Happy Birthday To Urbain Le Verrier, Who Discovered Neptune With Math Alone
“The other planets dutifully followed the laws of planetary motion, but Uranus appeared to violate them. Breaking Kepler’s laws, Uranus moved too quickly for decades, then at the right speed, then too slowly. The observations weren’t easily dismissable, but their physical cause was unknown. An additional planet beyond Uranus, gravitationally tugging on it, offered a potential solution. Determining the mass, orbital parameters, and location of an unseen world presented incredible calculational challenges.”
On March 11, 1811, Urbain Le Verrier was born. As a mathematician of tremendous skill in France, he had only a passing initial interest in astronomy, until the 1840s, when the influential François Arago suggested that he take up the puzzle of Uranus’ orbit, which appeared to violate the laws of planetary motion. Le Verrier theorized that if there were an outer planet beyond Uranus with the right mass and orbital parameters, it could cause these observed orbital anomalies. On August 31, 1846, Le Verrier composed a letter detailing his predictions and sent it to the Berlin Observatory. On September 23, the letter arrived. That very night, the portion of the sky where Le Verrier claimed a new planet should be was clear, and less than one degree away from his location, there it was: the planet Neptune.
Arago immortalized Le Verrier as the man who discovered a planet with the point of his pen. It remains an astronomical achievement of the highest order.
Ask Ethan: If The Universe Ends In A Big Crunch, Will All Of Space Recollapse?
“When you describe the Big Crunch, you talk about a race between gravity and the expansion of space. It’s not clear to me that if gravity wins that race, whether space stops expanding, or simply that the matter in space stops expanding. I’d love to hear your explanation of this.”
The Universe is expanding, and we can confirm this by looking at the relationship between how redshifted a galaxy’s light is compared with how far away it is from us. But if these galaxies, at some point in the far future, stop being redshifted and start moving closer and closer to us again, does that necessarily mean that the fabric of space is contracting? Is all of space necessarily recollapsing? Or could the galaxies simply be moving towards us, owing to some massive attraction, while the fabric of space doesn’t recollapse at all? Does a Big Crunch necessarily equate to a recollapsing Universe?
Even though we don’t know whether dark energy will reverse itself or not, we do know the answer to this question, and yes, a Big Crunch does mean recollapse! Find out why on this edition of Ask Ethan.
The Anthropic Principle Is What Scientists Use When They’ve Given Up On Science
“There can be no doubt that the Universe is governed by laws, constants, and observable properties, and that this very same Universe did, in fact, give rise to us. But that does not necessitate the Universe was required to have the exact properties it does in order to admit our existence, nor does it imply that a Universe that were different in some fundamental way would be an impossibility for observers. Most importantly, we cannot use the Anthropic Principle to learn why the Universe is the way we see it, as opposed to any other way.
The Anthropic Principle may be a remarkable starting point, allowing us to place constraints on the Universe’s properties owing to the fact of our existence, but that is not a scientific solution in and of itself. Our goal in science, remember, is to understand how the Universe arrived at its current properties through natural processes. If we replace scientific inquiry with anthropic arguments, we’ll never get there. The multiverse may be real, but the Anthropic Principle cannot scientifically explain why our Universe’s properties are what they are.”
It shouldn’t be a controversial statement to note the fact that we exist in the Universe, and that therefore the laws of physics and the phenomena in the Universe need to behave in a way that makes our existence possible. But sometimes, what starts off as a correct and innocuous statement gets applied in an extremely unscientific way, and that leads to a number of not-necessarily-correct conclusions being drawn by scientists who are unknowingly fooling themselves.
Don’t you get fooled; learn the difference between a good use and a real abuse of the Anthropic Principle. Otherwise, you might accidentally give up on science.
How Much Of The Dark Matter Could Neutrinos Be?
“If we restrict ourselves to the Standard Model alone, we simply cannot account for the dark matter that must be present in our Universe. None of the particles we know of have the right behavior to explain all of the observations. We can imagine a Universe where neutrinos have relatively large amounts of mass, and that would result in a Universe with significant quantities of dark matter. The only problem is that dark matter would be hot, and lead to an observably different Universe than the one we see today.
Still, the neutrinos we know of do behave like dark matter, although it only makes up about 1% of the total dark matter out there. That’s not totally insignificant; it equals the mass of all the stars in our Universe! And most excitingly, if there truly is a sterile neutrino species out there, a series of upcoming experiments ought to reveal it over the next few years. Dark matter might be one of the greatest mysteries out there, but thanks to neutrinos, we have a chance at understanding it at least a little bit.”
Dark matter is a form of matter that gravitates, but neither absorbs nor emits light, and has been frustratingly difficult to pin down and directly detect. There’s a known particle that has exactly those same properties: the neutrino! You might wonder, then, if perhaps neutrinos had the right value of mass and number, if they could make up the dark matter? And if not all of it, could they at least make up part of it? This is a question that astronomers and physicists have pondered for decades, and we might be closer than ever to the actual answer.
How much of the dark matter can neutrinos actually be? Find out today!
What Was It Like When Planet Earth Took Shape?
“There was almost certainly a high-energy collision with a foreign, out-of-orbit object that struck our young Earth in the early stages of the Solar System, and that collision was required to give rise to our Moon. But it was very likely much smaller than Mars-sized, and it was almost certainly a sturdy strike, rather than a glancing collision. Instead of a cloud of rock fragments, the structure that formed was a new type of extended, vaporized disk known as a synestia. And over time, it settled down to form our Earth and Moon as we know them today.
At the end of the early stages of our Solar System, it was as promising as it could be for life. With a central star, three atmosphere-rich rocky worlds, the raw ingredients for life, and with gas giants only existing much further beyond, all the pieces were in place. We know we got lucky for humans to arise. But with this new understanding, we also think the possibility for life like us has happened millions of times before all throughout the Milky Way.”
One of the deepest existential questions we can ask about the Universe is how, after more than 9 billion years, all the phenomena in our cosmic history led to the creation of planet Earth. Going from an environment where stars were actively forming to one where the Sun, Earth, and all the other planets were in place is a daunting task for people who create scientific simulations of our early environment, and involves gravitational interactions, planetary migrations and ejections, and even enormously energetic collisions between planets and proto-planets.
Yet somehow, it all came together, and gave rise to us. From what we’re learning, we might not even be all that rare. Come check out the current story.
How Much Of The Unobservable Universe Will We Someday Be Able To See?
“You might think that if we waited for an arbitrarily long amount of time, we’d be able to see an arbitrarily far distance, and that there would be no limit to how much of the Universe would become visible.
But in a Universe with dark energy, that simply isn’t the case. As the Universe ages, the expansion rate doesn’t drop to lower and lower values, approaching zero. Instead, there remains a finite and important amount of energy intrinsic to the fabric of space itself. As time goes on in a Universe with dark energy, the more distant objects will appear to recede from our perspective faster and faster. Although there’s still more Universe out there to discover, there’s a limit to how much of it will ever become observable to us.”
The Universe is a huge, vast, enormous place. It’s been 13.8 billion years since the Big Bang occurred, which translates into an observable Universe that’s 46 billion light years to its edge, and contains some 2 trillion galaxies in various stages of evolutionary development. But that’s not the end of what we’ll ever be able to observe. As time goes on, light that’s presently on its way to our eyes will eventually catch up, revealing a future visibility limit that’s even larger than the present observable Universe. When we add it all up, we’ll find that we more than double the number of galaxies we can observe, even though we can barely reach 1% of them.
How does this all work? Find out the limits of the observable and unobservable Universe today!
Celebrate The 50th Anniversary Of Apollo 9, Which Made The Moon Landing Possible
“Successfully landing on the Moon and returning astronauts to Earth would require novel technology: the Lunar Module. The crew of James McDivitt, David Scott, and Rusty Schweickart rocketed into space aboard a Saturn V on March 3, 1969. From low Earth orbit, they performed the first crewed flight of Apollo’s Lunar Module. They successfully demonstrated module docking and extraction, proving Apollo was capable of a successful landing and return.”
We’re fast approaching the most famous anniversary of all: the 50th anniversary of the Apollo 11 moon landing, coming up this July. Yet on our way there, it’s important to remember all the steps that were necessary in getting us there. On March 3rd, 1969, Apollo 9 launched, remaining in low-Earth orbit and successfully testing a whole slew of new technologies, from life support systems to docking, extraction, and a simulated descent, landing, and ascent of the Lunar Module. It marked the first time a complete Apollo spacecraft with all components necessary for a lunar landing and return were launched. In essence, this was the mission that proved the Apollo program has the right stuff!
Come take a look back and celebrate the 50th anniversary of the Apollo 9 mission, one of only two Apollo missions whose crewmembers are all still alive today!
Ask Ethan: Why Don’t Gravitational Waves Get Weaker Like The Gravitational Force Does?
“You have stated:
1) The strength of gravity varies with the square of the distance.
2) The strength of gravity waves, as detected by LIGO, varies directly with the distance.
So the question is, how can those two be the same thing?”
Here’s a puzzling fact for you: if you get ten times as far away from a source of gravitational waves, how much less would you expect the signal to be in your gravitational wave detector? For light, brightness falls off as the inverse of the distance squared: it would be 1/100th as bright. For the gravitational force, it also falls off as the inverse of distance squared: 1/100th the force. But for gravitational waves, the signal strength only drops as the inverse of the distance; the signal would be 1/10th the original strength.
Why is this? Believe it or not, it’s mandated by physics! Come find out the deep truth behind why on this special* edition of Ask Ethan!
(* – special because I had to derive this myself; nobody gives the full explanation anywhere I can find!)
Relativity Wasn’t Einstein’s Miracle; It Was Waiting In Plain Sight For 71 Years
“If the Universe had a frame of reference that was distinct from all the others, then there should be some measurement you could make that revealed to you how the laws of nature were different when you moved at one particular speed in one particular direction. But that is inconsistent with the Universe we have. No matter how fast you move or what direction you move in, the laws of physics are the same, and any physical experiment you can perform will give the same measurable results and result in the same physical phenomena.”
When we think about Einstein and the principle of relativity, we normally talk about the Michelson-Morley experiment, which showed that the speed of light remained constant whether it was aligned with or at an angle to Earth’s motion. We might think about the Lorentz transformations like time dilation or length contraction. Certainly, those results played a role, but Einstein himself was thinking about a puzzle that came to light much earlier: about what’s physically occurring to cause Faraday’s law of induction. If you move a bar magnet into a stationary coil of wire, you generate an electric current. If you move a coil of wire onto or off of a stationary bar magnet, you also generate an equal intensity electric current. But the physics of how is entirely different!
Why are they equivalent? How can we reason our way into this? It was thinking about this that led Einstein to relativity. Come see how he got there, from a result 71 years in the making.
Earliest Signal Ever: Scientists Find Relic Neutrinos From 1 Second After The Big Bang
“This cosmic neutrino background (CNB) has been theorized to exist for practically as long as the Big Bang has been around, but has never been directly detected. Because neutrinos have such a tiny cross-section with other particles, we generally need them to be at very high energies in order to see them. The energy imparted to each neutrino leftover from the Big Bang corresponds to only 168 micro-electron-volts (μeV) today, while the neutrinos we can measure have many billions of times as much energy. No proposed experiments are theoretically capable of seeing them.
But there are two ways to see them indirectly: from their effects on the CMB and on the large-scale structure of the Universe.”
When we look at the Universe, one of our great cosmic quests is to go earlier than ever before. To the first galaxies, the first stars, the first atoms, and even earlier, if possible. That’s how we put the best theories of our cosmic origins, like the Big Bang, to the ultimate test. The earliest observable signal from the classical Big Bang is a bath of neutrinos and antineutrinos, which froze-out when the Universe was just 1 second old. For generations, this was regarded as an undetectable prediction, but there are two ways that they might affect observable features of the Universe.
It’s 2019, and we’ve now seen them both. The results? The cosmic neutrino background looks exactly like the Big Bang predicts. Come get the incredible scoop!