Contrabang! #26 Often In Error But Seldom In Doubt

This Is Why ‘Physical Cosmology’ Was Long Overdue For The 2019 Nobel Prize (link)

In the mid-20th century, ‘physical cosmology’ was considered an oxymoronic joke. Today, it’s Nobel-winning science.

He's not wrong, except the reason is that the Nobel prize has itself become a joke too. Most of the big ideas of "physical cosmology" like dark energy, dark matter, black holes, etc. are absurd, and the long-term effect of giving this prize to Jim Peebles (plus the one they gave in 2011 for dark energy) will be to damage the reputation of what was once - perhaps - the most acclaimed award in all humanity.

Regardless of what you’re measuring, one fact remains true about any and all structures and objects in existence: they all formed naturally in a Universe governed by the same laws and made up of the same components everywhere.

One of the big problems we talk about with the physicists is they never challenge their core assumptions. Another problem - even bigger, perhaps - is that they don't even track their assumptions. That's an important thing, even when the assumption is reasonable. As a software engineer, when I review the code written by others I'm not just looking at code quality and correctness, but also in trying to surface whatever assumptions may have been made. This sometimes unveils subtle bugs, and helps give a better understanding of the risks involved with the work and where trouble may come from.

These physicists don't do that. Once a theory is "settled science" (by which they mean there's a consensus, which isn't a scientific concept) they build on top of that with yet more assumptions, and then more yet again. They never are faced with having to take live traffic on the stack of assumptions they've made. (That is, have it all tested by reality.) In their world, they can keep explaining away all inconsistencies with more complexity and promises that future evidence will be better.

Ethan vows that we can at least be certain that the universe is governed by the same laws at all times and in all places. That's a very old assumption made in the Western tradition, but it is still an assumption. We don't actually know that it's true. For instance, the gravitational constant is notoriously slippery, and can't be established with high precision. Some scientists have observed that many of the larger dinosaurs don't seem to have been structurally feasible, and have proposed that gravity was weaker in earlier era. The speed of light also shows some variation, frustrating scientists who eventually redefined the meter in terms of the speed of light, supposedly making that little problem go away. Now, maybe it's perfectly reasonable to make the assumption that the physical laws and constants are fixed, but that assumption needs to be tracked, otherwise scientists become overconfident that they are standing on much more solid ground than they really are.

In physical cosmology, what you do is you start with:

• the known laws of physics,
• the relevant physical ingredients for the system you’re considering,
• the initial conditions of your physical system that your Universe begins with,
• and an accurate model for the interactions among the ingredients (including the background of spacetime).

Once you have all of that, then you do the calculations to derive what you expect to exist within our Universe. When your observations come in, you compare them with your theoretical expectations. Where observational and theoretical cosmology meet is where we, at long last, can scientifically determine what does and doesn’t accurately describe our Universe.

There is a major logical error going on here, which is the declaration that in physical cosmology they start with initial conditions - which they have no way to measure. Instead, they've taken current conditions and used the known (and proposed) laws of physics to walk back to some theoretical initial conditions. They then use those same laws of physics to "prove" that we end back up in the current state.

In the middle of the 20th century, legendary physics curmudgeon Lev Landau famously said, “Cosmologists are often in error but seldom in doubt.” With the 2019 Nobel Prize in Physics going to Jim Peebles, perhaps the world will recognize it’s long past time to retire Landau’s quote. We may live in a dark Universe, but the science of physical cosmology has shed a light on it like nothing else.

It is amusing to see Ethan dismiss a quote about cosmologists' arrogance with such self-assured bravado.

For The Last Time, No, A NASA Engineer Has Not Broken Physics With An Impossible Engine (link) 

We previously described Ethan as the King of the No-Comma but perhaps it should have been titled Queen of the No-Comma, because he delivers this one with some sass. The No-Comma is a lecturing, almost condescending rhetorical advise that helps us understand why other physicists might perceive the astrophysicists as a bit smug. I have trouble reading this title in anything but the voice of the comic book guy from The Simpson's.

Dark Matter’s Biggest Problem Might Simply Be A Numerical Error (link)

In principle, if you can write down the initial conditions describing the Universe at some early time — including what it’s made of, how those contents are distributed, and what the laws of physics are — you can simulate what it will look like at any point in the future.

In principle, you can't, as consequence of two of the biggest scientific insights of last century. Heisenberg's Uncertainty Principle tells us that we can never perfectly know the state of any system, not even of a single particle. Chaos Theory tells us even slight non-linearities in real-world system turn small differences in initial conditions into large differences in outcomes. The idea of the universe as a mechanical clock that you can just wind forward and backwards with perfect, calculable determinism is not realistic.

The 1990s also saw the first simulations of dark matter halos that form under the influence of gravity. The various simulations had a wide range of properties, but they all exhibited some common features, including:

• a density that reaches a maximum in the center,
• that falls off at a certain rate (as ρ ~ r^-1 to r^-1.5) until you reach a certain critical distance that depends on the total halo mass,
• and then that “turns over” to fall off at a different, steeper rate (as ρ ~ r^-3), until it falls below the average cosmic density.

Here he just casually throws out some mathematical symbols without defining them. Either he's being very lazy, or he's hoping to intimidate non-technical readers so they'll just trust that he is correct and move along.

This problem, known as the core-cusp problem in cosmology, is one of the oldest and most controversial for dark matter. [...] However, it’s also possible that they don’t represent real physics, but rather represent a numerical artifact inherent to the simulation itself.

It's also possible that it's a "conceptual artifact" inherent to the simulation itself.

For decades, contrarians opposed to dark matter have latched onto these small-scale problems, convinced that they’ll reveal the flaws inherent to dark matter and reveal a deeper truth.

Yes, if you question a hypothetical state of matter that is sprinkled liberally where needed to make the equations work, you must be a contrarian. He is wrong that we're convinced we'll reveal the flaws to dark matter and reveal a deeper truth. No, we're convinced we'll reveal the flaws inherent to dark matter and that's enough by itself. (In the long-run, I suppose, the truth can only be found if the distracting lies are done away with.) He reveals a flaw in the mindset of these people, which is that they will only discard one idea if a better one is immediately available to replace it. They're like the girls who will never break up with a guy until the next one is lined up. Branch swingers, we call them. Ethan just can't fathom that we'd reject some theory because it's false, and not because we have a different theory we want to promote and get some smart-boy internet points for being right.

If this new paper is correct, however, the only flaw is that cosmologists have taken one of the earliest simulation results — that dark matter forms halos with cusps at the center — and believed their conclusions prematurely. In science, it’s important to check your work and to have its results checked independently. But if everyone’s making the same error, these checks aren’t independent at all.

No, that can't be right. Peer-reviewed is the gold standard, and anyone who disagrees with any peer-reviewed science is a contrarian.