonance, or any resonance for that matter would change under different strengths of external forces like gravity.
    Science knew resonance of resonant systems, like atoms, changes under pressure from external forces well before Albert was born.

  15. The electron configuration surrounding cesium atoms is slightly deformed/ prolates from a different altitude within a gravitational potential gradient elongates the electron configuration… effectively acting like a longer pendulum swing which records a longer second compared to another clock without a deformed/ prolated electron configuration. This is known.

  16. Overwhelming. You have, however, exposed two, for now, flaws in my thinking, while trying to grasp this. So, many thanks for that! I’m really struggling to verbalize them, so please forgive my simplistic attempts. First, if I drop a mechanical timepiece into, say, molasses, then it would slow down but that doesn’t mean that time itself has slowed down. Second, how can one calibrate the most accurate timepiece in the world and then how to verify it is indeed working? Thanks again for shaking my brain!

  17. Light is both a wave and a particle. Electricity is both a current and a voltage. Electricity has natural ways of "transforming" its properties from one to the other. Why not light, gravity, and everything else? Are we too "static" in our thinking?

  18. I dont think we will ever understand the mysteries of the universe, not because it's too complicated, but due to the inability of our sensory organs to perceive it. We are like a fish trying to climb a tree.

  19. proving GR is like flat earth group proving Earth is flat. west was coned by Eddington bending of star light by space matter ejected by sun. it was presented as gravity as proof Einstein GR. After 11 decade, last thing Anglo- American want to admit that they were coned by agent who's mission was to undermine Ailed science due to his religion background. so prof will continue. if Man had correct understanding of atom, they would know the reason for all gathered data. Ferydoon Shirazi. MG1