Einstein’s ‘Imaginary Elevator’ Thought Experiment Proven Right Again

By Bill Andrews | June 4, 2018 4:26 pm

Well, Einstein’s done it again!

That is to say, the gravitational theories of Albert Einstein have once again been confirmed, and to a new degree of precision. The equations of general relativity predicted a certain quantity would be zero, and physicists at the National Institute of Standards and Technology (NIST) have calculated a record-low, unbelievably tiny result — basically, as good to zero as we can get.

So what did they measure? The variation between different ultra-precise atomic clocks around the world as it orbited the sun. It’s … a bigger deal than it sounds like.

Elevator Action

Part of Einstein’s genius was his ability to think things through using just his imagination. These so-called gedankenexperiments (“thought experiments”) yielded many of his insights in formulating the theory of general relativity, which focuses on gravity’s effects.

Among the more famous examples is one focusing on an imaginary elevator. Someone inside would be unable to distinguish a gravitational field from acceleration — the downward pressure you normally feel from Earth pulling at you could just as easily be the elevator accelerating ‘upward’ toward you in zero gravity. Stuck inside the elevator, with no windows, you couldn’t tell the difference.

The NIST team tested another aspect of the thought experiment, which says that everything inside the elevator would feel the same accelerations, and their relative properties would remain constant — zero change. It’s an idea called local position invariance (LPI). They used Earth itself as the elevator, and compared the “ticks” of a dozen atomic clocks all over the planet. After studying nearly 15 years’ worth of data the results were in: the difference was just 0.00000022 plus or minus 0.00000025. Pretty close to zero!

The results appeared today in Nature Physics.

Like Clockwork

It’s closer to zero than we’ve ever gotten before, thanks to improved tech, particularly the incredible accuracy of today’s atomic clocks, “so stable that they could be in error by no more than a thousand seconds over the life of our universe, ~14 billion years,” according to the paper.

Unfortunately, it’s also about as close as scientists can come with those clocks too — but new atomic clocks are already in the works and should provide even finer measurements in years to come.

But why bother, when we’re already so close to zero? Well, this isn’t just about NIST showing off. Because LPI should be a fundamental property of the universe, it’s part of the calculation of some of nature’s other fundamental values, such as the mass of certain particles. Having an improved figure for LPI means better numbers for everything else.

Plus, of course, confirming once again that, yep, ol’ Einstein really knew what he was talking about. Not that it’ll stop scientists from trying to find out otherwise.

MORE ABOUT: Einstein, physics
  • https://www.facebook.com/numberofGod Douglas J. Bender

    I have a theory which, if correct, would imply that there IS a fairly simple way to discern whether one is experiencing gravity or an acceleration. I could very well be mistaken, but my idea involves differing “gravitational potential” (is that even a thing?) and rotation. I am NOT a kook or a mad scientist (for that matter, I’m not even a scientist; I do have a Bachelor’s degree in Applied Mathematics, though).

    My theory would be relatively simple to test. Nothing fancy involved. Just simple physics, and “weightlessness” in a falling airplane compared with true “weightlessness” in space (i.e., comparing a scenario in gravity with the same scenario without gravity; there would be no need to include any acceleration in the latter case).

    I have a very convincing (to me, and I think to a majority of my imaginary friends) thought experiment which seems to support my claim. But I am quite aware of my own relative ignorance of much of even the basic physics involved. But ignorance has never stopped me from forming an opinion before.

    • OWilson

      So, don’t keep it all to yourself, we are all ears! :)

      “Gravity”, defined as the “force that pulls”, can be simulated (created) in quite a few ways, by a simple stationary mass, acceleration of moving frames of reference, like vehicles and elevators, rotation (centrifugal force), as in rotating space ships, fairground rides and swinging weights on a string around your head, and of course the bending of Einstein’s space-time.

      Pinning down exactly what gravity IS though, rather than what gravity DOES, is still a challenge for science.

      Maybe you could help? :)

      • https://www.facebook.com/numberofGod Douglas J. Bender

        Not likely. :-)

        And I have to think more about my thought — I don’t think it’s publicly presentable yet (neither am I, but that’s another story).

    • RB

      The two situations you would use, the falling plane and being in orbit, are really the same situation since both are just falling curves in a curved spacetime. You need to generate a non free fall acceleration, like the mechanical acceleration of the elevator, to show the equivalence of something in both situations. Plus be careful because there is a real difference between an accelerating elevator and the gravitational force and that is the tidal force, which will not appear in the accelerating elevator and so you would need to use Einstein’s full field theory which accounts for this discrepancy, not Newton’s laws. If you don’t know the tensor calculus necessary to use his field equation I would recommend Leonard Susskind’s youtube video series on the subject. If you already know 3d calculus and linear algebra it doesn’t take long to learn tensor calculus.

      • https://www.facebook.com/numberofGod Douglas J. Bender

        It sounds to me as though I “rediscovered” tidal forces. I also “rediscovered” a theory from the 1700s about extending the numbering system in order to divide by zero. And, I “rediscovered” the “pilot-wave theory” to explain the double-slit experiments. I also postulate that Schroedinger’s dog killed Schroedinger’s cat. I guess I am centuries behind my time.

        • RB

          It depends on how the stretching due to the tidal force affects the rotation you are considering.

          • https://www.facebook.com/numberofGod Douglas J. Bender

            I did not consider any stretching in my idea, though I don’t think it would affect my idea in any significant way. But the key to the idea is how (if) the “differential” effect of gravity (even over very small — say, inches? — distances) could be noticed in the response/action of a rapidly rotating disk.

          • Emmette Davidson

            Perhaps you have “rediscovered” frame-dragging as well. 😉

          • https://www.facebook.com/numberofGod Douglas J. Bender

            No, that’s too recent a theory for my oeuvre.

          • Emmette Davidson

            In reality, there’s only the experiential present moment, supported by consistent history traversed by your pilot wave within Bohm’s existential complementarity.

          • https://www.facebook.com/numberofGod Douglas J. Bender

            Wasn’t that an episode of “The Big Bang Theory”?

          • Emmette Davidson

            I wouldn’t know about that.

          • https://www.facebook.com/numberofGod Douglas J. Bender

            Unless my humor perfectly parallels theirs, the answer would be “No”.

          • Emmette Davidson

            Good. Wouldn’t’ve expected Hollywood writers to realize the sublime truth of the duality of existence, as they’re stuck with the vulgar nonsense of multidimensionality, per “scientific consensus.”

            We’re one simple unfalsifiable theory away from straightening all this mess out; perhaps yours. It is said the Bodhisattva will save us from all the numberless delusions by entering all the world’s boundless gateways.

          • https://www.facebook.com/numberofGod Douglas J. Bender

            Jesus is the Way, the Truth, and the Life.

          • Emmette Davidson

            No argument there. “The Light” too. And The Bodhisattva for sure, at least.

  • http://www.mazepath.com/uncleal/EquivPrinFail.pdf Uncle Al

    Falsify Einstein’s inertial elevator (Equivalence Principle) with a pair of shoes – one hour.

    1) Baryogenesis: post-Big Bang excess matter over antimatter; 2) Sakharov conditions. Vacuum is trace chiral anisotropic toward hadrons; 3) Extreme opposite shoes embed within a vacuum left foot with measurably different energies, following-identical minimum action trajectories.

    Microwave rotational spectra of mixed geometrically extreme molecular enantiomers in 3:1 R:S ratio do not exactly superpose –
    opposite shoes fitted to a vacuum left foot. Asymmetric spectral line broadening is sufficient. brightspec(.)com offers 40,000:1 signal to noise. DOI:10.1515/zna-1986-1107 is a 30:1 S/N achiral exemplar.

    D_3-trishomocubane-2-carbonitrile is the test molecule. Look.

  • http://www.mazepath.com/uncleal/EquivPrinFail.pdf Uncle Al

    Stereogram of the test molecule’s enanti0mers, below. Note R versus S spatial ordering of bonds to carbons 6&10, 7&11. CTRL- and CTRL+ adjust image size fore easy viewing. Rotation is around the center of mass in the plane or normal to it (degenerate for a prolate top).


  • Kurt Stocklmeir

    for years I have talked about this – gravity can some times be repulsive – when there are big tidal forces associated with gravity a particle like an electron will have an increase of wave length – big tidal forces can increase wave length of a particle – using quantum mechanics as wave length increases speed decreases – speed of an electron will decrease – gravity will make an electron have a decrease of speed – a particle can stop because of gravity and the particle will move away from mass that is creating gravity – spring constant of time and space is not linear – forces created by shape of time and space are not linear like forces will decrease less fast than 1/rr – this can do a lot of things like make it look like there is dark matter and make it look like there is dark energy – speed of time is not linear around mass – clocks will prove my theories are right when they are a small distance from mass and when there are big tidal forces – different particles will fall at different speeds depending on wave length when there are big tidal forces Kurt Stocklmeir

    • http://www.mazepath.com/uncleal/EquivPrinFail.pdf Uncle Al

      If you are a rubber sheet gravitation guy, a gravitational well is hyperbolic geometry space. Make it elliptic and it is repulsive instead. Get back to us after you reduce to practice.


    • Kurt Stocklmeir

      Time and space have negative not linear elasticity – time and space have a negative not linear spring constant. If the shape of time and space around a star creates gravity toward the star – far from the star it will be more simple for time and space to have a shape that creates gravity – gravity decreases less fast than 1/rr – if there is a star a lot like a black hole the shape of time and space around the star will stop a black hole from being made because of how elastic time and space is. Time and space are not elastic to an extreme – time and space will fight against getting expanded and compressed. If I stretch a rubber band after a certain distance the rubber band will fight to an extreme against being expanded more because it has not linear elasticity – spring constant is not linear. Because time and space have negative elasticity the shape of time and space creates forces away from mass. This is simple to prove. Some waves of time and space are gravity waves torsion waves shear waves and Love waves – speed of these waves can be used to find elasticity constant. Kurt Stocklmeir


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