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Comment by kghose | Hacker News Reader

I found this a rather good explanation (well written article). My favorite para is in the closer:

"Others say that Wetterich’s interpretation could help to keep cosmologists from becoming entrenched in one way of thinking."

I like this attitude. Science is about playing with hypotheses and trying out new ideas. The most important thing for me is for my viewpoint to be zipped around and turned on its head - just for fun. I think it makes the mind more nimble.

Also, could a physicsy person elaborate a bit more on why we can't test increasing mass? Is it in the same class as 'we can't actually measure the increasing distance in the cosmic expansion, because locally, nothing is expanding'?

Thanks

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I am not sure to understand your question, it has been said in the article that if everything's mass was increasing proportionally we could not test it since we have to compare two things to see an increase. But I am no physicist I don't know if there would be another way actually to test mass increase without comparing two objects.

What about a test over time?

I'd guess the time scale required is a bit long....

I know what you mean. But an object of 1Kg today would still be 1Kg in 1000 years since everything gained mass (that includes what you are using to calculate the mass)... but like I said in my first response I am in no way the best person to give an answer to this question (still I lost karma :P). It is just a subject I find interesting!

> But an object of 1Kg today would still be 1Kg in 1000 years since everything gained mass

Yes, but a 1m rule will get longer if everything gained mass, won't it? (I mean, the meter will get shorter, and the atoms should get bigger, even after compensating for the change on meter. Is there something I'm missing?)

Mass is relative, measured by a standard object of arbitrary mass to which we've given a value. What we consider a "kilogram" is determined by one specific object sitting in a vault somewhere, and if that object were to be halved or doubled without us realizing it, then the official value of the kilogram would be similarly halved or doubled.

Since we determine the mass of things by comparing them against that object, if everything in the universe changes mass in precisely the same way at precisely the same rate then we would have no way of knowing. All we can do is compare them with each other, and relative to each other the masses would remain the same.

What about astronomical objects that are distorted by gravitational lensing? Even if the mass of everything is increasing, couldn't we still note any otherwise-anomalous universal change in the presentation of many such systems?

This seems to make assumptions about a relationship between mass and gravity that may or may not hold as "mass changes" in this way, but it's certainly something to look at.

I didn't understand this part of the article. We can measure the mass difference because, according to the theory, that is what we are measuring when we see a redshift. Should we not be able to measure the redshift in a laboratory, given equipment of high sensitivity and a large enough time delta for the change to register?

Edit: Looks like Le_SDT beat me to it :)

I would imagine so, that part confused me as well. It's possible that the level sensitivity required is just too extreme, and would be subject to too much local interference.

There's one such test [1] that I find interesting that suffers from similar problems. It tries to detect gravitational waves traveling through the universe by pointing a laser at a mirror at the end of a 4km tunnel and measuring any changes in the total distance.

[1] http://en.wikipedia.org/wiki/LIGO

Could you give an example of something that can be measured absolutely?

I'm not sure if this is the answer you're looking for, but degrees/radians are considered dimensionless in that they're defined by the ratio of two lengths.

There's no way for the value of 1 radian to magically 'double' without causing π radians to magically amount to a full circle, which would seriously warp Euclidean geometry as we know it.

If time is relative, and mass is relative, and space is relative ... then what's the point of science?

This remind me of the "gravity is entropy because everything is holographic" hypothesis made by physicist whose name I can't remember, when he had his passport stolen and had to wait in Paris for a week before they make him a new one :)

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