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Ethan Siegel
44,093 followers -
Science writer, professor and theoretical astrophysicist
Science writer, professor and theoretical astrophysicist

44,093 followers
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“But the fact that you can see cosmic ray muons at all is enough to prove that relativity is real. Think about where these muons are created: high in the upper atmosphere, about 30-to-100 kilometers above Earth’s surface. Think about how long a muon lives: about 2.2 microseconds on average. And think about the speed limit of the Universe: the speed of light, or about 300,000 kilometers per second. If you have something moving at the speed of light that only lives 2.2 microseconds, it should make it only 0.66 kilometers before decaying away. With that mean lifetime, less than 1-in-10^50 muons should reach the surface. But in reality, almost all of them make it down.”

Relativity, or the idea that space and time are not absolute, was one of the most revolutionary and counterintuitive scientific theories to come out of the 20th century. It was also one of the most disputed, with hundreds of scientists refusing to accept it. Yet with less than $100 and a single day’s worth of labor, there’s a way you can prove it to yourself: by building a cloud chamber. An old fishtank, some 100% ethyl or isopropyl alcohol, a metal base with dry ice beneath it and only a few other steps (see the full article for instructions) will allow you to construct a detector capable of seeing unstable cosmic particles. Yet these particles – and you’ll see about 1-per-second – would never reach Earth’s surface if it weren’t for relativity!

Come learn how you can validate Einstein’s first great revolution all for yourself, and silence the doubts in your mind. Nature really is this weird!

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"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day."

There are many times throughout history that science -- and scientists -- have gotten it wrong. And there are many topics today that are quite polarized, from the Big Bang and evolution to vaccines, fluoridation, chemtrails and climate change. There are many public debates that play out, sometimes in nasty ways, surrounding all of these topics. Yet today marks the 97th anniversary of the most famous debate in the history of science, and there are important lessons from that momentum 1920 event that we seem to have forgotten today. If your goal is to convince other people that you're right, don't bother reading this. But if your goal is to arrive at a scientifically robust conclusion, and to make sense of the Universe based on that, read on.

The most important rule in debating science is to identify would take to convince us that our position is wrong. Come and find out what that's all about!

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“Incredibly, all it took was volcanism, wind passing over the ocean, and the natural process of rain to bring a habitable environment to the middle of the ocean. The arrival of not only single-celled life but also complex plants, animals and fungi was not merely serendipitous, but inevitable, given how powerful winds and ocean currents are.”

The Galapagos Islands house some of the world’s most unusual and uniquely adapted plants and animals in the world. This includes giant trees that evolved from the humble dandelion, tortoises the size of boulders, and birds and iguanas that feed beneath the sea. It shouldn’t be a big surprise that plants and animals made it to this remote region of Earth, given wind, ocean currents and flying/swimming animals. But it is surprising that they were able to thrive on these volcanic islands, given that igneous rock has none of the properties you need for rich, fertile soil. Yet the physics of the islands themselves allow them to create their own rain, which leads to the incredible habitats they now exhibit today. All it takes, after that, is the arrival of plants and animals capable of filling those niches.

Come get the story of how science brought habitability to the Galapagos Islands!

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“Above a certain mass, the atoms inside large planets will begin to compress so severely that adding more mass will actually shrink your planet. This happens in our Solar System, explaining why Jupiter is three times Saturn’s mass, but only 20% physically larger. But many solar systems have planets made out of much lighter elements, without large, rocky cores inside.”

You might think that Jupiter is the largest planet in the Solar System because it’s the most massive, but that’s not quite right. If you kept adding mass to Saturn, it would get larger in size, but if you kept adding mass to Jupiter, it would shrink! For a given set of elements that your planet is made out of, there’s a maximum size it can reach, that’s somewhere in between the mass of Saturn and Jupiter in general. Our Solar System is on the dense side of things, meaning that we’ve discovered a large number of exoplanets out there that are approximately twice the physical size of Jupiter without becoming brown dwarfs or hydrogen-fusing stars. For worlds like WASP-17b, where we’ve measured both the radius and mass, we find that they’re only about half the mass of Jupiter, despite being double the size.

Come get the full scientific story, and some very informative and illustrative images with no more than 200 words, on today’s Mostly Mute Monday!

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“Maybe “economic freedom” of water providers is more important than clean, safe drinking water to you? Maybe the rights of corporations to mine, refine, ship, sell and burn fossil fuels are more important than returning Earth to a mid-18th-century climate? And maybe your personal right to spread preventable diseases to newborn babies is more important than the personal freedom consequences of mandatory vaccination policies?

I can’t answer those questions for you; those are questions that should rightly be decided by political institutions. But no one should doubt or deny the science behind those issues. That should be the starting point that everyone agrees on. It’s a sad state of affairs — and why so many of us marches — that it isn’t.”

It’s been two weeks since we’ve gone through reader comments, so that means twice the fun and twice the educational opportunity! From the March for Science to the proton’s spin, from black holes to nuclear fusion, from the most distant galaxy to derailing tactics from the anti-science crowd, and from entropy and identical states to the heroism and tragedy of Fred Hoyle, you won’t want to miss this spectacular tour de force recap.

Come get an amazing dose of inimitable bonus science on this spectacular edition of our comments of the week!

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“Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?”

Black holes were one of the first consequences of general relativity that were predicted to exist, and the more we’ve studied the Universe, the more interesting they’ve become. We’ve calculated their physical sizes, their effects on the curvature of spacetime, their apparent angular sizes, and the properties of matter that gets caught in an accretion disk around them. But we’re about to take another giant leap forward: we’ve about to directly observe one for the first time. Sure, it will be in radio frequencies rather than visible light, but we should be able to directly image the event horizon, and contrast those observations with our best predictions. What should that event horizon look like, though, and why – if it’s completely black – should we be able to see it at all? The answers are both fascinating and informative, and when the results are released later this year, you’ll want to know.

Come learn all about it on this week’s Ask Ethan!

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“This null result — the fact that there was no luminiferous aether — was actually a huge advance for modern science, as it meant that light must have been inherently different from all other waves that we knew of. The resolution came 18 years later, when Einstein’s theory of special relativity came along. And with it, we gained the recognition that the speed of light was a universal constant in all reference frames, that there was no absolute space or absolute time, and — finally — that light needed nothing more than space and time to travel through.”

In the 1880s, it was clear that something was wrong with Newton’s formulation of the Universe. Gravitation didn’t explain everything, objects behaved bizarrely close to the speed of light, and light was exhibiting wave-like properties. But surely, even if it were a wave, it required a medium to travel through, just like all other waves? That was the standard thinking, and the genius of Albert A. Michelson was put to work to test it. Because, he reasoned, the Earth was moving around the Sun, the speed of light should get a boost in that forward direction, and then have to fight that boost on the return trip. The perpendicular direction, on the other hand, would be unaffected. This motion of light should be detectable in the form of interferometry, where light was split into two perpendicular components, sent on a journey, reflected, and then recombined.

The null results of this experiment changed the Universe, and the technology is still used today in experiments like LIGO. Come learn about the greatest failed experiment of all-time!

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“What we’re seeing right now is a response from the community is what we’d expect to an alarm that’s crying “Wolf!” There might be something fantastic and impressive out there, and so, of course we have to look. But we know that, more than 99% of the time, an alarm like this is merely the result of which way the wind blew. Physicists are so bored and so out of good, testable ideas to extend the Standard Model – which is to say, the Standard Model is so maddeningly successful – that even a paltry result like this is enough to shift the theoretical direction of the field.”

The Standard Model of particle physics – with its six quarks in three colors, its three generations of charged leptons and neutrinos, the antiparticle counterparts to each, and its thirteen bosons, including the Higgs – describes all the known particles and their interactions in the Universe. This extends to every experiment ever performed in every particle accelerator. In short, this is a problem: there’s no clear path to what new physics lies beyond the Standard Model. So physicists are looking for any possible anomalies at all, at any theoretical ideas that lead to new predictions at the frontiers, and any experimental result that differs from the Standard Model predictions. Unfortunately, we’re looking at thousands of different composite particles, decays, branching ratios, and scattering amplitudes. Our standards for what’s a robust measurement and a compelling result need to be extremely high.

The newest LHCb results offer a hint of something interesting, but it’s got a long way to go before we can say we’ve discovered anything new. Come find out what we’ve seen today!

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“With two up quarks -- two identical particles -- in the ground state, you'd expect that the Pauli exclusion principle would prevent these two identical particles from occupying the same state, and so one would have to be +1/2 while the other was -1/2. Therefore, you'd reason, that third quark (the down quark) would give you a total spin of 1/2. But then the experiments came, and there was quite a surprise at play: when you smashed high-energy particles into the proton, the three quarks inside (up, up, and down) only contributed about 30% to the proton's spin.”

You might think that the proton, made up of three spin=1/2 quarks, has a spin of 1/2 for that exact reason: you can sum three spin=1/2 particles together to get 1/2 out. But that oversimplified interpretation ignores the gluons, the sea quarks, the spin-orbit interactions of the component particles. Most importantly, it ignores the experimental data, which shows that the three valence quarks only contribute about 30% of the proton’s spin. Our model of the proton has gotten more sophisticated over time, as advances in experiment and in Lattice QCD calculations have shown that the majority of the proton’s spin comes from the internal gluons, not from the quarks at all. The rest comes from orbital interactions, with the low-momentum gluons requiring a more sophisticated electron-ion collider to experimentally examine.

After decades of mystery, we’re finally closing in on exactly why a proton spins. Find out the surprising physics behind the simple answer!

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“They showed how aging stars that were massive enough, such as Red Giants and Supergiants, could find it energetically feasible to create all the elements up to iron in their cores. The even-higher elements could be produced in the extreme conditions of a supernova explosion, upon which the full gamut of elements would be released into space.”

Throughout the 1940s, 50s and even 60s, a debate as to the origin of the Universe raged in astrophysics. Was the Big Bang theory, where the Universe emerged from a hot, dense state some finite time ago, or the Steady-State theory, where the Universe always had the same density and properties, correct? Two very different pictures of the Universe emerged, but more interestingly, they each predicted a very different origin for the chemical elements in the Universe. The Big Bang theorists preferred a Universe where the hot, dense stage of the early, post-Big Bang Universe created the heavy elements, while the Steady-State camp predicted those elements would originate in stars. 60 years ago, in 1957, theory and experiment came together to show that stellar nucleosynthesis is the answer.

That didn’t mean the Big Bang was wrong, but it did mean that the build up of the periodic table didn’t happen early; it happened late! Come get the full story thanks to the incredible Paul Halpern.
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