Why are so many objects in space shaped like discs?

It's one of the most consistent patterns in the unviverse. What causes it?

MICHELLE THALLER: Rick, you have noticed one of the most wonderful and consistent patterns in the whole universe. The universe is very good at making spinning discs. Our solar system is a disc, and all the planets go around in basically the same plane, and they all go around in the same direction. Why should that be?

There are discs all over the place. I mean, think about the rings of Saturn. The rings of Saturn are also very, very thin, and they all go around in the same direction. Galaxies, spiral galaxies are one big disc with everything moving around a common center. Discs seem to be something that the universe likes to make. And, in fact, that really is true. And it has to do with a number of things. It has to do with the force of gravity and something called the conservation of angular momentum.

Now, gravity is very good at bringing stuff together and bringing it together so it becomes denser and denser and begins to fall into the center. Our solar system formed out of a giant cloud of dust and gas about 4 and 1/2 billion years ago. It was actually many trillions of miles across at first, but it had to get much smaller in order for the densities to get high enough and the temperatures also to get warm enough inside to give birth to the Sun, actually ignite a star. So you have this collapsing cloud of dust.

OK, well, you can sort of understand that gravity wants to bring all that together, but why does it start to spin up? There's something called the conservation of angular momentum. And that basically says that if anything has any spin at all, even just a little bit of motion, as gravity brings it together and makes it smaller, that spin is accelerated; it's sped up. And probably the example most people know best of all – you can actually feel this if you want to do this – but an ice skater. If you've seen an ice skater do a spin, usually what they do is that they have their arms outstretched, and they're spinning around relatively slowly. And then they bring their arms in, and they spin faster and faster. It's kind of amazing that any person can keep their balance when they do that. That is an application of the conservation of angular momentum. You have an extended body, your arms are out, and you're spinning slowly. In order to conserve the energy in that spin, as that body becomes smaller, the spin goes faster and faster. And so what happens in these clouds is that a cloud usually has just a tiny little bit of a drift velocity. It's going around the galaxy or maybe a nearby star exploded, and it's kind of all moving in one direction. The cloud itself has a little bit of velocity as a cloud, as a whole. Particles inside that cloud could be going any which way.

But as the cloud begins to come together under gravity, any little bit of spin gets accelerated, actually becomes faster. And so as the cloud collapses, any little directional drift becomes a spin, and the cloud itself begins to spin around. OK, so that gets you a spinning cloud. Why does it collapse down into a disc? And this is an interesting bit of physics that has to do with things like collisions. In the case of a very large cloud that's forming a star, it might not even be that things are colliding directly, but gravitationally they're influencing them as you go by. As you go by different parts of mass, they tug on each other with their gravity. So this whole cloud is spinning, and things begin to interact gravitationally. They begin to collide with each other. The particles have motion in every direction. Some are going up, and some are going down. And as they start to hit each other, that's kind of balanced out; that up and down is sort of canceled out, but everything has the same motion as the cloud is spinning. So that's basically the only thing that's left over at the end. Everything gets canceled out as all these things collide and interact, but the spin of the cloud is still there. And so over time, you collapse down into a disc. So the only reason you make discs is because of this law of conservation of angular momentum, and the idea of gravity brings things together. Have those two things working side-by-side, and you get a disc. And that's why our solar system formed that way. The planets then formed out of that spinning disc of gas. So it makes sense that they're all going in the same direction. They all formed out of the gas going around the Sun in that way.

  • Spinning discs are everywhere – just look at our solar system, the rings of Saturn, and all the spiral galaxies in the universe.
  • Spinning discs are the result of two things: The force of gravity and a phenomenon in physics called the conservation of angular momentum.
  • Gravity brings matter together; the closer the matter gets, the more it accelerates – much like an ice skater who spins faster and faster the closer their arms get to their body. Then, this spinning cloud collapses due to up and down and diagonal collisions that cancel each other out until the only motion they have in common is the spin – and voila: A flat disc.
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Yale scientists restore brain function to 32 clinically dead pigs

Researchers hope the technology will further our understanding of the brain, but lawmakers may not be ready for the ethical challenges.

Still from John Stephenson's 1999 rendition of Animal Farm.
Surprising Science
  • Researchers at the Yale School of Medicine successfully restored some functions to pig brains that had been dead for hours.
  • They hope the technology will advance our understanding of the brain, potentially developing new treatments for debilitating diseases and disorders.
  • The research raises many ethical questions and puts to the test our current understanding of death.

The image of an undead brain coming back to live again is the stuff of science fiction. Not just any science fiction, specifically B-grade sci fi. What instantly springs to mind is the black-and-white horrors of films like Fiend Without a Face. Bad acting. Plastic monstrosities. Visible strings. And a spinal cord that, for some reason, is also a tentacle?

But like any good science fiction, it's only a matter of time before some manner of it seeps into our reality. This week's Nature published the findings of researchers who managed to restore function to pigs' brains that were clinically dead. At least, what we once thought of as dead.

What's dead may never die, it seems

The researchers did not hail from House Greyjoy — "What is dead may never die" — but came largely from the Yale School of Medicine. They connected 32 pig brains to a system called BrainEx. BrainEx is an artificial perfusion system — that is, a system that takes over the functions normally regulated by the organ. Think a dialysis machine for the mind. The pigs had been killed four hours earlier at a U.S. Department of Agriculture slaughterhouse; their brains completely removed from the skulls.

BrainEx pumped an experiment solution into the brain that essentially mimic blood flow. It brought oxygen and nutrients to the tissues, giving brain cells the resources to begin many normal functions. The cells began consuming and metabolizing sugars. The brains' immune systems kicked in. Neuron samples could carry an electrical signal. Some brain cells even responded to drugs.

The researchers have managed to keep some brains alive for up to 36 hours, and currently do not know if BrainEx can have sustained the brains longer. "It is conceivable we are just preventing the inevitable, and the brain won't be able to recover," said Nenad Sestan, Yale neuroscientist and the lead researcher.

As a control, other brains received either a fake solution or no solution at all. None revived brain activity and deteriorated as normal.

The researchers hope the technology can enhance our ability to study the brain and its cellular functions. One of the main avenues of such studies would be brain disorders and diseases. This could point the way to developing new of treatments for the likes of brain injuries, Alzheimer's, Huntington's, and neurodegenerative conditions.

"This is an extraordinary and very promising breakthrough for neuroscience. It immediately offers a much better model for studying the human brain, which is extraordinarily important, given the vast amount of human suffering from diseases of the mind [and] brain," Nita Farahany, the bioethicists at the Duke University School of Law who wrote the study's commentary, told National Geographic.

An ethical gray matter

Before anyone gets an Island of Dr. Moreau vibe, it's worth noting that the brains did not approach neural activity anywhere near consciousness.

The BrainEx solution contained chemicals that prevented neurons from firing. To be extra cautious, the researchers also monitored the brains for any such activity and were prepared to administer an anesthetic should they have seen signs of consciousness.

Even so, the research signals a massive debate to come regarding medical ethics and our definition of death.

Most countries define death, clinically speaking, as the irreversible loss of brain or circulatory function. This definition was already at odds with some folk- and value-centric understandings, but where do we go if it becomes possible to reverse clinical death with artificial perfusion?

"This is wild," Jonathan Moreno, a bioethicist at the University of Pennsylvania, told the New York Times. "If ever there was an issue that merited big public deliberation on the ethics of science and medicine, this is one."

One possible consequence involves organ donations. Some European countries require emergency responders to use a process that preserves organs when they cannot resuscitate a person. They continue to pump blood throughout the body, but use a "thoracic aortic occlusion balloon" to prevent that blood from reaching the brain.

The system is already controversial because it raises concerns about what caused the patient's death. But what happens when brain death becomes readily reversible? Stuart Younger, a bioethicist at Case Western Reserve University, told Nature that if BrainEx were to become widely available, it could shrink the pool of eligible donors.

"There's a potential conflict here between the interests of potential donors — who might not even be donors — and people who are waiting for organs," he said.

It will be a while before such experiments go anywhere near human subjects. A more immediate ethical question relates to how such experiments harm animal subjects.

Ethical review boards evaluate research protocols and can reject any that causes undue pain, suffering, or distress. Since dead animals feel no pain, suffer no trauma, they are typically approved as subjects. But how do such boards make a judgement regarding the suffering of a "cellularly active" brain? The distress of a partially alive brain?

The dilemma is unprecedented.

Setting new boundaries

Another science fiction story that comes to mind when discussing this story is, of course, Frankenstein. As Farahany told National Geographic: "It is definitely has [sic] a good science-fiction element to it, and it is restoring cellular function where we previously thought impossible. But to have Frankenstein, you need some degree of consciousness, some 'there' there. [The researchers] did not recover any form of consciousness in this study, and it is still unclear if we ever could. But we are one step closer to that possibility."

She's right. The researchers undertook their research for the betterment of humanity, and we may one day reap some unimaginable medical benefits from it. The ethical questions, however, remain as unsettling as the stories they remind us of.