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Comment by cantrevealname | Hacker News Reader

OK, here's a wacky theory about why this is happening: The article says that the kilogram copies are brought to Paris to be compared. Therefore the copies are undergoing significant acceleration (e.g., transported on airplanes or trains) while the original in Paris remains stationary.

From the stationary kilogram's point of view, all of the other kilograms had undergone relativistic mass increases during the time of their travel. Suppose a tiny amount of this mass increase is somehow actually retained when all the transported kilograms are brought to the same frame of reference (i.e., when the airplanes land in Paris).

What's a simple way to disprove this idea?

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The "mass" gained from motion is really just the extra energy. When the energy is removed from the point of view of the stationary kilogram, all the extra "mass" is gone too.

Right, in other words, you only have extra mass during the time that you are at a higher velocity.

And, specifically, you only have "extra" mass from the viewpoint of someone traveling at a different speed or direction. From your own frame of reference, your mass never changes.

Yes I know that. That's why I said if the mass were "somehow actually retained". I'm positing that the some of the extra energy somehow becomes real mass. Yes, this is not how special relativity works. That's why I said "wacky theory". But is there a simple and obvious way to falsify this?

Sure, you will only need two approximately equal masses, a high precision scale and a round-trip airplane ticket. Seems easy enough for me. Strictly speaking this seems like the most obvious way to test your theory. Of course it would be mighty odd if you would find any effect, but who knows?

If all of the kilograms were undergoing radioactive decay, then the ones that traveled back and forth would be younger, and thus heavier, because of the twin paradox. You'd probably need a new undetectable form of radioactive decay and relativistic trains to make this plausible.

I know you didn't imply this, but there is no reason that every "what if" needs to be tested or falsified.

I imagine that the possible deviations from General Relativity have been thoroughly mapped out and tested, where possible.

I'm not sure you're right, but I totally agree with the idea behind your idea, which seems to be that it's better to explain the difference rather than work around it.

From a coder's perspective, I'm looking at this like you can either identify the root cause and fix the system itself, or you can start putting in spaghetti code to fix it.

Now, if the system itself isn't behaving like you expected, it makes sense to me that there's something more fundamental going on that needs to be looked into. Why work around the problem when the problem itself could be telling you something very interesting and useful?

The article implied that most scientists believe that the change is explained by unknown chemical processes involving no new physics.

Since you use equations of relativity to calculate the mass increase, you could use the same equations to calculate the mass at rest and show that it doesn't increase.

well, you seems to be on to something. These other kilos are kept at different places that have different gravitation (no mentioning that they control for that) - thus different time. So 1 year for IPK in Paris isn't a precise 1 year for its copy in another place. So whatever changes happen to the kilos they happen a bit quicker for some and a bit slower for the others.

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