A weekend trip to verify general relativity

8 years ago, for the 100th anniversary of the theory of relativity [Tom] decided to test the general theory of relativity.

As he was going to Mt Rainier (5400ft high) with his children for the weekend, he brought in his van 3 cesium clocks while leaving other atomic clocks at his home for comparison. The theory behind the test is that if you’re are at higher altitudes, then your speed (in a galactic coordinate system) is higher than the one you’d have at sea level and therefore time would go “slower” than at lower altitudes.

[Tom] brought 400 pounds of batteries, 200 pounds of clocks and left his car turned on during his 2 days stay in the ‘Paradise Lodge’. He used 120V DC to AC converters and chose to bring 3 cesium clocks to have a triple redundant  setup. When he came back home, he had the good surprise of finding a time difference of 23ns. This is a great application for those rubidium sources you’ve been scavenging.

[Thanks Indyaner via Reddit]

71 thoughts on “A weekend trip to verify general relativity

  1. What’ he couldn’t just use a digital watch? Anyway this is really cool, but where did he put the wife and kids? Seriously, this thing should have been built into a trailer and have its own gas generator (in addition to the batteries) to be car independent. Nice work.

    1. I fear I’ve already bitten here, but 23ns on a digital watch? With the (relatively) extreme inaccuracies / drift of the quartz resonator that drives it? I do hope one is trolling sir!

  2. I call foul…everyone knows the odometers on the Honda vehicles are somewhat inaccurate, how about the DC hmm? Does that affect the clocks? Is the DC slower in an Odyssey minivan at altitude?

    The above is a joke, okay. Neat science.

  3. “The theory behind the test is that if you’re are at higher altitudes, then your speed (in a galactic coordinate system) is higher than the one you’d have at sea level and therefore time would go “slower” than at lower altitudes.”

    You got your explanation wrong- the time difference is due to the earth’s gravitational field being weaker at altitude, the clock is farther from the center of the earth. Special relativity really doesn’t have enough of a effect to measure, and with an altitude difference of only 5400 feet, the galactic coordinate system does not apply at all.

      1. Also, Special Relativity requires that the inertial frames be moving at constant velocities with respect to each other. The moment you accelerate, Special Relativity breaks down and you fall into the realms of General Relativity.

        This means, since Earth is rotating, objects on its surface exhibit an acceleration pointed towards the axis of rotation. Special Relativity does not apply here.

        1. TRON, I believe once the traveling is done, there is no acceleration of one clock with respect to the other, so special relativity would apply in that sense. However, in this case the effect of general relativity is much greater due to gravity differences.

          So I agree for the most part, but I think your second sentence is inaccurate.

          1. Thinking about it more, I realize that there is in fact no relative velocity between the two clocks at all. For that reason special relativity does not apply.

          2. Actually, there is still acceleration when the travelling stops. Even if moving on a straight line without accelerating, the moment you stop your velocity decreases, hence accelerating, Special Relativity breaks down again [see Twin Paradox].
            A much easier method of verifying Relativity, though General Relativity at that, is by using the GPS system in your phone/automobile. The General Relativity is the reason it works.

          3. Also, thinking about your statement, you are likely to be correct on stating that there should be no relative acceleration between the two objects due to the rotation of the Earth; however, consider the curvature of the Earth itself. Surely then, as the motion is no longer rectilinear, there must be some relative acceleration, as the velocity vector of the vehicle is now more or less tangential to the surface it travels on.

  4. I wonder if he did any calculations on what the expected time difference would be given the altitude. It’d be interesting to know how close he was to what relativity predicts.

      1. got it backwards, the post says he calculated an expected 23ns, and measured between 20 to 30ns of offset

        the graph looks a bit jittery, so it would be hard to see the exact offset

    1. Personally I would have driven to Sunrise on the other side of the mountain, it’s another 1000 feet of elevation. Although it’s often closed due to snow, even in the summer.

  5. The time dilation seen in this experiment has nothing to do with velocity. It happens because gravity is slightly weaker at higher elevations (further from the earth).

    1. This has nothing at all to do with gravity, it has to do with the fact that your linear velocity in space increases with your altitude, due to the rotation of the earth.

      1. Linear velocity in space? relative to what? There is not preferred reference frame. So lets pick one, the reference frame of Tom’s house. Is the Paradise lodge moving closer to further from or somehow circling around Toms house? No it’s static in relation to Toms house and therefore a clock at Toms house and at the Paradise lodge should measure time the same. Why don’t they? Gravitation!

        1. The only way I see gravitation affecting this is changing the weight of some mechanical attribute of the clocks. Gravity does not affect time in any way. What is affected is the method we use to measure time. Time is an absolute and you have been sold a furffy. Einstein was wrong on that.

          1. mere denial of general relativity – in face of experimental proof (not just here in this experiment) – seems like maybe not such a good argument… just saying…

          2. No you are wrong. Also evolution is true, the US did land on the moon in 1969, there are no 100 mpg carburetors being suppressed by the oil companies, Oswald shot JFK, and Obama was born in Hawaii. Please go now.

      2. Linear velocity in “space” doesn’t matter. The observers and the clocks don’t move relatively to each other (not counting the time of car travel). Observers in “space” (let’s say on the Moon) would see the clocks ticking at different frequencies, but we’re all on Earth, I guess ;)

      3. On the linked site:
        “According to Einstein, fast-moving clocks run slow (special relativity), and high-elevation clocks run fast (general relativity).”
        The effects of special relativity would be far less in this experiment, as the difference in velocities is not that great. The effects of general relativity play the most significant role here, causing the clocks at altitude (weaker gravitational field) to gain time.

        1. Or if you live atop everest you will get to live in misery if at all and gain a few seconds in life . This is where all the speeding drivers should be sent perhaps.

  6. OK so let me preface this with I’m not a physicist. But It seems to me that there is a whole bunch of problems with this statement “theory behind the test is that if you’re are at higher altitudes, then your speed (in a galactic coordinate system)”. If I understand relativity correctly the basic premise is there is no preferred coordinate system. Such as some magical galactic coordinate system. So the top of mount Rainier is stationary in the reference frame of Tom’s home. The actual effects possible at play here are: 1. The effect of special relativity in that Toms car which for part of the trip (while driving) is in motion according to the reference frame of his home. 2. The effect of general relativity that space-time is not flat and bends around gravity wells. Therefore Mt Rainier being further from the gravity well of the earth experiences time differently.

    1.Since the movement of Tom’s car in relation to his house is VERY!! small in respect to the speed of light. The theory of special relativity should have a VERY!!! (probably not measurable in this case) small effect on how he experiences time with respect to his home.

    2. The real relativistic effect here is probably has more to do with the effects of general relativity in that toms distance from the earths gravity well is effecting his measurement of time.

    As a general rule time differences experienced on or near a planets surface are largely the effect of the planets gravitation. For example a satellite orbiting the earth is traveling very fast in the reference frame of the surface and therefor experiences the effects of special relativity. If you measure the actual clock drift of that satellite you will notice it is much larger than you would expect and of the wrong sign. That’s because in the case of a satellite the effects of special and general relativity cancel and the effects of general relativity dwarf those of special relativity.

    Like I said I’m not a physicist so I may misunderstand or have some of my facts a little off but I’m pretty sure the hackaday post is further off.

  7. “The theory behind the test is that if you’re are at higher altitudes, then your speed (in a galactic coordinate system) is higher than the one you’d have at sea level and therefore time would go “slower” than at lower altitudes.”

    Huh?

    1. Go back and read Einstein (and apparently Newton, too!) If you are sitting on a spinning object (the earth) your velocity increases as you increase your distance from the center of the spinning object. That’s Newton’s contribution. Your observation of time passage will be different from an observer at sea level because your velocity is different. That’s Einstein’s contribution.

      1. You’re incorrectly ignoring the effect of gravitational time dilation. The clock at lower gravitational potential (closer to the gravitational source) will run slower than one at higher gravitational potential. Therefore, the clock left at home would run slower. The linear velocity difference also has an effect, but is not the dominant term. The linear velocity would cause the clock taken to elevation to run slower, but it would not be as significant of a term.

      2. It’s a much smaller effect than the gravity. For example, if you double your distance from the center of the earth, your velocity will double. But the gravitational field will be reduced to the square root of its former value per the inverse square law.

          1. Yes, it will. I was comparing the two more or less asymptotically, though. Rotational velocity increases on the order of n, where n is the radius, while gravity decreases on the order of n^2. Hence gravity always dominates.

  8. This experiment like all other similar ones, is based on the premise that there exists an underlying substantial reality called time and that all clocks are measuring this substance. It is a premise which has neither experimental nor rational evidence.

    1. I believe he’s just measuring the relative passage of time between the clock left and home and the clocks that he took up the mountain. He’s not calling one of the clocks more objectively real than the other.

  9. Pun and Michael are correct. The clocks are not “moving” with respect to each other and are locked in the same frame. However, they are experiencing different gravity. This is the same thing that happens with the GPS satellites and the clock drift they have to account for.

    1. What I would like to see is evidence that the GPS satellites clocks are actually adjusted from time to time . Where are you getting this rubbish or is it just monkey hear ,monkey say?

      1. “To achieve this level of precision, the clock ticks from the GPS satellites must be known to an accuracy of 20-30 nanoseconds. However, because the satellites are constantly moving relative to observers on the Earth, effects predicted by the Special and General theories of Relativity must be taken into account to achieve the desired 20-30 nanosecond accuracy.”

        http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

        Or from wikipedia:

        “Without the use of general relativity to correct for time running more quickly by 38 microseconds per day in orbit, GPS would suffer gross malfunction.”

  10. I don’t see the data for the two days in the middle. That should show a steady increase to the higher level but they have been ommited? why.
    Additionally there is no source data only a graph. Could be made up !
    The blue clock is playing up so should be discarded in the mean calculation.
    The way I see it, a space ship travelling at speed comes back with a rider who is younger than his twin who stays. So time should slow , here it speeds up?

    1. That’s special relativity not general relativity.
      Assuming the author is fabricating his data – well maybe everyone is always fabricating their data. Oh no – I can’t trust anything… what to do ?

  11. There are preferred reference frames in both General and Special Relativity.

    In Special Relativity, the frame of reference is an object moving at a constant speed, and therefore undergoing no acceleration.

    In General Relativity, the preferred frame of reference is a body undergoing free-fall in a gravitational field.

    For Special Relativity, if an object is moving at a velocity greater than the reference frame, that object will experience time more slowly than the reference frame.

    For General Relativity, an object in experiencing a stronger gravitational field will experience time more slowly than an object experiencing a weaker gravitational field.

    Therefore, in this experiment each effect on the clocks would be expected to be opposite in sign, but with different magnitudes. In this case, the effect of gravity clearly dominates a possible effect due to differing velocities.

    To the strangely confident relativity deniers who have already posted, I invite you to read about the thousands upon thousands of experiments that confirm the accuracy of the theories to predict small-scale effects like this, as well as larger phenomena like the orbit of Mercury and gravitational lensing.

    The theories of relativity are the most verified scientific theories of all time, second only to Quantum Mechanics. Is that also a hoax? Considering the device you used to read this (a transistor based computer) was designed using principles from Quantum Mechanics, is your computer also a hoax? Or did you use a relay-based computer?

  12. There are preferred reference frames in both General and Special Relativity.

    In Special Relativity, the frame of reference is an object moving at a constant speed, and therefore undergoing no acceleration.

    In General Relativity, the preferred frame of reference is a body undergoing free-fall in a gravitational field.

    For Special Relativity, if an object is moving at a velocity greater than the reference frame, that object will experience time more slowly than the reference frame.

    For General Relativity, an object in experiencing a stronger gravitational field will experience time more slowly than an object experiencing a weaker gravitational field.

    Therefore, in this experiment each effect on the clocks would be expected to be opposite in sign, but with different magnitudes. In this case, the effect of gravity clearly dominates a possible effect due to differing velocities. Saying that the two clocks are not moving relative to each other is misleading because from the proper, non-accelerating frame of reference, both clocks are moving at different velocities compared to each other as they rotate along with the surface of the earth. Remember, moving at a constant speed in a circle does not mean constant velocity.

    To the strangely confident relativity deniers who have already posted, I invite you to read about the thousands upon thousands of experiments that confirm the accuracy of the theories to predict small-scale effects like this, as well as larger phenomena like the orbit of Mercury and gravitational lensing. The burden of proof is on you to show us why all these experiments are wrong, and are yet completely consistent with the predictions of Relativistic Theory.

    The theories of relativity are the most verified scientific theories of all time, second only to Quantum Mechanics. Is that also a hoax? Considering the device you used to read this (a transistor based computer) was designed using principles from Quantum Mechanics, is your computer also a hoax? Or did you use a relay-based computer?

  13. Gravitational acceleration does decrease with elevation, but you also have to consider the additional mass of whatever it is your standing on (In this case a mountain), and whether or not it is in isostatic equilibrium with the mantle. There are some other things too – Latitude for instance. The Earth bulges out a little bit at the equator (putting you farther away from the center of the planet) and the radius of the small circle of the lattitude you are at changes how much you are flung into space so to say, which also counters gravity

  14. I can not even read such a poorly written article and for anyone who questions my own grammar i don’t care because i’m not the one writing a story for the front page of a tech blog. HAD needs a better writing staff.

  15. come on, 23ns?? big deal.
    i’ve run experiments at my job, and i’ve found that if i bring an atomic clock to work and someone who has the day off keeps one with them, that the clock at my job runs at about 10% of the speed of the other clock.

  16. That’s what my car looks like when I go on a road trip with my mate who does GPS point logging for mapping. Has to bring at least a half dozen GPSes each time

  17. Be carefull and never go to Denmark with that car. Very recently a guy made the whole anti terror shibang go off because he had a wire sticked to a car battery and to cobber trails on the bottom of the car (testing charging while driving system).

  18. Typical American Way. Waste a full tank of gasoline for a few watts forth of electricity over two days. And all that because he didn’t feel like carrying the stuff in the room.

    And all that to prove basically nothing. We still don’t know if it was due voltage or temperature fluctuation or vibrations etc.

    It would be nice to have a graph of time difference and computed delta of clockspeeds, related to his voyage. Had he done that, then he’d have _something_.

    But to get the fuel for his new adventure, it seems someone would have to invade some oil-rich country or do some serious fracking or fuck-up Alaska…

  19. PAH! Special Relativity? General Relativity?? Time dilation and gravity wells?? All bogus.
    What this experiment proves (and we have all known it long before Einstein) is that time goes faster when you are on vacation. His fancy clocks prove it. Mr. Burger King is right, 23ns is nothing. Time passes MUCH more quickly on vacation that a mere 23ns.

    1. My own personal theory is that he had had enough of being in a cabin with the kids so he put the clocks forward a little so he could leave earlier. This explains why the is no intermediate data.

  20. I read all the comments, i read all the links, and I am still no closer to understanding HOW differences in gravity affect observed time.

    1. That’s general relativity. Being in a gravity field is the same as accelerating, they both cause time dilatation. That’s about as well as I understand it, though, so I obviously can’t explain any better.

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