Tag: cosmology

Numbers inevitable?

Why do we use numbers so much? Is it something about the world? Or is it more something about us? We discussed above the example of fundamental physics. And we argued that even though at the most fundamental level numbers really aren’t involved, our sampling of what happens in the universe leads us to a description that does involve numbers. And in this case, the origin of the way we sample the universe has deep roots in the nature of our consciousness, and our fundamental way of experiencing the universe, with our particular sensory apparatus, place in the universe, etc. As long as we preserve core aspects of our experience as what we consider conscious observers some version of numbers will in the end be inevitable for us. We can aspire to generalize from numbers, and, for example, sample other representations of computational reducibility. But for now, numbers seem to be inextricably connected to core aspects of our existence.

Black hole info paradox

The most famous paradox in physics nears its end

In a landmark series of calculations, physicists have proved that black holes can shed information, which seems impossible by definition. The work appears to resolve a paradox that Stephen Hawking first described 50 years ago. All this reinforces many physicists’ hunch that space-time is not the root level of nature, but instead emerges from some underlying mechanism that is not spatial or temporal. To many, that was the main lesson of the AdS/CFT duality. The new calculations say much the same thing, but without committing to the duality or to string theory. Wormholes crop up because they are the only language the path integral can use to convey that space is breaking down. They are geometry’s way of saying the universe is ultimately nongeometric.

2023-02-12: More on Feynman Path Integrals

The most powerful formula in physics starts with a slender S, the symbol for a sort of sum known as an integral. Further along comes a second S, representing a quantity known as action. Together, these twin S’s form the essence of an equation that is arguably the most effective diviner of the future yet devised.

The oracular formula is known as the Feynman path integral. As far as physicists can tell, it precisely predicts the behavior of any quantum system — an electron, a light ray or even a black hole. The path integral has racked up so many successes that many physicists believe it to be a direct window into the heart of reality.

RelMOND

Their theory, dubbed RelMOND, adds to the equations of general relativity an omnipresent field that behaves differently in different arenas. On the grandest scales, where the universe noticeably stretches as it expands, the field acts like invisible matter. In this mode, which Złosnik refers to as “dark dust,” the field could have shaped the visible universe just as dark matter would. The model faithfully reproduces the temperature of the CMB — the result that the duo published in their preprint — and Złosnik says it can also match the polarization spectrum and the matter distribution, although they have not yet published these plots.

In place of dark matter, they substitute a subtly modified force of gravity.

Chirality

Cosmic rays may explain life’s bias for right-handed DNA

Ultimately, the fact that researchers struggle to find a theory that balances the rise of chirality against the destruction of biological materials suggests that our ancestors may have been lucky to find that fine line. There is something special about planets like the Earth that protect this kind of chemistry.

2021-08-02: More details on this astounding achievement. They were able to sequence a 1.5 kilobase chiral DNA plus the Pasteur encoding stunt.

The chirally inverted L-DNA, possessing the same informational capacity but resistant to biodegradation, may serve as a robust, bioorthogonal information repository. Here we chemically synthesize a 90-kDa high-fidelity mirror-image Pfu DNA polymerase that enables accurate assembly of a kilobase-sized mirror-image gene. We use the polymerase to encode in L-DNA an 1860 paragraph by Louis Pasteur that first proposed a mirror-image world of biology. We realize chiral steganography by embedding a chimeric D-DNA/L-DNA key molecule in a D-DNA storage library, which conveys a false or secret message depending on the chirality of reading. Furthermore, we show that a trace amount of an L-DNA barcode preserved in water from a local pond remains amplifiable and sequenceable for 1 year, whereas a D-DNA barcode under the same conditions could not be amplified after 1 day.

2022-10-28: The same group doing the next step, a chiral RNA polymerase. This one is about 10% larger than previous work on the DNA polymerase as measured in kDA.

Zhu chemically synthesized a 100-kDA mirror-image T7 RNA polymerase, which enabled efficient and faithful transcription of high-quality l-RNAs as long as 2.9 kilobases. A massive, 883 amino acid protein, it lay well beyond the limits of traditional chemical synthesis. But an analysis of T7s x-ray crystal structure showed the enzyme could likely be split into 3 sections, each stitched from short segments. In solution, the fragments naturally folded into their proper 3D shapes and assembled themselves into a working T7.

The mirror-image RNAs fashioned by the polymerase were far more stable than the normal versions produced by a regular T7, because they were untouched by the naturally occurring RNA chewing enzymes that almost unavoidably contaminate such experiments and quickly destroy normal RNAs.

Now, Zhu needs to make the remaining components of a mirror-image ribosome. The 3 RNA fragments they synthesized make up 66% of the total mass of a ribosome. What remains are the 54 ribosomal proteins and several proteins that work in concert with the ribosome, all of which are smaller and thus likely easier to synthesize. Then the question is whether the full parts kit will assemble into a ribosome.

Even if they do, the resulting molecular machines might still not be functional. In order to churn out proteins, ribosomes must work in conjunction with a suite of additional helper proteins. To make this work inside a living cell, Church thinks it will be necessary to rewrite an organism’s genetic code so the engineered ribosome can recognize all those proteins, particularly the 20 that ferry amino acids for building new proteins.


2023-08-28: nonlinear optics to detect chirality

They have realized a technique that can completely distinguish enantiomers in solution in an all-optical manner: no chemical tags, no particular UV/VIS absorbance needed from the compound structures, etc. And it is extremely fast and extremely sensitive, as opposed to traditional methods like optical rotation, circular dichroism, etc.

2023-09-08: What about magnetism?

Magnetic surfaces on minerals in bodies of water on the primordial Earth, charged by the planet’s magnetic field, could have served as “chiral agents” that attracted some forms of molecules more than others, kicking off a process that amplified the chirality of biological molecules, from RNA precursors all the way to proteins and beyond. Their proposed mechanism would explain how a bias in the makeup of certain molecules could have cascaded outward to create a vast network of chiral chemistry supporting life.

It’s not the only plausible hypothesis, but “it’s one of the coolest because it ties geophysics to geochemistry, to prebiotic chemistry, and ultimately to biochemistry”

Primordial Magnetism

One possibility is that cosmic magnetism is primordial, tracing all the way back to the birth of the universe. In that case, weak magnetism should exist everywhere, even in the “voids” of the cosmic web — the very darkest, emptiest regions of the universe. The omnipresent magnetism would have seeded the stronger fields that blossomed in galaxies and clusters.

Reonization galaxy

For 100s of millions of years after the Big Bang, the entire universe was a thick soup of hydrogen atoms swimming in total blackness. So dense was this cosmic goulash that the first light from the first stars in existence couldn’t penetrate it — the hydrogen fog simply absorbed and scattered the starlight in circles, trapping the universe in a cosmic dark age as ever more stars, galaxies and black holes slowly smoldered to life. That all changed after 500 ma, when a grand cosmic makeover called the epoch of reionization began. As ancient galaxies grew ever larger and radiated more powerful energy, they began to burn away the cosmic fog that surrounded them by ionizing hydrogen atoms into a plasma of free protons and electrons. Suddenly, light could travel across the cosmos — first through “bubbles” of plasma surrounding large galaxies, then farther and farther as multiple bubbles began to expand and overlap. The galaxy group, named EGS77, dates to 680 ma after the Big Bang and appears to be surrounded by 3 overlapping bubbles of plasma — meaning these pioneering galaxies may have been caught in the act of reionizing their corner of the universe and bringing the cosmic dark ages to an end.