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Comment by SoftTalker | Hacker News Reader

"Dark matter is the mysterious, unknown substance that seems to make up the bulk of all the mass in the universe; for every 2 pounds (1 kilogram) of regular matter, there's roughly 10 pounds (5 kg) of dark matter."

...

"This symmetry would help explain why dark matter and regular matter have roughly the same abundances."

So 1 is "roughly the same" as 5, or is this an orders-of-magnitude comparison?

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It seems that yes, they're saying that 1 and 5 are roughly the same. Basically, why is the matter in the universe ~20% "non-dark", and not 1%, or .001%?

There’s that old joke that computer scientists think any numbers within a power of two are equal, physicists think any numbers within a power of 10 are equal, and mathematicians only distinguish between finite numbers and infinity.

Edit: and engineers are as precise as they are paid to be.

For software engineers, the only numbers are 0, 1, and infinity.

https://en.wikipedia.org/wiki/Zero_one_infinity_rule

And cows are spherical!

At some point of its lives. Yes. Is an universal true. Then the zygote starts splitting.

Having proved the contribution of these second and third order terms are between plus 10 and 20% over the range of interest we will multiply by a constant 1.15

between finite numbers and infinities. Plural, please, the discerning mathematician keeps a stable of infinities ;)

"The 80/20 rule"/The Pareto principle

> Mathematically, the 80/20 rule is roughly described by a power law distribution (also known as a Pareto distribution) for a particular set of parameters. Many natural phenomena distribute according to power law statistics. It is an adage of business management that "80% of sales come from 20% of clients." [1][2]

[1] https://en.wikipedia.org/wiki/Pareto_principle

[2] https://en.wikipedia.org/wiki/Power_law

Could you elaborate on how this is related? To me, the 80/20 rule and the 1:5 matter ratio seem like entirely separate concepts that coincidentally share the same ratio.

1:4, no?

Good point, I wasn't thinking and I equated ratios and fractions. That should make the 80/20 rule even less related to the 1:5 matter ratio?

Well 80:20 and 5:1 are pretty similar ratios.

Though really the issue with the comparison is that it implies that 80% (or ~83.3%) of the <something> is correlated to the light matter, and the other 20% (or ~16.7%) of the <something> is correlated to the dark matter. Maybe eventually we'll learn enough about dark matter and discover that, yeah actually, 1/6 of the life, or unobtanium, or whatever, is actually in the dark matter. But for now, I agree that the Pareto principle seems pretty irrelevant.

Since no one knows what dark matter is, there's no known connection between it and real matter, so 1:5 seems coincidental if it's free to be anything within the range 0 .. infinity. But there's no reason to think there is or isn't any connection, since nobody knows what it is.

Cosmology error bars can be very big, depending on the measurement. 500% difference is certainly bigger than some, but since the vacuum energy density appears to differ by a factor of 10^60 from prediction, it's not necessarily a show stopper. Arguably the biggest discovery in cosmology in the last few decades is how much we do not understand at all.

In astronomy and cosmology, 1 and 5 are the same number. Only the orders of magnitude matter when talking about large things. At atomic scales and in photon length the precise numbers do matter.

> In astronomy and cosmology, 1 and 5 are the same number. Only the orders of magnitude matter when talking about large things. At atomic scales and in photon length the precise numbers do matter.

"I am not interested in a more accurate value." said no scientist ever.

It's just easier to measure small things using big tools than to measure big things using small tools, hence astronomy has a disadvantage. Another one is that it isn't easy to create any experiments.

… if dark matter is something totally different from light matter there might be 1000x more of it.

They're describing relative mass, which is related to gravitational attraction and inertia, whether there is "more" is not something they measured.

What is "more"?

Total mass as measured by gravitation effect.

Also in astronomy, all elements other than hydrogen and helium are considered “metals”: https://public.nrao.edu/blogs/astronomy-is-metal/

It's really not an exact science...

Well, at astronomical scales, everything's mostly just hydrogen with tiny bits of hard stuff mixed in. :p

>It's really not an exact science...

I think this is the first time I've ever heard someone use this phrase in reference to an actual science

Well, I would say social sciences arent exact, economics might be a hard science of rules, but the outcomes are subject to too many factors to predict precisely, but it is still a science. Though, well, I am not really qualified to speak on such things, but I would imagine we are fairly precise in the field you guys are talking about.

Economics is a social science, the study of how people interact with things of value. It cannot be hard, since it has a feedback loop.

Thats kind of what I said, the rules are hard, supply and demand, time preference, marginal utility, those are forces that cant be argued with, but it doesnt mean they have precise predictive power.

bashing on "big science" seems to be the latest and greatest of the crapflood that is social media today

i saw a video addressing it the other day:

https://www.youtube.com/watch?v=xglo2n2AMGc

Sometimes science is more art than science. A lot of people don't get that.

Which is really funny, since Hydrogen can be metallic :) Especially so in astronomical scenarios.

https://en.wikipedia.org/wiki/Metallic_hydrogen

"Roughly the same abundances" meaning, why we usually (but not always) find evidence of dark matter in places, where we see regular matter.

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