Happy 230th Birthday, Enceladus, Our Solar System’s Greatest Hope For Life Beyond Earth
“It is still a complete unknown whether Earth is the only world in the Solar System to house any form of life: past or present. Venus and Mars may have been Earth-like for a billion years or more, and life could have arisen there early on. Frozen worlds with subsurface oceans, like Enceladus, Europa, Triton or Pluto, are completely different from Earth’s present environment, but have the same raw ingredients that could potentially lead to life as well.
Are water, energy, and the right molecules all we need for life to arise? Finding even the most basic organisms (or even the precursor components of organisms) anyplace else in the Universe would lead to a scientific revolution. A single discovered cell in the geysers of Enceladus would be the most momentous discovery of the 21st century. With the recent demise of Cassini, on the 230th anniversary of Enceladus’ discovery, the possibility of finding the incredible compels us to go back. May we be bold enough to make it so.”
On this date in 1789, William Herschel, armed with the most powerful telescope known to humanity at the time (you can get a lot of grant money when you discover the planet Uranus and name it after the King), discovered a relatively small moon of Saturn just 500 kilometers across: Enceladus. For some 200 years, Enceladus was never seen as more than a single pixel across, until the Voyager probes flew by it. What they revealed was a remarkable, unique world in all the Solar System. Now that the Cassini mission is complete, we can look back at all we know about this world, and all the signs point to a remarkable story: there’s a subsurface ocean, possibly suitable as a home for undersea life.
Is Enceladus truly our Solar System’s best hope for life beyond Earth? That’s debatable, but there’s every reason to be hopeful. Come get the story here.
This Is Why Time Has To Be A Dimension
“But even two different objects with the same exact three-dimensional spatial coordinates might not overlap. The reason is easy to understand if you start thinking about the chair you’re sitting in right now. It can definitely have its location accurately described by those three spatial coordinates familiar to us: x, y, and z. This chair, however, is occupied by you right now, at this exact moment in time, as opposed to yesterday, an hour ago, next week, or ten years from now.
In order to completely describe an event in spacetime, you need to know more than just where it occurs, but also when it occurs. In addition to x, y, and z, you also need a time coordinate: t. Although this might seem obvious, it didn’t play a large role in physics until the development of Einstein’s relativity, when physicists started thinking about the issue of simultaneity.”
When you describe where you are in the Universe, you typically think of the coordinates you’d need to give to describe your location. This includes an x, y, and z-direction: the three spatial coordinates corresponding to where we live in our three spatial dimensions. But this doesn’t fully tell you everything you’d need to know, because your location is defined not only by your spatial location but when you’re located there: you need a time coordinate, too. If we take a deep look into the relationship between space and time, first put forth by Einstein over a century ago, we’d find that it isn’t even enough to put in an additional coordinate. Time is more than a separate value; it’s every bit as much a dimension as any of the three spatial dimensions.
If you’ve ever wondered why we say that time is the fourth dimension, come read this. It couldn’t be any other way.
The Salmon Cannon Is A Stroke Of Scientific And Environmental Brilliance
“The spectacle of a large fish getting fired out of a cannon has taken the internet by storm. But the Whooshh Fish Transport System uses straightforward physics to solve a complex environmental problem. When placed inside an airtight tube, you can force objects forward by pressurizing air behind it or evacuating the air ahead of it. The pressure gradient exerts a net force on the object inside, accelerating it until it exits the tube. […] A brilliant application by Whooshh Innovations — to use this technique on salmon — is solving a pressing environmental problem.”
Hydroelectric dams are some of the most common sources of green energy found anywhere in the world. Although they generate large amounts of clean, renewable energy, they come along with a number of significant environmental impacts. In the Pacific Northwest of the United States, in addition to factors such as lake formation, pollution, waste management, and altering the downstream ecosystem, they also disrupt the upstream runs of spawning salmon. The traditional solution has been to install salmon ladders, but that has limited effectiveness and cannot restore the salmon to their initial, natural runs. Some of the larger dams are simply impassable.
But over the past decade, an innovative solution has emerged: firing the salmon over the dams with a Salmon Cannon. No, for real! Come get the science and see for yourself.
Ask Ethan: Where Is The Center Of The Universe?
“I am wondering how there isn’t a center of the universe and how the cosmic background radiation is [equally] far away everywhere we look. It seems to me that when the universe expands… there should be a place where it started expanding.”
Ah, the old center of the Universe question. If the Big Bang happened a long time ago, and we see galaxies moving away from us faster and faster the farther away they are, then where did the Big Bang happen? Where did the expansion start?
It seems like such a simple question, but it turns out this is the wrong question to be asking. The way space and the expanding Universe works is very different from the picture most of us have in our heads, which is much more like an explosion than like an expansion. Yet there’s a very large suite of evidence that points us away from an explosion.
Instead of asking *where* the Big Bang occurred, we should be asking *when* the Big Bang occurred. It makes a lot more sense when you think about it in those terms. Come and find out why.
Cosmic Rays Are More Energetic Than LHC Particles, And This Faster-Than-Light Trick Reveals Them
“The other option would be to catch these cosmic ray particles before they ever reached the Earth; you’d need to go to space to see them. But even if you did that, you’d be limited by the sensitivity of your detector and the amount of energy that could be directly deposited within it. Going to space also comes with a tremendous launch cost; the Fermi gamma ray telescope, which detects individual high-energy photons rather than cosmic rays directly, cost approximately $690 million, more than twice the projected cost of the entire Čerenkov Telescope Array.
Instead, by catching the particles and photons that result from a cosmic ray striking the atmosphere in over 100 locations across the globe, we can come to understand the origin and properties of these ultra-relativistic particles, as well as the astrophysical sources that create them. All of this is possible because we understand the physics of particles moving faster-than-light in one special medium: Earth’s atmosphere. Einstein’s laws might be unbreakable, but the trick of slowing light down enables us to detect something very cleverly that we wouldn’t be able to measure otherwise!”
If you want to measure a high-energy particle, you build an enormous detector. You do this because you want the particle and its decay products (or secondary particles) to deposit their energy in the detector, so you can reconstruct their position, momenta, charge, and other properties that will enable you to understand where they came from. But the Universe gives us particles that are far too high in energy for that to be a workable solution. So what do we do, as physicists?
We use all the tricks nature makes available to us, including slowing light down to leverage the phenemenon of Cherenkov radiation! Here’s how we’re reconstructing cosmic rays from the ground with this special type of light.
Forget About Electrons And Protons; The Unstable Muon Could Be The Future Of Particle Physics
“Humanity can always choose to build a bigger ring or invest in producing stronger-field magnets; those are easy ways to go to higher energies in particle physics. But there’s no cure for synchrotron radiation with electrons and positrons; you’d have to use heavier particles instead. There’s no cure for energy being distributed among multiple constituent particles inside a proton; you’d have to use fundamental particles instead.
The muon is the one particle that could solve both of these issues. The only drawback is that they’re unstable, and difficult to keep alive for a long time. However, they’re easy to make: smash a proton beam into a piece of acrylic and you’ll produce pions, which will decay into both muons and anti-muons. Accelerate those muons to high energy and collimate them into beams, and you can put them in a circular collider.”
There are lots of possibilities being discussed for how we could build a next-generation particle collider, capable of pushing past the frontiers where the LHC will be fundamentally limited. We could go to a larger proton collider, we could go back to doing high-precision collisions of electrons and positrons to create large numbers of the known, existing particles, or we could push the frontiers in an entirely new way: by colliding muons with anti-muons.
“But they only live for 2.2 microseconds,” you correctly object. Good thing we understand physics. If we can get the technology there, it’s the best option imaginable.
How Do We Know How Small An Elementary Particle Is?
“But here’s the thing: we don’t know that this is true. Sure, the Standard Model says that this is the way that things are, but we know that the Standard Model doesn’t give us the final answer to everything. In fact, we know that at some level, the Standard Model must break down and be wrong, because it doesn’t account for gravity, dark matter, dark energy, or the preponderance of matter (and not antimatter) in the Universe.
There has to be something out there more to nature than this. And maybe it’s because the particles that we think are fundamental, point-like, and indivisible today actually aren’t. Perhaps, if we go to high-enough energies and small-enough wavelengths, we’ll be able to see that at some point, between our current energy scales and the Planck energy scale, there’s actually more to the Universe than we presently know.”
Are the fundamental particles that we know of truly fundamental? Are they point-like entities, with no finite size, no internal structure, and no capacity to ever be split apart into smaller entities? According to the Standard Model, they are. But observationally, we know that the Standard Model isn’t all that there is. Moreover, we’ve got a long way to go (some 16 orders of magnitude) from our present experimental limits to the Planck scale, and what we think of as “fundamental” could undergo a revolution at any place, without any warning, if only we dare to look.
Right now, the particles we know of appear fundamental down to a limit of about 10^-19 meters, but it’s a long way down to forever. Here’s what we know today.
Why Is The Sky Dark At Night?
“The fact that saves us, which Olbers had no way of knowing back in his day, is not that the Universe isn’t infinite in extent (it still could be), but that it doesn’t go back, in its current form, for an infinite amount of time. The Universe we inhabit today had a beginning: a day without a yesterday. That beginning is known as the Big Bang, which puts a starting line for all the matter, radiation, energy, and light that possibly exists in the observable Universe.
The Universe hasn’t been around forever, and therefore we can only observe stars and galaxies that are a specific and finite distance away. Therefore, we can only receive a finite amount of light, heat, and energy from them, and there cannot be an arbitrarily large amount of light in our night sky.”
Ask a child what the color of the night sky is, and you’ll uniformly get the same answer: black. The night sky is one of the darkest things we have to look at in all of nature. And yet, the fact that the sky is completely dark at night is a bit of a paradox. If the Universe is full of light sources like stars and galaxies, and it’s truly infinite in extent, then no matter how far away you had to look to see it, eventually every line-of-sight you could imagine would end on a light source. Everywhere, in all directions, all you’d see was a bright light.
Yet, this clearly isn’t what happens in our Universe! This conundrum was known as Olbers’ Paradox, and was only solved in the 20th century. Here’s the ultimate answer!
Saturn, Not Earth Or Jupiter, Has The Largest Storms In Our Solar System
“But from December of 2010 to August of 2011, the largest storm of all occurred: on Saturn. For 200+ days, this Saturnian hurricane raged, maintaining its leading “head” until May. It came to encircle the entire planet, as methane-poor tail end stands out against the relatively methane-rich remainder. Viewed 11 hours (1 Saturn-day) apart, we determined the hurricane migrated across Saturn at 60 miles-per-hour (100 kph). These storms have occurred every 20-30 years since first observed in 1876, as hot air rises, cools and falls.”
Many worlds in our Solar System have enormous storms that occur in their atmospheres. Earth routinely experiences hurricanes, with wind speeds frequently in excess of 225 kph. But what happens on the giant worlds in our Solar System dwarf anything that happens on Earth. Saturn’s hurricane at its north pole is bigger and faster than any hurricane we’ve ever seen here. Jupiter’s great red spot is bigger than the entire Earth itself. But the largest storm of all?
Believe it or not, it’s a periodic weather event that appears to occur on Saturn every 20-30 years or so. Keep your eyes peeled in the 2030s, because it’s going to return!
Ask Ethan: Can Black Holes And Dark Matter Interact?
“If you do the math, you’ll find that black holes will use both normal matter and dark matter as a food source, but that normal matter will dominate the rate of growth of the black hole, even over long, cosmic timescales. When the Universe is more than a billion times as old as it is today, black holes will still owe more than 99% of their mass to normal matter, and less than 1% to dark matter.
Dark matter is neither a good food source for black holes, nor is it (information-wise) an interesting one. What a black hole gains from eating dark matter is no different than what it gains from shining a flashlight into it. Only the mass/energy content, like you’d get from E = mc2, matters. Black holes and dark matter do interact, but their effects are so small that even ignoring dark matter entirely still gives you a great description of black holes: past, present, and future.”
You might not be able to make a black hole out of dark matter entirely, but once a black hole exists, anything that falls past its event horizon will add to its mass, whether it’s particles, antiparticles, radiation or dark matter. And the longer black holes sit in the galaxy, the more and more dark matter will eventually fall in.
The question isn’t whether dark matter contributes to black holes; it’s how and how much. Let’s give you the answer on this edition of Ask Ethan!