Dark Matter and Gravity

Key Takeaways

1. Out there in the Universe, it isn’t just normal matter that’s present, but dark matter as well: a mysterious, invisible substance that, as far as we can tell, gravitates, but doesn’t interact through any other means.
2. When we look at the gravitational effects that massive objects have on space, we find dark matter forms a diffuse, halo-and-filament-like network of structure.
3. Normal matter, however, collapses into stars, galaxies, planets, and much more. If dark matter gravitates, and does so the same as normal matter does, then what prevents it from collapsing?

Here in our Universe, it may be the normal matter that we can directly detect, measure, manipulate, experiment with, and observe, but it’s the dark matter that represents most of the mass in the Universe. 

Whereas all the “stuff” that the planets, stars, gas, plasma, and dust are composed of represents about 4.9% of the total energy in the Universe, the mysterious dark matter — whose nature is unknown but for which the observational astrophysical evidence is overwhelming — makes up a whopping 27% of the cosmic energy budget. 

Only dark energy, making up 68% of the Universe, is more important from an energy density perspective.     READ MORE...

A Star Older Than the Universe

For as long as humans have contemplated the Universe, we’ve marveled at the vastness of it all. Was our Universe infinite? Was it eternal? Or did it spring into existence a finite amount of time ago? Over the 20th and 21st centuries, these existential questions for all-time have, one-by-one, fallen into the realm of science, and now have the best answers we’ve ever been able to assemble. 

As of today, in 2024, we can confidently state that we actually know how old the Universe is: 13.8 billion years old, marking time at the start of the hot Big Bang. If we could step back through time, we’d find that the universe as we know it was a very different place early on. Modern stars and galaxies arose from a series of gravitational mergers of smaller-mass objects, which themselves consisted of younger, more pristine stars. 

At the earliest times, there were no stars or galaxies, and even farther, no neutral atoms or stable atomic nuclei, going all the way back to the hot Big Bang. Today, astronomers and astrophysicists who study the early universe confidently state its age with an uncertainty of no more than ~1%: a remarkable achievement.      READ MORE...

Quantum Physics Simplified

Quantum mechanics is simultaneously our most powerful and weirdest scientific theory. It’s powerful because it offers exquisite control over the nanoworld of molecular, atomic, and subatomic phenomena. It’s weird because, while we have a complete mathematical formalism, we physicists have been arguing for more than a century over what that formalism means. In other words, unlike other physical theories, the mathematics of quantum mechanics has no clear interpretation. That means physicists and philosophers have been left arguing about which interpretation makes the most sense. Sometimes the idea of “simplicity” is invoked to answer that question.

The “simplest” explanation
There are two main parts of the quantum formalism. The first is what’s called the dynamical equation. This part gives us a mathematical description of how undisturbed systems evolve. We physicists love our dynamical equations — things like Newton’s equations for particles or Maxwell’s equations for electromagnetic waves. In classical physics, the dynamical equation was pretty much the end of the story. Nothing else was required and we came to think of those equations as existing “out there.” They were timeless laws of physics that never required any reference to what physicists were doing.     READ MORE...

Something is Created from Nothing

There are all sorts of conservation laws in the Universe: for energy, momentum, charge, and more. Many properties of all physical systems are conserved: where things cannot be created or destroyed.

We've learned how to create matter under specific, explicit conditions: by colliding two quanta together at high enough energies so that equal amounts of matter and antimatter can emerge, so long as E = mc² allows it to happen.

For the first time, we've managed to create particles without any collisions or precursor particles at all: through strong electromagnetic fields and the Schwinger effect. 

HERE's HOW...

Whoever said, “You can’t get something from nothing” must never have learned quantum physics. As long as you have empty space — the ultimate in physical nothingness — simply manipulating it in the right way will inevitably cause something to emerge. Collide two particles in the abyss of empty space, and sometimes additional particle-antiparticle pairs emerge. 

Take a meson and try to rip the quark away from the antiquark, and a new set of particle-antiparticle pairs will get pulled out of the empty space between them. And in theory, a strong enough electromagnetic field can rip particles and antiparticles out of the vacuum itself, even without any initial particles or antiparticles at all.

Previously, it was thought that the highest particle energies of all would be needed to produce these effects: the kind only obtainable at high-energy particle physics experiments or in extreme astrophysical environments. But in early 2022, strong enough electric fields were created in a simple laboratory setup leveraging the unique properties of graphene, enabling the spontaneous creation of particle-antiparticle pairs from nothing at all. 

The prediction that this should be possible is 70 years old: dating back to one of the founders of quantum field theory, Julian Schwinger. The Schwinger effect is now verified, and teaches us how the Universe truly makes something from nothing.  READ MORE...

More Galaxies Than Ever Imagined

The Universe is a vast place, filled with more galaxies than we’ve ever been able to count, even in just the portion we’ve been able to observe. Some 40 years ago, Carl Sagan taught the world that there were hundreds of billions of stars in the Milky Way alone, and perhaps as many as 100 billion galaxies within the observable Universe. 

Although he never said it in his famous television series, Cosmos, the phrase “billions and billions” has become synonymous with his name, and also with the number of stars we think of as being inherent to each galaxy, as well as the number of galaxies contained within the visible Universe.

But when it comes to the number of galaxies that are actually out there, we’ve learned a number of important facts that have led us to revise that number upwards, and not just by a little bit. Our most detailed observations of the distant Universe, from the Hubble eXtreme Deep Field, gave us an estimate of 170 billion galaxies. 

A theoretical calculation from a few years ago — the first to account for galaxies too small, faint, and distant to be seen — put the estimate far higher: at 2 trillion. But even that estimate is too low. There ought to be at least 6 trillion, and perhaps more like 20 trillion, galaxies, if we’re ever able to count them all. Here’s how we got there.

The first thing you have to realize about estimating the number of galaxies in the Universe is that the part of the Universe we can see — both today and ever, even into the infinite future — is and will always be finite. The Universe, as we know and perceive it, began with the hot Big Bang some 13.8 billion years ago. 

With some 1080 atoms within it, about five times as much mass in the form of dark matter, as well as billions of times as many photons and neutrinos, gravitation has had plenty of time to pull the matter into clumps, collections, groups, and clusters. This has led to the formation of stars and galaxies with a variety of different properties: masses, sizes, brightnesses and more.  READ MORE...

Changing the Laws of Physics

In an extremely cosmic-brain take, University of Rochester astrophysics professor Adam Frank suggests that a civilization could advance so much that it could eventually tinker with the fundamental laws of physics.

It's a mind-bending proposition that ventures far beyond the conventional framework of scientific understanding, a reminder that perhaps we should dare to think outside the box — especially as we continue our search for extraterrestrial civilizations.

If a civilization were to be able to change the laws of physics, "the very nature of energy itself, with established rules like energy conservation, would be subject to revision within the scope of engineering," Frank, who is part of the NASA-sponsored Categorizing Atmospheric Technosignatures program, wrote in an essay for Big Think.

Playing Games
For instance, as astrophysicist Caleb Scharf argued in an eyebrow-raising 2016 article, an alien civilization could conceivably be behind dark matter, the theoretical stuff that — as far as our current understanding of the universe is concerned — makes up the majority of mass in the universe.

Frank takes the concept even further, suggesting advanced alien civilizations could "mix and match physical laws any way they see fit."  It's all pretty far fetched, and the astrophysicist is the first to acknowledge that, pointing out that at this point it's primarily just "fun" to think about these things.

Frank concludes that while controlling these laws may be pretty unlikely, it's far more likely that they put "severe limits on life and what it can do."  So it's possible that "there simply is no way around the limits imposed by the speed of light," Frank concedes.  READ MORE...

Ancient Technology

We like to think of technological innovation as a gradual, steady, and fairly linear process. However, this is not necessarily the case. Archaeological excavations throughout the world reveal that, once in a while, ancient civilizations developed inventions that were decades if not centuries ahead of their time.

It is sometimes said that these inventions rival or outmatch modern science. This, too, is a misconception. While many ancient super technologies — from Roman concrete to Damascus steel — were once lost, they have since been recreated by present-day researchers. Usually, any difficulty in recreating them stems from the lack of original instruction rather than an inability to comprehend the invention itself.

Equally erroneous is the notion that ancient civilizations stumbled upon these technologies by accident, or that they were designed by idiosyncratic geniuses who were not representative of their day and age. Although many inventors mentioned in this article were indeed considered geniuses, they cannot and should not be separated from their surroundings. Their work is not anachronistic, but a testament to the ingenuity and scientific potential of their respective civilizations.

Greek fire: flames that don’t go out
When the Muslim fleet of the Umayyad Caliphate attempted to lay siege to the Byzantine city of Constantinople in 674, their ships were doused in flames. At first, the Muslims were not alarmed; fire was often used in naval warfare and could be put out easily with cloth, dirt, or water. This, however, was no ordinary fire. Once ignited, it could not be extinguished, and after the entire fleet had burned down, even the sea itself was set ablaze.

The Umayyad Caliphate met its doom at the hands of a new military invention known as Greek fire, Roman fire, liquid fire, or sea fire, among many other names. No recipe survives, but historians speculate it might have involved petroleum, sulfur, or gunpowder. Of the three, petroleum seems the likeliest candidate, as gunpowder didn’t become readily available in Asia Minor until the 14th century, and sulfur lacked the destructive power described by Arab observers.   READ MORE...              

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